Longer summers

January 11, 2018 School of Marine Sciences

Summer is coming to the Gulf of Maine — warmer than ever and as much as two months longer than just three decades ago, according to a research team led by Andrew Thomas of the University of Maine School of Marine Sciences. The study, published in the journal Elementa, examined the seasonality of sea surface temperature trends along the northeast coast of the United States.

For all but a small region immediately north of Cape Hatteras at the southern edge of their study area, the researchers confirmed that surface water temperatures shows an increasing trend over the last three decades, with the Gulf of Maine warming at about 0.4 degrees Celsius per decade.

The new analysis both mapped the geographic pattern of these trends and showed that the increase is actually much stronger than this in the summer and early fall months, from June to October, and weaker in the winter months. The impact of these seasonal differences was an increasing duration of the summer period — strongest in the Gulf of Maine, which had a trend of over two days per year.

The research builds on previous work by Thomas and his colleagues, including Andrew Pershing and Katherine Mills of Gulf of Maine Research Institute, and others from Bigelow Laboratory, Stony Brook University and NOAA. In a widely cited 2015 paper in Science, these authors analyzed sea surface temperature data showing that the Gulf of Maine region exceeded the global average rate of warming over the last 30 years, and noted that over the past decade the Gulf of Maine warmed faster than 99.9 percent of the global ocean. Looking at details behind these trends was a logical next step. They were motivated by several questions: Do overall warming trends occur equally throughout the year, or do they occur primarily in a particular season? Which regions are the most susceptible or resilient to changes in sea surface temperature?

With funding from the National Science Foundation and NASA, they took a higher resolution version of the same set of data — 33 years of satellite measurements — and zoomed in on the northeastern North American continental shelf region. Then they separated the data into months, so they could quantify and map seasonal trends. Their results showed patterns in space and over the seasonal cycle that were not evident in earlier studies.