In this session, we welcome contributions from these vast geological archives and model simulations aimed at reconstructing and understanding Earth’s climate system over the past 100 million years. These submissions may reflect long-term and/or short-term changes such as Milankovitch cyclicity to suborbital/millennial variability. Submissions working on chronological or stratigraphic fundamentals underpinning this interval are encouraged. We also welcome contributions from those seeking to better assess Earth’s climate system sensitivity through reconstructions of atmospheric CO2 concentrations and global or regional temperatures. This includes biodiversity dynamics and disruptions in warm marine and terrestrial states.
The goal of this session is to bridge the diverse community studying the nature of the warm climate states found in the Cretaceous and Cenozoic. We consciously welcome a broad range of approaches to facilitate synergies to learn from past warm climate conditions to navigate into the future warmer world. We especially welcome new approaches, including improved proxy calibrations, and more comprehensive inter-proxy and proxy-model comparisons, to obtain a better understanding of the uncertainties associated with paleotemperature reconstructions.
Orals: Tue, 5 May, 16:15–18:00 | Room 0.49/50
While the Miocene Climate Optimum (MCO) is viewed as an analogue for near-future conditions resulting from anthropogenic climate change, improving our understanding of this event requires the development of proxy records within a well-calibrated temporal framework. Large igneous province emplacement in the Columbia River Basalt Group (CRBG) has been suggested to cause elevated global temperatures and CO2 during the MCO, but assessing the connection between volcanism and warming requires robust timelines for proxy records of these events. While we have developed a new age model for CRBG volcanism based on high-precision U-Pb geochronology (Kasbohm et al., 2023) and a U-Pb age model for the MCO that reinforces the validity of astronomically tuned age models for this event (Kasbohm et al., 2024), only a small number of MCO proxy records have been age-calibrated through astronomical tuning. Existing boron isotope CO2 proxy records from the MCO were age-calibrated through biostratigraphy alone, hindering correlation to known intervals of CRBG volcanism. These records showed high-amplitude CO2 variability, calling into question the stability of the Miocene climate system.
Here, we present a new foraminiferal boron isotope record from International Ocean Discovery Program Site U1490 (Western Pacific Warm Pool), which has an astronomically tuned age model concordant with our radiometric ages for the MCO (Holbourn et al., 2024). This new record targets the onset of the MCO through the end of the main-phase CRBG volcanism (17.1-16 Ma) at ~15 kyr resolution, with lower resolution across the entire MCO (17.8-13 Ma). We find well-resolved and relatively stable pH values across the MCO, with sampling resolution that reveals orbital pacing of these records. Our reconstructed CO2 estimates show less variability than prior records, though we note somewhat variable correlation with changes in MCO benthic δ18O values, which may reflect dynamism in foraminifera’s habitat during the warmest conditions of the MCO. We observe little change in CO2 resulting from CRBG surface volcanism, and no strong correlation between CO2 changes and the tempo of CRBG eruptions. A transient uptick in CO2 prior to surface eruptions, as well as sustained somewhat higher values afterwards, may be explained by cryptic degassing of large amounts of CRBG magma trapped in the crust, but the magnitude of this CO2 change was small.
How to cite: Kasbohm, J., Jurikova, H., Holbourn, A., Nana Yobo, L., Wade, B., Ring, S., Planavsky, N., Rae, J., and Hull, P.: Testing the role of large igneous province volcanism in the Miocene Climate Optimum with a new boron isotope record from the Western Pacific Warm Pool, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14704, https://doi.org/10.5194/egusphere-egu26-14704, 2026.
The late Miocene and Pliocene were periods characterized by warmer-than-present climatic conditions and are therefore commonly used to investigate the possible effects of ongoing global warming. The Atlantic meridional overturning circulation (AMOC) is a crucial component of the climate system, since it involves oceanic currents and controls the redistribution of heat around the globe. Specifically, warm and saline water from the low-latitudes reaches the high-latitude North Atlantic, where it loses heat and sinks to form deep-water masses. This sinking generates strong bottom currents, which flow southwards, powering what is known as the global ocean conveyor belt. Understanding the generation and evolution of these water masses during past warm periods provides valuable insights into their potential response to ongoing increases in ocean temperatures. Recently, International Ocean Discovery Program (IODP) expeditions 395 and 395C made such investigations possible by recovering deep sea sedimentary sequences spanning the late Miocene and Pliocene in the high latitude North Atlantic region (60°N; Parnell-Turner et al., 2025). In this study, we investigate sediment samples from IODP Site U1562 (60°06.3006′N, 26°30.1044′W; ~2003m water depth), located at the edge of a sediment body deposited under the influence of deep-water currents (Björn Drift). This site exhibits continuous sedimentation and excellent microfossil preservation during the latest Miocene to Pliocene (~6.5–3.6 Ma). For our investigation, we use a combination of micropaleontological and geochemical proxies, including X-Ray fluorescence (XRF) core scanning, isotopic analysis of foraminiferal shells, and microfossil species identification and morphometrics. Combining these proxies allows for reconstructing the evolution of temperature, primary productivity, and ocean circulation in the region. Pronounced cyclic variations in calcium carbonate (CaCO₃) preservation indicate a highly dynamic depositional environment, likely controlled by changes in export production and bottom ocean dissolution related to deep-sea currents. These cycles are accompanied by distinct isotopic signatures, with intervals of high CaCO₃ content broadly corresponding to lighter δ¹⁸O values, and vice versa. The occurrence of planktonic foraminifera Orbulina universa, as well as calcareous nannofossils belonging to the genus Discoaster reveal periodically warmer conditions, driven by an overall increase in upper-ocean temperature or enhanced influence of warm currents associated with stronger AMOC. Further analyses will aim to better characterize these cyclic changes, link them to orbital cycles, and combine them with other sedimentological observations to reconstruct the evolution of AMOC during past warm intervals of the late Neogene.
References
Parnell-Turner, R.E., Briais, A., LeVay, L.J., and the Expedition 395 Scientists, 2025. Reykjanes Mantle Convection and Climate. Proceedings of the International Ocean Discovery Program, 395: College Station, TX (International Ocean Discovery Program). https://doi.org/10.14379/iodp.proc.395.2025
How to cite: Karatsolis, B. T., Pearson, P. N., Dunkley Jones, T., Suzuki, T., Müller, I. A., Sinnesael, M., Le Tuyet, N. P., Treand, C., Henderiks, J., Asanbe, J. D., Wade, B., and Claeys, P. and the Expedition 395 scientists: Micropaleontological and geochemical evidence for late Miocene to Pliocene warming in the high-latitude North Atlantic (IODP Site U1562)., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10100, https://doi.org/10.5194/egusphere-egu26-10100, 2026.
