The distribution and formative processes of latent-heat polynyas in East Antarctica

Abstract

A study of polynya characteristics in East Antarctica was undertaken using ice concentrations derived from special sensor microwave/imager data for the period July 1987-August 1994. The areas ofpolynyas were defined as having an ice concentration :=;75%. The analysis revealed a total of28 coastal polynyas within the study region. The spatial and temporal variability in areal extent was quantified. The timing of mean maximum area1 extent varied fromJune to October. The bathymetry and wind regime at each polynya site was examined to gauge the relative importance of these parameters in polynya formation and maintenance. In 20 locations, shallow banks and shoals form grounding zones for icebergs and anchoring sites for fast ice, which form barriers to the predominantly westward drift of the pack ice; elsewhere north-south coastal protrusions or alignments form similar barriers. The subsequent removal of newly formed sea ice from the lee of such barriers by katabatic and synoptic winds maintains areas of reduced ice concentration and open water. Very few coastal po1ynyas are attributed solely to katabatic outnow. The combined influence of bathymetry, topography and winds is responsible for the characteristics of the majority of polynyas. Many were considered to be marginal, characterised by occasional periods when the ice concentration falls below 75 %. An analysis of annual winter totals of areas with ice concentrations < 75 % shows no trends in total polynya areal extent over the period 1987-94. Known locations of emperor penguin (Aptenodytesforsteri) rookeries were also found to be associated with the locations of coastal polynyas.

Life Hung by a Thread: Endurance of Antarctic Fauna in Glacial Periods

“…Thus, a coastal polynya is typically a location where large amounts of sea ice are generated (''sea-ice factory''). At the sites of recurring coastal polynyas (e.g., in the Bellingshausen, Amundsen, and Ross Seas [Massom et al 1998, Zwally et al 2002, Arrigo and van Dijken 2003), only a thin ice cover, compared to the thicker surrounding pack ice, forms during wintertime, which allows a much earlier spring melt and an earlier start in photosynthetic primary productivity that nourishes the entire food web in the high Antarctic.…”

Seasonal changes in glacial polynya activity inferred from Weddell Sea varves

“…However, Antarctic polynyas mainly occur on the continental shelves as well as close to the coasts (Massom et al, 1998) and are latent-heat polynyas, driven by wind force (Barber and Massom, 2007), e.g. katabatic winds.…”

Potential regime shift in decreased sea ice production after the Mertz Glacier calving

“…An important feature of the GV regional icescape (that is, the interaction of topography, ice sheet/ice shelf configuration and fast ice) has been the blocking of the westward advection of sea ice [10][11][12] by the existence of the Mertz Glacier Tongue (MGT), together with a large iceberg (B9B) and surrounding fast ice. This promotes polynya activity, and hence dense shelf water formation, which is driven by cold offshore winds 13,14 . In the Adélie Depression, polynyas typically formed in the coastal bays (Commonwealth, Watt and Buchanan Bays labelled CB, WB and BB, respectively) and along the western lee of the MGT.…”