Sedimentation of planktonic foraminifera in the East China Sea: evidence from a sediment trap experiment

The particle flux from sediment traps moored in the East China Sea from the continental shelf to the Okinawa Trough between 25 February 1993 and 22 February 1994 was analyzed for particle transport processes based on planktonic foraminifera. Conventional sediment traps were moored at points from the continental shelf to the shelf edge. These experiments revealed that benthic foraminifera occurred along with planktonic foraminifera, with contained mud, particularly in sediment traps moored at 10–40 m above the bottom. This finding implies that surface sediment resuspension from the sea bottom is active in this region. In addition, time-series sediment traps were deployed in the Okinawa Trough at three depths (606, 813 and 1017 m) under the main stream of the Kuroshio Current. The total planktonic foraminiferal flux increased with increasing depth and was associated with very few benthic foraminiferal specimens in the two deeper traps. However, planktonic foraminiferal tests filled with mud as seen in traps on the continental shelf were not found in the three traps. This observation suggests that the planktonic foraminifera did not originate in the sediments of the continental shelf and were likely carried laterally during settling. Furthermore, based on comparing the species composition of the foraminiferal flux for the Okinawa Trough station with that for the shelf edge in late October, planktonic foraminifera were considered to arrive at the deeper traps in the Okinawa Trough from the Kuroshio front area which was characterized by high productivity.