Phytoplankton Productivity Down in Gulf of Maine

Phytoplankton Productivity Down in Gulf of Maine

The Gulf of Maine is growing warmer and saltier, and those changes have led to a substantial decrease in the productivity of phytoplankton that are the center of the marine food web. Specifically, phytoplankton in the gulf are now about 65 percent less productive than they were two decades ago, scientists from Bigelow Laboratory for Ocean Sciences reported in research published on June 7, 2022.

The Gulf of Maine helps fuel New England’s marine ecosystems and maritime economy. Like plants on land, phytoplankton absorb carbon dioxide from the atmosphere and use sunlight to grow via photosynthesis; they then become food for other organisms. Disruptions to the productivity of these microscopic organisms can lead to adverse effects on the region’s fisheries and the communities that depend on them.

Research published in 2021 showed that the Gulf of Maine has been warming faster than most ocean basins. In the new effort from Bigelow, funded in part by NASA, scientists showed how that warming has affected the phytoplankton.

The natural-color image above shows the northwest Atlantic Ocean blooming with phytoplankton on June 5, 2022, as observed by the Moderate Resolution Imaging Spectroradiometer on NASA’s Aqua satellite.

“Phytoplankton are at the base of the marine food web on which all of life in the ocean depends, so it’s incredibly significant that its productivity has decreased,” said William Balch, a Bigelow Laboratory scientist who co-led the study. “A drop of 65 percent will undoubtedly have an effect on the carbon flowing through the marine food web, through phytoplankton-eating zooplankton, and up to fish and apex predators.”

The findings are the result of an analysis of the Gulf of Maine North Atlantic Time Series (GNATS), a 23-year sampling program that has measured the temperature, salinity, and other chemical, biological, and optical properties of the gulf. Balch says the changes that they are recording show an intricate connection between the gulf and the greater Atlantic Ocean.

“It’s all being driven by this gigantic windmill effect happening out in the North Atlantic, which is also changing the circulation coming into the Gulf of Maine,” Balch explained. “There used to be these inflows from the North Atlantic bringing water from the southward-flowing Labrador Current, making the gulf cooler and fresher, as opposed to warmer and saltier, which is where we are now.”

Since 1998, Bigelow Laboratory has tracked biogeochemical changes in the gulf by collecting water samples via commercial ferries and research vessels cruising along the same routes repeatedly. They also use autonomous gliders that cross the same sampling lines.

Such in situ measurements are critical for making sure satellite observations are accurate and for filling in gaps on days when skies are cloudy or foggy. NASA acquires ocean color data through Aqua, Terra, and other satellites. The upcoming Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission is expected to significantly improve and extend observations of the many colors of the ocean associated with different types and concentrations of phytoplankton.

“We are focused very much on that lower level, the phytoplankton level,” said Bigelow Laboratory scientist and project co-lead Catherine Mitchell. “But the changes at that level can have all these implications at the higher species, the fisheries, the lobster, and all those kinds of industries that are important within the state of Maine and other states that border the gulf.”

“If you're trying to look at something like climate change,” Balch added, “the statistical power of sampling over and over again the same exact water masses is really powerful stuff.” The GNATS dataset is available for scientific, commercial, and educational purposes via NASA’s repository for in situ oceanographic and atmospheric data.

NASA Earth Observatory image by Lauren Dauphin, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Roberto Molar-Candanosa, NASA’s Earth Science News Team.

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