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Our Changing Gulf: More Precipitation is Muddying the Waters

Image courtesy Bigelow Laboratory for Ocean Sciences

The image doesn’t properly reflect the beauty of the Gulf of Maine but, for the purposes of this article, think of the Gulf as a great big bathtub. Like a bathtub, the Gulf of Maine is not particularly deep overall. It is enclosed by the submerged Georges and Brown Banks. One route conveys water into the Gulf of Maine from the North Atlantic, the Northeast Channel. Because it is relatively shallow, the Gulf warms quickly when the atmosphere warms. It also is fed by dozens of rivers. River water warms even faster than ocean water, thus the Gulf is being warmed in two ways. The water entering via the Northeast Channel is affected by a complex dance, called the Atlantic Meridional Overturning Circulation, between the ice cold Laurentian current and the warmer Gulf Stream. When the Laurentian current, generated in the Arctic, becomes weaker, more warm water from the Gulf Stream can push into the Gulf. When that current is stronger, colder water dominates. One of the effects of a warmer climate in New England is greater precipitation but not always as snow. “Average annual precipitation in the Northeast increased 10% from 1895 to 2011, and precipitation from extremely heavy storms has increased 70% since 1958,” stated the Environmental Protection Agency in its report What Climate Change Means For Maine, 2016. More rainfall means more river flow into the Gulf of Maine. The dissolved materials carried in that river flow can and will affect the Gulf’s biological productivity, as research at Bigelow Laboratory for Ocean Sciences in East Boothbay has shown.

Georges Bank in the US and Browns bank in Canada, act as walls for the Gulf of Maine, separating the Gulf from the greater North Atlantic Ocean. US Geological Survey image.

Senior research scientist Barney Balch studies the color of the Gulf. You and I may think the Gulf is primarily blue but Balch knows the Gulf’s true colors. And unfortunately, that color is tending toward yellow. The laboratory’s namesake, Henry Bigelow, spent twelve years studying all aspects of the Gulf of Maine in the early 20th century. To assess the Gulf’s color, he used a Forel-Ule scope — a row of test tubes in a wooden frame, filled with colored fluids that ranged from blue to green to yellow to brown. Comparing the tubes with the hue he saw before him at sea, Bigelow recorded the Gulf’s color at dozens of sites throughout his voyages. His color data sat largely unused before Balch discovered his records in an old book he bought years ago. Balch had been studying the Gulf’s color for some years before this. In 1998, he set up the Gulf of Maine North Atlantic Time Series (GNATS), a coastal time series. By sampling the same place over time, he hoped to understand better biological and chemical changes taking place in the Gulf. About ten times each year, Balch would drive a truck containing a mobile laboratory onto a passenger ferry crossing the Gulf of Maine. At a specific geographic point, Balch and colleagues took the same measurements year after year. Over two decades, Balch and his GNATS built a dataset that began to illustrate the effects of climate change on the Gulf. 

But Henry Bigelow’s data gave him a look at what the Gulf was like one hundred years earlier. And what he found was that the Gulf of Maine is not nearly as blue as it once was. Blue water typically means an absence of organic matter and plant material. Green water means lots of chlorophyll-producing plants, namely microscopic phytoplankton. Yellow or brown colors means there’s lots of dissolved and particulate organic matter in the water. By comparing current and historical data, Balch found that while the Gulf of Maine is still mostly blue in color in the central Gulf, it ranges toward yellow colors, especially in the more coastally-impacted regions. The trend toward yellow correlates to an increase in organic matter being injected into the Gulf from its many rivers. That rise is likely due to increased precipitation in the Gulf of Maine watershed, which ultimately empties into the Gulf. The net effect of all that dissolved and particulate material in the Gulf is to shade those phytoplankton living beneath it. The yellowish water absorbs the blue sunlight that many phytoplankton species need to photosynthesize and grow. Researchers have found that smaller phytoplankton are becoming more common and large phytoplankton species less common, which has implications on the structure of the Gulf of Maine food web.

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