“A handful of previous studies have documented surface lakes and streams on individual ice shelves over a span of a few years,” glaciologist Alison Banwell of the University of Cambridge wrote in a comment on the new research, published Wednesday in the journal Nature. “But the authors’ work is the first to extensively map meltwater features and drainage systems on all of Antarctica’s ice shelves, over multiple decades.”
The findings, presented Wednesday in a pair of papers in Nature, could upend our understanding of the way meltwater interacts with the frozen ice sheet. We now know that, rather than simply pooling where it melts in every case, liquid water may run for miles across the continent first — and that discovery comes with some worrying implications.
The major problem is that these drainage systems can carry meltwater from other parts of the ice sheet onto the continent’s vulnerable ice shelves. These are large, floating blocks of ice that jut out into the ocean from the edges of glaciers, helping to block and stabilize the flow of ice behind them. If these ice shelves weaken and break off, they can release a flood of ice into the ocean, raising sea levels in the process.
Now, the authors of the new research suggest that the transport of moving water onto and across Antarctica’s ice shelves could make them increasingly vulnerable to collapse as melt rates accelerate under future climate change.
When meltwater flows onto a shelf, it can run off into existing cracks in the ice, where it may freeze and expand, causing the cracks to widen, said Robin Bell, a glaciologist at Columbia University and co-author of the new research. Or the water might collect in a pool, where “it’s basically acting like an additional load on the ice shelf, which stresses it and causes it to fail,” she told The Washington Post.
Bell pointed to the famous collapse of the Antarctic Peninsula’s Larsen B ice shelf as an example of how meltwater can destabilize a glacier. Larsen B suffered a near-total disintegration in 2002, and scientists believe that the accumulation of meltwater — much of which may have originated on the shelf itself — had a lot to do with its demise. Shelves like Larsen B may become all the more vulnerable if they’re subjected to even more liquid water flowing in from other parts of the continent.
The new research included an examination of satellite imagery dating to 1973 and aerial photography from as far back as 1947, led by geophysicist Jonathan Kingslake of Columbia University and described in the first of the pair of papers. The analysis has revealed a number of previously unreported drainage systems carrying water onto and across some of the continent’s most notable ice shelves. Among these is the rapidly flowing Pine Island Glacier in West Antarctica, which scientists have identified as one of the top potential contributors to global sea level rise — it’s already losing about 50 billion tons of ice each year.
Even more worryingly, the researchers have suggested that the destabilizing effect of flowing meltwater on Antarctica’s ice shelves could result in a dangerous feedback loop on the ice sheet.
The researchers have found that most of the drainage systems originate within a few miles of regions dominated either by exposed rock or “blue ice,” places where the snow has become compressed and appears blue rather than white. Without a covering of white snow to reflect sunlight away from the surface, these parts of the ice sheet tend to absorb more solar energy and become warmer than surrounding areas, thereby producing more meltwater, which may then drain away and flow onto nearby ice shelves.
If the ice shelves then weaken and break off, they’ll allow a flood of ice behind them to go pouring into the ocean. This massive ice loss causes the ice sheet to become thinner, leading to more areas of exposed rock and blue ice — which in turn may increase the flow of meltwater.
That said, the new research has turned out at least one bit of promising news. In the second paper, led by Bell, the scientists have pinpointed one drainage system that actually appears to be stabilizing an ice shelf rather than weakening it.
A network of streams and ponds on East Antarctica’s Nansen Ice Shelf have produced a waterfall that exports liquid water straight off the surface of the ice, dumping it into the ocean before it has a chance to pool and cause damage. The researchers observed that as more meltwater is produced — during unusually warm periods, for instance — the drainage system adapts and expands so that it can transport more water. It’s capable of carrying an entire year’s worth of meltwater off the ice shelf in just a week’s time.
“This is the first time, to my knowledge, that such adaptability has been documented so comprehensively,” said Knut Christianson, a glaciologist at the University of Washington who was not involved with the new research, in an emailed comment to The Washington Post. But he added that it remains unclear how the drainage system might react to more dramatic environmental changes in the future.
However, the finding does suggest that, at least in some cases, these water transport systems may actually work to a glacier’s advantage. Where they may become a stabilizing force in the future vs. where they might cause damage will likely depend on a complex suite of physical factors, including snow cover, topology and various other landscape features in any given area that affect the way water flows.
Gaining a greater understanding of these processes will depend in large part on updating ice sheet models, which — until now — have generally failed to account for the movement of meltwater across the Antarctic ice sheet.
“Incorporating surface hydrology into ice-sheet-scale modeling is a relatively new endeavor,” Christianson noted. Observations like those described in the new research are a good start, but there are many physical processes affecting the flow of water that need to be better understood before the models can be improved.
“Work in these areas has begun, but the continental-wide observations (requiring high-resolution imagery) have only recently become available, and the scientific understanding must be grounded in these new observations, so there’s still much to be done,” Christianson said.
For now, just pointing out that water actually flows from one place to another across the Antarctic ice sheet — and has been doing so for decades — is an important service in and of itself, according to Bell. While there’s much uncertainty about how these systems will behave in the future, and how their behavior will influence the fate of the ice sheet, realizing how widespread they actually are is a critical step in our understanding of the processes shaping the Antarctic continent.
“The really important finding in both these papers is that water moves in Antarctica and isn’t just a stationary player,” Bell said.
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