Reconstruction of Ocean Structure and Circulation during the Extreme Warmth of the early-middle Eocene

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Project Highlights - Join a world-leading team striving to understand how carbon cycles around Earths surface during extreme climatic warmthLearn cutting-edge geochemical analyses for reconstructing past carbon cycling and climatic changeTest hypotheses that the size and volatility of carbon reservoirs at or near Earth's surface vary with background climate stateDetermine the deep-sea temperature response to large-scale perturbations of the carbon cycle1,2 during Eocene extreme greenhouse warmthOverview - During the early Eocene epoch, Earth witnessed its warmest temperatures of the past 90 million years, with the deep oceans up to 14degreesC warmer than today. These greenhouse climates have traditionally been regarded as uniformly warm and climatically stable, or equable. However, the last decade has seen the discovery of a number of hyperthermals (Fig. 1; rapid global warming events not dissimilar to our current anthropogenic warming) driven by large-scale releases of carbon from some as yet unknown source(s), challenging these traditional views of equability, and instead suggesting that greenhouse climates may be marked by pronounced instability.The most well-studied hyperthermals occur during a ~6 million year-long interval of progressive global warming culminating in the peak warmth of the early Eocene from 52 to 50 Myr ago1 (Fig. 1). The occurrence and relative size of these hyperthermals have been explained by a thermodynamic threshold for carbon release and a decrease in the size of carbon reservoirs during times of extreme warmth1. However, these hypotheses have proven difficult to test owing to the lack of continuous records from within the early Eocene and from the subsequent climatic cooling during the middle Eocene. This project will test hypotheses that the size and volatility of isotopically depleted carbon reservoirs should diminish during extreme global warmth1 and the corollary hypothesis that these carbon reservoirs should grow and become more volatile with subsequent cooling into the middle Eocene (an interval for which almost no high resolution records exist, Fig. 1). It will also evaluate the deep-sea temperature response2,4 to these carbon cycle-driven hyperthermals to provide valuable information on the sensitivity of Earths climate to large-scale carbon releases.This project will take advantage of new sequences from the Atlantic Ocean with the highest sedimentation rates available for the Eocene to allow an evaluation of the sensitivity of climate and the carbon cycle to Earths orbital cycles during extreme greenhouse warmth1,2,4 & subsequent global cooling.Methodology reconstruct orbital-scale variability in deep-sea temperatures and carbon cycling using high resolution isotope analyses of benthic foraminifera2,4 from expanded sequences from the equatorial Atlantic (IODP Exp. 207) and North Atlantic (IODP Exp. 342). O and C isotope (13C, 18O) analyses will be performed on the in-house Thermo-Scientific Delta+ stable isotope mass spectrometer. This project will also use ultra-high resolution XRay Fluorescence (XRF) scanning of the chemical elemental contents of sediment cores housed at Bremen to develop detailed astronomical age models. Because of the excellent preservation of planktic foraminifera, opportunity also exists to reconstruct the response of the surface ocean and thermocline across hyperthermal events and their longer-term response to the termination of the early Eocene greenhouse and onset of climatic cooling.