Fast Ice: Redux – West Antarctica
I want to return to an old subject. Early on in this blog I wrote a series of blogs about melting ice on land. Here are the links to those blogs. Fast Ice 1The End of Ice Warm Snow
These previous blogs talked about how glaciers and ice sheets that have their ends in the seas and at ice shelves have many interesting ways to melt. There is also the discussion of how in an atmosphere which is warming there is the possibility of their being more snow on the ice sheets in East Antarctia and Central Greenland. Hence, there is this idea of a balance, in this case the balance of mass of water in the ice sheets. There is melting and there is accumulation.
Figure 1: Figure and Caption Text from University of Texas (link
): Schematic of the West Antarctic ice sheet and its lithospheric setting. The interior ice reservoir is the portion of the ice sheet below the ice divide where the ice sheet is attached to its bed. This interior ice is penetrated and drained by the fast moving ice streams which flow between regions of relatively stagnant ice. The open arrows indicate the gliding of ice over its bed from the onset region toward the ice shelf. Beneath the ice streams the lubricating till is illustrated. The extensional nature of the underlying lithosphere is indicated by the sediment filled grabens beneath the ice streams.
These first blogs were written at the time of the publication of the first of the IPCC reports. One of the most controversial scientific issues at the release of the report was whether or not the melting of ice on land had been underestimated. This has continued to be an item of discussion in the scientific community. (I am of the opinion that most of our representation of the melting of land ice in models has been underestimated.)
I found a recent news article in EOS, The Transactions of the American Geophysical Union
especially interesting. The article is entitled West Antarctic Links to Sea Level Estimation
by David Vaughan, John Holt, and Donald Blankenship. This is a article that discusses the issues of understanding the evolution of the glaciers that make up the West Antarctic Ice Sheet. One of the first things that struck me is how dependent we are on satellite data to get information on the ice sheets. This is partly due to their remote location, but also due to the large spatial extent of the glacier and the need to have coordinated measurements of the glacier in order to determine the speed of movement, and hence, to calculate the mass balance.
The article by Vaughn, Holt, and Blankenship is careful to pose their discussion of the glaciers in terms of possible processes. For instance, given the dependence on the short-term satellite record, their is the question of whether or not we are seeing short-term variability or melting due to global warming. In this article, the authors focus on the Amundsen Sea Embayment ice sheet. They point out that atmospheric warming is not sufficient to cause melting of ice on the surface of the ice sheet. There is, however, increasing evidence that the warming of the ocean, especially at the bottom of the ice shelf that extends out into the ocean, is accelerating the melting of the glacier, and leading to the increased speed of the glacial movement.
A little more than a year ago I was lecturing at a summer school where Andrew Shepherd
gave a fascinating series of lectures on the Pine Island Glacier. This is another glacier in West Antarctica where there has been increasing motion and melting. These talks provided a convincing argument that warming in the ocean was not only contributing to the melting at the shoreline, but that the heating was being diffused into the interior of the glacier --- accelerating the motion. (Here are some cool figures and information from Shepherd and Wingham's 2007 paper in Science Recent Sea-Level Contributions of the Antarctic and Greenland Ice Sheets
Here is a link to a web page from the European Space Agency
, that talks about the space-based radar observations
that are used to study these remote glaciers. On the right of this page are some links to some interesting sites, some with pictures of melt rates in the glaciers of the West Antarctic Ice Sheet.