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Melting water under Antarctic glaciers is accelerating their retreat

Melting water under Antarctic glaciers is accelerating their retreat

View of the ice tongue of Denman Glacier in East Antarctica. -Jamin S. Greenbaum

Madrid, October 30 (European Press) –

Meltwater flowing into the sea from under Antarctic glaciers causes this Lose ice more quickly.

It is the result of a new modeling study of the Antarctic ice sheet conducted by scientists from Scripps Institution of Oceanography, University of California, San Diego.

Model simulations indicate that this effect is large enough to contribute significantly to sea level rise under high greenhouse gas emissions scenarios, the researchers report in the journal. “Science advances.”

Additional ice loss caused by meltwater flowing into the sea from beneath Antarctic glaciers is not currently accounted for in models that generate large sea level rise projections, such as those from the Intergovernmental Panel on Climate Change (IPCC). If this process turns out to be the main driver of ice loss across the Antarctic ice sheet, it could mean that current projections underestimate the pace of global sea level rise in the coming decades.

“Knowing when and how much sea levels will rise is critical to the well-being of coastal communities,” he says. It’s a statement Tyler Bailey, lead author of the study and a postdoctoral researcher at Scripps. “Millions of people live in low-lying coastal areas and we cannot adequately prepare our communities without accurate forecasts of sea level rise.”

The study, funded by the National Science Foundation (NSF), NASA, and the Cecil H. and the Ida M. Green Earth Science Foundation at the Scripps Institution for Geophysics and Planetary Physics, Modeled the retreat of two glaciers in East Antarctica until 2300 Under different emissions scenarios and projected contributions to sea level rise. Unlike previous models of the Antarctic ice sheet, this model included the effect of meltwater flowing from the bottom of the glaciers towards the sea. What is known as subglacial discharge.

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The two glaciers the study focused on, Denman and Scott, contain enough ice to cause sea levels to rise by about 1.5 metres. In the high emissions scenario (the IPCC SSP5-8.5 scenario, which assumes no new climate policy and a 20% increase in CO2 emissions by 2100), the model revealed that subglacial drainage increased the contribution of these glaciers to sea level rise by 15.7%. , from 19 mm to 22 mm by 2300.

These adjacent glaciers lie on a continental trench more than three kilometers deep; Once its retreat reaches the steep slope of the trench, its contribution to sea level rise is expected to accelerate dramatically. With the added influence of subglacial drainage, the model found that the glaciers retreated beyond this threshold About 25 years earlier than they did without her.

In addition to the understudied role of subglacial drainage in accelerating sea level rise, Greenbaum points to the importance of what humanity does in the coming decades to reduce greenhouse gas emissions. The model run in the low-emissions scenario did not show retreat of the glaciers into the trench. We avoided the resulting runaway contributions to sea level rise.

In Antarctica, subglacial meltwater is generated from melting that occurs where ice lies on continental rock. The main sources of heat that melt ice in contact with the ground are the friction of the ice on the rock and geothermal heat coming from the Earth’s interior that penetrates the crust.

Previous research has indicated that subglacial meltwater is a common feature of glaciers around the world, and that it is present beneath many other massive Antarctic glaciers. Including the notorious Thwaites Glacier in West Antarctica.

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When subglacial drainage flows seaward, it is thought to accelerate the melting of the glacier’s ice shelf, a long tongue of floating ice that extends seaward beyond the last part of the glacier still in contact with the land (known as the landline). Subglacial drainage is thought to accelerate the ice formation process.

According to Greenbaum, the idea that subglacial drainage causes more ice shelf melting is widely accepted in the scientific community but was not included in sea level rise projections because many researchers were unsure whether the effect of the process would be large enough to raise sea level. the sea. , This is mainly because its impacts are located around the ice shelf of the glacier.

Once the researchers combined the three models into one, they made a series of predictions for the year 2300 using NASA’s supercomputer. The projections included three main scenarios: a control scenario without increased ocean warming, a low emissions scenario (SSP1-2.6), and a high emissions scenario (SSP5-8.5). For each scenario, the researchers created forecasts with and without the influence of current subglacial drainage levels.

Model simulations revealed that the addition of subglacial drainage reconciled the observed melt rates at the Denman and Scott glaciers. In the control and low-emissions models, contributions to sea-level rise were close to zero or even slightly negative, with or without subglacial drainage at 2300. But in the high-emissions scenario, the model found that subglacial drainage increased the contribution. From these glaciers sea level rises from 19 mm to 22 mm in the year 2300.

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In the high emissions scenario that included subglacial drainage, the Denman and Scott glaciers retreated into the three-kilometre-deep trench beneath them in 2240, about 25 years earlier than they did in the model without subglacial drainage. Once the main lines of the Denman and Scott Glaciers retreat beyond the edge of this trench, Its annual contribution to sky-rocketing sea levels, It peaks at 0.33 mm per year, about half the current annual contribution to sea level rise from the entire Antarctic ice sheet.

“Subglacial meltwater has been inferred under most, if not all, Antarctic glaciers, including the Thwaites, Pine Island and Totten glaciers. All of these glaciers are receding and contributing to sea level rise,” Bailey said. We show that subglacial drainage can accelerate its retreat. “It is urgent that we model these other glaciers so we can get an idea of ​​the scale of the impact that subglacial drainage is having.”

This is what the researchers do in this study. According to Bell, they are about to submit a research proposal to expand their new model to include the entire Antarctic ice sheet. “This also means that our results are probably a conservative estimate of the impact of subglacial drainage. However, we still cannot determine how much sea level rise this process will accelerate,” Greenbaum says. Let’s hope it’s not too much“He concludes.