Publication Date:
2012-02-23
Description:
We determined the isotopic composition of neodymium (Nd) and lead (Pb) of past seawater to reconstruct water mass exchange and erosional input between the Arctic Ocean and the Norwegian-Greenland Seas over the past 5 Myr. For this purpose, sediments of ODP site 911 (leg 151) located at 900 m water depth on the Yermak Plateau in the Fram Strait were used. The paleo-seawater variability of Nd and Pb isotopes was extracted from the sea water-derived metal oxide coatings on the sediment particles following the leaching method of Gutjahr et al. (2007). All radiogenic isotope data were acquired by Multi-Collector (MC) ICP-MS. The site 911 stratigraphy of Knies et al. (2009) was applied.
Surface sediment Sr and Nd isotope data, as well as downcore Sr isotope data obtained on the same leaches are close to seawater and confirm the seawater origin of the Nd and Pb isotope signatures. The deep water Nd isotope composition extracted from site 911 was in general more radiogenic (εNd = -4.3 to -10) than present day deep water (-10.1 to -11.8) in the area of the Fram Strait (Andersson et al., 2008) and does not show a systematic long-term trend over time. In contrast, the radiogenic isotope composition of Pb evolved from 206Pb/204Pb ratios around 18.55 to more radiogenic values around 19.15 between 2 Ma and today.
Over the past 5 million years the data indicate that overall mixing of water masses from the Arctic Ocean and the Norwegian-Greenland Seas have controlled the Nd isotope signatures on the Yermak Plateau. Prior to 1.7 Ma the Nd isotope signatures were somewhat less radiogenic than waters from approximately the same depth in the central Arctic Ocean (Haley et al., 2008) pointing to a greater influence of inflowing waters from the Norwegian-Greenland Seas. After 1.7 Ma intermediate waters in the central Arctic and on Yermak Plateau have varied around similar values indicating general water mass mixing conditions similar to today.
In contrast, the Pb isotopic composition increased after 2.2 Ma, which resembles the Pb isotope evolution of the deep Arctic Ocean as recorded by sedimentary ferromanganese micronodules (Winter et al., 1997) and the Pb isotope evolution of North Atlantic Deep water in the North-Atlantic recorded by ferromanganese crusts (Burton et al., 1997; Reynolds et al., 1999). This indicates that the Pb isotope composition of deep waters in the Fram Strait was strongly influenced by Pb inputs resulting from incongruent weathering and preferential release of radiogenic Pb originating from glacially weathering old continental landmasses, such as Northern Canada, Greenland, or parts of Svalbard over the past 2 Ma.
References:
Andersson, P.S., Porcelli, D., Frank, M., Björk, G., Dahlqvist, R. and Gustafsson, Ö. (2008): Neodymium isotopes in seawater from the Barents Sea and Fram Strait Arctic-Atlantic gateways. Geochim. Cosmochim. Acta 72, 2854-2867
Burton, K., Ling, H.F. and H.L. O‘Nions (1997) Closure of the Central American Isthmus and its effect on deepwater formation in the North Atlantic. Nature, 386, 382-385
Gutjahr, M., Frank, M., Stirling, C.H., Klemm, V., van de Flierdt, T. and Halliday, A.N. (2007): Reliable extraction of a deepwater trace metal isotope signal from Fe-Mn oxyhydroxide coatings of marine sediments. Chemical Geology 242, 351-370
Haley B. A., M. Frank, R.F. Spielhagen and A. Eisenhauer (2008): Influence of brine formation on Arctic Ocean circulation over the past 15 million years. Nat. Geosci. 1, 68–72
Knies, J., J. Matthiessen, C. Vogt, J.S. Laberg, B.O. Hjelstuen, M.Smelror, E. Larsen, K. Andreassen, T. Eidvin and T.O. Vorren (2009): The Plio-Pleistocene glaciation of the Barents Sea–Svalbard region: a new model based on revised chronostratigraphy. Quaternary Science Reviews 28, 9-10, 812-829
Reynolds, B., M. Frank and R.K., O‘Nions (1999) Nd- and Pb-isotope time series from Atlantic ferromanganese crusts: implications for changes in provenance and paleocirculation over the last 8 Myr. Earth and Planetary Science Letters, 173, 381-396.
Winter, B.L., C.M. Johnson and D.L. Clark (1997): Strontium, neodymium, and lead isotope variations of authigenic and silicate sediment components from the Late Cenozoic Arctic Ocean: Implications for sediment provenance and the source of trace metals in seawater. Science 61, 4181-4200
Type:
Conference or Workshop Item
,
NonPeerReviewed
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