WASHINGTON – Lower levels of oxygen in oceans, particularly off the Northwest coast, could be another sign of fundamental changes linked to global climate change, scientists say.

They warn that the oceans’ complex undersea ecosystems and fragile food chains could be disrupted.

In some spots off Washington and Oregon, the almost complete absence of oxygen has left piles of Dungeness crab carcasses littering the ocean floor, killed off 25-year-old sea stars, crippled colonies of sea anemones and produced mats of potentially noxious bacteria that thrive in such conditions.

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 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.

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