Interannual Variation of Modified Circumpolar Deep Water in the Dotson‐Getz Trough, West Antarctica

Widespread ice shelf thinning has been recorded in the Amundsen Sea in recent decades, driven by basal melting and intrusions of relatively warm Circumpolar Deep Water (CDW) onto the continental shelf. The Dotson Ice Shelf (DIS) is located to the south of the Amundsen Sea polynya, and has a high basal melting rate because modified CDW (mCDW) fills the Dotson‐Getz Trough (DGT) and reaches the base of the ice shelf. Here, hydrographic data in the DGT obtained during seven oceanographic surveys from 2007 to 2018 were used to study the interannual variation in mCDW volume and properties and their causes. Although mCDW volume showed relatively weak interannual variations at the continental shelf break, these variations intensified southward and reached a maximum in front of the DIS. There, the mCDW volume was ∼8,000 km3 in 2007, rapidly decreased to 4,700 km3 in 2014 before rebounding to 7,300 km3 in 2018. We find that such interannual variability is coherent with local Ekman pumping integrated along the DGT modulated by the presence of sea ice, and complementing earlier theories involving shelf break winds only. The interannual variability in strength of the dominant south‐southeast coastal wind modulates the amplitude of Ekman upwelling along the eastern boundary of the Amundsen Sea polynya during the austral summers of the surveyed years, apparently leading to change in the volume of mCDW along the DGT. We note a strong correlation between the wind variability and the longitudinal location of the Amundsen Sea Low. Plain Language Summary Recent widespread thinning of floating ice shelves around the Amundsen Sea coast has been shown to result from flows of relatively warm water into ocean cavities below the ice shelves. Dotson Ice Shelf is located in the center of the Amundsen Sea, and has seen high rates of ice loss from ocean‐driven melting as warm water spreads southward from the Southern Ocean along the Dotson‐Getz Trough. We analyzed long‐term hydrographic observations from seven oceanographic surveys along the trough between 2007 and 2018 to understand the variation of warm water properties. We show that the warm water volume varies significantly from year to year, and that this variability is largely driven by local winds which are, in turn, connected to the broader scale atmospheric circulation. These results provide insights into how variability in atmospheric circulation due to climate change will affect the water masses on the Antarctic coast and ho