Dynamics of Water Mass Exchange Across the Central Ross Sea Slope

The central Ross Sea slope (CRSS) is a critical region for water mass exchange, significantly influencing the physical and biological processes of the Ross Sea shelf and the global overturning circulation. This study utilizes a high-resolution ocean-ice shelf-sea ice coupled model to investigate the mechanisms driving this exchange, involving the onshore transport of circumpolar deep water (CDW) and the offshore transport of dense shelf water (DSW). Combining numerical simulations and mooring observations, this work reveals high-frequency oscillations with a periodicity of similar to 32 hr in CDW transport induced by Topographic Rossby Waves and DSW transport induced by cyclonic eddies. These findings provide evidence for earlier theoretical work using idealized models that suggest such oscillations. Meanwhile, we found that the net cross-slope transport is dominated by low-frequency processes, the contributions of which are quantified using momentum diagnostics. The DSW outflow is driven by bottom Ekman transport linked to the strong Antarctic Slope Current (ASC), as significant as interfacial form stress in previous studies. Sea surface height gradient, resulting from the displacement of less dense water by the DSW in the bottom layer, can drive the onshore transport of CDW. While such DSW-CDW transport relation bears similarity to that proposed by previous work focusing on continental troughs, we found that on the slope, the CDW onshore transport is also modulated by the baroclinic pressure gradient resulting from density variations and by horizontal advection associated with the spatial variation of ASC. These findings enhance the accuracy of water mass exchange estimates across the CRSS. Plain Language Summary The water mass exchange in the central Ross Sea slope (CRSS) region involves the onshore transport of warm circumpolar deep water and the offshore transport of dense shelf water-the predecessor of the global ocean bottom water mass. The inflow of warm water affects the heat content, basal melting of ice shelves, and ecosystem productivity in the shelf region, while the dense shelf water outflow affects the ocean meridional overturning circulation. This study clarifies the dynamical processes controlling the cross-slope exchange on the CRSS by analyzing the momentum equations of ocean water. The results indicate that the moderate steepness of the CRSS facilitates wave-like temporal variations in the volume transport of these water masses, while these processes do not play a big role in the net transport of these waters. The net transport of water masses is primarily driven by the pressure gradient force and further modulated by the coupled slope current-front system, which acts to inhibit warm water intrusion and enhance the export of dense shelf water. These findings offer valuable insights for more accurate estimates of water mass transport across the CRSS.