Please join us next Friday, March 12, at 2 pm for a Geochemistry Seminar by LDEO alum Dr. Jesse Farmer (Ph.D. '16), an assistant professor in the School for the Environment at the University of Massachusetts Boston. His research utilizes geochemical measurements of marine fossils to decipher how, why, and how quickly Earth’s carbon cycle changed during intervals of climate instability in Earth’s history. With this knowledge, he seeks to understand better how human carbon emissions will affect our future climate. This is a special Lamont75 Seminar, where eminent alums and former staff showcase their research and reflect on what makes LDEO special.
Uncovering Bering Land Bridge history using the marine nitrogen cycle
Beringia, the region between the Lena River in northeastern Russia and the Mackenzie River in northwestern North America, has experienced profound changes in relative sea level that fundamentally reshaped Northern Hemisphere terrestrial and ocean connections. Today, Beringia centers on the Bering Strait, a ~50 m deep gateway that links the Pacific and Atlantic Oceans via the Arctic Ocean. This modern arrangement has been ephemeral over recent Earth history, with a ~1000 km-wide land bridge at the Last Glacial Maximum (LGM, ~20,000 years ago) providing the long-proposed route by which humans first migrated to North America. However, direct information on past Beringian sea level has only existed for times after the LGM. This greatly limits our knowledge of the timing of and environmental context for past migrations, including that of our human ancestors.
Here I will present new reconstructions of past Bering Strait flooding using foraminifera-bound nitrogen isotopes to trace the “fingerprint” of Pacific nitrogen input into the Arctic Ocean. Results show that the Bering Strait was flooded immediately prior to the LGM and date the last formation of the Bering Land Bridge to ~36,000 years ago. These results require much higher global mean sea level prior to the LGM than previously thought, and limit the duration over which the land bridge was available for terrestrial migrations. I will also discuss two continuing research directions: An extension of the nitrogen isotope approach through the Late Pleistocene, and corroborating evidence for a late land bridge formation from terrestrial paleogenomics.
