We welcome studies that advance new biomarkers or methods for applying them to modern environments and the geological past. Such research may focus on tracing carbon dynamics in various systems, reconstructing environmental factors like temperature, rainfall, biogeochemical cycles, human impact, and vegetation variations. Relevant topics include biosynthesis and phylogeny of source organisms, processes of transport and diagenesis, calibrations to environmental parameters, proxy development, and applications for understanding past environmental change.
Paleoclimate records play a crucial role in improving the performance of climate models by enhancing our mechanistic understanding of climate dynamics and providing an independent framework for evaluating model simulations through model–data comparisons. However, for such comparisons to be successful, reliable climate reconstructions are required, particularly with respect to their seasonal sensitivity. To achieve this, we need robust proxies supported by a solid mechanistic understanding.
In this work, we aim to provide a solid foundation for the use of the lacustrine alkenone paleothermometer in mid-latitude freshwater lakes. Alkenones are temperature-sensitive molecules produced by haptophyte algae from the order Isochrysidales. The alkenone unsaturation degree has been linked to temperature and has been widely used to reconstruct past sea surface temperatures. Alkenones are also present in lakes, although they do not occur in all lakes. In freshwater lakes, alkenone-producing Isochrysidales belong to a phylogenetically distinct group compared to those found in saline lakes and marine environments. Previous work on Swiss lakes has shown that alkenones are relatively common in mid-latitude European lakes, are produced between ice-out and the establishment of lake stratification, and record water temperature, as found in high-latitude lakes. However, this group remains poorly characterized, particularly regarding its life cycle and genetic diversity, which limits our understanding of the lacustrine alkenone proxy in freshwater lakes.
To address these knowledge gaps, we monitored two Swiss lakes, Lake St. Moritz, an alpine lake, and Lake Greifen, a lowland lake, by combining alkenone characterization with DNA sequencing of small subunit (18S), internal transcribed spacers (ITS 1 and ITS2) and large subunit ribosomal RNA (5.8S and 28S) marker genes targeting Isochrysidales. Using this approach, we aim to: (i) refine the identification of the Isochrysidales present in both lakes; (ii) characterize the temporal dynamics of the Isochrysidales community in terms of structure and abundance throughout the bloom period; (iii) identify the life cycle stage during which alkenones are produced; and, (iv) determine the environmental controls on the Isochrysidales bloom timing.
How to cite: Martin, C., Marchand, L., Richter, N., Dubois, N., and Amaral-Zettler, L.: Back to alkenone sources: molecular profiling of alkenone-producing Isochrysidales in Swiss lakes using targeted DNA amplicon sequencing , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20214, https://doi.org/10.5194/egusphere-egu26-20214, 2026.
Throughout the past century, eutrophication and climate change have strongly impacted temperate lakes, resulting in greater algal productivity and shifts in phytoplankton community composition. In many lakes cyanobacterial blooms have become more common, reducing water quality, negatively impacting aquatic food webs, and affecting the cycling of carbon and other nutrients. Appropriate management of aquatic systems to mitigate and avoid these problems is informed by monitoring data, but direct observations are often limited to recent decades. Paleolimnological approaches can extend the observational window and contextualize long-term changes of algal communities in response to climatic and environmental forcings. However, it remains challenging to reconstruct changes in algal productivity and community assembly, particularly the relative abundance of cyanobacteria to eukaryotic algae, throughout the geologic past.
Here, we present two recently developed lipid-based proxies that can be used to reconstruct broad shifts in algal community composition: (1) the Phytol:Sterol Index (PSI), which represents the relative abundance of the chlorophyll side-chain, phytol, to phytosterols from eukaryotic algae and (2) hydrogen isotope offsets between phytol and the common membrane lipid C16 fatty acid (δ2HC16:0 Acid/Phytol), which is higher for lipids produced by cyanobacteria and green algae than for other eukaryotic algae. We demonstrate the utility of these proxies in a collection of short sediment cores from lakes in the Swiss Plateau (Murtensee, Greifensee, and two hydrologically distinct basins of Zugersee), all of which experienced extreme eutrophication in the mid- to late 20th century, followed by partial recovery to lower nutrient levels. We found significant changes in lipid distributions coincident with the main period of increasing total phosphorus inputs. During this time, PSI increased in all four lake records, indicating that more of the algal biomass accumulating in the sediments was derived from cyanobacteria. In Murtensee, PSI and δ2HC16:0 Acid/Phytol co-varied, while in Greifensee the initial increase in cyanobacteria was followed by a period of low PSI and high δ2HC16:0 Acid/Phytol values, consistent with observations of abundant green algae during this later period.
We cross-compared our lipid biomarker data with cyanobacterial and plastid 23S rRNA amplicon sequencing variants (ASVs) of DNA extracted from the cores. In general, there was good agreement between PSI and the abundance of cyanobacterial ASVs. However, during periods when the cyanobacterial DNA was primarily from small-celled taxa such as Synechococcus, such as the early 20th century in Murtensee, PSI was low relative to the abundance of cyanobacterial ASVs. This suggests that small but numerous cyanobacteria might be overrepresented in sedimentary DNA relative to their biomass, likely related to the polyploidy of their chromosomes.
Overall, sedimentary PSI appears to be a robust and analytically straight-forward indicator of cyanobacterial abundance. Due to the greater mass of phytol needed for δ2H measurements, chromatographical challenges can limit the application of δ2HC16:0 Acid/Phytol in some sediments, such as those from Zugersee. The combination of these new lipid-based proxies with other tools, including sedimentary DNA, pigments, and microfossil analyses can provide the most comprehensive picture of past algal community composition.
How to cite: Ladd, N., Klatt, A., Nelson, D., Wälchli, J., Wietelmann, T., and Dubois, N.: New lipid-based proxies for past cyanobacterial abundance , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11425, https://doi.org/10.5194/egusphere-egu26-11425, 2026.
Lakes play an important role in paleoclimate studies as they archive high-resolution and continuous records. However, the climatic proxies developed for lake settings are limited. Among all, the lipid biomarkers have been widely studied, as they are ubiquitously distributed and efficiently carry environmental information. One prominent example is the branched glycerol dialkyl glycerol tetraethers (brGDGTs), produced by bacteria, use to quantitatively reconstruct the temperature and pH based on lake sediment. However, due to the influence of confounding factors and not fully determined producer species, temperature reconstruction based on brGDGTs could yield uncertainties as large as 4°C. Having complementary and independent temperature proxies appears to be essential.
