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. Plain Language Summary: Atlantic Water (AW) entering the Arctic Ocean from the Nordic Seas is considered a heat reservoir because it is warmer than the Arctic Ocean. The AW flows along the boundaries around the basin margins, known as the AW boundary current. The AW boundary current gradually deepened after entering and sat at approximately 200–800 m near the Chukchi slope. The AW boundary current exhibited quasi‐seasonal and quasi‐monthly (approximately 28 days) variations, confirmed using near‐bottom temperature data and data‐assimilated Hybrid Coordinate Ocean Model outputs. The variations are due to the geostrophic current caused by the pressure gradient due to the difference in the sea surface height (SSH) between the Chukchi Shelf and Canada Basin, which are located in the southwest and northeast of the Chukchi slope, respectively. Due to the difference in the SSH around the Chukchi slope, the geostrophic current is in the opposite direction to the AW boundary current and can suppress it. Sea surface height is affected by wind stress curl, and sea ice dampens atmospheric forcing. These findings imply that a longer sea‐ice‐free season in the Arctic can amplify changes in the AW boundary current. Key Points: The near‐bottom temperature observed at a depth of ∼1,300 m near the Chukchi slope showed quasi‐seasonal and quasi‐monthly variationsThe variations are related to the wind‐induced change in intensity of the Atlantic Water (AW) boundary current along the Chukchi slopeHYCOM outputs showed a more common occurrence of weaker AW boundary currents when sea ice melted compared to that in the past [ABSTRACT FROM AUTHOR]