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Understanding the extreme greenhouse of the Eocene (56–34Ma ago) is key to anticipate potential future conditions. During the Eocene, the Antarctic continent remained mostly ice-free despite large temperature swings. Seemingly contradictory indications of ice and thriving vegetation complicate modelling efforts to explain the Antarctic Eocene climate. We use global climate model simulations to show that extreme seasonality mostly limited ice growth. Without ice sheets, much of the Antarctic continent saw monsoonal conditions. Perennially mild and wet conditions along Antarctic coastlines support vegetation reconstructions, while extreme seasonality elsewhere promoted intense weathering shown in proxy records. The results can thus explain the coexistence of warm and wet conditions in some regions, while small ice caps could form near the coast. The resilience of the climate regimes seen in these simulations agrees with the longevity of warm Antarctic conditions during the Eocene, but also challenge our view on glacial inception.

The early Eocene (~56-49 Ma) is punctuated by several transient global warming events, known as hyperthermals, superimposed on very high mean global temperatures and elevated atmospheric CO2 levels. Hyperthermal events, such as the well-documented Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma), are characterized by negative carbon isotope excursions. These are interpreted as perturbations in the global exogenic carbon pool and deep ocean carbonate dissolution - signifying massive carbon injection into the ocean-atmosphere system. High resolution analysis of sedimentary archives has evidenced that hyperthermals initiated during maxima in orbital eccentricity, suggesting a climatic trigger for carbon input. Cyclostratigraphy, therefore, provides a unique tool to complement proxy records in the characterization of hyperthermal. Indeed, the identification of an orbital signature in marine and continental sedimentary succession provides an ideal trait-d’union between stratigraphic observation and paleoceanographic/paleoclimatic interpretation.Here we present a cyclostratigraphic study of early Eocene marls and chalks from core RH-323, collected from the northern Negev Desert in Israel. The PETM in this region is well described but other hyperthermals are essentially unexplored. The unique location of this sedimentary succession, accumulated on a continental slope of the South Tethys at ~ 500–700 m paleo-depth, provides new insights into the relationship between global oceanic perturbation and local variability in a relatively arid region. Eccentricity-dependent variation in magnetic susceptibility and bulk stable oxygen and carbon isotope data from this locality allowed us to develop an astronomically tuned age model, which contributes to the identification of important hyperthermals, including the PETM, ETM2 and ETM3. The patterns also allow for cycle and event-based correlation to and comparison with oceanic records such as Ocean Drilling Program (ODP) Sites 1262 (Atlantic Ocean) and 1209 (Pacific Ocean) and with outcropping sections of the Tethys such as those of Contessa Road and Bottaccione (Gubbio, Italy). Emerging from these comparisons are remarkable patterns in the occurrence of cherts, with potential relevance for the global silicon cycle.

The Miocene Climatic Optimum (MCO, ~17-15 Ma) was a relatively warm interval that interrupted the Cenozoic cooling trend and bears analogies with projected end-of-the-century climate. Proxy data and model simulations indicate temperatures were on average ~7 – 8°C higher than present day and atmospheric pCO2 values were 500-600 ppmV. At high latitudes, upper ocean temperatures were ~10 – 15°C warmer than present day, but available tropical temperature records are limited. Importantly, to be able to use Miocene paleoclimate records to quantify key climate parameters like the polar amplification of climate change, accurate reconstructions of tropical surface oceans are required.We present high resolution Early to Middle Miocene (~15 – 18 Ma) records of tropical sea surface temperature (SST) variability based on the lipid biomarker paleothermometer TEX86 at Ocean Drilling Program (ODP) Site 959 in the eastern equatorial Atlantic Ocean and at ODP Site 1007 at Bahama Bank in the western tropical Atlantic Ocean. The age model for both sites is based on chemo- and biostratigraphy. Moreover, analyses of bulk carbonate oxygen- (δ18O) and stable carbon (δ13C) isotope ratios at ~2 – 4 kyr resolution at Site 959 facilitated orbital tuning to eccentricity, obliquity and precession. Bulk elemental composition records, total organic carbon concentrations and dinoflagellate cyst assemblages were also generated to assess paleoenvironmental change.At both sites, warming associated with the onset of the MCO (~17 Ma) was identified as an average SST increase of ~2°C (using the TEX86-H calibration). At ~16.8 Ma, bulk carbonate δ13C gradually increased by ~1‰ at both sites, indicating the onset of the Monterey carbon isotope excursion. Combined with available temperature information from the high latitudes and deep ocean, we assess meridional temperature gradients across the MCO.At ODP Site 959, sediments are characterized by alternations of biogenic silica, carbonates, and terrigenous material (i.e., clays). Following the onset of the MCO (~17 – 16.5 Ma), high variability in the oceanographical setting is reflected in striking Babio peaks, indicating productivity changes. These peaks coincide with lowest SSTs (~28°C) and increased dust supply (increased Fe and Ti) on precession and obliquity timescales. In the same interval, (inner-) neritic dinoflagellate species indicate increased water column stratification. Heterotrophic dinocyst groups vary on timescales coherent with the other geochemical records, relative to comparably stable background abundances of oceanic genera throughout the MCO. Combined, this suggests that a highly dynamic monsoon-driven upwelling regime was present at Site 959 during the MCO. Combined, these patterns imply a highly dynamic African monsoon-driven upwelling regime that intensified at the onset of the MCO.

