Research involving Kiwi scientists has shown that surface seawater, heated by the sun, is a key factor in why the base of the Ross Ice Shelf (RIS) in Antarctica has melted faster than average.
Findings could have major implications for models trying to figure out the impact of global warming on ice in Antarctica and forecasting global sea level growth.
"At the moment, there is a whole range of modeling that attempts to understand what might happen in the future," said Niwa chief researcher for marine physics. Mike Williams.
"Some of the sciences we did have not been incorporated into such studies and models. That's what we really care about," he said.
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"Incorporating this process in future studies is a further step towards understanding whether we have a new mechanism that is risky, creating a risk, or where everything is under control and not something that needs to be urgently alarmed."
RIS was the size of Spain, Williams said. At the front, along the northern edge, where it met the ocean, it could be about 200 to 250 meters thick. It rose to 1 to 1.5 kilometers, where the ice was above the ground.
Williams, along with Niwa Naval Physicist Dr. Craig Stewart and Cambridge University scientists and the British Antarctic Survey, studied the northwestern corner of RIS, near Ross Island, for several years to make a record of how melting, control processes are melting.
They collected data from anchoring installed under Ross Ice Field with instruments for measuring temperature, salinity and currents. Part of the anchoring was also the echo that pointed up to the bottom of the ice to measure the melting rate.
The berth was 7 km from the front of the ice shelf and was installed through a hole drilled through 260 m of ice, with 600 m of ocean below the shelf.
The researchers found that the melting in the study area was strongly influenced by the seasonal influx of surface water heated by the sun, from the Polynesia Ross Sea – an open water area surrounded by ice.
While the average melting rate across the RIS of 500,000 square meters is approximately 0.1 m per year, in the northwest sector it is more than 1 m per year. The melt rates in the monitored area were approximately three times faster in the summer than the rest of the year.
Despite this, RIS is now considered almost equilibrium. This meant that the amount of lost ice was balanced by the ice flowing from Antarctica and the snow falling to the top of the shelf.
"The equilibrium term is to say that all the things we lose are about the same as all the things we get." If scientists could say, this was the case with all RIS, although one of their challenges was a limited number of direct smelting measurements.
"It's important on this story that we can't just look at things on an annual average. We have to think about what's happening on a seasonal basis, ”Williams said.
There was a vulnerability to what could be a faster way for change than through some other processes where deeper water came and thawed ice.
"Here's the chance at the end of the Antarctic winter, where the sun comes to warm the ocean and drive the melt, it's a ride where we think what you might call a place where it is possible." "If he breaks away from this place, he can start retreating," Williams said.
"That could be a really important process, as it could have an impact on the ice shelf."
Study article, published in Nature GeoscienceRecent modeling has shown that the rapid melting identified by the research has affected a structurally critical area in which changes in ice thickness could affect the flow rate of the entire ice shelf.
The summer sea ice concentration in the Ross Sea is projected to decrease by 56% by 2050, and the ice-free period is expected to be prolonged, the article said. As a result, the meltdown of the frontal RIS base seemed to grow rapidly.