Achilles’ heel of ice shelves is beneath the water, scientists reveal. First, let’s get this out of the way: Achilles’ Heel = fatal vulnerability in the otherwise invulnerable. Ice sheets are Achilles? And otherwise invulnerable? What could this even mean?
Iceberg production and melting causes 2,800 cubic kilometres of ice to leave the Antarctic ice sheet every year. Most of this is replaced by snowfall but any imbalance contributes to a change in global sea level.
So far, so good.
New research, led by academics at the University of Bristol with colleagues at Utrecht University and the University of California, has used satellite and climate model data to prove that this sub-shelf melting has as large an impact as iceberg calving for Antarctica as a whole and for some areas is far more important.
The findings, published today [15 September] in Nature, are crucial for understanding how the ice sheet interacts with the rest of the climate system and particularly the ocean.
So, ice sheets sometimes melt from the bottom, and this melting can be significant for the total amount of ice moving off Antarctica and into the ocean as water. But:
Professor Jonathan Bamber, from the University of Bristol’s School of Geographical Sciences, said: “Understanding how the largest ice mass on the planet loses ice to the oceans is one of the most fundamental things we need to know for Antarctica. Until recently, we assumed that most of the ice was lost through icebergs.
“Now we realise that melting underneath the ice shelves by the ocean is equally important and for some places, far more important. This knowledge is crucial for understanding how the ice sheets interact now, and in the future, to changes in climate.“
“By the ocean”? So, we’re not talking about melting on the underside of ice sheets up on land, but rather those already floating in the ocean? One itsy problem – if they are already floating in the ocean, then melting them doesn’t “contributes to a change in global sea level” much.* And does Bamber mean ‘ocean temperatures around Antarctica’ when he says ‘changes in climate’? Because unless there’s some other mechanism by which the climate causes floating ice to melt from the bottom, that has got to be what he means, right?
This bit of Science! reporting isn’t helping anyone understand anything, or perhaps more accurately, is shedding more confusion than light.
* except for the possible expansion of the water if it gets warmer, which can be significant, maybe, but isn’t under discussion in this article. In general, melting ice that is already floating in the ocean is like melting the ice in your ice tea: you cup doesn’t overflow when the ice in it melts, unless the ice was somehow above the lip of the cup already.