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Abstract

Ocean-induced melting below ice shelves is one
of the dominant drivers for mass loss from the Antarctic
Ice Sheet at present. An appropriate representation of subshelf melt rates is therefore essential for model simulations
of marine-based ice sheet evolution. Continental-scale ice
sheet models often rely on simple melt-parameterizations,
in particular for long-term simulations, when fully coupled
ice–ocean interaction becomes computationally too expensive. Such parameterizations can account for the influence
of the local depth of the ice-shelf draft or its slope on melting. However, they do not capture the effect of ocean circulation underneath the ice shelf. Here we present the Potsdam
Ice-shelf Cavity mOdel (PICO), which simulates the vertical overturning circulation in ice-shelf cavities and thus enables the computation of sub-shelf melt rates consistent with
this circulation. PICO is based on an ocean box model that
coarsely resolves ice shelf cavities and uses a boundary layer
melt formulation. We implement it as a module of the Parallel
Ice Sheet Model (PISM) and evaluate its performance under
present-day conditions of the Southern Ocean. We identify a
set of parameters that yield two-dimensional melt rate fields
that qualitatively reproduce the typical pattern of comparably high melting near the grounding line and lower melting
or refreezing towards the calving front. PICO captures the
wide range of melt rates observed for Antarctic ice shelves,
with an average of about 0.1 m a−1
for cold sub-shelf cavities, for example, underneath Ross or Ronne ice shelves, to
16 m a−1
for warm cavities such as in the Amundsen Sea region. This makes PICO a computationally feasible and more
physical alternative to melt parameterizations purely based
on ice draft geometry.