Sea-surface temperature variability and deep water reorganisation in the subtropical North Atlantic during Isotope Stage 2–4
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Two sediment cores from a high-accumulation sediment drift at similar to 3000-m water depth in the western North Atlantic are investigated in order to examine possible linkages between subtropical surface and bottom water properties, and global climate oscillations during the last glacial-interglacial cycle. Planktonic foraminiferal assemblages and the delta(18)O of Globigerinoides ruber both document large sea-surface temperature oscillations (3-4degreesC) that appear to co-vary with Greenland ice core records. Short episodes of sea-surface cooling as far south as the Blake Outer Ridge at similar to 33degreesN are inferred from increased abundance of the polar species Neogloboquadrina pachyderma sinistral during the ice core stadials events. Nutrient proxy records suggest that the deep waters flooding the site alternated between a northern (North Atlantic Deep Water) and a southern (Southern Ocean Water) source. In most cases, warm surface water conditions (interstadials) were accompanied by a strong North Atlantic Deep Water component in the bottom water circulation. However, the transitions into Interstadial 14 and 12 seem to be marked by a similar to 1500-yr lag between surface water warming, and the deep water circulation shift, as recorded by %CaCO3 and delta(13)C of benthonic foraminifera. (C) 2002 Elsevier Science B.V. All rights reserved.