If you’ve jumped into Casco Bay this summer, you may have noticed that it’s distinctly warmer than in years past. That’s because the Gulf of Maine heated up faster than 99% of the global ocean between 2004 and 2013 and has continued to warm ever since. Even if you didn’t feel the change on your last beach day, the sea life around you certainly did.

Why is the Gulf of Maine changing so quickly?

The biggest drivers of temperature are currents, which are different types of water that influence our gulf. The ocean is not one big standing pool of the same water. Instead, certain sections of water flow within and around others, depending on two main characteristics: temperature and salinity. The temperature of the water and the amount of salt help determine its density, which helps to determine how it flows. Oceanographers call a section of water that has the same characteristics and moves together a “water mass.”

Water masses function much like oil and vinegar do when you make salad dressing. Vinegar is denser than oil, so it sinks to the bottom. So, the colder and saltier water will sink down while the warmer and fresher water is less dense and tends to stay near the surface. These differences in density are what drive water masses to flow in the form of currents.

In Maine, a lot of the water that flows around our coast first passes near Labrador, Canada. The cold, relatively fresh water flows down past Atlantic Canada and takes a sharp westward turn at the tip of Nova Scotia. Though this water may not be the ideal temperature for swimming, many of the organisms on which our economy relies thrive on the water from the Labrador Current. However, in more recent years a different current, called the Gulf Stream, has been impacting Maine more profoundly. Compared to the Labrador Current, the Gulf Stream is much warmer and contains much more salt. As the global ocean absorbs heat from the atmosphere, the Gulf Stream current has moved north, and its warm, salty offshoots are spilling more into the Gulf of Maine. For a visual, watch this video explainer from the Gulf of Maine Research Institute.

The contributions from different currents into the Gulf of Maine also determine the chemical conditions that dictate the capacity for shelled organisms to grow. Warmier, saltier waters mean we’re not seeing drastic changes in the seawater chemistry from water mass shifts now, but there is a potential tipping point in the future. Recent research shows that by 2050, the survival of bottom-dwelling shelled marine species (think lobster) may be significantly compromised.

Even if you haven’t noticed the changes in the water, marine animals certainly have. Given the economic importance of our seafood industry, we are mindful about the possible implications for Maine’s fisheries. As our gulf warms, the distribution of commercially-important cold-water species shifts northward to remain in their ideal temperature range. Impacts are being felt throughout the food chain: between 2008 and 2018, algae growth dropped by 50%. Researchers attributed this decline in primary productivity, which is what helps to feed marine life such as lobsters and clams, to the nutrient-poor waters being pushed into the Gulf of Maine via the Gulf Stream. 

You can support the numerous organizations working to understand changes in the Gulf of Maine and helping our coastal communities adapt by donating your time or money. The Gulf of Maine Research Institute, Bigelow Laboratory for Ocean Science, The Nature Conservancy, the Downeast Institute, Friends of Casco Bay and many other groups up and down the coast are modeling the future and working with fisheries to adjust. You can get involved by purchasing local seafood (including kelp!) and contributing to citizen science projects. If you love and care about the future of our coast, each of us can take action to adjust and prepare for continued changes in our treasured Gulf of Maine.