Amur freshwater helps freeze a Pacific factory of life
The Sea of Okhotsk covers about 1.58 million square kilometres between Kamchatka, the Kurils, Hokkaido, Sakhalin, and Siberia, averaging 859 metres deep and plunging to 3,372. Amur River freshwater lowers surface salinity so winter ice forms readily, blocking navigation with floes.
As the ice grows it squeezes out salt, and the dense brine sinks and flows east into the Pacific, carrying oxygen and nutrients that support rich marine life. Some parts of the sea have warmed by as much as 3°C since preindustrial times. It connects to the Sea of Japan westward through Sakhalin Gulf and the Strait of Tartary and southward through La Pérouse Strait.
The International Hydrographic Organization closes the sea in the south-west at La Pérouse Strait and in the south-east along a line from Cape Noshap on Hokkaido through the Kuril Islands to Cape Lopatka at the tip of Kamchatka, so that every narrow channel in between counts as part of the Okhotsk. Apart from Hokkaido, the surrounding shores are administered by Russia. Japan held southern Sakhalin and the Kurils until 1945 and still claims the southern Kurils as its Northern Territories.
It is the coldest sea in East Asia and the southernmost sea in the Northern Hemisphere to freeze each winter, with conditions in the north and west close to Arctic. Two pressure systems, the Siberian High over the continent and the Aleutian Low over the North Pacific, set the winter winds. When the low sits south-west of its usual spot near Kamchatka, easterlies bring milder weather; when it moves north, frigid northerly blasts thicken the ice.
January and February are the coldest months, with mean February air near minus 20°C in the north-east and colder still along the northern and western coasts, while August averages about 12°C there. From October to April the northern sea is mostly frozen and receives little precipitation.
Source: Sea of Okhotsk
