A continuum model (PSUMEL1) of ice melange and its role during retreat of the Antarctic Ice Sheet

Rapidly retreating thick ice fronts can generate large amounts of melange (floating ice debris), which may affect episodes of rapid retreat of Antarctic marine ice. In modern Greenland fjords, melange provides substantial back pressure on calving ice faces, which slows ice front calving rates. On the much larger scales of West Antarctica, it is unknown if melange could clog seaways and provide enough back pressure to act as a negative feedback slowing retreat. Here we describe a new melange model, using a continuum-mechanical formulation that is computationally feasible for long-term continental Antarctic applications. It is tested in an idealized rectangular channel and calibrated very basically using observed modern conditions in Jakobshavn fjord, West Greenland. The model is then applied to drastic retreat of Antarctic ice in response to warm mid-Pliocene climate. With melange parameter values that yield reasonable modern Jakobshavn results, Antarctic marine ice still retreats drastically in the Pliocene simulations, with little slowdown despite the huge amounts of melange generated. This holds both for the rapid early collapse of West Antarctica and for later retreat into major East Antarctic basins. If parameter values are changed to make the melange much more resistive to flow, far outside the range for reasonable Jakobshavn results, West Antarctica still collapses and retreat is slowed or prevented only in a few East Antarctic basins.