Fossil ikaite, preserved as the pseudomorph glendonite, occurs in vast amounts in Jurassic and Cretaceous successions in the high Arctic. Thermodynamics predict that ikaite is only stable at near-freezing temperatures and glendonite is thus widely used as a paleo-indicator of cold climate conditions, conflicting with traditional views of a very warm and equable Mesozoic greenhouse. Here, we show based on a multi-proxy investigation of Jurassic and Cretaceous glendonites from Siberia and Svalbard that this one-dimensional view detracts from their exceedingly complex biogeochemistry. NanoSIMS analyses of a Jurassic glendonite from Siberia produced large C-isotope gradients (> 40‰) over micrometer distances hinting at strong kinetic fractionation that is coupled to the formation of various precipitates, including an inclusion-rich primordial phase with C-isotope values as low as -38‰ that records methane oxidation. In line with previous results from Siberia, all investigated glendonites from the Cretaceous of Svalbard contain methane gas (700 - 2500 ppb/g) with enriched δ13C-CH4 signatures (-44 to -50‰ V-PDB), depleted δ2H--CH4 (-285 to -245‰ V-SMOW), and relatively large proportions of C2-C5 gas. Such values are potentially indicative of thermogenic methane gas sourced from structure II gas hydrates. Organic geochemistry of glendonites from Svalbard shows the presence of abundant hopanes, including bisnorhopanes with a CSIA signature of -41‰, suggesting activity of sulfide oxidizing bacteria possibly also linked to the inclusion of oil droplets. Moreover, exceptionally heavy bulk δ34Scas values of +46.2‰ clearly link marine ikaite formation in deep time to sulfate-driven anaerobic methane oxidation. Marine ikaite formation and preservation is thus a highly complex process, driven by temperature and (bio)chemical processes in the sea floor, complicating its use as a simple paleoclimate proxy. Regardless, glendonite episodically trapped large amounts of greenhouse gases and stored those for hundreds of millions of years, making this authigenic mineral a potential recorder of past carbon cycle perturbations.

The Oligocene (33.9 – 23.03 Ma ago) and early Miocene (23.03 – 19 Ma) experienced large climate and ice sheet fluctuations in a most likely unipolar icehouse, with glaciation limited to the Southern Hemisphere. This time interval provides a useful test case for studying polar amplification patterns under atmospheric greenhouse gas concentrations similar to those projected for the future. Large-amplitude climate variability has been recorded close to Antarctica during this time interval, but climatic and environmental conditions and variability in the tropical band are poorly knownpaleoceanographic conditions and sea (sub)surface temperatures (SSTs) will deliver an insight into the climate variability and sensitivity of the lower latitudes under unipolar conditions.Reconstructed surface oceanographic conditions and variations in the depositional environment are based on bulk carbonate stable isotope ratios (δ18O, δ13C), weight% carbonate, magnetic susceptibility and dinoflagellate cyst assemblages at Ocean Drilling Program Site 959, offshore Ghana.. In addition, long term SSTs reconstructions for the Oligocene and early Miocene equatorial Atlantic are derived from lipid biomarker-based paleothermometry (TEX86). Lastly, long term (~31 Ma – 19Ma) atmospheric CO2 concentrations based on stable carbon isotopic fractionation of marine organic carbon and alkenones were generated.The organic carbon isotopic fractionation showshat pCO2 ranged from 280 – 570ppm between ~19 – 33 Ma and shows no signs of large variability, which is consistent with previous findings. The TEX86 indicates that the average SSTs during the Oligocene was ~27℃ which is ~1 – 4℃ colder than in the west Equatorial Atlantic (e.g., ODP Site 929, Ceara Rise), using the same transfer function. Dinoflagellate cyst assemblages indicate upwelling alternated with strong stratification events on ~50 to 100 kyr timescale. Monsoonal upwelling could explain the lower SSTs at Site 959 which is consistent with modern east-west gradients. Subsequent comparison of our equatorial SST record with general circulation modelling studies and SST records from high latitudes should reveal the polar amplification of warming and climate sensitivity on long and short (orbital) timescales during the Oligocene.

