Ocean circulation around the Antarctic coastal margins plays a critical role in heat delivery to Antarctica, melting ice shelves. However, until recently, satellite-based sea-level observations have been limited by the presence of sea ice. With improved algorithms, it is now possible to monitor sea-level fluctuations over most of the Southern Ocean, including sea ice-covered areas. We identified several clockwise gyres along East Antarctic coastal margins in satellite-derived dynamic ocean topography (DOT). Singular value decomposition analyses revealed that the coastal DOT deepening and anomalous clockwise circulation consistently occur during the positive phase of the southern annular mode (SAM), which is associated with negative wind stress curl anomalies. Shifting of the SAM to a more positive phase since the 20th century and its expected continuation into the coming century could lead to enhanced clockwise gyres along East Antarctica, contributing to increased poleward ocean heat transport.

To investigate CO2 sink capacity in the western Arctic Ocean (north of 65°N), we conducted underway, ship-based observations of partial pressures of CO2 (pCO2) and total dissolved inorganic carbon (TCO2) in surface seawater in early winter (November 2018). From these two properties of the seawater inorganic carbon system, we calculated total alkalinity (TA). In the early winter, surface seawater pCO2 in most places was lower than atmospheric pCO2. The weighted mean of the air-sea fluxes of CO2 were calculated to be -7.5 ± 1.6 mmol m−2 d−1. The calculated fluxes implied that the area acted as a moderate sink for atmospheric CO2 in early winter, and its rate of CO2 uptake was comparable to that (-8.0 ± 1.7 mmol m−2 d−1) in summer (late August-September 2017). Spatial variations of surface seawater pCO2 in the early winter could be attributed mostly to conservative changes of TCO2 and TA, which together accounted for more than 70% of the pCO2 variations. In the marginal ice zone, however, there was a drawdown of surface seawater pCO2 by 70-90 matm due to horizontal advection of water with an anomalously high temperature from the Pacific Ocean and its subsequent cooling. We found that TA was an important determinant of the spatial variations of pCO2 in the western Arctic Ocean because of the conservative nature of the changes of TA and TCO2 during mixing of water masses. This conservative behavior was observed in both the early winter and summer.