In the Southern Ocean the Antarctic Circumpolar Current flows continuously eastward, except near the Antarctic coast. It has multiple fronts. The Ross Sea and Weddell Sea embayments are half covered by ice shelves. The mainly ice-covered Arctic Ocean has wide continental shelves and receives large quantities of river runoff resulting in low salinities. Eight seas surround the central Arctic - the Barents, Kara, Laptev, East Siberian, Chukchi, Beaufort, Lincoln and Greenland, as well as the channels of the Canadian Arctic Archipelago. North Atlantic water enters the Barents Sea and cold water and ice exit via the East Greenland Current. The Labrador Sea links Baffin Bay to the North Atlantic. The Bering Sea and Sea of Okhotsk are marginal seas of the North Pacific and Pacific water enters the Arctic via Bering Strait. Ocean warming caused 1.1 mm/yr of sea level rise from 1992 – 2010, with glacier melt accounting for 0.86 mm and Greenland and Antarctica 0.60 mm. Arctic ice is ~60 percent first year and 40 percent multiyear. Its extent has decreased dramatically since the 1980s, especially in September. Antarctic sea ice is mainly seasonal. Recently, it had been increasing until 2016. Coastal polynyas are major sea ice producers.