Distribution of Particulate Organic Matter in the Southern East China Sea:Implications in Production and Transport

Abstract

Repeated surveys in October, 1992 and May, 1993 in the southern East China Sea showed a high abundance of particulate organic carbon in the upwelling area around the shelf break northeast of Taiwan. Particulate nitrogen was well correlated with particulate organic carbon with a ∆C/∆N atomic ratio of 6.3-6.7. The vertical distribution of the particulate organic carbon had a surface maximum at many stations. Such distribution was not directly related to phytoplankton biomass but controlled by the primary production rate which also showed an eminent maximum close to the surface. The POC residence time in the upper water column varied from 2 tol9 days for different water types. For the coastal water and upwelling center, the residence time was calculated to be 3-8 days; for the nutrient-poor shelf and Kuroshio waters, 7-19 days. The sinking flux of particulate organic carbon at the bottom of the euphotic zone in the Kuroshio water was calculated from the standing stock and the particle residence time to be 3.3mmol C/m^2/d, which represents 18% of the potential primary productivity; the sinking flux of particulate nitrogen 0.29 mmol/m^2/d. Beneath the Kuroshio current in the Okinawa Trough, we found patches of relatively high particulate organic carbon concentration at depths between 500 and 750 m on both cruises. This was the first evidence of the lateral transport of particulate organic carbon across the shelf break to the deep sea off northeastern Taiwan. Such a process may have been responsible for the enrichment of organic carbon in the sediments on the slope.