Collaborative Research: Ice sheet sensitivity in a changing Arctic system - using geologic data and modeling to test the stable Greenland Ice Sheet hypothesis

DESCRIPTION: There is enough water in the Greenland Ice Sheet (GrIS) that, were it to melt, it would raise sea level in most coastal cities significantly with huge consequences for society. In the face of accelerated ice sheet contribution to sea level rise, it remains uncertain how the GrIS will adjust to a warming Arctic, declining sea ice and related changing precipitation patterns. This is a concern, given that future sea level rise is strongly dependent on the GrIS response to arctic change. The scientific community is currently undecided between a model of a dynamic GrIS that becomes greatly reduced during warm periods and a model where it is relatively stable, even through periods warmer than today. This proposal addresses the idea that increased arctic precipitation offsets GrIS mass loss during times of elevated temperature. The researchers will test this by contributing significant new information on arctic system change and related GrIS dynamics during past and ongoing warm periods, and employing an ice sheet modeling effort synthesizing all new data aimed at both past and future GrIS simulations. The researchers explicitly combine multiple scientific disciplines to provide a better understanding of how key arctic system components such as precipitation, temperature, sea-ice cover and GrIS mass balance are interconnected. The results will be of fundamental relevance to the fates of the arctic system, the GrIS and global sea level rise. This project will train six graduate students and one post-doctoral researcher. The cross-cutting research program is paralleled by the scope of the outreach plan, to develop a variety of deliverables, including development of an iBook and public outreach events. In addition the team will participate in public outreach events in Buffalo and New York City, where the public and scientists interact in a casual setting. Finally, this work has synergies with ongoing missions at NASA and other programs within the NSF. Technical: Due to recent advances in numerical ice sheet models and new sub-ice topography of Greenland, combined with finely-tuned field approaches and geochronologic techniques, the time is ripe for a coordinated, cross-disciplinary effort focusing on cryosphere variability in a warming Arctic; the Greenland Ice Sheet (GrIS) and sea ice constitute the largest, and most critical components of the arctic cryosphere. The hypothesis that increased arctic precipitation can counterbalance GrIS mass loss during times of elevated temperatures stems from recent findings suggesting that it may be more stable than expected during interglacials. The researchers will: generate new GrIS margin reconstructions during and since the mid-Holocene Thermal Maximum (9,000 to 5,000 years ago), with a powerful approach that combines lake sediment stratigraphy with new sub-ice topography and novel high-sensitivity cosmogenic isotope methods; develop new Holocene climate reconstructions of moisture, temperature and sea ice conditions from lake and ocean sediments and an advanced synthesis of existing arctic ice core and other paleoclimate data; and employ state-of-the-art numerical ice sheet modeling fueled by ice margin and climate reconstructions to test a range of climatic and dynamic controls on GrIS change. If the idea is supported, then it would suggest a relatively stable GrIS during warm periods. If, however, this project provides evidence that the GrIS retreated considerably during the warmer-than-present mid-Holocene and in turn, that the GrIS has reacted more sensitively to temperature than to precipitation change, the results would support a tightly coupled ice sheet size-temperature link and in turn, a much greater near-term GrIS contribution to sea level rise. Either result will be of fundamental relevance to the fates of the arctic system, the GrIS and global sea level rise.