Sr-Nd-Pb Isotope Composition of Eirik Drift Silt as a Proxy for South Greenland Ice Sheet Retreat during the Last Five Interglaciations

Proxy-based approaches are needed for reconstructing the Greenland Ice Sheet response to interglacial climate change because direct geological evidence for past ice extent is lacking and model-based estimates of ice-sheet retreat often disagree. We use the Sr-Nd-Pb isotope composition of silt in a core (MD99-2227) from the Eirik Drift off south Greenland as a proxy for the presence/absence of the ice sheet on south Greenland's bedrock terranes. Silt discharged in glacial meltwater streams is transported by ocean currents to Eirik Drift. If a given terrane is deglaciated during an interglaciation, then its isotopic signature will be absent in Eirik Drift sediment. We will present complete Sr-Nd-Pb isotope composition of silts from Marine Isotope Stages (MIS) 11, 9 and 7 from the Eirik Drift. Together with existing isotope data from MIS 5e and 1, we will estimate the magnitude of ice-sheet retreat during the last five interglaciations. The isotopic composition of over thirty MIS 11 silt samples from MD99-2227 suggest that south Greenland may have been largely deglaciated during this interval. In particular, high ɛ_Nd values and low ⁸⁷Sr/⁸⁶Sr during MIS 11 diverge from the isotope composition of Greenlandic Precambrian bedrock, evidence that there was little or no glacial erosion supplying source material ultimately transported to the core site. Isotopic mixing models suggest that MIS 11 silt contribution from south Greenland's Precambrian bedrock terranes decreased by a factor of three or four relative to the MIS 5e interglaciation, when we infer that none of the Greenlandic terranes were completely deglaciated. During MIS 9, ⁸⁷Sr/⁸⁶Sr and ɛ_Nd attain values that are intermediate to the isotope composition of MIS 11 and 5e silt, which may suggest decreased contribution of Greenlandic sediment relative to MIS 5e.