The Non-Local Impacts of Antarctic Subglacial Runoff

Little is known about Antarctic subglacial hydrology, but based on modeling, theory and indirect observations it is thought that subglacial runoff enhances submarine melt locally through buoyancy effects. However, no studies to date have examined effects of runoff on sea ice and oceanography on the continental shelf. Here we use modeled and observational estimates of runoff to force a regional model of the Amundsen Sea Embayment. We find that runoff enhances melt locally (i.e., within the ice-shelf cavity), increasing melt at Thwaites ice shelf by up to 15 Gt/a given estimates of steady runoff, and up to 25 Gt/a if runoff is episodic as remote sensing measurements suggest. However runoff also has smaller non-local effects on melt through freshwater influence on flow and stratification. We further find that runoff reduces summer sea-ice volume over the continental shelf (by up to 10% with steady runoff but over 30% with episodic runoff). Furthermore runoff is much more effective at reducing sea ice than an equivalent volume of ice-shelf meltwater-due in part to the latent heat loss associated with submarine melting. Results suggest that runoff may play an important role in continental shelf dynamics, despite runoff flux being small relative to ice-shelf melting-and that runoff-driven melt and circulation may be an important process missing from regional Antarctic ocean models. A number of floating ice shelves in Antarctica are exposed to warm waters which lead to strong melting, limiting shelves' ability to buttress against ice flow from the continent and also bringing warmed and freshened waters to the ocean surface-waters which in turn influence seasonal sea ice near the continent and insulate the deep ocean from the cold atmosphere. Meanwhile, large rivers under the Antarctic ice sheet carry melt from the ice sheet base to the ocean cavities beneath ice shelves. While a few studies have looked at the role these rivers play in ice-shelf melt, they do not examine the effects on ocean properties and sea ice in the open ocean. We find that these "rivers" not only amplify melting under ice shelves, but have far-reaching impacts on ocean circulation. We find that while the direct contribution of water from these subglacial rivers is small compared to that of ice-shelf melt, there is a disproportionate impact on seasonal sea ice. Modeled and observed subglacial runoff estimates are used to force a regional model of the Amundsen Sea EmbaymentRunoff influences melt rates regionally as well as locally, and leads to reduction of summer sea ice volume on the continental shelfRunoff impacts on sea ice differ qualitatively from those of an equivalent volume of ice-shelf melting