Abstract
AbstractThe surface flooding of Antarctic sea ice in summer covers 50% or more of the sea-ice area in the major summer ice packs, the western Weddell and the Bellingshausen-Amundsen Seas. Two CRREL ice mass-balance buoys were deployed on the Amundsen Sea pack in late December 2010 from the icebreaker Oden, bridging the summer period (January–February 2011). Temperature records from thermistors embedded vertically in the snow and ice showed progressive increases in the depth of the flooded layer (up to 0.3–0.35 m) on the ice cover during January and February. While the snow depth was relatively unchanged from accumulation (<10 cm), ice thickness decreased by up to a meter from bottom melting during this period. Contemporaneous with the high bottom melting, under-ice water temperatures up to 1°C above the freezing point were found. The high temperature arises from solar heating of the upper mixed layer which can occur when ice concentration in the local area falls and lower albedo ocean water is exposed to radiative heating. The higher proportion of snow ice found in the Amundsen Sea pack ice therefore results from both winter snowfall and summer ice bottom melt found here that can lead to extensive surface flooding.
Highlights
Snow ice, formed by the sea-water flooding of basal layers of the snowpack on sea ice and subsequent freezing, has been found throughout the Antarctic pack ice zone (e.g. Eicken and others, 1994; Worby and others, 1998; Jeffries and others, 2001)
The formation process can be relatively continuous over large regions of the Antarctic sea-ice zone, since high ocean heat flux melts ice from the bottom, while redistribution and precipitation of snow occurs on the top
The ocean heat flux during January from S-Buoy ocean properties would give a melt rate of only 0.6 cm d−1 compared to measured melt rate of 1.4 cm d−1 from ice thickness changes
Summary
Snow ice, formed by the sea-water flooding of basal layers of the snowpack on sea ice and subsequent freezing, has been found throughout the Antarctic pack ice zone (e.g. Eicken and others, 1994; Worby and others, 1998; Jeffries and others, 2001). The formation process can be relatively continuous over large regions of the Antarctic sea-ice zone, since high ocean heat flux melts ice from the bottom, while redistribution and precipitation of snow occurs on the top. Both processes, either independently or in concert, can cause the interface between the snow and the ice to be lowered below sea level and become ‘primed’ for flooding (Lytle and Ackley, 2001). The material within the column of ice itself has been transformed as if on a ‘vertical conveyor belt’, melting from the bottom and reforming through new snow, flooding and slush freezing on the top and so, may have nearly completely different composition at the end than it did at the beginning of winter (Lytle and Ackley, 2001; Maksym and others, 2012)
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