Surface Melting an Increasing Factor in East Antarctica?

Or so says Climate Denial Crock of the Week. There’s no real text behind the headline, just a link to a WSJ video. This seems to be about Meltwater produced by wind–albedo interaction stored in an East Antarctic ice shelf, J. T. M. Lenaerts et al., Nature Climate Change (2016) doi:10.1038/nclimate3180, published online 12 December 2016. Here’s the abstract:

Surface melt and subsequent firn air depletion can ultimately lead to disintegration of Antarctic ice shelves1, 2 causing grounded glaciers to accelerate3 and sea level to rise. In the Antarctic Peninsula, foehn winds enhance melting near the grounding line4, which in the recent past has led to the disintegration of the most northerly ice shelves5, 6. Here, we provide observational and model evidence that this process also occurs over an East Antarctic ice shelf, where meltwater-induced firn air depletion is found in the grounding zone. Unlike the Antarctic Peninsula, where foehn events originate from episodic interaction of the circumpolar westerlies with the topography, in coastal East Antarctica high temperatures are caused by persistent katabatic winds originating from the ice sheet’s interior. Katabatic winds warm and mix the air as it flows downward and cause widespread snow erosion, explaining >3 K higher near-surface temperatures in summer and surface melt doubling in the grounding zone compared with its surroundings. Additionally, these winds expose blue ice and firn with lower surface albedo, further enhancing melt. The in situ observation of supraglacial flow and englacial storage of meltwater suggests that ice-shelf grounding zones in East Antarctica, like their Antarctic Peninsula counterparts, are vulnerable to hydrofracturing7.

The paper itself may be marvellous, I wouldn’t know, it is paywalled. I don’t understand the bit about the katabatic winds properly: in my world, katabatic winds are cold, which is why they flow off the continent. If they were warm, they wouldn’t. I can see that they will entrain air from outside the boundary layer that would be warmer, but if they warm too much again they stop flowing. The bit about winds blowing the snow clear and exposing blue ice is familiar, though. And that the albedo of such ice is lower than the snow is kinda obvious. That East Antarctic (as opposed to West) ice shelves are warm enough to melt from above is something of a surprise for me. ScienceDaily’s Mysterious ‘crater’ on Antarctica indication of vulnerable ice sheet is the same story I think, and includes “The crater isn’t new; we found it on satellite images from 1989. The amount of melt water differs immensely from year to year, but it clearly increases during warm years”. Ah, but that is them finding it retrospectively: it probably wasn’t known in my time.

What seems to be missing is context: how large is the melt, what fraction of snowfall is it, what would it be if translated into mm of SLR?

Apparently co-incidentally Scientists confirm that warm ocean water is melting the biggest glacier in East Antarctica (an improvement on the dreadful fb link I got it from, titled “warm ocean water is slamming into – and melting – the biggest glacier in East Antarctica. Which is really Ocean heat drives rapid basal melt of the Totten Ice Shelf in “Science Advances” by Stephen Rich Rintoul et al., 16 Dec 2016: Vol. 2, no. 12, e1601610, DOI: 10.1126/sciadv.1601610. This essentially confirms what we already knew, because altimetry tells you the surface is sinking, but it is nice to have direct observations. Sub-ice-shelf melting was a thing the glacios loved, well before I left.