High‐frequency time‐series autonomous observations of sea surface pCO2 and pH

Carbon dioxide partial pressure (pCO2) in surface water was continuously measured every 3 h from July 2012 to June 2013 using an autonomous pCO2 system (MAPCO2) deployed on a moored buoy on the East China Sea shelf (31°N, 124.5°E). Sea surface pCO2 and pH had the largest variations in summer, ranging from 215 to 470 μatm, and 7.941 to 8.263 (averagely 8.084 ± 0.080), respectively. They varied little in winter, ranging from 328 to 395 μatm, and 8.003 to 8.074 (averagely 8.052 ± 0.010), respectively. The seasonal average sea surface pCO2 was respectively 335 ± 70 μatm, 422 ± 43 μatm, 362 ± 11 μatm, and 311 ± 59 μatm in summer, autumn, winter, and spring, and was overall undersaturated with respect to atmosphere on a yearly basis. Although the average sea surface pCO2 in summer was below the atmospheric level, the net CO2 flux has suggested a CO2 source status due to the influence of typhoon. Our observation thus demonstrated the significant, even dominant impact of episodic typhoon events on surface ocean CO2 chemistry and air–sea CO2 gas exchange, which would be impossible to capture by shipboard observation. The high wind stress and curl associated with the northward movement of typhoon induced complex sea surface water movement, vertical mixing, and subsequent biological drawdown, which differed in pre‐, onset, and post‐typhoon stages. Based on our estimates, the degassing fluxes during typhoon reached as high as 82 mmol m−2 CO2 and 242 mmol m−2 CO2 in summer and autumn, respectively, accounting for twice as large as the summer CO2 sink during non‐typhoon period, and 28% of the total CO2 source in autumn.

Wu Y., Dai M., Guo X., Chen J., Xu Y., Dong X., Dai J. & Zhang Z., in press. High‐frequency time‐series autonomous observations of sea surface pCO2 and pH. Limnology and Oceanography. Article.

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