Interglacial Surface Ocean Temperatures Reveal Strong Ocean-Atmosphere Linkages Between the Subtropical and Subpolar Regions

Investigating ocean-atmospheric processes of past interglaciations may provide a better understanding of the climatic development of the present warm period. Here we present a detailed reconstruction of the meridional sea surface temperature (SST) across MIS 11 using three sites: ODP 958 (off NW Africa), ODP 975 (western Mediterranean Sea) and M23414 (subpolar NE Atlantic). Sea surface temperatures (SST) were derived from foraminiferal assemblages and alkenones, further supported by planktic and benthic O-isotope records as well as by iron content, the latter as indicator for Saharan dust export and continental dryness. On a large scale, reconstructed SSTs reveal a close synchronism of environmental changes between all three sites. It shows that, before full interglacial conditions became established, there was a long-lasting, glacial- interglacial transition with a total temperature increase of about 10°C in the subtropical as well as in the subpolar North Atlantic. After the main glacial-interglacial transition was over, SSTs continued to rise and reached their maximum during, what could be considered, the upper main phase of high sea-level stand in MIS 11. In the western Mediterranean SSTs show several cooling events with amplitudes of up to 4°C during the early full-interglacial warm period. Off NW Africa this phase is characterized by rather humid conditions, as inferred from strongly decreased values of iron in the sediments, and successive changes in the foraminiferal assemblages. We assume that these rather wet conditions at the lower latitudes were related to an intensification of the West African monsoon that increased summer moisture flux over Northwest Africa and runoff into the Mediterranean. At the same time increased abundance of subtropical, deep- dwelling foraminiferal species are found in the subpolar region implying a strong linkage between the subtropical atmospheric circulation regime over NW Africa and the northward propagation, of relatively warm water masses from the south. The demise of peak interglacial conditions was associated at all sites with a progressive surface ocean cooling, altogether indicating a remarkable good coherency of the overall climate development within this North Atlantic sector during MIS 11.

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