The Antarctic Convergence

THE ANTARCTIC CONVERGENCE

The Antarctic Convergence zone is not a precise line; it can vary between seasons or annually. Normally between latitude 49 and 55S, you can detect changes in the ocean, and in the climatic conditions. If the Drake Passage is calm as you cross the Convergence zone, you may experience a sudden fog bank, then a drop in temperature.

The Southern Ocean is divided into two hydrological zones by the convergence, which is defined as a line along which the cold, northbound Antarctic surface water sinks beneath the relatively warmer Sub-Antarctic water. During the southern summer, the sea temperature may drop from 7C to 3C, marking the difference between the Antarctic and Sub-Antarctic zones.

These zones, thus formed, are significant because they not only influence the distribution of marine life, but also because they determine the properties of the air masses above them, which contributes to the understanding of the meteorology of the southern hemisphere.

Influenced by the wind and the rotation of the earth, at around 5 to 10 degrees south of the Convergence zone, there is an area of divergence of the surface waters, with consequent up welling, which coincides with the boundary between the East and West wind belts. These areas are often marked by heavy concentrations of feeding sea birds.

You’re now in Antarctic waters, although the Antarctic Convergence probably forms the extreme north limit of drift ice, but ice is very rarely found so far north.

Large tabular icebergs have been sighted recently, off sub-Antarctic Campbell Island, the most southerly of New Zealand’s outlying islands, a mere 600km from the NZ mainland, for the first time in half a century. The most northerly iceberg was sighted at 51°S

The Southern Ocean is the term generally used for the circumpolar body of water lying north of Antarctica. The northern limit is not precisely, defined but is usually accepted by the latitude 55S.

According to New Zealand scientist, Lionel Carter, the coincidence of large collapses of the Antarctic ice shelves, and its downstream effects on global oceans and a rapidly changing climate, cannot be dismissed.