Participants in the REU summer internship program at Bigelow Laboratory learn how to do oceanographic fieldwork on an educational research cruise aboard the R/V Bowditch in 2023. David Fields photo
For climate scientists, the ocean’s temperature is of significant concern. As with most healthy systems, balance is critical; there are consequences if it’s too cold or warm.
Researchers at the Bigelow Laboratory for Ocean Sciences have consistently observed a warming trend in the Gulf of Maine, resulting in the decline of vital aquatic organisms and kelp forests.
If they can more accurately measure the Gulf of Maine’s warming rate, they can better predict the future impacts of climate change — at least, that’s the hope.
For over 20 years, Bigelow’s Gulf of Maine North Atlantic Time Series (GNATS) has been used to validate satellite-based measurements of ocean color using on-the-water observations.
When the program began in 1998, Senior Research Scientist Barney Balch led a team of scientists across the Gulf. Funded by NASA, primarily to confirm whether satellite data was providing an accurate account of conditions, the team gathered information on nutrient and carbon concentrations, optical properties such as ocean color, and details about the biological communities at the base of the food web.
Sure enough, what was intended as a three-year research initiative evolved into a series used to explore the Maine coast’s dynamic past, present and future.
Senior Research Scientist Catherine “Cath” Mitchell said the series is an example of how collecting data can have unexpected benefits later. She recently secured funding from NASA to resume annual research cruises from next year through 2027.
The updated GNATS program will use the laboratory’s new research vessel, the R/V Bowditch, to enhance local research.
“I’m excited about getting more collaborators involved,” Mitchell said. “If we can create opportunities for other scientists to take advantage of the fact that we’re already out there measuring these things, that would do wonders to advance the science of the Gulf of Maine.”
The R/V Bowditch, docked at Bigelow Laboratory, is being adapted as part of the GNATS program to monitor changing conditions and validate satellite data in the Gulf of Maine. The instrument on the front is the radiometer the team uses to measure ocean color. Cath Mitchell photo
GNATS, like the insect
David Drapeau, a team member since GNATS inception under Blarch’s leadership, said the program’s acronym is pronounced like the tiny, winged insect.
“It follows the footsteps of two well-known programs in the oceanographic community,” said Drapeau, citing the Bermuda Atlantic Time Series (BATS) and the Hawaii Ocean Time Series (HOT). “It aims to validate satellite ocean color data, but one advantage of doing this work in our backyard is that we can study changes that emerge over time.”
Reflecting on the team’s humble beginnings, Drapeau noted that 1998, the GNATS lab was housed in a 20-foot shipping container transported by truck.
They worked on the Scotia Prince, a massive 500-foot vessel similar to a cruise ship, which he described as “ideal for data collection.” Given its size, it could handle rough seas and was relatively affordable — $400 for a group of three, compared to chartering a research vessel for a day, costing over $10,000.
The ferry took a direct route from Portland to Nova Scotia, which the team continues to use today. Note, without necessary Coast Guard approvals for international work, the transect extends two-thirds of the way across the Gulf of Maine.
“We took water samples every 18 miles along that line,” Drapeau said. “That was determined by the ferry’s speed, traveling at 18 knots, which allowed us an hour to process each sample.”
GNATS has now upgraded to high-speed catamarans that travel up to 40 knots, shortening processing times to 20 minutes and the trip time in total.
“Even as equipment and technology improve, we collect data using the same methods,” Drapeau said. “If our calibration becomes inconsistent, we won’t be able to accurately determine if the Gulf is warming. It’s no use if we’re comparing apples to oranges.”
Senior Research Associate Dave Drapeau prepares the Bowditch before a shakedown cruise in August to test new instruments and protocols before beginning official data collection for GNATS in 2025. Cath Mitchell photo
Tracking climate ‘change’
Fieldwork can be costly. When researchers secure a three-year grant, they are often allotted two or three cruises to collect water samples and measure site-specific phenomena.
Given that limitation, Drapeau said it’s tough to document changes besides weather patterns, which vary annually. Proving climate change, for example, requires decades of data collection and analysis.