Australia’s Neogene hydroclimate evolved in response to continental drift and major global climate reorganizations, yet the magnitude and spatial structure of these changes remain poorly constrained. Moreover, the ability of climate models to reproduce Australian hydroclimate variability during deep-time warm periods has rarely been evaluated against geological data. Here, we reconstruct hydroclimate evolution across the Northwest Shelf of Australia over the past 23 million years using a continent-scale compilation of downhole natural gamma radiation (NGR) records and directly compare these reconstructions with climate model simulations.
We integrate NGR measurements from 105 industrial and scientific boreholes into a regionally coherent stratigraphic framework using automated Dynamic Time Warping, with biostratigraphic age control providing temporal calibration. High-resolution (~100 kyr) time-slice reconstructions reveal pronounced spatiotemporal variability in terrigenous input, reflecting changes in precipitation and continental runoff.
The reconstructions indicate persistently humid conditions during the Early Miocene, followed by an abrupt transition to widespread aridity at ~18-17 Ma. This major hydroclimate shift is not reflected in HadCM3 simulations, which instead suggest wetter conditions than those inferred from the NGR reconstruction across subtropical Australia during this interval. A subsequent increase in hydroclimate variability at ~6.5 Ma, marked by elevated NGR values, aligns with enhanced modeled precipitation and is consistent with an intensified Leeuwin Current and southward migration of the Intertropical Convergence Zone, pointing to a transient return to wetter conditions. Lower NGR values during the Late Pliocene indicate the onset of a transitional phase preceding the establishment of fully arid conditions by ~2.4 Ma.
Together, these results demonstrate that the magnitude and spatial complexity of Neogene Australian hydroclimate variability inferred from geological records exceed those predicted by state-of-the-art climate models. The pronounced data-model mismatch in the Early and Middle Miocene highlights persistent challenges in simulating regional hydroclimate responses in warmer-than-present greenhouse climates. These findings underscore the importance of geological benchmarks for evaluating model performance and improving projections of future hydroclimate change.
How to cite: Samant, R., Farnsworth, A., Bialik, O. M., Back, S., Reuning, L., Gallagher, S., Sarr, A. C., and De Vleeschouwer, D.: Neogene Australian hydroclimate variability exceeds model predictions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4308, https://doi.org/10.5194/egusphere-egu26-4308, 2026.
Reconstructing terrestrial climate conditions in the high Arctic during the Late Miocene (∼11.6–5.3 Ma) is essential for understanding how polar environments respond to warmer-than-present global climates. However, direct land-based climate archives from the Arctic are rare, limiting understanding of terrestrial climate sensitivity under greenhouse-gas concentrations comparable to present and near-future conditions. Here we present a terrestrial proxy record from speleothems collected in a cave in eastern North Greenland (∼80.3°N). Speleothem growth phases indicate repeated intervals of sustained permafrost absence, implying significantly warmer and wetter conditions than today under moderate atmospheric CO₂ forcing and elevated regional sea-surface temperatures. Trace-element variability further suggests episodic glaciation in North Greenland during the Late Miocene, pointing to a highly dynamic cryosphere. Together, these results highlight pronounced terrestrial climate variability in the Arctic under warm background conditions broadly relevant to future climate trajectories. This new archive provides an important benchmark for assessing high-latitude climate sensitivity and feedbacks in a warming world.
How to cite: Moseley, G. E., Koltai, G., Baker, J. L., Wang, J., Stoll, H., Donner, A., Anders (née Friedrich), L., Spötl, C., Smith, M. P., Scholz, D., Cheng, H., Hartland, A., Hejny, C., and Edwards, R. L.: Reconstructing Late Miocene Arctic Climate from North Greenland Speleothems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2851, https://doi.org/10.5194/egusphere-egu26-2851, 2026.
Earth’s climate and ocean circulation have reorganized profoundly since the late Miocene. Global compilations of sea surface temperature reconstructions indicate cooling trends during the late Miocene and the Pliocene-Pleistocene periods. However, there is no long-term high-resolution temperature record from the northwestern Pacific yet. Here we present a new, extremely high-resolution (1-3 kyr), continuous alkenone sea surface temperature record spanning the past 10 million years from the subarctic front region of the northwestern Pacific. On glacial-interglacial timescale, SST variance and dominant frequencies changed stepwise, defining three phases: strong-amplitude variability (~5–9°C) at 0–1.7 Ma, moderate variability (~2–5°C) at 1.7–5.6 Ma, and weak variability (~1–2°C) at 5.6–9 Ma. Band-pass filtering isolates 405, 100, 41 and 21/19 kyr components, revealing pervasive orbital pacing and reproducing the three-phase structure. On long-term timescale, our results exhibit multistage process of the North Pacific cooling with related climate changes during the time period. In particular, the late Miocene (5-7 Ma) cooling can be compared with that of the late Pliocene-Pleistocene periods (1-3 Ma). Further comparisons between our temperature record at the subarctic front region with those from the western and eastern equatorial Pacific have been conducted, anticipating being able to reconstruct the evolution/variability of the subarctic front and its relationship with the evolution of the North Pacific subtropical gyre during the northern hemisphere glaciation.
How to cite: Lee, K. E. and Ko, T. W.: Multistage process of North Pacific cooling during the past 10 million years, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18266, https://doi.org/10.5194/egusphere-egu26-18266, 2026.
High reconstructed temperatures and pCO2 concentrations during the Miocene Climatic Optimum (MCO; ~17-15 Ma) make it a possible analog for future warm climates. Proxy sea surface temperature (SST) reconstructions often indicate warm high latitudes, with a relatively small latitudinal temperature gradient. However, Earth system models generally do not yield the relatively flat latitudinal temperature gradients given by proxy reconstructions, and instead have cooler polar regions and somewhat warmer tropics. In tropical regions, this proxy-model disagreement may be due to habitat depths below the surface mixed layer, where the proxy would record temperatures from deeper, cooler waters, whereas the model output is simply SST. At high latitudes, however, the proxy-model disagreement cannot be fully explained by habitat depth or seasonal temperature, leaving two possibilities: one, that the models do not fully capture the Earth System; or two, that proxies are impacted by widespread non-thermal effects.
