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During the early Paleogene, a long-term warming trend of Earth’s climate was punctuated by a major global warming event, known as the Paleocene-Eocene Thermal Maximum (PETM) and marked by a carbon isotope excursion (CIE) and an acidification episode. The associated worldwide environmental perturbations are best studied in open marine settings, and resulted in a major extinction event in deep-sea benthic foraminifera, followed by migration and diversification. Yet, the evolutionary impact on shelf foraminiferal faunas is still poorly constrained due the inherent stratigraphic complexities in these environments. In order to understand the prelude and aftermath of peak warming during the PETM, we study the South Dover Bridge core (SDB), drilled in the US Atlantic Coastal Plain in Maryland. Here, the Paleocene-Eocene transition is stratigraphically well constrained by calcareous nannoplankton and stable isotope records. Additionally, the PETM is regionally characterized by the appearance of fine-grained sediments, known as the Marlboro Clay, contrasting with the late Paleocene glauconitic sands. Our newly generated high-resolution foraminiferal stable isotope, biotic and grain size data enable an assessment of the stratigraphic completeness of this site, and the disentanglement of the successive recovery-phases, by correlation across the paleoshelf.The mid-shelf benthic foraminiferal assemblage we recorded in the upper Paleocene indicates well-oxygenated, continuously oligo- to mesotrophic bottom water conditions. These conditions were temporarily interrupted during a pre-PETM CIE, which initiated minor, but prominent, changes in foraminiferal assemblage. The relationship with the PETM is still unclear, but it may indicate that the latest Paleocene climate was not as stable as previously assumed and instead exhibited a more gradual change towards the PETM. At the onset of the PETM diversity decreases, as more stress-resistant benthic taxa become predominant and planktic abundances increase. This probably points to periodically dysoxic bottom waters due to river-induced stratification, resulting from enhanced regional river outflow, as well as to a shift to episodic food fluxes to the sea floor.The studied expanded SDB sequence also presents an excellent and nearly complete record of the PETM isotope recovery phase. Throughout this recovery phase a third, more diverse foraminiferal assemblage starts to prevail, indicating a gradual return to sustained high food levels and increasing oxygen levels, related to a decrease of river influence. Species, dominant during the core phase of the PETM, like Anomalinoides acutus or Pseudouvigerina wilcoxensis, show strongly declining numbers in the recovery phase. Other taxa, like Cibicidoides alleni, returned to the shelf ecosystem, after disappearing nearly completely from the sediments during the initial PETM CIE interval. This coincides with reduced planktic foraminiferal abundances and a tendency towards more silty and less clayey sediments, linked to renewed bottom current activities and winnowing.The lack of severe benthic extinction among shelf-dwelling benthic foraminifera and the observed lateral variability in environmental conditions, demonstrate how foraminiferal shelf communities can adapt to massive global carbon perturbations. As more regional data will become available, these will enable more constraints on environmental parameters and variations along the Atlantic Coastal Plain prior and during the PETM.

The early Eocene (56 to 48 million years ago) is inferred to have been the most recent time that Earth's atmospheric CO2 concentrations exceeded 1000 ppm. Global mean temperatures were also substantially warmer than present day. As such, study of early Eocene climate provides insight into how a super-warm Earth system behaves and offers an opportunity to evaluate climate models under conditions of high greenhouse gas forcing. The Deep Time Model Intercomparison Project (DeepMIP) is a systematic model-model and model-data intercomparison of three early Paleogne time slices: latest Paleocene, Paleocene-Eocene thermal maximum and early Eocene climatic optimum. A previous article outlined the model experimental design for climate model simulations. In this article, we outline the methodologies to be used for the compilation and analysis of climate proxy data, primarily proxies for temperature and CO2. This paper establishes the protocols for a concerted and coordinated effort to compile the climate proxy records across a wide geographic range. The resulting climate atlas will be used to constrain and evaluate climate models for the three selected time intervals, and provide insights into the mechanisms that control these warm climate states. We provide version 0.1 of this database, in anticipation that this will be expanded in subsequent publications.

Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high (> 800 ppmv) atmospheric CO2 concentrations. Although a post-hoc intercomparison of Eocene (~50 million years ago, Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the latest Paleocene and the early Eocene. Together these form the first phase of DeepMIP – the deeptime model intercomparison project, itself a group within the wider Paleoclimate Modelling Intercomparison Project (PMIP). The experimental design consists of three core paleo simulations and a set of optional sensitivity studies. The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, orbital configuration, solar constant, land surface parameters, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological datasets, which will be used to evaluate the simulations, will be developed.

Transient greenhouse warming events in the Paleocene and Eocene were associated with the addition of isotopically-light carbon to the exogenic atmosphere–ocean carbon pool, leading to substantial environmental and biotic change. The magnitude of an accompanying carbon isotope excursion (CIE) can be used to constrain both the sources and amounts of carbon released during an event, as well as to correlate marine and terrestrial records with high precision. The Paleocene Eocene Thermal Maximum (PETM) is well documented, but CIE records for the subsequent warming events are still rare especially from the terrestrial realm. Here, we provide new CIE records for two of the smaller hyperthermal events, I1 and I2, in paleosol carbonate, as well as two additional records of ETM2 and H2 in the Bighorn Basin. Stratigraphic comparison of this expanded, high-resolution terrestrial carbon isotope record to the deep-sea benthic foraminifera records from ODP Sites 1262 and 1263, Walvis Ridge, in the southern Atlantic Ocean corroborates that the Bighorn Basin fluvial sediments record global atmospheric change. The stratigraphic thicknesses of the eccentricity-driven hyperthermals in these archives are in line with precession-forcing of the 7 m thick fluvial overbank-avulsion sedimentary cycles. Using the CALMAG bulk oxide mean annual precipitation proxy, we reconstruct similar or slightly wetter than background soil moisture contents during the four younger hyperthermals, in contrast to drying observed during the PETM. Soil carbonate CIEs vary in magnitude proportionally with the marine CIEs for the four smaller early Eocene hyperthermals. This relationship breaks down for the PETM, with the soil carbonate CIE ~ 2–4‰ less than expected if all five linearly relate to marine CIEs. If the PETM CO2 forcing was similar but scaled to the younger hyperthermals, photosynthetic isotope fractionation or soil environmental factors are needed to explain this anomaly. We use sensitivity testing of experimentally determined photosynthetic isotope discrimination relationships to show that factors other than the recently demonstrated pCO2 sensitivity of C3 plants carbon isotope fractionation are required to explain this anomaly.

Re-examination of a sediment core collected by the Deep Sea Drilling Project (DSDP Site 277) on the western margin of the Campbell Plateau, Southwest Pacific Ocean (paleolatitude of ∼ 65° S), has identified an intact Paleocene–Eocene (P–E) boundary overlain by a 34 cm-thick record of the initial phase of the Paleocene–Eocene Thermal Maximum (PETM) within nannofossil chalk. The upper part of the PETM is truncated, either due to drilling disturbance or a sedimentary hiatus. An intact record of the onset of the PETM is indicated by a gradual decrease in δ13C values over 20 cm, followed by a 14 cm interval in which δ13C is 2‰ lighter than uppermost Paleocene values. After accounting for effects of diagenetic alteration, we use δ18O and Mg/Ca values from foraminiferal tests to determine that intermediate and surface waters warmed by ∼ 6° at the onset of the PETM prior to the full development of the negative δ13C excursion. After this initial warming, sea temperatures were relatively stable through the PETM, but declined abruptly across the unconformity that truncates the event at this site. Mg/Ca analysis of foraminiferal tests indicate peak intermediate and surface water temperatures of ∼ 19 and ∼ 32 °C, respectively. These temperatures may be influenced by enhanced poleward ocean heat transport during the PETM and surface water values may also be biased towards warm season temperatures.