Effects of regional fast-ice and iceberg distributions on the behaviour of the Mertz Glacier polynya, East Antarctica

Abstract

An observational account of research carried out in July-August 1999 shows that grounded iceberg and related fast-ice distributions, and periodic "break-outs" of fast ice (in winter as well as at other times), have an important impact on the size and behaviour of the Mertz Glacier polynya, East Antarctica, and a smaller polynya to the east. Analysis of satellite and in situ data shows that a semi-constant "stream" of thick broken-out fast ice and other large floes from the east extends westwards from north of the glacier terminus to form a compact barrier to the net west-northwesterly export of ice formed in the polynya. An annual fast-ice promontory to the west further narrows the outlet path. As a result of this and high ice-production rates, the polynya periodically "back-fills", significantly reducing the open-water area present. Intervening "flush-outs" by synoptic storm events clear the polynya region to some extent before it back-fills again. This cycle continued from mid-March until early October in 1999, when a significant change in the regional ice drift occurred. A preliminary comparison with data from 1998 indicates that the timing and magnitude of the processes may vary interannually. Similar morphological features were also observed in 1963 (on a declassified photoreconnaissance satellite image).

Fast ice distribution in Adélie Land, East Antarctica: interannual variability and implications for emperor penguins Aptenodytes forsteri

“…The northern boundary, which is closely aligned with the continental shelf break (Fig. 3), is typically separated from the moving pack ice by a series of flaw leads, while the eastern margin is closely associated with the adjacent Mertz Glacier Polynya (Massom et al 2001). Comparison of the fast ice extent shown in Fig.…”

“…Responding rapidly to atmospheric and oceanic forcing, it is a sensitive indicator of climate change and/or variability (Murphy et al 1995, Heil 2006. As it can attain a considerable thickness (> 5 m for perennial fast ice, Massom et al 2001), it likely comprises a substantial proportion of the total Antarctic sea ice volume (Giles et al 2008) and forms an important component of the ocean freshwater budget. Moreover, fast ice is of critical ecological importance as a key habitat for microorganisms (Garrison 1991), a region of enhanced primary productivity (Satoh & Watanabe 1988, Arrigo et al 1993, McMinn et al 2000 and a breeding platform for Weddell seals Leptonychotes weddelli (Thomas & DeMaster 1983) and emperor penguins (Kirkwood & Robertson 1997a, Kooyman & Burns 1999.…”

Simulated melt rates for the Totten and Dalton ice shelves

“…5.1) attests to the scale of the ocean cavity being of the correct order. Fast ice is included from the maps of Fraser et al (2012) with a 5 m draft (Massom et al, 2001). …”

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

“…Observations of the George V Land (hereinafter GV) continental shelf from 1999-2004 describe a dual system of dense shelf water formation from enhanced sea ice production in the polynyas over the Adélie and Mertz Depressions [7][8][9] . 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. In the Mertz Depression, a smaller polynya formed in the western lee of the grounded iceberg B9B, which moved into the region from the Ross Sea in 1992 10 . Both the MGT and B9B have had fast ice extensions (sometimes referred to as 'daggers'), which formed each winter around the grounded icebergs to their north and contributed to the respective polynya zones (Fig.…”