Variation of turbidity and particle transport in the bottom layer of the East China Sea

Abstract

Abstract Field surveys of the bottom turbid layer were undertaken from the Changjiang estuary to the mid-continental slope area in the East China Sea to study the bottom turbid layer formation process and ascertain the role of material transport. A dramatic development of bottom turbid layers in the continental shelf area of the East China Sea was observed from summer to fall. This seasonal variation is relatively consistent with seasonal changes in the discharge of suspended particles (SS) from the Changjiang. The SS forming the bottom turbid layer in the East China Sea are often fine-grained particles transported from the continental coastal area, which undergo continuous settling and resuspension during transport. Through the convectively mixed seawater season, the average current velocities at the bottom B+10 m layer at the edge of the continental shelf were approximately 5.2 cm/s in an east-northeast direction, but 2.9 cm/s almost-true north during the stratified season. With the 200 m-depth contour as the benchmark, the bottom current at the continental shelf edge flowed from inside the continental shelf outward during the mixing season, and from outside the continental shelf inward during the stratified seawater season. The average horizontal flux of the SS is 60 mg/m 2 /s during the mixing season and 24 mg/m 2 /s during the stratified season with almost the same direction as that of the bottom current. The direction of the SS horizontal flux in the bottom layers is dominated by the bottom current, which is driven by the strong south–north monsoon in the East China Sea.