Observed Seasonal Evolution of the Antarctic Slope Current System off the Coast of Dronning Maud Land, East Antarctica

The access of heat to the Antarctic ice shelf cavities is regulated by the Antarctic Slope Front, separating relatively warm offshore water masses from cold water masses on the continental slope and inside the cavity. Previous observational studies along the East Antarctic continental slope have identified the drivers and variability of the front and the associated current, but a complete description of their seasonal cycle is currently lacking. In this study, we utilize two years (2019-2020) of observations from two oceanographic moorings east of the prime meridian to further detail the slope front and current seasonality. In combination with climatological hydrography and satellite-derived surface velocity, we identify processes that explain the hydrographic variability observed at the moorings. These processes include (a) an offshore spreading of seasonally formed Antarctic Surface Water, resulting in a lag in salinity and thermocline depth seasonality toward deeper isobaths, and (b) the crucial role of buoyancy fluxes from sea ice melt and formation for the baroclinic seasonal cycle. Finally, data from two sub-ice-shelf moorings below Fimbulisen show that flow at the main sill into the cavity seasonally coincides with a weaker slope current in spring/summer. The flow is directed out of the cavity in autumn/winter when the slope current is strongest. The refined description of the variability of the slope current and front contributes to a more complete understanding of processes important for ice-shelf-ocean interactions in East Antarctica. Ice shelves are the floating extensions of a land ice sheet. Along most of the East Antarctic coast, the water temperature below the ice shelves is close to the freezing point (-2 degrees C). This limits the melting of the ice from below. In front of the ice shelves, relatively warm water (1 degrees C) is located, but it usually cannot reach the ice due to a strong alongshore current, the Antarctic Slope Current. Here, we use temperature, salinity, and velocity observations from moored instruments at two locations within this current to investigate how it changes throughout the year. Our analyses are supported by two other data sets. We observe that changes in temperature, salinity, and velocity during the year happen earlier at the coast than offshore. In addition, we find that yearly sea ice melt during austral summer contributes to speeding up the Antarctic Slope Current in autumn. When the current is weakest, we observe a southward flow close to the seafloor toward Fimbulisen Ice Shelf, and a northward flow away from the shelf when the slope current is strongest. A better understanding of the Antarctic Slope Current is important to predict ice shelf melting in the future. The seasonal maximum in thermocline depth and minimum in subsurface salinity occurs up to 6 months later over 2,200 m than 1,100 m isobath Buoyancy fluxes from sea ice melt play an important role in seasonal variations in the baroclinic slope current strength Flow into the Fimbulisen cavity is strongest in spring/summer when the Antarctic Slope Current is weakest