by Sarah Derouin Thursday, November 8, 2018
The Southern Ocean Carbon and Climate Observations and Modeling project (SOCCOM) set out four years ago to study the Southern Ocean and its role and influence on global climate. The main mission of the project was to increase Southern Ocean observations, especially during the frigid winter months, to better understand climate change and biogeochemistry.
Following the success of the Argo program — an autonomous float project that measured salinity and temperature in oceans — the SOCCOM team added biogeochemical sensors to the floats.
As they drift across the ocean, the SOCCOM floats take measurements along depth cycles. The floats have buoyancy engines that deflate and inflate bladders on board, changing their volume and allowing the floats to sink or rise. A typical mission cycle begins with a 1,000-meter descent from the surface, where they drift with the current for five to 10 days. Then the floats further descend to 2,000 meters depth, where the bladders immediately inflate and cause the floats to rise toward the surface. During the ascent, which takes four hours, the floats collect measurements through the water column. Once back at the surface, they link up with satellites and upload the data they collected. After an hour or less at the surface, they submerge again and repeat the process, says Alison Gray, a physical oceanographer at the University of Washington.
The floats are robust, designed to last at least three years. “The floats don’t care if it’s dark or if it’s stormy when they are at the surface. So as long as there’s no sea ice they just [cycle] year-round,” Gray says. And if there is sea ice, the floats can adjust. “They’re evaluating the data that they’re getting on the fly,” she says. “As they near the surface, they start looking for water properties that would indicate the presence of sea ice. Essentially, they’re looking to see if the temperature of the water is at the freezing point.” If the floats are under ice, they will save the data and go into another mission cycle, uploading whenever they reach an ice-free surface.
The first fleet of 20 floats was deployed in 2014 and by June 2018, there were more than 100 SOCCOM floats in the Southern Ocean. Since their release, the floats have made more than 3.5 million measurements, all of which are saved and available to the public at https://soccom.princeton.edu/content/data-access.
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