In an attempt to elucidate matters, we investigated clumped isotopes in coccoliths (cocco-Δ47) at Southern Ocean sites 1168 (South Tasman Sea) and 751 (Kerguelen Plateau) and compare these results to previously published biomarker-based temperature proxies (UK’37 and TEX86) at Site 1168. Clumped isotope samples were screened for good preservation, and contain little or no diagenetic carbonate. Unlike most temperature proxies, cocco-Δ47 values are independent of seawater chemistry and do not exhibit species- or strain-specific offsets, instead yielding an absolute growth temperature. Additionally, coccoliths and alkenones are derived from the same organisms, and should be directly comparable. During peak warmth (~16.5 Ma), cocco-Δ47 values yield temperatures of 12.0 ± 2.8 and 7.3 ± 2.8 °C at Sites 1168 and 751, respectively, and agree well with latitudinal averages of climate model output. At Site 1168, previously published UK’37 and TEX86 yield much higher temperatures (27 °C SST and 21 °C 0-200 m temperatures, respectively; Guitián and Stoll P&P, 2021; Hou et al. Clim. Past, 2023). The difference in proxy temperature estimates is large and cannot be reconciled with modern ranges in seasonal SST or photic zone habitat depth temperature. Mixing effects and physiological influences will be further explored.
How to cite: Rice, A., Bernasconi, S. M., Jaggi, M., and Stoll, H. M.: Exploring proxy-proxy and proxy-model (dis)agreements during the leadup to the Miocene Climatic Optimum in the Southern Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17248, https://doi.org/10.5194/egusphere-egu26-17248, 2026.
The Plio–Pleistocene transition represents the shift from a warmer Pliocene to a cooler Pleistocene, offering key insights into climate sensitivity to CO₂ forcing and ice-volume changes. However, the upper-ocean thermal response of the Pacific mid-latitudes and upwelling regions remains poorly constrained, despite their critical role in global climate and ocean circulation. Here, we present paired UK′37–TEX86 upper-ocean temperature records spanning 3.4–2.4 Ma from the subtropical and equatorial Pacific at ODP Site 1012 (California Margin), IODP Site U1338 (Eastern Equatorial Pacific, EEP), and DSDP Site 593 (Tasman Sea). Surface sediment data in these regions indicate that UK′37 reflects annual mean sea surface temperatures. In contrast, high GDGT [2/3] ratios (>7) observed in surface sediments and downcore records suggest that TEX86 records shallow subsurface temperatures, likely near the nitrite maximum, as inferred from matching TEX86 temperatures to climatological annual mean temperature profiles, regardless of the calibration used. In upwelling regions, this depth correlates strongly with thermocline depth, indicating deeper (shallower) TEX86 recording depths during weakened (intensified) upwelling. Downcore UK′37 SST records from both subtropical sites indicate warmer-than-present Pliocene conditions, ~5 ºC cooling during the M2 glaciation, warming at KM5c, and a long-term cooling after the Mid-Pliocene Warm Period (MPWP), whereas SSTs at the equatorial Pacific site show no significant Pliocene–Pleistocene cooling trend. However, TEX86-derived subsurface temperatures exhibit significant Pliocene-Pleistocene cooling across all three regions. Based on the UK′37–TEX86 temperature difference (ΔT), we infer weaker upwelling along the California Margin during the MPWP, possibly linked to an intensified North American Monsoon (NAM) that weakened upwelling-favorable winds, followed by stronger upwelling under a weakened NAM during the early Pleistocene. In contrast, there is no change in upwelling in the EEP from the Pliocene to the Pleistocene. In the Tasman Sea, UK′37 likely records northward-sourced surface waters transported by the East Australian Current, whereas TEX86 reflects subsurface South Antarctic Mode Water (SAMW). The convergence of UK′37 and TEX86 temperatures between 3.1 and 2.6 Ma likely indicates northward migration of the Subtropical Front, allowing SAMW to shoal and influence surface conditions at the site. Overall, during the Plio–Pleistocene transition, the mid-latitude Pacific experienced an expansion of cold high-latitude waters. This study highlights the usefulness of paired UK′37–TEX86 analyses in advancing our understanding of upper-ocean thermal evolution across diverse Pacific hydrological settings during past key climate transitions.
How to cite: Azharuddin, S., Ho, S. L., Hefter, J., McClymont, E., and Groeneveld, J.: Upper-ocean temperature and upwelling variability across the Pacific during the Plio–Pleistocene transition: Insights from UK′37 and TEX86, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8860, https://doi.org/10.5194/egusphere-egu26-8860, 2026.
Global cooling during the Eocene-Oligocene Transition (EOT; 33.9 Ma) drove pronounced environmental and biotic shifts across the globe. However, the paleo-climatic response on the North American continent remains debated, especially in the high-elevation Cordillera, which may have been cold and dry already before the EOT. To test the response of this high-elevation terrain to global climate forcing, we studied three sedimentary sections in SW Montana (Easter Lily, Black Butte and Lion Mountain) that span the Eocene-Oligocene boundary and contain calcretes for paleo-environmental reconstructions. Dual clumped isotope thermometry in the Easter Lily section shows cooling of ~2°C during the earliest Oligocene followed by warming to pre-EOT temperatures. This indicates that EOT cooling was only transient and that long-term temperatures during the early Oligocene were similar to the late Eocene. In addition, calcrete oxygen (δ18O) and carbon (δ13C) isotope ratios within the three sections do not record major changes across the EOT. Instead, large differences are observed among the studied sections in δ18O values (up to 2‰) and especially in δ13C values (up to 6‰). This suggests strong heterogeneity of the intermontane paleo-environments in SW Montana, with individual basins recording different temperatures and degrees of aridity. Such a topographically and climatologically complex landscape may have produced the diverse endemic mammal fauna observed in these fossil localities.
How to cite: Meijer, N., Seymour, N., Methner, K., Fiebig, J., and Mulch, A.: Calcrete clumped and stable isotopes reveal transient cooling and heterogeneous Eocene-Oligocene paleo-environments in SW Montana, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18001, https://doi.org/10.5194/egusphere-egu26-18001, 2026.
The response of the climate system to rapid carbon-cycle perturbations can be constrained by studying past transient climate events such as the Paleocene–Eocene Thermal Maximum (PETM, ~56 million years ago). The PETM is marked by a massive input of isotopically light carbon, as recorded by a 3–4‰ negative carbon isotope excursion (CIE) in sedimentary records globally. Estimates of the duration of the rapid onset of the CIE range from a few hundred to several thousand years. The exact duration remains poorly constrained due to the scarcity of marine sedimentary records that 1) have sufficiently high sedimentation rates to resolve rapid decadal- to centennial scale transitions, 2) provide robust controls on sedimentation rates and event timing, and 3) preserve proxy data that record perturbations of the dissolved inorganic carbon (DIC) pool. Consequently, the rate of carbon release during the CIE onset, and its relevance for understanding anthropogenic climate change, remains unclear.
