The Arctic was around 4-5C warmer in summer during peak Last Interglacial (LIG), compared to the preindustrial. However this summer warming was not accurately captured by CMIP models until 2020. Before then the lack of LIG Arctic warmth in CMIP models was most commonly postulated to be due to a lack of dynamic vegetation feedbacks. However in 2020 a UK CMIP6 model accurately captured the summer warming (Guarino et al., 2020). The warming in this model is due to a complete summertime loss of Arctic sea ice, rather than dynamic vegetation feedbacks. Whilst marine data, until 2023,  were not adequate for assessing the accuracy of this modelled LIG Arctic sea ice loss (Kagayama et al., 2021), this has now been rectified by valuable new marine core evidence from the Arctic (Vermassen et al., 2023). Here, we show firstly why we are confident that melt pond physics (albedo feedbacks) are sufficient to melt LIG sea ice, raise the Arctic temperature, and also why they are important for the accurate projection of Arctic sea ice loss during warm climate – including the future (Diamond et al., 2021; 2024). Secondly, we quantify the Arctic warmth, and discuss the nature of polar amplification in CMIP models, during the LIG (Sime et al., 2023). We find an Arctic-wide warming of 3.7±1.5 K at the LIG, alongside a climatological minimum sea ice area of 1.3 to 1.5 million km2, i.e that the peak LIG Arctic likely experienced a mixture of ice-free and near-ice-free summers.

How to cite: Sime, L., Diamond, R., Schroeder, D., Sivankutty, R., and Guarino, M. V.: An ice free Arctic during the Last Interglacial: CMIP6-PMIP4 progress on Arctic sea ice , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4746, https://doi.org/10.5194/egusphere-egu24-4746, 2024.

The marine isotope stage (MIS) 11 interglacial, which occurred approximately 424 to 374 thousand years ago, is a period of significant climatological interest due to its unusual duration and intensity of warm conditions under relatively subdued orbital forcing, a phenomenon often referred to as the “MIS 11 paradox”. This study focuses on understanding the factors behind this paradox and its implications for the formation of Deep Water in the North Atlantic.

We examined the upper-ocean structure in the Iceland Basin during MIS 11, a key region for modern deep-water formation. By analyzing geochemical measurements, including stable nitrogen isotopic ratios and carbon and oxygen isotopic ratios of planktic foraminifera, we reconstructed the upper-ocean structure and its potential role in driving the Atlantic Meridional Overturning Circulation (AMOC) during MIS 11.

The findings reveal that MIS 11 experienced an initial AMOC intensification, followed by a secondary strengthening prior to the onset of the climatic optimum. The secondary intensification was attributed to the gradual reduction of northern-hemisphere sea ice, allowing for a northward extension of surface-ocean currents. This resulted in the maintenance of an anomalously deep summer mixed layer in the polar Nordic Seas during MIS 11 compared to the Holocene. The deep-water formation in the Nordic Seas played a crucial role in extending the enhanced warming of the northern hemisphere and delaying the onset of the next glacial interval.

While the contemporary Atlantic Ocean primarily relies on deep-water formation in the eastern subpolar region, the study suggests that the relative importance of deep-water formation in polar regions may increase under extreme scenarios of anthropogenic warming. By studying MIS 11 as a potential analog for Earth's contemporary climate system, we provide valuable insights into the long-term fate of the AMOC and its implications for global climate.

This study also highlights the significance of understanding the convective behavior of the subpolar Atlantic for a comprehensive understanding of the AMOC during MIS 11. We present new geochemical measurements and reconstructions of upper-ocean structure in the Iceland Basin, shedding light on the potential link between summer mixed-layer depth and deep-water formation.

How to cite: Thibodeau, B., Doherty, J., Alonso-García, M., Band, S., Gonazalez-Lanchas, A., Not, C., and Ren, H.: Instability in upper-ocean structure and its implications for Deep Water formation during marine isotope stage 11, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14193, https://doi.org/10.5194/egusphere-egu24-14193, 2024.

Global ocean circulation is controlled by deep water formation in the high latitude Atlantic and Southern Oceans. There is no deep water formation in the modern North Pacific due to a strong salinity gradient (or halocline) which makes the deep Pacific relatively homogenous. There is evidence to suggest that this halocline was weaker in the Late Pliocene (3.3 – 2.6 Ma) which allowed for active deep water formation. Coupled stable isotope and trace element records from benthic foraminifera at the Northwest Pacific ODP Sites 1208 (3346 m depth) and 1209 (2387 m depth) indicate deep water formation in the North Pacific during the Late Pliocene. Heavier oxygen isotopes at the shallower site 1209 require that the two sites were bathed in deep waters formed in different locations. Trace metal analysis (Mg/Ca) shows that there was a marginally colder, and thus fresher, water mass at the shallower site 1209 which is partially consistent with modelling results showing a fresher North Pacific Deep Water reaching intermediate depths in the Late Pliocene, while the deeper site was bathed in southern sourced waters. The benthic isotope values at the two sites converged during the glacials of the Early Pleistocene after the intensification of Northern Hemisphere Glaciation (iNHG, c. 2.7 Ma). This convergence was coincident with a global drop in sea levels suggesting that sea level changes, potentially by constricting water mass transport through the Indonesian Gateway, may have modulated the strength of North Pacific Deep Water formation in the Pliocene. This would mean that the complete cessation of North Pacific Deep Water does not occur until considerably after the iNHG.

