Rapid fusion of the world's largest ice platform related to solar heat in the ocean

An international team of scientists has discovered that some of the world's largest sea ice is melting 10 times faster than expected due to solar warming of the ocean.

In a Ross Icepack study 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, reported in the newspaper Nature Geoscience, show that the ice melts much faster than we thought because of the flood of hot water.

"The stability of ice shelves is generally thought to be related to their exposure to the deep warm waters of the oceans, but we have found that surface water heated by the sun also plays a crucial role in melting ice shelves", said Dr. Craig Stewart, first author, of the National Institute of Water and Atmospheric Research (NIWA) of New Zealand, who led the work while a PhD student. student at the University of Cambridge.

Although interactions between ice and oceans occur hundreds of meters below the surface of ice shelves, they have a direct impact on sea level over the long term. Ross ice pack stabilizes the West Antarctic ice cap by blocking ice from the world's largest glaciers.

"Previous studies have shown that when ice plateaus collapse, glacier feeding can be multiplied by two or three," said co-author Dr. Poul Christoffersen of the Scott Polar Research Institute. from Cambridge. "The difference here is the sheer size of the Ross ice floe, which is a hundred times larger than the ice floes already gone."

The team collected four years of data from an oceanographic mooring under Ross ice floes by NIWA collaborators. Using instruments deployed in a 260-meter deep borehole, the team measured temperature, salinity, melting rates, and ocean currents in the cavity under the ice .

The team also used an extremely accurate and tailor-made radar system to measure changes in ice thickness. Supported by New Zealand Antarctic and the Scott Centenary Scholarship 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 map the melting rates at the base.

Data from mooring instruments showed that sun-heated surface water was flowing into the ice cavern near the Ross Island, resulting in a three-fold increase in the rate of discharge. melt during the summer months.

The melt is affected by a large open ocean area in front of the ice shelf that is empty of sea ice due to strong offshore winds. This area, known as the Ross Sea polynya, quickly absorbs solar heat in summer and this solar heat source clearly influences melting in the ice cavity.

The results suggest that conditions in the ice platform cavity are more closely associated with the ocean and atmosphere surface than previously assumed, which means that melting rates near the ice front will react quickly to changes in the highest layer of the ocean.

"Climate change is likely to reduce sea ice and increase surface temperatures in the Ross Sea, suggesting an increase in melting rates in this region," 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 takes place 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 all the 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 up to 900 km," Christoffersen said.

Although Ross' ice floe is considered relatively stable, new discoveries show that it may be more vulnerable than expected. The point of vulnerability lies in the fact that surface water heated by the sun enters the cavity near a stabilizing anchor point, which could be jeopardized if the basal fusion s & # 39; He intensified further.

The researchers point out that the melting measured by the study does not imply that the ice floe is currently unstable. The pack ice has evolved over time and the melting ice lost due to the influx of hot water is largely offset by ice inputs from glacier feeding and ice. Snow accumulation. This balance, however, depends on the stability provided by the anchoring point of Ross Island, which the new study identifies as a point of future vulnerability.