Sediment cores from the Mid-Norwegian Margin, IODP Expedition 396 recovered several glendonite (calcite) pseudomorphs after cold-water ikaite, CaCO3•6H2O, within sediments deposited during the Paleocene-Eocene Thermal Maximum hyperthermal and the early Eocene greenhouse. This presents an apparent climate paradox, since during this time interval, deep sea bottom water temperatures are not believed to have been lower than c. 10 °C anywhere on Earth, mostly much warmer (Meckler et al., 2022 and references therein), far above temperatures typical for natural ikaite formation (Vickers et al., 2022 and references therein). The glendonites are found in close association with ash horizons from the nearby North Atlantic large igneous province (NAIP), with some actually in the infill of a hydrothermal. This, coupled with the presence of glendonites in sediments of the same age from Svalbard and Denmark (Spielhagen and Tripati, 2009; Vickers et al., 2020), may point to volcanically-driven climate and environmental changes in this region, perhaps on temporal and spatial scales hitherto unresolved by global-scale datasets. Here, we present reconstructed ikaite crystallisation temperatures from clumped isotope palaeothermometry and biomarker sea surface and air temperature reconstructions from glendonite-bearing horizons in ash-rich sediments at four IODP Expedition 396 sites. We find that the glendonites indicate bottom water temperatures considerably lower than the majority of other localities so far studied for this time interval (0 – 10 °C). The biomarker signals are harder to interpret, but may indicate sea surface and air temperatures significantly lower than many other studies across this time interval. We discuss possible causes and mechanisms for this cooling, and the conditions driving ikaite growth, focussing on whether these both may be linked to NAIP volcanism.

Rapid climatic and carbon cycle upheavals in the early Eocene have been of strong interest for the past decades. Multiple of these events represent global warming events (i.e. hyperthermals), including the Paleocene Eocene Thermal Maximum (PETM; 56 Ma), but global data coverage is still too limited to fully resolve the spatial patterns of climate, ecosystems and hydrology for the other hyperthermals. This is particularly due to the lack of continuous continental margin sequences suitable for high-resolution paleoclimate reconstructions.We present high-resolution, multi-proxy records of climatic and environmental changes across multiple hyperthermals from Core RH-323, Northern Negev Desert, Israel. Lower Eocene sediments, dominantly orbitally paced alternations of marls and chalk, were deposited in the Tethys Ocean at a latitude of ~15º N, on the northward dipping slope of the presumably dry northern bound of the African continent. They provide a unique opportunity to capture tropical climate variability and continental-hydrological response to hyperthermals. We reconstruct regional variability of (sub)surface temperature, plankton ecology and continental hydrology by TEX86 paleothermometry, bulk carbonate isotope ratios, magnetic susceptibility, bulk-XRF and dinoflagellate cyst (dinocyst) assemblages.We identify various hyperthermal events, including the PETM, ETM2 and ETM3, based on combined chemo- and biostratigraphy. During the PETM, TEX86-based temperatures indicate a warming of 3­–4 ºC, coinciding with a high abundance of representatives of the classic warm water dinocyst genus Apectodinium. The PETM is marked by a thin marl-rich interval at the onset, followed by a carbonate-rich interval during the body, suggesting very different hydrological forcing of siliciclastic input than recorded at mid-latitude sites. We interpret this to reflect strong seasonality (possibly monsoon like) with periods of intense precipitation followed by prolonged drought. Interestingly, subsequent smaller hyperthermals seem to predominantly coincide with increased siliciclastic content, thus representing episodes of increased (seasonal) precipitation.

High latitude warmth during the Eocene greenhouse climate has posed many challenges for climate modelling studies. Recent improvements in both the proxy records and model simulations are bringing these closer together, particularly regarding the meridional temperature gradient. Yet, it remains difficult to understand the climatic conditions around the greenhouse-icehouse transition which involved the glaciation of Antarctica. How can we explain indications of ice near the Antarctic coast well before the transition, especially since Antarctic glaciation is thought to express strong hysteresis? How did Antarctica remain mostly ice-free and vegetated through large climatic swings during the Eocene? If Antarctic warmth was so resilient, which process was responsible for its eventual demise?We consider a set of existing climate simulations for the middle-to-late Eocene (42-34Ma) using the CESM model (Baatsen et al. 2020)1. The original set of simulations was expanded to include possible scenarios of orbital forcing, atmospheric composition, and the continental geometry. In addition, we look at the output from DeepMIP simulations for the early Eocene. Using these results, we make a detailed study of the Antarctic climate and find that most of the continent saw monsoonal conditions during the Eocene. Only a small corridor near the coast experienced perennially mild and wet conditions, explaining the presence of temperate to paratropical vegetation. Further inland, we see a rapid increase in temperature seasonality along with the appearance of a summer monsoon. Summertime warmth made most of the Antarctic continent a hostile place for any significant ice growth. Meanwhile, mountainous regions near the coast were suitable candidates for the formation of ice caps that may have grown substantially during cooler intervals.Our simulations can explain seemingly contradictory indications from proxy records, as well as strong regional variations in the Antarctic climate. The monsoonal nature of this climate during the Eocene proves to be particularly resilient to the changes in external forcing considered here. Identifying the potential mechanism to break up the monsoonal regime and eventually lead to Antarctic glaciation remains the subject of ongoing work.1. Baatsen, M., von der Heydt, A. S., Huber, M., Kliphuis, M. A., Bijl, P. K., Sluijs, A., & Dijkstra, H. A. (2020). The middle to late Eocene greenhouse climate modelled using the CESM 1.0.5. Climate of the Past, 16(6), 2573–2597. doi: 10.5194/cp-16-2573-2020.

