Search

Much of our understanding of Earth's past climate comes from the measurement of oxygen and carbon isotope variations in deep-sea benthic foraminifera. Yet, long intervals in existing records lack the temporal resolution and age control needed to thoroughly categorize climate states of the Cenozoic era and to study their dynamics. Here, we present a new, highly resolved, astronomically dated, continuous composite of benthic foraminifer isotope records developed in our laboratories. Four climate states-Hothouse, Warmhouse, Coolhouse, Icehouse-are identified on the basis of their distinctive response to astronomical forcing depending on greenhouse gas concentrations and polar ice sheet volume. Statistical analysis of the nonlinear behavior encoded in our record reveals the key role that polar ice volume plays in the predictability of Cenozoic climate dynamics.

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.

Abstract. The early Eocene (56 to 48 million years ago) is inferred to havebeen the most recent time that Earth's atmospheric CO2 concentrationsexceeded 1000 ppm. Global mean temperatures were also substantially warmerthan those of the present day. As such, the study of early Eocene climate provides insightinto how a super-warm Earth system behaves and offers an opportunity toevaluate climate models under conditions of high greenhouse gas forcing. TheDeep Time Model Intercomparison Project (DeepMIP) is a systematicmodel–model and model–data intercomparison of three early Paleogene timeslices: latest Paleocene, Paleocene–Eocene thermal maximum (PETM) and earlyEocene climatic optimum (EECO). A previous article outlined the modelexperimental design for climate model simulations. In this article, weoutline the methodologies to be used for the compilation and analysis ofclimate proxy data, primarily proxies for temperature and CO2. Thispaper establishes the protocols for a concerted and coordinated effort tocompile the climate proxy records across a wide geographic range. Theresulting climate “atlas” will be used to constrain and evaluate climatemodels for the three selected time intervals and provide insights into themechanisms that control these warm climate states. We provide version 0.1 ofthis database, in anticipation that this will be expanded in subsequentpublications.

The response of the Earth system to greenhouse-gas-driven warming is of critical importance for the future trajectory of our planetary environment. Hyperthermal events - past climate transients with global-scale warming significantly above background climate variability - can provide insights into the nature and magnitude of these responses. The largest hyperthermal of the Cenozoic was the Paleocene-Eocene Thermal Maximum (PETM ∼ 56 Ma). Here we present new high-resolution bulk sediment stable isotope and major element data for the classic PETM section at Zumaia, Spain. With these data we provide a new detailed stratigraphic correlation to other key deep-ocean and terrestrial PETM reference sections. With this new correlation and age model we are able to demonstrate that detrital sediment accumulation rates within the Zumaia continental margin section increased more than 4-fold during the PETM, representing a radical change in regional hydrology that drove dramatic increases in terrestrial-to-marine sediment flux. Most remarkable is that detrital accumulation rates remain high throughout the body of the PETM, and even reach peak values during the recovery phase of the characteristic PETM carbon isotope excursion (CIE). Using a series of Earth system model inversions, driven by the new Zumaia carbon isotope record, we demonstrate that the silicate weathering feedback alone is insufficient to recover the PETM CIE, and that active organic carbon burial is required to match the observed dynamics of the CIE. Further, we demonstrate that the period of maximum organic carbon sequestration coincides with the peak in detrital accumulation rates observed at Zumaia. Based on these results, we hypothesise that orbital-scale variations in subtropical hydro-climates, and their subsequent impact on sediment dynamics, may contribute to the rapid climate and CIE recovery from peak-PETM conditions.

