Marine Ecosystems Under Threat from Expanding Underwater Deserts

Global warming has led to expansion of low oxygen underwater deserts in the tropical oceans over the past five decades which scientists view as a potential threat to marine ecosystems. Climate models predict that the t rend will continue threatening marine ecosystems.

The discovery concerns a layer of the ocean called the oxygen -minimum zone where concentrations of dissolved oxygen are particulary low.This zone has been expanding both upwards and downwards into the adjacent layers in tropical waters.

Researchers measured the oxygenation of the oceans at depths of between 300 and 700 metres during a series of observation cruises in tropical regions of the world’s three main oceans.Overall levels of oxygen have dropped in these zonee.Regions of the eastern tropical Pacific Ocean and the northern reaches of the Indian Ocean are now classed as suboxic meaning that the amount of oxygen has dropped sufficiently to harm the functioning of ecosystems.In suboxic waters nitrogen cannot react with oxygen to form biologically available nitrate.This means that organisms at the base of food chains such as plankton do not get enough nutrients to survive.