Comment on egusphere-2023-73

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> One of the last remaining Greenland Ice Sheet (GrIS) glaciers featuring a floating tongue &ndash; the Petermann Glacier Ice Shelf (PGIS) is seasonally shielded by the formation of sea ice arches in the Nares Strait. However, continued decline of the Arctic sea ice extent and thickness suggest that arch formation is likely to become anomalous, necessitating an investigation into the response of PGIS to a year round mobile and thin sea ice cover. We use a high-resolution 3-D ocean-sea ice-ice shelf setup featuring an improved sub-ice shelf bathymetry and a realistic PGIS geometry, to investigate in unprecedented detail, the implications of transitions in the Nares Strait sea ice regime; from <em>Thick Landfast</em> to <em>Thick Mobile</em> and <em>Thin Mobile</em>, on the PGIS basal melt. Across all three regimes, basal melting increases occur during summer, and under the deeper (&gt; 250 m) regions of the ice shelf. Diagnosing this variability via melt rate drivers suggest that a higher thermal driving under the deeper regions causes higher melt rates, which, as a secondary effect, increases the friction velocity slightly downstream. The increased meltwater production and a stronger melt overturning in the PGIS cavity deliver more meltwater from depth to the shallower regions which lowers the thermal driving and basal melt in these regions; with the winter season showing a converse pattern. Modulations in surface forcing under a mobile and thin sea ice cover act to enhance the heat transport in the cavity, enhancing the thermal driving and friction velocity at the ice shelf base, and thereby, the basal melt. Thermodynamically, under mobile sea ice, wind upwelled Atlantic Water (AW) from the Nares Strait enter the cavity. Additionally, when sea ice thins, convective overturning drives further upwelling of AW in winter. Mechanically, wind driven inflow intensifies, and is most pronounced under a (negligibly thin) mobile summer sea ice cover; and where it acts in concert with the stronger melt overturning to enhance the friction velocity which predominantly drives the basal melt under the deeper regions. These results suggest that the projected continuation of the warming of the Arctic Ocean until the end of the 21st century and the decline in Arctic sea ice extent and thickness will amplify the basal melt, impacting the long term stability of the Petermann Glacier and its contribution to the future GrIS mass loss and sea level rise.