The Arctic Ocean is a little like a soup plate. Deep central areas are surrounded by a rim of shallower shelf seas, beyond which lie the northern continents – North America and Eurasia – and the Atlantic and Pacific Oceans.

Water in the Arctic is constantly moving - both horizontally in currents that sweep around the pole - and vertically, through a process called ventilation. Cooling water in the Arctic freezes, forming sea ice and leaving much of its salt in the water below. This water becomes more salty (saline) and therefore denser – and sinks. It forms a mass of cold, dense water at the bottom of the Arctic Ocean ‘soup bowl’. As more water descends by this process of ventilation, the level rises up until this cold water mass spills over the rim (or shelf area - in the Atlantic, the Greenland-Shetland Ridge) and down into the depths of the Atlantic, forming a body of water known as the North Atlantic Deep Water. 

To replace deep water leaving the Arctic southwards, a compensating flow of warmer surface water is forced north up the Atlantic. This is known as the thermo-haline circulation.

Arctic Ocean water circulation (image courtesy of Encyclopedia of Earth)

However this is not the only system driving water into the Arctic Ocean. 10% of global river output empties out from North America and Eurasia into the Arctic, spreading a layer of cold, fresh water over the ocean surface.

Concern has grown in recent years as freshwater inflow to the Arctic increases through processes induced by global warming. A reduction in salinity of surface seawater may disturb the thermo-haline circulation, negatively affecting the flow of warm surface water northward, and potentially leading to climate cooling in Britain and Western Europe.

To learn more about ocean circulation visit this excellent resource:

Woods Hole Oceanographic Institute – Polar Ocean Circulation