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Seasonal Variations in the Siliciclastic Fluxes to the Western Philippine Sea and Their Impacts on Seawater ɛNd Values Inferred From 1 Year of In Situ Observations Above Benham Rise

Abstract : The Sr and Nd isotopic compositions of siliciclastic sediments and the Nd isotopic compositions of planktonic foraminifera are investigated in sediment trap samples collected in 2015 at water depths of 500 and 2,800 m to (1) track the seasonal changes in the sources and transport patterns of siliciclastic sediments to Benham Rise, (2) constrain the Nd isotopic compositions of the planktonic foraminifera throughout the water column, and (3) assess the influences of lithogenic inputs on the Nd isotopic compositions of the water masses. We demonstrate that volcanic matter and eolian dust are derived primarily from Luzon Island and the Ordos Desert, respectively. In addition, we show that reduced precipitation over Luzon Island and the weakened East Asian winter monsoon intensity result in mass fluxes from Luzon Island and the eastern Asian deserts to the sea, respectively, that are weaker in the winter than in the spring. Furthermore, the ɛNd values of the foraminifera collected at a water depth of 500 m change slightly in 2015, suggesting negligible impacts of lithogenic Nd inputs characterized by significant seasonal flux variations. In contrast, the ɛNd values of the planktonic foraminifera collected at a water depth of 2,800 m are systematically more radiogenic and appear to display seasonal variability. Such results suggest the rapid modification of ɛNd values during the settling of planktonic foraminifera by the precipitation of Mn coatings derived from water masses at deposition depths, with greater contributions of colder water masses originating from the volcanic Luzon Island margin during the winter.
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Submitted on : Thursday, August 4, 2022 - 8:05:36 AM
Last modification on : Friday, August 5, 2022 - 3:52:16 AM

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Zhaokai Xu, Tiegang Li, Christophe Colin, Peter D. Clift, Rongtao Sun, et al.. Seasonal Variations in the Siliciclastic Fluxes to the Western Philippine Sea and Their Impacts on Seawater ɛNd Values Inferred From 1 Year of In Situ Observations Above Benham Rise. Journal of Geophysical Research: Oceans, 2018, 123, pp.6688-6702. ⟨10.1029/2018JC014274⟩. ⟨insu-03745258⟩

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