Soon after the icebreaker Oden left the Arctic ice pack, it crossed a threshold into the Barents Sea, which technically is a part of the Arctic Ocean located north of Norway and Russia. On Monday, the crew of the Oden exchanged pleasantries with the crew of the Russian nuclear icebreaker Yamal, which was returning from an expedition to leave a Russian flag on the ocean bottom beneath the North Pole. The two ships passed in the fog, within radio range but unable to see each other in the mist. Around this time of year, the entire Barents Sea is more or less ice-free, but sea ice forms in the northern half during winter. The southern half of the sea remains ice-free year-round because the North Atlantic Current, an extension of the Gulf Stream, brings warmer waters to the region.