Marine Heatwave

Tidings | Aug 22, 2019

A map showing the how much different regions in the Gulf of Maine are warming.

As many are now aware, the Gulf of Maine is one of the fastest-warming ocean ecosystems on the planet. Over the last 30 years, the Gulf of Maine warmed at a rate of 0.06°C per year (0.11°F per year) — more than three times the global average. Over the last 15 years, this region has warmed at more than seven times the global average rate. At both time scales, the Gulf of Maine warmed faster than 99% of the global ocean.

This year has officially crossed the threshold for what scientists call a “marine heatwave.” This phrase describes an area of the ocean experiencing temperatures above the 90th percentile for more than five consecutive days. The most recent Gulf of Maine heatwave started on July 20 and continued for more than a month. Moreover, only 40 days in 2018 did not reach heatwave levels, and you have to go back to September 2017 to find a sustained period below heatwave levels.

Amid this especially warm year, the Gulf of Maine officially experienced its second warmest-ever day on August 8. On that day, the average sea surface temperature in the Gulf of Maine reached 20.52°C (68.93°F), as measured by satellites operated by NOAA and NASA. This is only 0.03°C (0.05°F) shy of the record set in 2012.

"This year really brings home the connection between Atlantic circulation and the temperatures in the Gulf of Maine,” says Chief Scientific Officer Dr. Andrew Pershing. “The satellite images from this year show a persistent mushroom-shaped blob of very warm water at the mouth of the Northeast Channel — a deep gully that leads into the Gulf of Maine. Essentially, shifting ocean currents are functioning like a hot water tap that dumps directly into the Gulf of Maine.”

The Gulf of Maine is warming faster than most places on the planet. Listen to GMRI experts explain this warming in this video from our Gulf of Maine, Explained series.