Publication Date:
2012-02-23
Description:
We determined the isotopic composition of neodymium (Nd), lead (Pb) and beryllium (Be) of past seawater to reconstruct water mass exchange and erosional input between the Arctic Ocean and the Norwegian-Greenland Seas (NGS) over the past approximately 5 Myr. For this purpose, sediments of ODP site 911 (leg 151) from 900 m water depth on Yermak Plateau in the Fram Strait were leached to extract the isotopic composition of past bottom water from early diagenetic metal oxide coatings on the sediment particles [1].
Nd isotope signatures extracted from site 911 agree well with the present day deep water &Nd signature of -11.8 ± 0.4 [2]. Overall the Nd isotope composition was more radiogenic in the core section older than 2.7 Ma (&Nd = -9 to -10) and then progressively decreased to less radiogenic values (&Nd = -11 to -12) similar to the present isotopic composition. 206Pb/204Pb ratios evolved from 18.7 to more radiogenic values around 19.2 between 2 Ma and today.
The &Nd data indicate that mixing of water masses from the Arctic Ocean and the NGS has controlled the Nd isotope signatures of deep waters on the Yermak Plateau since the onset of the Northern Hemisphere Glaciation (NHG). In contrast, the 206Pb/204Pb of deep waters in the Fram Strait appears to have been dominated by glacial weathering inputs from old continental landmasses, such as Greenland or parts of Svalbard since 2 Ma. The changes in the &Nd and 206Pb/204Pb were similar to those found for the central Arctic Ocean and the North Atlantic (derived from Fe-Mn crusts).
A record of cosmogenic 10Be normalized to 9Be in the same leaches shows a strikingly similar short term variability to those of &Nd and 206Pb/204Pb suggesting that all three isotope systems have been influenced by the same process controlled by the extent of continental ice sheets and the associated weathering inputs.
[1] Gutjahr et al. (2007) Chemical Geology 242, 351–370.
[2] Andersson et al. (2008) GCA 72, 2854–2867.
Type:
Conference or Workshop Item
,
NonPeerReviewed
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