Reuters: Alaska U.S. and Canadian scientists are headed far north on a joint mission to map the still mysterious floor of the Arctic Ocean, as questions of sovereignty and mineral rights swirl around the region. The five-week mission, the third joint expedition in as many years, employs two powerful icebreakers from the nations’ Coast Guard fleets. Both are scheduled to depart Monday, from ports in Alaska and Canada’s Nunavut territory respectively, for a rendezvous point at sea, said …