Extent of the southern Greenland Ice Sheet during the Last and Penultimate Interglacials

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 sedimentological data (% silt & % sand) and geochemical (Nd-Sr-Pb isotopes) from the silt fraction of 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 archives 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 enhanced accumulation of the % silt record suggests a significantly longer period of terrestrial sediment input during TII than TI (17 kyr vs. 5 kyr) in agreement with prior Ti, Fe, and magnetic records. Our TI Sr-Nd-Pb isotope records indicate that the terrestrial sediment pulses are derived from the southern Greenland Ketilidian, Archean and Nagssugtoqidian terranes, with enhanced Western Boundary Under Current deposition occurring during the mid-Holocene. This conclusion is supported by low ɛNd values and relatively non-radiogenic 87Sr/86Sr ratios during the mid-Holocene as compared to sediments from 12-9 ka. During TII, the radiogenic isotope records show that the sediments from 135-128 ka were also likely sourced from the southern Greenland Ketilidian, Archean and Nagssugtoqidian blocks as defined by the very negative ɛNd values (~-19.6) with an absence of material that was derived from sources brought in by the WUBC based on the sediment samples relatively high 87Sr/86Sr ratios. In contrast, sediments from 128-118 ka have less negative ɛNd values (~-14.1) consistent with an enhanced supply of Proterozoic or younger affinity sources, likely from the Ketilidian block of southern-most Greenland. This variation in the sediment sources suggests that the Nagssugtoqidian and Archean blocks were predominately ice free by ~128 ka and therefore not contributing sediment with only an ice cap remaining over the southern Ketilidian province, in agreement with recent data for reduced ice-cover and enhanced vegetation cover over southern Greenland during Marine Isotopic Stage 5e. The period of enhanced sediment flux 128-118 ka corresponds with the +6 m sea level high stand. With an ice cap remaining only on the southern tip of Greenland, our 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.