Ocean Drifters Aid University Study of Currents

Rhode Island Sea Grant-funded researchers track water circulation patterns in the hopes of finding the origins of currents and how nutrients are transported.

By Alex Elvin | Courtesy of the Vineyard Gazette

A team of scientists and teachers last month deployed a small fleet of devices off Lucy Vincent Beach in the hope of tracking their journey to Narragansett Bay. Most of the 10 devices, known as ocean drifters, sailed past Noman’s Land and across Rhode Island Sound, confirming a link between Narragansett Bay and the waters south of the Vineyard.

Tracking a journey from waters off the Vineyard to Narragansett Bay in Rhode Island.

Tracking a journey from waters off the Vineyard to Narragansett Bay in Rhode Island.

Chris Kincaid, a professor of oceanography at the University of Rhode Island, and his colleagues have been trying to understand circulation within Narragansett Bay, which lies about 25 miles west of Vineyard Sound. Among other things, they hope to reveal the origin of the currents, along with the critical nutrients they carry.

“We know that there is a lot of nitrogen in the bottom water of Rhode Island Sound,” Mr. Kincaid told the Gazette this week. But he said those nutrients are mostly trapped at the bottom by changes in the water density. “To get marine growth, you need nitrogen to be where the sunlight is, near the surface,” he said. “Our hypothesis is that there’s a lot of material that fuels the ecosystem that comes in this coastal current from the area of Martha’s Vineyard.”

The study has a number of applications, including the tracking of oil spills and floating garbage. But the ultimate goal is fisheries management. The study has received funding from Rhode Island Sea Grant, a partnership that includes URI and the National Oceanic and Atmospheric Administration, which regulates offshore fisheries.

Researchers have long used drifters to track ocean currents, but efforts in the region have focused mostly on the Gulf of Maine and George’s Bank. The website for NERACOOS (Northeastern Association of Coastal Ocean Observing Systems) provides data for the drifter program run by NOAA’s Northeast Fisheries Science Center.

“We have had a few dozen drifters in that area in other years,” said James Manning, an oceanographer at the center who has worked extensively with ocean drifters in the region. “But this new batch is certainly going to help with the [modeling] of that current.” He added that more data throughout the year was needed to understand the averages.

The drifters deployed in May were unique in that they reached farther down than others (up to six metres), tapping into the subsurface flow, although still far above the bottom. Other instruments are sometimes tethered to the sea floor to measure the deeper currents. Those instruments have revealed a counterclockwise current in Rhode Island Sound, but did not answer the question of where the water originates.

 

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