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.

The Amundsen Sea polynya (ASP) is reportedly the most productive among the coastal polynyas around Antarctica. However, observational constraints limit our understanding of the biological pump and carbon cycle in the ASP. We measured various carbon‐related parameters such as primary production, bacterial production, sinking flux of particulate organic carbon (POC), and accumulation of organic carbon in the sediment as well as hydrographic parameters during field observations and by instrument moorings. Over 95% of the photosynthetically produced POC was converted to suspended POC and/or dissolved carbon forms in the upper ~400 m layer. We postulate that most of the carbon transported to the water column by the biological pump in the ASP was flushed out of the shelf without being sequestered for long‐term storage in sediments. Lack of bottom water formation due to intrusion of Circumpolar Deep Water in the lower layer reduces carbon sequestration efficiency.

Recent rapid thinning of West Antarctic ice shelves are believed to be caused by intrusions of warm deep water that induce basal melting and seaward meltwater export. This study uses data from three bottom-mounted mooring arrays to show seasonal variability and local forcing for the currents moving into and out of the Dotson ice shelf cavity. A southward flow of warm, salty water had maximum current velocities along the eastern channel slope, while northward outflows of freshened ice shelf meltwater spread at intermediate depth above the western slope. The inflow correlated with the local ocean surface stress curl. At the western slope, meltwater outflows followed the warm influx along the eastern slope with a ~2–3 month delay. Ocean circulation near Dotson Ice Shelf, affected by sea ice distribution and wind, appears to significantly control the inflow of warm water and subsequent ice shelf melting on seasonal time-scales.

The vertical migration of zooplankton and micronekton (hereafter ‘zooplankton’) has ramifications throughout the food web. Here, we present the first evidence that climate fluctuations affect the vertical migration of zooplankton in the Southern Ocean, based on multi-year acoustic backscatter data from one of the deep troughs in the Amundsen Sea, Antarctica. High net primary productivity (NPP) and the annual variation in seasonal ice cover make the Amundsen Sea coastal polynya an ideal site in which to examine how zooplankton behavior responds to climate fluctuations. Our observations show that the timing of the seasonal vertical migration and abundance of zooplankton in the seasonally varying sea ice is correlated with the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO). Zooplankton in this region migrate seasonally and overwinter at depth, returning to the surface in spring. During +SAM/La Niña periods, the at-depth overwintering period is shorter compared to −SAM/El Niño periods, and return to the surface layers starts earlier in the year. These differences may result from the higher sea ice cover and decreased NPP during +SAM/La Niña periods. This observation points to a new link between global climate fluctuations and the polar marine food web.