Abstract
The factors that control the partial pressure of carbon dioxide ( p CO 2 ) in the Pacific sector of the Southern Ocean were investigated in April 2018, onboard the icebreaker, ARAON. The mean (± 1σ) of the sea surface p CO 2 was estimated to be 431 ± 6 μatm in the north of the Ross Sea (NRS), 403 ± 18 μatm in the Amundsen–Bellingshausen Sea (ABS), and 426 ± 16 μatm in the western Antarctic Peninsula and Weddell Sea (WAP/WS). The controlling factors for p CO 2 in the NRS appeared to be meridionally different based on the southern boundary of the Antarctic Circumpolar Current (SB; ~62.5°S in the Ross Sea). The sea surface p CO 2 exhibited a strong correlation with salinity and the difference between the O 2 /Ar (ΔO 2 /Ar) values of the sample and air-saturated water in the north and south of the SB, respectively. The p CO 2 in the ABS and western WAP/WS displayed a strong correlation with salinity. Furthermore, ΔO 2 /Ar and sea ice formation appear to be the dominant factors that control p CO 2 in the Confluence Zone (CZ) and northern parts of WAP/WS. The estimated air–sea CO 2 fluxes (positive and negative values indicate the source and sink for atmospheric CO 2 , 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 CO 2 flux were observed in the CZ. Our results are the most recent observation data acquired in austral autumn in the Southern Ocean.