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Northern Hemisphere climate control of the Bengali rivers discharge during the past 4 Ma

Abstract : Nd isotopes are useful tracers for paleoceanography due to the short Nd residence time in seawater and the large differences between the isotopic signatures of various geological reservoirs. Therefore, var epsilonNd variations reflect the geological history of individual oceanic basins. Using a differential dissolution technique, which extracts Nd isotopes of seawater trapped in MnO2 coatings and carbonates in marine sediment, we measured almost two hundred samples from ODP Sites 758 and 757 in the Northern Bay of Bengal covering the last 4 Ma. For the first time, we have shown a covariation between var epsilonNd and δ18O over at least the last 800 ka. We also show that from 4 Ma to 2.6 Ma, var epsilonNd is almost constant and starts to fluctuate at 2.6 Ma when northern glaciations increased. From 2.6 Ma to 1 Ma the fluctuation period is close to 40 ka while from 1 Ma to present it is dominantly 100 ka. We attribute these findings to mixing between Himalayan river water (that ultimately originates as Indian summer monsoon rain) and normal Bay of Bengal seawater. Previous studies on seawater, using var epsilonNd, δ18O analyzed on planktonic foraminifera and sedimentary data, can be integrated into this model. A simple quantitative binary mixing model suggests that the summer monsoon rain was more intense during interglacial than glacial periods. During last glacial episode, the monsoon trajectory was deviated to the east. At a large scale, the Indian monsoon is fully controlled by the variations in Northern Hemisphere climate but with a complex response function to this forcing. Our study clearly establishes the large potential of Nd isotope data to evaluate the hydrological river regime during the Quaternary and its relationship with climate fluctuations, particularly when the sediment archive is sampled close to sediment sources.
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Submitted on : Wednesday, December 22, 2010 - 2:18:00 PM
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Alexandra T. Gourlan, Laure Meynadier, Claude J. Allègre, Paul Tapponnier, Jean-Louis Birck, et al.. Northern Hemisphere climate control of the Bengali rivers discharge during the past 4 Ma. Quaternary Science Reviews, Elsevier, 2010, 29, pp.2484-2498. ⟨10.1016/J.QUASCIREV.2010.05.003⟩. ⟨insu-00549742⟩



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