Scarier at the moment to fish than to humans but of increasing concern to all, dead zones are areas of the ocean along coasts with low levels of oxygen at the sea floor. Many dead zones are occurring near the mouths of major river systems when fertilizer run-off, especially during flooding, supplies nutrients to phytoplankton which multiply rapidly. Organic matter produced by phytoplankton sinks to the bottom of the ocean where bacteria break it down. The bacteria use oxygen in the process and release carbon dioxide, depleting available supplies of oxygen needed by other forms of aquatic life.
To learn more about dead zones, access Creeping Dead Zones by NASA's Goddard Earth Sciences Data and Information Services Center. The site includes satellite views of dead zones, a world map of dead zones, and links to further information.
