We applied a three-dimensional ocean circulation model to the cavity underneath Ekströmisen, one of the Eastern Weddell Ice Shelves, and the adjacent open ocean. The main objective of this study is to describe ice-ocean interactions and resulting freshwater fluxes within the cavity and their contribution to the thermohaline driving forces of the Coastal Current. This study is characterized by temporally and spatially high resolution analyses of circulation patterns, basal melt rates and water mass configurations as well as their seasonal variations. To achieve these aims, new geometric data sets of water column thickness and ice shelf draft are compiled for the region. The vertically integrated mass transport within the model domain is dominated by a 0.6 Sv cyclonic gyre, which spans from the western part of the cavity onto the shelf region in front of the ice shelf. The resulting mass transport is partly driven by an ice pump process, which is related to an average mass loss of 0.98 mice a-1 at the ice shelf base. No accretion of marine ice has been found. The narrow continental shelf permits a strong interaction with the Coastal Current and associated heat transports into the ice shelf cavity. Sensitivity studies with artificially extended continental shelves indicate the importance of precise and high resolution geometries in numerical models, especially in key regions as across the narrow continental shelf. An extension of the shelf width by only 11 km reduces the basal melt rate in the cavity by approximately 30%, causing warmer and saltier water masses in the outflow. Color tracer experiments, visualizing the temporal variations of the flow regime, help to distinguish and locate seasonally varying source regions of water masses, penetrating into the ice shelf cavity and providing strong ice shelf - ocean interactions.