Accomplishment Based Renewal: Intensification of the Hydrologic Cycle during the Paleocene-Eocene Thermal Maximum

Earth has experienced just over 1°C of fossil fuel carbon dioxide-driven global warming to date. The impacts of this warming on the global hydrologic cycle are already evident. The projected 4-5°C of warming by 2300 under a business-as-usual fossil fuel use scenario is predicted to further intensify the hydrologic cycle.

The resulting impacts on societies’ water security would be significant, and likely create widespread hardship for nations across the globe, rich and poor. Climate models, tested by their ability to replicate past changes in climate, are an important tool to plan for and minimize those impacts. The Paleocene-Eocene Thermal Maximum (PETM, roughly 55 million years ago) serves as a crucial case study to test climate models.

It also provides a real-world example of the sensitivity of the climate system to a massive carbon dioxide input. The proposed project will use coastal sediments to develop proxy records of water chemistry and onshore hydrology across the PETM. These new data will be compared with climate model studies of that ancient natural climate event.

The educational Broader Impacts of the proposed project include support for a graduate student and for undergraduate participants.

Although considerable geologic evidence exists for a shift in hydroclimate during the PETM, additional observations are required to assess regional/local changes, particularly as relates to extremes on annual or shorter time scales. To this end, this project will estimate regional changes in coastal hydrography/chemistry along both coasts of the US utilizing shallow marine siliciclastic sections in outcrops and cores.

Preliminary data indicate significant changes in runoff (& erosion) and thus precipitation, very likely in the amplitude of wet/dry cycles and/or heavy precipitation events (e.g. atmospheric rivers, extratropical cyclones). Building on prior results, in collaboration with colleagues novel isotopic and geochemical proxies will be employed, along with traditional proxies, to constrain local changes in coastal ocean hydrography/chemistry.

The observations will be compared against output of recently completed GCM simulations of the PETM utilizing high resolution models including the Community Atmosphere Model. The primary focus of the comparisons will be on changes in the seasonal cycles of precipitation and frequency of extreme events (i.e., heavy precipitation or droughts).

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.