International Ocean Discovery Program (IODP) Expedition 396 recovered expanded PETM successions on the Norwegian Margin, including a microlaminated CIE onset interval that preserves decadal-scale variability. We document the first occurrence of haptophyte alkenones from the onset of the PETM CIE and present a high-resolution record of their stable carbon isotopic variability (δ¹³Calk) across the onset interval. The δ¹³Calk records variations in the (isotopic) composition and concentration of the dissolved inorganic carbon (DIC) pool. We show that the δ¹³Calk record is not strongly influenced by local (volcanically induced) input of ¹³C-depleted carbon based on high-resolution sedimentary mercury and polyaromatic hydrocarbon data from this interval. Finally, we provide robust age control from the diatom laminations, enabling a direct and well-constrained estimate of the duration of the global CIE onset interval.
How to cite: Nelissen, M., Bats, Y., Furlong, H., Verkooijen, S., Frieling, J., Jones, M., Mather, T., Scherer, R., van der Meer, M., Schouten, S., Peterse, F., Sluijs, A., and Brinkhuis, H.: New constraints on the duration of the onset of the PETM carbon isotope excursion, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20142, https://doi.org/10.5194/egusphere-egu26-20142, 2026.
The trend of hydroclimatic variability represents a major area of concern in the context of global warming. The Pliocene–Pleistocene Transition (PPT) provides a valuable geological analogue, characterized by a dramatic shift in global ice volume and temperature. Here we present a pollen-based quantitative summer precipitation record spanning 3.4–2.4 Ma, derived from a fluvio-lacustrine sequence from the Datong Basin in the mid-latitude East Asia. Pollen data were converted to precipitation estimates using a pollen-derived Weighted Averaging Partial Least Squares (WA-PLS) model. Our results show that the summer precipitation remained broadly stable across the PPT, with no clear long-term trend. Instead, pronounced changes occur in precipitation variability. Before ~2.9 Ma, the late Pliocene hydroclimate showed large-amplitude fluctuations, with more frequent wet and dry extremes. After 2.9 Ma, variability decreases, and extreme values became less frequent, indicating a transition to a more stable rainfall regime. Spectral analyses further support this regime shift in the frequency domain: while ~100-kyr eccentricity-scale variability dominated the late Pliocene hydroclimate, it weakened and became less coherent following 2.9 Ma. Under future warming scenarios, these results imply that changes in hydroclimatic variability may represent a critical source of risk to mid-latitude Asian climate systems.
How to cite: Ge, J., Long, H., Cheng, L., Wang, H., and Seppä, H.: Reduced precipitation variability over mid–latitude East Asia during the Pliocene-Pleistocene Transition, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18622, https://doi.org/10.5194/egusphere-egu26-18622, 2026.
Paleoproxy records of bottom water temperature (BWT) have been used to investigate past reconfigurations of ocean circulation, infer changes in global ice volume following deconvolution of benthic oxygen isotopes, and extract information about average surface climate in warm, equilibrated states. Despite the wealth of BWT data available for the past 5 Myrs, persisting uncertanties in the proxy systems and methods most widely used to derive BWT have led to different, at times conflicting, views of climate and sea level variability across key Plio-Pleistocene transitions. Here we present ongoing work to better constrain the long-term evolution of Plio-Pleistocene BWTs using clumped isotopes from benthic foraminifera, bypassing well-known pitfalls affecting other temperature indicators and opening new avenues of leverage in multiproxy comparisons. Our results question previous definitions of the relationship between mean ocean BWTs and global ice volume, with puzzling implications for the so-called intensification of Northern Hemisphere glaciations after the mid-Piazencian Warm Period and the expected influence of ice-sheets on global climate. Moreover, these new records support the use of mean ocean BWT as a reflection of average surface climate beyond the Miocene, thereby showing great potential to inform the development of new paleo-informed climate models.
How to cite: Domínguez Valdés, E., Kocken, I. K., Agterhuis, T., Müller, I. A., van der Kloos, R. M., Hendriks, P., Bode, N. J., Lourens, L. J., and Ziegler, M.: More Ice in Warmer Worlds? Reassessing Plio-Pleistocene Climate Relationships, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20224, https://doi.org/10.5194/egusphere-egu26-20224, 2026.
Marine Isotope Stage (MIS) 31 is an interglacial period during the later part of the Early Pleistocene, which is often referred to as a super-interglacial due to the perceived strong warming in the polar regions. The new atmospheric pCO2 stack from Nuber et al. (2025; https://doi.org/10.21203/rs.3.rs-6480074/v1) indicates levels reaching up to 285 ppm, placing MIS 31 into the same range as interglacial MIS 11c, the last interglacial MIS 5e or the Holocene. Based on the LR04 isotope stack, the timing of MIS 31 was defined as the period from 1081 to 1062 ka. However, in records from the mid-latitudinal North Atlantic, interglacial oceanographic conditions started much earlier, i.e., around 1092 ka, and the interval from 1092-1062 ka is perceived to represent MIS 31. Last year, the PMIP-Interglacials working group decided to include a MIS 31 time slice into the scenarios to be modelled. So, the database presented here aims to compile paleoclimatic and paleoecological information for the model-data comparison. Currently, the database includes 113 sites, of which 89 are from the marine environment and 13 are loess records. The sites are globally widely distributed and 45 sites provide direct temperature information either as sea-surface temperature or as lake water temperature reconstructions. After evaluating the respective age models, we will use the compiled data to produce time slice reconstructions for the early and peak interglacial phases of MIS 31.
How to cite: Voelker, A. H. L. and Ogretmen, N.: Paleoclimatic conditions during Marine Isotope Stage 31 – a global database for PMIP Interglacials, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3542, https://doi.org/10.5194/egusphere-egu26-3542, 2026.
The Indonesian Throughflow (ITF) is a key component of the Indo-Pacific Warm Pool (IPWP) and global ocean circulation, regulating the transfer of heat and freshwater from the Pacific to the Indian Ocean. Here we reconstruct surface and thermocline hydrographic variability of the ITF over the past 150 kyr using paired δ¹⁸O and Mg/Ca records from Globigerinoides ruber, Pulleniatina obliquiloculata, and Neogloboquadrina dutertrei in sediment core MD10-3334 (0.22°N, 119.30°E; 1169 m water depth) from the northern Makassar Strait. The records reveal pronounced glacial–interglacial variability in upper-ocean thermal structure and ITF dynamics. During the last two deglaciations (~27 and ~144 ka), upper thermocline warming preceded sea-surface warming resulting in a smaller vertical temperature gradient (i.e., deepening of the thermocline), which suggests an increase in La Niña–like mean state conditions associated with enhanced heat accumulation in the IPWP and intensified subsurface ITF transport. In contrast, the mid-Holocene and early Marine Isotope Stage (MIS) 5e are characterized by a progressive cooling of thermocline temperatures (increasing vertical temperature gradients), suggesting a reduced subsurface heat transport, consistent with a weakened ITF. These changes likely reflect adjustments in zonal and/or monsoonal wind-driven circulation and upper-ocean stratification linked to orbital-scale shifts in ITCZ position, sea level, and seasonal insolation. Our results suggest changes in the vertical temperature gradients in the Makassar Strait that we interpret as a measure of ITF strength and highlight the critical role of subsurface processes in modulating tropical Indo-Pacific climate variability across glacial–interglacial timescales.