Superimposed on long-term late Paleocene–early Eocene warming (~59 to 52 million years ago), Earth’s climate experienced a series of abrupt perturbations, characterized by massive carbon input into the ocean-atmosphere system and global warming. Here, we examine the three most punctuated events of this period, the Paleocene-Eocene Thermal Maximum and Eocene Thermal Maximum 2 and 3, to probe whether they were initiated by climate-driven carbon cycle tipping points. Specifically, we analyze the dynamics of climate and carbon cycle indicators acquired from marine sediments to detect changes in Earth system resilience and to identify positive feedbacks. Our analyses suggest a loss of Earth system resilience toward all three events. Moreover, dynamic convergent cross mapping reveals intensifying coupling between the carbon cycle and climate during the long-term warming trend, supporting increasingly dominant climate forcing of carbon cycle dynamics during the Early Eocene Climatic Optimum when these recurrent global warming events became more frequent.

The Central Atlantic Magmatic Province (CAMP) eruptions are generally regarded as the main driver of major environmental change and mass-extinction across the Triassic-Jurassic (T-J) boundary (~201.3 Ma). CAMP emissions have been invoked as the main trigger for the formation of abnormal pollen and spores during the end-Triassic crisis that may have led to forest dieback and proliferation of pioneer species. Proposed scenarios include extensive climate change leading to wildfire activity, acid rain, and increased UV-B radiation due to ozone depletion. More recently, volcanogenic mercury (Hg) has been implicated in the occurrence of mutations in fern spores. However, Hg-dynamics in deep-time remain poorly understood and require further examination. Here, we explore a new long-term (Rhaetian to Sinemurian) bulk Hg-concentration record combined with Hg-isotope data to understand the link between floral turnovers and the Hg-cycle.Shallow marine sediments sampled from the Schandelah-1 core in northern Germany contain a record of cyclical shifts in malformed fern spores coinciding with fluctuations in carbon isotopes, increased levels of weathering, and Hg-enrichments. Similarly, increased mutagenic spore abundances with accompanying Hg-isotope records confirm the volcanogenic origin of Hg at the T-J boundary, showing a sharp positive excursion in mass-independent fractionation (MIF) of odd-numbered Hg-isotopes. Hettangian cyclicity is clearly reflected in the Hg-isotopic signals, showing positive excursions in mass-dependent/independent fractionation records (d202Hg and D199Hg) during periods of sedimentary Hg-enrichment. In addition, the Hettangian Hg-isotopic signature clearly deviates from Rhaetian signatures, which hints at climate-controlled mechanisms being responsible. Atmospheric Hg-loading via volcanism can explain the synchronous enrichments of Hg concentrations at the T-J boundary interval in multiple sites across the globe. In contrast, the origin of this periodic Hg-loading is more difficult to pinpoint, but it becomes clear that Hg is showing shifts in speciation and closely tied to terrestrial vegetation development. Orbitally induced changes to the regional hydrological regime, resulting in increased wildfire activity, monsoonal intensity, and soil erosion, potentially redistributed Hg stored in soil and/or bedrock reservoirs causing a shift to more mobile Hg-species. Overall, this shows a more dominant role of climate-induced Hg-remobilisation, rather than direct volcanic emissions, to disturbance in terrestrial vegetation.

Sedimentary bulk organic matter and various molecular organic components exhibit strong CO2-dependent carbon isotope fractionation relative to dissolved inorganic carbon sources. This fractionation (εp) has been employed as proxy for paleo-pCO2. Yet, culture experiments indicate this CO2-dependent εp is highly specific at genus and even species level, potentially hampering the use of bulk organic matter and non-species specific organic compounds. In recent years, significant progress has been made towards a CO2 proxy using controlled growth experiments with dinoflagellate species, also showing highly species-specific εp values. These values were, however, based on motile specimens and it remains unknown whether these relations also hold for the organic-walled resting cysts (dinocysts) produced by these dinoflagellate species in their natural environment. We here analyze dinocysts isolated from core-tops from the Atlantic Ocean and Mediterranean Sea, representing several species (Spiniferites elongatus, S. (cf.) ramosus, S. mirabilis, Operculodinium centrocarpum sensu Wall & Dale (1966) (hereafter referred to as O. centrocarpum) and Impagidinium aculeatum) using Laser ablation – nano Combustion – Gas Chromatography – Isotope Ratio Mass Spectrometry (LA/nC/GC-IRMS). We find that the dinocysts produced in the natural environment are all significantly more 13C-depleted compared to the cultured motile dinoflagellate cells, implying higher overall εp values and, moreover, exhibit large isotope variability. Where several species could be analysed from a single location, we often record significant differences in isotopic variance and offsets in mean δ13C values between species, highlighting the importance of single-species carbon isotope analyses. The most geographically expanded dataset, based on O. centrocarpum, shows that εp correlates significantly with various environmental parameters. Importantly, O. centrocarpum shows a CO2-dependent εp above ~240 μatm pCO2. Similar to other marine autotrophs, relative insensitivity at low pCO2 is in line with a carbon concentrating mechanism being active at low pCO2, although we here cannot fully exclude that we partly underestimated εp sensitivity at low pCO2 values due to the relatively sparse sampling in that range. Finally, we use the relation between εp and pCO2 in O. centrocarpum to propose a first pCO2 proxy based on a single dinocyst species.

