Dissolved and particulate organic carbon in the southern East China Sea

This work reports distributions of dissolved organic carbon (DOC) and parti culate organic carbon (POC) observed along a cross-shelf transect in the so uthern East China Sea from 1994 to 1996. DOC concentrations were relatively high (> 85 mu M) in inner shelf and slope waters but low (ca. 65 mu M) aro und the shelf break, where Kuroshio upwelling occurred. Such distribution p attern showed little temporal variations. Colloidal organic carbon (COC), d efined as dissolved organic carbon with molecular weight above 1000 Da, was further separated for analysis. Although the coastal water in the inner sh elf and the Kuroshio surface water over the slope had similar DOC concentra tions, the partitions between COC and the low molecular weight DOC were dif ferent. The coastal water contained less COC than the oligotrophic slope wa ter, suggesting a lower production rate and/or a higher breakdown rate in t he coastal water. The POC distribution showed a decreasing trend from the i nner shelf to the slope with a local maximum at the shelf break, where POC was enriched due to enhanced primary productivity induced by upwelling. The average POC inventory was about 1/10 that of the DOC. A mid-depth maximum was repeatedly observed above the slope, indicating lateral transport of PO C offshore from the shelf. The net exports of DOC and POC from the shelf ar e estimated to be 414 and 106 Gmol C/yr, respectively, but the POC export a long the bottom boundary layer is unaccounted for in our assessment. (C) 20 00 Elsevier Science Ltd. All rights reserved.