16 Arctic ports: Murmansk (ice-free, the Atomflot base), Arkhangelsk (White Sea), Sabetta (Yamal LNG), Dudinka (Norilsk's port, up the Yenisei: carved as a channel), Tiksi and Pevek on the Northern Sea Route; Churchill (Hudson Bay grain), Iqaluit, Resolute (Northwest Passage) and Prudhoe Bay (Alaska's North Slope oil); Longyearbyen (Svalbard coal), Sisimiut and Ilulissat (west Greenland); Tromso, Hammerfest (LNG) and Kirkenes (iron ore) in northern Norway. Murmansk, Arkhangelsk and the Norwegian ports are in the Northern Europe market.
Routing runs to 80.5 N, but only lanes to or from an Arctic port may go north of 66 N; between two other ports the Arctic counts as land, so every lane that existed before is unchanged. So the Arctic routes are sailed through Arctic ports: Rotterdam to Pevek goes along the Northern Sea Route, and a summer Europe-Asia run is e.g. Rotterdam - Pevek - Yokohama.
Seasonal closures (in saves with them), on real dates: the Northern Sea Route (a stretch of sea from the Kara Sea to the Chukchi Sea: every lane through it) open 1 Jul to 15 Nov; the Northwest Passage (the Canadian archipelago) open 15 Aug to 5 Oct; and the ports Churchill (open 11 Jul to 14 Nov), Iqaluit (1 Jul to 31 Oct), Prudhoe Bay (1 Aug to 30 Sep), Ilulissat (16 May to 14 Jan) and Arkhangelsk (16 May to 30 Nov). Murmansk, northern Norway, Longyearbyen and Sisimiut stay open all year (the Gulf Stream). A ship won't start a leg through a closed route it can't finish in time; the route screen lists each leg's closures, and the map shows a closed route iced over.
Icebreakers: a nuclear icebreaker stationed on the Northern Sea Route (Murmansk, Sabetta, Tiksi, Pevek) or the Northwest Passage (Resolute, Iqaluit, Prudhoe Bay) keeps it open all winter, leading convoys through the ice like the Sea of Okhotsk ones; only a nuclear one can ("Only a nuclear icebreaker can keep the Northern Sea Route open through the Arctic winter."). A diesel one can keep Arkhangelsk open (the White Sea).
Maritime Empire