The late Paleocene and early Eocene (LPEE) are characterized by long-term (million years, Myr) global warming and by transient, abrupt (kiloyears, kyr) warming events, termed hyperthermals. Although both have been attributed to greenhouse (CO2) forcing, the longer-term trend in climate was likely influenced by additional forcing factors (i.e., tectonics) and the extent to which warming was driven by atmospheric CO2remains unclear. Here, we use a suite of new and existing observations from planktic foraminifera collected at Pacific Ocean Drilling Program Sites 1209 and 1210 and inversion of a multiproxy Bayesian hierarchical model to quantify sea surface temperature (SST) and atmospheric CO2over a 6-Myr interval. Our reconstructions span the initiation of long-term LPEE warming (~58 Ma), and the two largest Paleogene hyperthermals, the Paleocene–Eocene Thermal Maximum (PETM, ~56 Ma) and Eocene Thermal Maximum 2 (ETM-2, ~54 Ma). Our results show strong coupling between CO2and temperature over the long- (LPEE) and short-term (PETM and ETM-2) but differing Pacific climate sensitivities over the two timescales. Combined CO2and carbon isotope trends imply the carbon source driving CO2increase was likely methanogenic, organic, or mixed for the PETM and organic for ETM-2, whereas a source with higher δ13C values (e.g., volcanic degassing) is associated with the long-term LPEE. Reconstructed emissions for the PETM (5,800 Gt C) and ETM-2 (3,800 Gt C) are comparable in mass to future emission scenarios, reinforcing the value of these events as analogs of anthropogenic change.
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Free, publicly-accessible full text available September 3, 2025
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Multiple abrupt warming events (“hyperthermals”) punctuated the Early Eocene and were associated with deep-sea temperature increases of 2 to 4 °C, seafloor carbonate dissolution, and negative carbon isotope (δ13C) excursions. Whether hyperthermals were associated with changes in the global ocean overturning circulation is important for understanding their driving mechanisms and feedbacks and for gaining insight into the circulation’s sensitivity to climatic warming. Here, we present high-resolution benthic foraminiferal stable isotope records (δ13C and δ18O) throughout the Early Eocene Climate Optimum (~53.26 to 49.14 Ma) from the deep equatorial and North Atlantic. Combined with existing records from the South Atlantic and Pacific, these indicate consistently amplified δ13C excursion sizes during hyperthermals in the deep equatorial Atlantic. We compare these observations with results from an intermediate complexity Earth system model to demonstrate that this spatial pattern of δ13C excursion size is a predictable consequence of global warming-induced changes in ocean overturning circulation. In our model, transient warming drives the weakening of Southern Ocean-sourced overturning circulation, strengthens Atlantic meridional water mass aging gradients, and amplifies the magnitude of negative δ13C excursions in the equatorial to North Atlantic. Based on model-data consistency, we conclude that Eocene hyperthermals coincided with repeated weakening of the global overturning circulation. Not accounting for ocean circulation impacts on δ13C excursions will lead to incorrect estimates of the magnitude of carbon release driving hyperthermals. Our finding of weakening overturning in response to past transient climatic warming is consistent with predictions of declining Atlantic Ocean overturning strength in our warm future.
Free, publicly-accessible full text available June 11, 2025 -
Abstract Future environmental change may profoundly affect oceanic ecosystems in a complex way, due to the synergy between rising temperatures, reduction in mixing and upwelling due to enhanced stratification, ocean acidification, and associated biogeochemical dynamics. Changes in primary productivity, in export of organic carbon from the surface ocean, and in remineralization deeper in the water column in the so‐called “twilight zone” may substantially alter the marine biological carbon pump, thus carbon storage in the oceans. We present different proxy records commonly used for reconstructing paleoproductivity, and re‐evaluate their use for understanding dynamic change within and between different constituents of the marine biological pump during transient global warming episodes in the past. Marine pelagic barite records are a proxy for carbon export from the photic and/or mesopelagic zone, and are not positively correlated with benthic foraminiferal proxies for arrival of organic matter to the seafloor over three early Eocene periods of global warming (Ocean Drilling Program Site 1263, SE Atlantic). These two proxies reflect processes in different parts of the water column, thus different components of the biological pump. An increase in temperature‐dependent organic carbon remineralization in the water column would have caused decreased arrival of food at the seafloor, starving the benthic biota and explaining the differences between the proxies, and may have led to ocean deoxygenation. Carbon cycle modeling demonstrates the feasibility of enhanced water‐column remineralization to explain both Site 1263 records, suggesting that this mechanism amplifies
p CO2increase, representing a positive feedback during hyperthermal warming. -
Abstract Earth's hydrological cycle was profoundly perturbed by massive carbon emissions during an ancient (56 Ma) global warming event referred to as the Paleocene‐Eocene thermal maximum (PETM). One approach to gaining valuable insight into the response of the hydrological cycle is to construct sea‐surface salinity (SSS) records that can be used to gauge changes in the rates of evaporation and precipitation during the PETM in such climatically sensitive areas as the circum‐Antarctic region. Here, we pair oxygen isotope (δ18O) and magnesium‐calcium (Mg/Ca) measurements to reconstruct PETM sea‐surface temperatures (SSTs) and δ18O composition of seawater (δ18Osw) at austral Site 690 (Weddell Sea). Several discrepancies emerge between the δ18O‐ and Mg/Ca‐based SST records, with the latter indicating that the earliest PETM was punctuated by a short‐lived ~4°C increase in local SSTs. Conversion of the δ18Oswvalues to SSS reveals a ~4 ppt decrease ~50 ka after peak PETM warming at Site 690. This negative SSS (δ18Osw) anomaly coincides with a prominent minimum in the planktic foraminifer δ18O record published for the Site 690 PETM section. Thus, our revised interpretation posits that this δ18O minimum signals a decrease in surface‐ocean δ18Oswfostered by a transient increase in mean annual precipitation in the Weddell Sea region. The results of this study corroborate the view that the poleward flux of atmospheric moisture temporarily increased during a distinctive stage of the PETM.
