The northern East China Sea (a.k.a., “The South Sea”) is a dynamic zone that exerts a variety of effects on the marine ecosystem due to Three-Gorges Dam construction. As the northern East China Sea region is vulnerable to climate forcing and anthropogenic impacts, it is important to investigate how the remineralization rate in the northern East China Sea has changed in response to such external forcing. We used an historical hydrographic dataset from August 1997 to obtain a baseline for future comparison. We estimate the amount of remineralized phosphate by decomposing the physical mixing and biogeochemical process effect using water column measurements (temperature, salinity, and phosphate). The estimated remineralized phosphate column inventory ranged from 0.8 to 42.4 mmol P m-2 (mean value of 15.2 ± 12.0 mmol P m-2). Our results suggest that the Tsushima Warm Current was a strong contributor to primary production during the summer of 1997 in the study area. The estimated summer (June - August) remineralization rate in the region before Three-Gorges Dam construction was 18 ± 14 mmol C m-2 d-1.