How to cite: de Graaf, F., Thornalley, D., Burls, N., Foster, G., Brown, R., and Ford, H.: The cessation of North Pacific Deep Water formation over Northern Hemisphere Glaciation., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2148, https://doi.org/10.5194/egusphere-egu24-2148, 2024.

The larger-scale oceanic gyre circulation regulates temperature, salinity and nutrient flow throughout the ocean, profoundly influencing the biological environment and climate. Here, we investigate the response of the Pacific gyre circulation during the warm climate of the early Eocene in eight models from the Deep-Time model intercomparsion project (DeepMIP). Our DeepMIP results suggest a northward expansion of the North Pacific subtropical gyre by up to 10 degrees latitude in the Eocene, maintaining a similar strength to the present day. This simulated poleward expansion of the North Pacific gyre circulation is corroborated by proxy evidence, including poleward shifts in low sedimentation rate and high clay concentration during the Eocene. In the southern Pacific, the super subtropical gyre is much stronger during the Eocene due to the southward position of Australia that leads to a wide-open Indonesian gateway. The poleward shifted boundary between the subtropical and subpolar gyre in North Pacific occurs as a result of the northward shifted westerly winds maxima, as also corroborated by an analysis of the Sverdrup transport. The Sverdrup transports describes the upper circulation during the Eocene further poleward than modern day mainly due to their continental differences. The upper circulation corresponds to Sverdrup transport up to ~53°N for the North Pacific, slightly further north than modern day of 50°N, and up to ~55°S for the South Pacific that is much further south than in the modern ocean and continents (~45°S).

How to cite: Zhang, Y. and M. de Boer, A.: Poleward expansion of North Pacific gyres circulation during the warm early Eocene inferred from inter-model comparisons, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2206, https://doi.org/10.5194/egusphere-egu24-2206, 2024.

Since the middle Miocene climatic transition, Earth’s climate has steadily cooled. The Late Miocene Global Cooling (LMGC) and the Northern Hemisphere Glaciation (NHG) were key cooling events. I analyzed changes of radiolarian microfossil assemblages to try to reconstruct the paleoceanographic changes during the last 10 million years at Ocean Drilling Program (ODP) Site 1208 to better understand the climate-cooling mechanism. I reconstructed sea surface temperatures (SSTs) based on extant radiolarian species from 0 to 10 million years ago to verify the suitability of radiolarian-based SSTs. A comparison with previously published alkenone-based SSTs at Site 1208 indicated that radiolarian-based SSTs for the Miocene based on only extant species are satisfactory. However, large discrepancies were observed between radiolarian-based and alkenone-based SSTs during the LMGC and NHG. I attributed these discrepancies to a sustained influence of subsurface water (~50 to 100 m) on assemblages of radiolarians during extreme cooling events. Relative abundances of other radiolarian groups indicated that during the LMGC there was a reorganization of regional paleoceanography that probably weakened the Pacific Meridional Overturning Circulation, increased meridional temperature gradient, and caused a southward migration of the subtropical front.  It is probable that North Pacific Intermediate Water expanded southeastward during the NHG.

How to cite: Matsuzaki, K.: Evolution of the Central Northwest Pacific paleoceanography over the past 10 million years focusing on the Late Miocene Global Cooling (ODP Site 1208), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21, https://doi.org/10.5194/egusphere-egu24-21, 2024.

Pronounced warming in the geological record negatively impacts ecosystems. To show the impact on different parts of the marine calcareous plankton, we present an integrated record, from two Tethyan sections, Madeago and Terche (northeastern Italy), of the planktic foraminiferal and calcareous nannofossils response to the Eocene Thermal Maximum 2 hyperthermal (ETM2, ~54 Ma). The main result of our study is the striking planktic foraminiferal dwarfism (up to ~40% decrease in test-size compared to pre-event values) recorded at the ETM2 impacting both surface and deeper dwelling species. To a lesser extent, calcareous nannofossils exhibited a size reduction as documented by an increase of ‘small placoliths’. 
Causes to explain the dwarfism can be manifold. Enhanced metabolic rate in response to warming requires more food to support growth, thus a strategy to optimize resource uptake is to enlarge surface area/volume ratio by reducing the cell mass and therefore the test-size. Deoxygenation is not likely a driver as the dwarfing occurred in both mixed layer than deeper dwelling taxa, which oxygen limitation typically limited to the thermocline.  Our foraminiferal size data from Site 1263 (Atlantic Ocean) and Site 1209 (Pacific Ocean) highlight that the pronounced dwarfism is restricted to the Tethyan area. We record local increase in productivity in our sections not observed in the open ocean sites. This could have limited the growth of symbiont bearing taxa, as in modern ocean the size of symbiont bearing taxa decreases towards to shore due to increases in productivity reducing light availability. Reduced symbiosis though cannot be the only factors as it cannot explain the dwarfing of the deep-dweller taxa in our Tethyan sections. The warming at our site is similar to open ocean sections and cannot explain this different response. Therefore, we hypothesise that local drivers could have acted additively to warming such as the input of biolimiting/toxic metals from the volcanic emissions of the Veneto Volcanic Province, which was active during the ETM2. We find the smallest size in close temporal association with peaks in magmatic derived Hg/Th-Hg/Rb recorded just before and at the ETM2 which cannot be brought into our sections through weathering. The lack of dwarfisms associated with Hg peak above the ETM2 at Terche, when warming would have ended, suggests that the volcanic input by itself was not sufficient to cause dwarfism. We speculate that volcanism could have acted synergistically causing the uniqueness of dwarfism in the global context of warming. The size reduction lasted several thousand years thus implying long term impacts of such additive drivers.