3-hydroxy fatty acids (3-OH FAs) were recently proposed as temperature and pH proxies in soils and may hold the potential to be also applied to lakes. These compounds are membrane lipids produced by Gram-negative bacteria. Similar to brGDGTs, their distribution was related to environmental variables. To date, 3-OH FAs were mainly investigated in soils [1] with only 3 studies, all in the Chinese region, in lakes. A linear correlation between some of the 3-OH FA isomers (i.e. the Ratio of Anteiso-C13 to Normal-C13 ̶ RAN13)and mean annual air temperature (MAAT) was observed in Chinese lakes [2]. In contrast, we did not observe such a correlation in 52 lake sediments of the French Alps and 20 lakes of Southern Chile [3]. This suggests that the relationship between MAAT and 3-OH FA distribution in lakes is complex and cannot be systematically reflected by a linear correlation. Nevertheless, this relationship needs to be further investigated using additional samples from all over the world.
This study aims to present the first global analysis of lacustrine 3-OH FAs and their relationship with MAAT. In addition to first studies, we analyzed these lipids in 220 lakes distributed worldwide over a large range of latitude and elevation, with MAATs ranging from -14.2°C to 27.7°C. Principal Component Analysis (PCA) was first applied to the whole dataset (220 lakes) to investigate the changes in 3-OH FA distribution with location. In addition, both linear (including the RAN13 index) and non-linear models (based on machine learning algorithms) are currently used to examine the relationship between 3-OH FA distribution and MAAT. This will bring new insights into the applicability of the 3-OH FAs as lacustrine temperature proxies at the global scale. 3-OH FAs could then be applied to paleotemperature reconstructions from lake sediment cores, complementarily of and independently from existing proxies such as brGDGTs.
References: [1] Véquaud et al. (2021). Biogeosciences 18, 3937-3959. [2]Yang et al. (2021). Org. Geochem. 160, 104277. [3] Ke et al., Org Geochemistry, under revision.
How to cite: Ke, S., Sabatier, P., Anquetil, C., and Huguet, A.: Development of a global lacustrine temperature calibration based on 3-hydroxy fatty acid membrane lipids, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19917, https://doi.org/10.5194/egusphere-egu26-19917, 2026.
Lipid biomarkers such as glycerol dialkyl glycerol tetraethers (GDGTs) and 3-hydroxy fatty acids (3-OH FAs) are widely used proxies for paleoenvironmental reconstruction. To evaluate their applicability in high-latitude environments, we analyzed samples from seven soil trenches collected at 5 cm intervals to a depth of ~40 cm, fifteen surface soils, and nine fjord sediments from the Ny-Ålesund region of Svalbard. The datasets were compared to assess the relative performance of lipid-based proxies under Arctic conditions. Soils from Svalbard display higher proportion of 6-methyl branched GDGTs compared to most global soils. Although the overall concentrations of branched and isoprenoid GDGTs are relatively low, likely due to the cold climate and short growing season. The microbial lipid derived pH proxy, performs reliably in extreme setting. In contrast, the temperature index, MBT′5ME values show substantial variability despite limited temperature variation, suggesting that temperature is not the sole factor affecting the lipid distribution. Depth-profile analyses of brGDGTs in moss-dominated soils reveal that moss-covered areas contribute significantly to brGDGT abundance. Moss-derived organic matter enhances bacterial activity and lowers the fungal-to-bacterial ratio within the microbial community. This interpretation is supported by stable carbon isotope (δ¹³C) and total organic carbon (TOC) data, which suggest that mosses are the primary source of organic carbon supporting brGDGT production. Overall, finding highlight the important role of moss cover in regulating microbial processes and GDGT distributions in Arctic soils, emphasizing the need to consider vegetation effects when applying lipid-based proxies in high-latitude paleoclimate reconstructions.
How to cite: Kumar, V., Roy, B., Tiwari, M., Thamban, M., and Sanyal, P.: Understanding Microbial Lipid (GDGTs and 3-OH FAs) Responses Across Arctic Ecological Gradients, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3820, https://doi.org/10.5194/egusphere-egu26-3820, 2026.
Lipid biomarkers preserved in marine sediments provide powerful tools for reconstructing past climate and environmental change. However, their interpretation critically depends on understanding the processes governing their production, transport, and preservation, as different water-column processes can substantially modify the environmental signals transferred to sedimentary archives. This study investigates four different lipid biomarkers (long-chain fatty acids [LCFA], n-alkanes, alkenones, and glycerol dialkyl glycerol tetraethers [GDGTs]) at three key stages of their source-to-sink pathway: production, transport in the water column, and deposition and preservation in surface sediments to shed light on their controlling processes factors. A particular focus is placed on tracking sea surface temperature (SST) signals encoded in some of these lipids at each key stage, thereby refining the current framework for biomarker-based paleotemperature reconstruction in the study region.
We collected suspended particulate matter from six southwest Iberian Margin stations (JC089 cruise, August 2013) using in situ filtration pumps yielding 38 samples (~1188 L on average per sample) from surface to ~3000 m depth at discrete fluorescence and turbidity maxima. Surface sediments from the same locations and 25 additional core-top samples were also analyzed. LCFA, n-alkanes, and alkenones were quantified using GC-FID, while GDGTs were analyzed by HPLC. Associated SSTs were reconstructed using the Uk′₃₇ and TEX₈₆ indices, with Bayesian calibrations applied to both proxies.
In the water-column, concentrations of terrestrial lipids (n-alkanes and LCFA) are highest in the upper photic zone with no clear onshore–offshore trend, reflecting mixed atmospheric and riverine inputs. Alkenones are predominantly found in nearshore waters within the photic zone and decrease in concentration with distance offshore, reflecting in situ production linked to primary productivity. Elevated GDGT concentrations are found above ~2000 m within the warm, saline, and relatively turbid Mediterranean Outflow Water (MOW). While this distribution suggests some lateral transport, the absence of alkenones at these depths points to substantial in situ GDGT production.
Both alkenone (12.6–22.3 °C) and GDGT-derived SSTs (14.6–20.0 °C) exhibit a cold bias relative to surface CTD measurements in the water column. A similar cold bias is observed in surface sediments, where reconstructed SSTs (15.7–19.0 °C for alkenones; 14.6–19.2 °C for GDGTs) are lower than World Ocean Atlas annual mean values. We attribute these differences to variations in production depth and seasonal bias and furthermore rule out a significant influence from terrestrial GDGT input or riverine nutrients.
Future application of compound-specific radiocarbon and stable isotope analyses (δ¹³C, δ²H) on alkenones will further strengthen the mechanistic link between modern lipid cycling and paleoenvironmental reconstructions.
How to cite: U.Nanayakkara, N., R. Magill, C., De Jonge, C., Eglinton, T., S. Wijker, R., Stoll, H., Hodell, D., J. Sierro, F., and Ausin, B.: Source-to-sink controls on lipid biomarkers and temperature signals in the Atlantic Iberian margin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18675, https://doi.org/10.5194/egusphere-egu26-18675, 2026.
