The extent of the ice on the Polar Ocean is dependent on the low salinity of the Arctic waters - a saltier sea would not freeze over to such a degree. The Polar Ocean is separated from the Atlantic Ocean by a barrier of islands that inhibits their inter-circulation. This island chain is formed from what was once a single island known as Iceland. It consisted of lavas that erupted from the Mid-Atlantic Ridge as the crustal plates of Europe and North America (the Eurasian Plate and the North American Plate) moved away from one another. As this movement continued, enlarging the Atlantic Ocean, Iceland, straddling the mid-oceanic ridge, split into two parts, each moving in opposite directions. The continuing volcanic activity spawned a string of new islands in the growing gap between the two parts. Almost 180 degrees away, at the opposite side of the Arctic Ocean, the same crustal movements were responsible for closing the Bering Strait, the gap between North America and Asia, and fusing the two areas into one vast Northern Continent. As a result the Polar Ocean is now practically landlocked, and is fed by the rivers of the surrounding supercontinent.
This northern polar body of water is almost landlocked and contains a permanent icecap, which has a considerable influence on the environment of the surrounding continent and contributes substantially to the stability of the region's cold climate. The icecap is maintained only because the Polar Ocean is fed by enormous quantities of freshwater by the rivers of the surrounding continent. This gives the sea an unusually low salinity and therefore a strong tendency to freeze over.
In winter the Polar Ocean is largely barren. In spring, however, the sunlight produces a bloom of unicellular algae near the surface, which provides food for the microscopic animal life that forms the basis of the oceanic food chain. In spring, shoals of pelagic fish come northwards through the northern island barrier to feed on the zooplankton, bringing with them countless numbers of seabirds.
Among the organic detritus on shallower areas of the ocean bed are found banks of shellfish.