Ecological significance of biogenic silica in the East China Sea

Field observations were carried out in the East China Sea (ECS) in October 2000, May 2001 and April-May 2002. Biogenic silica (BSi) in core sediments, sediment traps, and suspended particulate matter (SPM) was measured; silicate profiles in pore waters were examined. The concentration of BSi in SPM was high in coastal areas. The content of BSi in ECS sediments is less than 1%, as the result of tremendous riverine input of terrigenous weathered materials. For the ECS Shelf, the dissolution of BSi in sediment cores is important to maintain high levels of silicate in the water column, supporting prolific primary production by diatoms. BSi burial efficiencies, that is, the silica accumulation rate divided by the sum of the silica accumulation rate and the benthic silicate flux, are estimated to be 36 to 97%, higher than in the Equatorial Pacific Ocean and higher than the global ocean average. BSi regeneration efficiency, that is, the ratio of BSi vertical flux minus the BSi accumulation rate relative to BSi vertical flux, is ca. 80% for the ECS. A silica budget was established for the ECS shelf, and the model output shows that major silicate input comes from the Kuroshio, followed by silicate from the riverine inflow and the Taiwan Strait. About 75% of gross BSi production dissolves in the water column over the ECS Shelf.