We invite contributions from the field of micropaleontology that focus on the development and application of microfossils (including, but not limited to, coccolithophores, diatoms, dinoflagellates, foraminifera, ostracods, radiolarians, and pollen) as proxies for paleoenvironmental and paleoclimatological reconstructions and tools for stratigraphic correlation. We particularly encourage the submission of multi-proxy approaches, merging micropaleontological information with geochemical and paleobiological information. The application of microfossils as stratigraphic markers and advancing multivariate statistical techniques with a focus on microfossil assemblages is encouraged.
This study investigates the modern distribution, diversity, composition, and extreme preservation challenges of shallow-water benthic foraminifera along the nearshore marine mud flats of French Guiana. This coastal environment is overwhelmingly controlled by the vast, high-flux discharge of sediment and organic matter (OM) from the Amazon River system, creating a highly stressed habitat for calcifying organisms. Quantitative analysis reveals a severely constrained and moderately diverse fauna. The community structure is heavily skewed towards extremely small species (e.g., Ammonia, Elphidium), and a few robust calcareous taxa (e.g., Eponides). The dominance of stress-tolerant genera is consistent with a highly turbid, high-organic, and potentially low-oxygen environment.
The primary finding is the exceptionally poor preservation of calcareous foraminiferal shells, acting as a powerful taphonomic filter. This dissolution is a direct consequence of the extremely high rates of OM decomposition within the muddy sediments. Microbial breakdown (remineralization) of the abundant Amazon-derived OM rapidly consumes oxygen and generates large quantities of carbon dioxide (CO2). This CO2 increases the concentration of carbonic acid (H2CO3) in the sediment pore waters, leading to a significant pH decrease. The resulting undersaturation (Ω < 1) with respect to CaCO3 minerals (calcite and aragonite) triggers the rapid chemical dissolution of the foraminiferal tests. The poor buffering capacity of the fine-grained, terrigenous muds exacerbates this effect. In addition to the completely preserved foraminifera, almost all samples contain an impressive number of hardened, brown molds (ˈSteinkerneˈ) that capture the original shape of the foraminifera's chamber arrangement, as well as the space once occupied by the living cell. Here, the original calcium carbonate shell is dissolved by acidic waters over time. What remains is a three-dimensional "negative" of the shell's interior.
The sedimentary environment of the French Guiana mud flats represents an end-member environment where near-complete post-mortem dissolution of the calcareous fraction severely biases the fossil record and acts as an effective taphonomic filter. The observed foraminiferal census, dominated by Ammonia, Elphidium and a very few robust taxa, therefore represents a highly-biased reflection of the original living community. This has significant implications for paleoenvironmental reconstructions based on foraminifera in similar high-organic-flux, tropical deltaic systems, highlighting the need to account for dissolution-driven loss of the calcareous fraction.
How to cite: Lendla, J., Langer, M., Fajemila, O. T., and Antoine, P. O.: Distribution, Diversity and Preservation of Shallow-Water Foraminifera in the Extremely Organic-Rich Mud Flats of French Guiana, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3103, https://doi.org/10.5194/egusphere-egu26-3103, 2026.
The shallow marine environment of the Eastern Mediterranean Sea is an ultra-oligotrophic system that provides essential ecosystem services, yet it is increasingly exposed to anthropogenic pressures, including fish farming, desalination activities, and municipal and industrial pollution. Understanding ecosystem responses to disturbance and subsequent recovery is therefore critical for sustainable marine management.
For three decades (1987-2017), the primary source of anthropogenic pollution along the Israeli coast was the Shafdan sewage outfall, which enriched the surrounding environment with nutrients, organic matter, and heavy metals. This long-term pollution history, followed by recent recovery, offers a unique natural laboratory to investigate benthic foraminiferal responses to sustained anthropogenic stress and post-impact recovery.
Two sediment gravity cores were collected at ~36 m water depth near the Shafdan outfall: one from a formerly polluted site (PL3; 0.2 km north of the outfall) and one from a more distal reference site (PL29; 5.5 km north). Sedimentological and geochemical analyses included total organic carbon, grain-size distribution, and mineral and elemental composition. Micropaleontological analyses focused on down-core dead benthic foraminiferal assemblages, complemented by living (Rose-Bengal stained) foraminifera from surface sediments. We assessed changes in species composition, community structure, dominant taxa, and diversity patterns. Ecological status was evaluated using three biotic indices (Foram-AMBI, TSI-Med, FSI) and two diversity indices (ES100 and Exp(H’bc)).
Distinct assemblage shifts corresponding to pre-pollution, pollution, and post-pollution phases were identified at the Shafdan site. Pre-pollution sediments (20-6 cm in core-depth) were characterized by predominance of sensitive taxa such as Ammonia parkinsoniana and Adelosina species whereas the polluted interval (6-2 cm) was characterized by a marked decline in sensitive species and dominance of opportunistic taxa as foraminifera from Ammonia tepida group. During the post-pollution phase (2-0 cm), sensitive taxa recolonized the sediments; however, opportunistic species remain abundant, indicating that recovery is ongoing and not yet complete. Foram-AMBI values clearly increased during the pollution interval, while TSI-Med fluctuations were strongly influenced by grain-size variability. In contrast, FSI and diversity indices showed limited down-core variation.
These results highlight the value of benthic foraminifera as sensitive tracers of both anthropogenic impact and recovery, and demonstrate the robustness of Foram-AMBI for reconstructing historical environmental conditions. Incorporating down-core foraminiferal records into monitoring frameworks can substantially improve long-term assessments of ecological status and inform marine conservation and management strategies in ultra-oligotrophic systems.
This research was conducted as part of the project no. 0005817 «REFORM – REFerence conditions based on historical FORaminiferal Monitoring» funded by the Israeli Ministry of Science and Technology (2024–2026) and the University of Haifa Institutional Postdoctoral Scholarship funded by Graduate Studies Authority – Bloom Graduate School (2024–2025).
How to cite: Trubin, Y., Bookman, R., and Hyams-Kaphzan, O.: Foraminiferal Records of Pollution and Environmental Resilience in the Eastern Mediterranean Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4899, https://doi.org/10.5194/egusphere-egu26-4899, 2026.
Mollusc shells, though often microscopic in size, are preserved ubiquitously in archaeological sites due to their robust calcareous composition that withstands post-depositional stresses. Invariably, ‘flotation’ – a method used conventionally to retrieve botanical remains in archaeological sites – also usually recovers tiny but intact mollusc shells. In archaeological research practice, morphometry-based species identification of mollusc shells has, over the past few decades, proven to be an accessible tool to reconstruct locale-specific past environments at ancient human settlements. Broadening the ambit of the utility of mollusc microfossils, isotopic studies have further allowed us to tap into the chemical composition of these shells to yield insights into the environments in which they lived and formed.
In particular, the stable oxygen isotope composition of the shells (δ¹⁸Oshell) of freshwater and terrestrial mollusc is directly contingent on the oxygen isotope composition of the water body (δ¹⁸Owater) in which the organism lived. The latter, in turn, is driven primarily by the rainfall received, the evaporation dynamics vis-à-vis precipitation as well as the ambient temperature. Therefore, δ¹⁸Oshell in archaeological contexts – and otherwise – has been used extensively in recent decades to retrieve information about past hydrological conditions. That said, however, their immense potential as palaeo-environmental proxies has remained under-utilised in Indian and South Asian archaeological contexts, where most mollusc recoveries rarely find mention in archaeological literature or, if they do, are limited solely to morphology-based species identification.
Here, we present a high-resolution record of δ¹⁸Oshell from the Neolithic/Chalcolithic site of Tigrana, Haryana, a site that falls in the wider network of other Mature Indus Valley Civilisation sites (~5200-3900 BP). Shells under examination here were recovered from well-marked stratums during the excavation seasons through 2019-2024; alongside botanical remains (grains, wood). Of the three morphotypes (or, species/genera) identified from those recovered, only one (here, Bithynia sp.) has been used for stable oxygen and carbon isotope analyses to pre-empt any interference potentially arising from species-based fractionation. The same single-specie aliquots were used for radiocarbon dating. Additionally, the inorganic δ¹⁸O data has been supplemented with that of organic plant matter (δ¹³C) wherever possible.
We observe values ranging from -5.07‰ VPDB to -0.66% VPDB between a period of 4500 to 3800 years BP. The period 4300 BP to 4150 years BP, in particular, witnesses rapid fluctuations of the order of 3-4‰ VPDB, indicating abrupt changes in the rainfall and local evaporative regimes in the location in the above timeframe.
This work carries importance not only in terms of utilising micropalaeontological recoveries for palaeo-environmental reconstruction; but also in-terms of ascribing a climatic agency for the gradual decline of the Indus Valley Civilisation. It is noteworthy that most climate records from North-West India, based on isotopic assessments of molluscs, reconstructed for this purpose have been constructed from lake cores. These records, inevitably, carry ‘averaged-out’ signatures, for lakes collect waters through relatively large time-scales. This study, by contrast, is one of the first few attempts at reconstructing a climate-record directly from mollusc shells recovered in-situ from the archaeological site itself.
How to cite: Chaturvedi, R., Parmar, N., Pokharia, A. K., Baghel, P., Sharma, R., Thirumalai, K., and Ghosh, P.: Rainfall Reconstruction through Isotope Signatures of Mollusc Micro-fossils from a Late Holocene Archaeological Site in North West India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18781, https://doi.org/10.5194/egusphere-egu26-18781, 2026.
The Cambrian microbial-dominated reefs, associated with archeocyaths, are considered to exhibit a style of bioconstruction similar to the Late Paleozoic microbial-sponge consortiums (James and Gravestock, 1990; Wood et al., 1993; Zhuravlev, 1996).
Microbial reefs from the Early Cambrian containing archeocyaths have been reported globally (Debrenne et al., 1989; Gandin & Debrenne, 2010). In the Anti-Atlas, stromatolite-dominated microbial reefs remained relatively stable until the Atdabanian (Lower Cambrian), after which they were replaced by thrombolitic reefs with archeocyaths that became widespread during this period (Álvaro & Debrenne, 2010). In the Fouanou syncline of the Western Anti-Atlas, thrombolite reefs with archeocyaths are more common in the subtidal limestones of the Igoudine Formation (the basal formation of the Tata Group), characterized by successive phases of reef growth, and separated by growth interruption surfaces (Azizi et al., 2022). These calcareous microbial thrombolites are tabular to dome-shaped, with dark micritic mesoclots of various sizes and shapes, with a maximum diameter of up to 20 mm, forming upward-growing dendritic structures. They contain numerous calcimicrobes, including Renalcis, aggregates of Epiphyton, and, to a lesser extent, tubes of Girvanella (Zhang et al., 2015). These calcimicrobes are associated with archeocyaths of irregular (more abundant) and regular (less abundant), small, dispersed inside and around these thrombolite reefs. Three genera of irregular archeocyaths, preserved in their growth position, have been identified: Dictyocyathus, Erismacoscinus, and Agastrocyathus.
The Cambrian reefs of the Western Anti-Atlas provide fascinating examples of early bioconstructions that illustrate the evolution of reef ecosystems and the interactions between microbial organisms and metazoans, showing significant morphological diversity influenced by environmental factors such as depth, hydrodynamics, as well as sedimentation and microbial influence (Gandin and Debrenne, 2010).
Keywords: Cambrian reef, thrombolites, archaeocyaths, microbial consortia, paleoenvironment, Western Anti-Atlas, Morocoo.
How to cite: El Bakhouch, A., Azizi, A., Kerner, A., and El Hariri, K.: Thrombolite reefs with archaeocyaths from the Fouanou syncline, Anti Atlas, Morocco: implications for early Paleozoic bioconstruction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15249, https://doi.org/10.5194/egusphere-egu26-15249, 2026.
The Niger Delta is one of the most polluted deltaic ecosystems globally, with decades of oil spills and leakages severely impacting aquaculture, local flora, and water quality. This study investigates the environmental health of the Imo River estuary, a primary sink for regional pollutants. Benthic foraminifera were utilized as environmental proxies due to their high abundance, rapid reproduction rates, and sensitivity to physicochemical shifts. Analysis of benthic assemblages, stable isotopes, and heavy metal concentrations revealed an ecosystem under extreme physiological stress, characterized by significantly low species diversity and a dominance of stress-tolerant taxa. The presence of negative δ13C values indicates significant deterioration in the quality of organic matter, alongside a notable increase in acidity. This has a detrimental effect on calcareous benthic foraminifera due to lower pH levels. Our findings provide a critical baseline for evaluating the long-term impact of oil contamination and offer a quantitative metric to assess the efficacy of ongoing remediation and clean-up efforts in the region.
How to cite: Fajemila, O. T., Martínez-Colón, M., Olayiwola, M. A., and Langer, M.: Benthic Foraminifera as Indicators of Oil-Induced Stress in the Imo River Estuary (Niger Delta, Nigeria), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5485, https://doi.org/10.5194/egusphere-egu26-5485, 2026.
Foraminiferal Mg/Ca and δ¹⁸O are widely used to reconstruct ocean temperatures. Comparisons between proxy-derived temperatures from surface sediments and modern gridded climatologies are commonly used to infer the recording season and habitat depth of planktic foraminifera, while down-core proxy variations are typically interpreted as reflecting past oceanographic changes at the site or region. Using these approaches requires the assumption that proxy-derived temperatures from a single site represent the mean hydrographic conditions of the corresponding spatial grid used in proxy–model or proxy–proxy comparisons. However, the extent to which this assumption holds across spatially distributed surface sediments remains poorly constrained. Sediment heterogeneity, sampling, and foraminiferal ecological processes could introduce additional variability into foraminiferal proxy data. To address these issues, here we estimated upper-ocean temperatures from the Mg/Ca ratio and δ18O of both surface and subsurface-dwelling foraminifera from multiple surface sediments within seven 1°×1° grids, which correspond to the typical spatial resolution of gridded climate fields, around the Okinawa Islands in the Northwest Pacific. The results suggest that the spread of Mg/Ca- and δ¹⁸O-derived temperatures within individual grid cells reaches up to ~4 °C, which is comparable to the typical glacial–interglacial temperature range in this region, despite the nearshore setting and lack of strong dynamic ocean processes. The Mg/Ca and δ¹⁸O-derived temperature variability differ among species, with subsurface dwellers exhibiting larger variability (~1.1 ºC, 1σ) than surface dwellers (~0.6 ºC, 1σ). To further characterize the contributions of individual processes to observed proxy variability, we used the forward model Sedproxy to simulate the variability induced by seasonal and depth occurrence of foraminifera. This variability is largely attributable to seasonal occurrence in surface-dwelling species, whereas in subsurface-dwelling species it cannot be explained by seasonality alone and likely also reflects variability in calcification depth within the upper thermocline, where temperatures change most rapidly with depth. In summary, our results attempt to quantify the contributions of ecological and sampling-related processes to proxy variability within a grid of nearby surface sediments. We therefore suggest that such variability provides an estimate of proxy uncertainty that should be taken into account in paleoceanographic reconstructions. While the magnitude may depend on regional setting, systematic assessments across regions and species are needed to better constrain proxy uncertainty and avoid over-interpreting proxy-derived temperature differences.
