Variability in the Distribution of Fast Ice and the Sub‐ice Platelet Layer Near McMurdo Ice Shelf

Abstract

Variability in the volume of supercooled Ice Shelf Water outflow in McMurdo Sound is reflected in the thickness and distribution of fast ice and the sub‐ice platelet layer beneath. Ground‐based electromagnetic induction and drill hole surveys of the distribution and thickness of ice shelf‐influenced fast ice and the sub‐ice platelet layer in McMurdo Sound were carried out in late spring of 2011, 2013, 2016, and 2017. In 2011 and 2017, thicker sub‐ice platelet layers of up to 7.5 and 6 m were observed, respectively. Fast ice formation throughout the winters of 2011 and 2017 was influenced by a higher occurrence of strong southerly wind events and resultant activity of the Ross Sea Polynya. In contrast, lower wind conditions in 2016 led to largely undisturbed sea ice growth and anomalously extensive fast ice coverage. A thinner sub‐ice platelet layer of up to 4 m was observed in 2016. In 2011 and 2017, substantial and variable sub‐ice platelet layers were detected in a region of exchange of water masses between the Ross Sea and the McMurdo‐Ross ice shelf cavity, which were not observed in 2013 and 2016. We hypothesize that a higher frequency of strong southerly wind events, resultant polynya activity, and High Salinity Shelf Water production over winter accelerates circulation and increases melting in the proximal shallow McMurdo Ice Shelf and the deeper Ross Ice Shelf regions of the conjoined cavity. The outflow of supercooled Ice Shelf Water and sub‐ice platelet layer formation in McMurdo Sound are consequently promoted.

Satellite altimetry detection of ice shelf-influenced fast ice

“…The outflow of supercooled ISW from the McMurdo Ice Shelf cavity augments fast ice formation (Robinson et al, 2014), fast ice thickness (Gough et al, 2012, Langhorne et al, 2015 and forms a thick SPL in McMurdo Sound (Dempsey et al, 2010, Gough et al, 2012, Langhorne et al, 2015. In the central-western region of the sound, a consistent pattern of thicker ice shelf-influenced fast ice with a substantial SPL beneath has been observed in proximity to the ice shelf 105 margin in multiple studies, e.g., Brett et al (2020), Price et al (2014). This pattern is driven by the outflow of supercooled ISW from the centre and west of the McMurdo Ice Shelf cavity and its subsequent circulation along the Victoria Land Coastline (Hughes et al, 2014, Lewis and Perkin, 1985, Robinson et al, 2014.…”

“…In the western Ross Sea, an interactive system is at play between coastal polynyas, the conjoined McMurdo and Ross Ice Shelf, and fast ice in the field study area in McMurdo Sound (Brett et al, 2020). McMurdo Sound is geographically delineated by the Victoria Land Coastline in the west, Ross Island in the east, and the McMurdo Ice Shelf in the south (Fig.…”

“…This pattern is driven by the outflow of supercooled ISW from the centre and west of the McMurdo Ice Shelf cavity and its subsequent circulation along the Victoria Land Coastline (Hughes et al, 2014, Lewis and Perkin, 1985, Robinson et al, 2014. The effect of supercooled ISW is most pronounced within ~30 km of McMurdo Ice Shelf (Brett et al, 2020, Hughes et al, 2014 but could extend 200-250 km to the north (Stevens et al, 2009, Hughes et al, 2014. ISW circulation has been modelled to increase fast ice growth by 9 ± 4 cm yr −1 110 100 km north of the ice shelf edge (Hughes et al, 2014).…”

Referee comments

“…Printer-friendly version Discussion paper Line 71. I suggest the authors include the work of Price et al (2014) and Brett et al (2020) as they also report on the accumulation of sub-ice platelet layers under the sea ice.…”

Response to Anonymous Referee #1

“…Line 71. I suggest the authors include the work of Price et al (2014) and Brett et al (2020) as they also report on the accumulation of sub-ice platelet layers under the sea ice. #The suggested references have been included.…”