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A variable Holocene climate has been shown for most global regions. In the Atlantic region ocean circulation has been proposed as one major factor involved in these climate fluctuations. Changes in the Atlantic ocean-circulation have the potential to alter the heat budget between the hemispheres and to amplify the effect of other climate forcing factors. Here we present a multi proxy study of lake sediments from Nightingale Island, situated in the Tristan da Cunha island group in the central South Atlantic, which displays a highly variable climate during the Holocene. Almost 10 m of sediments were retrieved from an overgrown lake. The cored sequence comprises 1 m of peat overlain by 8 m of lacustrine sediments with peat on top, and shows a high degree of variability in terms of lithology, geochemistry and pollen composition. More than 50 radiocarbon dates, mainly from terrestrial macro-fossils, form the basis of the chronology. The bottom of the sequence is dated to c. 10.7 kyr BP. At around 8.7 kyr BP a significant hydrological shift changed the local environment from a fen to a lake, which is clearly seen as a transition from peat to gyttja. This hydrological shift was probably caused by a northward displacement and possibly also intensification of the westerlies following the Holocene thermal optimum in Antarctica. The lake sediments following this transition are exceptionally rich in organic matter with recurrent short periods with higher minerogenic content. Such periods also have elevated C/N ratios and higher percentages of pollen taxa of upland-type as well as decreased sulphur content and less local bog/aquatic pollen types. These periods were most likely the result of increased surface run-off caused by higher precipitation, which brought minerogenic matter and terrestrial organic matter, and more pollen from the catchment vegetation to the lake. One of these high precipitation periods coincides with the Northern Hemisphere 8.2 kyr event. Coupled atmosphere-ocean model simulations of this assumed glacially triggered fresh-water pulse in the Labrador Sea have shown an almost immediate response in the Tristan da Cunha region; dwindling thermohaline circulation (THC) in the north increases sea surface temperatures (SST) in the central South Atlantic resulting in increased air humidity and precipitation. The proxy signature of the assumed response of the 8.2 kyr event on Nightingale Island is more or less identical to at least six other phases, which would imply that all the high precipitation periods were triggered by increased SSTs. Periods of increased precipitation, but with a different signature, can also be seen in the bottom peat. All these high precipitation periods, assumed to have been caused by high SSTs, are fairly well correlated to periods of increased IRD and weaker THC in the North Atlantic, especially before 4 kyr BP, implying a bipolar seesaw mechanism in action in the Atlantic Ocean during the Holocene.
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