Monday, March 8, 2010

Ocean Dead Zones: low oxygen areas are still growing

Ocean researchers and many conservationists have heard of oceanic low-oxygen or "dead zones" wherein large areas of ocean have lower-than-normal levels of oxygen. To a large extent, these areas are normal or somewhat predictable - deepwater and seasonal movements of water; all part of the ocean's normal process of oxygen intake, use, and replenishment.

But there are more and more signs from throughout the world that these dead zones are becoming more frequent and growing in size. From both coasts of Africa, to South America to the Pacific Northwest, dead zones are becoming a real problem, killing off some aquatic species, displacing others, and affecting the ocean's relationship with the atmosphere - a relationship that provides a majority of our breathable air.

A recent article in the online McClatchy newspaper outlines what has been happening in the Pacific Northwest, along the Oregon/Washington coastline. Some scientists believe it's too soon to tell whether the root cause - a warming of the surface waters that acts as a cap to suppress the normal cycle of deepwater to shallow, or upwellings and downwellings - is due to global warming, but it's high on their list of suspects.

Some might think that it's a sign of ocean acidification, but this is a different process taking place here, as well illustrated in the article. However, in any case, the net effect of the coast of Oregon and Washington is tangible, with piles of dead Dungeness crab and 25-year old sea stars littering a sea floor covered with a higher-than-normal bacteria layer.

"Areas of hypoxia, or low oxygen, have long existed in the deep ocean. These areas — in the Pacific, Atlantic and Indian oceans — appear to be spreading, however, covering more square miles, creeping toward the surface and in some places, such as the Pacific Northwest, encroaching on the continental shelf within sight of the coastline.

'The depletion of oxygen levels in all three oceans is striking,' said Gregory Johnson, an oceanographer with the National Oceanic and Atmospheric Administration in Seattle."

If these low-oxygen zones continue to increase in size and/or frequency, the ocean ecology will have to make adjustments, some that will be severe and that we will feel as they impact commercial fisheries. But scientists are not sure just how far-ranging these changes could be. After all, they have no reference models or examples to turn to - we are heading into unknown territory.

"Scientists are unsure how low oxygen levels will affect the ocean ecosystem. Bottom-dwelling species could be at the greatest risk because they move slowly and might not be able to escape the lower oxygen levels. Most fish can swim out of danger. Some species, however, such as chinook salmon, may have to start swimming at shallower depths than they're used to. Whether the low oxygen zones will change salmon migration routes is unclear.

Some species, such as jellyfish, will like the lower-oxygen water. Jumbo squid, usually found off Mexico and Central America, can survive as oxygen levels decrease and now are found as far north as Alaska."

Read entire McClatchy article.

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