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

项目要点-加入一个世界领先的团队，努力了解极端气候变暖期间地球表面周围的碳循环了解尖端的地球化学分析，以重建过去的碳循环和气候变化测试假设，即地球表面或附近的碳库的大小和挥发性随着背景气候状态的变化确定深海温度对始新世极端温室升温期间碳循环的大范围扰动的响应1，2概述-在始新世早期，地球经历了过去9000万年来最热的温度，深海温度比今天高出14摄氏度。这些温室气候传统上被认为是均匀温暖、气候稳定或稳定的。然而，在过去的十年里，由于一些未知来源(S)的碳的大规模释放，已经发现了一些高温(图1；快速的全球变暖事件，与我们目前的人为变暖没有什么不同)，挑战了这些传统的均衡性观点，相反，表明温室气候可能具有明显的不稳定性。最广泛研究的高温发生在全球逐渐变暖的大约600万年的间隔期间，最终在始新世早期52年至50年的升温高峰(图1)。这些高温的发生和相对大小可以通过碳释放的热力学阈值和极端温暖时期碳库大小的减少来解释。然而，由于缺乏始新世早期和随后始新世中期气候冷却的连续记录，这些假说被证明是很难检验的。该项目将检验这样的假设，即在极端全球变暖期间，同位素耗尽的碳库的大小和挥发性应该减少1，以及这些碳库应该随着随后冷却到始新世中期(几乎没有高分辨率记录，图1)而增长和变得更易挥发的推论。它还将评估深海温度对这些碳循环驱动的高温的响应2，4，以提供关于地球气候对大规模碳释放的敏感性的有价值的信息。该项目将利用来自大西洋的新序列，这些新序列具有可用于始新世的最高沉积速率，以评估极端温室气体变暖1，2，4和随后的全球变冷期间气候和碳循环对地球轨道循环的敏感性。方法利用来自赤道大西洋(IODP Exp.)扩展序列的海底有孔虫2，4的高分辨率同位素分析重建深海温度和碳循环的轨道尺度变化。207)和北大西洋(IODP Exp.342)。氧和碳同位素(13C，18O)分析将在内部的Thermo-Science Delta+稳定同位素质谱仪上进行。该项目还将使用超高分辨率X射线荧光(XRF)扫描不来梅沉积物岩心的化学元素含量，以开发详细的天文年龄模型。由于浮游有孔虫保存得很好，也有机会重建表层海洋和温跃层在高温事件中的反应，以及它们对始新世早期温室终止和气候冷却开始的较长期反应。

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.