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Abstract Chert, porcelainite, and other siliceous phases are exceptionally common in Atlantic sedimentary records of the early Eocene, but the origins of these facies remain enigmatic. The early Eocene was also the warmest interval of the entire Cenozoic Era, punctuated by numerous discrete warming events termed “hyperthermals,” the largest of which is termed the Paleocene‐Eocene Thermal Maximum (~56 Ma). Here we present new and published lithologic and carbon isotope records of silica‐bearing lower Eocene sediments and suggest a link between the ubiquitous Atlantic cherts of that time period and hyperthermal events. Our data demonstrate that many of these Atlantic siliceous horizons coincide with negative carbon isotope excursions (a hallmark of hyperthermal events), including a previously unrecognized record of the Paleocene‐Eocene Thermal Maximum in the South Atlantic. Hyperthermal‐associated silica burial appears to be focused in the western middle to high latitudes of both the North and South Atlantic, with no association between siliceous facies and hyperthermal events found in the Pacific. We also present a new model of the coupled carbon and silica cycles (LOSiCAR) to demonstrate that enhanced silicate weathering during these events would require a rapid increase in total marine silica burial. Model experiments that include previously suggested transient reversals in the pattern of deep‐ocean circulation during hyperthermals demonstrate that such a mechanism can explain the apparent focusing of elevated silica burial into the Atlantic. This combination—a silicate weathering feedback in response to global warming along with a circulation‐driven focusing of silica burial—represents a new mechanism for the formation of deep‐sea cherts in lower Eocene Atlantic sedimentary records and may be relevant to understanding chert formation in other intervals of Earth history.
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Abstract Cyclostratigraphy and astrochronology are now at the forefront of geologic timekeeping. While this technique heavily relies on the accuracy of astronomical calculations, solar system chaos limits how far back astronomical calculations can be performed with confidence. High‐resolution paleoclimate records with Milankovitch imprints now allow reversing the traditional cyclostratigraphic approach: Middle Eocene drift sediments from Newfoundland Ridge are well‐suited for this purpose, due to high sedimentation rates and distinct lithological cycles. Per contra, the stratigraphies of Integrated Ocean Drilling Program Sites U1408–U1410 are highly complex with several hiatuses. Here, we built a two‐site composite and constructed a conservative age‐depth model to provide a reliable chronology for this rhythmic, highly resolved (<1 kyr) sedimentary archive. Astronomical components (g‐terms and precession constant) are extracted from proxy time‐series using two different techniques, producing consistent results. We find astronomical frequencies up to 4% lower than reported in astronomical solution La04. This solution, however, was smoothed over 20‐Myr intervals, and our results therefore provide constraints on g‐term variability on shorter, million‐year timescales. We also report first evidence that the
g 4–g 3“grand eccentricity cycle” may have had a 1.2‐Myr period around 41 Ma, contrary to its 2.4‐Myr periodicity today. Our median precession constant estimate (51.28 ± 0.56″/year) confirms earlier indicators of a relatively low rate of tidal dissipation in the Paleogene. Newfoundland Ridge drift sediments thus enable a reliable reconstruction of astronomical components at the limit of validity of current astronomical calculations, extracted from geologic data, providing a new target for the next generation of astronomical calculations. -
The cause of the end-Cretaceous mass extinction is vigorously debated, owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary. Disentangling their relative importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing, impact, and extinction. We used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing. We found support for major outgassing beginning and ending distinctly before the impact, with only the impact coinciding with mass extinction and biologically amplified carbon cycle change. Our models show that these extinction-related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide, thus limiting the global warming otherwise expected from postextinction volcanism.