The Paleocene-Eocene Thermal Maximum (PETM; 56 Ma) and Eocene Thermal Maximum 2 and 3 (ETM2; 54.06 Ma and ETM3; 52.87 Ma) were three of a series of abrupt climate and carbon cycle perturbations, characterized by massive carbon input into the ocean-atmosphere system and strong global warming. These abrupt events, termed hyperthermals, potentially represent ‘tipping points’ at moments in time when the resilience of the system was low and reinforced by strong internal feedbacks, such as the catastrophic release of carbon from submarine methane hydrates. Alternatively, external mechanisms such as volcanism may have played a pronounced external role during the PETM. Here, we evaluate if the hyperthermals indeed resulted from reduced Earth System resilience and tipping point behaviour through the mathematical analyses of climate and carbon cycle indicators, namely, oxygen and stable carbon isotope ratios of deep ocean foraminifer calcite, across the late Paleocene and early Eocene. Our combined analysis using Dynamic Indicators of Resilience (DIORs) and Convergent Cross Mapping (CCM) reveals a loss of resilience and an increase in the causal interaction between the carbon cycle and climate towards the PETM, ETM2, and ETM3. A novel, windowed CCM approach indicates a tight coupling between carbon and climate across the early Eocene, further supporting dominant climate forcing on carbon cycle dynamics. This indicates that the internal rather than external mechanisms were responsible for the hyperthermals, suggesting a secondary role for endogenic processes such as volcanism. Furthermore, the CCM analysis in conjunction with the absence of major positive feedbacks such as the presence of polar ice caps during early Eocene could be employed to stipulate that these hyperthermal events may be caused by the increase in coupling between the carbon cycle and climate systems, eventually pushing both systems towards a tipping point through increasing positive feedbacks.

Oceanic Anoxic Event 2 (ca. 94 Ma; OAE2) was one of the largest Mesozoic carbon cycle perturbations, but associated carbon emissions, primarily from the Caribbean large igneous province (LIP) and marine burial fluxes, are poorly constrained. Here, we use the carbon cycle box model LOSCAR-P to quantify the role of LIP volcanism and enhanced marine organic carbon (Corg) burial as constrained by the magnitude and shape of the positive stable carbon isotope (δ13C) excursion (CIE) in the exogenic carbon pool and atmospheric pCO2 reconstructions. In our best fit scenario, two pulses of volcanic carbon input—0.065 Pg C yr–1 over 170 k.y. and 0.075 Pg C yr–1 over 40 k.y., separated by an 80 k.y. interval with an input of 0.02 Pg C yr–1—are required to simulate observed changes in δ13C and pCO2. Reduced LIP activity and Corg burial lead to pronounced pCO2 reductions at the termination of both volcanic pulses, consistent with widespread evidence for cooling and a temporal negative trend in the global exogenic δ13C record. Finally, we show that observed leads and lags between such features in the records and simulations are explained by differences in the response time of components of the carbon cycle to volcanic forcing.

Model simulations of past climates are increasingly found to compare well with proxy data at a global scale, but regional discrepancies remain. A persistent issue in modeling past greenhouse climat...

TEX86 is a paleothermometer based on Thaumarcheotal glycerol dialkyl glycerol tetraether (GDGT) lipids and is one of the most frequently used proxies for sea-surface temperature (SST) in warmer-than-present climates. However, the calibration of TEX86 to SST is controversial because its correlation to SST is not significantly stronger than that to depth-integrated surface to subsurface temperatures. Because GDGTs are not exclusively produced in and exported from the surface ocean, sedimentary GDGTs may contain a depth-integrated signal that is sensitive to local subsurface temperature variability, which can only be proved in downcore studies. Here, we present a 15 Myr TEX86 record from ODP Site 959 in the Gulf of Guinea and use additional proxies to elucidate the source of the recorded TEX86 variability. Relatively high GDGT[2/3] ratio values from 13.6 Ma indicate that sedimentary GDGTs were partly sourced from deeper (> 200 m) waters. Moreover, late Pliocene TEX86 variability is highly sensitive to glacial-interglacial cyclicity, as is also recorded by benthic δ18O, while the variability within dinoflagellate assemblages and surface/thermocline temperature records (Uk’37 and Mg/Ca), is not primarily explained by glacial-interglacial cyclicity. Combined, these observations are best explained by TEX86 sensitivity to sub-thermocline temperature variability. We conclude that the TEX86 record represents a depth-integrated signal that incorporates a SST and a deeper component, which is compatible the present-day depth distribution of Thaumarchaeota and with the GDGT[2/3] distribution in core tops. The depth-integrated TEX86 record can potentially be used to infer SST variability, because subsurface temperature variability is generally tightly linked to SST variability. Using a subsurface calibration with peak calibration weight between 100–350 m, we estimate that east equatorial Atlantic SST cooled by ~4.5 °C between the Late Miocene and Pleistocene. On shorter timescales, we use the TEX86 record as an Antarctic Intermediate Water (AAIW) proxy and evaluate climatological leads and lags around the Pliocene M2 glacial (~3.3 Ma). Our record, combined with published information, suggests that the M2 glacial was marked by AAIW cooling during an austral summer insolation minimum, and that decreasing CO2 levels were a feedback, not the initiator, of glacial expansion.

