What happens to a particle of water suspended in a river such as the Merrimack as it enters the sea? Where does it end up? How long does it take for this particle to exit the continental shelf and make its way across the Atlantic
What happens to a particle of water suspended in a river such as the Merrimack as it enters the sea? Where does it end up? How long does it take for this particle to exit the continental shelf and make its way across the Atlantic? These are the questions being answered by the GOMI drifter project. Beginning in 2012, several satellite-tracked drifters were built and deployed each year by local schools in the North Shore of Boston and monitored for months at sea as they reported their positions every few hours.
The drifter tracks are displayed, served, and archived on a NOAA computer where oceanographers as well as the general public can access the data. The primary purpose of the deployments is to provide data in validating local ocean circulation models. We can think of these drifters as the “weather balloons” of the sea. They are following the currents in the same way that balloons follow the winds and the information is used to test numerical simulations of the ocean current. Most of the drifters built by GOMI projects are designed to mark the upper meter of the ocean but some are tethered to subsurface drogues (or sea anchors) to follow the currents deeper in the water column.
As seen in the photo of Beverly High School students, the standard surface drifter is constructed in the classroom with commonly available materials (aluminum square pipe mast, aluminum rod spars, canvas cloth sails, lobster buoy flotation, and a set of hose clamps) that are cut, drilled, glued, secured, and decorated by the students. The cell-phone-sized satellite transmitter which gets lashed on top is supplied by the Gulf of Maine Lobster Foundation in Kennebunk, ME working closely with NOAA’s Northeast Fisheries Science Center in Woods Hole, MA. Well over 100 schools around the region have been involved since the project started in 2003 resulting in over 1000 multi-month tracks with bi-hourly fixes.
While we strive to maintain oceanographic standards in terms of the shape and size of drifters, we experiment with the materials used to build the various drifter designs. With help from Brad Balkus at the Nock Middle School, for example, a biodegradable plastic housing was developed using their 3-d printer. In a recent development this past year, GOMI has also been involved with designing and testing a eco-friendly drogued drifter including a surface float made of natural mushroom material. Emily Flaherty’s group at the Salem Sound Coast Watch facility conducted the experiment with a series of deployments. As with any tethered drogue in shallow waters, there were some issues with premature groundings and damage to the float (see photo) but they were nevertheless the first to demonstrate the possibility of using this eco-friendly material. The students were also involved with constructing the drogue.
In addition to the North Shore deployments, GOMI has been involved with studies in Cape Cod Bay and the Bay of Fundy. In collaboration with the Wellfleet Bay Wildlife Sanctuary in Wellfleet, MA, dozens of drifters have been deployed each fall to simulate the flow and strandings of cold-stunned turtles that have occurred there in increasing numbers the last few years on Cape Cod beaches. A manuscript is underway to describe the physical oceanographic processes that contribute to hypothermic turtles coming ashore during cold windy conditions. Multiple clusters of GOMI-drifters deployed in the bay over the last few years document the variability of the surface currents and the complexity of the process.
GOMI has also made several deployments each year in the northern reaches of the Bay of Fundy with scientists at Acadia University in Nova Scotia. Here the drifter tracks document not only the enormous tidal flow in this region but the retentiveness of the system. Dozens of drifters have each traveled thousands of kilometers moving at multiple knots back and forth with the tide with little or no net movement (See Fig. 5 and 6) In other words, the tidal process tends to dominate the flow in this area so that sub-tidal wind and coastal current effects are minimal. The GOMI deployments made in the Bay of Fundy are also contributing to the study of harmful algal blooms (HABs) that occur there each summer. Another manuscript is underway to model the process of toxic algae collecting in this area and occasionally leaking into the great Gulf of Maine.
In engaging young students in this process, we hope to recruit some local “physical oceanographers” to sustain these observations into the next decade or two. With subtle changes in the water masses entering the Gulf of Maine over climatic time scales, can we document a change in the flow fields off our coast?
Jim Manning has been at NOAA’s Northeast Fisheries Science Center for 30+ years. After a bachelor's degree in mathematics (UMO) and master’s degree in oceanography (URI), his career has been largely devoted to 