August 25, 2011
A recent paper by Shuman et al (2011) in the Journal of Glaciology examined the thinning and retreat of glaciers feeding the area that used to contain Larsen Ice Shelf B and the southern end of Larsen Ice Shelf A. They found that the thinning of over 80 meters occurred over large areas of Hektoria, Jorum, Evans, Crane and Green Glaciers. Terminus retreat of five kilometers of the primary glaciers from late 2002-2009 occurred for Larsen B. The rapid loss of thickness and retreat has accompanied the expected and observed acceleration of the glaciers after ice shelf loss. The removal of an ice shelf is a substantial reduction in the backforce on a feeder glacier, or like taking off the brakes. Pine Island Glacier is another example where this is of concern. The Shuman et al (2011) paper particularly the figures are compelling and prompted me to take a look at one embayment in the Larsen A region that is experiencing ongoing glacier retreat. The area has been mapped by USGS and is referred to as the Nordenskjöld Coast. We will look at the unnamed embayment marked B, between Drygalski and Dinsmoor Glacier. This embayment which has formed in the last decade is 25 square kilometers in area.The above map indicates the extensive retreat due to the Larsen A ice Shelf loss that took place in the mid-1990’s and the development of the embayment by 2009. The five glaciers that feed it flow from the center of the Antarctic Peninsula, upper left in the image below. . The embayment itself has numerous icebergs suggesting the rapid ice discharge from the glaciers feeding this bay. This bay has been ice covered for a long time, transitioning from a grounded ice sheet to an ice shelf environment 10,700 years ago, and which has persisted since (Brachfield et al, 2003). The embayment did not expanded notably from the Landsat imagery from 2001 to 2009, as seen in the 2001 Landsat. In 2011 the retreat was significant as seen in MODIS imagery from Jan.27 the embayment has developed two lobes (note black arrows in image below.. The southern lobe has expanded by 1.5 km. The northern lobe by a smaller amount, but the area between glacier 4 and 5 is now a headland, indicating at least 500 meters of retreat.. The glaciers in this bay do not appear to have large floating sections generating tabular icebergs at this point, such as are evident on Fleming Glacier.