By Lauren Morello
Rising temperatures are shrinking Arctic sea ice, and in Canada’s Northwest Territories, that means more and stronger storm surges, according to a new study.
An analysis of lakebed sediments from one section of the outer Mackenzie Delta shows surges have become more intense and frequent over the past 150 years as the region has warmed and ice has retreated.
The sharpest increase in surge activity came after 1980, in concert with the steepest declines in Arctic sea ice cover, concludes the research, which has been published online by the journal Geophysical Research Letters.
More than a decade after a storm surge swamped the shoreline of one of the lakes included in the new study, vegetation is still struggling to recover.
Credit: Joshua Thienpoint/Queen's University.
“We’re losing Arctic sea ice, and it’s getting stormier up there,” said lead author Jesse Vermaire, who conducted the research as a post-doctoral fellow in the laboratory of Carleton University geography professor Michael Pisaric. “You’re getting conditions that are ripe for these rare events — for these really large storms to impact coastal regions there.”
The region’s vulnerability to storm surge is likely to increase as the climate warms and the area covered by sea ice shrinks further, he said. The area covered by Arctic sea ice reached a new yearly low last summer, shattering the record set in 2007 and continuing a decades-long decline.
As that ice disappears, it leaves larger sections of Arctic coastlines without an icy barrier to blunt the impact of waves and surges. And it opens larger sections of open ocean. That means surface winds have more contact with ocean water, producing larger waves.
With sea level also rising, “I’d anticipate that with future climate warming, these large storm surges will increase in the area, and people need to plan for that,” Vermaire said.
But flooding isn’t the only risk Arctic coasts face as seas recede. Increased surges and larger waves can also take a bite out of shorelines, as many coastal communites across the Arctic have discovered.
In Alaska, worsening erosion has prompted some coastal villages to make plans to relocate inland at a cost of hundreds of millions of dollars — a decision that a recent federal analysis warns “is likely to become more common in the future for many coastal regions.”
In the sparsely populated Mackenzie Delta, however, scientists weren’t sure whether shrinking ice had already altered storm surge patterns. To help answer that question, the new study’s authors zeroed in on an area battered by a major storm surge in 1999.
That event sent salty Beaufort Sea water churning across 47 square miles of coastal land. Its effects are still apparent today. Normally green delta land is covered with dead brown vegetation in areas inundated during that massive surge 14 years ago.
But with instrumental records of storm surge, collected by tide gauges, reaching back only a few decades — and interrupted in many places by periodic equipment trouble — scientists were not sure how that 1999 event stacked up, historically.
It was hard for them to say whether the strength or frequency of surges in the area had changed.
Parts of the Mackenzie Delta that have escaped major storm surges are carpeted with healthy vegetation.
Credit: Trevor Lantz/University of Victoria
So the researchers went digging — literally. They extracted sediment cores from three of the Mackenzie Delta’s many lakes. A pair of lakes located close together, roughly 3.5 miles from the Beaufort Sea coast, were swamped by the 1999 storm surge. A third, larger lake, about 28 miles from shore, was not.
Comparing the cores from the two lakes close to shore with the lake further inland helped the researchers determine whether any storm surges larger than the 1999 event had occurred within their study area, as well as reconstruct a record of surges there over the past 400 years.
The scientists analyzed their three lake sediment cores in chunks about a tenth of an inch wide, using a variety of radiocarbon dating techniques to match layers of each core with the time period they represented.
Storm surges, even big ones, don’t produce larger layers within sediment cores, Vermaire said. But they do tend to sweep large particles of sand and sediment into lakes during their powerful spread inland — bigger than particles deposited by winds during periods without significant surge.
That rule of thumb helped the researchers identify traces of past storm surges within their sediment cores by looking at particle size. The scientists also examined changes in microscopic marine algae, called diatoms, trapped within each core layer.
Surges that sweep in salty ocean water, turning delta lakes brackish, make it hard for diatoms that prefer fresher water to survive. That opens the door for diatoms that thrive in saltier environments.
In the end, the researchers’ careful analysis revealed that the 1999 storm surge that pummeled the two lakes close to shore was, indeed, the largest in at least four centuries.
“It really stood out as a unique event in the last 400 years,” Vermaire said.
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