Tropical Atlantic Hydrologic Change during the Paleocene-Eocene Thermal Maximum

气候模型预测了全球蒸发和降水模式(水文循环)在变暖的世界中可能会有怎样的不同表现。全球水文循环的预测变化对干旱、火灾、极端天气事件和洪水的频率和严重程度具有区域影响。这个项目试图利用沉积记录来研究地球历史上过去一段温暖时期的水文循环是如何变化的。该项目的目标是一个研究得很好的古代全球变暖事件：5600万年前的古新世-始新世最高温度。通过分析这一时期保存在深海沉积物中的微化石的化学成分，研究人员可以限制被认为对水文变化特别敏感的地区的蒸发和降水平衡的变化。这些结果将与最新一代全球气候模型进行的气候变暖模拟进行比较。这种数据模型的比较将改进对持续气候变化下未来水文变化的预测。该项目还将为研究生提供培训和经验，并为服务不足社区的本科生提供暑期实习计划。全球蒸发和降水模式的未来变化是人为气候变化数值模拟强调的最紧迫的关注领域之一。研究地球地质历史中过去的暖事件提供了一个机会来检验气候模型在预测区域水文变化方面的技能。最近对古新世-始新世最热时期(PETM，约5600万年前)异常温暖状况的最新气候模型模拟表明，热带大西洋在较温暖的条件下特别容易向更干旱(蒸发更多，降水更少)的状态转变。该项目将使用热带大西洋的深海沉积物岩心，通过地球化学方法限制跨PETM的区域水文变化，以检验这一模型预测。通过分析海洋钻探项目地点1258(热带北大西洋德梅拉拉隆起)表层浮游有孔虫中的氧同位素，将限制跨PETM的区域水文变化。由于有孔虫中的氧同位素反映了温度和海水成分的组合，因此也将测量相同有孔虫的镁/钙比(mg/Ca)，以校正温度影响，从而产生跨PETM的表层海水氧同位素组成变化的记录。这一变化的意义和程度将与最近使用NCAR的同位素启用的社区地球系统模型(ICESM)对始新世变暖的模拟进行比较。拟议工作中开发的方法还将应用于已公布有孔虫的氧同位素和镁/钙记录的其他几个地点，从而产生一个关于整个PETM水文变化的全球数据模型合成。这种比较要么将增强对变暖条件下区域水文变化的模型预测的信心，要么将确定需要改进的领域。该项目将支持一名博士生，并提供分析地球化学和气候模型解释方面的培训和经验。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Climate models predict how global patterns of evaporation and precipitation (the hydrologic cycle) may behave differently in a warmer world. Predicted changes to the global hydrologic cycle have regional implications for the frequency and severity of drought, fire, extreme weather events, and flooding. This project seeks to use the sedimentary record to study how the hydrologic cycle changed during a past warm interval in Earth’s history. The project targets a well-studied ancient global warming event: the Paleocene-Eocene Thermal Maximum, 56 million years ago. By analyzing the chemistry of microfossils preserved in deep-sea sediments from this time period, the researchers can constrain how the balance of evaporation and precipitation changed in regions thought to be particularly sensitive to hydrologic change. The results will be compared to simulations of climatic warming carried out by the latest generation of global climate models. This data-model comparison will improve predictions for future hydrologic variations under ongoing climate change. This project will also provide training and experience for graduate students, and summer internship programs for undergraduate students from under-served communities.Future changes to global patterns of evaporation and precipitation are one of the most pressing areas of concern highlighted by numerical simulations of anthropogenic climate change. Studying past warm events in Earth’s geological past provides an opportunity to test climate model skill in predicting regional hydrologic change. Specifically, recent climate model simulations of the anomalously warm conditions during the Paleocene-Eocene Thermal Maximum (PETM, ~56 million years ago) suggest that the tropical Atlantic Ocean was particularly susceptible to a pronounced shift towards a more arid (more evaporation, less precipitation) state under warmer conditions. This project will test that model prediction by geochemically constraining regional hydrologic change across the PETM using deep-sea sediment cores from the Tropical Atlantic. Regional hydrologic change across the PETM will be constrained by analyzing oxygen isotopes in surface-dwelling planktonic foraminifera at Ocean Drilling Project Site 1258 (Demerara Rise, Tropical North Atlantic Ocean). Since oxygen isotopes in foraminifera reflect a combination of temperature and seawater composition, the magnesium to calcium ratio (Mg/Ca) of the same foraminifers will also be measured to correct for temperature effects, producing a record of changing oxygen isotopic composition of surface seawater across the PETM. The sense and magnitude of this change will be compared to recent simulations of Eocene warming using NCAR’s isotope-enabled Community Earth System Model (iCESM). The methods developed in the proposed work will also be applied to several other sites with published foraminiferal oxygen isotope and Mg/Ca records, producing a global data-model synthesis for hydrologic change across the PETM. This comparison will either bolster confidence in model predictions for regional hydrologic change under warmer conditions, or else identify areas for improvement. The project will support a PhD student and provide training and experience in analytical geochemistry and climate model interpretation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.