In the Antarctic, both the position and the character of the boundary between the ranges of sub-Antarctic and Antarctic species may be explained by differences in meteorological conditions. When the speed of the wind is small there is a distinct boundary along the line of the polar front. When the wind changes, the position of the front changes too, and the convergent motion may be replaced by a divergent one [Wyrtki, 1960ab]. This results in a mutual penetration of Antarctic and sub-Antarctic plankton through the polar front and the formation of a mixing zone.