That’s where time series come into play.
Secondary to its funding goals, GNATS data has revealed shifts in the Gulf of Maine and subsequent implications.
“There are two aspects to our work,” Drapeau said. “Routine measurements and the surprises we encounter.”
Drapeau reflected on some cruises the team took last April. Unlike regular procedures, they towed nets, which, when they were extracted from the water, were covered in a thick brown substance comparable to mud.
“We discovered a significant bloom of dinoflagellates, a type of phytoplankton,” Drapeau said. “The species itself wasn’t unusual, but to see such a large bloom at that time of the year was. Sure enough, other scientists and fishermen reported the phenomenon, and as a result, a small working group was formed to investigate further.”
While that instance could have been seen just as “being out on the water,” he acknowledged other studies that, thanks to GNATS data, have been equally if not even more revelatory.
Participants in the REU summer internship program at Bigelow Laboratory learn how to do oceanographic fieldwork aboard the R/V Bowditch in 2023. Collecting water samples, they sample everything from oxygen levels and bacteria counts to zooplankton populations. David Fields photo
The proof is in the pudding
Oceanographic measurements between September 1998 and December 2010 were used to identify changes in the Gulf of Maine’s physical, chemical and biological characteristics in an article published in the Journal of Geophysical Research: Biogeosciences.
GNATS samples collected during extreme precipitation (four of the eight wettest years of the last century) between 2005 and 2010 reflected a notable decline in the amount and productivity of phytoplankton.
The study found that stratification occurred, isolating the surface water from the bottom water and reducing the exchange of nutrients between organisms. This was reflected in the ocean color data, which appeared yellower than usual.
Findings indicate that precipitation, particularly river discharge, influence the productivity of the Gulf; colored dissolved organic matter and detrital material compete with phytoplankton for light absorption.
“More definitive conclusions can be drawn from time series,” said Drapeau, referencing another article published by the Inter-Research Science Center. “Our analysis of GNATS data revealed that the ocean’s surface was cooling in the spring but warming in the other seasons. This trend coincides with a decline in primary production, associated with changes in chlorophyll, particulate organic carbon, temperature and residual nitrate levels.”
In layman’s terms, the report suggests that factors beyond weather are contributing to the observed changes, linking the warming phenomenon to saline North Atlantic Slope water entering the Gulf of Maine.
“Analyzing an ecosystem is complicated,” Drapeau said. “Looking at a snapshot isn’t enough. It’s important to contextualize time series by supplementing it with data from other projects. This is especially relevant in our case, as studying a transect on a moving vessel has its complications.”
The research team managing GNATS now includes Research Associate Sunny Pinkham (left) and Research Technician Brynn Presler-Marshall (right). On the shakedown cruise in August, the team was joined by former Bigelow Laboratory staff previously involved in the program, including Bruce Bowler (center). Farley Miller photo
Future endeavors
As it nears its 25th anniversary, the GNATS program has completed 217 Gulf of Maine crossings with over 50 scientists on its team (at one point or another).
Transitioning from the Scotia Prince to the 48-foot R/V Bowditch has required adjustments, including bumpier rides and more frequent refueling. However, as Drapeau likes to say, “With change comes advantages.”
Collecting ocean color data requires sunlight, and weather can be finicky. Now, the new vessel allows the team to adapt to the forecast.
“We don’t have to load up our mobile laboratory and drive to some faraway port anymore,” Mitchell said. “We can just drive down the hill to our dock. It makes it much easier to jump on the boat quickly and go when the conditions are right.”
The setup has also encouraged the team to rethink how science can improve the program, such as enhancing sample collection and updating instrument software.
In August, the team launched its first “shakedown” cruise, setting the stage for future research. Bruce Bower and Jelena Godrijan, two scientists who, like Drapeau, had previously participated in the program under Balch’s leadership, returned to assist with the expedition.
“It’s hard to know what might come next,” Drapeau said. “But if there’s a time to learn more about the Gulf of Maine, it’s now.”