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Display sedimentary (231)Pa/(230)Th ratios the strength of Atlantic deep water circulation? An approach for the past 30,000 years

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Lippold, J. , Christl, M. , Gruetzner, J. , Lahaye, M. , Winter, D. and Mangini, A. (2008): Display sedimentary (231)Pa/(230)Th ratios the strength of Atlantic deep water circulation? An approach for the past 30,000 years , Goldschmidt Conference, Vancouver .
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Abstract:

The applicability of 231Pa/230Th as a tracer for the Atlantic Meridional Overturning Circulation (AMOC) is still a great matter of discussion. Recently published results from the Bermuda Rise [1] challenged the idea of interpreting high 231Pa/230Th ratios as reduced AMOC during cold events like Younger Dryas or Heinrich-1 [2]. Although the effect of particle flux and particle composition has been studied and modelled in detail [3][4], there are still significant gaps in both our understanding of this proxy and in the spatial coverage of downcore 231Pa/230Th data. Applying ICP-MS and (newly) low energy AMS [5], we measured 231Pa/230Th profiles along a transect from the North-(ODP 983), to the West- (ODP 1063) and South-(ODP 1089)Atlantic Ocean covering the past 30,000 yr. During Heinrich-Events 1 and 2, ODP 1063 reveals high 231Pa/230Th, but also high diatom abundances. ODP 983 displays extreme holocene 231Pa/230Th values during times of vigorous AMOC accompanied by increased diatom appearance, too. This qualitative concordance of 231Pa/230Th and diatom abundance may point to the conclusion that high 231Pa/230Th are not solely caused by diminished AMOC but also may be influenced by a change of the prevailing water mass (e. g. the injection of southern and silicate rich waters to the North-Atlantic). The Southern Atlantic Site (ODP 1089), in contrast, remained under the influence of 231Pa-depleted Antarctic Bottom Waters reflected by constantly low 231Pa/230Th ratios below the production ratio of 0.093.

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