Sea surface temperature (SST) reconstructions based on isoprenoid glycerol dialkyl glycerol tetraether (isoGDGT) distributions from the Eocene southwest (sw) Pacific Ocean are unequivocally warmer than can be reconciled with state-of-the-art fully coupled climate models. However, the SST signal preserved in sedimentary archives can be affected by contributions of additional isoGDGT sources. Methods now exist to identify and possibly correct for overprinting effects on the isoGDGT distribution in marine sediments. We here use the current proxy insights to assess the reliability of the isoGDGT-based SST signal in 69 newly analysed and 242 re-analysed sediments ODP Site 1172 (East Tasman Plateau, Australia) following state-of-the-art chromatographic techniques, in context of paleo-environmental and paleoclimatologic reconstructions based on dinoflagellate cysts. The resulting ~130 kyr-resolution Maastrichtian-Oligocene TEX86-based SST record confirms previous conclusions of anomalous warmth in the early Eocene sw Pacific and remarkably cool conditions during the mid-Paleocene. Dinocyst diversity and assemblages show a strong response to the local SST evolution, supporting the robustness of the TEX86 record. Soil-derived branched GDGTs stored in the same sediments are used to reconstruct mean annual air temperature (MAAT) of the nearby land using the MBT'5me proxy. MAAT is consistently lower than SST during the early Eocene, independent of the calibration chosen. General trends in SST and MAAT are similar, except for: 1) an enigmatic absence of MAAT rise during the Paleocene-Eocene Thermal Maximum and Middle Eocene Climatic Optimum, and 2) a subdued middle–late Eocene MAAT cooling relative to SST. Both dinocysts and GDGT signals suggest a mid-shelf depositional environment with strong river-runoff during the Paleocene-early Eocene, progressively becoming more marine thereafter. This trend reflects gradual drying and more pronounced wet/dry seasons in the northward drifting Australian hinterland, which may also explain the subdued middle Eocene MAAT cooling relative to that of SST. The overall correlation between dinocyst assemblages, marine biodiversity and SST changes suggests that temperature exerted a strong influence on the surface-water ecosystem, probably in part through sea level changes caused by steric effects. Finally, we find support for a potential temperature control on compositional changes of branched glycerol monoalkyl glycerol tetraethers (brGMGTs) in marine sediments. It is encouraging that a critical evaluation of the GDGT signals confirms the vast majority of the generated data is reliable. However, this also implies the high TEX86-based SSTs for the Eocene sw Pacific, and the systematic offset between absolute TEX86-based SST and MBT'5me-based MAAT estimates remain unexplained.

Ocean currents can transport sinking particles hundreds of kilometers from their origin at the ocean surface to their burial location, resulting in an offset between sea surface temperatures (SSTs) above the burial site and the particle’s origin. Quantifying this offset in particles carrying molecules used in SST proxies can reduce uncertainty in paleoclimate reconstructions. In the Mediterranean Sea, where δ18Oforaminifera, UK’37- and TEX86-based SSTs can exhibit large offsets from surface conditions, understanding the possible contribution of lateral transport to proxy bias can provide additional insight when interpreting paleoclimate records.In this study, Lagrangian particle tracking experiments are performed using the NEMO flow field to simulate transport and allow for a quantitative estimate of transport bias. The model determines the ocean surface origin locations of foraminifera and sedimentary particles that carry alkenones or GDGTs to compare with surface sediment datasets for δ18Oforaminifera, UK’37 and TEX86, respectively. A range of sinking speeds appropriate for the export of organic matter (6, 12, 25, 50, 100, 250, and 500 m/d) is used in the model to represent different export modes (i.e., individual coccoliths, coccospheres, aggregates), where the three fastest sinking speeds can also represent sinking foraminifera. Results show that lateral transport bias is generally small within the Mediterranean Sea and cannot explain the large offsets in proxy-based SST reconstructions in this basin.

