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Abstract:
We combine the stable silicon isotope composition (delta Si-30) of diatoms and the radiogenic neodymium isotope compositions (epsilon(Nd) of past seawater extracted from the authigenic fraction of the sediments di (Mn-Fe coatings of particles and benthic foraminifers), as well as the radiogenic isotope compositions (Nd, Sr) of the detrital material itself to reconstruct silicic acid utilisation, water mass mixing, and upwelling intensity from the same marine sediments in the Peruvian upwelling region during the past 20,000 years. Additionally, the sedimentary signals were compared to the water column isotope compositions. Along the Peruvian shelf, the dissolved epsilon(Nd) in the water column ranges from -5.7 to +0.6. The corresponding epsilon(Nd) signatures of the coatings and the benthic foraminifers of the surface sediments range from -4.5 to +1.8 and from -2.5 to +2.2, respectively. The detrital epsilon(Nd) (Sr-87/Sr-86) signatures range from -63 to 0 (0.70508-0.71049). All phases show a trend from more radiogenic epsilon(Nd) values in the north towards less radiogenic values in the south broadly reflecting local weathering inputs and hinterland geology. The epsilon(Nd) signatures of the coatings extracted from sediment core SO147-106KL located in the present day centre of coastal upwelling near 12 degrees S have been essentially constant (-1.5) throughout the past 20,000 years, while the detrital epsilon(Nd) (Sr-87/Sr-86) varied between values of -0.7 (0.70620) during the Last Glacial and -4.5 (0.70849) during the late Holocene reflecting changes in the origin of the sediment and current transport from a more northerly towards a more southerly source and from overall stronger to weaker upwelling. The delta Si-30 signature of both total biogenic opal (delta Si-30(opal)) and of hand-picked diatoms (delta Si-30(diatom)) ranged from +0.3%0 (Last Glacial) to +1.4%0 (late Holocene) confirming large variations in upwelling intensity driving silicic acid utilisation by diatoms. Our combined bSiO(2) MAR, delta Si-30(opal) and detrital radiogenic isotope results demonstrate that the strongest El Nifio-Southern Oscillation conditions off Peru of the past 20 ka have prevailed during the past 5 ka. (C) 2013 Elsevier Ltd. All rights reserved.
