Glaciology: Ice-shelf stability questioned.

Abstract

Surface lakes and streams are forming on Antarctica's ice shelves, making them susceptible to instability and possible collapse. But rivers could mitigate this effect by efficiently exporting meltwater to the ocean. See Letters p.344 & p.349 The collapse of ice shelves can be hastened by surface meltwater that can seep into crevasses and refreeze, causing hydrofracturing. Such a mechanism was observed in the collapse of the Larsen B Ice Shelf on the Antarctic Peninsula. Robin Bell et al. show that in the Nansen Ice Shelf, Antarctica, a surface river has been in operation for over a century. The river terminates in a waterfall that can drain all of the surface meltwater produced annually by the ice shelf in one week. Thus, for the Nansen it seems that this surface drainage mechanism might be preventing meltwater from destabilizing the ice shelf. It isn't clear at present why meltwater is retained in some systems and drained in others, but the finding suggests that meltwater may not be a universally destructive force. Elsewhere in this issue, Jonathan Kingslake et al. report on the extent of meltwater across Antarctica and find that surface drainage systems have existed for decades as far as 85° S. Melt ponds and streams form across Antarctica, but their full extent and the duration of their existence have remained unclear. Now, Jonathan Kingslake et al. show that surface drainage systems, including interconnected ponds and streams, have existed for decades as far as 85° S and up to 1,300 metres elevation. They show that surface water can be transported more than 100 kilometres, creating pond networks almost 80 kilometres long. Although the implications of the findings for ice-sheet dynamics are not explored, the study demonstrates that surface water drainage is more extensive than previously thought, and is probably a persistent feature of the Antarctic Ice Sheet. Elsewhere in this issue, Robin Bell et al. report on the influence of surface meltwater on Antarctic ice-shelf stability and find that it might not be a universally destructive force as was previously thought.