The largest ice on the planet melts 10 times faster than expected

An international team of scientists has discovered that some of the world's largest ice shelf melts 10 times faster than expected because of the solar heating of the surrounding ocean.

In a study of the Ross ice floes of Antarctica, which covers an area roughly equivalent to that of France, scientists spent several years creating a record of how the northwestern sector of this vast pack ice interacts with the ocean below.

Their results, published in the journal Nature Geoscience, show that ice melting is much faster than previously thought because of the inflow of hot water.

"In general, it is thought that the stability of ice trays is related to their exposure to warm water from the depths of the ocean, but we have discovered that surface water heated to the energy also play a critical role in ice melt, "summarizes Dr. Craig Stewart of the National Research Institute of Water and Atmosphere (Niwa) in New England. Zeeland, who did the work while a PhD student at the University of Cambridge, UK.

Although the interactions between ice and the ocean, which occur hundreds of meters below the surface of the ice shelves, seem distant, they have a direct long-term impact on the sea level. Ross 's stabilizes the Antarctic ice sheet from the West by blocking the ice flowing from the world' s largest glaciers.

"Previous studies have shown that when ice plateaus collapse, glaciers that feed can speed up one or two or three factors," says co-author Poul Christoffersen of the Scott Polar Research Institute's Cambridge. "The difference here lies in the large size of the Ross ice floe, which is 100 times larger than the ice floe that we have already seen disappear," he says.

The team collected data on four years of oceanographic mooring installed by Niwa collaborators under the Ross Ice Shelf. Using instruments deployed in a well 260 meters deep, the team measured temperature, salinity, melting rate and ocean currents in the cavity under the ice.

The team also used a highly accurate custom radar system to study changes in ice thickness. With the support of New Zealand Antarctica and the Scott Centenary Fellowship of the Rutherford Foundation at the Scott Polar Research Institute, MM. Stewart and Christoffersen traveled more than 1,000 km on snowmobiles to measure the thickness of the ice and determine the melting rate. basal

Melting rates tripled in summer

Data from instruments deployed at anchor showed that surface water heated by the sun flowed into the cavity under the pack ice near Ross Island, which cast over the months. d & # 39; summer.

The melt is affected by a large open sea area in front of the pack ice, which is empty of sea ice due to strong sea winds. This area, known as the Ross Sea polynya, rapidly absorbs solar heat in summer and this solar heat source clearly has an influence on melting in the ice cavity.

The results suggest that conditions in the ice cavity are closer to the surface of the ocean and the atmosphere than previously badumed, implying that melting rates near ice front will react quickly to changes. in the upper layer of the ocean.

"Climate change is likely to result in a decrease in sea ice and higher temperatures at the ocean surface in the Ross Sea, suggesting that melting rates in this region will increase at the same time. future, "said Stewart.

The potential for increased melting rates in this region has implications for the stability of the pack ice due to the shape of the pack ice. The rapid fusion identified by the study occurs under a thin and structurally significant part of the ice floe, where ice is spreading against the island of Ross. The pressure of the island, transmitted through this region, slows the flow of the pack ice.

"The observations we made at the front of the pack ice have direct consequences for many large glaciers flowing into the pack ice, some 900 km away," Christoffersen said. Although Ross's pack ice is considered relatively stable, new discoveries show that it may be more vulnerable than previously thought.

The point of vulnerability lies in the fact that water from the surface heated by the sun flows into the cavity near a stabilizing attachment point, which could be affected if the basal melting takes place. Intensified further. The researchers note that the fusion measured by the study does not imply that the pack ice is currently unstable.

The pack ice has evolved over time and the melting ice lost during melting due to the warm water inlet is roughly balanced with the ice inputs from the ice and ice feed. of snow accumulation. However, this balance depends on the stability provided by the anchor point of Ross Island, which the new study identifies as a point of future vulnerability.