Jesse Farmer
Jesse Farmer is an Assistant Professor in Geology and Paleoclimate in the School for the Environment at the University of Massachusetts Boston. His research uses geochemical measurements on the organic and inorganic constituents of fossil marine carbonates to decipher how, why, and how quickly Earth’s biogeochemical cycles changed during intervals of climate instability in Earth’s history. With these data, he seeks to better understand the mechanisms by which biogeochemical changes impact, and are in turn impacted by, Earth’s climate state. Jesse has an ScB from Brown University, a PhD from Columbia University, and performed postdoctoral research jointly between Princeton University and Max Planck Institute for Chemistry.
Arctic paleoceanography and global sea-level change: Evidence from foraminifera-bound nitrogen isotopes
Although the Arctic is the most rapidly warming region on Earth today, gaining perspective on modern Arctic changes with paleoceanographic records has been challenged by longstanding disagreements over Arctic chronostratigraphy and complications with applying established carbonate paleoceanographic proxies to Arctic sediments. Here I turn to a different archive of paleoceanographic information within Arctic foraminifera: the organic matter trapped within their carbonate tests. We have measured planktonic foraminifera-bound nitrogen isotopes (FB-d15N) from ten sediment cores in the western (Amerasian) and eastern (Eurasian) Arctic basins covering the last ~50,000 years. Results from the western Arctic show pronounced, 3‰ FB-d15N declines shortly before the Last Glacial Maximum (LGM) and corresponding FB-d15N increases late in deglaciation. Interpreting these records using observations of the modern Arctic Ocean nitrogen cycle, we conclude that the shallow Bering Strait was flooded just 10,000 years before the LGM. This requires elevated global mean sea level during Marine Isotope Stage 3 and a much faster rate of ice sheet growth leading up to the LGM than indicated by previous sea-level proxies, with implications for the internal climate feedbacks responsible for Pleistocene ice-age cycles. Additionally, correlated Arctic-wide patterns in FB-d15N allow for the chemostratigraphic identification of sedimentary units associated with glacial inception, deglaciation, and the Holocene in the Arctic Ocean, facilitating improved multiproxy understanding of Arctic climate and ecosystem change across ice-age cycles. Last, I will discuss recent progress toward understanding past and present Atlantic-Arctic nutrient connections through new FB-d15N records from the Nordic Seas.