How to cite: Tung, R.-Y., Ho, S. L., Dolman, A. M., Laepple, T., Jonkers, L., Lee, P.-T., Shen, C.-C., Wang, P.-L., and Itaki, T.: Large variability in planktic foraminiferal Mg/Ca and δ18O revealed by nearby surface sediments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16070, https://doi.org/10.5194/egusphere-egu26-16070, 2026.
In order to assess and monitor the health of West African ecosystems, a vast biomarker-based BEACON program has been initiated. This study presents preliminary and partial results comparing two sectors of the Ebrié (Jacqueville bridge) and Densu (Gahna) lagoons. It is based on the analysis of benthic foraminifera from thirty-three (33) samples of surface sediments from these lagoon beds, including fifteen (15) from Ghana and eighteen (18) from Côte d'Ivoire. On the whole, the foraminifera identified fall into ten genera left in open nomenclature. These are the genera Ammotium, Ammobaculites, Ammonia, Amphistegina, Quinqueloculina, Cribloelphidium, Nonion, Miliammina, with a few rare planktonic individuals in the genera Globigerina, Globorotalia (cultrata). A qualitative analysis of these benthic individuals was carried out. The genera Amphistegina, Ammonia, Cribloelphidium and Nonion were found to have calcareous haline tests coiled in a planispiral or trochospiral mode. We also find the Quinqueloculina genus, with a porcelain test in an elongated and milioline mode. The living conditions of these foraminifera are closely linked to the existence of an aerated environment favoring the permanent renewal of oxygen in the bottom sediments. They are abundant in the Densu lagoon and in very low proportions in the Ebrié lagoon. In contrast, benthic forms with elongated, agglutinated testes, such as Ammotium, Ammobaculites and Miliammina, characterize poorly oxygenated waters, i.e. oxic to anoxic or eutrophic waters. They are very well represented in the Ebrié lagoon and rare in the Densu lagoon. From the above, this distribution of benthic foraminifera shows that the Ebrié lagoon (Jacqueville bridge) is very confined and disoxic compared with the Densu lagoon. The presence of planktonic foraminifera such as the genera Globigerina, Globorotalia suggests a marine influence in both lagoons.
Keywords : Ebrié lagoon, Densu lagoon, foraminifera, biomarkers, anoxia
How to cite: Yao, N. J.-P., Akita, L. G., Gnakabi, E. A. M., and Kader, B.: Foraminiferal assemblage as environmental indicators: A case study from Ebrie (Cöte d'Ivoire) and Densu (Ghana) Estuaries, West Africa., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5671, https://doi.org/10.5194/egusphere-egu26-5671, 2026.
This study presents a detailed facies analysis of the lower Priabonian La Tossa Formation, a mixed carbonate-siliciclastic succession deposited in the eastern sector of the Ebro basin (South-Pyrenean foreland basin). Through integrated macro- and micro-facies interpretations, we reconstruct the palaeoecological evolution of a shallow-water carbonate ramp system and asses its response to environmental and climatic shifts during the lower late Eocene. Sedimentation was strongly influenced by coeval fan-delta systems along the basin margins, which directly influenced the facies belt distribution and composition. A total of 13 different facies were identified, arranged along a transect from proximal to distal ramp settings. Their spatial and stratigraphic organisation reflects the interplay of global climatic trends, regional tectonics and local environmental controls.
The facies model for the lower interval of the succession is characterized by proximal ramp facies consisting of siliciclastic-influenced packstones, dominated by Campanile and acervulinid-gypsinid foraminifera. These deposits transition laterally into Nummulites packstones, with localized Nummulites banks. Basinwards, the facies grade into coral frame- and cluster-reefs, which in some sections exhibit coralline algal crusts, and rhodoliths associated with encrusting foraminifera facies. The distal ramp facies are distinguished by the presence of orthophragminids and bryozoan-rich limestones, interbedded with marls devoid of macrofossils, as well as bryozoan and hexactinellid sponge’s marls. Interspersed with this facies belt pattern are two episodes of coralline algal maërl environment. The two maërl levels extend from proximal zones, where they overlie the Campanile sandstones, to distal zones, where they overlie the orthophragminid facies. The upper interval reflects a distinct evolution into a purely carbonate-dominated system. The low-energy proximal ramp setting, consists of porcelaneous foraminifera-rich grainstones with abundant Nummulites, bivalves and echinoids. These units grade into coral frame reef facies with encrusting foraminifera, which in the distal ramp settings transition into marls and orthophragminid-rich limestones.
The changes in facies indicate that climatic oscillations influenced the distribution of benthic communities in this region of the western Tethys. The development of maërl environments and the stabilization of the platform into a purely carbonate system in the upper interval of the succession, suggest cooler climatic periods. This evolution of facies thus reflects the climatic shift from greenhouse to icehouse conditions during the onset of the late Eocene, which led to the Antarctic glaciation in the earliest Oligocene.
Keywords: Ebro basin, Tossa Formation, palaeoecology, late Eocene, facies analysis
How to cite: Acosta Fernández, L. C., Ferràndez Cañadell, C., and Bover Arnal, T.: Palaeoclimatic influence on the evolution of a lower Priabonian mixed carbonate-siliciclastic system in the Ebro Basin (NE Spain), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5502, https://doi.org/10.5194/egusphere-egu26-5502, 2026.
Reconstruction of the Eemian interglacial environmental dynamics (MIS 5e, 130-115 ka) is essentially based on the study of long palynological sequences but remains limited in Western Europe due to the scarcity of lacustrine deposits. Therefore, calcareous tufas have been favoured in recent years as they are widely distributed on the continent and are particularly useful for the study of Pleistocene interglacials. These carbonate deposits identified in alluvial valleys with calcareous substratum are formed in temperate climates and in waters at ambient temperature. An approach combining malacology and isotopic geochemistry (δ18O and δ13C of tufa calcite) used on several Pleistocene calcareous tufas has demonstrated its effectiveness for the detailed reconstruction of environments and climates of past interglacials.
This study mainly focuses on the malacological contribution. Mollusc carbonated shells are particularly well-preserved in calcareous sediments such as tufas and are powerful bioindicators for palaeoenvironmental studies. Indeed, these small organisms are very dependent on their environment and have reduced mobility and thus provide a strong local signal of plant cover. In addition, identification to the species rank allows deeper palaeoenvironmental interpretations.
This study of Eemian calcareous tufas along an east-west transect in temperate Europe aims to report on the evolution of malacofaunas and associated environments during this period. Similar data obtained for the Holocene show a decrease in biodiversity towards the west, linked to a distancing from the main European refuge area, the Carpathian Mountains. Since the current distributions of species on the continent are intrinsically linked to Quaternary climate fluctuations, the existence of a similar gradient remains to be demonstrated for Pleistocene interglacials. This study will ultimately improve knowledge on the chronology of the Eemian interglacial in Europe (palaeoenvironmental axis), on the current and fossil distribution of molluscs (biodiversity/palaeobiogeography axis) and will establish the palaeoenvironmental context of associated archaeological sites. Two Eemian tufas form the core of this project: Resson (France) and Burgtonna (Germany). This communication will present the preliminary results obtained at both sites.
At Resson, the malacological analysis highlights the importance of this site as a new reference sequence of the Eemian in northwestern Europe by uncovering several diagnostic species of the period and identifying the maximum forest development at the top of the sequence, in agreement with the results of isotopic geochemistry for the climatic optimum.
Burgtonna tufa, formerly known through the work of Mania (1978), has been selected for its impressive malacological content (more than 50 species and 8 phases of forest cover development) and the accuracy of the chronological attribution to the Eemian. Field observations and preliminary results confirm the excellent preservation of shells and the richness of the malacological cortege.
How to cite: Sambourg, E., Limondin-Lozouet, N., Dabkowski, J., Herisson, D., and Flichet, V.: Reconstruction of environmental and climatic dynamics during the Eemian (MIS 5e, 130-115 ka) in temperate Europe through malacological and isotopic analysis of calcareous tufas , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5310, https://doi.org/10.5194/egusphere-egu26-5310, 2026.
Evolutionary developmental biology seeks to elucidate the developmental mechanisms underlying phenotypic evolution. Central to this endeavour is the quantitative analysis of morphological variation, for which morphometric approaches have become indispensable tools across micropaleontology.
The suitability of ostracods (bivalved microcrustaceans) for evolutionary, developmental, and paleoecological investigations stems from several key attributes: near-ubiquitous distribution across marine and freshwater habitats, remarkable taxonomic and morphological diversity, sensitivity to environmental parameters, and an exceptional fossil record with calcified carapace valves that preserve fine morphological details across geological time scales. These characteristics make ostracods powerful proxies for paleoenvironmental reconstruction and biostratigraphy. While morphometric methods are widely applied to other microfossil groups, their use in ostracods remains comparatively limited, largely because the labor-intensive nature of manual data acquisition constrains dataset size, scalability, and reproducibility despite their considerable potential.
To address this bottleneck, we evaluate the efficacy of AutoMorph (Hsiang et al. 2016), a high-throughput imaging pipeline, for automated extraction of size and shape data from ostracod valves. We apply this approach to two lacustrine ostracod species, Leucocythere dorsotuberosa and Leucocytherella sinensis, sampled from four lakes across the Tibetan Plateau—a region offering both exceptional ecological diversity and significant paleoclimatic archives.
Our findings demonstrate that AutoMorph successfully extracts morphometric measurements and coordinate data from ostracod valves, reducing processing time by approximately 90% compared to traditional manual methods while minimizing subjective bias inherent in landmark placement.
This methodological advancement facilitates the generation of large-scale spatial and temporal datasets from both modern and fossil assemblages, which enables more comprehensive investigations of ecological responses to environmental change and evolutionary processes. The utilization of tools like AutoMorph can, thus, fundamentally expand existing micropaleontological methodologies, enabling robust, high-throughput quantitative analyses and opening new avenues for comparative and integrative research not only for ostracods.
How to cite: Höhle, M., Frenzel, P., Schwalb, A., Haberzettl, T., Wang, J., Zhu, L., and Wrozyna, C.: Testing the applicability of automated size and shape analyses in non-marine ostracods-A case study from the Tibetan Plateau, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6343, https://doi.org/10.5194/egusphere-egu26-6343, 2026.
Sulfate (SO42-) is the second most abundant anion in seawater. Nevertheless, its long-term accumulation and variability throughout Earth's history remains largely uncertain. Considering the preservation potential of benthic foraminifera in the fossil record, geochemical signatures of large tropical benthic foraminifera (LBF) are an important tool for paleoclimatic proxies. Considering their significant deposit of high-magnesium calcite within fragile tropical ecosystems largely threatened by climate change, an improved understanding of both their calcification processes and geochemical signatures in the face of climate change environmental variables, is of main interest, particularly as LBF have not been as intensively studied as planktonic - and smaller benthic foraminifera. The study of Marginopora sp., an ubiquitous LBF in tropical regions of the Pacific Ocean, provides a unique opportunity to reconstruct changes in environmental parameters in seawater over time. Cultures of Marginopora sp. from New Caledonian environments were performed with modern and decreased seawater pH values and modern and increased [SO42-]sw to calibrate impact of seawater sulfate concentration on both S/Ca concentrations and δ34S composition of the S incorporated in the shells of Marginopora sp.. Here, we present S/Ca data and other Element/Calcium ratios derived from LA-Q-ICP-MS (NWR193UC & Thermo Fisher Scientific iCAP-Q) and solution SF-ICP-MS (Thermo Fisher Scientific Element-2) analyses, as well as sulfur isotope data acquired from Isotope Ratio Mass Spectromety (IRMS with Elementar vario EL cube). As already described in previous studies looking at the geochemical signatures of small benthic foraminifera, S/Ca ratios within Marginopora sp. test, increased with increasing seawater S/Ca concentration. However, and contrarily to what was reported previously, the Mg/Ca content of Marginopora was observed to decrease with increasing S/Ca calcite content, highlighting potential differences in calcification disruption between low-Mg and high-Mg calcitic foraminifers when exposed to an increase in seawater sulfate concentrations.
How to cite: Walla, T., Dissard, D., Jauffrais, T., de Nooijer, L., Marchand, C., and Reichart, G.-J.: New Caledonian Large Benthic Foraminiferal S/Ca signatures as sulfate seawater proxies: Results from controlled growth experiments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8443, https://doi.org/10.5194/egusphere-egu26-8443, 2026.
During the Miocene (c. 23–10 Ma), a large wetland with shallow lakes and swamps developed in Western Amazonia (Hoorn et al., 2010). This predominantly aquatic environment – the ‘Pebas system’ – was colonized by rapidly evolving endemic invertebrate faunas, with mollusks and ostracods being the best documented (e.g., Wesselingh, 2006; Purper, 1979).
Over the last four decades, ‘Pebasian’ ostracods have been thoroughly studied. However, most research has focused on the genus Cyprideis Jones, which typically constitutes the bulk of the ostracod fauna (Purper, 1979; Muñoz-Torres et al., 1998; Gross et al., 2014).
In this study, we focus on the genus Perissocytheridea Stephenson (Cytheridae). The material examined consists of approximately 1,400 mostly well-preserved valves and carapaces. These specimens come from 14 fertile samples, collected from eight outcrops in the Iquitos region (Peru), which cover the Middle Miocene mollusk biozones MZ4–MZ8 (Wesselingh et al., 2006).
Eight taxa were identified. The most abundant are Perissocytheridea ornellasae and Perissocytheridea? elongata, followed by Perissocytheridea sp. 1, Perissocytheridea sp. 2 and fewer specimens of P. acuminata and Perissocytheridea sp. 3. All taxa appear to be endemic to the Pebas system. Notably, the specimens assigned to Perissocytheridea sp. 2 and Perissocytheridea sp. 3 display ‘inverse’ hinges. Perissocytheridea sp. 2 is recorded only in the stratigraphically oldest sections (mollusk zone MZ4; Boca Napo and Santa Teresa localities), together with Perissocytheridea sp. 1. In contrast, P. ornellasae occurs in samples from several localities and biozones (MZ5, MZ7 and MZ8), and is associated with P.? elongata in MZ7 (Puerto Almendras) and with P. acuminata in MZ8 (Palo Seco). The later was only recorded from one sample in the youngest biozone (MZ8). Unfortunately, in the samples analysed from MZ6 we not recorded Perissocytheridea.
