Biosphere Journal Entry
Biosphere Journal Entry
Ocean Dead Zones Spreading (May 24, 2010)
Huge piles of dead crabs were found along Pacific Northwest beaches in recent years. Elizabeth Gates/PISCO.
New research shows lower oxygen levels are triggering an alarming rise in ocean dead zones, coastal areas where few living organisms are found. One such dead zone is found on coasts of the Pacific Northwest. In 2006, plunging oxygen levels in some areas along the coasts of Oregon and Washington killed crabs and weakened sea anemone colonies. The disaster spawned huge mats of bacteria that thrive in oxygen-poor conditions.
Dead zones are often found on coasts where pollution from farms and cities is dumped into the sea. The pollution triggers a chain reaction that robs seawater of oxygen. Nutrients increase blooms of microscopic algae. After the algae die, decomposition by bacteria gobbles up oxygen. Stress spreads up and down the food chain and fish swim away from the area.
In the United States, the problem is worst where big rivers, like the Columbia in the Pacific Northwest and the Mississippi in the South empty into the sea. The situation has likely grown even worse in the Gulf of Mexico since the disastrous oil spill. Ocean dead zones are growing worldwide. The rise has also been linked to global climate change. Rising temperatures create large pockets of warmer surface water. The warmer water act as a cap that interferes with natural ocean currents. This keeps surface oxygen from refreshing oxygen-depleted deeper waters. Areas of oxygen-poor water have expanded in the Atlantic, Pacific, and Indian oceans. These areas are now larger and closer to the surface and coasts than in the past.