How to cite: D’Onofrio, R., Barrett, R., Schmidt, D. N., Fornaciari, E., Giusberti, L., Frijia, G., Adatte, T., Sabatino, N., Monsuru, A., Brombin, V., and Luciani, V.: The ETM2 in the Tethys Realm: Extreme Planktic Foraminiferal Dwarfism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20177, https://doi.org/10.5194/egusphere-egu24-20177, 2024.

The Early Eocene Climatic Optimum (EECO) was the warmest sustained episode of global warming during the Cenozoic, accompanied by major alterations in land-based and marine biota. Initially identified through stable oxygen isotope minimum values between ~52—50 Ma (herein labelled ‘peak-EECO phase’) and later extended to a broader timeframe (53—49 Ma) anchored on stable carbon isotope excursions, the EECO provides a crucial window for exploring the long-term, macroevolutionary consequences of warm climates on marine primary producers. The fossil remains of coccolithophores and other calcareous nannoplankton have been studied previously in the mid- and high latitudes, where the EECO is characterized by a transition from assemblages dominated by the genus Toweius (Prinsiaceae) to the enduring presence of the genus Reticulofenestra (Noelaerhabdaceae), as is still the case for their descendants in modern assemblages (Gephyrocapsa spp. and Emiliania huxleyi).

Using a newly collected nannofossil record from the equatorial Atlantic (ODP Site 1258), we detail changes in low-latitude calcareous nannofossil assemblages throughout the various stages of the EECO and the subsequent early to middle Eocene cooling transition (EMET). The decline in Toweius spp. occurred in two steps: first, at the start of the peak-EECO phase (~52 Ma), with abundance plummeting to about one-third of previous levels, followed by its final and permanent decline and the first continuous occurrence of Reticulofenestra spp. at the end of the peak-EECO phase (~50 Ma). The EECO is also marked by a broad acme of Discoaster spp., as previously reported at several sites. Here we also report on distinct abundance increases in Campylosphaera, Umbilicosphaera and Calcidiscus. These genera declined in abundance by the conclusion of the EECO (~49 Ma) in conjunction with the rapid and sustained expansion of Reticulofenestra, marking the EMET.

Multivariate statistical analysis of nannofossil datasets at Site 1258 and sites from higher latitudes highlights the occurrence and prevalence of specialist taxa exclusively in the tropics, revealing a distinct tropical signature atop the previously identified latitudinal expansion of (sub)tropical taxa during the EECO. Compositional contrasts between the tropical and higher-latitude sites diminished significantly after the EECO, coinciding with the decline of taxa with inferred high thermal optima in the tropics. Our combined results suggest the highest biogeographical differentiation of tropical nannoplankton assemblages from the subtropics (e.g., ODP Sites 1263 and 1210) during the EECO, contrary to some expectations related to a much flatter meridional thermal gradient. The restructuring of the nannoplankton communities after the EECO, however, points to increased connectivity and dispersal between the two regions. It is important to explore the regional driving forcings (e.g., ocean circulation, temperature, nutrient availability, and biotic interactions) on local phytoplankton community structures in the tropics in order to understand broadscale changes in biogeographical and macroevolutionary patterns.

How to cite: Asanbe, J. and Henderiks, J.: Major shifts in low-latitude calcareous nannofossil assemblages across the Early Eocene Climatic Optimum (~53—49 Ma), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10705, https://doi.org/10.5194/egusphere-egu24-10705, 2024.

Thousands of gigatons (~2500-4500 Gt) of carbon were released into the ocean and atmosphere system over several thousand years during the Paleocene-Eocene Thermal Maximum (PETM, ca. 56 Ma), a transient period of global warming, is considered an important analog for future greenhouse conditions. It was accompanied by a significant carbon cycle perturbation, intensified weathering and hydrological cycling, and ocean deoxygenation. Although ocean deoxygenation across the PETM is reported widely, its mechanism in the open ocean remains uncertain. We here present magnetic and geochemical analyses of sediments from the Eastern Equatorial Pacific (EEP) Ocean. We find that iron fertilization during the PETM by eolian dust and volcanic eruptions fueled EEP ocean productivity. This process led to increased organic matter degradation and oxygen consumption in intermediate waters, leading to deoxygenation. Our findings suggest that iron fertilization could be an important driver of open ocean oxygen loss, as a side effect of global warming. Our observation is important in the emerging discussion of how global warming will reduce dissolved oxygen in the open ocean and, in turn, affect the marine fishery industry and future food security.

How to cite: jiang, X., Yao, W., zhao, X., sun, X., Roberts, A., and Sluijs, A.: Iron fertilization-induced deoxygenation of Eastern Equatorial Pacific intermediate waters during the Paleocene-Eocene Thermal Maximum, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2571, https://doi.org/10.5194/egusphere-egu24-2571, 2024.