Several intraspecific variations were observed. For example, specimens assigned to P.? elongata from MZ7 (Puerto Almendras and Tamshiyacu) exhibit smooth, reticulated, or strongly ornate surfaces, as well as the presence of nodes, which appear to have an ecophenotypic origin. Additionally, analyses of the ontogeny of P. ornellasae, Perissocytheridea sp. 1 and Perissocytheridea sp. 2, suggests that it is possible to distinguish a form of incipient sexual dimorphism in the final instars.
Although numerous references exist to ‘Pebasian’ ostracods with ‘inverse’ hinges, all previously documented cases correspond to the genus Cyprideis (Purper & Pinto, 1983, 1985; Whatley et al., 1998; Gross et al., 2013, 2014). The presence of such ‘inverse’ forms may indicate reproductive isolation and, consequently, sympatric speciation, as suggested for the ‘Cyprideis species flock’ (Gross et al., 2014). Nevertheless, the trigger for the occurrence of these ‘inverse’ forms in ‘Pebasian’ ostracods remains unknown.
How to cite: Zamudio, M. B., Gross, M., Salazar-Rios, A., and Piller, W. E.: Revision of Amazonian Perissocytheridea Species (Ostracoda, Crustacea) from the Pebas Formation (Middle Miocene), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10513, https://doi.org/10.5194/egusphere-egu26-10513, 2026.
The uplift of the Qinghai-Tibet Plateau is considered a major driver of the Cenozoic environmental evolution in Asia. The paleoenvironment reconstruction of the Qinghai-Tibet Plateau provides valuable insights into the study of uplift history and environmental evolution of the plateau. The continuous Cenozoic sediments preserved in the Lunpola Basin, northern Tibet, make it an ideal area for investigating the paleoenvironment of the Qinghai-Tibet Plateau. However, there is still no consensus on the reconstructions of paleoelevation and paleoclimate or on the chronological assignment of their corresponding results. This study focuses on the lacustrine strata of the Dingqinghu Formation in the Lunpola Basin. We combine U-Pb zircon dating with biostratigraphic evidence to place the study section within the Late Oligocene, providing a well-constrained chronological framework. The sporopollen data reveal a paleovegetation landscape consisting of coniferous forest in high-midlands, mixed coniferous and broad-leaved forests in mid-lowlands, and shrubs and herbs distributed within forests. This indicates an obvious vertical vegetation zonation in the Lunpola area. On the basis of sporopollen records, we defined three sporopollen zones and identified a paleoclimatic change characterized by an initial humid phase, a subsequent shift to relatively arid condition, and a final return to a humid climate. The paleoelevation reconstruction carried out on this basis enables us to exclude plateau uplift as a primary driver of the climate change in this period. Furthermore, the observed coupling between the arid trend and contemporaneous global temperature change might suggest that this aridification is linked to the global climate change associated with Antarctic ice-sheet expansion.
How to cite: Deng, J. and Fu, X.: Paleoenvironment of Late Oligocene in the central Qinghai-Tibet Plateau: Insights from Sporopollen Fossils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10890, https://doi.org/10.5194/egusphere-egu26-10890, 2026.
The Indonesian Throughflow (ITF) is a critical conduit for the inflow of Pacific waters into the Indian Ocean. It has long been considered a potential switch in controlling global climate events. Previous work has primarily focused on Pleistocene glacial-interglacial variability, and there have been few records of ITF variability from the highly dynamic Late Miocene period. In this study, we present two new high-resolution sea surface temperature (SST) records from Site U1482 spanning the Late Miocene Cooling (LMC) to investigate the changing dynamics in the ITF between 8-4 Ma. The two records we have used are based on Mg/Ca analysis of Trilobatus sacculifer and on TEX86. One limitation of many studies is that Mg/Ca analysis has been performed at much higher resolution than TEX86. However, here, owing to the high preservation of glycerol dialkyl glycerol tetraethers (GDGTs), we were able to reconstruct TEX86-derived temperatures at about 21 ka resolution high enough to match cycles in Mg/Ca-derived SST. Before the LMC, there is a strong connection between the two records. Both records show the major cooling event around 6.5 Ma associated with the LMC as well as prominent transient cooling events between 6.5-5.5 Ma. However, in the early Pliocene at 5.2 Ma, the two records diverge markedly, with the Mg/Ca-based record recording several cooling episodes that are not reflected in the TEX86 data. Based on previous work, the TEX86H proxy, which employs a nonlinear fit to better reflect SSTs above those of the modern era, matches Austral Summer SSTs in this region. Interestingly, the TEX86H data at this point aligns more closely with temperature trends in the West Pacific Warm Pool (WPWP) than local Mg/Ca. Given that the TEX86H data have been interpreted as Austral summer SSTs, this suggests that in the Early Pliocene, there was a shift in the ITF, allowing seasonal throughflow directly from the WPWP. Given that the WPWP currently exerts little influence, this shift has critical implications for ocean circulation and for the impact of the end of the LMC and the onset of the very warm Early Pliocene. This may help explain the rapid warming at the end of the LMC. It also demonstrates the importance of multi-proxy analysis being done at a similar resolution.
How to cite: Petrick, B., Holbourn, A., Jöhnck, J., Kuhnt, W., and Elling, F.: Understanding changing Indonesian Throughflow dynamics during the Early Pliocene using differences between TEX86 and foraminiferal Mg/Ca, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2156, https://doi.org/10.5194/egusphere-egu26-2156, 2026.
The genus Coccolithus includes some of the most widespread and abundant coccolithophore species during the early Eocene. While the early Eocene saw major evolutionary turnover within the calcareous nannoplankton, in particular during the Early Eocene Climatic Optimum (EECO; ~53–49 Ma), Coccolithus remained consistently common throughout the extremely warm EECO and the subsequent cooling interval. Notably, early Eocene Coccolithus exhibited substantially broader morphological variability than its modern representatives, spanning wide ranges in coccolith size and shape. This high intrageneric diversity may in part explain why this taxon remained ecologically prominent. Different Coccolithus species/morphotypes and their specific traits could reveal what selective pressures favoured this group across climatic extremes. Here, we quantify intrageneric morphological variability by combining species-level assemblage counts with coccolith biometry in 53 deep-sea sediment samples from ODP Site 1258 (Demerara Rise, equatorial Atlantic). This dataset provides an opportunity to better understand the adaptive flexibility and resilience of the Coccolithus lineage during the early Eocene. For example, preliminary data reveal that small species were more common (C. pauxillus and C. pelagicus <5 μm) during the EECO, while a shift towards larger species and morphotypes (e.g., C. formosus and C. pelagicus >5 μm) is observed afterwards. Supported by biometric analysis, these patterns indicate long-term community shifts in mean cell size and associated physiological strategies under prolonged greenhouse conditions.
How to cite: Asanbe, J. and Henderiks, J.: Quantifying intrageneric morphological variability and evolution in Coccolithus across the Early Eocene Climatic Optimum in the equatorial Atlantic (ODP Site 1258), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12330, https://doi.org/10.5194/egusphere-egu26-12330, 2026.
The Middle to Late Miocene constitutes a critical time interval on a global scale. The continental reorganization that occurred during this time caused the establishment of a near-modern monsoonal wind system in the Indian Ocean (IO). Furthermore, this period is characterised by the succession of climatic scenarios linked to the Middle Miocene Climatic Transition (MMCT) and the subsequent northward shift of the Westerlies region during the Late Miocene. How these processes affected and interactedi with the surface ocean dynamics in the southern IO remains poorly understood. In this regard, Ocean Drilling Program (ODP) Site 752, located on the west flank of Broken Ridge (30° 53.475ˈS/93° 34.652ˈE), constitutes a key location to investigate how the aforementioned processes interacted with the surface current in the eastern sector of the southern IO across the Middle to Late Miocene.
Changes in the nannofossil assemblage between 7.31 and 16.06 Ma at Site 752 were evaluated to ascertain variations in the surface ocean conditions. A total of 122 samples (temporal resolution of ~60 kyr) were analysed for this purpose. The clustering ordination method UPGMA (Bray-Curtis) revealed a total of 5 clusters (Cluster 1-5). Cluster 5 was additionally divided into two sub-clusters (Cluster 5a-5b). The oceanographic conditions were inferred based on the abundance of the main nannofossil species constituting the clusters: Reticulofenestra minuta, Calcidiscus leptoporus, Coccolithus pelagicus, Reticulofenestra haqii, Reticulofenestra producta, Reticulofenestra pseudoumbilicus, and Reticulofenestra perplexa. Subsequently, the assemblage data were compared with a set of global climatic and geochemical data to ascertain the effect of global processes on the regional oceanographic configuration across the Middle to Late Miocene.
Total organic carbon (TOC) and Total Inorganic Carbon (TIC) were measured to ascertain variation in the carbon flux to the ocean floor. Additionally, bulk, organic, and benthic foraminiferal δ13C analyses were performed in order to track productivity changes and variations in the nutrient cycle during the studied time interval in the southern IO and compared with the observed variations in the nannofossil assemblage. Benthic δ13C was measured on two foraminifera species (Lobatula wuellerstorfi and Cibicidoides mundulus).
Our data indicate that the surface water of the southern IO was characterised by low nutrient availability and high temperature conditions during the Middle Miocene. After the MMCT, the surface ocean experienced an increase in nutrient availability, which was concomitant with a decrease in δ18O. Maximum surface ocean nutrient conditions were recorded after ~9.9 Ma, coeval with the establishment of the Late Miocene Cooling. A comparison between the nannofossil assemblage data at Site 752 and eNd records available in the literature confirmed the hypothesis that warm water input from the Pacific Ocean into the southern IO increased between ~10.7 – 9.9 Ma. Furthermore, the comparison of the assemblage data against δ13C, TOC, and TIC measured at ODP Site 752 allowed us to disentangle the local processes driving changes in the IO surface water conditions.
How to cite: Puentes Jorge, X., Del Gaudio, A. V., Piller, W. E., De Vleeschouwer, D., Hechemer, T., and Auer, G.: Middle to Late Miocene paleoceanographic evolution of the southern Indian Ocean (ODP Site 752) inferred from nannofossil assemblages and carbon isotopes , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17585, https://doi.org/10.5194/egusphere-egu26-17585, 2026.
Today, Antarctica appears as a continent locked in eternal ice and snow, but its sedimentary record preserves rich fossil archives of past life. Because present-day Antarctic landmasses have already been circling in polar latitudes for more than 300 million years, many Antarctic fossil occurrences derive from past high-latitude palaeoecosystems without modern analogue. Of special importance are exceptional plant-fossil assemblages—some classic, some only recently discovered—from the early Mesozoic of the Transantarctic Mountains. These yield exquisitely preserved plant compressions and anatomically preserved biotas in silicified peat and wood, allowing detailed insights into the biology and ecology of past polar forests during times of global warmth. The Late Triassic vegetation of Gondwana is particularly well-known. It was dominated by Dicroidium seed-ferns, conifers, ginkgoes, cycads, and diverse fern communities, and documents sophisticated adaptations to extreme seasonal light regimes, including widespread deciduousness, growth dormancy, and specialized understorey life strategies. There is now increasing evidence that such high-latitude ecosystems acted as evolutionary refugia during major biotic crises. The iconic Triassic Dicroidium plants, for example, survived the end-Triassic mass extinction in Gondwanan high-latitude populations and persisted there long into the Jurassic, far beyond their time of disappearance at lower latitudes. Recent discoveries from previously unexplored regions of northern Victoria Land substantially expand this perspective, revealing unexpected growth strategies, complex ecological interactions, and evidence for extreme evolutionary stasis. Taken together, the fascinating fossil record of the Transantarctic Mountains highlights the varied roles of high-latitude palaeoecosystems in plant evolution during times of global change.
How to cite: Bomfleur, B.: The green poles of a warmer past: how Antarctic polar forests shaped plant evolution , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-23290, https://doi.org/10.5194/egusphere-egu26-23290, 2026.
The study of sedimentary basins´ evolution, ocean circulation patterns, inter-basin connectivity and past marine ecosystems´ spatial distribution often relies on paleobathymetric reconstructions. Foraminiferal abundance and assemblage data can be powerful proxies to unravel the paleodepth history of a given location. In this study, we compare different routinely-used foraminifera-based paleodepth proxies, including the ratio between planktic and benthic foraminifera (P/B ratio), as well as habitat depth ranges of benthic foraminiferal taxa. The respective transfer functions were subsequently applied on a ~100 m sedimentary sequence, at International Ocean Discovery Program (IODP) Site U1460. The targeted IODP Site is situated near the shelf break of the Southwestern Australian continental margin and the selected interval recorded approximately ~450 kyr of glacial-interglacial sea-level variability spanning the Early-Middle Pleistocene Transition (EMPT; 1.25-0.6 Ma). The EMPT, characterized by the transition from a 41-kyr to a 100-kyr glacial-interglacial cyclicity and amplified glacio-eustatic fluctuations, provided the ideal framework for determining: i) the paleodepth evolution of the continental shelf; ii) the temporal and spatial sensitivity of these proxies to the glacial-interglacial forcing. Collectively, the analyzed proxies revealed a deepening of the continental shelf before the onset of Marine Isotope Stage (MIS) 24, followed by a progressive, step-wise shallowing trend. Our research also highlighted the effectiveness and limitations of foraminifera-based paleodepth proxies in a shallow-water setting, where ecological variability exerts a dominant role on foraminiferal assemblages. We observed that the ratio of planktic to benthic foraminifera and its derived paleodepth curves consistently track the global glacial-interglacial sea-level variability. Nevertheless, the calculated absolute depth values are unrealistically high for a continental shelf setting, likely implying the overlapping of an ecological signal dominating the P/B ratio. Conversely, absolute paleodepth values derived solely from the benthic foraminifera depth ranges reflected more realistic bathymetric estimates for a carbonate ramp than those provided by the P/B ratio. However, this approach failed to resolve the glacial-interglacial cyclicity due to a too broad depth zonation of the total benthic assemblage. For a better depth resolution, a more specific selection of benthic taxa is necessary.
How to cite: Arrigoni, A., Piller, W. E., Kranner, M., Mamo, B., and Auer, G.: Temporal and spatial sensitivity of foraminifera-based paleobathymetry proxies: an Early-Middle Pleistocene Transition case, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18014, https://doi.org/10.5194/egusphere-egu26-18014, 2026.
