Air-sea CO_2 exchange process in the southern Yellow Sea in April of 2011, and June, July, October of 2012

摘要

The partial pressure of CO_2 (pCO_2) and air-sea CO_2 exchange flux (FCO_2) in the southern Yellow Sea (SYS, 120-125 °E, 31.5-37°N) were investigated basing on the field surveys conducted in April of 2011, and June, July, October of 2012. With significant spatial variations, surface pCO_2 ranged from 243 to 574 |μatm, 206 to 620 μatm, 102 to 655 μatm and 328 to 557 μatm in April, June, July and October, respectively. Nearshore area of Shandong Peninsula and Jiangsu Shallow (depth < 50 m) were pCO_2-supersaturated (pCO_2=400-600 μatm), as the result of intensive water mixing which brought the bottom CO_2-rich water to the surface layer. Conversely, offshore area of SYS center (depth > 50 m) was pCO_2-undersaturated (pCO_2 < 390 μatm) in April, June and October, but supersaturated in July. Phytoplankton production sustained by abundant nutrient and suitable hydrodynamic conditions was of great importance for this undersaturated pCO_2. Moreover, extreme low pCO_2 (pCO_2 < 300 μatm) was observed in the Changjiang plume (32.5-33.5 °N, 123-125 °E) in July, which was also related with the biological uptake of CO_2. Average air-sea CO_2 exchange flux of the SYS in April, June, July and October was -3.16 ± 0.40 mmol m~(-2) d~(-1), -4.56 ± 0.34 mmol m~(-2) d~(-1), -0.36 + 0.51 mmol m~(-2) d~(-1), and 6.67 ± 0.57mmol m~(-2) d~(-1), respectively. As a whole, the SYS behaved as a weak CO_2 sink during April to October, with an average flux for about -0.35 mmol m~(-2) d~(-1). As for the controlling factors for pCO_2 variation, temperature played the dominant role in October, whereas the non-temperature factors, such as vertical mixing, Changjiang plume and biological activity, were considered as the primary controlling factors in June and July. Spatially, the control of temperature on pCO_2 was predominant in the offshore SYS; the non-temperature factors were predominant in the shallow nearshore area, especially in coast of Shandong Peninsula and the Jiangsu Shallow.