Collaborative Research: Holocene glacier length variations along the spine of the American Cordilleras and their climatic significance

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The worldwide retreat of glaciers over the past century is one of the clearest signals of global warming, but it raises two basic questions that remain hazy: how anomalous are current glacier extents, and what were long-term glacier trends prior to the industrial era? This project will reconstruct how often during the Holocene (the last 11,000 years) a dozen glaciers down the length of the Americas, from the Arctic to Patagonia, were larger versus smaller than today. We take a community-based approach to reduce cost, with active glacier scientists collecting samples gratis during their own field campaigns to contribute to this project. Our results will provide a geologic lens through which to view modern climate change, and offer a paleo-test for computer models used to simulate glacier responses to future warming -- important to freshwater resources in some areas and global sea level rise. We will reconstruct glacier histories by applying the in situ 14C-10Be chronometer to several samples of proglacial bedrock at each glacier terminus. This technique is able to determine what portion of the Holocene a glacier advanced beyond and retreated behind its current terminus by quantifying the buildup of both 14C and 10Be during periods of exposure and the preferential loss of 14C during episodes of ice cover due to its much shorter half-life. Our latitudinal transect is designed to maximize understanding of how glaciers responded to orbital variations, as well as how climate may have been coupled between the low and high latitudes and across the hemispheres. Given that Holocene glacier trends may have varied substantially with latitude, the broad scale of our reconstructions will also provide the context needed for evaluating current glacier retreat around the world.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.