From New York University
NYU researcher unlocks mystery of recurring hole in Antarctica’s sea ice
Located at the southernmost tip of the Atlantic Ocean, Antarctica’s Weddell Sea is one of the most ice-covered bodies of water on the planet. During the winter, the pack ice extends well north, reaching all the way to 60°S. However, there is a recurring anomaly in this otherwise unremitting sea of ice – a huge area of open water that forms in the ice pack during the coldest part of the year. The opening is known as the "Weddell Polynya" and can occupy an area of 100,000 square miles (larger than the island of Great Britain).
But the exact timing, location, and shape of the Weddell Polynya are all irregular. How and why this hole in the ice forms are questions that have vexed scientists for nearly three decades. Many researchers have speculated that the Maud Rise, a massive seamount that rises from the ocean floor beneath the Weddell Polynya, must play a role in the polynya’s formation, but a conclusive explanation has remained elusive.
In the June 1st issue of Science ["Explaining the Weddell Polynya – a Large Ocean Eddy Shed at Maud Rise" (pp. 1697-1700)], NYU Ocean Scientist David M. Holland provides an explanation for the Weddell Polynya’s formation. Professor Holland found that a horizontal cyclonic eddy that spins off of the Northeast flank of Maud Rise is responsible for the polynya. These findings were based on analysis of a sea-ice-ocean computer model simulation.
Previous theories speculated that the Weddell Polynya was the result of warmer, deep-ocean water being forced to the surface as it flowed over Maud Rise. Professor Holland found, however, that this warmer water is too dense to be forced to the surface in this manner.
Professor Holland said, "The occurrence of the Weddell Polynya and its study is important for at least two reasons. First, it impacts the global ocean circulation by modifying the rate of formation of the coldest and densest waters found in the global ocean. These waters are important to our climate because they fundamentally affect the way heat is transported around the planet.
"Second, this polynya may affect the global carbon cycle. Cold oceans are efficient absorbers of carbon dioxide, a major atmospheric greenhouse gas. A sea-ice cover generally blocks that absorption; but when large areas -- such as the Weddell Polynya -- are opened, the exposed cold ocean surface is able to soak up large amounts of atmospheric carbon dioxide.
"Finally, it should be noted that there is great uncertainty about how human conduct is affecting the polar ice caps. But before we can definitively answer such complex questions, we must first better understand the natural mechanisms that affect the polar ice caps. This research is a step towards improving that understanding."
David M. Holland received his Ph.D. in Atmospheric and Oceanic Sciences from McGill University. He is on the mathematics faculty at NYU and is a core member of the Center for Atmosphere-Ocean Science, a newly-established program of the Courant Institute of Mathematical Sciences and the Faculty of Arts and Science. The study was funded by the Office of Polar Programs of the National Science Foundation.