Solving the Mystery of Antarctic Polynyas

Why is the scientific community interested in Antarctica?

Thanks to the treaty, Antarctica has remained largely preserved from human activities such as mining or weapon testing. At the same time, it serves as a barometer of climate change.

Researchers from diverse fields, ranging from Astronomy to Environment, conduct research that would be impossible to do elsewhere. Environmental scientists take particular interest in this polar continent and can study various phenomena such as ozone depletion and sea-level rise.

Moreover, the Antarctic Treaty specifically states that scientific investigation and scientific cooperation should be free to be performed. This allows the peaceful coexistence of research stations from all over the globe.

And occasionally, there are times when the place offers mysteries and puzzles that drive and challenge researchers. One such mystery is the appearance of giant holes in the Antarctic ice in 2016 and 2017.

What are Polynyas?

Usually, by the end of austral winter, Antarctic seas freeze up to create nearly 18 million square kilometers of ice. This is about twice the size of the United States.

In September 2017, scientists observed holes spanning thousands of square kilometers in satellite images of this Antarctic ice. The first appearance was right above the Maud Rise undersea mountain.

Ice holes are termed as Polynyas, and they occur naturally in smaller rectangular or oval shapes with length scales of the order of 100 km. They are caused by strong winds and other ocean dynamics.

The maud rise Polynya was 9600 square km when first discovered in mid-September. By late October, it had reached 80,300 square km before merging with the Antarctic sea with the onset of summer.

This was the first time such a hole has appeared in the Antarctic ice since 1970.

This unusual occurrence and the enormous size piqued the curiosity of many researchers who came up with different theories to explain the anomaly. But until now, the reason has remained a mystery.

Polar cyclones: a plausible cause?

In a study titled Polar Cyclones at the Origin of the Reoccurrence of the Maud Rise Polynya in Austral Winter 2017, atmospheric forces play a major role in the formation of open-ocean polynyas. These are polynyas occurring in the middle of Antarctic ice packs.

It is based on 2017's Maud Rise polynya that appeared in the Lazarev Sea sector, east of the Weddell Sea.

Using satellite images and reanalysis data at the high spatiotemporal resolution, researchers found that severe cyclones lead to a strong divergence in the sea ice field, opening up the polynya.

According to the study, such cyclones were unusual at this point in the season. The cause of these cyclones is believed to be the transport of heat flux and moisture toward Antarctica.

The warm and moist air from the west side of the southern Atlantic Ocean significantly increased the potential for a cyclone in the area.

This is not unlike coastal polynyas that happen because of strong winds, as opposed to thermodynamic factors.

The consensus now is that the sea-mountain pushes the warm, dense, salty water upwards to the ocean’s surface. In the presence of a big storm, it gets mixed with the cool, fresher water floating atop the Weddell sea, leading to this phenomenon.

An article in Nature Magazine also explored a similar theory, attributing the opening of the polynyas to Southern Hemisphere climate anomalies. The article suggests that "ocean preconditioning and meteorological perturbations are responsible for the appearance of polynyas."

It also focuses on the origins of these conditions in climate change.

According to the author of this article, Ethan Campbell, these polynyas are not only caused by climate change but could further worsen it. This is because the melting of polar ice releases a significant amount of carbon dioxide that was trapped in the ice into the atmosphere.

Not only is the temperature of the water affected, but the frequency and intensity of cyclones also get disturbed by climate change. As a result, the chances of such giant polynyas opening up rise significantly.

This is a cause for concern as it disrupts the global ocean circulation. 

Research sources

This research draws upon the satellite images but is also shaped from data collected by sensors strapped to seals and float robots. These robots were originally deployed by the Southern Ocean Carbon and Climate Observations and Modeling Project to study the parts of the Antarctic that cannot be accessed by humans.

Coincidentally, they became trapped in this spot, gathering important information. This information is particularly important as the images simply reveal the holes but do not give any insight into its effect on the water column.

The recorded data showed how deep ocean mixing happens in polynyas. Deep ocean mixing is the mixing of warm upper-ocean water and freezing, slow-moving lower-ocean water.

Implications of the study on polynyas

It is now widely accepted that cyclones can trigger polynyas to open up again. With rising temperatures, polar cyclone activity is likely to amplify. At the same time, it is becoming harder for these holes to refreeze due to climate change, as the oceans get warmer.

RELATED: ANTARCTIC SEA ICE IS SHRINKING DRAMATICALLY AFTER DECADES OF GROWTH

Some people imagine Antarctica to be a dead expanse of ice, but there are all kinds of the phenomenon occurring spontaneously. These are things we didn’t previously know or anticipate.

Interesting as these activities are, they also carry a warning message to a world that is just waking up to the reality of climate change.