The Ross Ice Shelf, a country-sized colossus of chilly residue hanging off continental Antarctica, is the world’s largest floating chunk of ice – and a marvellous place to conduct some cryospheric scientific research. What lies beneath the ice can tell you a lot about its future, and the best way to explore it is to drill.
To wit, the multidisciplinary Aotearoa New Zealand Ross Ice Shelf initiative spent last December to this January drilling hot water boreholes into said ice shelf, and it’s safe to say that they’ve found something unexpected. As was recently highlighted by a piece over on National Geographic, the underside of the Ross Ice Shelf isn’t currently melting.
The presence of a basal layer of flat ice crystals suggests that the seawater there – at least, in the spots they drilled – is actually freezing into place instead. This is potentially quite significant, but in order to understand why, we need to take a few steps back.
Ice shelves are constantly changing, internally and externally. Although the process is not yet perfectly understood, it's suspected that lower layers are somewhat melted due to warm oceanic waters flowing towards and chipping away at them.
This process, one of many, contributes to the instability of ice shelves. In case you've temporarily forgotten, the world is warming, and so are its oceans. It’s not unreasonable to think that this might mean ice shelves are going to melt faster from beneath and become more unstable as time goes on.
Indeed, this is what such expeditions are designed to discover, and the latest is one of very few to engage in such drilling activities in this particular part of the world.
As noted by the team’s recent piece over at The Conversation, the underbelly of the Ross Ice Shelf was “covered in ice crystals”, albeit temporary ones. At this point, it’s unclear what this means for its overall stability.
Ross has come and gone plenty of times over recently geological history, but what of its future? Does this frozen underbelly suggest that it's got an ephemeral barrier against basal melting by warming seawater, or does it not make a significant difference?
“These are very early results from a very localised area and so need to be taken in context when looking at an ice shelf the size of Spain through a 25 centimeter hole,” Alex Brisbourne, a glaciologist with the British Antarctic Survey and who wasn’t involved in the project, told IFLScience.
Instead of uniform warming and thawing across the continent, the BAS highlights that the “Antarctic Peninsula and large parts of West Antarctica warmed significantly over the second half of the 20th century” in comparison to its other realms, where temperatures have remained somewhat stable over the past few decades.
This variation in warming, along with a handful of other factors, mean that Antarctica’s ice – land or sea-based – is responding unevenly to the rising mercury.
“The Ross Ice Shelf is generally regarded as stable,” Brisbourne added. Unlike plenty of other ice shelves in the region, Ross has not experienced a “warm water incursion beneath, or warm atmosphere above, and so hasn't thinned as rapidly.
“We know of processes occurring beneath ice shelves with a ‘cold cavity,’ such as the Ross, which can result in both melting and localised freezing, which is what these ice crystals at the base indicate,” Brisbourne added. “As such, these results are perhaps not that surprising.”
As the Ross is so “poorly studied,” however, this study will be “extremely useful” when it comes to understanding its present and future behaviour.
In any case, such pioneering research underscores the fact that both climate change and ice shelves are complex phenomena. This isn’t a simple X leads to Y situation, and the new result from the Ross Ice Shelf encapsulates this rather strikingly.
Ice shelves are already on the sea, so their collapse doesn’t directly translate to a rise in sea level. Such shelves, however, do hold back a lot of landlocked ice, and their disappearance can potentially open the metaphorical and literal floodgates, like removing a blockage from a drain.
The Ross Ice Shelf’s vulnerability to climate change, then, is a key research query with significant implications. This latest finding simply adds an extra layer of complexity to its behavior.