The evolution of typhoon activity in Taiwan at glacial-interglacial timescales remains poorly constrained, as modelling past typhoon trajectories is challenging and terrestrial archives rarely extend beyond the Holocene due to high erosion rates. However, the land-to-sea transfer of terrestrial material is mainly controlled by typhoons, with more than 75% of the annual flux occurring within less than 1% of the year. Particulate organic carbon (POC) transferred during typhoon-induced floods represents 77 to 92% of the annual biospheric (vegetation- and soil-derived) POC flux. Consequently, investigating changes in the flux of biospheric terrestrial POC in marine sediments off eastern Taiwan, where rivers connect directly to the canyon regardless of the relative sea-level due to the absence of a broad continental shelf, provides an opportunity to assess past variations in typhoon activity.
At this end, we analyzed lipid biomarkers together with sedimentological and geochemical parameters from a sediment core collected offshore eastern Taiwan. Coarser grain sizes, higher TOC, long chain n-alkanes and soil-derived brGDGTs (IIIa/IIa < 0.59) accumulation rates during the deglaciation relative to the Holocene indicate substantially enhanced land-to-sea carbon transport linked to more frequent and/or more energetic turbidity activity. In addition, higher CPI values and reduced age offsets between planktonic foraminifera and bulk organic matter radiocarbon dating over the same interval point to a larger fraction of biospheric terrestrial POC transfer to the marine sediments compared to the Holocene. Together, these results point to an enhanced typhoon activity affecting Taiwan during the deglaciation, in agreement with recent model simulations indicating a higher typhoon genesis potential at that time. Given the difficulties in simulating past typhoon activity in Taiwan, or in recording it from terrestrial archives, our approach provides an alternative way to constrain past changes in typhoon activity affecting the island. This also raises the possibility that, if typhoon activity affecting Taiwan were to increase due to a northward shift in typhoon pathways as projected under ongoing global warming, the eastern margin of Taiwan could turn into a carbon sink.
How to cite: Fenies, P., Ho, S. L., Bassetti, M.-A., Vazquez Riveiros, N., Hefter, J., Chang, Y.-P., Löwemark, L., Babonneau, N., Ratzov, G., Hsu, S.-K., and Su, C.-C.: Increased typhoon activity led to higher land-to-sea organic carbon export in the deglacial northwest subtropical Pacific: Insights from lipid biomarkers and sediment geochemistry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17006, https://doi.org/10.5194/egusphere-egu26-17006, 2026.
The lowland Maya of Mesoamerica were affected by multiple environmental stresses throughout their history, and many experienced a major demographic and political decline, or collapse, during a period of inferred intense multidecadal drought, approximately 1200- and 1000-years BP. Given regional variation in the timing and character of the collapse (Demarest, 2004; Hodell et al., 2007; Webster et al., 2007; Kennett and Beach, 2014; Douglas et al., 2015), much remains to be discovered about the complex interactions between climate and society in the Maya lowlands. To this end, we combine carbon and hydrogen isotopic analyses of leaf wax n-alkanes with quantification of faecal stanols and polycyclic aromatic hydrocarbons from a lake sediment core from the southwest lowlands to assess whether (1) palaeoecological evidence of land use is related to population change; and (2) whether population and land use are linked to changing precipitation. Our data reveal a transition from generally more intense fire use and C4 plant agriculture during the Preclassic (3500–2000 BP) to dense populations and reduced fire use during the Classic (1600–1000 BP). This is consistent with other evidence for a more urbanised and specialised society in the Classic. We do not find evidence of drought in the hydrogen isotope leaf wax record (δDlw), implying that local drought was not a primary driver of observed variability in land use or population change in the Classic-period southwestern lowlands. We present preliminary data from lake sediment cores from the northern lowlands.
How to cite: Gwinneth, B., Johnston, K., Breckenridge, A., Strachan, I., Marcoux, A., Martínez Dyrzo, H., Roy, P., and Douglas, P.: Reconstructing human-environment interactions in the Maya lowlands using lipid biomarkers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-456, https://doi.org/10.5194/egusphere-egu26-456, 2026.
Angkor was the capital of the Khmer Empire during approximately 9th to 15th CE. It relied on a sophisticated water management system to sustain a vast low-density urban population. For the last two decades, the decline of Angkor has been linked to hydroclimatic instability in combination with infrastructural failure. Recent archaeological evidence suggests that the decline of elite occupation within the civic-ceremonial core may have begun earlier, resulting from additional social, political, or economic drivers. Understanding the timing and potential causes of such changes is crucial for assessing the vulnerability of complex urban systems.
Sedimentary molecular biomarkers can provide insights into paleoenvironmental and anthropogenic changes. In particular, untargeted molecular fingerprinting is not constrained by predefined compound lists and analyzes thousands of molecular features simultaneously. This enables the detection of complex and overlapping source inputs and facilitates the identification of broader molecular shifts potentially associated with changing land use, ecosystem functioning, and anthropogenic activity.
Here we apply an untargeted molecular fingerprinting framework using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOFMS) to characterize sedimentary organic matter in lipid extracts from a sediment core retrieved from a pond inside the temple of Angkor Wat. GC×GC substantially increases chromatographic resolution and enables the detection of thousands of chemical features without a priori hypotheses and is thus suitable for the untargeted analyses. We investigate temporal shifts in molecular composition across the Angkorian and post-Angkorian periods to evaluate changes in organic matter inputs, microbial processing, and water quality, and discuss their implications for changes in urban land use and occupation patterns at the temple complex.
How to cite: Liu, W., Ruan, Y., Schefuß, E., Sistiaga, A., Korneliussen, T. S., Larsen, N. K., Ramsøe, A. D., Ruter, A., Siggaard-Andersen, M.-L., Demeter, F., Socheat, C., Pottier, C., Kjaer, K., Hinrichs, K.-U., Willerslev, E., and Wörmer, L.: Environmental and ecological change across Angkor’s transition inferred from untargeted molecular fingerprints, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17016, https://doi.org/10.5194/egusphere-egu26-17016, 2026.
The Younger Dryas (YD, 12,900-11,700 cal. yr BP) was a major abrupt cooling event caused by a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), which sharply reduced heat transport in the Northern Hemisphere. However, the magnitude, temporal pattern and seasonality expression of the YD cooling across Europe remain difficult to constrain due to the lack of quantitative proxies and confounding factors on proxy responses. Here, we aim to reconstruct YD mean annual temperatures of months above freezing (MAF) using temperature-sensitive bacterial membrane lipids, so-called branched glycerol dialkyl glycerol tetraethers (brGDGTs), stored in lake sediments from Retournemer (eastern France) and Steisslingen (southern Germany). In both lakes, brGDGT-derived MAFs show only a minor cooling (~1-2C) during the YD, whereas more established GDGT-based proxies indicate a deeper oxic layer and shifts in lake microbial communities consistent with colder and windier conditions across Europe. As such, our brGDGT records confirm that most of the cooling was expressed during winters, in line with previously suggested seasonality patterns. Subsequent examination of the much less explored branched glycerol monoalkyl glycerol tetraethers (brGMGTs) that are characterized by an additional carbon–carbon bond between their alkyl chains reveals a stronger response during the YD in both lakes. However, translation to absolute temperature is hampered by their distinct composition from that in East African lakes on which the only currently existing transfer function is based. Regardless, our results show that brGMGTs have potential as indicators of YD cooling in future studies.
