Storm‐induced changes in pCO2 at the sea surface over the northern South China Sea during Typhoon Wutip

In situ oceanographic measurements were made before and after the passage of Typhoon Wutip in September 2013 over the northern South China Sea. The surface geostrophic circulation over this region inferred from satellite altimetry data features a large‐size anticyclonic eddy, a small‐size cyclonic eddy, and smaller‐size eddies during this period. Significant typhoon‐induced changes occurred in the partial pressure of CO2 at the sea surface (pCO2sea) during Wutip. Before the passage of Wutip, pCO2sea was about 392.92 ± 1.83, 390.31 ± 0.50, and 393.04 ± 4.31 μatm over the cyclonic eddy water, the anticyclonic eddy water, and areas outside two eddies, respectively. The entire study region showed a carbon source (1.31 ± 0.46 mmol CO2 m−2 d−1) before Wutip. In the cyclonic eddy water after Wutip, high sea surface salinity (SSS), low sea surface temperature (SST), and high pCO2sea (413.05 ± 7.56 μatm) made this area to be a carbon source (3.30 ± 0.75 mmol CO2 m−2 d−1). In the anticyclonic eddy water after Wutip, both the SSS and SST were lower, pCO2sea was also lower (383.03 ± 3.72 μatm), and this area became a carbon sink (–0.11 ± 0.55 mmol CO2 m−2 d−1), in comparison with the pretyphoon conditions. The typhoon‐induced air‐sea CO2 flux reached about 0.03 mmol CO2 m−2 d−1. Noticeable spatial variations in pCO2sea were affected mainly by the typhoon‐induced mixing/upwelling and vertical stratifications. This study suggests that the local air‐sea CO2 flux in the study region was affected significantly by oceanographic conditions during the typhoon. Key Points Typhoon Wutip generated significant changes in oceanographic conditions in the surface mixed layer over the northern South China Sea Wutip enhanced the pCO2sea in the cyclonic eddy and surrounding water and decreased the pCO2sea in the anticyclonic eddy water The noticeable spatial variation in pCO2sea was affected mainly by the storm‐induced mixing and associated changes in stratifications