Coccolith fluxes and species assemblages at the shelf edge and in the Okinawa Trough of the East China Sea

Coccolith assemblages and flux were investigated in detail by both time-series and short-term sediment trap experiments from the shelf edge to the Okinawa Trough in the East China Sea. Time-series sediment traps were moored at water depths of 600, 800, and 1040 m (50 m above the bottom) from March 1993 to February 1994 in the western region of the Okinawa Trough. A short-term sediment trap array was also moored for 2 days in both February and October 1993 at the shelf edge. The seasonal assemblage patterns of coccoliths can be recognized in time-series sediment traps and were reflective of the overlying surface water masses. Emiliania huxleyi dominated the community from April to May, while Florisphaera profunda was dominant from October to December at all three depths in the time-series traps. In the time-series traps, coccolith fluxes increased markedly at 800 and 1040 m, indicating lateral input of coccoliths. These results revealed that biogenic particles are transported by lateral advection in the middle and deep layers, or that a nepheloid layer exists. On the other hand, settling coccolith assemblages and fluxes were clearly different between the western region of the Okinawa Trough and the continental shelf edge. A comparison between traps at the two sites indicated that settling coccolith assemblages and fluxes in the deep water in the western region of the Okinawa Trough are influenced mainly by lateral transportation in the direction of the Kuroshio Current. (C) 2002 Elsevier Science Ltd. All rights reserved.