New research has identified the “missing piece of the puzzle” in the melting of the West Antarctic ice sheet, showing that the collapse of the ice sheet in the Ross Sea region could be prevented if we stick to the low emissions path.

Potential global sea level rise of more than 5 meters recorded on the West Antarctic Ice Sheet; Therefore, understanding whether areas of the ice sheet that appear “stable” today will melt in the future is critical to predicting how much and how quickly it will melt. Our seas will rise all over the world.

One area that is currently stable is the Siple Coast of West Antarctica, where rivers of ice flow over the continent and into the Ross Sea. This ice flow is slowed by the Ross Ice Shelf, a floating mass of ice almost the size of Spain that acts as support for the ice sheets. Compared to other ice shelves in West Antarctica, the Ross Ice Shelf has very little melting at its base due to the very cold ocean waters passing through the ocean gate beneath it.

But this area of ​​the ice sheet was not always stable. Radiocarbon dating of sediments beneath the ice sheet shows that the ice sheet retreated (melted) hundreds of kilometers about 7,000 years ago and then advanced (grew) again to its present position over the last 2,000 years.

In a new study by an international team including GNS Science Te Pū Ao, Te Herenga Waka—Victoria University of Wellington and NASA’s Jet Propulsion Laboratory, Nature CommunicationComputer modeling was used to explain this retreat and advance of the ice sheet. These simulations examined how changes in the ocean and crust affect the ice sheet.

“When we plan the future response of the ice sheet, we have to deal with many uncertainties about what processes drive the behavior of the ice sheet. Our study aimed to uncover what happened to the West Antarctic Ice Sheet in this region in the past, so that we can better predict what will happen in the future,” says lead author, GNS Science Dan Lowry, an ice sheet and climate modeler.

Mixing in ocean depths is a key factor in the behavior of the West Antarctic ice sheet

Salt is released when water on the ocean surface freezes into sea ice. This creates very dense, cold, salty water that can penetrate deep into the ocean, including oceanic cavities such as the space beneath the Ross Ice Shelf. This dense water acts as a barrier between warmer ocean water and the ice shelf, preventing melting. But Antarctic ice cores and the geological record show that this ocean mixing was weaker in the past; This means the melting rate could be faster.

As the ice sheet shrinks in size, the change in ice load causes the Earth’s crust to slowly rise in response. This rate of uplift of the Earth’s crust depends on the viscosity or “stickiness” of the mantle layer beneath the Earth’s crust. Crustal uplift caused by ice sheet retreat thousands of years ago may have re-anchored floating ice, allowing the ice sheet to stabilize and then advance again.

Comparing the geological record with simulations of ice sheet flow under different scenarios of mantle stickiness and ocean mixing rates, the study found that ice sheet regression and advance are best explained by changes in ocean temperature, but the rate of crustal response is also influenced by how ice sheet flow occurs. ice sheet is sensitive to ocean The ice sheet, ocean, and solid land interact and influence each other.

Mitigation still matters

Recent research has shown that in another part of West Antarctica, the Gulf of the Amundsen Sea, oceanic spaces beneath ice shelves are already warm, melting is continuing, and further melting is “inevitable” even as global emissions decline.

But Lowry says this new study shows that it’s still possible to prevent the West Antarctic Ice Sheet from retreating in the Seaple Beach area.

“Our modeling helped us understand what caused changes in the past; We know that by reducing greenhouse gas emissions to meet the Paris Agreement goal, we can limit ocean warming to levels that will not lead to ice sheet collapse. “This region is vulnerable, but we are not there yet.”

Global climate models operating under high emissions scenarios show less sea ice formation and less deep ocean mixing. This could lead to the same cold-to-warm ocean change seen thousands of years ago and a significant retreat of the ice sheet.

Lowry says the simulations include a wider range of processes than previous models; such as sea level changes that occur near the ice sheet as it melts due to the gravitational influence of the ice sheet.

“We worked harder and tested these hypotheses more robustly than ever before. This is an issue that the scientific community has been trying to solve for several years; getting these results is like finding the missing piece of the puzzle that keeps the ice sheets moving.”