Investigating how the early Eocene (∼56–48 million years ago) hydrological cycle operated under elevated atmospheric CO2 concentrations and globally higher temperatures can provide important insights into understanding of current climate change and projects of future climate. Here, we investigate the global and zonal-mean rainfall patterns during the early Eocene using an integrated data-model approach. We leverage insights from the DeepMIP-Eocene suite of model simulations in combination with a compilation of paleobotanical proxies of precipitation. In short, the mid- and high latitudes, as well as the tropical band, are characterized by a thermodynamically-dominated hydrological response to warming, and overall wetter conditions (“wet-gets-wetter”). A more complex picture is painted for the subtropics. Although these are overall characterized by negative precipitation-evaporation anomalies (“dry-gets-drier”) in the DeepMIP models, there is surprisingly large inter-model variability in mean annual precipitation. Intriguingly, we find that models with weaker meridional temperature gradients (e.g., CESM, GFDL) are characterized by a reduction in subtropical moisture divergence, leading to an increase in MAP. These model simulations agree more closely with our new proxy-derived precipitation reconstructions and other key climate metrics and imply that the early Eocene was characterized by reduced subtropical moisture divergence. If the meridional temperature gradient was even weaker than suggested by those DeepMIP models, circulation-induced changes may have outcompeted thermodynamic changes, leading to wetter subtropics, thus going against the “wet-gets-wetter, dry-gets-drier” paradigm. This highlights the importance of evaluating multiple climate metrics against sets of simulations and can provide food for thought for DeepMIP phase two.

How to cite: Cramwinckel, M. J. and the DeepMIP-Hydrology Team: Response of the Hydrological Cycle to Early Eocene Warmth: Insights from DeepMIP-Eocene, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5915, https://doi.org/10.5194/egusphere-egu24-5915, 2024.

Eocene warmth has been used as one of the best analogues for future anthropogenic warming. How East Asian hydroclimate responds to the increased temperature during the Eocene is still elusive. Here, we present a combined element and isotopic geochemistry study of an Eocene lacustrine sequence covering the period 46-33 Ma from Weihe Basin, central China. Based on the formation process of lake carbonate and the paleosol CO₂ barometer equation, a calculation model of lake carbonate carbon isotope (δ¹³Ccarb) that is suitable for open lake basins with low productivity is proposed. The sensitivity analysis of the Eocene lacustrine carbonate δ¹³Ccarb  show that the SRF is the main influencing factor of the carbon isotope fractionation. The reconstructed SRF of the Eocene is generally high, with an average value of ~215 g C/m²/yr, revealing a relatively warm and humid environment in the Weihe Basin. After ~41 Ma, the SRF gradually decreased, indicating that the climate in the Weihe Basin gradually became colder and drier. This trend is consistent with the global cooling, especially at ~36 Ma, ~33 Ma (the Eocene-Oligocene transition EOT) showing the most significant reduction. The reconstructed precipitation oxygen isotope (δ¹⁸Op) in the Eocene warmth is characterized by a positive value (~-6 ‰) in the northwest inland region, and relatively negative  values in the central region such as the Weihe Basin and Lanzhou Basin (~-10 ‰), and the Qinghai-Tibetan Plateau area (~-11 ‰). This kind of distribution is similar to modern precipitation δ¹⁸Op, indicating that a prototype of the East Asian summer monsoon circulation has probably formed in the Middle Eocene.

How to cite: Wang, K., Lu, H., Sun, W., Liang, C., Zhang, H., Wang, Y., Lv, H., Wang, J., Zhang, H., and Lai, W.: The oxygen and carbon isotope records of East Asian climate variations during the Eocene warm periods from Weihe Basin, central China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7727, https://doi.org/10.5194/egusphere-egu24-7727, 2024.

The Asian summer monsoon (ASM) is a seasonal response of the coupled land-ocean-atmospheric system, which influences more than 60% of the world’s population. Although progress has been made in understanding the ASM variability and its prediction, the timing and governing factors for the ASM initiation are still debatable as recent proxy evidence and modeling studies suggested the initiation of a wet-dry monsoonal climate from the Cretaceous period (145 million years ago, Ma) to the early Miocene or late Oligocene epoch, ∼25-22 Ma. Capitalizing on an ensemble of paleoclimate simulations for the early Eocene (56-48 Ma), we show that the Asian wet season was considerably weaker and shorter than present in the absence of an elevated heat source like the Tibetan Plateau in the early Eocene. The deficient upper tropospheric meridional temperature gradient couldn’t drive the seasonal northward migration of the precipitation band over South Asia. Additionally, the weaker cross-equatorial moisture flow was mechanically blocked by the Gangdese mountain along the southern edge of Asia, leading to significantly dry conditions in South Asia. The enhanced atmospheric greenhouse gases were inadequate to strengthen the seasonal circulation and precipitation variability to the present level. We argue that an altered wet and dry seasonality over South Asia was not necessarily qualified as the Eocene ‘monsoon’.

How to cite: Santra, A., Capitanio, F. A., Dommenget, D., Goswami, B., Farnsworth, A., Hutchinson, D. K., Arblaster, J. M., Lunt, D. J., and Steinig, S.: Did monsoon govern the Asian rainy season in the early Eocene? An ensemble paleoclimate simulation perspective., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3742, https://doi.org/10.5194/egusphere-egu24-3742, 2024.

