Nearly two dozen Greenpeace activists are said to be locked down at various positions on the icebreaker Nordica to protest Shell's plans to start drilling for oil in the arctic waters off the Alaskan coast.
"We are here on behalf of the nearly 400,000 people around the world who in just a couple of months have spoken out demanding that Shell cancel its reckless campaign of arctic destruction," Greenpeace campaign manager in Finland Tapio Laakso said in a statement. "Oil companies know full well that an oil spill off the Alaskan coast would devastate the environment and prove impossible to clean up."
Greenpeace says it is "fundamentally wrong" for companies like Shell to profit from melting sea ice in arctic regions.
Shell has plans to drill up to five exploratory wells off Alaska's coast this year.
Greenpeace activists occupied a Shell drill ship departing from New Zealand waters to Alaska earlier this year.
There was no public comment from Shell. The U.S. government has approved Shell's 450-page oil-spill response plan for work in the arctic.