New research shows that the ice shelf that forms a buttress against the flow of one of Antarctica’s major ice sheets to the ocean is collapsing at an accelerating rate.
Image Credit: Shutterstock.com / Stu Shaw
The future of the Ice Sheet that is key to holding back one of the fastest moving glaciers in Antarctica has been up in the air for some time. Researchers have been unsure as to the extent of the effect that climate change has been having on the ice sheet holding back the advance of the Pine Island Glacier.
Scientists have seen that the ice sheet supporting the ground-based Pine Island Glacier is changing rapidly, thinning and receding, in turn contributing to sea-level rise. But the extent of this degradation has been somewhat uncertain.
The difficulty in assessing the Pine Island Glacier is partially because the ice sheet is hard to access. Remote in terms of research bases, reaching the Pine Island Glacier requires making many short trips by air, with these aerial journeys made hazardous by low-cloud coverage.
Walking across the ice sheet is equally dangerous because it is punctuated with crevasses, while sea-ice surrounding this important glacier prevents access from the sea. Fortunately, advances in satellite monitoring are finally allowing researchers to obtain a true picture of how quickly the Pine Island Glacier is thinning.
This is the approach taken by a team of scientists from the University of Washington and the British Antarctic Survey, and what they have discovered is troubling. The team has found that the timeline of Pine Island Glacier’s ultimate collapse into the sea has likely been shortened.
We may not have the luxury of waiting for slow changes on Pine Island; things could actually go much quicker than expected. The processes we’d been studying in this region were leading to an irreversible collapse, but at a fairly measured pace. Things could be much more abrupt if we lose the rest of that ice shelf.
Ian Joughin, The Applied Physics Laboratory, The University of Washington
Joughin is the lead author of a paper detailing the team’s findings published in the latest edition of the journal Science Advances¹.
Why is the Pine Island Glacier so important?
The Pine Island Glacier is one of the largest and most important ice streams in Antarctica, with water from the glacier flowing into the Amundsen Sea, joining the Thwaites Ice Stream in draining around 5 percent of the Antarctic Ice Sheet.
Despite the uncertainty in the rate at which this glacier is advancing, the speeding up of this melting is already widely acknowledged as Antarctica’s largest contributor to sea-level rise.
The Pine Island Glacier contains roughly 180 trillion tons of ice, which if it were to reach the sea could result in a sea-level rise of over one and a half feet. It is already responsible for over half a millimeter of sea-level rise each year, and while that may not sound like a tremendous amount, this contribution is only set to rise as the global climate continues to warm.
Should both this glacier and the neighboring Thwaites Glacier flow completely into the ocean this could release the greater West Antarctic Ice Sheet into the oceans.
The ice shelf located at Pine Island is vital in holding back this flow as it acts as a buttress against this larger, more unstable ice sheet. If this buttress is removed the West Antarctic Ice Sheet would flow to the oceans more or less unimpeded. The net result of this; a rise in sea levels of several feet over the coming few centuries.
Just as the true extent of the melting of the ice shelf holding back the Pine Island Glacier was questionable, so too have been the mechanisms driving this thinning over the past five years.
What is causing ice sheet melting at the Pine Island Glacier?
The shrinking of the ice shelves supporting both the Pine Island Glacier and the Thwaites Glacier has been a subject of intense scientific interest over the past few decades. The main mechanism which has thus far been identified as responsible for this thinning is warm ocean currents melting the underside of the ice sheets.
This process was driving the motion of the Pine Island Glacier towards the ocean in the two decades between 1990 and 2009, causing it to almost double from around 2.5 kilometers per year to approximately 4 km kilometers per year at its height.
Following this period of acceleration, the glacier’s rate of progress had seemed to stabilize. This steady period lasted until around 2019 when once again, the glacier began to advance at an accelerating rate.
This new research indicates that there could be another mechanism at play driving this new period of acceleration. Joughin points towards internal forces acting upon the glacier influencing this new period of accelerating advancement.
Between 2017 and 2020 the ice shelf lost around 20 percent of its total area as chunks of ice broke away from its main body. This process was captured by the Copernicus Sentinel-1 satellites. Joughlin’s team took these satellite images and reassessed them, finding that the recent deterioration of the ice shelf was not caused by direct melting caused by warm ocean currents.
Instead, by focusing on two specific points on the glacier’s surface the team found that an ice flow model developed by the University of Washington could account for the observed acceleration and the losses experienced by the ice shelf throughout these three years.
“The ice shelf appears to be ripping itself apart due to the glacier’s acceleration in the past decade or two,” says Joughlin. The researcher adds that whilst this speed up is not currently catastrophic, if what remains of the ice shelf breaks up the progress of the glacier towards the oceans will accelerate considerably.
The loss of Pine Island’s ice shelf now looks like it possibly could occur in the next decade or two, as opposed to the melt-driven subsurface change playing out over 100 or more years. So it’s a potentially much more rapid and abrupt change.
Pierre Dutrieux, Ocean Physicist, British Antarctic Survey and a co-author on the Science Advances paper
Source
¹Joughin. I., Shapero. D., Dutrieux. P., et al, [2021], ‘Ice-shelf retreat drives recent Pine Island Glacier speedup,’ Science Advances, [DOI: 10.1126/sciadv.abg3080]
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