Estimation of typhoon-enhanced primary production in the South China Sea: A comparison with the Western North Pacific

Typhoon-enhanced primary production (PP) in the ocean has long been neglected, as it is a big challenge to estimate such PP due to the lack of ocean color data obscured by clouds and rainfall that accompany typhoons and complicated biological responses. In this study, we developed a statistical approach, based on all the typhoons passing though the South China Sea (SCS) and the Western North Pacific Subtropical Ocean (WNPSO) during 2003 and 2012. We then estimated the annual and interannual carbon fixation induced by typhoons in the SCS and the WNPSO. The annual mean carbon fixation due to typhoons in the whole SCS was estimated to be approximately 2.716±0.304 Mt (1 Mt=1012 g), equivalent to 5-15% of the new PP of the SCS. This suggests that typhoons contribute to the biological carbon fixation in the SCS. In terms of the WNPSO, the annual mean carbon fixation due to typhoons was only about 2.112±0.640 Mt, although the area is much larger and super typhoons occur more frequently. The main reason for the smaller value in the WNPSO is that the cold nutrient-rich water is more difficult to be brought to the upper layer to support the growth of phytoplankton due to thicker mixed layer depth and deeper nutricline depth in the WNPSO in comparison with those in the SCS. In addition, typhoon-enhanced PP tended to be higher in the El Niño years in the WNPSO due to increased occurrence of super typhoons, while it was lower in the La Niña years. However, no obvious relationship with El Niño-Southern Oscillation (ENSO) was found in the SCS during the study period.