How to cite: Agusta, V. C., Elliot, M., Bassinot, F., Lo, L., Rivoal, M., Richard, P., Manssouri, F., Govin, A., and Kissel, C.: Changes in the surface and subsurface temperature across Glacial-Interglacial transitions in the Indonesian Throughflow over the past 150-kyr: A perspective from the northern Makassar Strait, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12158, https://doi.org/10.5194/egusphere-egu26-12158, 2026.
The late Miocene cooling (LMC; ~7–5.4 Ma) represents a major global climate transition associated with declining atmospheric CO₂, large-scale aridification, and reorganization of terrestrial ecosystems. While cooling at high and mid latitudes during this interval is well documented, temperature changes in the tropical oceans appear muted. Existing tropical sea-surface temperature (SST) reconstructions based on alkenone unsaturation (UK’37) are limited by proxy saturation at ~29 °C, potentially leading to an underestimation of tropical warmth. Here, we investigate tropical upper-ocean temperature evolution during the late Miocene using coccolith clumped isotope (∆47) thermometry, which reflects habitat-depth temperatures rather than regressed SSTs.
We present new coccolith ∆47 temperature records from ODP Site 926 (Ceara Rise) spanning the late Miocene and compare them to late Pleistocene glacial and interglacial intervals from nearby ODP Site 925. Coccolith-enriched sediment fractions were carefully isolated and screened prior to ∆47 analysis. Results indicate muted tropical cooling of ~3 °C during the LMC, consistent with global temperature compilations. Notably, reconstructed late Miocene upper-ocean temperatures (~20–25 °C) are similar to those observed during Pleistocene interglacials, despite fundamentally different climate states characterized by Antarctic-only glaciation in the late Miocene and bihemispheric glaciation in the Pleistocene.
These findings suggest that muted tropical cooling during the late Miocene is not solely an artefact of alkenone saturation.
This study underlines the potential of coccolith clumped isotopes to provide constraints on upper-ocean temperatures, avoiding uncertainties associated with regressing proxy signals to SST. However, changes in coccolithophore depth habitat and water-column stratification remain key uncertainties. Ongoing paired coccolith–foraminifera ∆47 and foraminifera δ¹⁸O analyses will improve interpretations of tropical ocean temperatures and vertical gradients across contrasting climate states.
How to cite: Leusch, M., Jaggi, M., Bernasconi, S., and Stoll, H.: Similar Tropical Upper-Ocean Temperatures in the Late Miocene and Pleistocene Interglacials, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7307, https://doi.org/10.5194/egusphere-egu26-7307, 2026.
Carbonate clumped isotope thermometry is a powerful tool increasingly utilized across earth science disciplines. This proxy measures the thermodynamically controlled bonding of heavy rare isotopes 13C and 18O within the same CO2 molecule (mass 47) derived from carbonate acid digestion. Unlike the widely used Mg/Ca thermometer, △47 thermometry is independent of seawater chemistry changes, including past pH, dissolved inorganic carbon, and carbonate saturation states, although it typically requires larger sample sizes and yields lower precision.
Here, we report on the establishment of a small-sample carbonate △47 measurement method using a Thermo Fisher Kiel IV coupled to a MAT253Plus mass spectrometer at the State Key Laboratory of Marine Geology, Tongji University. Using an aliquot mass of ~120 μg, we achieved a reproducibility for the IAEA-603 standard (n = 35) of 0.04‰ in △47, 0.02‰ in 13C, and 0.05‰ in 18O (1 SD). We applied this method to planktonic foraminifera G. sacculifer from ODP Site 762 in the eastern Indian Ocean. The measured △47 values were 0.666‰ (n = 17, 1 SE = 0.009‰) for the 5.95 Ma interval and 0.673‰ (n = 35, 1 SE = 0.005‰) for the 3.95 Ma interval. Using the recalculated Kele et al. (2015) calibration (Bernasconi et al., 2018), we reconstructed SSTs of 26.8±6.0°C at 5.95 Ma and 24.7±3.4°C at 3.95 Ma. For comparison, temperatures reconstructed using Mg/Ca analysis were 25.9°C at 5.95 Ma and 23.5°C at 3.95 Ma, based on the calibration by Anand et al. (2003). The results demonstrate strong consistency between the two proxies, validating the utility of △47 for paleotemperature reconstruction even when temperature variations are subtle.
Keywords: Clumped isotope (△47), Mg/Ca thermometry, Temperature reconstruction, Foraminifera
How to cite: Ding, Y. and Tian, J.: Reconstructing Late Miocene and Early Pliocene Sea Surface Temperatures: A Comparison of △47 and Mg/Ca Thermometry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11064, https://doi.org/10.5194/egusphere-egu26-11064, 2026.