The Paleocene-Eocene Thermal Maximum (PETM) is recognized as one of the potential analogues in the geological record for present-day global warming. The aim of the International Continental Scientific Drilling Program (ICDP) project PVOLC is to test the hypothesis that voluminous magmatism in sedimentary basins in the NE Atlantic triggered the PETM. Two ICDP boreholes are planned to core the boundary in the Limfjorden area in Denmark in 2022. PVOLC will be conducted in conjunction with IODP Exp 396 on the mid-Norwegian continental margin. The North Atlantic Igneous Province (NAIP) was is a large igneous province (5–10 million km3 magma) that coincided with both the opening of the NE Atlantic Ocean and the greenhouse conditions of the early Paleogene. The close temporal correlations suggest a possible causal relationship between the NAIP and both the climatic and tectonic changes around 56– 54 Ma. In particular, the main acme of NAIP activity occurred across the Paleocene–Eocene Thermal Maximum (PETM), an extreme hyperthermal event that represents the warmest conditions of the last 60 million years. The NAIP is among several proposed candidates for driving global warming through CO2/CH4 emissions, both by magmatic degassing and through contact metamorphism around shallow intrusions in organic rich sedimentary basins. What is needed to refine the role of the NAIP during the PETM are key sedimentary sequences that contain abundant volcanic and climatic proxies in the same section, thereby allowing a precise geochronology of events to be attained. The sediments exposed on the Fur island, Denmark, are a key sequence of PETM and post-PETM strata with little thermal overprint and hundreds of well-preserved volcanic ash layers from the NAIP. The effects of Quaternary glaciotectonism have disturbed this key stratigraphic interval at Fur, but seismic surveys indicate that undisturbed strata are found a few km to the south. The ICDP PVOLC project plan is to drill both the Paleocene-Eocene and the Cretaceous-Paleocene boundaries, hopefully recovering pristine cores suitable for high-resolution geochemical and climatic studies.

Sea surface temperature (SST) reconstructions based on isoprenoid glycerol dialkyl glycerol tetraether (isoGDGT) distributions from the Eocene southwest (sw) Pacific Ocean are unequivocally warmer than can be reconciled with state-of-the-art fully coupled climate models. However, the SST signal preserved in sedimentary archives can be obscured by contributions of additional isoGDGT sources. We here use current proxy insights to assess the reliability of the isoGDGT-based SST signal in 69 newly analysed and 242 re-analysed samples covering the Maastrichtian to Oligocene from ODP Site 1172 (East Tasman Plateau, Australia) following state-of-the-art chromatographic techniques. We then reinterpret the record in context of paleo-environmental and paleoclimatologic reconstructions based on dinoflagellate cysts. Our ~130 kyr-resolution SST record reaffirms previous reconstructions of anomalous warmth in the early Eocene sw Pacific and remarkably cool conditions during the mid-Paleocene. Dinocyst diversity and temperature-sensitive taxa show a strong response to the local SST evolution, supporting the robustness of the marine biomarker record. In addition, the long-term isoGDGT and dinocyst records provide further support for an apparent temperature control on compositional changes of branched glycerol monoalkyl glycerol tetraethers (brGMGTs), recorded in the same samples.Soil-derived branched GDGTs (brGDGTs) stored in the same sediments are used to reconstruct mean annual air temperature (MAAT) of the nearby land through the MBT’5me proxy. General trends in SST and MAAT are similar, except for 1) an enigmatic absence of MAAT rise during the Paleocene-Eocene Thermal Maximum and Middle Eocene Climatic Optimum, and 2) a subdued middle–late Eocene MAAT cooling relative to SST. Both dinocyst assemblages and brGDGT indices (the isomerization index) suggest a mid-shelf depositional environment with strong river-runoff during the Paleocene-early Eocene, becoming more open marine thereafter. This trend reflects gradual drying and more seasonal precipitation regime in the northward drifting Australian hinterland. The overall correlation between dinocyst assemblages, biodiversity and SST changes suggests that temperature and associated environmental changes exert a strong influence on the surface-water ecosystem.

Simulations of the geological past using General Circulation Models (GCMs) are computationally expensive. Mainly because of the long equilibration time scales, most of these GCMs have ocean components with a horizontal resolution of 1° or coarser. Such models are non-eddying and the effects of mesoscale ocean eddies on the transport of heat and salt are parameterized. However, from present-day ocean modeling studies, it is known that eddying ocean models better represent regional and time-mean ocean flows compared to non-eddying models. At the same time, proxy data from sediment sample sites represent climate at specific locations. Hence, the coarse ocean resolution of typical palaeo-GCMs lead to a challenge for model-data comparison in past climates.Here we present the first simulations of a global eddying Eocene ocean with a 0.1° (horizontal) resolution model, which are initialized and forced with data from a coarser resolution (1° horizontally) equilibrated coupled ocean-atmosphere GCM. We investigate the response of the model equilibrium state to the change in ocean resolution and the consequences this has for model-data comparison in the middle-late Eocene (38Ma). We find that, compared to the non-eddying model, the eddying ocean resolution of palaeomodels reduce the biases in both sea surface temperatures and biogeographic patterns which are derived from proxy data.