The Peruvian upwelling system (PUS) sits within the intense, shallow oxygen minimum zone (OMZ) of the eastern tropical South Pacific and is strongly influenced by the El Niño Southern Oscillation (ENSO). El Niño suppresses the upwelling off Peru by weakening the trade winds and allowing warm surface waters to shift eastward, which deepens the thermocline. In contrast, La Niña generally strengthens the trade winds, shoals the thermocline, and enhances upwelling. This study reconstructs Peruvian upwelling variability by using fossil benthic foraminifera assemblages to infer past fluctuations in bottom-water oxygen and productivity. We analysed 168 samples from two sediment cores collected offshore Peru from the center of current OMZ; G10 (14.23° S, 76.40° W; 312 m water depth) and G14 (14.38° S, 76.42° W; 390 m water depth) spanning the last 25,000 years, with average resolution of 113 years. Detecting subtle faunal changes typically requires counting at least 300 specimens per sample, and the identification accuracy and speed depends on the experience of the taxonomist. We trained a CNN to identify and count benthic foraminifera, achieving 92.0% classification accuracy, 93.4% precision, and 92.4% recall. Automated results closely matched manual counts across 31 samples (from both cores at multiple depths), including species abundances, diversity metrics, multivariate assemblage patterns, and bottom-water oxygen estimates, demonstrating the model’s suitability for palaeoecological applications.
We next applied the CNN model to the remaining samples to reconstruct downcore changes in assemblage composition and bottom water oxygenation using the extended Benthic Foraminifera Assemblage index (BFAex). Low- diversity, and high-density assemblages dominated by thin, elongated tests persisted throughout much of the record, consistent with typical OMZ communities. Bolivina humilis was the dominant species across most of the record, whereas Fursenkoina spp. dominated in several intervals in the Heinrich Stadial 1 (H1S), coinciding with high denitrification and a modest increase in organic-matter input. Additionally, Suggrunda porosa, B. costata, B. plicata, Epistominella obesa, and Cassidulina limbata were among the major species. Reconstructed bottom-water oxygen was generally below 0.1 mL/L, however, H1S exhibits several peaks, some exceeding 1 mL/L. Moreover, H1S also shows the largest oxygen variability, potentially reflecting a stronger transmission of ENSO-related perturbations to the seafloor when sea level was 100 m lower than today. During the early and late Holocene, oxygen levels remained at or below the modern value (0.1 mL/L), implying a persistently developed OMZ. Several stratigraphic intervals, including early Glacial, the last Glacial Maximum, middle Holocene, Bølling-Allerød (BA), and many samples from late Holocene show a complete absence of benthic foraminifera. CT scans of two 10 cm-long sections (from BA and late Holocene) reveal “ghost” foraminifera outlines and the presence of gypsum crystals. These observations suggest post-depositional removal of carbonate tests, either during core storage or via early diagenetic dissolution. This latter interpretation is more likely and supported by the coincidence of barren intervals with low enrichment of redox-sensitive metals, reduced denitrification, and low sedimentation rates, conditions generally associated with more oxygenated periods on the Peruvian margin.
How to cite: Hayat, S., Mojtahid, M., Cardich, J., Elliot, M., Garidel-Thoron, T. D., Carré, M., Gutiérrez, D., Salvatteci, R., Barras, C., and Geslin, E.: High-resolution reconstruction of Peruvian OMZ bottom-water oxygen since the last deglaciation using automated benthic foraminifera identification, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20159, https://doi.org/10.5194/egusphere-egu26-20159, 2026.
BENTHONIC FORAMINIFERA AND GEOCHEMICAL TRACERS AS INDICATORS OF THE ENVIROMENTAL HEALTH OF LA PAZ LAGOON, B.C.S.
Geological Oceanography.
Magallanes Cordova Karla Grisel¹, Sánchez González Alberto².
¹ Faculty of Marine Biology, Universidad Autónoma de Baja California Sur, La Paz, B.C.S., ²Centro Interdisciplinario De Ciencias Marinas del Instituto Politécnico Nacional, La Paz, B.C.S.
Kama_22@alu.uabcs.mx, alsanchezg@ipn.mx
Abstract. The health of transitional marine environments can often be compromised by inputs of particulate and dissolved material from runoff originating in urban settlements adjacent to coastal zones. In the present study, the abundance of benthic foraminifera was analyzed, the mean grain size was determined, and the contents of organic carbon and calcium carbonate were quantified in two sediment cores collected from the La Paz Lagoon, with the aim of inferring the environmental health conditions of the area. The absence of benthic foraminifera in both sediment cores may be associated with unfavorable environmental conditions. Organic carbon content ranged from 0.2 to 1.1%, showing a decrease with increasing sediment depth. Calcium carbonate content ranged from 0.3% to 0.9%, with variations of approximately 0.20% throughout the core depth. Mean grain size showed a predominance of fine sands (60%–80%). Mean grain size exhibited a decrease from the base to the upper part of both cores. The absence of benthic foraminifera suggests unfavorable environmental conditions and is associated with the decrease in organic carbon and calcium carbonate values, indicating that their availability may not be sufficient to support benthic fauna. A significant reduction is evident compared to the results obtained in 2024 by Sánchez and Gómez. The predominant sediments are fine sand with little silt, which have a reduced capacity to retain organic matter, thereby affecting the feeding of these organisms and confirming the low sedimentary quality. The current absence of foraminifera indicates that conditions have worsened beyond the tolerance of stress-related species such as the genera Ammonia and Elphidium, which previously accounted for more than 80% of dominance.
Keywords: Organic carbon, Calcium carbonate, Sediment, Cores, Isotopes.
How to cite: Magallanes, K.: Benthonic foraminifera and geochemical tracers as indicators of the enviromental health of La Paz lagoon, B.C.S., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16595, https://doi.org/10.5194/egusphere-egu26-16595, 2026.
The Plio-Pleistocene Transition (PPT, 2.7-2.4 Ma) marks a major climatic reorganization with the onset of Northern Hemisphere glaciation. While the western Mediterranean1 has served as a standard for biostratigraphic and paleoceanographic reconstructions during this period, the eastern Mediterranean, remains less explored. This study (3.7–2.3 Ma) provides the first quantitative planktonic foraminiferal data from ODP Leg 160 Site 967 (Eratosthenes Seamount, 2554 mbsf, well-developed sapropel), aiming to elucidate regional similarities and differences in faunal dynamics and bioevents across the two basins.
The Mediterranean biostratigraphy1 for studied time interval is mainly based on genus Globorotalia, but the eastern record shows low abundance respect to the western ones.
Despite astronomically tuned sapropel records, the biostratigraphic correlation is very difficult.
When compared the eastern Mediterranean Site 967 to western planktonic foraminiferal biozones, key bioevents, including the Last Occurrence (LO) of Globorotalia puncticulata dated at 3.57 Ma, and First Occurrences (FO) of Globorotalia bononiensis and Globorotalia crassaformis, show approximately synchronous timings but contrast in relative abundances. Notably, the LCO of G. bononiensis at 2.46 Ma in the western Mediterranean appears inconsistent in the eastern record, whereas G. crassaformis provides a more reliable marker, suggesting a need for revised regional biozonation schemes.
An outstanding feature is the temporal disappearance of Globorotalids (G. bononiensis and G. crassaformis) at ca. 2.4 Ma, an event not observed in western records where these taxa continued to persist beyond this interval.
The Neogloboquadrina atlantica signature, although resemble the western Mediterranean cooling signal, is minimally expressed in the eastern Mediterranean, emphasizing limited Atlantic water influence and distinct oceanographic control. Also, the Sphaereodinellopsis signal seems to mimic very well the western record with a synchronous LO at ca. 3.2 Ma.
As expected from the palaeoceanography of the eastern Mediterranean, micropaleontological analyses reveals a warm-water and oligotrophic assemblages including Globigerinoides ruber white (morphotypes Type b-platys, c-elongate, d-kummerform), Globoturborotalita rubescens, Globigerinoides obliquus, the Trilobatus sacculifer gr., Orbulina universa, and Globigerinella spp. Conversely, nutrient-dependent and cooler-tolerant species, such as Turborotalita quinqueloba, Globigerinita glutinata, and Globigerina bulloides, peak in abundance near sapropels, marking episodic productivity increases.
High Globigerinoides abundances underscore sustained warm, salty, and stratified water conditions, punctuated by clear paleoenvironmental shifts from red-to-black sapropel phases (~3.2 Ma). This shift is characterized by an acme end of Neogloboquadrinids and incipient warming and increased humidity, shown in oxygen stable isotope G. ruber signal. Another outstanding change is the G. ruber white morphotype faunal turnover and reductions in Globigerinoides obliquus around 3.0 Ma.
As final remarks, the acme end of Trilobatus sacculifer gr., the LO of total Globorotalids and LRO of Globigerinoides obliquus seem to approximate the Gelasian boundary (~2.6 Ma), with important paleoenvironmental and ecological reorganization marked by the decline of warm taxa and an expansion of cooler and productive waters.
Correlation reveals similarities and differences in planktonic foraminiferal abundance highlighting complex basin-specific responses to global climate forcing. These findings advance understanding in paleoceanography and biostratigraphic correlation frameworks crucial for reconstructing PPT climate evolution.
1Lirer, F. et al. (2019). Earth-Science Reviews, 196, 102869
How to cite: Raimondi, M., Margaritelli, G., Foresi, L. M., and Lirer, F.: Differences and similarities in Plio-Pleistocene Planktonic Foraminifera through the western and eastern Mediterranean basins: Insights from ODP Site 967 (3.7–2.3 Ma), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-460, https://doi.org/10.5194/egusphere-egu26-460, 2026.
The middle to late Eocene represents a critical interval of global climatic transition following the Middle Eocene Climatic Optimum, yet its expression across the Arabian Plate remains poorly constrained due to limited deep-marine records and long-standing assumptions of regional stratigraphic hiatuses. Here, we present the first comprehensive documentation of the planktonic foraminiferal genus Hantkenina from Saudi Arabia, based on integrated micropaleontological and geochemical analyses of the Rashrashiyah Formation in the Sirhan–Turayf Basin, northwestern Saudi Arabia. Seven species (Hantkenina dumblei, H. australis, H. longispina, H. compressa, H. primitiva, H. alabamensis, and H. nanggulanensis) are identified and calibrated to planktonic foraminiferal biozones E13–E14 and calcareous nannoplankton zones NP17–NP18, confirming the presence of both Bartonian and Priabonian marine sediments and challenging previous interpretations of a middle–late Eocene depositional hiatus in the region. There is a clear bimodal pattern to the stratigraphic distribution of Hantkenina, with occurrences concentrated in the upper and lower portions of the succession and a period of diminished abundance or disappearance in between. Stable oxygen and carbon isotope analyses (δ18O and δ13C) derived from benthic foraminifera (Uvigerina) reveal alternating intervals of warming and cooling, with reconstructed bottom-water temperatures ranging from approximately 23°C to 30°C. The presence of Hantkenina is closely linked to milder intervals, highlighting the genus's noticeable sensitivity to temperature and confirming its significance as a dependable indicator in paleoclimatic and paleoecological studies. An unconformity at the top of the Rashrashiyah Formation indicates the erosion of the uppermost Eocene and Oligocene sediments, attributed to the combined influence of global eustatic sea-level fall during the Eocene–Oligocene transition and regional tectonic uplift associated with Red Sea rifting. These findings refine the Eocene stratigraphic framework of the Arabian Plate and highlight the valuable application of planktonic foraminifera in reconstructing paleoclimate conditions and marine ecosystem responses during major climate transitions.
How to cite: Korin, A., Allam, S., Hikmahtiar, S., and Michael, K.: First Record of Hantkenina from Saudi Arabia and its Paleoclimatic Significance across the Bartonian–Priabonian Transition, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7515, https://doi.org/10.5194/egusphere-egu26-7515, 2026.
Understanding intermediate-depth ventilation processes in the North Pacific during past warm periods is essential for assessing the climatic role of ocean circulation dynamics, which significantly influence global climate change and the carbon cycle. Over the last two decades, considerable efforts have focused on understanding the evolution of North Pacific Intermediate Water (NPIW) during the Holocene (~11,700 years to present), providing the background climate state for modern anthropogenic global warming. While modern NPIW primarily ventilates from the Okhotsk Sea, the Holocene ventilation history of Okhotsk Sea Intermediate Water (OSIW) still remains unresolved: epibenthic δ13C records suggest a 30–50% reduction in oxygenation during the Holocene optimum, whereas most benthic foraminiferal-based oxygen concentrations and radiolarian assemblages indicate well-ventilated conditions in the mid-Holocene. To resolve this discrepancy, this study reconstructs the OSIW evolution pattern from its source region (the Okhotsk Sea northern shelf) using the radiolarian assemblages, revealing an evolution pattern consistent with prior radiolarian reconstructions. Meanwhile, we introduce a novel quantitative approach—Cycladophora davisiana morphometric parameters—providing, to our knowledge, the first time series of C. davisiana size distributions. New radiolarian size data demonstrate that mid-Holocene peaks in C. davisiana abundance are not primarily driven by food supply (vital effects), supporting the hypothesis of well-ventilated OSIW due to reduced freshwater input and saltier surface water. These findings not only advance quantitative methods in radiolarian-based micropaleontology but also help reconcile the intermediate-water ventilation conundrum in the Okhotsk Sea since the Holocene.
How to cite: Dong, Z., Shi, X., Zou, J., and Liu, Y.: Revisiting Holocene North Pacific Intermediate Water ventilation through the lens of radiolarian morphometric analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17237, https://doi.org/10.5194/egusphere-egu26-17237, 2026.
How paleoceanographic changes modulated the influence of surface primary production on deep-ocean settings at the Iberian Margin remains a matter of debate. Here, we address this question for the mid-Brunhes interval by integrating high-resolution micropaleontological records of calcifying phytoplankton with a suite of surface and deep-ocean geochemical proxies, as well as a detailed assessment of ichnological content, sediment colour, and bioturbation. These analyses are based on the Atlantic Iberian Margin sedimentary core IODP Site U1385. Our data indicate that the transfer of organic matter from the surface ocean to the seafloor was strongly modulated by both orbital- and suborbital-scale paleoclimate variability during Marine Isotope Stages (MIS) 12 to 9 (~450–339 ka). Variations in assemblage composition and abundance of calcareous nannofossil and ichnological characterization, together with changes in sediment composition, suggest that surface ocean conditions and production patterns were not always recorded in the deep-ocean environment. The sensitive response of macrobenthic tracemaker communities, coupled with variable sedimentary characteristics, highlights the influence of bottom-water conditions and ventilation on organic matter preservation and benthic ecosystem dynamics. These findings underscore the importance of integrating multiproxy records to achieve a more comprehensive understanding of paleoclimate and paleoceanographically-driven surface to deep-ocean coupling.
