The seasonal appearance of ice shelf water in coastal Antarctica and its effect on sea ice growth

Abstract

[1] In this paper we report measurements from the first year-round mooring underneath sea ice in McMurdo Sound, Antarctica, which we combine with full-depth ocean profiles to identify the incremental appearance of potentially supercooled ice shelf water (ISW). We investigate the effects of ISW on sea ice using observations of sea ice growth and crystal structure together with under-ice photography. We show that the appearance of ISW at the surface leads to a disruption in the columnar texture of the sea ice, but that persistent growth enhancement occurs only once the entire water column has cooled to the surface freezing point. In doing so, we demonstrate the possibility of inferring the presence of ISW beneath sea ice through crystallographic analysis of cores. These findings will be useful for both modeling and observing the extent of ISW-enhanced ice growth. In addition, we found that the local growth of first-year landfast sea ice only accounted for half of the observed increase in salinity over the water column, which indicates that polynyas are responsible for approximately half of the salt flux into McMurdo Sound.

Flow and mixing near a glacier tongue: a pilot study

“…9) were also the warmest and saltiest observed at this location. Wintertime results from a site several km to the south of the present field site in Erebus Bay showed how fronts passed through the observation site changing the local density structure markedly in only a few hours (Mahoney et al, 2011). These data end a month prior to our measurements and at the end of their record their temperatures were around 0.02 • C colder than our observations -more in keeping with previous CTD work (Fig.…”

“…This might be a diurnal cycle in scattering due to biological modulation as, despite the 24 h daylight, a variation in signal can persist in the region (personal communication A. Mahoney;Leonard et al, 2010) or due to variations in platelet/frazil ice concentration . Our sampling coincided with a period when the pulse occured near midnight local time (∼11:00 UTC) so it was co-located temporally with what should be a biologically-induced maximum data return (i.e.…”

“…2), at least during winter Mahoney et al, 2011). The primarily diurnal tides in the region are around 1 m in peak-peak elevation (Goring and Pyne, 2003) with a ∼14 day spring-neap cycle ( Fig.…”

“…Hellmer, 2004;Sirevaag et al, 2010;Rignot et al, 2010;Dimentrenko et al, 2010;Mahoney et al, 2011) where relatively long timescales and complex thermohaline and pressure effects interact with cryospheric topography that is continually changing. Oceanic mixing in polar waters includes different processes relative to those occurring at lower latitudes.…”

Evaluation of CryoSat-2 derived sea-ice freeboard over fast ice in McMurdo Sound, Antarctica

“…3) is located in the southwestern Ross Sea and occupies an area of �6400 km 2 . McMurdo Sound's proximity to ice shelves and the outflow of cold ice-shelf water from the ice-shelf cavity contributes to sea-ice formation in this area (Purdie and others, 2006;Dempsey and others, 2010;Mahoney and others, 2011;Gough and others, 2012;Price and others, 2014). This influence is hypothesized to be present in similar settings around the Antarctic with potential basin-wide implications (Hellmer, 2004;Bintanja and others, 2013).…”