CAREER: Quantifying Western Atlantic Climate and Seasonality across the Plio-Pleistocene Regional Molluscan Extinction

Over the past ~4 million years, 70-80% of mollusk species (clams, scallops, etc.) living in the waters of the Atlantic & Gulf Coasts have disappeared. New species originated to replace those that went extinct, and the mollusk population remains quite diverse today. The cause of this great turnover in species has not been established. The primary hypothesis is that declining water temperatures pushed out warm-water-loving species and replaced them with those that could inhabit cooler waters. The researcher will produce robust, quantitative temperature estimates from sites up and down the East Coast over the past 3-5 million years and compare those to extinction patterns of marine mollusks to test this hypothesis. In addition to addressing the root cause of the extinction, these data will reveal information about the thermal tolerances of studied mollusk species and determine whether those are fixed or flexible (meaning a species could adapt to live in different water temperatures than it currently inhabits). This will have implications for the survival of mollusks living in American waters (including those farmed for aquaculture like clams and scallops) in the coming decades and centuries as ocean temperatures warm. The researcher will share their findings with the public through a number of outreach projects and exhibits in partnership with the UMich Museum of Natural History. They will create an authentic research experience course to introduce more undergraduates to research in a way that lowers barriers-to-entry. The researcher will conduct a program of isotopic measurements on fossil mollusks using the clumped isotope paleothermometer (D47), including calibrations of modern marine gastropods and bivalves. Use of this new method is vital, as preliminary D47-based temperature estimates differ greatly from historical oxygen-isotope-based estimates which are flawed due to their poor constraints on past oxygen isotopic composition of seawater (d18Osw). Data generated here will directly address questions of niche stability in mollusk taxa through determination of changes (or lack thereof) in thermal tolerances over time and space. 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.