Plain Language Summary: The Early Eocene Climatic Optimum (EECO) is an interval of prolonged warmth that occurred ∼53 to 49 million years ago. Planktic foraminifera are important (alongside coccolithophores) for understanding the carbon cycle and determining export production in the ocean. To understand how foraminifera can be impacted by extreme heat, we analyzed samples from the Pacific Ocean through measuring changes in (a) the relative abundance, that is, the count of different taxa in a sample, and (b) body (shell) size of planktic foraminifera. At the start of the EECO, the abundance of the genera Morozovella and Chiloguembelina decreased. Despite this decline, the number of foraminifera being buried and the size of the largest shells in a sample does not change. We attribute this to the increased abundance of the genus Acarinina. In general, the accumulation of foraminifera remains stable while the relative abundance of foraminifera to coccolithophores decreases. Together, this implies that coccolithophores are increasing in abundance, and/or mass. During the EECO, one group of foraminifera was able to counterbalance the decrease in abundance of other genera. This highlights the resilience of open‐ocean carbonate production and the base of the marine food web. The Early Eocene Climatic Optimum (EECO; ∼53 and 49 Ma) records the warmest long‐term global average temperature and highest CO2 levels of the Cenozoic. Multiple transient global warming events occur within the EECO, offering an opportunity to investigate the impact of extreme heat on planktic foraminifera. Pacific Ocean Drilling Program (ODP) Sites 1209–1210 (Shatsky Rise) provide an excellent age model and stable isotope records to link biotic data with the carbon cycle across the interval here analyzed (55.6 and 49.93 Ma). We combine carbonate production proxies with changes in planktic foraminiferal assemblages and test‐size. Our data show that during the EECO planktic foraminiferal assemblages were permanently modified, besides transient changes. At the EECO onset, abundance of the genera Morozovella and Chiloguembelina decreased at 53.28 and 52.85 Ma, respectively, confirming published Atlantic Ocean data and thus the global decline of these genera. Given the dominance and large size of Morozovella in early Eocene tropical assemblages, we postulated that this change would have reduced foraminiferal production and the assemblage test‐size. In contrast, we record a slight increase in test‐size within assemblages, controlled by the now dominant genus, Acarinina. The decrease in coarse fraction weight, partially controlled by dissolution, during times of stable foraminferal mass accumulation rate indicates enhanced calcareous nannofossil productivity reducing the foraminiferal contribution to the sediment. During the EECO, despite the decrease in abundance of some genera, species replacement within communities highlights the resilience of pelagic carbonate production, emphasizing the critical role of planktic foraminifera in regulating the marine food web and global carbon cycling. Key Points: At the EECO onset, the abundance of the planktic foraminiferal genera Morozovella and Chiloguembelina decreased and never recoveredSpecies replacement and test‐size increase within assemblages sustained production of pelagic carbonate by foraminiferaGreater adaptability and flexibility of the genus Acarinina led to its dominance over the more specialized morozovellids [ABSTRACT FROM AUTHOR]

During the Palaeocene-Eocene Thermal Maximum (PETM) about 56 million years ago, thousands of petagrams of carbon were released into the atmosphere and ocean in just a few thousand years, followed by gradual sequestration over approximately 200,000 years. If silicate weathering is one of the key negative feedbacks that removed this carbon, a period of seawater calcium carbonate saturation greater than pre-event levels would be expected during the event's recovery phase. In marine sediments, this should be recorded as a temporary deepening of the depth below which no calcite is preserved-the calcite compensation depth (CCD). Previous and new sedimentary records from sites that were above the pre-PETM CCD show enhanced carbonate accumulation following the PETM. A new record from an abyssal site in the North Atlantic that lay below the pre-PETM CCD shows a period of carbonate preservation beginning about 70,000 years after the onset of the PETM, providing the first direct evidence for an over-deepening of the CCD. This record confirms an overshoot in ocean carbonate saturation during the PETM recovery. Simulations with two earth system models support scenarios for the PETM that involve a large initial carbon release followed by prolonged low-level emissions, consistent with the timing of CCD deepening in our record. Our findings indicate that sequestration of these carbon emissions was most likely the result of both globally enhanced calcite burial above the CCD and, at least in the North Atlantic, an over-deepening of the CCD.