Abstract
Abstract. Ice-shelf–ocean interactions are a major source of freshwater on the Antarctic continental shelf and have a strong impact on ocean properties, ocean circulation and sea ice. However, climate models based on the ocean–sea ice model NEMO (Nucleus for European Modelling of the Ocean) currently do not include these interactions in any detail. The capability of explicitly simulating the circulation beneath ice shelves is introduced in the non-linear free surface model NEMO. Its implementation into the NEMO framework and its assessment in an idealised and realistic circum-Antarctic configuration is described in this study. Compared with the current prescription of ice shelf melting (i.e. at the surface), inclusion of open sub-ice-shelf cavities leads to a decrease in sea ice thickness along the coast, a weakening of the ocean stratification on the shelf, a decrease in salinity of high-salinity shelf water on the Ross and Weddell sea shelves and an increase in the strength of the gyres that circulate within the over-deepened basins on the West Antarctic continental shelf. Mimicking the overturning circulation under the ice shelves by introducing a prescribed meltwater flux over the depth range of the ice shelf base, rather than at the surface, is also assessed. It yields similar improvements in the simulated ocean properties and circulation over the Antarctic continental shelf to those from the explicit ice shelf cavity representation. With the ice shelf cavities opened, the widely used three equation ice shelf melting formulation, which enables an interactive computation of melting, is tested. Comparison with observational estimates of ice shelf melting indicates realistic results for most ice shelves. However, melting rates for the Amery, Getz and George VI ice shelves are considerably overestimated.
Highlights
Ice shelf melting, which accounts for 55 % of the ice mass loss from Antarctica, is one of the main sources of freshwater input to the Antarctic coastal ocean
A z∗ vertical coordinate has been included within the NEMO framework (Madec and the NEMO team, 2016), and the ice shelf module as well as the ice shelf parametrisation are developed using this vertical coordinates and considering ice shelf melting as a mass flux
The work represents the first step toward a couple ice sheet–ocean model
Summary
Ice shelf melting, which accounts for 55 % of the ice mass loss from Antarctica, is one of the main sources of freshwater input to the Antarctic coastal ocean. When the inflow has a temperature at or close to the surface freezing point (HSSW or WW), melting at depth is accompanied by partial refreezing at higher levels, as the falling pressure results in a rising freezing point temperature In this case, the out-flowing water mass produced is designated as ice shelf water (ISW), and has a temperature below the surface freezing point. Global conservation is an important issue, as the ocean–sea-ice model is used as a component within Earth system models To tackle this issue, a z∗ vertical coordinate has been included within the NEMO framework (Madec and the NEMO team, 2016), and the ice shelf module as well as the ice shelf parametrisation are developed using this vertical coordinates and considering ice shelf melting as a mass flux. In a summary section (Sect. 6), the major results as well as the remaining issues are highlighted, and we conclude with details of code availability
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