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In the Kitikmeot Sea and the surrounding waters of the Canadian Arctic Archipelago, the daily ebb and flow of the tide shapes the relationships between the ecosystem and the people in the region. Like elsewhere, celestial forces drive the tidal cycle. But here, the behavior of sea ice adds another potent dimension. And as a new study shows, with sea ice declining because of climate change, Arctic communities are set to face longer seasons of more extreme tides and stronger tidal currents. The result could be a self-reinforcing cycle of sea ice melting, ecosystem changes, and increasingly dangerous conditions for the people who live here.
The tide flows into the Kitikmeot Sea from the Atlantic Ocean through Victoria Strait in the east and from the Arctic Ocean through the Dolphin and Union Strait in the west. Victoria Strait, however, is prone to being blocked by sea ice during the winter. Strong currents deform and push the ice together, building up layers and creating a barrier up to 10 meters thick, says Lina Rotermund, an ocean researcher at Dalhousie University in Nova Scotia, and lead author of the new study.
Sea ice also affects tides in an unexpected way—the friction between the ice and water slows down the tidal currents, she says.
Together, the blockage and friction reduce the height of tides and current speeds by over 50 percent in the Kitikmeot Sea during periods of high sea ice compared with the ice-free seasons, according to the study. In the western Canadian Arctic Archipelago, the ice’s effects make winter tides approximately 25 percent lower. But with sea ice melting expected to continue across the Arctic because of climate change, higher and stronger tides will occur earlier in the spring and continue later into the fall—something that the local communities are not used to.
One effect of the tide, says Igor Polyakov, an oceanographer at the University of Alaska Fairbanks who was not involved with the study, is that it transports heat from the bottom layers of the ocean. In the eastern Arctic Ocean, the recent strengthening of tidal currents has already brought more heat than usual from the interior of the ocean to the surface causing more sea ice to melt—setting up a reinforcing cycle, Polyakov says.
In the Kitikmeot Sea, tidal mixing is most prevalent in the narrow, shallow straits. Already, this reinforcing cycle is causing sea ice to melt earlier, opening ice-free areas known as polynyas during the winter. Polynyas pose a travel risk, says Bill Williams, an oceanographer with Fisheries and Oceans Canada and coauthor of the study, because the Inuit use the sea ice to hunt and move between communities.
“Polynyas are nothing new for the Inuit, but a longer open water season, with its stronger tides and more heat in the ocean, means we could see these ice-free regions expanding and posing additional travel risks,” he says.
Tidal currents also mix nutrients from the bottom layers of water to the surface. This is especially important in the Kitikmeot Sea because fresh water from the region’s rivers sits on top of the layer of water that contains the most nutrients and hinders mixing. The shallow seafloor geography in the straits also blocks much of the nutrient-rich water from the surrounding area from entering the basin. This makes tidal currents one of the predominant ways of getting the limited supply of nutrients to the surface to drive production and support the region’s food web. The amplification of tidal currents because of sea ice loss would increase this mixing. However, the food web is complex and it’s unclear whether this would be an overall benefit or hindrance for local wildlife.
“Studies like this are very important and useful because the effects of tides on Arctic waters and the ecosystem are often understated,” says Polyakov.