Marine Isotope Stage 11 (MIS 11): Analog for Holocene and future climate?

Pleistocene interglacials are often considered to be possible geological analogs for the climatic development of the Holocene epoch. Marine isotope stage 11 (MIS 11), a prominent interglacial 400 ky ago, is of particular interest because of the similarity between orbitally driven insolation variations then and now. We have examined the record of climatic conditions during MIS 11 at two locations on rapidly accumulating sediment drifts in the North Atlantic, and made a comparison with global records in order to assess the duration, stability, and amplitude of the interglacial. Deep-sea cores from ODP Sites 980 and 983 have sedimentation rates in excess of 10 cm/kyr, and have been sampled at 2-3 cm intervals, yielding century-scale resolution of millennial-scale variability. We used stable isotopes of oxygen in foraminifera to assess climatic and hydrographic conditions at the sea surface and in the deep ocean. Different age models were evaluated, including one tuned to orbital insolation variations and one based on a constant accumulation model. These chronologies indicate that the relatively ice-free portion of MIS 11 lasted longer than other peak interglacials. Sea surface warmth in the subpolar North Atlantic lasted even longer, a minimum of 30 kyr. Throughout this interval, oxygen isotope ratios in Neogloboquadrina pachyderma (dextral), a proxy for sea-surface temperature (SST), did not vary more than 0.25 per mil, or ∼1°C, from the long-term mean. This is in strong contrast to the large temperature oscillations in the subsequent glaciation, MIS 10. During both the interglacial and glacial, a gradient in planktonic oxygen isotope ratios was maintained between the two sites, counter to the modern salinity-driven gradient in seawater oxygen isotope ratios, and therefore consistent with a persistent similar N-S temperature gradient. Oxygen isotope ratios recorded during MIS 11 in both planktonic and benthic foraminifera are similar to values that characterize the Holocene. Thus ice-volume (sea-level), ocean temperature, local salinity, and the isotopic composition of ice sheets were similar, in sum, to today. Any departure from the modern values in one of these climate components would have had to be compensated by some combination of the others. We conclude that the elapsed portion of the Holocene has been similar to MIS 11 in mean climate state and degree of stability, without nearly approaching its duration. Both the forcing and response of climate during MIS 11 appear to be appropriate analogs for the natural development of recent and future climate.