How to cite: Gonzalez-Lanchas, A., Dorador, J., Rodríguez-Tovar, F. J., and Flores, J.-A.: Linking surface and deep-ocean ecosystem dynamics across the mid-Brunhes at the Iberian Margin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18462, https://doi.org/10.5194/egusphere-egu26-18462, 2026.
The Qom Formation was deposited in the Central Basin of Iran, representing the northern part of the Tethyan Seaway during the Burdigalian (Lower Miocene). This study focuses on the deep marine marls of member e of the Qom succession in the Dochah section. This study integrates lithostratigraphy, calcareous nannofossils, oxygen and carbon isotopes of planktonic foraminifera, and oxygen isotopes measured on gypsum crystals. Deposition of evaporites started in the lower Burdiglian in the basin, increasing upwards. During middle to late Burdigalian, salinity increased in the basin due to tectonic activity and a relatively warm and definitely arid climate. The negative water budget resulted in precipitation and sedimentation of gypsum and halite. The oxygen isotope data measured on gypsum crystals indicate a primary, syn-depositional origin for these evaporite minerals. In addition, the oxygen measured on the planktonic foraminifera (average: -4.18‰ VPDB) indicate that the biota lived in a surface water with relatively normal salinity. We concluded that the evaporites were formed on the sea-bottom due to an increasing bottom water salinity under increased water column stratification. The Qom Basin shows similarities to the deep Mediterranean basin during the Messinian Salinity Crisis, where largest part of the evaporites precipitated under water from a deeper-water brine with increasing salinity in a stratified water column. However, the high diversity of calcareous nannoplankton coexistent with planktic foraminifera observed in the Qom succession is interpreted as reflecting high-frequency, low-amplitude sea-level fluctuations within the Milankovitch band with establishment of a temporary connection to the open-marine realm. These oscillations alternated between more open-marine conditions and short-lived stressed intervals, during which basin restriction, enhanced evaporation and episodic evaporite deposition occurred. Subsequently, thin evaporite layers that formed on the seafloor, were later fragmented and dispersed within the marls during diagenesis. Overall, this study provides new insights into the detailed paleoenvironmental evolution of the northern part of Tethyan seaway.
Keywords: Qom Formation, Paleosalinity, Tethyan Seaway, Evaporites, Nannoplankton
How to cite: Sharifi-Yazdi, M., Vasiliev, I., Schӧpfer, K., and Wagreich, M.: Deeper-water gypsum formation constrained by micropaleontology and stable isotopes in the Burdigalian, northern Tethyan Seaway (Qom Formation), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14225, https://doi.org/10.5194/egusphere-egu26-14225, 2026.
Algal symbiosis facilitates the success of Large Benthic Foraminifera (LBF) as major carbonate producers in the ocean. Throughout the evolution of these associations, microalgae and their foraminiferal hosts are exposed to periodic changes in external conditions (e.g. tidal and daily cycles), driven by astronomical cycles such as Earth’s rotation and orbital motions. Many other unicellular and multicellular organisms have evolved biological rhythms, with period lengths similar to those of environmental cycles, as adaptations to these periodic changes. These rhythms can either be exogenously driven as responses to environmental cycles or can emerge from endogenous molecular pacemakers. It has been shown that organisms with internal periods closely aligned with the environmental cycles gain significant advantages. However, climatic changes can lead to disruptions and desynchronization of biological rhythms with adverse effects on the fitness of organisms and ecosystem functions, making the characterisation of biological rhythms an important subject in LBF ecology. While biological rhythms in microalgal model systems, such as diatoms (e.g., Phaeodactylum tricornutum) and dinoflagellates (e.g., Symbiodiniaceae), have gained increasing attention, little is known about the persistence of rhythmic processes in associations with LBF. These foraminifers exhibit reticulopodial locomotion and photoprotective behaviour in response to diurnal changes in irradiance, which are widely regarded to be governed by their microalgal symbionts.
In this experimental study, we characterise the behavioural and holobiont-wide molecular rhythms of the diatom-bearing calcareous LBF Heterostegina depressa. Cultured cells were maintained under light-dark conditions (14:10, LD), at a constant temperature of 25°C. For the behavioural characterisation, locomotor activity was quantified using time-lapse imaging. Behavioural recordings with lengths ranging from 3 to 7 days were conducted to assess rhythmicity and determine dominant period lengths. Transcriptomic dynamics were assessed through bulk RNA sequencing, de novo transcriptome assembly, and subsequent differential gene expression analysis. Cells for the differential gene expression analysis were sampled every 4 hours over a 48-hour period. Rhythm analysis of the activity patterns derived from behavioural recordings revealed substantial inter-individual variability, with some individuals exhibiting recurring spikes in activity with a period length of 24 hours. Additionally, we identified a set of significantly rhythmic transcripts, cycling with a period length of 24 hours.
Our findings suggest that timepoints of observations in studies of LBF ecology need to account for temporal changes across a 24-hour period, even under constant temperature conditions. Beyond these findings, we present insights from locomotion behaviour and gene expression under constant dim light (LL) conditions, highlight enriched pathways, and discuss potential endogenously driven rhythms in transcript expression.
How to cite: Schoerghofer, A., Mat, A., Nagy, M., Wulf, P., Scaramuzza, F., and Tessmar-Raible, K.: A characterisation of biological rhythms in behaviour and holobiont-wide gene expression in the foraminifer Heterostegina depressa from laboratory culture, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20075, https://doi.org/10.5194/egusphere-egu26-20075, 2026.
Foraminifera are remarkably diverse unicellular eukaryotes that inhabit almost all marginal marine environments and perform crucial functions for a multitude of biotic and abiotic processes. Large benthic foraminifera (LBF) such as Amphistegina lobifera are essential contributors to marine carbon and nitrogen cycling, carbon sequestration, and overall biomass in their corresponding ecosystems. Furthermore, many LBF - including A. lobifera – have obligate photosymbiotic relationships with microalgae (predominantly diatoms of the family Fragilariaceae), which assist in the formation of the foraminifera’s calcareous shell.
Shallow marine habitats are often severely impacted by anthropogenic activities due to the introduction of multiple organic and inorganic pollutants by agricultural, domestic, and industrial sources. Among these pollutants, heavy metals are particularly problematic because of their toxicity and long-lasting impact on affected environments. We exposed 140 A. lobifera individuals to various concentrations of selected metals (Fe, Mn, Ni) to evaluate possible effects on their metabolism. During incubation, the cultures were provided with 13C- and 15N-labeled microalgae as a food source, which allows for the quantification of food uptake and metabolic activity via isotope-ratio mass spectrometry. For assessing the health of the photobionts, both the maximum quantum efficiency of photosystem II and photoactive area were measured via pulse-amplitude modulation fluorescence imaging. This novel combination of analytical methods allowed us to examine the complex host-endosymbiont reactions to heavy metal pollution in detail.
Within the first 10 days of contaminant exposure, almost all incubated individuals exhibited a reduction in C and N ingestion, as well as a decline in photosynthetic area and maximum quantum yield. Conversely, after 15 days of incubation an increase in food C and especially N uptake was noticeable in certain cultures, while the activity and health of the photobionts further declined. This metal-specific decoupling between host and photosymbiont implies differential stress tolerance of the partners towards environmental pollutants and exemplifies the necessity for further research in order to fully understand the implications of anthropogenic pollution in coastal marine areas for marine microbial communities.
How to cite: Plakolm, L., Nagy, M., Palme, T., Wanek, W., Schagerl, M., Tyszka, J., and Lintner, M.: Effects of heavy metal pollution (Fe, Mn, Ni) on the large benthic foraminifera Amphistegina lobifera: implications for metabolic function and coevolved host-endosymbiont interactions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14963, https://doi.org/10.5194/egusphere-egu26-14963, 2026.
Rapid urbanization and industrialization have left a persistent imprint on freshwater ecosystems, particularly in metropolitan regions where lakes act as both sinks and archives of anthropogenic pollution. The present study investigates the potential of ostracods as proxies of anthropogenic impacts by studying several surface water sites for an actualistic calibration and by applying a multi-proxy approach to a short core from lake Müggelsee for testing ostracod performance in paleoenvironmental reconstruction of pollution history.
The 26 surface water sites investigated are situated in the east, center and west of the city and reflect different kinds and degrees of anthropogenic impacts. Water types sampled comprise lakes, ponds, rivers and artificial canals. Almost all samples contain ostracods, proving their general availability for analyses in these contexts. One exception is the artificial, concrete covered canals with high turbulence caused by currents and whirling due to ship traffic, where fine-grained sediments and ostracods are broadly lacking. Opportunistic species tolerating oxygen deficiency dominate within the ostracod fauna. The other fossils the >125 µm size fraction are primarily molluscs.
Müggelsee is the largest lake within the Berlin urban region and is fed and drained by the river Spree entering the Berlin area here. The 70 cm long sediment core B25-MS1, taken from Müggelsee in 2025, allows us to study ostracods through time. The core records transitions from massive black muds to laminated black-greenish muds and surficial blackish muds, reflecting varying redox conditions linked to changing organic matter contents. The ostracod assemblages are dominated by candonids, Darwinula stevensoni, Limnocytherina sanctipatricii and Physocypria kraepelini . Their distribution shows marked stratigraphic shifts: The lowermost section below 56 cm sediment depth is characterised by taxa typical for a dense cover of submerged macrophytes. Afterwards and up to the limit between the black and the black-greenish mud at 22 cm, phytal species decrease in proportion, but cold-water taxa are still abundant pointing to a moderate pollution level and cooler conditions probably associated with the end of the Little Ice Age. The black-greenish mud between 22 cm and 7 cm yields the highest ostracod densities and a maximum of Neglecandona neglecta pointing to high organic pollution. Phytal ostracods decrease considerably with the vanishing of submerged macrophytes due to plankton blooms during the second half of the 20th century when not properly treated and increasing sewage water outfalls caused rising trophic conditions in water bodies in and around Berlin. The last phase shows similar ostracod distributions as before the maximum pollution but phytal taxa do not recover and Darwinula stevensoni becomes even more abundant.
Overall, our study shows the potential of ostracod data from water body sediments to reveal increasing anthropogenic impact in the vicinity of Berlin, corresponding to phases of city’s industrial development, post-war and 1990s changes in wastewater management, and modern water quality status. Müggelsee thus exemplifies how urban freshwater archives record the Great Acceleration in local ecological systems. These findings provide crucial baselines for restoration strategies in alignment with the EU Biodiversity Strategy for 2030 and the EU Water Framework Directive.
How to cite: Wagner, N., Schmitz, O., Enayati, A., Roberts, P., von Rintelen, K., Volosky, D., and Frenzel, P.: Tracing Anthropogenic Impacts in an Urban Environment: Ostracod Evidence From Lake Müggelsee and Other Water Bodies of Berlin, Germany, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-427, https://doi.org/10.5194/egusphere-egu26-427, 2026.
Quasi-historical narratives describe extensive birch (Betula pubescens) woodland in Iceland “milli fjalls og fjöru” (lit. between the mountains and the shore) when humans first colonised it in the late 9th century. It has been estimated that prior to human settlement up to 25% of the island supported woodland; today, only c. 1% of Iceland supports woodland. Kjarardalur in western Iceland is home to a surviving birchwood known as Síðumúlaskógur (c. 1 km2). A small wetland hollow (c. 5 m2) is located within Síðumúlaskógur, exceptional for Iceland in terms of the environmental and ecological context. The pollen preserved within the sediments of this hollow provide a unique opportunity to examine the history of an Icelandic birchwood from just before human settlement down to the present. Therefore, a 30 cm core was extracted from the wetland hollow which was sub-sampled for pollen analysis. In all, there were 24 sub-samples, with a resolution of one sample per centimetre between 877 CE and 1693 CE, the chronological framework defined by tephrochronology and supplemented by radiocarbon dating. This research considers why Síðumúlaskógur was able to survive into the present when so much woodland was lost elsewhere in Iceland; including areas immediately adjacent to Síðumúlaskógur that should, in theory, also continue to support birch woodland.
How to cite: Riddell, S. and Erlendsson, E.: Síðumúlaskógur: the saga of an Icelandic birchwood narrated by pollen, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1871, https://doi.org/10.5194/egusphere-egu26-1871, 2026.
The Tajik Basin, located in southern Tajikistan, is a Cenozoic foreland basin preserving relatively complete marine sedimentary sequences. This study conducts a quantitative biostratigraphic analysis of calcareous nannofossils from a Paleocene to Eocene section West to the Kurgan-Tyube (Qurghonteppa) of the northeastern Tajik Basin. The investigated interval comprises mudstone, marl, sandstone, silty mudstone, gypsum, and clay interbeds. Calcareous nannofossil assemblages, including 31 genera and 75 species, were identified. With the analysis of calcareous nannofossil data, the section was constrained to the latest Paleocene through the end of the Eocene. Within the bottom unit of the section (the Ganjina Unit), index fossils for the Paleocene-Eocene boundary, including Discoaster backmanii, Tribrachiatus orthostylus, and Discoaster diastypus, were identified. Alongside these, characteristic taxa of the Paleocene-Eocene Thermal Maximum (PETM), namely Rhomboaster bramlettei and Discoaster araneus (collectively referred to as the R-D assemblage), were also recorded. The fossil assemblage within this interval is predominantly composed of long-ranging species such as Prinsius martinii and Coccolithus pelagicus, indicating a warm, shallow marine environment with high productivity. The early Eocene in the study section was characterized by a significant increase in the diversity and abundance of Discoaster and the thriving of Coccolithus pelagicus, during which fossil abundance and diversity reached a peak, reflecting a comprehensive recovery of the marine ecosystem during this period. The middle to late Eocene was marked by the continued prosperity of the genus Discoaster, albeit with changes in species composition, and the emergence of Reticulofenestra as the dominant taxon. During this period, fossil abundance declined, and the community structure underwent significant turnover, directly responding to global temperature changes and nutrient fluctuations. These characteristics of biotic succession show consistency with the manifestations of the biostratigraphic patterns from the late Paleocene to the end of the Eocene in shallow marine deposits.
Acknowledgements: This research was supported by the National Natural Science Foundation of China (Nos. 42072001, 41930218), National Key R&D Program of China (Grant No. 2023YFF0804000).
How to cite: Jiang, T., Zhou, Q., and Cao, W.: The Paleocene to Eocene calcareous nannofossil assemblage from Kurgan-Tyube West section in the Tajik Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2887, https://doi.org/10.5194/egusphere-egu26-2887, 2026.
