DOI: 10.18739/a2ms3k306
title: Marine Test of the Sensitivity of Ice Streams Entering Baffin Bay to Ocean Warming from LGM through Deglaciation, with an Emphasis on Central West Greenland Ice Streams

description: The proposed research will evaluate how ocean warming contributed to past ice sheet dynamics through study of the Last Glacial Maximum (LGM) through early Holocene behavior of ice streams draining into Baffin Bay. This research will provide a new context for understanding ice sheet response to past warm periods, in particular, the Bølling/Allerod interstadial period, which hosted rapid sea level rise and abrupt climate warming after the LGM. At the LGM the Greenland Ice Sheet (GrIS) was one of three large ice sheets terminating via large, fast flowing ice streams into Baffin Bay. This project will study the past history, dynamics, and ice-sheet ocean interactions in Baffin Bay, and the role of ocean warming in ice sheet demise, via multi-proxy analysis of existing (2008 and 2009) sediment cores from the West Greenland continental slope. Data from this proposal will be used to model freshwater flux from the ice streams, and will provide new information on what role the Greenland Ice Sheet played in past sea-level rise as the LGM ice sheet began to shed as much as 4.6 m of sea level equivalent. The research will test three hypotheses using foraminiferal faunas, sediment mineralogy, stable isotope analyses, stratigraphy of iceberg rafted detritus (IRD), and visible diffuse spectral reflectance data: 1. The western margin of the GrIS advanced during stadials and retreated during interstadials in response to the presence or absence of ocean warming via the West Greenland Current. 2. Peaks of ice-berg rafted material (IRD) result from two distinct processes: Proximal IRD is derived from retreat of the GIS off the shelf edge, whereas distal IRD results from collapse of the Laurentide Ice Sheet and Innutian Ice Sheet/NW Greenland margins in northern Baffin Bay. 3. Advection of warm water along the West Greenland margin causes enhanced melting of northern Baffin Bay icebergs and sea ice at the polar front, forming an IRD belt along the W. Greenland margin, which preserves a record of ice sheet-discharge events under conditions of ocean warming. The GrIS is losing mass in response to modern warming. It stores enough fresh water to raise global sea level by 6.5 m, making its sensitivity to warming a major societal concern. It is anticipated that the sensitivity and response of the GrIS to past warming, which are the foci of this project, will help constrain projections of the future evolution of the GrIS. Intellectual Merit: The Principal Investigators will reconstruct the Late Quaternary-Holocene behavior of Jakobshavns Isbrae (JAKIB) in western Greenland, one of the largest ice streams draining the modern Greenland Ice Sheet (GrIS). The period from the Last Glacial Maximum (LGM) to the present will be studied because it involves the most recent large scale change in the mass-balance of the ice sheet, it is the period that will be best preserved in continental shelf sediments, and it is the period for which the highest resolution proxy records of paleo-climate from the Greenland ice cores are available. Given the scale of this ice stream and the size of its associated drainage basin, the investigation will provide information on the Late-Quaternary-Holocene behavior and stability of a major area of the GrIS. This research will allow assessment of the links between deglaciation and internal and external environmental controls, such as the influence of inflowing Atlantic Water, and will facilitate modeling of the likely future behavior of the GrIS. The Principal Investigators will participate in a research cruise of the British Research Vessel, Sir James Clark Ross, to West Greenland in the late summer of 2007 and collaborate with British colleagues on the post-cruise, interdisciplinary program of laboratory work and modeling. Well-dated, high-resolution sediment records from a transect of sites extending from the shelf edge and along the shelf trough, to sites within Disko Bugt both proximal and distal to the modern ice margin will be acquired on the basis of geophysical data. The hypotheses to test using these cores are: Hypothesis 1: Glacier ice extent and interactions between the West Greenland Current and the GIS are recorded in the foraminiferal faunas, mineralogical variations, and Sm and Nd isotopic compositions of the sediments. Hypothesis 2: The West Greenland Current has changed in strength, flowpath and watermass composition from the LGM through the Holocene. These variations have played and continue to play a key role in ice-sheet behavior. Broader Impacts: The underlying rationale for this research is to determine if recent (last ~ 100 yr) observed changes to the mass balance of the GrIS reflect natural variability in ice sheet dynamics, or if they relate to anthropogenically-induced climate warming. Key to resolving this is an understanding of ice sheet behavior since the LGM and including periods in the past near Greenland that were as warm or, even warmer than today, such as the middle Holocene optimum. This research will make new discoveries concerning the timing and extent of the Greenland Ice Sheet at the LGM on its western margin, and the behavior of the JAKIB ice stream during deglaciation, new information that will inform paleoceanographers and climate and sea-level modelers. This project is an international effort. It will support a U.S. PhD student, and two undergraduate students. It will involve international student exchanges between the University of Colorado and the United Kingdom. The data acquired will be lodged in the NOAA Paleoclimate Database. CORES: 2008-070CC - 68.228N -57.618W JR175-VC20 - 68.201N -57.756W JR175-VC35 - 67.701N -59.342W