High-tech mooring will measure beneath Antarctic ice

VIMS Assistant Professor Elizabeth Shadwick (holding yellow rope) helps deploy her mooring into the frigid waters of the Southern Ocean from the RV Laurence M Gould. Credit: VIMS.

Earth’s oceans have soaked up about a third of the carbon dioxide added to the atmosphere by humans through use of fossil fuels and other activities. That’s good news for those concerned with greenhouse warming, but bad news for the marine life that’s sensitive to the increasing acidity extra CO2 brings to ocean waters.

Dr. Elizabeth Shadwick, an assistant professor at William & Mary’s Virginia Institute of Marine Science, has now deployed a high-tech mooring beneath the seasonally ice-covered waters around Antarctica to better understand ocean acidification in polar regions, particularly during the poorly studied winter months. Funding for her work comes from the National Science Foundation’s Office of Polar Programs.

To date, knowledge of CO2 levels in the Southern Ocean around Antarctica relies almost exclusively on data collected by research vessels and resupply ships during summer’s brief window of ice-free water. Shadwick’s mooring will extend this record year round, right through the long polar winter.

The mooring, a line anchored to the seafloor in about 1,600 feet of water and held vertically by beach-ball-size floats, terminates about 60 feet below the sea surface, well beneath the scour of winter sea ice. It includes cutting-edge sensors that can measure concentrations of dissolved every three hours throughout the mooring’s six-month deployment. Other sensors will measure pH, temperature, salinity, and dissolved oxygen. All data are stored in waterproof memory cards until the mooring is retrieved.

“The autonomous sensors will allow us to monitor the full annual cycle of carbon dioxide in Antarctica’s coastal waters, for the first time,” says Shadwick. She and VIMS marine technician Olivia De Meo plan to recover the just-deployed mooring in early May—late autumn in Antarctica—when they will also deploy a second identical mooring to be recovered the following December.

Deployment and retrieval takes place from the U.S. research vessel Laurence M. Gould. Retrieval involves using stored GPS coordinates to relocate the mooring—which is not visible at the surface—then freeing it from its seabed tether by pinging a release mechanism with an acoustic signal. The mooring can then float to the surface, where crewmembers hook it with a grapple and hoist it aboard.

Acidification in the Southern Ocean

Because the Southern Ocean plays such an important role in the global carbon cycle—storing almost half the human-induced emissions that have been taken up by seawater—data from Shadwick’s moorings should lead to a better understanding of global climate change and an improved ability to predict its worldwide impacts.

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