Antarctic sea ice, 1973-1976, NASA4)

From 1974 to 1976, a large hole opened up in the Antarctic ice4). The size of the hole was over 500km diameter, a hole with a surface area nearly equal to that of the whole of Japan. The place was the South Atlantic, called the Weddel sea, where it is thought that the world's heaviest deep water is produced and sinks to the bottom of the sea. Coriolis' force has a stronger effect at the poles than it does at the equator, so if a convective current occurred there, it would be strongly acted upon by the rotation of the earth. Convective activity associated with the creation of heavy deep water is thought to be a cause of this kind of hole, but for some reason over the last 20 years no such similar holes have been observed, so the details of the hole's creation remain a mystery.