A model of tidally dominated ocean processes near ice shelf grounding lines

Glaciological processes at grounding lines, which divide floating ice shelves from grounded ice sheets, may strongly influence the dynamics and evolution of inland ice. Therefore, understanding the oceanic forcing on ice shelves in this region is of importance to predictions of cryospheric change and sea level rise. As the ocean cavity shallows toward the grounding line, tidal mixing becomes proportionately more important until a tidal front forms, beyond which the water properties are vertically homogenized. The extent of this mixed zone is relevant to several questions because a fully mixed region behaves differently to the stratified ocean offshore. In this study a highly simplified one-dimensional model is used to examine the size, properties, and sensitivities of the mixed zone. The model suggests that most grounding line mixed zones are small, implying that the usual models representing a stratified ocean are generally valid if tidal mixing is also taken into account. Modeled mixed zones can be significant in near-freezing regions with vigorous tides and a shallowly sloping cavity, but even these areas are smaller than previously proposed. It therefore seems that upwelling of warm water, rather than mixing in tidal zones, generally maintains ice shelf basal melting near grounding lines. Where mixed zones are present, the model suggests that they insulate the grounding line from offshore ocean waters. The model illustrates the origin of Ice Shelf Water plumes and confirms that unlike elsewhere in the cavity, melting in the mixed zone increases linearly in response to ocean warming.