Oceanic Anoxic Event 2 (OAE2; latest Cenomanian–earliest Turonian) represents a major perturbation of the global carbon cycle and marine ecosystems, yet its expression along the southern Tethyan margin remains incompletely constrained. We present new quantitative calcareous nannofossil data from the Oued Kharroub section (central Tunisia), integrated with carbon-isotope stratigraphy (δ¹³C), carbonate content, and total organic carbon (TOC), to investigate surface-water environmental changes across OAE2. The Oued Kharroub section spans nannofossil zones UC3 to UC8 and records a positive δ¹³C excursion that allows identification of the main phases of OAE2. Calcareous nannofossil assemblages display pronounced variations in abundance, diversity, and composition through the event. Species richness and Shannon diversity index values decrease significantly during the main build-up and plateau of the δ¹³C excursion, coinciding with reduced CaCO₃ content and increased TOC. Assemblages during this interval are dominated by the opportunistic taxon Watznaueria barnesiae, whereas meso- to eutrophic indicators such as Biscutum constans and Zeugrhabdotus erectus show strong short-term fluctuations, suggesting unstable surface-water conditions. Morphometric analyses of W. barnesiae reveal a statistically significant reduction in coccolith size during the core of OAE2, with minimum values coinciding with peak TOC levels, followed by partial size recovery in the post-OAE2 interval. This pattern indicates subtle but detectable calcification stress affecting even ecologically tolerant taxa under peak anoxic conditions. A short-lived increase in Eprolithus floralis near the onset of the event, together with the decline of warm-water taxa, may reflect a weakly expressed cooling episode tentatively linked with the Plenus Cold Event.
How to cite: Granero Ordóñez, P., Wagreich, M., Wolfgring, E., and Hazod, T.: Calcareous nannoplankton response to Oceanic Anoxic Event 2 on the southern Tethyan margin (Bahloul Formation, Tunisia), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4257, https://doi.org/10.5194/egusphere-egu26-4257, 2026.
Radiolarian biozonations constitute an important tool in Cenozoic stratigraphic studies in polar regions. Neogene-Quaternary radiolarian biostratigraphical schemes have been established mainly in low latitude regions, but only a few attempts have been carried out in the high-latitude North Atlantic. In this study, we quantitatively analyze a radiolarian zonation for the Late Pliocene-Holocene (3 Myr to present) at IODP Site U1314 (Gardar Drift, 56.36°N, -27.88°E, 2820 m water depth). The present study focuses on taxa of both stratigraphic importance and of limited occurrence. Specifically, we determined several radiolarian bioevents, some of which are the first time that they are found in the North Atlantic, such as the last occurrences of Druppatractus irregularis Popofsky and Cycladophora sakaii, and first occurrence of Cycladophora davisiana Ehrenberg. In addition, we described two new radiolarian species; Pseudocubus abruptus n.sp. and Spongasteriscus chiasmos n.sp., whose biostratigraphic ranges are also defined and have the potential to be used as biomarkers across the high-latitude North Atlantic Ocean.
In addition to the new radiolarian biostratigraphic record, on-board bio and magnetostratigraphy, refined relative paleointensity and physical property records, and published isotope stratigraphy and radiocarbon ages were used to construct an integrated chronostratigraphic framework at Site U1314 to constraint the new radiolarian bioevents. The stratigraphic distributions of these marker species indicates that the radiolarian scheme proposed herein has a potential to be applied in a broader region, from the mid-latitude North Atlantic, north of about 40°N to the Norwegian Sea. Furthermore, comparison of the radiolarian bioevents with other northern hemisphere datasets provides novel perspectives on the evolutionary dynamics, ecological adaptation and origins of radiolarian lineages.
How to cite: Hernández-Almeida, I., Hatakeda, K., Reilly, B., and Bjørklund, K.: Integrated stratigraphy and new radiolaria bioevent constraints of Late Pliocene to Holocene sediments from the subpolar North Atlantic (IODP Site U1314), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5313, https://doi.org/10.5194/egusphere-egu26-5313, 2026.
The 4.2 ka event is widely recognized as a major cooling and aridity episode across the Northern Hemisphere. However, its specific impact on the Korean Peninsula remains under-researched compared to neighboring China. In this study, we present a 9,000-year hydroclimatic reconstruction from the subalpine Sara-oreum wetland on Jeju Island, using diatom assemblages and monitoring data. Contrary to the typical "drought" narrative of the 4.2 ka event, our findings reveal prevailing humid conditions on Jeju, evidenced by an increase in summer-associated tychoplanktonic species. This moisture pattern aligns with records from Southern China, suggesting a southward shift of the westerly jet that anchored the monsoonal rain belt over the region. Furthermore, strong correlations between lake-level indicators (PC1 and sand content) and the δ¹⁸O records from Xianglong Cave and the Westerlies Effect Index highlight the sensitivity of Jeju’s diatom records to large-scale atmospheric circulation. This study underscores the complex spatial heterogeneity of the 4.2 ka event and its linkages to westerly jet variability.
How to cite: Cho, A.: Holocene Hydroclimatic Variability on Jeju Island, Korea: Reassessing the 4.2 ka Event via Diatom Records and Westerly Jet Dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6209, https://doi.org/10.5194/egusphere-egu26-6209, 2026.
Diatoms are excellent environmental proxies due to their often species-specific, narrow environmental tolerances, but the annual succession of diatom communities in coastal seas remains deficiently known. This knowledge gap constrains our ability to reconstruct past seasonal changes in marine systems, as variation in seasonal conditions strongly impacts the composition of diatom species assemblages, and consequently assemblages preserved in the sediments. In particular species dynamics related to sea ice are still underexplored, as ice-cover restricts undisturbed access. Automated sequencing sediment traps offer an effective solution to overcome these challenges, even during the ice-cover period.
In this PhD project, the seasonal succession of coastal diatom communities, as well as their contribution to vertical particulate organic matter fluxes and sedimentation are studied over multiple years in Tvärminne Storfjärden, Gulf of Finland. The aim is to enhance our understanding of the seasonal patterns of diatom species succession and sedimentation at a high temporal resolution, with a focus on understanding seasonal environmental drivers of species assemblage composition and the development of paleoenvironmental reconstruction methods. The data is collected with automated sequencing sediment traps, moored to the sea floor to continuously collect vertical material fluxes settling from the sea surface at a two-week temporal resolution. Two sediment traps are deployed at depths of 15 m and 27m (approximately 3 meters above the seabed) to assess how processes like decomposition and predation impact the vertical sediment flux. Diatom assemblages are analysed by microscopic identification and compared to simultaneous environmental measurements of e.g., sea-surface temperature, salinity and sea-ice cover to assess species-specific seasonal ecologies and deposition patterns. In addition, bulk organic geochemical analysis renders information about carbon flux and sources to the seafloor. Enhanced seasonal ecological information will improve diatom-based methods, enabling more accurate reconstructions of past and predictions of future coastal environments. Also, the advancement provides valuable insights into the impacts of ongoing environmental change and anthropogenic pressure on aquatic systems and, ultimately human well-being.
How to cite: Railo, S., Weckström, K., Heikkilä, M., and Saarni, S.: Seasonal succession of diatoms in the coastal Baltic Sea: insights into diatom-based proxy for past environmental change, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8107, https://doi.org/10.5194/egusphere-egu26-8107, 2026.
The Jurassic–Cretaceous boundary, conventionally placed at the base of the Berriasian, remains one of the most contentious horizons in the Phanerozoic timescale because the basal Berriasian is difficult to correlate consistently across Austral, Tethyan, and Boreal realms. Recent refinements in calcareous nannofossil biostratigraphy, notably the zonation proposed by Casellato and Erba (2021), together with emerging high-resolution carbon-isotope records from multiple basins, promise more robust global constraints on this transition. Although not tied to a single global event, the Jurassic–Cretaceous interval registers evolutionary turnover and reorganization of marine ecosystems, including shifts in carbonate production, ocean circulation, and floral assemblages, yet efforts to resolve their timing and drivers are hampered by fossil preservation/provincialism, stratigraphic discontinuities, and limited high‑precision geochronology.
The BH-02 well (207 m thick, Tithonian–Berriasian, Manifa and Sulaiy formations) in central Saudi Arabia offers a suitable archive to address these issues. High‑resolution calcareous nannofossil biostratigraphy/counting, integrated with correlations to calpionellid and calcareous nannofossil biozonations in Kuwait, enables recognition of key bioevents across the Jurassic–Cretaceous transition, while complementary strontium isotope geochronology, detailed cyclostratigraphy, and Bayesian astrochronology refine the temporal resolution to less than 100 kyr. Within this integrated scheme, the δ¹³Ccarb record captures both the early Tithonian and Late Berriasian carbon‑isotope excursions, which are placed in a high‑resolution age model together with Nannofossil Calcification Events I and II and the Late Berriasian Nannoconus Event, thereby constraining the coupling of biotic and isotopic change along the southern Tethyan margin.
Cyclostratigraphic analysis of high-resolution gamma-ray and potassium logs (~20,000 data points) using multitaper spectral methods, evolutive harmonic analysis, correlation coefficient spectra, band-pass filtering, and wavelet analysis reveals a pervasive ~7 m cycle interpreted as long eccentricity (405 kyr). Extraction of 30 E405 cycles implies a duration of ~12.1 Myr for the studied interval, in close agreement with independent Sr-isotope estimates of ~11.9 Myr (137.9–149.8 Ma). Age–depth modelling is achieved using astroBayes, a Bayesian inversion framework that jointly assimilates astrochronologic and radioisotopic constraints to reduce interpolation uncertainties between dated horizons and to resolve subtle changes in sedimentation rate while considering prior information on sedimentation and potential hiatuses.
This integrated stratigraphic, geochemical, and astrochronologic framework provides a precisely constrained, orbitally calibrated reference section for the Jurassic–Cretaceous boundary on the Arabian Plate. Comparison with coeval successions reveals contrasting carbon-isotope trends between the Tethyan and Boreal realms, reflecting a decoupling of oceanographic conditions through the J/K transition with recoupling during the Weissert Event, signaling a renewed phase of oceanic connectivity.
How to cite: Haj messaoud, J., Thibault, N., Boehm, N., Finkbeiner, T., and van Buchem, F.: Bayesian astrochronology and radioisotope geochronology reveal contrasting carbon-isotope and biotic turnovers across the Jurassic–Cretaceous boundary in Tethys and Boreal realms, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9480, https://doi.org/10.5194/egusphere-egu26-9480, 2026.
Keywords: Culture experiment, Size, Proxy development, Phenotypic adaptation
The carapace of ostracods (small crustaceans) protects their soft body from harsh conditions. Its size can vary distinctly within one species but major causes for this variability remain uncertain. Cyprideis torosa is a widespread brackish water ostracod-species with high morphological variability, making it a well-suited study object relating environmental conditions quantitatively to its morphology. Since this species lives in habitats with great spatio-temporal variability, lab-cultures are highly valuable for studying its phenotypic adaptation to different conditions.
In June 2024 location water and sediment samples were collected from the Marano Lagoon (North Italy). The samples provided three levels of salinity (PSU 7.7, 16.1 and 29.6) which were used to start experimental cultures (sediment from PSU 7.7 served as origin of all ostracod specimens). All three levels of salinity were incubated at four different constant temperature conditions ranging from 15 to 35°C. One set of cultures was placed outside the building, being exposed to fluctuating temperatures. Size and other morphological features were analysed to identify specific environmental influences on its morphological characteristics.
Our study reveals that temperature and salinity play an important role on size variability and variance of the carapace. Individuals living in higher salinities and cooler temperatures grow bigger. The opposite is true for extreme conditions (high temperatures) or low salinities. While high temperatures cause significantly smaller carapaces at high salinities, they lead only to higher variances in lower salinities without affecting the average size. The average size of one outside culture (PSU 7.7) reveals that size may be unaffected by diurnal changes. The results were compared to C. torosa valves collected from ostracods grown in the lagoon (PSU 22.7). The length of the individuals of this sample correlates best with rather extreme conditions in our cultures. The length/height ratio of left valves of natural environments (such as lagoon sample, permanent culture and naturally grown ostracod culture starters) are similarly low to each other, corresponding only to the experimental grown ostracods in high mesohaline salinity at 30°C, while other experimental grown individuals show a higher ratio in average.
Our results indicate that salinity as well as temperature influence the size of C. torosa simultaneously and requires further morphological analysis to separate these factors.
How to cite: Kukacka, P., Berndt, C., Berger, I., Nagy, M., Melis, R., Salvi, G., and Heinz, P.: Impact of temperature and salinity on the morphological variability of lab-grown Cyprideis torosa (Jones, 1850) (Ostracoda), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14021, https://doi.org/10.5194/egusphere-egu26-14021, 2026.
The Cenozoic Era provides a key framework for investigating how ocean oxygenation and marine productivity responded to past global warming events, offering valuable analogues for ongoing and future climate change. Here, we integrate foraminifera-bound nitrogen isotopes (FB-δ¹⁵N) with stable carbon and oxygen isotopes (δ¹³C, δ¹⁸O) to reconstruct nitrogen-cycle dynamics, water-column oxygenation, and photosymbiotic behaviour in planktic foraminifera across the Middle Eocene Climatic Optimum (MECO; ~40 Ma), a major greenhouse interval lasting ~500–600 kyr. The dataset is based on planktic foraminifera from two Atlantic sites spanning contrasting latitudes: subtropical ODP Site 1051 and subantarctic ODP Site 702. FB-δ¹⁵N records from both sites show a marked and coherent decrease during the MECO, reaching minimum values at peak warming. This trend indicates a general reduction in water-column denitrification, a process that generally occurs under extremely low oxygen conditions, suggesting that prolonged warming was not associated with widespread deoxygenation in the global ocean . These results are consistent with patterns observed during other Cenozoic hyperthermals (e.g. PETM, EECO, MCO) and imply that enhanced deep-water ventilation and/or reduced biological productivity counteracted warming-driven oxygen loss. Paired δ¹³C and δ¹⁸O data confirm persistent vertical habitat partitioning among planktic foraminiferal taxa, despite partial convergence in δ¹⁸O values during the MECO, indicating upper-ocean thermal homogenization and temporary niche compression. This preservation of depth-related ecological structure supports the interpretation of interspecific FB-δ¹⁵N offsets as reflecting distinct symbiotic strategies. Lower δ¹⁵N values in Acarinina and Globigerinatheka relative to Subbotina confirm their photosymbiotic nature, while systematic differences between the two symbiotic genera suggest dinoflagellate symbionts in Acarinina and non-dinoflagellate algae (e.g. diatoms or coccolithophorids) in Globigerinatheka. The contrasting evolutionary trajectories of these taxa, recording a decline for Acarinina and expansion for Globigerinatheka during and after the MECO, likely reflect differences in symbiont flexibility and sensitivity to photic-zone environmental change. Overall, this study provides the first reconstruction of the nitrogen cycle across the MECO and demonstrates the value of FB-δ¹⁵N, combined with δ¹³C–δ¹⁸O constraints, as a dual proxy for local and global denitrification and planktic foraminiferal ecology during sustained greenhouse warming.
