A new perspective for the sediment provenance evolution of the middle Okinawa Trough since the last deglaciation based on integrated methods

Abstract

The sediment in the Okinawa Trough (OT) preserves considerable information regarding land-ocean interactions and palaeoenvironmental evolution in the East Asian marginal seas. More specifically, the sediment provenance in the OT must be studied to recover this information. However, arguments about this remain, especially regarding the contribution of Yellow River (YR)-derived materials to middle OT depositions. To resolve this problem, we systematically investigated a gravity core (M063-05; 3.87 m in length, since the last deglaciation) collected from the middle OT by integrating environmental magnetism, diffuse reflectance spectroscopy, and transmission electron microscopy, as well as analyses of sediment grain size, clay mineralogy, and major elements. Our results indicated that sediment from the YR has contributed dominantly to this core since the last deglaciation. Limited contributions were also made from the Yangtze River and Taiwan rivers during the Holocene. Terrigenous inputs derived from the YR could be well characterized by the ratio of hematite/(hematite + goethite). Additionally, the Kuroshio Current (KC) activity since the last deglaciation, which is an important influencing factor for sediment provenance changes, was well deciphered using a new proxy Rel(DM) (relative contribution of detrital ferrimagnetic minerals to bulk magnetic properties). Based on comprehensive analyses of our results and previously published studies, we hypothesised that, during the last deglaciation, abundant resuspended sediment from the palaeo-YR mouth was transported to the East China Sea (ECS) continental shelf edge and the northern OT through seaward bottom flow and further spread into the middle OT. Since the Middle to Late Holocene, the central mud area of the South Yellow Sea and the mud area southwest off Cheju Island may have become the main sources to provide YR-derived materials to the middle OT. However, the mud-area-derived sediment could only be restricted to a small range owing to the hindrance of the strengthened KC. This study provides a new perspective for sediment provenance evolution of the middle OT since the last deglaciation and proposes new methods and parameters for future research on palaeoenvironmental evolution in the ECS. (C) 2019 Elsevier B.V. All rights reserved.