New Production and F-ratio on the Continental Shelf of the East China Sea: Comparisons Between Nitrate Inputs From the Subsurface Kuroshio Current and the Changjiang River

Abstract

This paper reports the first results of the direct measurements of nitrate-based new production and f-ratio on the continental shelf of the East China Sea. The Kuroshio-induced upwelling off north-eastern Taiwan and river runoff from the Changjiang are two principal sources of new nitrogen on the shelf. New production ranged from 70 to 1610mgCm−2d−1, and values of the f-ratio were 0·17 to 0·82. Enhanced new production in the upwelling was significantly related to the ambient nitrate concentration. This implies that the nutrients brought up to the euphotic zone by the intrusion of the subsurface Kuroshio water were quickly reflected by the enhancement of new production. The prediction of f-ratio is feasible in the upwelling region from two ship-measured parameters: light intensity and surface nitrate concentration, but not feasible in the river-influenced shelf waters. New production on the riverine shelf waters, in contrast, was not related to the nitrate input from the Changjiang, but was positively (P<0·05) related to water temperature. Low rates of NO3−utilization imply that factors other than nitrate (e.g. phosphate or light) could be the limiting factors determining the new production dynamics in the river mouth.