Going with the flow

Cumulative tracks of the seven surface drifters between May 10 and June 4, 2016 (figure courtesy of Rutgers University).

On May 10, 2016, the United States Coast Guard released seven surface drifters into the Atlantic Ocean between Massachusetts and New Jersey in an effort to validate a variety of ocean current models and HF radar-derived surface current measurements. The drifters provide ground truth data that are compared to model forecasts and land-based current observations to assess the overall performance of these models and measurement techniques.

Perhaps the simplest of all oceanic observation instruments, surface drifters are designed to float at the surface and literally “go with the flow” at the mercy of ocean currents. Modern drifters like these are outfitted with small GPS devices which allow them to be tracked in real-time as they embark on their journey. Normally they are dispensable, since it is more expensive to retrieve them than to construct new units.

Surface ocean currents are measured from land using high frequency (HF) radar techniques. Maps such as these provide a snapshot of our coastal oceans.
Surface ocean currents are measured from land using high frequency (HF) radar techniques. Maps such as these provide a snapshot of coastal ocean currents.

On Friday, June 3, research staff in the Ocean Observation Laboratory (OCEANOL) at UMass Dartmouth’s School for Marine Science and Technology (SMAST) received word that one of these drifters had washed ashore not far from their marine campus in New Bedford, MA. The GPS coordinates showed the instrument in the vicinity of Slocum Neck, South Dartmouth, MA. OCEANOL, which has been maintaining HF radar sites throughout MA and RI for more than a decade, was already a participator in this field study. Research Associate Matt Grossi and Research Technician Kate Tremblay spent many weeks leading up to the drifter deployment ensuring that all of the northern HF radar sites were operating well and that the data were being received in real-time so that the HF radar-derived surface currents could be compared to the drifter data. Additionally, in more of a happy coincidence than strategic planning, OCEANOL also deployed their Slocum glider Blue just south of Martha’s Vineyard one week after the drifters went into the water. Over the next three weeks, Blue would traverse nearly 500 km in the same region many of these drifters have been floating around.

The surface drifter the washed ashore on Friday, June 3, 2016 was found resting comfortably on Barney's Joy Beach, South Dartmouth, MA.
The surface drifter was found resting comfortably on Barney’s Joy Beach, South Dartmouth, MA.

On Saturday morning, June 4, Matt set out on a scavenger hunt to find and retrieve the stranded piece of equipment. The drifter was eventually located on Barney’s Joy Beach, a beautiful private beach in South Dartmouth, MA. A local resident took a break from mowing her lawn to happily escort Matt about a mile down private dirt roads, driveways, and mowed paths through her farm property to allow him access to the gated beach. “It was like Geocaching,” he quipped. “There are many different drifter designs, so I didn’t know what exactly I was searching for. I just assumed it would be obvious when I saw it and hoped it would be easy to get to.” He was right. With GPS in hand, the bright red drifter was spotted about a half kilometer (1/3 mile) down the pristine beach, partially buried in the sand and covered in seaweed. Matt transported the instrument to SMAST, where it was cleaned and safely stored.

The successful recovery of this otherwise disposable drifter offers the possibility of giving it a second life, allowing it to contribute further to scientific research in the future. At the very least, as project coordinator Hugh Roarty of Rutgers University stated, the folks at SMAST now have “an excellent souvenir from an experiment that is going superbly.”

Matt Grossi, Research Associate at UMass Dartmouth's School for Marine Science and Technology, takes a "drifter selfie" before transporting it back to their research facility.
Matt Grossi, Research Associate at UMass Dartmouth’s School for Marine Science and Technology, takes a “drifter selfie” before transporting it back to their research facility in New Bedford.

The Ocean Observation Laboratory at UMass Dartmouth’s School for Marine Science and Technology would like to thank Cheryl (no last name given) of Barney’s Joy Beach, South Dartmouth, MA for assisting our research staff with gaining access to the private beach.