Assessment of austral autumn air-sea CO₂ exchange in the Pacific sector of the Southern Ocean and dominant controlling factors

The factors that control the partial pressure of carbon dioxide (pCO(2)) in the Pacific sector of the Southern Ocean were investigated in April 2018, onboard the icebreaker, ARAON. The mean (+/- 1 sigma) of the sea surface pCO(2) was estimated to be 431 +/- 6 mu atm in the north of the Ross Sea (NRS), 403 +/- 18 mu atm in the Amundsen-Bellingshausen Sea (ABS), and 426 +/- 16 mu atm in the western Antarctic Peninsula and Weddell Sea (WAP/WS). The controlling factors for pCO(2) in the NRS appeared to be meridionally different based on the southern boundary of the Antarctic Circumpolar Current (SB; similar to 62.5 degrees S in the Ross Sea). The sea surface pCO(2) exhibited a strong correlation with salinity and the difference between the O-2/Ar (Delta O-2/Ar) values of the sample and air-saturated water in the north and south of the SB, respectively. The pCO(2) in the ABS and western WAP/WS displayed a strong correlation with salinity. Furthermore, Delta O-2/Ar and sea ice formation appear to be the dominant factors that control pCO(2) in the Confluence Zone (CZ) and northern parts of WAP/WS. The estimated air-sea CO2 fluxes (positive and negative values indicate the source and sink for atmospheric CO2, respectively) range from 3.1 to 18.8 mmol m(-2) d(-1) in the NRS, -12.7 to 17.3 mmol m(-2) d(-1) in the ABS, and -59.4 to 140.8 mmol m(-2) d(-1) in the WAP/WS. In addition, biology-driven large variations in the air-sea CO2 flux were observed in the CZ. Our results are the most recent observation data acquired in austral autumn in the Southern Ocean.