How to cite: Panbut, C., Hendriks, P., Lane, C. S., Engels, S., Sachse, D., Hoek, W. Z., and Peterse, F.: Towards quantifying Younger Dryas cooling in Europe using lipid biomarkers archived in lake sediments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3374, https://doi.org/10.5194/egusphere-egu26-3374, 2026.
As the largest volcanic eruption in the Quaternary period, the ~74 ka Toba super eruption’s impact on the global heat budget and monsoon systems has been prominently debated. Despite particular focus on its consequences in India as one of the key regions of early modern human dispersal — ranging from catastrophic to minimal — high-resolution proxy evidence from geological archives that empirically support the claims has been scarce. In this study, we trace pre- and post-Toba monsoonal dynamics from a finely laminated sedimentary section from the Arabian Sea that brackets Toba tephra as an event marker of the eruption. The sediment core SO130-289KL was retrieved from the northeastern margin of the Arabian Sea outside of the upwelling zone (Sindh continental margin), at a water depth of 571 m, which today lies within the oxygen minimum zone (OMZ). The site is sensitive to both monsoon seasons, as the South Asian summer monsoon controls sedimentary dynamics, whereas the wind strength of the winter monsoon primarily influences the sea surface temperatures (SSTs). Thus, the sediment core sensitively records the evolution of South Asian summer and winter monsoons. In order to reconstruct the regional climatic response to Toba at near-annual resolution, we produced time-series data of elemental and SST variations using µm-scale measurements (100–200 µm resolution) by x-ray fluorescence (µXRF) scanning and mass spectrometry imaging (MSI) techniques, respectively. The µXRF elemental data trace terrestrial components primarily sourced by runoff from the summer monsoon, which are complemented by the glycerol dialkyl glycerol tetraether-based SST calculations from MSI that are affected by OMZ intensity. On the other hand, the alkenone measurements from MSI more sensitively trace SST variations that are primarily governed by the winter monsoon. Supplemented by conventional biomarker and stable hydrogen and carbon isotope measurements, which trace precipitation and vegetation dynamics over the Indus River catchment, respectively, our multi-proxy data contribute to a better understanding of the impact that the Toba eruption had on the regional climate, environment, and eventually, contemporaneous humans.
How to cite: Park, J., Liu, W., Wörmer, L., Schefuß, E., Lückge, A., Altun, J., Taubner, H., Hinrichs, K.-U., and Obreht, I.: South Asian monsoon response to the ~74 ka Toba super-eruption revealed by µm-scale imaging on Arabian Sea sediment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11753, https://doi.org/10.5194/egusphere-egu26-11753, 2026.
Compound-specific stable isotope analysis (CSIA) of organic biomarkers enables reconstruction of past environmental and climatic conditions by resolving the isotope composition of individual molecular compounds. Among these applications, hydrogen isotope (δD) measurements of leaf wax n-alkanes are widely used to infer changes in hydroclimate, including variations in precipitation isotopic composition, moisture source, and evaporative conditions. Because long-chain n-alkanes are resistant to degradation and preserve a terrestrial signal in sedimentary archives, their δD values provide a robust proxy for past continental hydroclimate across a wide range of depositional settings.
Despite this utility, CSIA of organic biomarkers is frequently limited by the low abundance of target compounds, particularly in sedimentary archives where concentrations vary strongly across stratigraphy and compound class. This limitation is especially acute for δD measurements, which typically require injected analyte masses of several hundred nanograms to achieve acceptable precision on gas chromatography-isotope ratio mass spectrometry (GC-IRMS) systems. Because hydrogen isotope analysis relies on pyrolytic conversion to H2, δD measurements generally operate at lower absolute signal intensities than compound-specific δ13C analyses, placing them closer to instrumental sensitivity limits where background correction, baseline placement, and nonlinear response exert a proportionally greater influence on measured isotope ratios. As a result, δD analysis of individual low-abundance compounds is often precluded, necessitating pooled samples or coarse sampling intervals that suppress short-duration climate signals and limit the achievable resolution of paleoclimate reconstructions.
Here, we assess the feasibility, limitations, and uncertainty structure of isotope dilution (ID) for δD measurements of leaf wax n-alkanes using internationally recognized, isotopically characterized n-alkane standard mixtures. Isotope dilution offers a potential strategy to stabilize isotope measurements through controlled mixing of a low-abundance analyte with an isotopically characterized spike, thereby increasing the total amount of analyte contributing to the measurement and reducing uncertainty associated with low signal intensities. Controlled mixing experiments isolate the effects of nominal mixing ratio, isotope contrast between spike and sample, and signal intensity on back-calculated isotope values. These tests provide a framework for quantifying uncertainty propagation in ID-CSIA and for defining practical constraints on its application. Our results establish conditions under which isotope dilution can yield accurate and precise δD measurements for low-abundance compounds and provide methodological guidance for extending CSIA into concentration regimes that are otherwise analytically inaccessible, enabling higher-resolution paleoclimate reconstructions and expanding the range of sedimentary archives amenable to biomarker isotope analysis.
How to cite: Lupien, R., Traphagan, J., and Juchelka, D.: Isotope dilution to enhance δD measurability in low-abundance n-alkane samples, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7259, https://doi.org/10.5194/egusphere-egu26-7259, 2026.
The Tortonian stage (11.6–7.2 Ma) represents a warm interval preceding the Late Miocene Cooling (7.5–5.5 Ma), during which high-latitude temperatures exceeded modern values by up to ~17°C. Atmospheric CO2 reconstructions during the Tortonian are poorly constrained, with existing proxy records suggesting either high CO2 levels, reaching ~790 ppm at ~11 Ma (Mejia et al., 2017), or more moderate and relatively stable CO2 conditions.
Here, we present new high-latitude pCO2 reconstructions based on alkenone carbon isotopic fractionation (εp) from Ocean Drilling Program (ODP) Site 1088 in the subantarctic South Atlantic, covering the interval from 11.6 to 9.0 Ma. Combined benthic and bulk carbonate δ13C and δ18O records are used to identify the Tortonian thermal maximum and to guide targeted, higher-resolution sampling. Sea surface temperatures are reconstructed from alkenone Uk′₃₇ ratios using the Bayspline calibration (Tierney et al., 2018), and εp is calculated from compound-specific δ13C measurements of the C37:2 alkenone. The isotopic composition of dissolved inorganic carbon is estimated from planktonic foraminiferal (G. bulloides) δ13C, accounting for the temperature-dependent fractionation between DIC and aqueous CO2.
pCO2 concentrations are then reconstructed using a probabilistic εp model (Stoll et al., 2019) that explicitly incorporates coccolithophore cell size, growth rate, and light availability. Coccolith size and thickness distributions are quantified from circular polarized image analyses, while growth rates are inferred from temperature and nutrient availability.
