Importance of water mass formation regions for the air-sea CO2flux estimate in the Southern Ocean

Abstract

[1] CARIOCA drifters and ship data from several cruises in the Subantarctic Zone (SAZ) of the Pacific Ocean, approximately 40°S–55°S, have been used in order to investigate surface CO2 partial pressure (pCO2) 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 CO2 to the atmosphere. Using an empirical linear relationship between DIC, sea surface temperature (SST), and MLD, we then combine DIC with AT based on salinity and compute pCO2. Finally, we derive monthly fields of air-sea CO2 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 pCO2, and as a result, our estimates (0.05 ± 0.03 PgC yr−1) indicate that the Pacific SAZ acts as a weaker sink of CO2 than suggested by previous studies which neglect these source regions.