A Northwest Passage navigable several months a year is one of the warming Arctic’s biggest prizes — and potential sources of conflict.

Dall’s report on the Black Current was unequivocal. “The Kuro Siwo sends no recognizable branch northward, between the Aleutians and Kamchatka,” he wrote. “No warm current from Bering Sea enters Bering Strait. The strait is incapable of carrying a current of warm water of sufficient magnitude to have any marked effect on the condition of the Polar

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