How to cite: Sigismondi, S., Auderset, A., Henehan, M., Martínez-García, A., and Luciani, V.: Planktic foraminifera-bound nitrogen isotopes across the Middle Eocene Climatic Optimum (MECO, ~40 Ma): implications for photosymbiosis and community change in the Atlantic Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14640, https://doi.org/10.5194/egusphere-egu26-14640, 2026.
Boron isotopes (δ¹¹B) measured in planktonic foraminifera are widely used to reconstruct past surface ocean pH and atmospheric pCO₂, yet their application in tropical regions relied on understanding of species-specific ecology and size-dependent vital effects. Here we present new data from Globigerinoides ruber (sensu stricto) and Trilobatus sacculifer spanning the last ~60 kyr from Tropical Atlantic Ocean. Our dataset comprises paired analyses of multiple size fractions (200–250 µm, 250–300 µm, 300–355 µm, and ≥355–400 µm), which enabled an assessment of species’ vital effects and how they vary with size. During the Younger Dryas, Heinrich Stadial 1 and Heinrich Stadial 4, G. ruber varied from ~19.0–19.5‰ (200–250 µm), increased to ~19.0–20.0‰ (250–300 µm) and reached values up to ~20–21‰ in the largest studied size fraction (300-350 µm). This positive relationship between δ¹¹B and test size demonstrates a pronounced size-dependent enrichment, consistent with strong biological control and near-surface calcification. In contrast, T. sacculifer exhibits lower δ¹¹B values during the same intervals, ranging from ~18.5–19‰ (200–250 µm), 18.25-17.80 ‰ (250-300 µm), 18.2-19‰ (300-355 µm). Paired species analyses from identical depth horizons reveal persistent interspecific offsets, with G. ruber recording higher δ¹¹B values than T. sacculifer across all size fractions. These offsets are maintained throughout YD, HS1, and HS4. The magnitude of size-related offsets within each species (up to ~1‰) is comparable to the expected glacial–interglacial δ¹¹B signal, underscoring the first-order importance of size fraction. We conclude that robust δ¹¹B-based reconstructions in the Equatorial Atlantic require strict size-fraction control and species-specific ecological interpretation. These findings highlight that different planktonic foraminifera record distinct levels of the upper ocean carbonate system during periods of rapid climate change, providing new constraints on tropical ocean buffering during abrupt climate events.
Keywords: Boron Isotopes, Globigerinoides ruber, Trilobatus sacculifer, Tropical Atlantic Ocean
How to cite: Azevedo, A., J. Henehan, M., J. Jiménez-Espejo, F., and Jovane, L.: Species- and size-dependent δ¹¹B signatures of abrupt climate events in the Equatorial Atlantic, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14993, https://doi.org/10.5194/egusphere-egu26-14993, 2026.
Oxygen Minimum Zones (OMZ) are water layers characterized by low oxygen saturation state in response to a complex interplay of biological, chemical, and physical processes. Modern OMZs are typically found along the western side of continents (i.e., Arabian Sea, Eastern Pacific Ocean, Eastern Tropical Atlantic Ocean, and the Southeast South Atlantic Ocean). Low oxygen conditions can however be more widely prevalent in shallower, continental shelf environments. Here, we study the evolution of bottom water oxygen conditions of Brazil’s continental shelf Santos Basin from the Southeast Atlantic. The Santos Basin which is located near the Cabo Frio upwelling system. We reconstructed bottom water oxygen conditions using the enhanced Benthic Foraminifera Oxygen Index (EBFOI) using samples from the Santos Basin Slope core C4-GC-2 ( 25°51.519’S/ 45°30.685’W, 395 m water depth). These data are integrated with mineralogical analysis and oxygen and carbon stable isotope data from the benthic foraminifera Cibicidoides spp. The age model was constructed based on four radiocarbon dating samples, which covers most part of the Heinrich Stadial 1 (HS1, 17.8–15.7 kyr). From 16.8 kyr to 16 kyr the continental shelf of Santos Basin was characterized by low oxic conditions as revealed by relatively low EBFOI values (1.9-5.3). The mineralogical analysis from the studied core revealed the presence of pyrite during this time interval, which together with geochemical proxy signatures, indicates low oxygenation of bottom-water conditions, with the development of localized anoxic microenvironments within the sediments. Notably, at 15.8 kyr marine oxygenation decreased to suboxic conditions (EBFOI = -20.3). Elevated δ¹⁸O values indicate cold conditions during HS1, likely associated with intensified upwelling, while low δ¹³C values are comparable to those recorded in Eastern Pacific intermediate waters during the same interval. The dominance of low-oxygen tolerant benthic foraminifera suggests reduced bottom-water oxygenation at ~395 m depth, consistent with a shoaling or expansion of the regional OMZ rather than methane seepage. These conditions were likely sustained by poor ventilation during HS1, limiting benthic foraminiferal diversity.
Keywords: Benthic Foraminifera Assemblage, Isotope Geochemistry, Oxygen Minimum Zone
How to cite: Santana, M. E., Queiroz Azevedo, A., Frontalini, F., J. Jiménez-Espejo, F., A. A. Hoogakker, B., R. Gonçalves, T., Mulato, J., and Jovane, L.: Variability of oxygenation index in the Southwestern South Atlantic Ocean during Heinrich Stadial I based on geochemical proxies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15385, https://doi.org/10.5194/egusphere-egu26-15385, 2026.
The detailed biomineralization mechanisms of planktic and benthic foraminifera is still enigmatic
and a topic of active research. Much progress has been achieved in developing biomineralization
models for some benthic hyaline species (e.g. Erez, 2009; de Nooijer, 2014) and in discovering that
the original phase composition of planktic Orbulina universa (d’Orbigny, 1839) is metastable
vaterite and not calcite, supporting a non-classical crystallization pathway for this important
species (Jacob et al. 2017). It is, however, less clear to date whether these results can be replicated
in other foraminifera species and models for their formation can be generalized.
To extend our earlier studies on planktic species, we studied four species of benthic foraminifera
from the Australian Great Barrier Reef, namely Amphistegina lobifera (Larsen, 1976),
Baculogypsina sphaerulata (Parker and Jones, 1860), Calcarina capricornia (Mamo, 2016) and
Marginopora vertebralis (Quoy and Gaimard, 1830). Samples were collected alive and pulse
chase labelled with Sr in aquaculture before carrying out a detailed, multi-scale study of their
architecture. We used Electron Backscatter Diffraction, Nano-SIMS, Focussed Ion Beam assisted
Transmission Electron Microscopy, Micro-Raman Spectroscopy and Photo-induced Force
Microscopy (Otter et al. 2021) to elucidate and compare phase compositions, micro-architecture
and organic chemistry of the shells. Our results contribute to understand the details of
foraminiferal biomineralization and to develop a general model for shell formation across all
foraminifera species.
de Nooijer , L.J. et al. (2014). Biomineralization in perforate foraminifera. Earth-Science Reviews
135, 48-58.
Erez, J. (2003). The source of ions for biomineralization in foraminifera and their implications for
paleoceanographic proxies. Reviews in Mineralogy and Geochemistry 54, 115-149.
Jacob, D.E. et al. (2017). Planktic foraminifera form their shells via metastable carbonate phases.
Nature Communications, 8, 1265
Otter, L.M. et al. (2021) Nanoscale Chemical Imaging by Photo‐Induced Force Microscopy:
Technical Aspects and Application to the Geosciences. Geostandards and Geoanalytical Research
45, 5-27.
How to cite: Jayasoma, K., Jacob, D., Otter, L., Morales, L., Wirth, R., and Schreiber, A.: A closer look at benthic foraminifera shells – implications for biomineralization mechanisms, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15793, https://doi.org/10.5194/egusphere-egu26-15793, 2026.
Deposits associated with MIS 3 have been recently described and dated along the coastal margin of the Southern Atacama Desert. These deposits generally exhibit a wide heterogeneity of littoral facies, including beaches, deltaic fans, dunes, and coastal lagoons. In some of these marine terraces, coastal boulder deposits interpreted as tsunami-related have been identified, extending the chronology of major earthquakes and tsunamis in northern Chile and expanding the current geodynamic scenario of a tectonically active coastline back to the terminal Pleistocene.
This work describes deposits from a coastal lagoon exposed in an abandoned quarry at the mouth of the Copiapó River (northern Chile). The stratigraphic succession reaches approximately 22 m in thickness and has been dated at its base and top, yielding ages of 42,431 ± 1,891 yr and 35,984 ± 277 yr, respectively. The lower and middle sections consist of centimeter-thick layers of gypsum and gray argillites, occasionally containing solenoid bivalves and the abundant benthic foraminifera Ammonia confertitesta, with less frequent Buliminella sp., Bolivina sp., and some planktonic forms as Orbulina universa. Interbedded within these deposits are thicker beds (25–165 cm) of gray arkosic sands, slightly micaceous, showing normal grading and horizontal planar lamination. These levels exhibit tabular geometry and slightly erosive base, dominating the middle and upper parts of the section and defining a coarsening-upward sequence. Additionally, near the base, two layers of fine yellowish sands (<20 cm thick) with gravels and highly erosive surfaces have been identified, containing abundant bioclastic remains, echinoderm spines, siliceous sponge spicules, plant debris and large fragments of Late Miocene calcarenites eroded from surrounding outcrops. The foraminiferal specimens in these layers are relatively scarce, although they exhibit a similar assemblage characterized also by the occurrence of numerous individuals of Cibicides spp. Their tests are commonly broken and/or abraded, which strongly suggests the simultaneous presence of allochthonous marine taxa together with autochthonous groups, providing robust evidence of a high-energy marine inundation of the coastal lagoon.
This stratigraphic succession records the progressive and increasingly frequent arrival of sheet floods into a coastal lagoon from alluvial fans which are likely located at the inland reliefs. The lagoon was connected to the sea and intermittently isolated from the marine basin by a littoral barrier that has not been preserved in the outcrops. During its early stages of evolution at least two high-energy episodes are recorded, in which marine flooding transported sediments from the shallow marine zone, littoral barrier and nearby cliffs into this area. In MIS 3 deposits, that are exceptionally exposed in the Southern Atacama, these findings extend the chronology of major earthquakes and tsunamis and underscore the value of foraminiferal as proxies for coastal dynamics, salinity variability, and high‑energy marine events in the recent Quaternary geological record.
The authors thank project PID2021-127268NB-I00 funded by MCIN/AEI /10.13039/501100011033 and by FEDER/UE
How to cite: Frías Álvarez, M., Abad, M., Fernández, R., Ruiz, F., and Izquierdo, T.: Micropaleontological insights into Late Pleistocene coastal lagoon and tsunami deposits at Copiapó mouth river (Southern Atacama Desert), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18846, https://doi.org/10.5194/egusphere-egu26-18846, 2026.
The Upper Cretaceous Chalk Group of the United Kingdom (UK) preserves one of the most complete and fossiliferous records of greenhouse marine conditions, spanning the Cenomanian–Maastrichtian (~100–72 million years ago). While the Chalk has been intensively studied, a large proportion of its macrofossil record remains under-utilised because specimens collected over the past two centuries commonly lack precise stratigraphic or chronological attribution. Previous studies have demonstrated that nannofossil biostratigraphy of the chalk matrix attached to such specimens provides an effective means of unlocking the ‘dark data’ preserved in historic museum collections. Here we update and expand on those pilot studies by applying the biostratigraphic framework developed within the Chalk Sea Ecosystems (ChaSE) project to a wide range of macrofossil groups to investigate temporal and regional patterns in ecosystem change.
We apply calcareous nannofossil biostratigraphy to re-date >1,500 macrofossil specimens housed at the Natural History Museum, London (NHMUK), many of which are from now-inaccessible localities and are labelled only with broad lithostratigraphic or geographic information. Small, non-destructive samples taken from the chalk matrix associated with individual macrofossils yield diverse nannofossil assemblages, with preservation ranging from poor to moderate. Despite the variability in preservation, key marker species and bioevents were identified, allowing for confident placement within UK Chalk litho- and biostratigraphic schemes. The reliability matrix being developed will strengthen these results by evaluating a range of criteria (e.g. taxonomic clarity, morphological specificity, geographical and temporal distribution, rarity, preservation quality; Tangunan et al., 2024). This approach aims to provide robust age constraints at sub-stage to zonal resolution, substantially improving the stratigraphic utility of specimens previously unsuitable for quantitative analysis.
To complement the museum-based work, targeted field sampling was conducted at key Chalk localities across England, including Yorkshire, Devon, Dorset, Folkestone, and Eastbourne. These sites span northern, central, and southern Chalk provinces and capture spatial variability across the Cretaceous Chalk Sea. Field-derived calcareous nannofossil datasets will be integrated with the re-dated museum material to refine correlations and to investigate temporal and regional patterns in extinction timing and ecosystem change.
The resulting framework will enable both nannofossil and macrofossil occurrences to be analysed within a consistent temporal context across major Cretaceous climatic and oceanographic perturbations, including the Mid-Cenomanian Event and Oceanic Anoxic Event 2, as well as the transition from peak Turonian warmth into Late Cretaceous cooling. By transforming historic museum collections into stratigraphically resolved datasets, the ChaSE project demonstrates the critical role of calcareous nannofossil biostratigraphy in maximising the scientific value of museum archives and provides a foundation for whole-ecosystem reconstructions of Chalk Sea resilience under extreme greenhouse climates.
Reference
Tangunan, D., Bown, P., Hampton, M., Fogerty, T., Gale, A., Twitchett, R., Underwood, C., Witts, J. and Gallagher, L., 2024. Multivariate evaluation rubric for assessing the reliability of Cretaceous nannofossil index taxa and bioevents. Journal of Nannoplankton Research, 42(S), pp.119-119.
How to cite: Tangunan, D., Witts, J. D., Gallagher, L., Stukins, S., Bernard, E., Collins, K., D'Souza, L., Day, M., Ewin, T., Howard, R., Hughes, Z., Jones, M., Miller, G., Todd, J. A., Gale, A. S., Underwood, C., Twitchett, R. J., and Bown, P. R.: Unlocking UK Chalk macrofossil collections using calcareous nannofossil biostratigraphy: Insights into Late Cretaceous ecosystem change, resilience, and extinction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19472, https://doi.org/10.5194/egusphere-egu26-19472, 2026.
