Sea-surface temperature and f-ratio explain large variability in the ratioof bacterial production to primary production in the Yellow Sea

To determine whether parameters related to hydrography and phytoplankton ut ilization of nitrogenous nutrients are responsible for the variability in r atios of euphotic zone-integrated bacterial production (BP) to primary prod uction (PP), we measured bacterial production, primary production, new prod uction, regenerated production and environmental variables in the euphotic zone in May 1995 and June 1996 at a frontal region in the Yellow Sea. The B P/PP ratios were highly variable with different hydrodynamic conditions, ra nging from 0.03 for mixed waters to 0.40 for stratified waters. The BP/PP r atios were significantly correlated (r(2) = 0.64, p < 0.01) with water-colu mn stability of the euphotic zone and, to a greater degree, with sea-surfac e temperature (SST; r(2) = 0.74, p < 0.001). SST was also closely correlate d with water-column stability (r(2) = 0.91, p < 0.0001). An inverse relatio nship was found (r(2) = 0.61, p < 0.01) between BP/PP and f-ratios, indicat ing close association of the variability of the BP/PP ratios with the relat ive utilization of nitrogen by phytoplankton. High BP/PP values were found when the euphotic zone was stratified and phytoplankton mostly depended on ammonium for nitrogen source, and low BP/PP values were found when the euph otic zone was completely mixed and phytoplankton mostly depended on nitrate . Our results suggest that both turbulent mixing and water temperature were underlying physical forces regulating variations in BP/PP ratios in the Ye llow Sea. It might be possible to predict energy pathways in the Yellow Sea and, presumably, in other marine environments by remote-sensing of SST and ocean color.