How to cite: Santos, M., Wijker, R., and Stoll, H.: Reconstructing sea surface temperature and atmospheric CO₂ across the Tortonian using alkenone εp records from South Atlantic ODP Site 1088, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7288, https://doi.org/10.5194/egusphere-egu26-7288, 2026.
Certain haptophyte algae produce a recalcitrant suite of long-chain (C37-C39) methyl and ethyl ketones called alkenones. These compounds are widely applied in paleoclimate studies due the temperature sensitivity of the ratio of di- to tri- unsaturated alkenones, most commonly quantified in the UK’37 index. However, phylogenetic effects and other physiological effects can alter the intercept of the UK’37 relationship to temperature, complicating the application to past climates. Here we present results of two strains of Group II (brackish) and four strains of Group III (open marine) haptophytes batch cultured under different temperatures, light levels, and CO2 (aq) concentrations. One Group III strain was also continuously cultured in a turbidostat.
The alkenone response to temperature differs per strain, as has previously been found in culture studies. Additionally, when applying core top calibrations commonly used in paleoclimate studies, UK’37 consistently under-predicts batch culture growth temperature. We further find no systematic control on the offset between alkenone unsaturation calibrations from core top and expected values in batch culture for a given strain. When considering data from multiple strains, the offset from expected values in UK’37 and UK38Me, but not UK38Et, correlate to ratio of the alkenone concentration relative to particulate organic matter. In cells harvested with a higher proportion of alkenones relative to particulate organic carbon, this cold offset is diminished and temperature prediction for UK’37 and UK38Me is more consistent with core top calibrations.
In addition, we compare nutrient replete continuous culture results to batch culture of the same strain to assess if the alkenone unsaturation response to temperature similar.
How to cite: Rice, A., Torres-Romero, I., Zhang, H., Wijker, R. S., Clark, A. J., Jaggi, M., and Stoll, H. M.: Phylogenetic effects of alkenone unsaturation in cultured Group II and Group III haptophytes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7314, https://doi.org/10.5194/egusphere-egu26-7314, 2026.
Climate models are based on our understanding of the Earth climate system. To improve their accuracy, we rely on regional paleotemperature reconstructions, that can also be used to validate model outputs. Many existing paleoclimate proxies reconstruct mean annual or summer temperatures. Spring, which is essential for biodiversity and agricultural activities, is underrepresented, resulting in an incomplete perception of past climate, especially regarding seasonal variations. Lacustrine alkenones are lipid biomarkers that appear as a promising paleothermometer to quantitatively record spring temperatures in freshwater lakes. They are long chain ketones (35 to 42 carbons) with a varying number of double bonds (2 to 4) produced exclusively by the haptophyte phytoplankton in the Order Isochrysidales. These algae were found to respond to water temperature changes by altering relative proportions of the produced alkenones. The UK37 index has been extensively used to reconstruct sea surface temperatures in the past. Alkenone producing algae are divided into three major phylogenetic groups shaped largely by salinity. Among these groups, Group I dominate freshwater lakes, making them potential powerful tools for reconstructing continental spring temperatures. Alkenone seasonality was resolved in several studies conducted in high-latitude lakes which found alkenones occurring at the ice-off (spring-summer). The question arises regarding which seasonal temperatures are recorded by the UK37 index in mid latitude lakes? When other proxies show great uncertainty, three robust in-situ calibrations with low uncertainties were developed for the correlation of UK37 values to temperatures in high-latitude lakes. However, so far, no monitoring studies have been conducted in mid-latitude lakes, and no in-situ calibration has been established. Therefore, we conducted high-frequency monitoring of alkenone production in two Swiss lakes with very distinct settings for comparison: Greifensee (453masl, lowland and not ice-covered), and Lake St. Moritz (1768masl, alpine and ice-covered). The monitoring consisted in taking water samples over a full year on Greifensee, and from spring to summer in Lake St. Moritz, and retrieving sediment traps regularly to study alkenone deposition into the sediments in parallel with production in the water. We also collected environmental data such as salinity, nutrient contents, chlorophyll concentrations, temperature, and light radiation. We describe the seasonality of alkenone production in these two lakes and draw the first calibrations between the UK37 and temperature. The timing of alkenone production will be compared with variations in the environmental parameters to estimate the bloom drivers. With this work, we aim to establish a reliable continental spring temperature proxy.
How to cite: Marchand, L., Martin, C., Richter, N., Amaral-Zettler, L., and Dubois, N.: Seasonality of Group I alkenone production and in-situ UK37-Temperature calibrations for mid-latitude Swiss lakes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1451, https://doi.org/10.5194/egusphere-egu26-1451, 2026.
Present-day biodiversity and landscapes in Europe reflect millennia of human influence. Particularly, the ‘medieval agricultural revolution’ marked large-scale movements of people, plants, and livestock, and major shifts in agricultural practices, coinciding with the Medieval Climate Anomaly. Understanding how this biodiversity emerged, and how it contributes to the resilience of socio-ecological systems is critical for future climate-adaptive land-use planning and management. Existing human-ecodynamic reconstructions are largely based on archaeological sites and mires, and therefore often lack the spatial representativeness beyond an individual site, continuous depositional archives, or the temporal resolution and ecological breadth needed to assess biodiversity, land-use history, and species vulnerability in detail.
The ERC synergy project “MEMELAND – Molecular Ecology of Medieval European Landscapes” addresses these gaps through an interdisciplinary multi-lake, multiproxy framework. As part of this project, we will investigate lake sediment records from 50 lake pairs across a latitudinal gradient in Europe. Each pair consists of one lake located near a high-status (elite) site and one “control” lake from a nearby area lacking direct archaeological evidence for medieval elite activity. Such baselines from nearby “pristine” lakes are rarely established but are essential for disentangling natural from anthropogenic drivers of change.
Here we present our faecal biomarker framework to reconstruct grazing and manuring intensity during the medieval period using sterols, stanols, and bile acids measured as concentrations and depositional fluxes. To improve source attribution, we are developing a diet-controlled livestock reference library that characterizes sterol/stanol and bile-acid fingerprints and diagnostic ratios under historically plausible feeding regimes. We further leverage MEMELAND’s sedaDNA component to benchmark biomarker-derived livestock inputs against taxonomically resolved signals of domestic animals and land-use indicators. In this complementary approach, faecal biomarkers constrain the magnitude of livestock input, while sedaDNA refines the source and ecological context.