Nearly 100 million people live in and depend on the Sahel for agriculture and natural resources. The region is sensitive to natural climate and environment variations caused by the seasonal movement of the tropical rainbelt. In the paleoclimate record, insolation plays a clear role on West African Monsoon strength, but responses to other forcings like temperature, greenhouse gases, ice volume, and land surface cover are unclear due to the lack of highly resolved, terrestrial records that span major global and regional shifts through time. Here we present leaf wax precipitation and vegetation records from five targeted study windows throughout the last 25 million years, derived from long-chain n-alkane hydrogen (δD_wax) and carbon (δ¹³C_wax) isotopes, respectively, in a sediment core from ODP Site 959 in the Gulf of Guinea, where westerly winds and major river systems transport Western Sahel-sourced material. Analyses of trend and variability document a range of rainfall and vegetation responses to orbital forcings in different boundary conditions in the Oligocene, Miocene, Pliocene, and Pleistocene. We find that both the climate and environment was more variable in times of higher CO₂ and global temperatures, suggesting an increase in ecosystem instability moving forward into the future. Because of the high resolution and temporal coverage of these new biomarker isotope records, we can examine relationships between precipitation and vegetation fluctuations, even prior to C₄-expansion when there was a strong correlation despite minimal variation in δ¹³C_wax in a C₃ world. Further, we find a drying trend throughout the record, demonstrating that vegetation on long timescales was decoupled from hydroclimate and was like driven by global CO₂, advancing our understanding of climate and ecosystem relationships across the Cenozoic.

How to cite: Lupien, R., Uno, K., and de Menocal, P.: Orbital-scale climate and environmental responses of the Western Sahel to shifts in Cenozoic boundary conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7676, https://doi.org/10.5194/egusphere-egu24-7676, 2024.

Massive additions of ¹³C-depleted carbon to the atmosphere-ocean system at 55.9 Myr ago led to global warming of 5–8 °C, profound floral/faunal turnovers and alteration of the global hydrological cycle at the Paleocene-Eocene boundary. Climate and environmental changes over the late Paleocene and Paleocene-Eocene Thermal Maximum (PETM) are well-preserved in continental deposits, formed in the subtropical zone (paleolatitude ~35 °N), in the Tremp-Graus Basin, northern Spain. One of the key exposures is the Esplugafreda section, which is made up of ~250 m of red mudstones with abundant paleosols and contains numerous multi-episodic channel-like bodies of calcareous conglomerates and calcarenites. The paleosols contain abundant centimeter-sized soil nodules and gypsum indicating a semi-arid to arid paleoenvironment. The Paleocene-Eocene (P-E) boundary is located near the top of the continental section, based on a 6‰ negative carbon isotope excursion (CIE). The CIE spans more than 15–20 m of yellow cumulate paleosols formed during the Paleocene-Eocene Thermal Maximum (PETM). The post-PETM interval in the Esplugafreda section comprises 20 m of red paleosols rich in gypsum and characterized by normal soil nodule δ¹³C values.

Here, we report the first carbonate clumped isotope thermometry data of selected soil carbonate bearing paleosol layers of the Esplugafreda sequence to quantify the magnitude of warming recorded in the sediments of this terrestrial subtropical site across the Paleocene-Eocene boundary. Soil nodules originated from red mudstone paleosols making up the upper part of the upper Paleocene Esplugafreda Formation and PETM yellow soils collected at two nearby sites. The nodules were sampled with a hand driller for Δ₄₇ measurements, which were done using a Kiel IV carbonate device coupled to a Thermo Scientific 253 Plus IRMS at the Institute for Nuclear Research, Debrecen, Hungary. Stable carbon, oxygen isotope and clumped isotope compositions were calculated as the average of 8–16 replicate analyses of 100–150 μg of carbonate. The carbon and oxygen isotope ratios are reported in δ notation in per mil (‰) relative to the Vienna Pee Dee Belemnite (VPDB), while the temperature-dependent mass 47 anomaly on the I-CDES_90°C scale. Temperatures were calculated using the Kele et al. (2015) calibration modified by Bernasconi et al. (2018) and the Anderson et al. (2021) calibrations.

Soil carbonates of the Esplugafreda formation yield δ¹³C_carb values between –8.55 and –5.85 ‰, while the PETM yellow soil carbonates are significantly more negative (–13.84 to –10.12 ‰), in good agreement with previous measurements. A much smaller, ~1.2 ‰ difference can be observed in the oxygen isotope compositions between these carbonates (δ¹⁸O_carb: –5.46 to –4.13 versus –6.35 to –4.47 ‰). The Δ₄₇-based paleotemperatures (T_47carb) indicate mean soil carbonate formation of 33.8±9.5 °C during the late Paleocene, which are close to modern summer temperatures of subtropical regions. By contrast, a much higher mean temperature was recorded by soil carbonates of the PETM yellow soils (39±8.5 °C) with extreme (>40 °C) temperatures occurring 4 times more frequently than over the late Paleocene.

This study was supported by the NKFIH through the OTKA K-137767 project.

How to cite: Újvári, G., Kele, S., Rinyu, L., Payros, A., Pujalte, V., Schmitz, B., and Bernasconi, S. M.: Soil carbonate Δ47 paleotemperatures across the Paleocene-Eocene boundary: the Esplugafreda terrestrial record, Spain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10082, https://doi.org/10.5194/egusphere-egu24-10082, 2024.

