Areas of hypoxia, or low oxygen, have long existed in the deep waters of the Pacific, Atlantic and Indian oceans, but appear to be growing according to scientists. These “dead zones” appear to be spreading even into continental shelf areas and even approaching the surface. The lack of oxygen is so bad in some areas that the ocean floor is littered with animals such as Dungeness crab. These growing zones of low oxygen could be another sign of global climate change, since higher temperature water holds less dissolved oxygen and the ocean is increasing in its CO2 concentration.
Another possible impact of growing “dead zones” is the drastic alteration of complex and fragile food webs found throughout the various ecosystems in which these low oxygen areas are growing. Warm water acts as a cap on the ocean’s surface. This warm water cap interferes with the natural circulation that normally allows deeper waters to reach the surface, a process called upwelling. The water coming up from the deep is cooler and rich in nutrients. These nutrients support local ecosystems, and if they were to cease, the ecosystem would also.
For more information about these anoxic zones, please visit Growing low-oxygen zones in oceans worry scientists.