Wind-Induced Quasi-Seasonal and Quasi-Monthly Variations of Near-Bottom Temperature on the Chukchi Slope of the Southwestern Canada Basin

The time series of near-bottom temperatures collected from September 2018 until August 2020 from an array of three current- and pressure-recording inverted echo sounders showed quasi-seasonal and quasi-monthly (∼28 days) variations at a depth of ∼1,300 m near the Chukchi slope in the western Arctic Ocean. They revealed an increase of ∼0.1°C during the winter-spring period compared with the summer-fall period. These variations were observed in the data-assimilated Hybrid Coordinate Ocean Model (HYCOM) outputs near the observation site (correlation coefficient >0.7). They confirmed that variations in near-bottom temperature are related to changes in the intensity of the Atlantic Water (AW) boundary current, concurrent with the deepening of the lower AW layer by approximately 50 m. The difference in sea surface height (SSH) between the Canada Basin and the Chukchi Shelf increased because of the negative wind stress curl (WSC) and retarded the AW boundary current according to the geostrophic effect. When the near-bottom temperature increased during the winter-spring period, the SSH in the Chukchi Shelf was lower than that in the summer-fall period because of the less negative WSC. Quasi-monthly variations were related to SSH on the Chukchi Shelf owing to the negative WSC. HYCOM outputs from 1994 to 2015 showed that the AW boundary current weakened more recently than in the past due to the increased melting of sea ice. The results imply that a longer sea-ice-free season in the Arctic amplifies changes in the AW boundary current and deep ocean temperature owing to increased atmospheric forcing.