The Gulf of Maine is changing colors – and the shift could have major implications for the gulf’s complex food chain.

Researchers at Bigelow Laboratory for Ocean Sciences in East Boothbay and the U.S. Geological Survey have been investigating a dramatic decline in overall productivity of plant and animal life in the Gulf of Maine. The research teams believe that increased precipitation during the past 80 years – including a string of historically wet years over the past decade – is dumping more of the tea-colored water common in Maine rivers into the gulf.

The addition of that darker water appears to be giving the gulf’s historically blue-green waters more of a yellowish tinge. In turn, the tiny phytoplankton that are the backbone of the food chain are finding it more difficult to compete for the sunlight they need to survive and thrive – a scenario that could worsen if the changing climate leads to higher precipitation in the region, as many climate models predict.

“Phytoplankton are the basis of the food web,” said William Balch, senior research scientist at Bigelow Labs. “These phytoplankton are food for the larvae of the fish that will be food on your plate in eight years.”

The Gulf of Maine has been described as being in “the cross hairs of climate change.” Water temperatures rose faster in the gulf from 2004 to 2013 than in every other oceanic region on Earth except one, a fact that scientists suggest could help explain the ongoing plight of Atlantic cod populations and of species such as northern shrimp.

STUDYING DISCHARGES INTO GULF

Balch and his co-researchers – including U.S. Geological Survey scientists Thomas Huntington and George Aiken – have focused on whether heavier precipitation trends and river discharges are affecting the overall productivity of the Gulf of Maine. For the past 18 years, Balch has collected samples from the same transect, or narrow section, between Portland and Yarmouth, Nova Scotia, as part of a NASA-funded research project. Satellite imaging and other modern technology make it relatively easy to gauge color changes in the oceans today.

But in fitting tribute to a pioneer of his field, it was Balch’s discovery of detailed color measurements taken by Henry Bryant Bigelow – the namesake of Bigelow Labs – that has allowed researchers to show that the Gulf of Maine of today likely looks different than the one experienced by mariners a century ago.

“The beauty of this is that he was using a scientifically reproducible method … and because he had the foresight to do that, we were able to compare that to today,” Balch said.

Considered one of the founding fathers of modern oceanography, Bigelow served on the faculty at Harvard University for more than 60 years. One of his legacies – in addition to the creation of the Woods Hole Oceanographic Institute – is an extensive body of work on the fish, phytoplankton and waters of the Gulf of Maine that he compiled over more than a decade.

BENEFITING FROM A PIONEER’S WORK

It was during some of those research missions aboard his schooner, Grampus, that Bigelow began recording the color of the gulf’s waters using a simple technique developed several decades earlier. He then included his detailed findings in one of the tomes that he published – books that Balch would purchase a century later from an antiquarian book seller for his own collection.

“It was the best antique book purchase I ever made,” Balch said. “I use these as references.”

In a research paper published in February in American Geophysical Union’s scientific journal, the team hypothesized that the amount of “dissolved organic carbon” and sediments being discharged into the gulf from rivers has increased significantly during the past 80 years. Compounding the situation, four of the eight wettest years since the 1800s have occurred during the past decade or so, resulting in a “massive pulse” of organic materials flowing into the Gulf of Maine.

Balch compared the darker-colored river water containing dissolved organic carbons to tea that has been “steeped” in leaves and dirt. The darker waters flowing into the gulf from rivers in Maine – or indirectly from the Gulf of St. Lawrence via the Scotian Shelf Current – reduce the amount of light available to phytoplankton, which are tiny plants that need sunlight for photosynthesis.

BIGGEST COLOR SHIFT ALONG COASTS

In fact, the gulf’s greenish-blue hue is partly attributable to the enormous amount of chlorophyll-containing phytoplankton that, in turn, helped make the gulf such productive fishing grounds.

“Normally the ocean is blue with little light absorption,”Aiken said in a written statement. “When there is a lot of chlorophyll-containing phytoplankton (microscopic plants) in the water, the water has a greenish color, just like plants do on land. However, the dissolved organic matter delivered to the Gulf of Maine by rivers has a yellowish-brown ‘tea’ color which gives the normally blue ocean a yellow tint. This organic matter also absorbs light necessary for photosynthetic organisms, and can thereby influence the ecology of the Gulf of Maine.”

The decades-long shift toward yellower waters is most noticeable along Maine’s coastal areas, the researchers said. The group’s research paper predicts that river discharges of dissolved organic carbons into the gulf could increase nearly 30 percent over the next 80 years, further affecting the abundance of phytoplankton that are so critical to the food chain.

Balch said the Gulf of Maine “is a big place but it responds over long time periods.” Yet it was often easy to see changes in water color up to 50 miles off the coast of Maine after some of the massive storms in recent years resulted in large plumes of sediment-laden river water emptying into the gulf, he said.

“We have 18 years of data” from the transect studies, Balch said. “At least on this time scale, we are seeing a big change.”

Adding in the color data collected by Henry Bryant Bigelow allows the researchers to jump from offering observations on a 20-year scale to a century scale, he said.