Understanding past climate informs our future scenarios. Proxy data and climate models are vital for studying past climate change, but discrepancies often arise between these approaches. This study introduces an innovative approach that reconciles proxy data with models by decomposing the physical processes driving monsoon precipitation changes. Focusing on East Asian Summer Monsoon (EASM) precipitation across significant periods in the PMIP, our analysis highlights: 1) the dominance of dynamic effects over thermodynamic effects during the mid-Holocene, 2) contrasting impacts of thermodynamic and dynamical processes during the Last Glacial Maximum, and 3) distinct regional controls of thermodynamic and dynamical processes in the mid-Piacenzian warm period, reflecting diverse water vapor sources. The study concludes that decomposing the physical processes of precipitation aids in reconciling records and simulations. It asserts that simulations consistently yield a decomposed process that spatially aligns with the records. The mismatch between records and simulations primarily arises from simulation biases in the relative contributions of the decomposed physical processes to precipitation changes, suggesting a need for improvement in simulations.

How to cite: Sun, Y., Wu, H., Ding, L., and Ramstein, G.: Decomposition of Monsoon Dynamics: Reconciling Data and Model Comparison for Geological Time Periods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3844, https://doi.org/10.5194/egusphere-egu24-3844, 2024.

For millions of years, the Mediterranean Sea has regularly experienced episodes of disrupted thermohaline circulation and increased primary productivity that resulted in a largely anoxic water column. These anoxic episodes are typically related to a more humid climate over Northern Africa and are captured in the sedimentary record as organic-rich sapropel layers. Given the excellent preservation of organic molecules in them, sapropels are extraordinary archives for the marine and continental ecosystems associated with the unique conditions that prevailed during their formation. We applied metagenomic environmental DNA (eDNA) analysis to recent sapropels (< 175 kyr) from the Eastern Mediterranean, including Sapropel S5 deposited during the Last Interglacial, and benchmarked obtained results with high resolution geochemical and molecular biomarker records. Ancient eDNA analysis enables reconstructions across all domains of life, including those components of the ecosystem that do not leave fossils or are not recorded in the fossil record. In the case of Mediterranean sapropels, this approach reveals information on both terrestrial and marine ecosystems. We provide detailed insight into vegetation changes in the Nile River Basin during the different, climatically diverse episodes of sapropel deposition. On the marine side, we reveal how water column ecology and major elemental cycles adapted to this massive ecosystem overhaul.

How to cite: Wörmer, L., Fernández-Guerra, A., Morard, R., Zure, M., Pedersen, M. W., Hassenrück, C., Kucera, M., Willerslev, E., and Hinrichs, K.-U.: Nile Basin vegetation and Mediterranean water column ecology during Sapropel formation , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19216, https://doi.org/10.5194/egusphere-egu24-19216, 2024.

The Pliocene-Pleistocene transition and Middle Pleistocene Transition (3.4–2.5 million years ago and ~1.2-0.6 million years ago respectively) represent major shifts in the Earth’s climate, with both being associated with global cooling, sustained and transient changes in ocean circulation, and the development and stabilization of large ice sheets in the northern hemi- sphere. These ice sheets waxed and waned over the last 2.5 million years and are the key mode of climate variability in this ice house world. Knowledge of the relationship of climate and CO₂ on this timescale has to date been hampered by low resolution and imprecise records of CO₂ once beyond the reach of the ice core records. Here we show orbitally resolved and multisite records of CO₂ from boron isotopes across both transitions, and progress towards a highly resolved multi-basin stack of records. We find a persistent relationship between CO₂ and climate state, which implicates CO₂ decrease as a major contributor to both climate transitions, but also highlights non-linear responses in temperature and sea level as well as significant leads and lags on orbital timescales. Our findings confirm that changes in atmospheric CO₂ play a key role in long-term Plio-Pleistocene climate and implicate the repeating transfer of carbon from the atmosphere to the ocean as a key mechanism in major climate transitions of the last 3 million years.

How to cite: Chalk, T., Brown, R., Nuber, S., Hain, M., Yu, J., Rae, J., and Foster, G.: Continuous records of δ11B-CO2 covering the Plio-Pleistocene boundary and the Mid Pleistocene Transition show orbital carbon-climate coupling., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13057, https://doi.org/10.5194/egusphere-egu24-13057, 2024.

Equilibrium climate sensitivity (ECS) quantifies the amount of warming resulting from a doubling of the atmospheric CO₂ forcing. Despite recent advancements in climate simulation capabilities and global observations, there remains large uncertainty on the degree of future warming. To help alleviate this uncertainty, past climates provide a valuable insight into how the Earth will respond to elevated atmospheric CO₂. However, there is evidence to suggest that ECS is dependent on background climate warmth, which may interfere with the direct utilization of paleo-ECS to understand present-day ECS. Thus, it is important that a range of different climate states are considered to better understand the factors modulating the relationship between CO₂ and temperature. In this study, we focus on three time intervals: the mid-Pliocene Warm Period (3.3 – 3.0 Ma), the mid-Miocene (16.75 – 14.5 Ma), and the early Eocene (~50 Ma), in order to sample ECS from Cenozoic coolhouse to hothouse climates. Here, we combine the Bayesian framework of constraining the ECS and its uncertainty with several published methods to estimate the global mean surface temperature (GMST) from sparse proxy records. This framework utilizes an emergent constraint between the simulated GMST changes and climate sensitivities across the model ensemble. For each time interval, we employ a combination of parametric and non-parametric functions, coupled with a probabilistic approach to derive a refined estimate. Preliminary results for the Pliocene indicate a GMST reconstruction of approximately 19.3°C, which is higher than previous estimates that were derived using only marine records. Using this estimate, we calculate an ECS that is also higher than previously published values, especially due to the inclusion of high-latitude terrestrial temperature records into our estimates. Intriguingly, using the consistent methodology, our calculated ECS for the early Eocene is lower than that of the mid-Pliocene. This result does not support an amplified ECS in hothouse climate, and points to a potentially important role of ice albedo feedback in amplifying the ECS in coolhouse climate. Ongoing work will apply the same methodology to the mid-Miocene and further investigate the source for the estimated ECS state dependency between these climate intervals.

