Collaborative Research: The fingerprint of abrupt temperature events throughout Greenland during the last glacial period

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The Atlantic Meridional Overturning Circulation (or AMOC) is an important part of the global three-dimensional ocean circulation (global ocean conveyor belt) that includes the well-known, northward-flowing Gulf Stream current that redistributes heat and thereby affects climate. The AMOC is expected to weaken or even collapse in the coming centuries, with several recent studies suggesting that this weakening has already begun. The AMOC collapse would not only severely impact climate in the North Atlantic region but would also weaken the monsoon rains that a large portion of the global population depends on for their livelihood. Studying ice cores can shed light on past changes in the strength of the AMOC and can help scientists better understand the stability and behavior of this important ocean circulation system. Greenland ice cores and ocean sediment records show that during the last Ice Age (100,000 to 20,000 years ago) the AMOC repeatedly collapsed and restarted, resulting in a series of extreme climate oscillations commonly known as Dansgaard-Oeschger (D-O) cycles. Each D-O event consists of an abrupt (decadal-scale) warming episode (increase of 8-15 degrees Centigrade) observed in Greenland ice cores, leading to a few millennia of warmer climate followed by a gradual cooling back to full glacial conditions. The proposed research will develop temperature records from two Greenland ice cores to determine both the geographic distribution as well as the intensity of the D-O events throughout Greenland. These records will provide a spatial ?fingerprint? of the D-O events, which can be used a forensic tool to determine the location of D-O warming and the migration of the sea-ice edge around Greenland during these events. These data will be included in climate simulations using state-of-the-art global climate models to improve our understanding of the physical nature of these enigmatic events. The research will contribute to reliable timescales for the two ice cores, with benefits to the wider ice core community. The work will support an early-career scientist and a graduate student and will also provide outreach to public schools. Understanding the physical processes that drive the Earth?s climate system throughout a Dansgaard-Oeschger (D-O) event remains an important open scientific question in paleoclimate research. The spatial pattern of D-O warming holds clues to the origin of D-O events, in particular whether the critical geographic area is located in the Labrador Sea or in the GIN (Greenland, Iceland, Norwegian) seas. Ultra-high-resolution stable isotope records from these ice cores document changes in the hydrological cycle associated with these abrupt warming episodes. Climate models show that the southern Dye-3 ice core is more sensitive to abrupt climate change than previously analyzed ice cores, giving the possibility of observing for the first time the temperature imprint of a Heinrich event (a natural phenomenon in which large armadas of icebergs break off from glaciers and traverse the North Atlantic Ocean), as well as the largest D-O warmings ever observed. Isotope enabled climate model simulations will provide improved interpretation of changes in second-order isotope parameters (deuterium- and 17O excess) through D-O and Heinrich-events.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.