Knowing the thickness of the Antarctic sea ice is crucial to gauging the environmental health of the polar region, particularly now with the looming problems of global warming.

Measuring sea ice in such remote regions with harsh conditions, however, can be challenging. Ships have difficulty reaching areas with thicker sea ice to make visual observations and drill holes into the ice to make measurements.

Satellite data also need to be validated as snow cover on the ice can skew measurements. However, scientists have come up with a solution using an underwater robot, which made it possible for them to take accurate measurements of sea ice thickness in areas that were once difficult to access.

On Monday, an international group of scientists from the U.S., U.K. and Australia unveiled the first detailed, high-resolution 3D maps of the Antarctic sea ice, which were developed based on the measurements made by an autonomous underwater vehicle, or AUV, called SeaBED.

For their study published in the journal Nature Geoscience on Nov. 24, Ted Maksym, a sea ice expert at the Woods Hole Oceanographic Institution in Massachusetts, and colleagues used the submersible robot to analyze sea ice spanning an area of 500,000 square meters in two expeditions in previously difficult to reach sites around the Antarctic Peninsula in 2010 and 2012.

Unlike with most conventional oceanographic survey instruments that look downward, the yellow underwater robot measuring about two meters long and weighing almost 200 kilograms, uses an upward-looking sonar to measure and map the underside of ice floes while it operated from up to 30 meters underwater with its twin-hull design giving it enhanced stability to take low-speed photographic surveys.

"What this effort does is show that observations from AUVs under the ice are possible and there is a very rich data set that you can get from them," Maksym said. "This work is an important step toward making the kinds of routine measurements we need in order to really monitor and understand what's happening with the ice and the large-scale changes that are occurring."

The SeaBED measurements suggest that the thickness of sea ice in some areas is thicker than previously believed, with thickness reaching up to about 17 meters in some areas and the average thickness ranging between 1.4 meters and 5.5 meters.

The researchers likewise found that over three-fourths of the mapped ice was deformed, which means that large slabs of ice have collided with each other to form bigger and denser bodies of frozen water.

"Our surveys indicate that the floes are much thicker and more deformed than reported by most drilling and ship-based measurements of Antarctic sea ice," the researchers wrote. "On average, Antarctic sea ice may be thicker than previously thought."

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