Ice Extent and Late Glacial and Deglacial History of W. Hunafloi, NW Iceland: Combining Terrestrial and Marine Evidence

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ABSTRACTOPP-0004233AndrewsThe late Quaternary extent and thickness of ice and the deglacial chronology of the Northwest Peninsula of Iceland are poorly constrained. The Principal Investigators will conduct a collaborative research project on the glacial and deglacial history of the western coastline and uplands of western Hunafloi, NW Iceland, and the adjacent marine trough, Hunafloaall. The proposal builds on marine cruises in 1996, 1997 and 1999, and on a pilot field program conducted in the summer of 2000. The purpose of the project is to resolve the late Quaternary glacial history of part of NW Iceland and to correlate the terrestrial record with the marine record. This research will add new insight into the glacial history of marine arctic margins and a very old debate on biological "refugia."At least two models for the reconstruction of glacial extent during the Lower Glacial Maximum (LGM) and subsequent retreat have been suggested for Iceland, but these are based on only limited radiocarbon dates. In the NW Peninsula, the glacial reconstructions vary from an extensive ice cover model with no ice free areas to a refugia model in which ice free areas existed on the high plateaus with vascular plants surviving glaciation. These studies are based entirely on terrestrial glacial evidence and interpretations, but this must be intimately linked to the offshore sedimentary record of glacial and marine sediments. High-resolution 3.5 kHz acoustic stratigraphy and marine cores from the Hunafloaall trough suggest that the LGM extent may have been relatively restricted. In Hunafloaall, a basal dimicton containing foraminifera, is overlain by a thin (2 m) sequence of IRD-rich glacial-marine and marine sediments. Basal dates on the IRD-rich muds indicate deglaciation occurred by 13 thousand years ago (ka). Dates from the dimictons are finite and 20 ka. Such a thin deglacial sequence provides a major contrast with SW Iceland where the deglacial sediments reach thickness of 10-40+ m. The virtual absence of deglacial sediments in Hunafloaall is perplexing and raises serious questions of ice extent and chronology on the adjacent NW Peninsula.Cosmogenic isotope exposure dating techniques will be used to constrain "maximum" and "minimum" models of glacial extent. Specifically, 3He and 36CI isotopes will be used to date the basaltic upland surfaces, end and lateral moraines, and glacial erratics. Tephrachronology and physical properties of the sediment samples will be used to link the terrestrial and marine records. The Principal Investigators will continue their field and laboratory investigations on: 1) the vertical and lateral extent of glaciation along this coastline, including collection of samples for cosmogenic isotope exposure dating; 2) the pattern and timing of deglaciation and any subsequent glacier expansion; 3) investigation of the marine cores with the view toward discriminating between tills and glacial marine dimictons, and with a focus on more accurately dating the onset of deglaciation; and 4) changes in relative sea level as a measure of ice load and history. The field work will continue and expand a pilot program that began in summer of 2000, involving the Universities of Colorado, Iceland, Goteborg, and Edinburgh.