We ask which faecal biomarkers and diagnostic ratios are most robust across heterogeneous European lake systems, whether paired-lake comparisons reveal consistent spatio-temporal contrasts in land use during the medieval period, and whether eutrophication trajectories track enhanced nutrient loading associated with grazing and manuring. Besides the sedaDNA data, biomarker results are further integrated with palynological proxies, hyperspectral imaging, geochemistry (µXRF), and chronostratigraphic approaches to identify and contextualize land-use signatures in sediment archives.
On our poster, we present an overview of this biomarker contribution to MEMELAND and look forward to discussing it with you.
How to cite: Schneider, T., Brown, A. G., Mackay, H., Lang, A., Hamerow, H., Mottl, O., and Dubois, N.: Sedimentary faecal biomarkers in European lakes: tracing land-use activity during the medieval agricultural revolution, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7602, https://doi.org/10.5194/egusphere-egu26-7602, 2026.
The Mongol Empire (13th - 14th century CE) was the largest contiguous land empire in world history. However, it is not yet known how an urban lifestyle in its first capital Karakorum was sustained in the heart of the Mongolian steppe. One aspect of this is how food supply and subsequent delivery of raw materials was secured.
Therefore, we aimed at characterizing soil resources in Sarlag Tolgoi, an ancient settlement about 50 km northwest of Karakorum. We took samples of a transect through the settlement and reference samples of undisturbed soil, serving as control. We (i) analyzed these samples regarding their phosphorus concentration as waste marker and (ii) the sterol and bile acid concentration in cases where phosphorus levels were elevated, in order to reconstruct past settlement structures and the fingerprint they left on the surrounding environment.
We found a tenfold increase of phosphorus concentrations from 2 to 20 mg P kg-1 in the topsoil from the surrounding area compared to the soil within the settlement itself. This clearly supports the hypothesis of anthropogenic influence at this site. A closer examination of those samples with increased phosphorus concentration by sterol and bile acid analysis revealed hotspots of an ancient faecal input by grazing animals - mainly cattle and sheep - within the settlement. Furthermore, the applied ratio (epi-5β-stigmastanol/5β-stigmastanol + epicroprostanol/coprostanol) revealed no indication of faecal input from horses, whereas low proportions of coprostanol suggested limited human faecal input. Therefore, we suppose that horses and ditches for human waste were outside of the settlement area.
In conclusion, our results demonstrate that Mongolian steppe soils preserve ancient fingerprints of human settlement associated with the Mongol Empire, expressed through changes in both, their morphology, and chemical signature. These findings highlight the considerable potential of basic soil science approaches to refine and strengthen archaeological interpretations in this region. Moreover, complementary chemical analyses provide valuable insights into past lifeways and human-environmental interactions. While the unambiguous attribution of signals to specific historical periods remains challenging, future integration of compound-specific biomarker dating in the vicinity of archaeological findings holds strong promise for achieving more robust chronological resolution.
How to cite: Koch, I., Mörchen, R., Bemmann, J., Reichert, S., and Amelung, W.: Reconstruction of ancient land-use in the Orkhon Valley, Central Mongolia, by waste markers: phosphorous, sterol and bile acid analyses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9870, https://doi.org/10.5194/egusphere-egu26-9870, 2026.
During the recent decades, human activity led to vast and rapid changes in algal communities through pollution, alteration of catchment areas and climate change. As a consequence of such stressors, lake conditions can offer favourable conditions for the formation of harmful algal blooms (HABs) of cyanobacteria. The rise of bloom-forming taxa and toxin-producing taxa are threatening ecosystem services provided by lakes. Understanding the dynamic nature of algae and these stressors is crucial for developing effective mitigation strategies to preserve or potentially restore the integrity of aquatic ecosystems. Monitoring data is limited to a relatively recent period and thus sedimentary proxies facilitating the reconstruction of past cyanobacteria abundances are necessary to provide historical context for modern observations.
Recently, the phytol:sterol index (PSI), which corresponds to the ratio of phytol (produced by all algae including cyanobacteria) and specific phytosterols (produced only by eukaryotic algae) was proposed as a proxy for the relative abundance of cyanobacteria within the overall algal community (Klatt et al., 2025). Here, we aim to test the suitability of the PSI alongside other emerging sedimentary proxies to record cyanobacteria abundances and the abundance of HABs. To this end, we extracted short cores covering the past ~250 years from two of the Finger Lakes, Owasco and Skaneateles, in Upstate New York (USA) using a universal coring system in spring 2024. While Owasco Lake has experienced progressive eutrophication since the 1960s, nearby Skaneateles Lake with a much smaller watershed to lake surface area ratio remains oligotrophic. HAB occurrences in Owasco began several years before Skaneateles, but since 2017, HABs have occurred in both lakes, with greater prevalence in Owasco.
Bulk sediment analyses (% total organic carbon, C/N ratios) indicate an increase of algae productivity coinciding with the reported progressive eutrophication of Owasco Lake, while Skaneateles Lake shows rather stable conditions. This stability is also reflected in the PSI, which is about 0.25 in Skaneateles Lake throughout our record, indicating relatively low abundance of cyanobacteria. In Owasco Lake, on the other hand, PSI values reveal a marked increase to 0.45 after ~1950, consistent with a shift in community composition towards Cyanobacteria mid-20th century. We compare these results to compound-specific hydrogen isotope measurements of fatty acids and phytol, and the offsets between them, to further distinguish ecological changes in the lakes. Finally, we use sedimentary DNA (sedDNA) metabarcoding to validate our lipid data by assessing changes in the phytoplankton community and to identify the presence of bloom forming taxa. Overall, the combined results of our proxies are in accordance with observations, and further extend our knowledge of algal community composition prior to the monitoring period. This emphasises the potential of this proxy and the strength of multiproxy approaches.
Klatt, A., De Jonge, C., Nelson, D.B., Reyes, M., Schubert, C.J., Dubois, N., Ladd, S.N., 2025. Algal lipid distributions and hydrogen isotope ratios reflect phytoplankton community dynamics. GCA 394, 205–219. https://doi.org/10.1016/j.gca.2025.02.013
How to cite: Wietelmann, T., Nelson, D. B., Dutta, M., Leon, N., Wood, D., Scholz, C., Thomas, E., and Ladd, S. N.: Assessing sedimentary proxies to reconstruct the occurrence and extent of harmful algal blooms, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17853, https://doi.org/10.5194/egusphere-egu26-17853, 2026.
