Sr–Nd isotopic constraints on terrigenous sediment provenances and Kuroshio Current variability in the Okinawa Trough during the late Quaternary

Abstract

The Okinawa Trough in the East China Sea continuously receives terrigenous sediments from the surrounding East Asian continent during the late Quaternary, which makes it an ideal site for the studies of land–sea interaction and sediment source-to-sink transport. Geochemical and Sr–Nd isotopic compositions of the detrital sediments in the middle Okinawa Trough allow the provenance discrimination and the reconstruction of paleoenvironmental changes over the last 30ka. Large variations in 87Sr/86Sr ratios and εNd values occur between 14.0 and 7.1ka, suggesting a significant change in sediment provenances from the dominance of the Changjiang (Yangtze River) and/or continental shelf to that of Taiwan Island. During the last glacial maximum, the continental shelf was largely exposed and the fine-grained sediments from the Changjiang and the shelf with higher 87Sr/86Sr ratios and lower εNd values might be transported directly into the middle Okinawa Trough. With the sea level rise during the deglacial period, the strengthening Kuroshio Current increasingly delivered Taiwan-derived fine sediments (lower 87Sr/86Sr ratios and higher εNd values) to the middle trough, while the sediment contribution from the East Asian continent became subordinate. This study suggests that the changes in sea level and the Kuroshio Current pathway during the late Quaternary predominantly determined the dispersal and deposition of the terrigenous sediments in the Okinawa Trough, and the Kuroshio Current might have obviously influenced the Okinawa Trough since 14ka. This study illustrates that the radiogenic isotopic compositions of the fined-grained sediments are sensitive proxies to trace the sediment provenance and to reconstruct oceanic circulations in the west Pacific marginal seas.