The partial pressure of carbon dioxide and air–sea fluxes in the northern South China Sea in spring, summer and autumn

The distribution of pCO2 in the surface waters of the northern South China Sea (NSCS) was examined in the summer of 2000, the spring of 2001 and the late fall of 2002. For the offshore region >100 km away from the coastline, surface water pCO2 varied within a range of 360–450 μatm during all the surveys. Nevertheless, they were generally higher than atmospheric pCO2. Sea–air ΔpCO2 ranged in 50–100 μatm in the summer, 0–50 μatm in the spring and 0–90 μatm in the late fall. Average sea-to-air CO2 flux was 7 mmol CO2 m−2 day−1 in the summer and 1–3 mmol CO2 m−2 day−1 in the spring and fall. Nearshore pCO2 showed a very dynamic pattern likely associated with the regional hydrodynamic settings, yet again pCO2 in the surface water overall exceeded the air pCO2. Data from this study thus suggests that the NSCS served as a source of atmospheric CO2. Seasonal variations of the pCO2 in the NSCS outer shelf and slope surface waters were significantly influenced by sea surface temperature.