Lakes are key components of global carbon cycling, accounting for 6-16 % of natural methane (CH4) emissions. Methane release from lakes is largely regulated by aerobic methane oxidizing bacteria (MOB), which oxidize up to 75% of the methane produced in lakes to CO2. Over the past two centuries, anthropogenic environmental change and climate forcing have led to rapid changes in lake systems including eutrophication and stronger stratification. The implications of these ongoing processes for MOB communities and the key methane sink they represent remains unclear. A deeper understanding of how MOB communities in lakes responded to systemic change in the past is essential for discerning their future dynamics. This highlights the need for a reliable biomarker that can track changes in MOB communities in lakes across timescales. The hopanoid bacterial membrane lipids, bacteriohopanepolyols (BHPs), exhibit specificity to MOB types and genera, therefore holding potential as biomarkers allowing us to track community assemblages. The peri-alpine lake Rotsee, located in central Switzerland, is a prime example of a monomictic eutrophic lake, making it an ideal study site to further understand and develop BHPs as biomarkers for MOB communities. Here we present initial results of a seasonal study of Rotsee where we used BHPs coupled with eDNA to investigate the MOB assemblages in the lake’s present-day water column, allowing us to ascertain how rapidly seasonally changing conditions affect MOB communities and the lipid biomarker assemblages they produce. We carried out intact polar lipid (IPL) extraction on suspended particulate matter (SPM) filtered from Rotsee’s 16-meter-deep water column at three-meter intervals and at the oxycline, from August 2025 to January 2026, and at two depths (surface and 15 meters) from May to December 2019. IPLs were measured on an Ultra High Precision Liquid Chromatography-Quadrupole-Orbitrap High-Resolution Mass Spectrometer (UHPLC-Orbitrap-HRMS). Genetic material was extracted from the SPM samples and sequenced targeting bacterial 16S rRNA. Preliminary results show that MOB-specific BHPs: aminotriol, aminotetrol, and aminopentol, are present in the Rotsee water column. The relative abundances of BHPs in the epilimnion remains low and steady during spring and summer but spike during lake overturn in November, whereupon most of the methane is released and oxidized after accumulation in the hypolimnion. 16S rRNA data indicates that the MOB communities are entirely made up of Gammaproteobacteria and match BHP seasonal trends with MOB-specific sequences being more abundant during overturn in the surface water. Additionally, surface waters in November are characterized by a higher abundance of aminopentol, which is scarcely found during spring and summer. Interestingly surface water 16S rRNA data also show that the MOB community compositions change considerably in November and December, shifting from Methylomonas to Methylobacter-dominated. Therefore, preliminary results show that BHP abundances respond to seasonal MOB blooms and show promise towards tracking seasonal community dynamics in eutrophic stratified lakes.
How to cite: Cellino, L., De Jonge, C., Ajallooeian, F., Dubois, N., and Richter, N.: Lipid Biomarkers Respond to Seasonal Blooms of Methane Oxidizing Bacteria in a Eutrophic Lake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9089, https://doi.org/10.5194/egusphere-egu26-9089, 2026.
Rising atmospheric CO2 levels are enhancing primary production, which could result in higher carbon sequestration in biomass (C-fixation). This higher primary productivity, however, relies on a sustained supply of soil nutrients, particularly nitrogen (N). To understand whether climate change and rising CO2 levels have an impact on soil nitrogen availability on centennial to millennial timescales, a geological perspective can be used. For instance, the glacial-interglacial warming, and Holocene warm periods provide valuable natural analogues for investigating these long-term interactions. However, currently no quantitative methods exist to reconstruct soil nitrogen availability through time. To address this, we propose to develop novel proxies based on lipid biomarkers for essential processes in the soil N-cycle.
In aquatic systems, microbial membrane lipids are well established as biomarkers for specific steps in the N-cycle: for instance, heterocyte glycolipids (HGs), produced by heterocytous cyanobacteria, indicate biological nitrogen fixation. Further, microbial intact polar lipids (IPL), isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) and bacteriohopanepolyols (BHPs) are promising proxies for archaeal ammonia oxidation and bacterial nitrite-oxidation, respectively. We propose to test for these N-cycle biomarkers in soils. A pilot sample set of European surface soils was selected, consisting of both N-limited (N-) dryland (n = 8) and N-replete (N+) grassland soils (n = 4). Lipid extracts were analysed by UHPLC-HRMS to generate a high-resolution dataset of the complete lipidome. As a first step in the proxy development, we here present the BHP composition and changes in their relative distribution between in N- and N+ soils.
A total of 47 different BHPs were tentatively identified. In all samples, hydroxy BHPs are predominant components (50-60%). BHtetrol (BHT) is most abundant and all samples contain BHpentol and BHhexol. Amino-BHPs are less abundant in N- soils compared to N+ (2-7%; 10%). For example, aminotriol BHP is relatively increased in N+ soils. A total of 22 nucleoside BHPs were identified with either an adenine (adenosylhopanes) or inosine (inosylhopanes) headgroup that differ in amount and position of methylation on the BHP core or in the headgroup structure. Adenosylhopanes are relatively more abundant in N- than N+ soils (N-: 40-45%, N+: 20%). Inosylhopanes are present at a lower abundance, with 0-5% in N- and up to 10% in N+ soils. Based on changes in their occurrence, four adenosylhopanes and two inosylhopanes are tentatively proposed as N-cycle biomarkers. Specifically, three adenosylhopanes (diMe-adenosylhopane, diMe-adenosylhopane-headgroup-Me, Me-adenosylhopane-headgroup-diMe) and one Me-inosylhopane are exclusively found in N- soils. Likewise, an early adenosylhopane-headgroup-Me and an inosylhopane-headgroup-diMe only occur in N+ soils.
These results highlight the potential N-cycle lipid biomarkers in soils. The occurrence of other potential biomarkers (isoGDGTs, HGs) for the N-cycle will be tested for on the same soils. Moreover, we will apply an untargeted approach via computational MS to comprehensively characterize the whole soil microbial lipidome and evaluate the suite of potential lipid biomarkers associated with nitrogen cycling.
How to cite: Kerschhofer, F. P., Richter, N., Radujković, D., Verbruggen, E., Muñoz-Martín, M. A., Perona, E., Cantón Castilla, Y., Bauersachs, T., Ding, S., and De Jonge, C.: Intact polar lipids as biomarkers for nitrogen fixation and nitrification in European soils , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12957, https://doi.org/10.5194/egusphere-egu26-12957, 2026.
The Holocene temperature history of the lowland Amazon Basin remains poorly constrained, even though the region plays a key role in global climate, carbon cycling, and biodiversity. We present a Holocene record of glycerol dialkyl glycerol tetraethers (GDGTs) from a lake sediment core in the westernmost Amazon Basin, Bolivia, providing new constraints on regional temperature evolution and lake environmental conditions. The brGDGT based temperature reconstruction reveal a low amplitude, gradual warming trend throughout the Holocene. This pattern is consistent with other terrestrial records from tropical South America but contrasts with compiled tropical and global temperature reconstructions that suggest more pronounced early to mid-Holocene warmth followed by cooling. Our results therefore support the hypothesis that Holocene temperature evolution in tropical South America was distinct from that of other low latitude regions and from the global mean, highlighting the importance of regional climate dynamics and land surface feedbacks in shaping tropical climate trajectories.
