On the Role of Air-Sea-Ice Interactions off East Antarctica
Abstract
In some segments of the Antarctic continental shelf, salt released during sea-ice
production transforms near-freezing Antarctic surface waters into saltier (S > 34.52) and
denser Shelf Water. Near the shelf break of these locations, somewhat attenuated Shelf
Water outflows and sinks down the continental slope, entraining relatively warmer
Circumpolar Deep Water to form Antarctic Bottom Water. Thus, sea-ice formation plays
a climate-relevant role in the global Meridional Overturning Circulation.
Similar geographic and oceanographic characteristics are found off the Sabrina and
Adélie coasts in East Antarctica, therefore Shelf Water is unexpectedly found only in the
Adélie Depression and lacking in the Sabrina Basin. A combination of in-situ, remote,
and reanalysis datasets from 2003-2015 are used in this study to investigate the
conditions leading to Sabrina’s relatively passive role. For the first time, sea-ice
production rates are estimated combining both the net sea-ice volume exchanged across
the shelf break (export) and the volume variability farther inshore (growth).
The Sabrina Basin produces an average of 197 km^3/yr of sea-ice, 97% of which is
exported offshore across the western shelf break. Sabrina’s high sea-ice production rate
is well correlated (0.95) to divergent sea-ice motion within the interior of the shelf. In
contrast, the Adélie Basin produces only 34 km^3/yr of sea-ice. Sea-ice productivity
(production per unit area) in Sabrina Basin (4.6 m/yr) is comparable to the Ross Sea (4.5
m/yr), but still higher than the Adélie Basin (1.9 m/yr).
Based on the estimated contributions of salt, from sea-ice production, and
freshwater, from both sea-ice and glacial-ice melt, the salinity evolution of a thick
subsurface Thermostad Water layer is reconstructed for 2003–2015. A melt rate of 157.5
Gt/yr in the Totten Glacier and Moscow University Ice Shelf system is required to match
the Thermostad Water salinities measured during the summers of 2014 and 2015.
Shelf Water (S > 35.52) was initially produced during the winters of 2003-2008.
SW formation stopped, however, during 2008-2011 when summer sea-ice divergence
and cross shelf break export (~10 km^3) were at a minimum, which resulted in a
prominent Thermostad Water freshening of -5.07 ΔS per decade. In contrast, large
summer sea-ice exports (>30 km3) since 2011 have significantly increased the
Thermostad Water salinity at a rate of 2.16 ΔS per decade. Thus, it is projected that local
Antarctic Surface Water will form Shelf Water again by 2017, and the Sabrina Basin
could participate more actively in the global Meridional Overturning Circulation than it
has during the past decade.
Citation
Webb, Cody James (2017). On the Role of Air-Sea-Ice Interactions off East Antarctica. Master's thesis, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /173060.