Large uncertainty surrounds efforts to model the regional response to CO2-driven warming in the southwestern U.S. The region hosts a seasonally variable hydroclimate and significant topography – much of which is tied to the region’s complex Cenozoic geologic history. These intricacies are difficult to reconcile in models, leading to disagreement even on the modelled sign of future precipitation change in the southwestern U.S. Previous and new stable isotope analyses of pedogenic carbonates from the well-dated Santa Fe Group of New Mexico suggest a potential shift from a middle Miocene winter-wet climate towards the dual-wet season regime seen in the region today, where annual precipitation is relatively low but delivered in both the summer and winter. This shift in regime might be spurred by either a strengthening of the North American Monsoon or a weakening of the westerlies. New clumped isotope analysis of these pedogenic carbonates documents a long-term cooling of as great as 18.5 ± 10.3°C between the Miocene Climatic Optimum (MCO) and the Pleistocene. This Neogene cooling trend in New Mexico tightly tracks the global benthic δ18O record over the same period, as well as Pacific sea-surface temperature records. This correlation suggests that paleotemperature change throughout the record is controlled by global climate rather than a potential shift in carbonate formation season driven by a shift in the precipitation regime. However, climate models, including both modern ocean-equilibrated LongRunMIP and Middle Miocene simulations, are unable to match the degree of continental MCO warmth in New Mexico indicated in our data even at CO2 concentrations 8x higher than pre-industrial levels. Illustrating the magnitude of disagreement, Miocene and modern simulations respectively predict 4.6°C and 3.2°C of warming in New Mexico under a 560-ppm climate while the clumped isotope temperatures at the MCO are roughly 10°C warmer than modern mean annual temperatures in New Mexico. The disagreement between the magnitude of MCO warmth indicated by our clumped isotope record and that resulting from models can be explained either by (1) an underprediction of modelled temperature responses to CO2-driven warming in the southwestern U.S. or (2) other factors that modify local temperature, such as changes in elevation associated with ongoing rifting along the Rio Grande rift and/or long-wavelength uplift associated with passage of the Farallon plate beneath the southwestern U.S. Whether the discrepancy in magnitude is an indication of extreme warmth at the MCO in New Mexico or a result of paleotemperatures encapsulating tectonic signals, our record demonstrates that global drivers pace temperature change in the U.S. Southwest.
How to cite: Bernstein, R., Koning, D. J., Maloney, A., Spaur, S., Lee, O., Sanchez Ortiz, G., Methner, K., Mulch, A., Fiebig, J., Ibarra, D. E., Acosta, R. P., Snell, K. E., and Rugenstein, J. K. C.: Neogene U.S. Southwest Temperatures Paced by Global Climate, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14189, https://doi.org/10.5194/egusphere-egu26-14189, 2026.
The Paleocene–Eocene Thermal Maximum (PETM) is among the most extensively studied climatic events in Earth’s history, primarily due to its relevance as an analogue for future climate change. This brief interval (<200kyr) is marked by a pronounced global temperature increase of approximately 4–8°C and widespread environmental disruptions, including ocean acidification, sea-level rise, intensification of the hydrological cycle, ice-sheet retreat, and significant species extinctions. Despite its importance, ichnological analyses—an essential tool for paleoenvironmental interpretation—remain relatively scarce compared to other Earth science studies.
To address this gap, we performed an ichnological analysis across several sections of the Iberian Peninsula: four sites within the Pyrenean Basin (Esplugafreda, Serraduy, Campo, and Zumaia), representing a continental-to-marine transect in a deep-water gulf opening toward the Bay of Biscay, and one deep-sea section along the southern margin of the Iberian Massif, connected to the Tethys Sea (Río Gor). In the south-pyrenean foreland, conforming an elongated restricted basin, the onset of the PETM coincided with the extinction of the tracemaker community. After that, on the platform areas, trace fossil assemblages were re-established prior to the recovery of the carbon isotope excursion, whereas in deep-sea settings, assemblages only partially recovered even after the excursion ended. These findings indicate a prolonged tracemaker recovery period during the PETM, suggesting that deep-sea tracemaker communities experienced extended ecological stress. In the southern margin of the Iberian Massif (i.e., open ocean setting), during the PETM a high trace fossil abundance is recorded.
Finally, by comparing our results with those from other parts of the world (previous published studies and ongoing research), we can hypothesize why the PETM did not cause a global extinction in the macrobenthic tracer community.
How to cite: Miguez Salas, O., Valero, L., Rodríguez-Tovar, F. J., Lopez Blanco, M., Pujalte, V., and Garcés, M.: Ichnology of the Paleocene-Eocene Thermal Maximum , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5445, https://doi.org/10.5194/egusphere-egu26-5445, 2026.
Understanding the pace of past carbon-cycle disruptions is essential for contextualizing today’s rapid warming. The Paleocene–Eocene Thermal Maximum (PETM, ~56 Ma) is commonly invoked as an analogue for anthropogenic change, yet its comparatively protracted onset implies carbon release, warming, and acidification rates substantially slower than those observed today. In contrast, a short-lived 1–2‰ negative carbon isotope excursion immediately preceding the PETM, termed the pre-onset excursion (POE), has been reported from multiple sites, but its timing and duration remain controversial due to limited chronological control. Key questions therefore remain: How rapidly did climate and environmental change unfold during the POE, and can it provide a more appropriate rate analogue for near-future change? Here we analyze two high-sedimentation-rate paleo-shelf cores from the Mid-Atlantic Coastal Plain (Maryland, USA): South Dover Bridge (SDB) and Cambridge Dorchester Airport (Cam-Dor). High-resolution paleoclimate proxy time series from X-ray fluorescence (XRF) scanning are evaluated using spectral and tuning approaches, and astrochronologic robustness is assessed with statistical tests. Dominant stratigraphic cycles at ~10.5 m and ~2.0 m yield ratios consistent with short eccentricity (~100 kyr) and climatic precession (~20 kyr), implying a mean sedimentation rate of ~10 cm/kyr. The resulting astrochronology constrains the total duration of the POE to 6-8 kyr. Independent δ¹¹B constraints indicate that the POE was accompanied by measurable surface-ocean acidification of ~0.1–0.3 pH units. The inferred rate of pH decline during the POE is of the same order as the present, reinforcing the POE as a potential high-rate analogue and highlighting rapid recovery consistent with strong Earth-system buffering prior to full PETM feedback activation.
How to cite: Li, M., Jiang, Q., and Wu, Y.: A modern-like rate of climate change observed in the latest Paleocene, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6048, https://doi.org/10.5194/egusphere-egu26-6048, 2026.
Geological archives from past warm periods are essential for contextualising future climate change under ongoing global warming. However, interpreting these archives requires a robust understanding of how palaeotemperature proxies record oceanographic variability under modern boundary conditions. This study presents ongoing Holocene alkenone-based sea surface temperature (SST) reconstructions from marine sediment cores collected around Denmark. The primary aim is to constrain alkenone signal provenance through comparison with instrumental SST datasets, and to apply this understanding to reconstructions of Gulfstream variability during past warm climates.
The Danish coastal seas, including the Skagerrak–Kattegat region and shelf settings along the Jutland Peninsula, occupy a climatically sensitive position at the interface between warm Atlantic waters transported by the North Atlantic Current and waters derived from the Nordic Seas, Baltic outflow, and terrestrial runoff. Variability in this Atlantic inflow has been linked to changes in North Atlantic heat transport and proposed as a sensitive indicator of broader AMOC-related variability. As such, the Danish marine realm offers a strategic location for assessing how surface ocean temperatures respond to circulation changes under differing climate states.
