OCEAN CIRCULATION AND CLIMATE DURING THE STAGE 11 INTERGLACIAL INTERVAL

The Marine Isotope Stage 11 (MIS 11), an interglacial of 400ka is the period in the Pleistocene most similar to the Holocene in climate forcing by insolation and naturally occurring greenhouse gases and thus can be studied as an analog for the present and future climate. This project is a high-resolution analysis of the Stage 11 interglacial using a marine sediment core from ODP Site 984 on the Reykjanes Ridge in the North Atlantic. A multi-proxy approach is used to investigate the ‘super’ interglacial climate and ocean circulation of 400ka. The ice-rafting debris and sortable silt records from this period both demonstrate millennial scale variability, as in the Holocene. The sortable silt data indicate that thermohaline circulation varied in a similar fashion during Stage 11 as in the Holocene. These results suggest the existence of a persistent internal mode of variability in the ocean circulation-climate system. The ice-rafted debris levels in Stage 11 allow for the possibility of a diminished Greenland ice sheet, particularly late in the progression of the interglacial, beyond the elapsed duration of the Holocene. A glacial amplifier with a 18O threshold value of 3.5 per mil emerges from the paired IRD and isotope data, as do lower frequency circulation cycles from the sortable silt mean signal. An estimate of 16,500 –22,000 years for the duration of Stage 11 interglacial suggests that if these two similarly forced interglacials follow similar trajectories, the Holocene interglacial warmth would naturally continue many thousands of years into the future in the absence of anthropogenic perturbation.