Abstract
Abstract. Persistent outflow of supercooled ice-shelf water (ISW) from beneath McMurdo Ice Shelf creates a rapidly growing sub-ice platelet layer (SIPL) with a unique crystallographic structure under the sea ice in McMurdo Sound, Antarctica. A vertically modified frazil-ice-laden ISW plume model that encapsulates the combined non-linear effects of the vertical distributions of supercooling and frazil concentration on frazil-ice growth is applied to McMurdo Sound and is shown to reproduce the observed ISW supercooling and SIPL distributions. Using this model, the dependence of the SIPL thickening rate and depth-averaged frazil-ice concentration on ISW supercooling in McMurdo Sound is investigated and found to be predominantly controlled by the vertical distribution of frazil concentration. The complex dependence on frazil concentration highlights the need to improve frazil-ice observations within the sea-ice–ocean boundary layer in McMurdo Sound.
Highlights
Ice shelf basal melting removes more mass from the Antarctic Ice Sheet than iceberg calving does, but the three largest ice shelves, Filchner-Ronne, Ross, and Amery, contribute only 18 % of the net meltwater flux (Rignot et al, 2013)
As this study represents the first application of a two-dimensional ice-shelf water (ISW) plume model to the McMurdo Sound region, extensive tuning of the least constrained model parameters, including the ISW outflow properties, sub-ice platelet layer (SIPL) basal drag coefficient, frazil-ice crystal size distribution, ambient current speed, and Shields criterion was required to produce the distributions of ISW properties and SIPL thickness shown in Figs. 4a and 6, respectively
We demonstrated how the vertical distributions of supercooling and frazil ice concentration within an ISW plume jointly determine the growth of suspended frazil ice, and the rate of SIPL formation under sea ice and marine ice beneath ice shelves
Summary
Ice shelf basal melting removes more mass from the Antarctic Ice Sheet than iceberg calving does, but the three largest ice shelves, Filchner-Ronne, Ross, and Amery, contribute only 18 % of the net meltwater flux (Rignot et al, 2013). C. Cheng et al.: SIPL thickening rate and frazil-ice concentration in McMurdo Sound from plume theory (Holland and Feltham, 2006; Jenkins and Bombosch, 1995; Rees Jones and Wells, 2018; Smedsrud and Jenkins, 2004) but include three-dimensional ocean circulation models (Galton-Fenzi et al, 2012) and have been widely applied to assess the marine ice beneath FilchnerRonne (Bombosch and Jenkins, 1995; Holland et al, 2007; Smedsrud and Jenkins, 2004), Larsen (Holland et al, 2009) and Amery ice shelves (Galton-Fenzi et al, 2012), and SIPL under the sea ice in McMurdo Sound (Hughes et al, 2014, hereinafter HU14). The main objective is to explore the possibility of finding the quantitative relationship between the SIPL thickening rate and ISW supercooling Establishing such a relationship is of significance to the assessment of total seaice thickness and the oceanic heat flux associated with SIPL in McMurdo Sound and elsewhere. We conduct 211 sensitivity simulations with the purpose of quantitatively establishing the response of the SIPL thickening rate as well as the frazil-ice concentration to variations in ISW supercooling in McMurdo Sound
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