NSF Award
2202983
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.<br/><br/><br/>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.<br/><br/>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.