The Central Atlantic Magmatic Province (CAMP) eruptions are generally regarded as the main driver of major environmental change and mass-extinction across the Triassic-Jurassic (TJ) boundary (~201.3 Ma), but the exact mechanisms linking volcanism and extinction, resilience, and recovery remain poorly constrained. Volcanogenic mercury (Hg) has been implicated as the cause for mutations in spores/pollen indicating severe ecological stress in terrestrial vegetation. Indeed, elevated sedimentary Hg concentrations coincide with the extinction interval at multiple sites across Europe. Here we show, palynological and geochemical records that gives insight in the dynamics between the Hg cycle and terrestrial vegetation, indicating repeated phytotoxicity in Early Jurassic deposits.The abundance of mutagenic spores and the concentration of Hg are quantified in shallow marine sediments in the Schandelah-1 core (northern Germany) across the T/J boundary and the Early Jurassic (Hettangian). The results show increased mutagenic spore abundances with accompanying Hg/TOC anomalies across the end-Triassic extinction and within the lowermost Hettangian. This is consistent with studies from Sweden and Denmark and therefore confirming synchronous mutagenesis in and around coastal European margins. In addition, the Hettangian of Schandelah contains a record of long-term vegetational disturbance in the form of recurrent fern spikes and elevated mutagenic spore intervals, accompanied by Hg/TOC anomalies of similar magnitude. This suggests an overall link between volcanogenic pollution and vegetational disturbance. Based on qualitative analyses of organic matter (OM), which show an overall positive correlation between Hg concentration and terrestrial indicators, alternative sources for sedimentary Hg-enrichment such as vegetation reservoirs should be considered. This characterization of OM indicates an intermediate step in the Hg cycle, likely mediated by vegetation and/or climate feedbacks.Atmospheric Hg-loading via volcanism can explain the synchronous enrichments of Hg concentrations at the TJ boundary interval in multiple sites across the globe. In contrast, the Hettangian anomalies of Schandelah-1, appear to be mainly driven by environmental/ecological perturbations corresponding to intensifying warm/humid conditions. Extreme seasonality alternating between high rainfall and droughts, perhaps due to eccentricity maxima, leading to increased soil erosion, wildfires and transport/degradation of terrestrial OM could potentially recycle and redistribute Hg long after initial deposition. These implications suggest a more dominant role of climate-induced Hg-remobilization, rather than direct volcanic emissions, to the mutagenesis in terrestrial vegetation. This could, in addition, lead to asynchronous and local impacts mainly in the proximity of landmasses.

Rivers transport dissolved and solid loads from terrestrial realms to the oceans and between inland reservoirs, representing major mass fluxes on Earth's surface. The composition of river water and sediment provides clues to a plethora of earth and environmental processes, including weathering, erosion, nutrient and carbon cycling, environmental pollution, reservoir exchange and tectonic cycles. While there are documented, publicly available databases for riverine dissolved and suspended nutrients, there is no openly accessible, georeferenced database for riverine suspended sediment composition. Here, we present a globally representative set of 2828 suspended and bed sediment compositional measurements from 1683 locations around the globe. This database, named Global River Sediments (GloRiSe) version 1.0, includes major, minor and trace elements, along with mineralogical data, and provides time-series for some sites. Each observation is complemented by metadata describing geographic location, sampling date and time, sample treatment and measurement details, which allows for grouping and selection of observations, as well as for interoperability with external data sources and improves interpretability. Information on references, unit conversion and references make the database comprehensible. Notably, the close to globe-spanning extent of this compilation allows to derive data-driven, spatially resolved global-scale conclusions about the role of rivers and processes related to them within the Earth-system. GloRiSe version 1.0 can be downloaded from Zenodo (https://doi.org/10.5281/zenodo.4447435, Müller et al., 2021) and https://github.com/GerritMuller/GloRiSe.git (where updates with adapted version numbers will become available), along with a technical documentation and an example calculation in the form of a MATLAB script, that calculates the sediment-flux weighted major element composition of the annual riverine suspended sediment export to the ocean and related uncertainties.

The tropical thermocline may have played a crucial role in maintaining weaker sea surface temperature gradients during the early Pliocene and in the onset of late Pliocene northern hemisphere glaciation. Whereas the Pliocene Pacific thermocline evolution is well documented, complete records of Pliocene tropical Atlantic thermocline depths are limited to the Caribbean region. Here, we use the oxygen isotope gradient between surface to subsurface dwelling planktic foraminifera from Ocean Drilling Program Site 959 in the eastern equatorial Atlantic to track vertical changes in thermocline depth over the course of the Pliocene. This record shows that eastern equatorial Atlantic thermocline depth varied substantially during the early Pliocene, before finally deepening abruptly around 4.5 Ma to remain relatively stable until at least 2.8 Ma. Eastern equatorial Atlantic and Caribbean records are almost identical, suggesting a common control on the sudden step-wise thermocline deepening across the basin, in contrast to previous assumptions. The Pliocene evolution of the tropical Atlantic thermocline differs is remarkably from the Pacific, which is characterized by gradual basin-wide shoaling. It remains unclear what mechanisms were involved in the dichotomous thermocline evolutions. Whereas Central American Seaway closure may have shoaled the Pacific thermocline, it is not yet understood if and how this process may have deepened the Atlantic thermocline. A divergent evolution of temperatures of the source regions may explain the opposite thermocline developments observed, possibly amplified by a positive feedback loop involving tropical cyclone intensity.

Dissolved oceanic CO