How to cite: Albright, M. G., Weitzel, N., Inglis, G. N., Steinig, S., Renoult, M., Reichgelt, T., Fletcher, T., Tindall, J., and Feng, R.: Quantifying the State Dependency of Climate Sensitivity Across Cenozoic Warm Intervals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13307, https://doi.org/10.5194/egusphere-egu24-13307, 2024.

The early Eocene features distinctive coupling between biogeochemical cycles and climate, raising fundamental questions about Earth system functioning during major climate transitions and on orbital timescales. For instance, the transition to peak Eocene warmth is ushered in by a major shift in redox conditions and deep ocean circulation, while orbitally-paced hyperthermal events are associated with substantial carbon injections of uncertain origin.  CO₂ change is thought to play a key role in these events, yet despite recent progress, resolution is still lacking for most shorter time intervals.  Here we present new, high-resolution boron isotope data from both benthic and planktic foraminifera that shed new light on Eocene carbon cycling. Using new approaches for conversion of boron isotope data to pH and CO₂, we improve estimates of absolute CO₂ concentrations and the change in CO₂ over key events.  Our data demonstrate a pervasive link between CO₂ and climate in the Eocene hothouse over a range of timescales and provide novel constraints on carbon sources and climate sensitivity.

How to cite: Rae, J., Greene, S., Sexton, P., Adloff, M., Barnet, J., Burke, A., Foster, G., Gray, W., Henehan, M., Holo, J., Jurikova, H., Kirtland-Turner, S., Marquardt, J., Meckler, N., Ridgwell, A., Taylor, V., Westerhold, T., Whiteford, R., and Zachos, J.: Eocene CO2 on orbital to million year timescales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13009, https://doi.org/10.5194/egusphere-egu24-13009, 2024.

It is generally postulated that climatic change during the Paleocene – Eocene Thermal Maximum (PETM) was paced and/or caused by astronomical forcing, particularly eccentricity-modulated precession. Possible causal links include intermediate water warming and subsequent methane hydrate destabilization, increased climate sensitivity due to a warmer background state, and changes in hydrology and weathering. Current astrochronology places the PETM near a 405-kyr eccentricity maximum (Zeebe and Lourens, 2019), likely following a prolonged 2.25-Myr eccentricity minimum (Lourens et al., 2005). Similar orbital configuration sequences have been proposed for the Devonian Upper Kellwasser event (De Vleeschouwer et al., 2017) and the Cretaceous Oceanic Anoxic Event 2 (Batenburg et al., 2016). To understand how eccentricity could have made the Late Paleocene Earth System sensitive to a carbon-cycle perturbation with the amplitude of the PETM, we investigate both the equilibrium and transient climate response to changes in insolation. Specifically, our experimental set-up is to identify how rapid climate change events may unfold differently under high eccentricity (PETM) and low eccentricity (modern) regimes. We present results from equilibrium climate state simulations and transient climate responses to PETM emission scenarios, using the cGENIE Earth system model under a comprehensive set of eccentricity/precession configurations. Based on the outcomes of these simulations, we describe the differences in PETM expression in terms of climate and weathering regimes, depending on the astronomical configuration.

How to cite: Papadomanolaki, N. M. and De Vleeschouwer, D.: The sensitivity of the PETM carbon cycle perturbation to orbital configurations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8156, https://doi.org/10.5194/egusphere-egu24-8156, 2024.

Our climate is changing due to anthropogenic influences, and we are heading into climate conditions that are largely unknown to modern humans. Considering the great threat that anthropogenic climate change is, there is a need to accurately project how our climate will respond to warmer conditions in the future. Reconstructions of the Earth’s past show that many climatic features that we observe today have – to some extent – been present in the geological archive. So, we can study paleoclimate to advance our understanding of dynamics and processes in warm climates, as well as to explore responses and sensitivities of the Earth’s climate to forcing changes. Given the similarities between the past and the projected future, researchers have been trying to establish analogy between paleoclimate and future climate. This could include analogy in terms of elevated or rising CO₂ concentrations, elevated surface temperatures, and specific processes such as ice sheet melt or an AMOC weakening. However, often paleoclimate – future climate analogies are difficult to interpret, since conditions for analogy are not properly defined, or implications of the analogy are unclear or overstated.

In this work, we propose a practical methodological framework to assess paleoclimate analogy, for general use in the climate research community. The framework consists of five main steps: (1) stating the purpose (e.g. which processes are considered) and relevance of the analogy, (2) assessing feasibility of finding an analogy, (3) a detailed description of the followed methodology, (4) assessment of confidence in the analogue, and (5) clear communication regarding the potential as well as limitations of the analogy. As part of the framework, we identify three main types of analogy: (a) analogy in terms of forcing (e.g. CO₂ concentration), (b) in terms of response (e.g. surface temperatures) and (c) in terms of processes (e.g. tipping behavior). We will briefly treat example applications of the framework to highlight its potential, for different types of analogues on different time scales.

How to cite: Oldeman, A., Burton, L., Tindall, J., Dolan, A., Hill, D., Haywood, A., Baatsen, M., von der Heydt, A., and Dijkstra, H.: A framework for assessing paleoclimate analogy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16204, https://doi.org/10.5194/egusphere-egu24-16204, 2024.

