Structure and Transport of Atlantic Water North of Svalbard From Observations in Summer and Fall 2018.

The transport of warm Atlantic Waters north of Svalbard is one of the major heat and salt sources to the Arctic Ocean. The circulation pathways and the associated heat transport influence the variability in the Arctic sea ice extent, the onset of freezing, and marine ecosystems. We present observations obtained from research cruises and an autonomous underwater glider mission in summer and fall 2018, to describe the hydrographic structure, volume transport, and circulation patterns of the warm Atlantic Water Boundary Current between 12°E and 24°E north of Svalbard. The Atlantic Water volume transport reaches a maximum of 3.0 ± 0.2 Sv in October, with an intraseasonal variability of 1 Sv (1 Sv = 106 m3 s−1). During summer and late fall, we observed an Atlantic Water recirculation flowing westward (0.1–0.2 Sv) in the outer part of the section away from the shelf break. This counter current appears to be a part of an anticyclonic circulation in the Sofia Deep. The strength of the Atlantic Water recirculation and the Atlantic Water boundary current is very sensitive to the wind stress curl: The boundary current volume transport doubled in less than a week, corresponding to a transition from strongly negative (−10−6 N m−3) to strongly positive (10−6 N m−3) wind stress curl over the Sofia Deep. A previously unknown, deep bottom‐intensified current is observed to flow parallel to the boundary current, between the 1,500 and 2,000 m isobaths. Historical data in the region support the presence of the bottom‐intensified current. Plain Language Summary: Atlantic Water enters the Arctic Ocean along two pathways, through the Barents Sea and through Fram Strait west of Svalbard. Being warmer and saltier than the Arctic Ocean, the Atlantic Water is the main heat and salt source for the Arctic Ocean. The circulation pathways and the heat transported by the Atlantic Water influence the variability of the Arctic sea ice and the marine ecosystems. We present observations from research cruises and an autonomous underwater glider mission in summer and fall 2018, to describe the Atlantic Water structure and circulation between 12°E and 24°E north of Svalbard (an extension of the Fram Strait inflow). The Atlantic Water volume transport reaches a maximum of 3.0 ± 0.2 Sv in October, with an intraseasonal variability of 1 Sv (1 Sv = 106 m3 s−1). During summer and late fall, we observed Atlantic Water flowing westward (a counter current), north of the common eastward flowing Atlantic Water current. Observations suggest that the counter current is part of a clockwise circulation in the Sofia Deep, north of Svalbard. Our observations also reveal a previously undescribed deep, cold current flowing eastward into the Arctic Ocean. Historical data in the region support the presence of this deep current. Key Points: The average Atlantic Water inflow in summer and fall 2018 was 2.6 Sv, reaching 3 Sv in OctoberA recirculation in the Sofia Deep transports (0.1–0.2 Sv) Atlantic Water westwardA deep, bottom‐intensified current on the lower continental slope carries cold waters into the Arctic [ABSTRACT FROM AUTHOR]