A new study published in the journal Elementa has taken a look at the seasonality of sea surface temperature trends along the Gulf of Maine and its results may be well-received by tourists but certainly won’t be by fishermen. The investigation was led by Andrew Thomas from the University of Maine School of Marine Sciences along with a team of scientists who say that summer temperatures in the Gulf are lasting up to two months longer than is normal.
The foundation for this study was previous research that showed that the Gulf of Maine exceeded the global average of rate of warming over the last 30 years, warming faster than 99.9% of the global ocean. In fact, the Gulf of Maine has experienced warming at about 0.4 degrees Celsius per decade. Based on this knowledge, the scientists were interested in discovering when throughout the year the warming is most prevalent and where. To do so, they looked at data from 33 years of satellite measurements, paying special attention to seasonal trends.
"The temperature trends we see in this area are among the largest on the planet," said Thomas. "Two main drivers are likely at play. The Gulf of Maine is at the crossroads of two major large-scale processes, both of which are impacted by climate change. Our shelf is downwind of the jet stream coming off the continent. North or south shifts in jet stream position translate into changes in atmosphere-ocean heat transfer that heat and cool the shelf water." The study explains that higher atmospheric pressure and warmer air temperatures in spring and summer are linked to the extended summer ocean temperatures.
Their results show that from June to October, the rate of warming is much higher than during the rest of the year. Additionally, technically speaking, the summer season is actually getting longer (summer is defined as the number of days above a specific temperature each year). Since 1982, summer conditions have lengthened by 66 days (about 2 days for every year over 33 years). While Maine beach goers may enjoy this extended summer, it poses a threat to the fisheries industry.
"I'm an oceanographer, not a fish biologist," said Thomas. "But my fisheries colleagues on the team looked at that, and in a separate paper we showed that longer summers were linked to northward shifts in the fall population centers of American lobster, Atlantic herring, and Atlantic mackerel."
As with all species adapting to climate changes, some will thrive while others fail to survive. Lobster, herring, summer flounder, Acadian redfish and spiny dogfish all experience a rise in population sizes or total biomass; others, such as cod, have seen a decrease in biomass. This is because of the biology behind-the-scenes in such a warming scenario.
In the summer, warmer nutrient-poor water sits on top of the denser, cooler, nutrient rich water. If warmer temperatures last longer, less vertical mixing occurs, thus holding up the exchange of nutrients in the water column. "Stronger and longer summer stratification means weaker mixing and fewer and delayed nutrients coming to surface, a trend that will eventually mean the Gulf of Maine becomes less productive," said Thomas. That could have devastating impacts for Maine’s and all of New England’s economy.