The lack of a polynya, a strange ice-free region, in the Antarctic may be an indicator that heat is now trapped deep under the Antarctic Ocean.

The polynya was first discovered by scientists back in 1974 when the first satellite images of the Antarctic regions became available. Researchers found a large area that was devoid of ice in an ice pack located in the Weddell Sea. The polynya that that the scientists found stayed ice-free for around three entire winters before it froze over again.

"In 1974, newly available satellite observations unveiled the presence of a giant ice-free area, or polynya, within the Antarctic ice pack of the Weddell Sea, which persisted during the two following winters," said a team of researchers led by scientists from the McGill University. "Subsequent research showed that deep convective overturning had opened a conduit between the surface and the abyssal ocean, and had maintained the polynya through the massive release of heat from the deep sea."

The researchers determined  that the ice-free region occurred due to heat coming up from beneath the ocean. When it was first seen, the polynya was about the size of New Zealand. However, scientists are growing increasingly concerned over the fact that the polynya has not reoccured since the mid-1970s. While scientists came to the conclusion that the appearance of an ice free region in the Antarctic Ocean may be a rare event, new evidence indicates that the polynya may have been a common event in the past.

Using a large amount of data gathered by research ships and robotic floats in the southern oceans over the last 60 years, the team was able to determine that the disappearance of the polynya may be the result of climate change interfering with the heat release mechanism in the Antarctic Ocean. Due to changes in salinity, heat is trapped deep under the ocean. Since the rising heat from the ocean depths melts surface ice when it rises, scientists are concerned that the lack of polynya is another drastic side effect of climate change.

The new study indicates that the salinity of the ocean's surface has been gradually going down. Since salinity is one of the most important elements of releasing heat from within the ocean, the disruptions in ocean salinity may have shut down an important heat conduit in the south.

"Meanwhile, among the present generation of global climate models, deep convection is common in the Southern Ocean under pre-industrial conditions, but weakens and ceases under a climate change scenario owing to surface freshening," the team said. "A decline of open-ocean convection would reduce the production rate of Antarctic Bottom Waters, with important implications for ocean heat and carbon storage, and may have played a role in recent Antarctic climate change."

The researchers published their findings in the online journal Nature Climate Change.