In addition to temperature, GDGT distributions indicate four distinct phases of changing lake conditions over the Holocene, characterized by shifts in productivity and bottom water redox conditions. These variations likely reflect changes in local landscape development and catchment processes, as well as alterations in wind driven lake mixing. The most recent interval shows signatures consistent with enhanced productivity which may be linked to human activity in the catchment.
Together, these results provide new insights into the long-term temperature history of the western Amazon Basin and demonstrate the value of GDGTs for simultaneously reconstructing regional climate trends and lake environmental change in tropical lowland settings.
How to cite: Hällberg, P., Lombardo, U., Manzella, G., Schefuß, E., Stevens, T., and Peterse, F.: Holocene temperature and environmental reconstruction from Llanos de Moxos in western Amazon based on GDGTs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20912, https://doi.org/10.5194/egusphere-egu26-20912, 2026.
The East Sea, located on the northwest continental margin of the Pacific Ocean, acts an important marine environment sensitive to the global/regional climate change including the East Asian monsoon. GDGT (glycerol dialkyl glycerol tetraether), one of the membrane lipids originated from archaea or bacteria, has been broadly used as a ubiquitous biomarker for the paleoceanogprahic reconstruction. Although the numerous paleoceanographic results in the East Sea have been reported, the GDGT records and its application to the East Sea paleoceanography are still limited. In this study, we reconstructed the late Pleistocene seawater temperatures using hydroxylated and isoprenoid GDGTs using a sediment core 19ESDP-101 from the Hupo Trough of the southwestern East Sea (Japan Sea). Several temperature proxies were compared, alongside additional GDGT-derived indices and mean grain size. The temperature proxies yielded broadly consistent temperatures during the warm periods, but diverged in cooler intervals, where RI-OH′ values decreased sharply. These discrepancies reflect the different sensitivity to temperature, salinity, and depositional conditions. Proxy-derived temperatures were inversely correlated with sediment grain size, implying linkage between hydrographic and depositional environments. During the glacial periods, coarse-grained particles, low TEX86L values, and high terrestrial input were correlated, suggesting the sea-level control on environmental conditions. Nevertheless, the integration of multiple GDGT proxies from core 19ESDP-101 highlights the significance of local oceanographic settings in paleoenvironmental reconstruction and supports the selective use of TEX86L and OH-GDGTs.
How to cite: Park, Y.-H. and Khim, B.-K.: Biomarker record in the Hupo Trough of the southwestern East Sea since the late Pleistocene, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20044, https://doi.org/10.5194/egusphere-egu26-20044, 2026.
Paleoclimatic and paleoenvironmental reconstructions rely on proxies derived from physical, chemical or biological properties of the investigated archive. In order to achieve the highest spatial (hundreds of micrometers), and thus temporal resolution (subannual), various imaging techniques, such as hyperspectral imaging, computed tomography, mass spectrometry imaging (MSI), X-ray, and µXRF can be employed. However, proxies generally respond to multiple environmental variables (e.g., the GDGT-based proxy CCat is influenced by both water column temperature and nutrient concentrations). Multi-proxy studies are necessary to obtain a comprehensive understanding of past conditions and to disentangle individual biogeochemical processes.
A major roadblock in multi-proxy studies is the alignment of data across multiple datasets since manual matching of ‘wiggles’ (1D time series) can be deceptive. With imaging data this issue can be avoided since data can be matched in 2D space. Moreover, RGB images are routinely obtained alongside each method. This provides a shared data layer between methods.
Not all imaging methods can be performed on the exact same sample slice, and MSI even requires multiple samples from the same core depth to cover multiple mass windows. Consequently, four aspects are taken into account in our proposed workflow: (I) subsamples need to be referenced back to the core; (II) datasets are obtained at different positions and can have vastly different resolutions; (III) samples may be distorted during sample preparation - so even two MSI measurements from the same sediment section at the same resolution cannot be mapped directly onto each other. And although these distortions are generally small, investigating seasonal variations requires consistency at the scale of hundreds of micrometers; (IV) after a transformation between images has been found, the data needs to be transformed (i.e., resampled). This requires interpolation, which can alter properties such as sparsity. Hence, interpolation targets as well as the interpolation methods need to be selected with care.
In this work, we present a workflow capable of semi-automatically combining image datasets from (sections of) sediment cores from any two imaging methods. Advanced methods for laminated sediments are also presented, as they are particularly suitable for fine-scale matching. With this workflow we aim to replace the tedious manual teaching point selection by providing robust image registration methods for routine multi-proxy studies on subannual scales.
How to cite: Zander, Y., Liu, W., Wörmer, L., and Hinrichs, K.-U.: A Workflow for Combining microscale Imaging Techniques in Paleoclimatology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11129, https://doi.org/10.5194/egusphere-egu26-11129, 2026.
Unlocking the functional complexity of soil ecosystems requires robust methods for characterizing the diverse communities residing within them. While phospholipid fatty acid (PLFA) analysis has long served as a standard tool for quantifying soil microbial community composition, it is inherently constrained by low taxonomic resolution and a historical bias toward bacteria and fungi, often obscuring the contributions of other critical soil organisms. To address this gap, intact polar lipid analysis offers potentially deeper and more detailed insight into the soil (micro)biome. Here, we present a comprehensive lipidomic reference library built from intact polar lipids extracted from pure isolates and individual species spanning the tree of life, including bacteria, archaea, fungi, protists, plants, and soil fauna to enable high-resolution, culture-independent biodiversity assessments.
Using reversed phase UPLC separation followed by dual-polarity, high-resolution Orbitrap MS/MS and molecular networking, we captured over 140,000 molecular features and organized them into approximately 10,000 molecular families. This library covers ~30 phyla and >50 lipid classes, extending the analytical window far beyond PLFA to include diverse glycerophospholipids, glycolipids, sphingolipids, and neutral lipids. Hierarchical analyses reveal distinctive lipidomic architectures across taxonomic levels, with over half of the detected compounds appearing exclusive to single phyla. Beyond standard microbial signals, we identified rich lipid fingerprints specific for faunal and protist groups (e.g., Arthropoda, Nematoda, Mollusca, Amoebozoa), plastid-associated glycolipids in photosynthetic lineages, and characteristic archaeal membrane compositions. Clustering these features yielded thousands of phylum-exclusive molecular families, providing candidate biomarkers with built-in signal redundancy.
As a proof-of-concept, we detected these signatures in heterogeneous soil samples, supporting the feasibility of the approach while highlighting the need for broader validation of potential biomarker families. These findings establish a path toward high-resolution lipid-based mapping of soil community composition and food-web structure, offering a powerful, functional complement to existing genomic and biochemical approaches.
How to cite: Samrat, R. and Wanek, W.: Beyond microbes: mapping soil food web biodiversity via lipid fingerprinting, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10003, https://doi.org/10.5194/egusphere-egu26-10003, 2026.
