Air-sea temperature decoupling in western Europe during the last interglacial-glacial transition

A period of continental ice growth between about 80,000 and 70,000 years ago was controlled by a decrease in summer insolation, and was among the four largest ice expansions of the past 250,000 years1. The moisture source for this ice sheet expansion, known as the Marine Isotope Stage (MIS) 5a/4 transition, has been proposed to be the warm subpolar and northern subtropical Atlantic Ocean(1,2). However, the mechanism by which glaciers kept growing through three suborbital cooling events within this period, which were associated with iceberg discharge in the North Atlantic(3,4) and cooling over Greenland(5,6), is unclear. Here we reconstruct parallel records of sea surface and air temperatures from marine microfossil and pollen data, respectively, from two sediment cores collected within the northern subtropical gyre. The thermal gradient between the cold air and warmer sea increased throughout the MIS5a/4 transition, and was marked by three intervals of even more pronounced thermal gradients associated with the C20, C19 and C18' cold events. We argue that the warm ocean surface along the western European margin provided a source of moisture that was transported, through northward-tracking storms, to feed ice sheets in colder Greenland, northern Europe and the Arctic.