We use Holocene-age sediment cores to reconstruct SSTs using alkenone palaeothermometry, a biomarker-based proxy derived from marine haptophyte algae that records upper-ocean temperature conditions. Comparison of Holocene alkenone-derived SSTs with instrumental datasets provides a framework for assessing how proxy temperatures relate to observed surface ocean variability, including the influence of regional circulation changes, stratification, and potential freshwater input. This is of particular importance when examining alkenones, as these compounds may be transported by ocean currents, potentially biasing the recorded temperature signal if such effects are not accounted for. In addition to constraining proxy behaviour, the Holocene record is used to explore the expression of Holocene climate variability in the Danish coastal seas and its relationship to other North Atlantic records.
This Holocene–instrumental framework directly supports ongoing research investigating Gulfstream variability during the Eemian Interglacial (MIS 5e, or the Last Interglacial), a past warm period when the average global temperature was approximately 1–1.5 °C higher than present. Exceptionally thick Eemian marine clay sequences from the Vendsyssel region of Denmark are currently being analysed to develop high-resolution alkenone-based SST records capable of resolving multidecadal variability under warm-climate boundary conditions. Anchoring these reconstructions in a modern, provenance-sensitive analogue improves confidence in interpretations of Gulfstream behaviour during past warm periods and enhances the use of geological archives to inform expectations of future oceanographic change.
How to cite: Walker-Trivett, C., Kiel, E.-C., Śliwińska, K., and Snowman Andresen, C.: Gulfstream Variability in a Globally Warming World – The Forgotten Danish Archive, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11918, https://doi.org/10.5194/egusphere-egu26-11918, 2026.
Past greenhouse climates like the Early Eocene Climatic Optimum (~53-49 million years ago, Ma) provide an opportunity to assess the sensitivity of global temperature to greenhouse forcing, with proxy-based temperature reconstructions from such time intervals providing crucial benchmark data for evaluating Earth System Models. However, estimating global mean temperatures is complicated by sparse proxy evidence for surface temperatures and heterogenous warming patterns. For this reason, most depictions of global mean temperature evolution use temperature reconstructions from the deep ocean, a vast and (proposedly) relatively homogenous heat reservoir (e.g., Hansen et al., 2013; Westerhold et al., 2020). Deep ocean temperature reconstructions, however, are usually based on the oxygen isotopic composition (δ18O) of benthic foraminifera, which can additionally be influenced by the isotopic composition of seawater and other non-thermal factors.
Here we present new deep ocean temperature reconstructions for ~52–50 Ma from both the North Atlantic (IODP Site U1409) and the Pacific Ocean (ODP Site 1209) using clumped isotope thermometry, which is independent from seawater composition and less affected by non-thermal influences. We confirm previously reported deep North Atlantic temperatures exceeding δ18O-based estimates (Meckler et al., 2022). Crucially, our results show that deep ocean warmth is not a regional feature of the Atlantic Ocean, with similarly warm temperatures also found in the vast deep Pacific Ocean. The new data advocate for a revision of previous, δ18O-based estimates of global mean temperatures. Combined with new CO2 estimates, we derive an updated and more robust estimate of equilibrium climate sensitivity for the Early Eocene Climate Optimum, which is higher than most previous estimates, an important new constraint for Earth System Models.
References
Meckler, A.N., et al. (2022), Cenozoic evolution of deep ocean temperature from clumped isotope thermometry. Science 377, 86-90
Hansen, J., et al. (2013), Climate sensitivity, sea level and atmospheric carbon dioxide. Philos. Trans. A Math. Phys. Eng. Sci. 371, 20120294
Westerhold, T., et al. (2020), An astronomically dated record of Earth’s climate and its predictability over the last 66 million years. Science 369, 1383–1387
How to cite: Meckler, N., Taylor, V., Marquardt, J., Lypiridou, I., Ring, S., Rae, J., Sexton, P., Westerhold, T., Zachos, J., and Kirtland-Turner, S.: Globally warm deep ocean during the Early Eocene Climatic Optimum indicates high climate sensitivity to greenhouse gases, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19376, https://doi.org/10.5194/egusphere-egu26-19376, 2026.
The short-lived (~30 Kyr) warming C19r event or Late Lutetian Thermal Maximum (LLTM) is the hyperthermal recorded 41.52 Ma ago in the upper part of
magnetochron C19r. Like most Eocene hyperthermals, this event has been defined by a sharp negative excursion in the oxygen and carbon isotopic records in the Atlantic Ocean, including ODP Sites 1260, 1263 and 702 and in a land section in Spain. To understand how marine biota responded to past warming is crucial also for a future climatic perspective. However, differently from the early Eocene hyperthermals for which biotic response has been widely analyzed, the LLTM has been so far explored only for the benthic foraminiferal response. Planktic foraminifera, that are extremely sensitive to ocean changes, have a key role to evaluate how global warming affects marine ecosystems. We present here the impact on planktic foraminiferal communities to this event, at the south Atlantic Site 1263. Although the LLTM records a moderate temperature increase with respect to other Eocene warming events, planktic foraminiferal assemblages reveal to be extreme sensitive as showing marked variations that include a decline in abundance of the cold-index Subbotina and a not straightforward response of the mixed-layer warm-index taxa, suggesting possible ecological competition and different flexibility to challenge the new environmental conditions.
How to cite: Ferrando, F., Sigismondi, S., Westerhold, T., and Luciani, V.: Impact of the Late Lutetian Thermal Maximum (41.52 Ma) on plankticforaminiferal assemblages (Site 1263, Atlantic Ocean), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20368, https://doi.org/10.5194/egusphere-egu26-20368, 2026.
The early Eocene long-term warming was punctuated by relatively short (50 to 200 kyr) and abrupt warming events, which are used as analogues to understand current anthropogenic global warming. Among these hyperthermal events, the Eocene Thermal Maximum 2 (ETM2) corresponds to an orbitally paced release of 2,600 to 3,800 Gt of carbon at 54.1 Ma. It has primarily been identified in deep oceanic settings, while terrestrial and coastal records of this event remain scarce. Indeed, the ETM2 has only been identified in shallow marine settings in a few locations (Arctic, USA Atlantic coast, Egypt, India, and New Zealand), hindering a full understanding of its environmental impact.
