Mysterious and gaping holes in the Antarctic ice explained


Huge holes in the winter Antarctic ice floe have appeared sporadically since the 1970s, but the reason for their formation is largely mysterious.

Scientists, with the help of floating robots and seals equipped with advanced technologies, may now have the answer: the so-called polynyas (in Russian "open water") seem to be the result of storms and salt , according to new research.

The polynyas have attracted a lot of attention lately, as two very large ones have opened their doors in the Weddell Sea in 2016 and 2017; in the latter case, the open waters extend over 298,100 square kilometers (115,097 square miles), according to an article published in April in the journal Geophysical Research Letters.

Now, the most comprehensive study ever done on ocean conditions during polynya formation reveals that these open water expanses develop due to short-term climatic variations and particularly adverse weather conditions. Polynies also release a lot of heat from the oceanic depths into the atmosphere, which has implications for scientists. [Antarctica: The Ice-Covered Bottom of the World (Photos)]

The hole in the pack ice off the Antarctic coast was spotted by a NASA satellite on September 25, 2017.

The hole in the pack ice off the Antarctic coast was spotted by a NASA satellite on September 25, 2017.

Credit: NASA

"This could change weather conditions around Antarctica," Live Science told Ethan Campbell, Ph.D. in oceanography at the University of Washington. "Maybe further."

Researchers already suspected that storms had played a role in creating polynyas in recent years. An article published in April by atmospheric scientists in the Journal of Geophysical Research: Atmosphere evoked a particularly violent storm with a wind speed of up to 117 km / h in 2017.

But even though the winter storms of 2016 and 2017 have been extreme, temperate seas are the norm in winter Antarctica, said Campbell.

"It was only storms, we would see polynya all the time, but it's not the case," he said. Instead, large polynyas are relatively rare. There were three huge ones in 1974, 1975 and 1976, but nothing important until 2016.

Campbell and his team pulled data from two human-sized robotic floats deployed in the Weddell Sea as part of the National Carbon and Climate Carbon and Climate Modeling and Observation Project in the Southern Ocean. Science Foundation (SOCCOM). The floats drift in currents about a mile and a half from the surface of the ocean, said Campbell, collecting data on water temperature, salinity and carbon content.

For comparison purposes, researchers also used year-round observations by Antarctic research vessels and even scientific seals – wild pinnipeds equipped with small instruments to collect ocean data during their voyages. usual.

Together, these observations explain the entire history of the 2016 and 2017 polynyas. The first ingredient, Campbell said, was part of a climatic pattern called Southern Annular Mode, the polar version of El NiƱo. Cambell said that a regular climatic variation can result in winds farther away from the Antarctic coast, in which case they become weaker, or closer to the coast, becoming stronger. When variability brings the winds closer and stronger, it creates a warm, salty water rise from the depths of the Weddell Sea to the colder, cooler surface of the ocean. [In Photos: Research Vessel Headed to ‘Hidden’ Antarctic Ecosystem]

This type of climate and the resulting upwellings made the ocean surface exceptionally salty in 2016, explained Campbell, which allowed the water to mix. more easily vertically. (As a general rule, salinity differences separate the oceanic layers, just as the less dense hydrocarbons float above the water and refuse to mix.)

"The ocean was exceptionally salty on the surface, which made the barrier to mixing much lower," Campbell said.

From now on, the whole ocean we needed was a little hectic. And the winters of 2016 and 2017 provided the spoon. The big storms created wind and waves that mixed the water vertically, bringing warm water from the bottom of the ocean that melted the sea ice.

The effects of the polynyas that have formed are still somewhat mysterious. The researchers found that the ocean's interior below them cooled by 0.26 degrees Celsius (0.36 degrees Fahrenheit). This heat could change local weather conditions and even change the winds around the world, Campbell said.

More worrisome, he said, deep seawater exposed to the atmosphere at a polynya is potentially rich in carbon. The deep waters of Antarctica are the cemeteries of marine life, which release carbon during their decomposition. If this carbon enters the atmosphere via polynyas, these open water openings could contribute slightly to climate change, Campbell said.

Campbell said the new study should help scientists better understand climate change in Antarctica. Current models of Antarctica seem to predict more polynyas than it exists, Campbell said. Now, climate modellers will have more data to improve these predictions, creating a better virtual Antarctic to understand climate change.

The research was published June 10 in the journal Nature.

Originally published on Live Science.


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