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One variable in the increasingly complex equation of glacial loss and rising sea level is the role of that warm belt of deep ocean water along West Antarctica.
Teasing out all of these cause and effect patterns isn’t so simple. For instance, remember those intensified westerly winds that are forcing the upwelling of all that warm water? The westerlies have picked up strength thanks to other environmental factors, including the loss of ozone over the Antarctic, according to Martinson.
The disappearance of ozone, a greenhouse gas, has actually caused the atmosphere above Antarctica to cool, he explained. But the surrounding ocean hasn’t cooled off, and may be slightly warmer in recent years. The disparity has whipped up the westerly winds.
Back to the deep ocean water: That seawater is part of vast conveyor belt that begins in the Gulf of Mexico, chugs across the Atlantic Ocean and then begins to cool around Iceland, where it sinks down and separates from the surface water. It takes a spin around the Arctic before ending up at the bottom of the Southern Ocean, where it merges with the Antarctic Circumpolar Current.
The variable that Martinson wants to quantify revolves around heat flux between that deep ocean water and the cold surface where the glaciers float. How much heat vents to the atmosphere and how much heat contributes to glacial melt?
“It’s like ice cubes in a glass. They melt fast. Even cold water melts them fast,” Martinson said.
Each austral summer since 1993, the PAL LTER scientists have conducted a science cruise in a grid pattern along their study area, which extends about 200 kilometers off shore from the archipelago and about 500 kilometers south to Marguerite Bay. From those cruises, the team has data showing the deep-water warming trend — but they’re after a full-length film instead of a handful of important still shots.
“When we go down on the cruise every single year, it’s just a snapshot,” Martinson said. “If something exciting happens the day before the ship is there, or when the ship is not there, which is most of the year, we miss it.”
In conjunction with an International Polar Year project called SASSI (Synoptic Antarctic Shelf-Slope Interactions Study), Martinson deployed four moorings on the annual PAL LTER cruise this past January from the Antarctic Research Supply Vessel Laurence M. Gould. The moorings, which include another one that was set in 2007, will monitor water temperature over depths of 50 to 400 meters year-round to quantify the heat flux phenomenon.
SASSI itself is a program to monitor simultaneously how the deep ocean water makes its way onto the continental shelf around Antarctica and whether the mechanism is the same across the entire continental shelf, which should help polar scientists understand the physical processes involved, according to Martinson.