Thanks to new surveys that combine satellite imagery with data from swim robots and underwater elephant seals swimming in the sky With sensors on the head, the puzzle of the giant ice holes can be solved. The study, conducted by scientists from the US and Canada, has provided a better understanding of why such large holes form in sea ice called polynyas. why they appear only a few years; and what they could mean for global ocean circulation – and for the atmosphere. It appears in the Monday issue of the journal Nature.
"Observations show that the youngest Polynyas have emerged from a combination of factors – one of unusual ocean conditions and a series of very intense storms that swirled across the Weddell Sea with almost hurricane-like winds." Ethan Campbell, Ph.D. student at the University of Washington Oceanography and lead author of the study.
These storms have a dramatic effect in that they chop off the icy surface and disturb the water underneath, causing warmer, saltier waters to rise from the depths of the ocean. It has long been suspected that the heat of the deep ocean supports the Antarctic sea-ice openings seen in 2016 and 2017. However, this has never been directly observed. "It was exciting and surprising to see that the vertical mixing during the Polynyas was over a mile deep into the ocean," said Campbell.
However, a Polynya (Russian for Ice Hole) is more than just a peculiar force of nature that plunges the ocean from top to bottom.
"Antarctic winds and sea ice are changing, which implies that the prevalence and importance of Polynyas may also change," said biological oceanographer Pete Strutton, Associate Professor at the University of Tasmania's Marine and Antarctic Research Institute involved in the study. "Using these observations with computer simulations, we can begin to understand what the future holds for the Antarctic and what this means for the global climate."
The same heat rising from the depths of the ocean could, according to studies, melt ice shackles. If the gaps are large and long-lasting, they can affect the atmosphere. This is because deep water contains carbon from life forms that have sunk over time and dissolved on their way down. When this water reaches the surface, as is the case when storms contribute to a Polynya, this carbon can be released.
"This deep carbon reservoir has been trapped for hundreds of years, and in a Polynya it can be aerated the surface by this really violent mixing," Campbell said. "A major carbon outgassing event could really shake the climate system if it happens for several years in a row."
Climate models show that this carbon release in a Polynya, which is much larger than the 2016/2017 events, "could be significant and could do something about it," Campell added, it was not known how much carbon was in the last Polynyas was ejected, but undoubtedly it is far less than humans release into the atmosphere each year.
The new research was based on observations from the Carbon and Climate Observation and Modeling Project in the Southern Ocean, or Soccom, which is driving autonomous robotic instruments to monitor Antarctic conditions and their effects on climate change with the currents.
The study also relied on data from seals that swam under the sea ice with temporary satellite tags and showed normal water conditions over the years when no large polynyas formed. Then they beamed the data back to land.
"One of the best features of this work … is the way in which observations from many different platforms – satellites, robotic swimmers and marked animals – are brought together to create a picture of Polynyas that has not even been possible It would be a few years ago, "said Strutton, who is also affiliated with the Competence Center for Climate Extremes.
Next, the researchers want to investigate what influence Polynya had on biology in the region. Data from the swimming robots show large phytoplankton blooms that have developed after the two most recent Polynyas, and scientists want to better understand how they form and influence the ocean ecosystem.