Seafloor roughness reduces melting of East Antarctic ice shelves

Heat delivered by the ocean circulation is melting the Antarctic ice sheet from below. This melt is largest where warm Circumpolar Deep Water accesses the continental shelf and reaches the ice shelf cavities. Future melt rate projections are based on ocean thermal forcing derived from climate models, which tend to be biased warm around Antarctica. The bias has been attributed to unresolved ocean processes that occur at scales poorly represented in models. Using a high-resolution model of the Denman Glacier region we show that seafloor roughness unresolved in climate models suppresses the impact of warm water on ice sheet melting. Seafloor roughness slows down the shelf circulation, reducing the presence of warm water over the shelf and the heat transport towards the ice cavities. As a result, the total meltwater discharge drops by 4 Gt year-1. Our results suggest a mechanism missing in global ocean and climate models that could reduce the spread in climate projections. Bathymetry-based numerical simulations suggest small-scale seafloor roughness in the continental shelf of East Antarctica slows the circulation of circumpolar deep water and limits heat supply to the ice shelf-a mechanism missing from climate models.