Clay-sized sediment provenance change in the northern Okinawa Trough since 22 kyr BP and its paleoenvironmental implication

Provenances of clay-sized terrigenous sediments and a comprehensive interpretation of their high-resolution variations in the northern Okinawa Trough since the late last glaciation remain unclear, especially in regard to the Huanghe- and Taiwan-derived matter. Grain size, clay mineralogy, typical elemental ratio, oxygen isotope, and AMS 14C dating of core PC-1 in the northern Okinawa Trough were investigated to trace clay-sized sediment provenance and transport process and thus to recover their forcing mechanisms over the last 22 kyr. Variations in linear sedimentation rate, grain size, δ18O, Ti/Ca ratio, and clay minerals can be clearly divided into three distinct intervals, consistent with changes in sediment provenance that can be close related to sea-level fluctuation, evolution of the Tsushima Warm Current as well as influence from the East Asian monsoon climate evolution. During the late last glaciation period (Interval 1, 22–16 kyr BP) when the Tsushima Warm Current was absent in the East China Sea, the paleo-Huanghe mouth was situated close to the study area and thus the paleo-Huanghe could have played major role in sedimentation therein. In Interval 2 (16–7.3 kyr BP), global sea-level rise led to gradually retreating of the paleo-Huanghe mouth and thus decreasing terrigenous sediment supply from it to the study area. Since 7.3 kyr BP (Interval 3), some clay minerals from Taiwan might have been transported northward to the study area by the fully evolved Tsushima Warm Current, characterized by higher chlorite/kaolinite ratios. In contrast, the decreasing influence of the Huanghe-derived sediments during the strengthening of the Tsushima Warm Current periods was probably caused by the blocking effect of the Tsushima Warm Current. Particularly, chlorite/kaolinite ratio and smectite content in the Okinawa Trough sediment might be good proxies for indicating the Tsushima Warm Current-related sedimentary environment.