Here, we present a high-resolution multi-proxy record from a newly drilled 25-m-long core in southwest Belgium (Mons Basin), at a paleolatitude of ~40°N, combining Gamma-ray spectrometry, mineralogy (XRD bulk-rock and clays, TEM, grain-size) and organic geochemistry (δ13Corg, Rock-Eval®, and palynofacies). Sedimentological interpretation indicates a siliciclastic tidal shallow marine environment (a few tens of meters water depth). Using an age model based on nannofossils, dinocysts and cyclostratigraphy, the ETM2 is recorded over approximately 2.5 m by a ~1‰ negative carbon isotope excursion (CIE) located within the NP11 nannofossil biozone. The peak of this CIE corresponds, with a slight delay, to an increase in carbonate content and nannofossil abundance, suggesting enhanced primary productivity related to an intensified hydrological cycle and higher nutrient inputs during the ETM2. An increase in detrital input is also suggested by the transition to coarser grain size. After a progressive decline in kaolinite, illite, and chlorite contents in the clay fraction, smectite becomes the dominant clay mineral during the CIE, possibly pointing to a transgressive event in relation with the ETM2, as also suggested by palynofacies and dinocyst assemblages.
This study presents the first high-resolution record of the ETM2 in the coastal environments of the southern North Sea Basin, preserved in the Mons Basin. In these settings, the ETM2 is associated with a deepening trend, possibly related to sea-level rise, as well as with increased primary productivity and detrital inputs, which point to an enhanced hydrological cycle.
How to cite: Talon, J., Pellenard, P., Iakovleva, A., Shcherbinina, E., Martinez, M., Quesnel, F., Rusch, C., Dupont, N., Schnyder, J., Baudin, F., Dupuis, C., and Baele, J.-M.: Unravelling the impact of the Eocene Thermal Maximum 2 (ETM2) : A high-resolution shallow marine record from Belgium , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-305, https://doi.org/10.5194/egusphere-egu26-305, 2026.
The response of ice sheets and sea level to a warming climate is of global concern, with significant implications for human populations. To better understand these dynamics, especially during climates warmer than today, this project reconstructs sea-level and ice-sheet variability across six glacial-interglacial (G-IG) cycles of the late Cenozoic (~5 Ma), spanning the transition from the Pliocene greenhouse to the Pleistocene icehouse.
We use paired measurements of benthic foraminiferal δ¹⁸O and Mg/Ca ratios to reconstruct bottom-water temperature (BWT) and derive seawater δ¹⁸O (δ¹⁸Osw), a proxy for global ice volume. While effective for interglacials, the Mg/Ca proxy likely overestimates glacial lowstands due to non-thermal effects. To improve reconstructions, we integrate carbonate clumped isotope (Δ₄₇) thermometry, a seawater chemistry-independent BWT proxy, using material from Eastern Equatorial Pacific ODP Site 849. Though analytically demanding, Δ₄₇ offers a critical calibration check for Mg/Ca-derived BWTs.
Preliminary paired δ¹⁸O-Mg/Ca data from Oridorsalis umbonatus (3.35–2.0 Ma) at sub-millennial resolution reveal G-IG sea-level cycles with glacial lowstands lower than previous estimates. Δ₄₇-BWTs, available at lower resolution, broadly support the Mg/Ca-based reconstructions, reinforcing their validity despite limited precision and resolution.
Future work will refine the understanding of discrepancies between Mg/Ca- and Δ₄₇-derived BWTs, improving glacial sea-level estimates. This study aims to constrain sea-level variability rates and assess existing reconstructions, offering a more robust understanding of past ice-volume dynamics and informing projections of future sea-level rise.
How to cite: Koniarczyk, L., Friedrich, O., Meckler, N., and Taylor, V.: BENTHICS: Benthic Foraminiferal Temperature-Based High-Resolution Ice-Volume Reconstructions during Cenozoic Snapshots, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1424, https://doi.org/10.5194/egusphere-egu26-1424, 2026.
Posters virtual: Fri, 8 May, 14:00–18:00 | vPoster spot 4
EGU26-12459 | ECS | Posters virtual | VPS7
Oyster shells record seasonal climate variability in the middle Eocene Paris Basin under higher-than-modern temperatures and seasonal rainfall patternsFri, 08 May, 15:30–15:33 (CEST) vPoster spot 4
The Eocene experienced pronounced temporal changes in temperature and atmospheric pCO2, with multiple warming phases from the early to late middle Eocene. High-resolution, sub-annual palaeoclimate reconstructions are essential to evaluate the impact of elevated pCO2 on seasonal climate dynamics, providing critical insights for mitigating future climate crises. Middle Eocene Climatic Optimum (MECO), the Lutetian–Bartonian boundary warming event (~41 Ma) is particularly relevant, as current pCO2 levels are rising rapidly and could reach similar concentrations within a century.
Bivalvia shells, growing incrementally, record seasonal to even sub-daily climatic and environmental fluctuations throughout their life. Shells of the oyster Cubitostrea cubitus, a shallow-to-marginal marine cementing bivalve from the Sables du Guépelle Formation (~41 Ma) of the Paris Basin (~41° N palaeolatitude), contain very low Mn and Fe concentrations (<250 µg/g), indicating their pristinity. These shells are used as a palaeoclimate archive in a multiproxy approach that combines LA-ICP-MS trace element analyses and clumped isotope thermometry (Δ47), integrated with simulations from the Community Earth System Model (CESM). Sub-annual periodic variations in trace elements to Ca ratios along the oyster hinge indicate an oyster lifespan of ~16 months when aligned with monthly temperature variability from CESM simulations. Clumped isotope thermometry (Δ47-T) records a seasonal sea surface temperature (SST) amplitude of ~8 °C, where the summer temperature reaching 28.3 ± 4.4 °C (68% CI) and winter temperatures of 19.6± 3.5 °C. Summer δ18Ow (-1.1± 0.9 ‰), consistent with Bartonian seawater compositions (-0.5 to -1.0 ‰), indicate a strong seasonal marine influence in early Bartonian Paris Basin. In contrast, significantly lower winter δ18Ow values (-2.9± 0.7 ‰) reflect enhanced freshwater input, which is further supported by relatively lower Sr/Ca profile, a salinity indicator consistent with increased winter rainfall predicted by CESM simulations.
In summary, our preliminary results indicate that during the MECO, the Paris Basin experienced seasonal sea-surface temperature variability comparable to that of modern shallow waters along the French North Sea coast, but with higher temperatures of approximately 10 °C throughout the year. In contrast to the modern climate (in the region of : 0–5° E, 46–50° N), where annual precipitation is relatively evenly distributed, rainfall during the MECO appears to have been strongly seasonal.
How to cite: Mitra, A., Goderis, S., Baatsen, M., Zhao, X., Chaudhuri, S., Ledésert, B. A., Claeys, P., and Müller, I. A.: Oyster shells record seasonal climate variability in the middle Eocene Paris Basin under higher-than-modern temperatures and seasonal rainfall patterns, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12459, https://doi.org/10.5194/egusphere-egu26-12459, 2026.
