Grounding Zones: The "Inland" Dynamic Interface Between Seawater, Outlet Glaciers, Subglacial Meltwater Routing, and Ice‐Shelf Processes.

Projections of sea‐level rise from ice‐sheet shrinkage in a warming world have large uncertainties, linked to limited knowledge of changes at the ocean‐ice sheet interface. This interface most typically is modeled as a grounding line, across which still‐connected ice flows into the ocean to float as an ice shelf, or where icebergs calve from a cliff before the ice begins to float. But, extensive and rapidly increasing evidence shows that this is really a grounding zone, and that processes in this grounding zone omitted from many models could exert major controls on sea‐level rise. Plain Language Summary: Marine‐terminating glaciers flow into the ocean across extensive grounding zones. These kilometers‐long and glacier‐wide zones represent the last broad region of glacier contact with the rock and sediments below before the ice enters the ocean as a floating ice shelf or calved icebergs. Loss of this basal drag along with enhanced basal melting caused by tidally driven seawater intrusion leads to faster outflow and rapid thinning of the overlying ice. As a result of the local thinning, grounding zones retreat inland and sea level rises with more loss of previously grounded ice. Most ice‐sheet models used in sea‐level projections do not include grounding‐zone processes, but rather stop their ice‐ocean interactions at a grounding line. They are thereby omitting important dynamic feedbacks and underestimating future sea‐level contributions from the marine‐based sectors of the Greenland and Antarctic ice sheets. Key Points: Tidally modulated seawater intrusion leads to loss of ice‐bed contact as well as significant (maximal) basal melting within grounding zonesThe future dynamics of marine outlet glaciers are ultimately controlled by coupled processes operating within and through grounding zonesDespite the importance of grounding zones to ice‐sheet dynamics, most ice‐sheet models used in sea‐level projections do not include them [ABSTRACT FROM AUTHOR]