Importance of water mass formation regions for the air-sea CO sub(2) flux estimate in the Southern Ocean

CARIOCA drifters and ship data from several cruises in the Subantarctic Zone (SAZ) of the Pacific Ocean, approximately 40 degree S-55 degree S, have been used in order to investigate surface CO sub(2) partial pressure (pCO sub(2)) and dissolved inorganic carbon (DIC) patterns. The highest DIC values were determined in regions of deep water formation, characterized by deep mixed layer depths (MLD) as estimated from Argo float profiles. As a result, these areas act as sources of CO sub(2) to the atmosphere. Using an empirical linear relationship between DIC, sea surface temperature (SST), and MLD, we then combine DIC with A sub(T) based on salinity and compute pCO sub(2). Finally, we derive monthly fields of air-sea CO sub(2) flux in the SAZ. Our fit predicts the existence of a realistic seasonal cycle, close to equilibrium with the atmosphere in winter and a sink when biological activity takes place. It also reproduces the impact that deep water formation regions close to the Subantarctic Front (SAF) and in the eastern part of the SAZ have on the uptake capacity of the area. These areas, undersampled in previous studies, have high pCO sub(2), and as a result, our estimates (0.05 plus or minus 0.03 PgC yr super(-1)) indicate that the Pacific SAZ acts as a weaker sink of CO sub(2) than suggested by previous studies which neglect these source regions.