Greenland Deglaciation


The response of the Greenland Ice Sheet to present and future global warming is of significant concern as it has the capacity to raise sea level ~7 m if it entirely melted. The observational history of the Greenland Ice Sheet (GIS) is limited, however, to only the last several decades, requiring other methods for determining the sensitivity of this ice sheet to a warming climate. An alternative method for determining ice sheet sensitivity to climate change is to examine the response of ice sheets to past climate changes. Interglacial periods provide an opportunity to test the sensitivity of the GIS to climates warmer than present. Initial results from marine sediments indicate a substantial response associated with previous glacial terminations and subsequent interglacials (Fig .1).

Magnetic grain size and concentration records from piston core MD99-2227 taken on the Eirik Drift show that records extending back ~430 ka show increased magnetic grain size (lower kARM/k values) and concentration during the last 5 deglaciations (Fig. 1). Detailed study of these intervals over the last two terminations shows that this magnetic signature is not related to IRD, but rather reflects changes of the fine fraction that is hypothesized as a provenance signature of southern GIS deglaciation. The MD99-2227 magnetic records indicate that Marine Isotope Stage (MIS) 11, a prolonged interglacial from 420 to 400 ka represents the longest period of elevated sediment input presumably from the GIS for the last 430 kyrs implying significant GIS retreat (Fig. 2).

A significant missing component in paleo-reconstructions of GIS behavior has been the lack of an unambiguous ice sheet tracer. The development of such a tracer for GIS retreat and aerial extent is proposed using terrigenous provenance markers and the different bedrock terrane ages of southern Greenland (Archean versus varying Proterozoic ages). Specifically, streams are being sampled for suspended load sediment from the geologic terranes of southern Greenland. Suspended load sediments are being measured for trace-element and Sr-Nd-Pb isotope composition at the University of Wisconsin, and for magnetic properties at OSU. These data will be compared with sediment core data off of southern Greenland (Fig. 1) to help constrain the climate sensitivity of the southern GIS.

Figure 1. MD99-2227 magnetic record for the last 430 ka. From top to bottom: Relative magnetic grain size (purple) where smaller kARM/k values are coarser magnetic grain sizes (Evans et al., 2007); Planktonic δ18O (blue); benthic δ18O stack (Lisiecki and Raymo, 2005) scaled to sea level (Carlson, 2008); and June insolation at 60º N (red) (Berger and Loutre, 1991). Gray bars denote periods of increased magnetic grain size during interglacials.

Figure 2. Southern Greenland bedrock map. Inset shows location of the map (box). Geologic terranes are delimited along with MIS 5e GIS ice margins. Black dots denote field-sampling locations.