Oceanic Anoxic Event 2 (OAE 2; Cenomanian–Turonian) is an interval of environmental perturbation associated with elevated CO₂, linked to the activity of the Caribbean Large Igneous Province. It represents a natural experiment for investigating the response of marine organisms, including calcareous nannoplankton, to extreme oceanic disruption. This study focuses on Eprolithus floralis, a nannolith with cooler surface water affinity. Previous morphometric analyses documented size and morphological changes of E. floralis across OAE 2 in the Eastbourne section (UK). To assess whether this signal is global and to explore the drivers, we investigated the size, morphology, and abundance of E. floralis across: Clot Chevalier (France), Novara di Sicilia (Italy) -up to peak B- and Tarfaya (Morocco). Our results indicate that the morphometric and morphological response of E. floralis to OAE 2 consist of reproducible signals, although modulated by local paleoceanographic conditions. A reduction in mean total diameter during OAE 2 is observed in all sections, with minimum values at peak B of the δ13C, or slightly later at Tarfaya. Only at Novara di Sicilia E. floralis displays reduced dimensions prior to OAE 2. A post-OAE 2 size increase is observed in all records. Two morphotypes, spiky and rounded previously identified at Eastbourne, occur in all studied sections and show broadly similar patterns thus excluding a diagenetic control on nannolith morphology. Rounded E. floralis increases in abundance immediately prior to the onset of OAE 2 and dominates throughout the event (>50%), whereas spiky forms prevail in pre- and post-OAE 2 intervals. The spiky morphotype is larger than the rounded morphotype and, consequently, variations in total mean size reflect changes in morphotype dominance. Interestingly, the size offset between morphotypes varies geographically, being smaller at Eastbourne and Clot Chevalier (ca.0.2 μm) and larger at Novara di Sicilia and Tarfaya (ca.0.5 μm). No correspondence is observed between E. floralis size or abundance with the Plenus Cold Event, suggesting that temperature was not a primary control. Notably E. floralis is more common at Novara di Sicilia and Tarfaya possibly due to different oceanographic settings, being the two sections located in upwelling areas. We conclude that E. floralis responded globally to OAE 2 with size reduction and change in dominance of morphotype abundance. Size variation is comparable to that documented in Biscutum constans coccoliths. This correspondence suggests a common sensitivity to peak environmental stress, potentially linked to elevated CO₂ levels and increased concentrations of toxic trace metals. Importantly, regional variability provides insights into the adaptive strategies of E. floralis. The predominance of smaller, rounded morphotypes at Novara di Sicilia and Tarfaya suggests a preference for unstable conditions, such as those of upwelling. We speculate that the rounded morphotype may reflect a r-like strategy whereas the larger spiky were better adapted to more stable conditions.
How to cite: Bottini, C., Erba, E., and Tungo, E.: The response of calcareous nannofossil Eprolithus floralis to Oceanic Anoxic Event 2 (Cenomanian-Turonian, Late Cretaceous), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9070, https://doi.org/10.5194/egusphere-egu26-9070, 2026.
Biomineralization in marine calcifying organisms has traditionally been regarded as a process that involves proton release associated with calcium carbonate precipitation, which may lead to localized acidification. In several taxa, including foraminifera, pronounced pH gradients have been reported between calcification sites and the surrounding environment. However, it remains unclear whether strong proton extrusion into the external environment is universally required for shell formation.
In this study, we re-evaluated pH distributions during shell formation in juvenile pearl oysters (Pinctada fucata) using improved HPTS ratiometric fluorescence calibration combined with spatial analysis. We found that regions involved in shell formation, corresponding to extrapallial fluid domains inferred to represent calcification sites, consistently showed relatively higher pH values than internal soft tissues. The pH in these regions was approximately 7.8, which is slightly lower than that of the surrounding seawater (~8.0). At the spatial scale examined, no pronounced acidification was detected in the external environment outside the shell. By contrast, strongly acidic regions reaching pH ~6.0 were observed in internal tissues, which are likely associated with digestive organs. In addition, within or adjacent to the inferred calcification sites, moderately lower-pH regions (approximately pH ~7.0) were observed as ribbon-like distributions composed of small, discrete spots.
These observations indicate that shell formation in P. fucata does not depend on strong proton extrusion into the surrounding seawater, nor on extreme alkalization of the calcification site. Instead, pH regulation in this species appears to occur in a manner that is spatially separated from the surrounding seawater. This suggests that elevation of pH alone may not be the primary factor controlling calcification. Alternative mechanisms may therefore contribute to shell formation, including regulation of calcium concentration, modulation of ionic composition that inhibits calcification (e.g., Mg²⁺ and sulfate ions), and intracellular proton processing mediated by organic components.
Although acidification driven by carbon dioxide production is theoretically expected to accompany calcium carbonate precipitation, such changes could not be directly resolved under the imaging conditions employed in this study. Taken together, our results highlight diversity in proton regulation strategies among marine calcifying organisms and provide a basis for comparative discussions of shell formation mechanisms.
How to cite: Toyofuku, T., Nagaia, Y., Horikawa, Y., Kato, Y., Nagao, S., Atsumi, T., Kawano, J., and Suzuki, M.: Calcification without Strong Proton Extrusion in the Pearl Oyster Pinctada fucata, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4316, https://doi.org/10.5194/egusphere-egu26-4316, 2026.
This study is the first to examine dinoflagellate cyst sedimentary records (core MD02–2496) from the latest Pleistocene to the late Holocene along the Vancouver Island margin (Li et al., 2025). We identified 14 autotrophic and 26 heterotrophic taxa and defined four dinoflagellate cyst zones related to paleoclimatic and paleoceanographic conditions. Zone I (~14–~11.6 cal kyr BP) showed the lowest marine primary productivity (PP), evidenced by the lowest total cyst concentrations and fluxes, with Brigantedinium spp. dominating the assemblages. This was likely a result of cooler conditions associated with glacial meltwater input and weak coastal upwelling. Zone II (~11.6–~10.6 cal kyr BP) displayed a slight increase in both total cyst concentrations and fluxes, alongside a rapid rise in Operculodinium centrocarpum sensu Wall and Dale 1966 and the highest abundances of Nematosphaeropsis labyrinthus. This zone was likely linked to reduced meltwater input and enhanced coastal upwelling, which promoted nearshore PP. Zone III (~10.6–~8.2 cal kyr BP) exhibited a rapid increase in PP, demonstrated by maximum total cyst concentrations and fluxes, as well as higher abundances of autotrophic taxa. This zone was interpreted to reflect a strengthened California Undercurrent and increased upwelling, coinciding with the highest insolation intensity. High abundances of Impagidinium during this time indicated more open ocean conditions. A sharp increase in Operculodinium centrocarpum with short processes around 9–8.2 cal kyr BP may relate to the 8.2 ka event and a deceleration in sea-level rise. Zone IV (~8.2–2.3 cal kyr BP) suggested gentle fluctuations in PP, with overall declines in total cyst concentrations and fluxes, reaching their lowest point around 8.0 cal kyr BP. This was followed by a slight increase at approximately 6.5 cal kyr BP, before stabilizing. After incorporating geochemical proxies from the same sediment core (Chang et al., 2008, 2014), we compared our findings with previously published reconstructions of climatic and oceanographic conditions along the western margin of North America. This comparison revealed spatial and temporal differences in marine PP and sea surface temperatures, especially between the northern and southern regions.
Li, Z., Pospelova, V., Mertens, K.N., Chang, A.S., We, Y. 2025. A 12,000-year dinoflagellate cyst record on the Vancouver Island margin, Canada: tracing past climatic, primary productivity and oceanographic conditions. Palaeogeography, Palaeoclimatology, Palaeoecology, 667: 112876, 18 p. https://doi.org/10.1016/j.palaeo.2025.112876.
Chang, A.S., Pedersen, T.F., Hendy, I.L. 2008. Late Quaternary paleoproductivity history on the Vancouver Island margin, western Canada: a multiproxy geochemical study. Canadian Journal of Earth Sciences, 45: 1283–1297. https://doi.org/10.1139/E08-038.
Chang, A.S., Pedersen, T.F., Hendy, I.L. 2014. Effects of productivity, glaciation, and ventilation on late Quaternary sedimentary redox and trace element accumulation on the Vancouver Island margin, western Canada. Paleoceanography, 29: 730–746. https://doi.org/10.1002/2013PA002581.
How to cite: Pospelova, V., Li, Z., Mertens, K. N., Chang, A., and Wu, Y.: A 12,000-year record of dinoflagellate cysts from the Vancouver Island margin (NE Pacific): tracing past climatic, primary productivity, and oceanographic changes., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16135, https://doi.org/10.5194/egusphere-egu26-16135, 2026.
Larger benthic foraminifera (LBF) are key carbonate producers and nutrient recyclers in shallow tropical–subtropical seas, with much of their ecological success attributed to photosymbiosis with diverse microalgae. Beyond these well-studied living associations, foraminiferal tests also host post-mortem microbial colonizers that can drive early diagenetic alteration. Endolithic cyanobacteria are among the most effective carbonate microborers, yet their diversity and trace-forming styles in LBF tests remain poorly documented, limiting interpretation of micritization pathways and preservation bias in both modern and fossil foraminifera tests.
Here we present a preliminary, morphotype-based classification of endolithic cyanobacteria associated with five common LBF taxa collected from Aziziyah Corniche (near the King Fahd Causeway), Eastern Saudi Arabia (Arabian Gulf): Coscinospira hemprichii, Peneroplis planatus, P. pertusus, P. arietinus, and Sorites orbiculus. Specimens were hand-picked from a scoop of marine beach sediment, selecting tests that showed visible evidence of cyanobacterial infestation/bioerosion; therefore, the dataset is intended to characterize endolithic forms rather than quantify infestation frequency. We examined >40 tests using an embedding–casting approach (Logitech type 301 two part epoxy resin infiltration of microborings in vacuum, carbonate dissolution with dilute HCl to recover casts) combined with incident-light stereo microscopy and SEM. Endolithic forms were categorized by diagnostic boring architecture (e.g., filament diameter, branching frequency, chamber-wall penetration style, and distribution across whorls/chambers), with taxonomic assignment based on cast morphology where possible.
Across hosts, endolithic assemblages were dominated by Hyella (including an H. imanis-like morphotype; ~90% of observations), with Hyella forms consistently abundant in all five host taxa. At least three additional endolithic cyanobacterial morphotypes were observed but could only be assigned to genus-level. Boring patterns indicate active colonization of test walls that plausibly facilitates structural weakening and subsequent micritization during early taphonomy.
This morphotype inventory offers a practical reference for recognizing cyanobacterial microborings in LBF tests and for comparing bioerosion and micritization signatures among host taxa. The observed boring patterns further suggest that endolithic cyanobacteria can contribute to post-mortem test alteration, including micritization pathways that influence preservation in the fossil record.
How to cite: Amao, A. and Korin, A.: Endolithic cyanobacteria in larger benthic foraminifera: a morphotype-based classification framework for interpreting bioerosion and micritization, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22087, https://doi.org/10.5194/egusphere-egu26-22087, 2026.
While desalination is indispensable for freshwater security in arid regions, the ecological consequences of hypersaline brine discharge remain a concern. This study assesses the environmental conditions and benthic foraminiferal response near the Al-Dur Power and Desalination Plant in Bahrain, western Arabian Gulf. By analyzing physico-chemical parameters in water and sediment along a spatial gradient, we utilized foraminiferal community composition, diversity indices, and test preservation as proxies for environmental stress. Proximal to the discharge, we observed extreme hypersalinity (above 40 psu), reduced pH, and elevated concentrations of total organic carbon and heavy metals. These conditions correspond to a significant decline in biological status: living assemblages near the outflow exhibited reduced abundance and lower Shannon diversity (less than 2) compared to reference sites (above 2). Additionally, test discoloration, a key stress indicator, affected more than 50% of specimens near the discharge, versus lower than 50% at downstream sites. Our results delineate a localized impact zone where, despite the persistence of stress-tolerant taxa such as Ammonia, Elphidium, and Peneroplis, overall biodiversity is markedly reduced. As the first record of desalination-driven impacts on foraminifera in the western Arabian Gulf, this research provides a vital baseline and emphasizes the need for targeted mitigation strategies to protect vulnerable marine ecosystems amidst expanding desalination infrastructure.
How to cite: Prayudi, S. D., Tawabini, B. S., Amao, A. O., Garrison, T. F., Frontalini, F., and Kaminski, M. A.: Integrating Environmental Proxies and Benthic Foraminifera to Assess Desalination Outflow Impacts in the Western Arabian Gulf, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6519, https://doi.org/10.5194/egusphere-egu26-6519, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot 3
EGU26-12898 | ECS | Posters virtual | VPS26
Non-linear ecological responses of Ostracod communities to multi-metal pollution based on tolerance-weighted indices from the Vedaranyam shelf, Bay of Bengal, India.Tue, 05 May, 15:06–15:09 (CEST) vPoster spot 3
Benthic ostracods serve as effective bioindicators of sediment quality and metal enrichment in coastal systems, but quantitative tools linking their community structure to multi-metal contamination are limited. This study develops and validates two ostracod-based biotic indices, the Ostracoda Assemblage Pollution Index (OAPI) and its reduced form, Mini-OAPI, to evaluate benthic ecological responses to metal contamination on the Vedaranyam shelf, Bay of Bengal. Twenty-eight surface sediment samples were analysed for Fe, Mn, Cr, Cu, Ni, Pb, and Zn concentrations along with ostracod assemblage data. The indices integrate species diversity, functional guild composition, and normalized pollution load to produce a tolerance-weighted ecological deviation measure. The OAPI includes diversity, evenness, guild shift, and pollution load, performs best in data-rich settings, while Mini-OAPI shows stable diagnostic behaviour under data-limited conditions and consistently captures ecological responses along contamination gradients. Normalization to a 0-1 scale and the use of standardized disturbance classes (Low = 0.00-0.33; Moderate = 0.34-0.66; High = 0.67-1.00) ensure comparability across marine and estuarine systems. A unimodal diversity-pollution pattern consistent with the Intermediate Disturbance Hypothesis and weak Cu-organic associations indicate complex metal-biota interactions. These indices provide transferable, tolerance-weighted tools for ecological assessment and understanding ecosystem responses to environmental change.
Keywords: Ostracoda Assemblage Pollution Index (OAPI); Mini-OAPI; benthic bioindicators; non-linear ecological modelling; Intermediate Disturbance Hypothesis (IDH); copper paradox; marine pollution assessment.
How to cite: Palanichamy, P., Vimal Kanth, S., Chellamuthu, S. N., Subramani, R., and Hussain, S. M.: Non-linear ecological responses of Ostracod communities to multi-metal pollution based on tolerance-weighted indices from the Vedaranyam shelf, Bay of Bengal, India., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12898, https://doi.org/10.5194/egusphere-egu26-12898, 2026.
