The collapse of the ice sheet in the Ross Sea region can be avoided if we stick to a low-emissions strategy, according to new study that has discovered a “missing piece of the puzzle” around the melting of the West Antarctic Ice Sheet.
The West Antarctic Ice Sheet contains more than 5 meters of potential global sea-level increase, thus predicting how much and how quickly the world’s waters will rise depends on knowing whether or not the ice sheet’s “stable” areas would eventually melt.
The Siple Coast of West Antarctica, where rivers of ice flow over the continent and drain into the Ross Sea, is one such area that is now stable. The Ross Ice Shelf, a floating ice mass almost the size of Spain that supports the ice sheet glaciers, slows down this flow of ice. Because of the extremely cold ocean waters that pass through the ocean gateway below, the Ross Ice Shelf melts relatively little at its base when compared to other ice shelves in West Antarctica.
Yet stability hasn’t always been there in this area of the ice sheet. The ice sheet retreated (melted) hundreds of kilometers approximately 7,000 years ago, then within the previous 2,000 years, it readvanced (grown) to its current position, according to radiocarbon dating of sediments from beneath it.
A recent study published in Nature Communications by GNS Science Te Pū Ao, Te Herenga Waka—Victoria University of Wellington, and an international collaboration that included NASA’s Jet Propulsion Laboratory used computer model simulations to explain this retreat and advance of the ice sheet. These models examined the relationship between the ice sheet and variations in the ocean and Earth’s crust.
But this part of the ice sheet hasn’t always been stable. Radiocarbon dating of sediments from beneath the ice sheet indicates that it retreated (melted) hundreds of kilometers about 7,000 years ago, then within the preceding 2,000 years, it readvanced (grew) to its current position.
Computer model simulations were utilized in a recent study by GNS Science Te Pū Ao, Te Herenga Waka—Victoria University of Wellington, and an international cooperation that includes NASA’s Jet Propulsion Laboratory to explain this retreat and advance of the ice sheet. The study was published in Nature Communications. These models looked at how changes in the ocean and the Earth’s crust related to the ice sheet.
“When we project future ice sheet response, we have to grapple with many uncertainties about which processes drive ice sheet behavior. Our study sought to unravel what happened to the West Antarctic Ice Sheet in this region in the past, in order to better predict what will happen in the future,” Lead author Dan Lowry, an ice sheet and climate modeler at GNS Science, explains,
West Antarctic Ice Sheet’s Behavior is Mostly Driven by Deep Ocean Mixing
Salt is released when ocean water on the surface freezes into sea ice. As a result, extremely cold, salty water is created that is highly dense and can mix deep into the ocean, even in areas where the ocean isn’t as deep as the Ross Ice Shelf. In order to keep the ice shelf from melting, this thick water serves as a barrier between it and the warmer ocean water. However, geological records and Antarctic ice cores indicate that there was less ocean mixing in the past, suggesting that melting rates may have been higher.
The Earth’s crust gradually lifts up in reaction to the ice burden changing as an ice sheet diminishes in size. The viscosity, or “stickiness,” of the mantle, the layer of Earth beneath the crust, determines how quickly the crust is rising. The floating ice may have been re-grounded by crustal uplift that occurred thousands of years ago, enabling the ice sheet to stable and subsequently move once more.
Through a comparison of geological records with ice sheet flow simulations under varying mantle “stickiness” scenarios and rates of ocean mixing, the study concluded that variations in ocean temperature best explained the ice sheet’s advance and retreat, but that the rate of crustal response also affected the ice sheet’s ocean sensitivity. The water, the ice sheet, and the solid earth all interact and have an impact on one another.
Mitigation is Still Important
According to recent research, more melting is “unavoidable” even if global emissions are minimized in the Amundsen Sea Embayment, another area of West Antarctica, where the ocean cavities beneath the ice shelves are already warm and melting is beginning.
But according to Lowry, this new research indicates that there is still hope for stopping the West Antarctic Ice Sheet’s loss in the Siple Coast area.
“Our modeling has helped us understand what caused changes in the past; we know that by mitigating greenhouse gas emissions to meet the Paris Agreement target, it is possible to limit that ocean warming to levels that won’t cause collapse of the ice sheet. This region is vulnerable, but we’re not there yet.”
Deep ocean mixing and sea ice production are reduced in global climate models operating under high emissions scenarios. This might cause the same vast ice sheet retreat and ocean temperature shift that was seen thousands of years ago.
According to Lowry, a greater variety of processes were included in the modeling than in earlier iterations, such as variations in sea level brought about by the ice sheet’s gravitational pull as it melts.
“We went more complex, we’ve tested these hypotheses in a more robust way than has been ever done before. This is a topic that the scientific community has been trying to figure out for several years; obtaining these results is like finding that missing piece in the puzzle of what makes ice sheets tick.”
