This summer's heat wave in Atlantic Canada was reflected in sea surface temperatures from southern Nova Scotia to northern Newfoundland.

In much of the region, ocean temperatures at the surface last month were two to three degrees higher than the 20-year average, according to data from the Department of Fisheries and Oceans.

"It's getting up to the largest anomalies that we've seen for the 20-year record that we have," said Dave Hebert, a research scientist with DFO.

A chilly June meant the surface temperature was cooler than average that month.

But that changed with heat waves in July and August. Nova Scotia saw 53 days with air temperatures 25 C or higher.

"What we are seeing is the sea surface temperatures really mimicking our weather," said Hebert.

"The [surface] temperature is progressively getting warmer and warmer, and also the warm area has been moving northward from the Gulf of Maine to the Scotian Shelf to the Newfoundland Shelf."

This Fisheries and Oceans Canada map shows how much warmer or colder the temperatures are compared to a 20-year average. The darkest red indicates an increase of 3.5 C. (Submitted by Fisheries and Oceans Canada)

Over a two-month period, DFO maps show dark red blobs gradually engulfing the Atlantic Ocean surrounding the region.

"What's amazing is you can see the progression. It's now all the way over to Newfoundland," he said.

Much of Nova Scotia's south shore, Cape Breton, the Gulf of St. Lawrence and into the Cabot Strait averaged 20 C on the surface in the second half of August, as measured by satellite.

Ocean heat wave

Scientists at the Gulf of Maine Research Institute in Portland, Maine, said the Gulf of Maine crossed the threshold for a so-called marine heat wave this summer.

That's when an area of ocean experiences temperatures above the 90th percentile for more than five consecutive days. It lasted more than a month.

The institute said on Aug. 8 the average sea surface temperature reached 20.52 C, just below the warmest temperature ever. That was recorded in 2012, the wake-up year in the Gulf of Maine when 100-year records were broken.

Hebert said the warm water is not just at the surface.

At mid-level depths, it has been one to two degrees above average this summer, part of an overall trend of warming ocean conditions this decade.

In April, DFO scientists on board the Canadian Coast Guard vessel Hudson made a startling measurement, recording a temperature of 14 C in the 250-metre-deep Northeast Channel, 200 kilometres south of Nova Scotia.

The channel is where offshore water funnels into the Gulf of Maine.

Scientists will head out again Saturday on a fall scientific cruise. One of the first stops will be the Gulf of Maine and the Northeast Channel to see if the warm water persists.

'Regime shift' may be underway

On Aug. 30, the National Oceanic and Atmospheric Administration (NOAA) released a summary of marine ecosystem conditions on the Northeast Shelf, which runs from Cape Hatteras, N.C., up to the Canadian boundary.

The summary noted dozens of species are moving northward and into deeper water, bottom temperatures are rising with lower chlorophyll concentrations and smaller plankton blooms.

"Surface and bottom water temperatures collected over time indicate that a significant, sudden and persistent change, called a regime shift, may have occurred in Gulf of Maine water temperatures, with the last eight years the warmest in the time series by a wide margin," the Northeast Fisheries Science Center, an NOAA agency reported.

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