Researchers have identified the mechanisms behind the formation of a rare opening in the sea ice around Antarctica known as a polynya, which occurred during the winters of 2016 and 2017. The study, conducted by a team of researchers from the University of Southampton, the University of Gothenburg, and the University of California San Diego, focused on the Maud Rise polynya in the Weddell Sea. The researchers discovered that the polynya was the result of complex interactions between wind, ocean currents, and the unique geography of the ocean floor that transported heat and salt towards the surface.
The ocean around Antarctica freezes over in the winter, with sea ice covering an area about twice the size of the United States. While openings in the sea ice near the coast are common, it is rare for polynyas to form over the open ocean, far from the coast where the seas are deep. The Maud Rise polynya was first discovered in the 1970s and was assumed to be an annual occurrence. However, since then, it has only occurred sporadically and for brief intervals. The recent large and long-lived polynya in the Weddell Sea in 2017 was the first of its kind since the 1970s.
During 2016 and 2017, the circular ocean current around the Weddell Sea strengthened, causing the deep layer of warm, salty water to rise, facilitating the mixing of salt and heat into the surface water. This upwelling process helped to explain how the sea ice melted, but another process was needed for the polynya to persist. The researchers found that Ekman transport, a process where water moves at a 90-degree angle to the wind direction, played a crucial role in moving salt onto the sea mount and sustaining the polynya.
Polynyas are important areas for the transfer of heat and carbon between the ocean and the atmosphere, which can impact the heat and carbon budget of a region. The researchers also found that the processes involved in the formation of the Maud Rise polynya are contributing to a general reduction in sea ice in the Southern Ocean. This reduction in sea ice, which began around 2016, represents a negative trend in sea ice in the region for the first time since observations began in the 1970s.
The imprint of polynyas can have long-lasting effects on the ocean, altering water movements and current patterns. The dense waters that form in these areas can spread across the global ocean, impacting the overall circulation of the oceans. Understanding the processes driving the formation of polynyas, such as the Maud Rise polynya, is critical for predicting future changes in sea ice extent and circulation patterns in the Southern Ocean. The researchers used a combination of remote sensing data, observations from autonomous floats, and computational models to uncover the missing piece of the puzzle behind the formation and persistence of the Maud Rise polynya.
