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North-Central Section - 43rd Annual Meeting (2-3 April 2009)

Paper No. 4
Presentation Time: 9:00 AM

GEOCHEMICAL AND SEDIMENTOLOGICAL PROXIES FOR THE EXTENT OF THE GREENLAND ICE SHEET DURING THE PENULTIMATE INTERGLACIAL


COLVILLE, Elizabeth, Geology & Geophysics, University of Wisconsin-Madison, 1215 W Dayton St, Madison, WI 53706, CARLSON, Anders, Geology & Geophysics, University of Wisconsin-Madison, 1215 W. Dayton St, Madison, WI 53706, BEARD, Brian, Department of Geoscience, University of Wisconsin-Madison, NASA Astrobiology Institute, 1215 W. Dayton St, Madison, WI 53706, STONER, Joseph, College of Oceanic & Atmospheric Sciences, Oregon State University, Oregon State University, 104 COAS Administration Building, Corvallis, OR 97331 and HILLAIRE-MARCEL, Claude, Geotop, Université du Québec à Montréal, C.P. 8888, succ. Centre-Ville, Montréal, QC H3C 3P8, Canada, colville@geology.wisc.edu

The greatest uncertainty for future sea level rise is the contribution from the Greenland Ice Sheet (GIS) due to limited understanding of GIS sensitivity to a warming climate. To better understand GIS climate sensitivity, we present new geochemical (Nd isotopes) and sedimentological data (% silt) from sediment core MD99-2227 (58°12.64'N, 48°22.38'W, 3460 m of water depth) located on the Eirik Drift. Prior work indicates that this site records the sedimentological record of GIS deglaciation. With our new data, we provide constraints on the aerial extent of the southern GIS during the last (TI, 21-7 ka) and penultimate (TII, 135-118 ka) deglaciations and subsequent interglacials. The % silt record suggests a significantly longer period of terrestrial sediment input during TII than TI (18 kyr vs. 5 kyr) in agreement with prior Ti, Fe and magnetic records. During TII, the radiogenic isotope records indicate that the earlier part of this sediment input (137-128 ka) has an εNd signature consistent with input of sediment with a significant Archean province (εNd ~- 20) that is likely derived from the southern Greenland Archean block (~64 °N), whereas sediment from 127-118 ka have εNd values of ~-15. The Nd isotope signature of sediment from 125- 117 ka are consistent with an enhanced sediment supply of Proterozoic or younger affinity sources. This period of terrestrial sediment flux corresponds with the +6 m sea level high stand suggesting that the greatest GIS retreat occurred between 127-118 ka. If this younger sediment was derived from the Proterozoic Central Nagssugtoqidian Orogenic Belt (~67.5 °N), then the sediment data are consistent with ice sheet models that suggest a 3.9-4.8 m sea level contribution from the GIS to the +6 m sea level high stand. This sustained freshwater flux from Greenland may have reduced the surface density of the Labrador Sea, explaining the lack of Labrador Sea Water formation during this interglacial. Further Nd-isotope analyses combined with Sr and Pb isotope analyses of the silt fraction of suspended load sediment from Greenland streams will provide new end-member data that will aid in deciphering the provenance of the sediment.

Session No. 3

T5. Climate Change
Thursday, 2 April 2009: 8:00 AM-12:00 PM
Geological Society of America Abstracts with Programs. Vol 41, No. 4, p.7
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