Abstract

The dead zone, a hypoxic zone, is a region of low oxygen that results from runoff of high nutrients, such as nitrogen and phosphorus. Most of the marine life cannot survive in hypoxic conditions. Dead zones in the coastal oceans have spread exponentially since the 1960s and have serious consequences for ecosystem functioning. The formation of dead zones has been exacerbated by the increase in primary production and consequent worldwide coastal eutrophication. Enhanced primary production results in an accumulation of particulate organic matter, which encourages microbial activity and the consumption of dissolved oxygen in bottom waters. Dead zones have now been reported from more than 400 systems, affecting a total area of more than 245,000 square kilometers, and are probably a key stressor on marine ecosystems. Many factors influence the formation of dead zones in oceans. These Dead zones are reversible when the oxygen availability is revived. Dead zones are generally found near highly populated areas and even near coastlines. There are four types of dead zones that are Permanent, Temporary, Seasonal and Diel Cycling. Dead Zones have a profound and diverse effect on the marine environment.