Arctic Sea Ice Facts Max Area 7 million square miles (March) Min Area 4 million square miles (September) Avg. Thickness 10 to 20 feet Freezing Pt. of Seawater -1.8° C (29° F) Max Height of Pressure Ridges 15 to 30 feet Avg. length of stay for ice floes 2 to 5 years Floe Size Several feet to 6 miles wide Did you know? Pack ice (or sea ice) is made of frozen salt water; it is composed of pieces of ice of various shapes, sizes, and ages that are free to drift under the influence of winds and ocean currents. Sea ice generally forms in shallow seas around the Arctic Basin. Sea ice limits the amount of solar radiation reaching the Earth; reflecting more than 80% of the incoming sunlight. Sea ice substantially reduces the exchange of heat and mass (from evaporation) between ocean and atmosphere, acting as a natural barrier between the two systems. Polynyas are irregular openings in the pack ice caused by ocean currents and shifting wind flow patterns. It was through one of these that the submarine U.S.S. Skate surfaced (1959) close to the North Pole.

Sea Ice Research

The dominant feature of the Arctic Ocean, sea ice has been the subject of much scientific research. Unlike icebergs, which are composed of freshwater ice calved from glaciers and ice sheets, sea ice is in fact frozen salt water. In the northern hemisphere, sea ice is found as far south as the coast of Labrador, Cook Inlet (Alaska), in the Sea of Okhotsk and in the Baltic Sea. Summer coverage is confined mainly to the central Artic Ocean, the Greenland Sea and Canada's Arctic archipelago.

At the end of each winter 6 feet or less of first-year ice covers most of the shallow, shelf seas around the Arctic Ocean basin. However, sea ice rarely forms a flat, uniform sheet since the action of winds, waves, currents and tides moves and breaks the ice into floes of various sizes. Circling the Arctic Ocean in a clockwise direction, most floes take several years before they eventually escape, mainly between Spitzbergen and Greenland. They may then float as far south as Iceland before completely melting away. In certain places in the Arctic pack, the jamming and crushing of floes form pressure ridges and hummocks that may rise 20 feet or more above the general level of the pack.

Arctic sea ice research has undergone somewhat of a revolution with the development of satellite remote sensing during the late 20th century. Arctic sea ice can be viewed and studied on a routine basis and with significantly more detail. These sensors have the ability to monitor and record the considerable seasonal changes in ice extent. In addition, submarines and sea floor instruments using upward pointing sonar have been used to better understand ice topography and variations in ice thickness. Together with field data, these records have become key to understanding regional patterns and shifts.

Drift buoy observation and monitoring have revealed two major ice circulation systems in the Arctic Ocean -- an east to west Transpolar Drift in the Eurasian Arctic (northern Russia) and a clockwise Beaufort Gyre (north of Alaska and Canada).

Other studes have focused on the chemistry and composition of Arctic sea ice. Recent studies have revealed the formation process and structure of sea ice to be quite complex. During formation, ice crystals develop while salt is rejected and released into the underlying ocean, increasing the salinity and density of the surrounding surface waters. These denser waters gradually sink and can eventually contribute to the circulation of deeper waters in the Arctic Ocean.

Another focus of recent research has been the monitoring and evaluation of the increasing levels of pollution found in drifing sea ice floes. Incorporated during the freezing process in shallow Arctic seas, contaminants such as heavy metals, radionucleides from nuclear facilities, and sediment have been transported hundreds of miles from coastal areas to the deep Arctic. The future impacts of this phenomenon on the Arctic environment are not yet clearly understood.