Geochemical and carbon isotopic characterization of particles collected in sediment traps from the East China Sea continental slope and the Okinawa Trough northeast of Taiwan

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This paper reports results from various geochemical and carbon isotopic analyses of sediment particles collected at different water depths from an array of 5 sediment traps. The traps were deployed at places characteristic of distinct seafloor topography on the East China Sea continental slope and within the Okinawa Trough northeast of Taiwan during different durations from July 1993 to December 1995. Apparent sediment mass flux (ASMF) measurements show that particle fluxes are invariably high and fluctuate greatly within the canyons, as compared to those on the slope and in the Okinawa Trough, suggesting episodic sediment resuspension and a strong bottom transport from the East China Sea continental shelf to the Okinawa Trough within the canyons. The great terrigenous input thus overshadows any appreciable geochemical and isotopic changes in particles collected inside the canyons, which are otherwise seen in particles collected on the slope region where in situ biogenic input is enhanced by the intrusion of the nutrient-laden Kuroshio subsurface waters. In addition, the shipboard Acoustic Doppler Current Profiler (sb-ADCP) survey reveals that the persistent intrusion of the Kuroshio current then developed to a counter-clockwise circulation throughout all depths in the water column on the East China Sea continental slope. The countercurrent sweeps and redistributes the dispersed fine particles across the East China Sea continental slope, funnels massive sediments through the canyons, and deposits them on the northern slope of the Okinawa Trough. Our results are consistent with previous physical and hydrological observations. We thus conclude that all the spatial and temporal variability of geochemical and carbon isotopic characteristics of sediment particles collected in the region northeast of Taiwan can be attributed primarily to the nature of sediments sourced from the East China Sea continental margin, and the in situ biogenic modification in the water columns, as well as the dynamic transport of the dispersed fine particles by the counter flows developed in the region.