Map Illustrates Extent of the Planet’s Marine Dead Zones

A new NASA map illustrates the significant expansion of the world’s marine dead zones, deepwater regions where dissolved oxygen is so low marine species cannot survive. Many of these dead zones occur off densely populated coastlines, particularly along the eastern United States and in Northern Europe. Scientists produced the map using data from satellites that can detect high concentrations of particulate matter, an indicator of overly fertile waters that can create dead zones. The zones arise when fertilizers applied to crops wash into streams and rivers, eventually reaching coastal waters, where the excess nutrients trigger massive algae blooms. When the algae die, they sink to the ocean’s depths, where they essentially become fertilizer for microbes that decompose the organic matter and consume oxygen, suffocating marine life. In 2008, a study found that dead zones had spread exponentially since the 1960s, affecting more than 400 ecosystems and a total area of more than 152,000 square miles (245,000 square kilometers).