Abstract
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 sub-shelf 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.
Highlights
Dynamic ice discharge across the grounding lines into floating ice shelves is the main mass loss process of the Antarctic Ice Sheet
Cess the ice-shelf cavities and reach their grounding lines. This implies for example, that barriers like sills that may prevent intrusion of warm circumpolar deep water (CDW) are not accounted for and might explain why Potsdam Ice-shelf Cavity mOdel (PICO) melting is too high for the ice shelves located along the Southern Antarctic Peninsula
The model extends the one-horizontal dimensional ocean box model by OH10 to realistic ice-shelf geometries following the shape of the grounding line and calving front
Summary
Plumes evolve depending on the ice-shelf draft and slope, sub-glacial discharge and entrainment of ambient ocean water This approach has been applied to models with characteristic conditions for Antarctic ice shelves (Holland et al, 2007; Payne et al, 2007; Lazeroms et al, 2018) and for Greenland outlet glaciers and fjord systems (Jenkins, 2011; Carroll et al, 2015; Beckmann et al, 2018). 3, we derive a valid parameter range for present-day Antarctica and compare the resulting sub-shelf melt rates to observational data This is followed by a discussion of the applicability and limitations of the model This is followed by a discussion of the applicability and limitations of the model (Sect. 4) and conclusions (Sect. 5)
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