NASA-funded study: Gulf of Maine’s phytoplankton productivity down 65%

The Gulf of Maine is growing increasingly warm and salty, due to ocean currents pushing warm water into the gulf from the Northwest Atlantic, according to a new NASA-funded study. These temperature and salinity changes have led to a substantial decrease in the productivity of phytoplankton that serve as the basis of the marine food web. Specifically, phytoplankton are about 65% less productive in the Gulf of Maine than they were two decades ago, scientists at Bigelow Laboratory for Ocean Sciences in East Boothbay, Maine, report in new results published today.

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

“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,” says William Balch, the Bigelow Laboratory scientist who led the study. “A drop [of] 65% 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 results come from the research team’s analysis of the Gulf of Maine North Atlantic Time Series (GNATS), a 23-year sampling program of the temperature, salinity, chemical, biological and optical measurements of the gulf. These measurements are critical to make sure satellite observations from space are accurate. 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 explains. “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, the Bigelow Laboratory has tracked several biogeochemical changes in the gulf with GNATS. The team collects samples via commercial ferries and research vessels running the same routes repeatedly. They also use autonomous gliders that cross the same sampling line.

The GNATS dataset ultimately will compare changes observed directly on the gulf’s surface waters to observations by Terra, Aqua and other NASA satellites acquiring ocean color data. The measurements complement satellite observations from space that can sometimes be clouded by fog.

Data on the many colors of the ocean associated with different types of concentrations of phytoplankton within the GNATS dataset are expected to contribute to the upcoming observations by NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem mission, or PACE, which will help study phytoplankton communities and track harmful algal blooms that can disrupt ecosystems, fisheries and tourism in the Gulf of Maine.

“We are focused very much on that lower level, the phytoplankton level,” says 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.”

The GNATS dataset is available for scientific, commercial, and educational purposes via NASA’s repository for in situ oceanographic and atmospheric data.