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Images & Movies from NSIDC |
See Alsopress release: Antarctic Ice Shelves Breaking Up, Due to Decades of Higher Temperatures |
Below are four images showing the last year of evolution of the Larsen B ice shelf. Images are in either the thermal band (dark areas are warmer) or the visible band. Note presence of melt ponds in February 15 and possibly in the November 20 images.
Total shelf area lost over the four scenes is approximately 1839 km2; between March 23, 1998 and November 20, 1998 about 1037.5 km2; between November 20, 1998 and March 18, 1999 approximately 676.5 km2.
Note the differences between the northern and southern half of the calving front. The northern half of the front is curved, with myriad tabular bergs in front of it - very similar to what was seen across the entire front of the Larsen A during breakup. The southern half is also retreating, but is not "embayed." In the earlier images from February and March, the northern half again "led the way" in terms of breakup. Note also that the ice front on the November 20th image appears to have followed a crack barely visible on the February 15th image.
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Summertime images of this area consistently show melt ponding present in the northern half of the shelf, and absent in the southern half - so there is an implied link between extensive surface melting and breakup.
Recent models by Christina Hulbe indicate that the shelf ice stiffness suggests a low internal temperature. This implies that most of the shelf ice comes from cold glacial catchment areas in the mountains of the Antarctic Peninsula. Cold ice is stiff ice. This stiffness is a key factor in determining its stability. For the southern Larsen B, the glacial catchments are considerably further south, and presumably cooler. Downslope winds, following the glacier troughs, are probably also cooler on average and therefore would cause less surface melt. Thus, the southern section might be more stable than the north.
Surface flowstripes on both the Larsen A and Larsen B cross the entire former extent of those shelves, at least in the vicinity of Robertson Island (visible in SAR, but not the above AVHRR scenes). These features are inferred to form at the grounding line and above as part of glacier flow. Using this assumption and the ice flow speed provides an estimate of the minimum age of the shelves: about 400 years (if the flow speed observed at present has not changed much over time). In other words, it appears that the shelves were stable for centuries prior to the present events.
