Geochemical and Sedimentological Proxies for the Extent of the Greenland Ice Sheet During the Penultimate Interglacial

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 (Pb-Sr-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, 135-117 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 (135-125 ka) has an ɛNd signature consistent with an Archean province (ɛNd ~- 20) that is likely derived from the southern Greenland Archean block (~64 °N), whereas sediment from 125-117 ka have ɛNd values of -15. The Sr-Nd-Pb isotope signature of sediment from 125- 117 ka are consistent with a sediment source of Proterozoic or younger affinity. This period of terrestrial sediment flux corresponds with the +6 m sea level high stand suggesting that the greatest GIS retreat occurred between 125-117 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 3.5-4.5 m sea level contribution from the GIS to the +6 m sea level high stand. This sustained freshwater flux may have reduced the surface density of the Labrador Sea, explaining the lack of Labrador Sea deepwater formation during this interglacial. Further Pb-Sr-Nd-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 to MD99-2227, helping untangle the relative proportions of Archean and Proterozoic sediment and thus the aerial extent of the GIS during TII.