Atmospheric forcing of increased thermohaline overturning in the North Atlantic during the late Holocene
G. Bond, W. Showers, T. Marchitto, J. Lynch-Stieglitz, S. Hoffmann
Talk presented at 2001 Fall AGU
Abstract. New evidence from a series of fresh, high quality cores in the subpolar North
Atlantic suggests that the production of North Atlantic Deep Water (NADW) has
not been stable during the last few thousand years of the Holocene. Both benthic
carbon isotopic and cadmium:calcium ratios document a steady increase in NADW
production at the same time that sea surface temperatures fell and ice rafting
increased. The change in the deep water nutrient proxies is accompanied by higher
benthic oxygen isotope ratios, indicating a shift to denser (colder?) deep water at
the same time. We interpret this seemingly paradoxical increase in rate of NADW
production with deteriorating climate as a consequence of high northern latitude
atmospheric cooling during the Neoglacial episode of the mid to late Holocene. We
suggest that the cooling led to an increase in convection in the Greenland -
Norwegian Seas and subsequent increase in the cold and dense overflows that
feed NADW. We regard our findings as strong evidence that change in NADW
production during the late Holocene was forced by the atmosphere rather than by
mechanisms operating within the ocean. The change in North Atlantic deep
circulation has no consistent relation to the millennial-scale cyclicity that has been
recognized previously within the Holocene; if the North Atlantic's deep circulation
was altered during those events, it is masked in our records by the more prominent
longer term change tied to the atmospheric forcing.
Evolution of the North Atlantic’s climate over the last 3000 years and comparison with late MIS 5e
G. Bond, J. Lynch-Stieglitz, T. Marchitto
Project funded by NSF Earth Systems History program, 2001-2003
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