In the ocean convection occurs when the water at the sea surface is cooled. This causes an increase in water density at the surface and forces the water to sink. Because intense cooling is required to generate oceanic convection, the process occurs mainly in polar regions and is not as easily observed as atmospheric convection in the tropics.The photo shows a synthetic aperture radar image from the ERS-1 satellite over the Greenland Sea during February 1992. The image is about 6.4 km wide in both directions. Ice-covered water is grey/white, ice-free water is black.
A noticeable feature is the patchiness of the ice. Ice-covered regions are about 500 m in diameter and surrounded by ice-free regions of similar size. This is interpreted as a result of convection: When a convection cell develops, water sinks with great speed. Water is drawn in to fill the void and accumulates ice floes over the regions of sinking water. Rising water motion occurs at the perimeter of the convection cells. This water is warmer than the cooled surface water and melts the ice where it comes to the surface. This produces a patchwork of ice-covered and ice-free regions.
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