Open-Ocean Polynyas in the Cooperation Sea, Antarctica

Abstract

Abstract Extensive studies have addressed the characteristics and mechanisms of open-ocean polynyas in the Weddell and Cosmonaut Seas. Here, we show that more persistent open-ocean polynyas occur in the Cooperation Sea (CS) (60°–90°E), a sector of the Southern Ocean off the Prydz Bay continental shelf, between 2002 and 2019. Polynyas are formed annually mainly within the 62°–65°S band, as identified by sea ice concentrations less than 0.7. The polynyas usually began to emerge in April and expanded to large sizes during July–October, with sizes often larger than those of the Maud Rise polynya in 2017. The annual maximum size of polynyas ranged from 115.3 × 103 km2 in 2013 to 312.4 × 103 km2 in 2010, with an average value of 188.9 × 103 km2. The Antarctic Circumpolar Current (ACC) travels closer to the continental shelf and brings the upper circumpolar deep water to much higher latitudes in the CS than in most other sectors; cyclonic ocean circulations often develop between the ACC and the Antarctic Slope Current, with many of them being associated with local topographic features and dense water cascading. These oceanic preconditions, along with cyclonic wind forcing in the Antarctic Divergence zone, generated polynyas in the CS. These findings offer a more complete circumpolar view of open-ocean polynyas in the Southern Ocean and have implications for physical, biological, and biogeochemical studies of the Southern Ocean. Future efforts should be particularly devoted to more extensively observing the ocean circulation to understand the variability of open-ocean polynyas in the CS. Significance Statement An open-ocean polynya is an offshore area of open water or low sea ice cover surrounded by pack ice. Open-ocean polynyas are important for driving the physical, biogeochemical, and biological processes in the Southern Ocean. Extensive studies have addressed the characteristics and mechanisms of open-ocean polynyas in the Weddell and Cosmonaut Seas. The purpose of this study is to document the existence of more persistent open-ocean polynyas in the Cooperation Sea (60°–90°E) and explore the atmospheric and oceanic forcing mechanisms responsible for the formation of the open-ocean polynyas. Our results would offer a more complete circumpolar view of open-ocean polynyas in the Southern Ocean and have implications for physical, biological, and biogeochemical studies of the Southern Ocean.