Dynamics: Circulation

Arctic

Since humans first ventured into the ice-covered oceans, they knew that sea ice motion occurred on small scales, such as a few kilometers (a couple of miles). But it wasn't until the voyage of the Fram to the Arctic that scientists finally confirmed that sea ice also moves across large-scale regions, primarily from the wind.

The wind-driven Arctic ice circulation pattern has two primary components. First, the Beaufort Gyre is a clockwise circulation (looking from above the North Pole) in the Beaufort Sea, north of Alaska. This circulation results from an average high-pressure system that spawns winds over the region. A second component is the Transpolar Drift Stream, where ice moves from the Siberian coast of Russia across the Arctic basin, exiting into the North Atlantic off the east coast of Greenland.

Beaufort Gyre and Transpolar Drift Stream

Arctic Ocean circulation.
Image courtesy of Arctic Monitoring and Assessment Programme (AMAP), Figure 3.29, AMAP (1998).

Sea ice that forms or becomes trapped in the Beaufort Gyre may circulate around the Arctic for several years. Sea ice that forms or becomes trapped in the Transpolar Drift Stream generally leaves the Arctic more quickly, usually in one to two years. Because of this, sea ice in the Beaufort Sea has more time to grow and reach the thermodynamic equilibrium thickness, so it is thicker. Also, because of the circular rotation of ice in the Beaufort Sea, ice floes frequently bump into each other. Ice deformation is common and leads to thicker and more ridged ice compared to other regions. The Transpolar Drift Stream pushes some ice against northern Greenland and the Canadian Archipelago; the ice compresses and deforms into ridges, resulting in the thickest ice in the Arctic.

Arctic ice motion from 1978 to 2003

Plot showing mean (average) Arctic ice motion from 1978 to 2003. Arrows show the direction and velocity of the ice, with longer arrows representing higher velocities.
Image courtesy of the National Snow and Ice Data Center, University of Colorado, Boulder, CO

In both the Beaufort Gyre and Transpolar Drift Stream, most of the ice follows a large-scale pattern when considered over a long period of time; however, within this long-term pattern of movement, there can be a great deal of variation. For example, the Beaufort Gyre may completely reverse directions--and often does for short periods of time, such as after a storm from a low-pressure system that moves across the region. Likewise, the Transpolar Drift Stream may also reverse direction. The day-to-day variation in the large-scale circulation can be quite dramatic.

Antarctic

The Antarctic large-scale circulation of sea ice is generally in a clockwise direction (looking above the South Pole) around Antarctica, with gyres, or smaller rotations, in the Weddell and Ross Seas. There is an average northward component, so sea ice gradually moves to the northern ice edge after it forms.

Arctic ice motion from 1978 to 2003

Plot showing mean (average) Antarctic ice motion from 1978 to 2003. Arrows show the direction and velocity of the ice, with longer arrows representing higher velocities.
Image courtesy of the National Snow and Ice Data Center, University of Colorado, Boulder, CO

In the Arctic, land encircles much of the sea ice, constraining its flow, resulting in ridging and thicker sea ice. The overall flow of Antarctic ice is quite different. There is no northern land boundary for the northward flowing sea ice to run into, so the ice flows northward until it melts in warmer oceans and air temperatures. Because of this, Antarctic sea ice is younger and thinner, on average, than ice in the Arctic. Most sea ice in the Antarctic is less than a year old (see Thermodynamics in the Processes section).