Increasingly Mobile Sea Ice Means Arctic Neighbors May Pollute Each Others’ Waters

The movement of sea ice between Arctic countries is expected to significantly increase this century, raising the risk of more widely transporting pollutants like microplastics and oil, according to new research. The study, in the journal Earth’s Future, predicts that by mid-century, the average time it takes for sea ice to travel from one region to another will decrease by more than half, and the amount of sea ice exchanged between Arctic countries such as Russia, Norway, Canada and the United States will more than triple.

Increased interest in off-shore Arctic development, as well as shipping through the central Arctic Ocean, may increase the amount of pollutants present in Arctic waters. And contaminants in frozen ice can travel much farther than those in open water moved by ocean currents.

“As the Arctic warms and the summer sea ice cover retreats, we all know that things will be very, very different,” said coauthor Robert Newton, a senior research scientist at Columbia University’s Lamont-Doherty Earth Observatory. “Ice is a great platform for moving material, and one of our motivations was to think about how pollutants, and especially how oil from an accident, are likely to move around.”

Historically, floating masses of Arctic sea ice have been able to survive for up to 10 years, building up layers during much of the year, lasting through each summer and not moving very far during any given year, until finally floating out into warmer southern waters. As the climate warms, however, that pattern has been changing.

While overall, sea ice is thinning and melting entirely across vast regions in the summer, the more open water means the area of new ice formed during winter is actually increasing. This is the case particularly along the Russian coastline. The trend will probably soon extend into the  central Arctic Ocean. This thinner ice can move faster in the increasingly open waters of the Arctic, delivering the particles and pollutants it carries to waters of neighboring states.

“Ice moves faster, but as the climate warms, it doesn’t have as much time as before to travel before it melts,” said lead author Patricia DeRepentigny, a doctoral candidate at the University of Colorado, Boulder. “Because of that, we really see that it’s the regions that are directly downstream of each country’s waters that are going to be most affected.”

In a 2017 study led by Newton, a team including DeRepenigtny examined the movement of Arctic sea ice from the instrumental record starting in 1979, when the first continuous satellite observations began. That study was the first to document an increase in the amount of sea ice being transported from one region to another over the last four decades.

“That was really eye opening,” said DeRepentigny. “The follow-up question then was: How is this going to play out in the future? It opened a really big box of new questions.”

So the researchers used a global climate model, together with the Sea Ice Tracking Utility, to track sea ice from where it would form to where it would ultimately melt during the 21st century. They considered two different emissions scenarios: the more extreme “business as usual” scenario, which predicts warming of 4 to 5 degrees Celsius by 2100, and a warming scenario limited to 2 degrees Celsius, inspired by the Paris Agreement. They then modeled how sea ice would behave in both these scenarios at the middle and the end of the century.

In three of these four situations, including both mid-century predictions, the movement of sea ice between Arctic countries increased. But in the high-emissions scenario at the end of the century, the researchers found countries could end up dealing more with their own ice and its contaminants than ice from their neighbors. This is because with 4 degrees or more of warming by 2100, the majority of sea ice that freezes during winter would melt each spring in the same region where it formed.

Russia’s exclusive economic zone and the central Arctic Ocean are two places the researchers expect more new ice to form; this would make them major “exporters” of ice to other regions in the Arctic. An exclusive economic zone is an area extending 200 nautical miles from the coastline, over which a state has special rights regarding fishing, shipping and industrial activities like offshore oil drilling.  Five countries have exclusive economic zones in the Arctic Ocean: Canada, the United States, Russia, Norway and Denmark (which includes Greenland).

However, no country has exclusive rights over the middle of the ocean. If this region becomes more ice-free in summers, it will become an attractive shipping route, especially because ships won’t need to get permission from another country to travel through it.

“That has several implications,” said DeRepentigny. “Who’s responsible for contaminants and materials that melt in the central Arctic or get exported out of the central Arctic into different countries? It’s no longer just a national question.”

The study was coauthored by Alexandra Jahn of the University of Colorado Boulder, L. Bruno Tremblay of McGill University, and Stephanie Pfirman of Arizona State University.

Adapted from a press release by the University of Colorado, Boulder.