The Cretaceous period (145-66 Ma) experienced dramatic changes in climate, biogeochemistry, and biotic innovation. Climate varied between a super greenhouse and coolhouse world (O'Brien et al., 2017), multiple ocean anoxic events (OAEs) drove major changes in ocean chemistry and biodiversity (Jenkyns, 2010), and angiosperms became the most dominant land plant group on Earth (Lidgard and Crane, 1988, Condamine et al., 2020). However, we are unable to assess the role of pCO₂ in driving these climatic, biogeochemical, and biotic changes because there is no continuous, marine based, pCO₂ record for this period, mainly due to the lack of established marine-based proxies able to span this time interval.

To address this issue, we measured the carbon isotopic composition of the general phytoplankton biomarker, phytane, in ~50 sediment samples from Deep Sea Drilling Project Site 398 that span the early and middle Cretaceous (Hauterivian to Cenomanian). Additionally, we reconstruct sea surface temperature (SST) using the TEX₈₆ paleothermometer in the same sediments, providing a long continuous temperature record from a single site and thus bridging multiple important ‘gaps’ in the current record (O'Brien et al., 2017). Together, our findings provide the first continuous marine pCO₂ and temperature record of the early to mid-Cretaceous, spanning the Hauterivian to Cenomanian.

Our results indicate SSTs around 30-35 °C for most of the Hauterivian to Albian. There is a transient warming during OAE 1a (~120 Myr) followed by a more gradual warming into the Cenomanian. During the Cenomanian SSTs reach maxima of ~40 °C at this mid-latitude site, consistent with other SST records from this period that indicate extreme warmth. pCO₂ values during the Hauterivian to Albian vary between 1000 and 2000 ppmv, consistent with the elevated SSTs at this time. However, unexpectedly, we do not observe a rise in pCO₂ during the Cenomanian when SSTs reach their maxima. These results suggest that pCO₂ was not the main driver of the Cenomanian super hothouse.

References:

CONDAMINE, F. L., SILVESTRO, D., KOPPELHUS, E. B. & ANTONELLI, A. 2020. The rise of angiosperms pushed conifers to decline during global cooling. Proceedings of the National Academy of Sciences, 117, 28867-28875.

JENKYNS, H. C. 2010. Geochemistry of oceanic anoxic events. Geochemistry, Geophysics, Geosystems, 11.

LIDGARD, S. & CRANE, P. R. 1988. Quantitative analyses of the early angiosperm radiation. Nature, 331, 344-346.

O'BRIEN, C. L., ROBINSON, S. A., PANCOST, R. D., SINNINGHE DAMSTÉ, J. S., SCHOUTEN, S., LUNT, D. J., ALSENZ, H., BORNEMANN, A., BOTTINI, C., BRASSELL, S. C., FARNSWORTH, A., FORSTER, A., HUBER, B. T., INGLIS, G. N., JENKYNS, H. C., LINNERT, C., LITTLER, K., MARKWICK, P., MCANENA, A., MUTTERLOSE, J., NAAFS, B. D. A., PÜTTMANN, W., SLUIJS, A., VAN HELMOND, N. A. G. M., VELLEKOOP, J., WAGNER, T. & WROBEL, N. E. 2017. Cretaceous sea-surface temperature evolution: Constraints from TEX₈₆ and planktonic foraminiferal oxygen isotopes. Earth-Science Reviews, 172, 224-247.

How to cite: Graham, O. A., Witkowski, C. R., and Naafs, B. D. A.: Reconstructing Early to Mid-Cretaceous Climate Dynamics: A Continuous Marine pCO2 Record , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17733, https://doi.org/10.5194/egusphere-egu24-17733, 2024.

Reconstructions of global mean surface temperature (GMST) are one of the key contributions that palaeoclimate science can make to societally-relevant questions, for example, by providing the information required to derive equilibrium climate sensitivity from the geologic record and as a means of testing climate model performance under warmer-than-present conditions. One relatively simple method of doing so is to parameterize GMST as a function of the temperature of the deep ocean, which has the advantage that deep ocean temperature is relatively well constrained for much of the Cenozoic. A commonly-used transformation approach is based on a 1:1 deep ocean-GMST scaling factor prior to the Pliocene, which is a simple assumption, but to our knowledge, without a firm mechanistic basis. Here, we test the reliability of this assumption using output from a suite of climate model simulations, including those from the DeepMIP project, as well as curated data compilations for well-studied intervals throughout the Cenozoic. Our analysis demonstrates that a simple 1:1 scaling factor is likely to be a good approximation for much of the Cenozoic, possibly mechanistically rooted in an increasing winter bias in deep water formation offsetting an increase in polar amplification/stratification during intervals of global warmth. Building on this, we reevaluate the Cenozoic records of deep ocean temperature and derive a new, continuous record of GMST. Our record is substantially warmer than the most common previous approach for much of the Cenozoic, from which we derive GMST during the early Eocene Climatic Optimum of 31.3±1.3°C, supporting the notion of a greater-than-modern ECS in this past warm climate state.

How to cite: Evans, D., Brugger, J., Inglis, G., and Valdes, P.: The temperature of the deep ocean is a robust proxy for global mean surface temperature during the Cenozoic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19919, https://doi.org/10.5194/egusphere-egu24-19919, 2024.