Wednesday, January 4, 2012

The Antarctic Convergence

Map showing the Antarctic Convergence

The key to understanding the impressive diversity of wildlife in Antarctica is the Antarctic Convergence, which is basically a line encircling the continent ( between 50° and 60° S), where the warm, more saline waters coming south from the tropics meet the cold, denser and mainly non-saline waters moving north from the Antarctic. These conflicting currents clash, converge and sink. The mixing waters provide a conducive environment for an abundance of plankton, so the Convergence nourishes huge numbers of seabirds and mammals.

Large swarms of krill maybe ten of thousands of metres across, containing densities of as high as 10,000 per square metre! Such super-swarms may involve several million tonnes of krill and they move through the ocean almost like a single organism, making it easy for creatures that prey on them. This super abundance of prey in the Antarctic waters, in turn, supports an amazing density and diversity of wildlife. For example, it is estimated that seabirds alone take about 40 million tonnes of krill per annum! The largest animal on our Planet, the Blue Whale can consume between 4-6 tonnes of Krill in a day!