Sedimentation rates and provenance analysis in the Southwestern Okinawa Trough since the mid-Holocene

As a high-sedimentation rate depocenter along the path of the Kuroshio Current, the southwesternmost part of the Okinawa Trough is a key area to understand the Kuroshio history and sediments transportation. A 34.17-m-long sediment core was obtained by the advanced piston corer of Marco Polo/IMAGES XII MARION DUFRESNE during the May 2005 from the Southern Okinawa Trough at site MD05-2908. The recovered sediments were analyzed by AMS 14C dating, coarse size fraction (>63 μm) extraction and moisture content determination in order to study its sedimentation flux and provenance. The depth-age relationship of core MD05-2908 was well constrained by 17 14C dating points. The sediments span across the mid-Holocene (6.8 ka B.P.) and have remarkablely high sedimentation rates between 1.8 and 21-2 m/ka, which is well consistent with the modern observations from sediment traps. We identified five 70–200 a periods of abnormally rapid sedimentation events at 6790–6600 a B.P., 5690–5600 a B.P., 4820–4720 a B.P., 1090–880 a B.P., and 260–190 a B.P., during which the highest sedimentation rate is up to 21-2 m/ka. In general, the lithology of the sediments were dominated by silt and clay, associated with less than 5% coarse size fraction ( 63 μm). As the most significant sediment source, the Lanyang River in northeastern Taiwan annually deliver about 10Mt materials to the coastal and offshore region of northeast Taiwan, a portion of which could be carried northward by currents toward the study area. Therefore, we concluded that the 5 abnormally rapid sedimentation events may be related to intensified rainfall in Taiwan and thus increased materials to our study area at that time. However, a few extreme-rapid sedimentation events cannot be explained by normal river runoff alone. The large earthquakes or typhoons induced hyperpycnal discharge of fluvial sediment to the ocean may also act as a potential source supply to the Okinawa Trough. Supported by National Basic Research Program of China (Grant No. 2007CB815903), Key Project of National Natural Science Foundation of China (Grant No. 90411014) and National Natural Science Foundation of China (Grant Nos. 40776030 and 40506016)