Warmer ocean temperatures off Atlantic Canada continued in 2016, maintaining a trend that started earlier this decade, according to survey results from Canada's Department of Fisheries and Oceans.

On the Scotian Shelf off Nova Scotia, temperatures last year were as high as three degrees above the 30-year average used to establish climatic norms.

"It's not quite the same [record] level of 2012, but it's getting close to it," said Dave Hebert, a research scientist with DFO. He added that 2016 was probably the second warmest year on record.

Record temps happening all the time

Hebert said monitors moored to the ocean bottom 32 kilometres off Halifax actually reported the warmest temperatures yet in the fall of 2016. In October, water at the ocean bottom exceeded 11 C.

"We had record temperatures happening at that time. Way above everything," he said.

"You can see there's been a trend over that time period. The last couple of years have been way warmer than the previous years."

Every year the department measures temperatures throughout the water column off Newfoundland and Labrador, the Gulf of St. Lawrence, the Scotian Shelf, the Gulf of Maine and the Bay of Fundy.

What's warming the ocean bottom?

Last month, DFO published its sea conditions report for 2015. Those surveys also recorded above-normal temperatures, despite a brutally cold winter that year. The data gathered in 2016 has not yet been published.

Scientists have struggled to explain what is causing the most intriguing aspect of the recent trend: the warming of ocean bottom water, which is not influenced by surface weather events.

Hebert said the latest theory is based on model results that see the Gulf Stream moving northward and intersecting with the tail of the Grand Banks.

"That is stopping the cold Labrador Sea water from coming around the tail of the Grand Banks," he said. "That's where we normally get the cold water that refreshes the [Scotian] Shelf. That hasn't been happening.

"And what we are seeing is the warm slope water getting onto the shelf, sort of pumping more warm salty water, year after year, and the shelf will slowly change its conditions."

Historical data lack long-term trend

While there has been a warming trend in the last five to six years, Hebert said temperatures vary over the decades. Looking at historical data, "we can't see a trend that's significant," he said.

"If you picked another decade, you could say it's cold, it's cooling down a lot. So in terms of climate, it's always tricky in terms of that variability."