Yesterday I spent most of my day researching and writing a paper about hypoxia, a topic of oceanography that isn't terribly well understood. Here's a brief synopsis of the situation:
Hypoxia occurs when the level of dissolved oxygen in ocean water drops low enough to be harmful to life in the area. These low oxygen areas are not permanent features on the coast - they occur during the summer upwelling season. At that time, large amounts of nutrients are brought to the ocean surface, allowing phytoplankton to bloom. Eventually that growing phytoplankton will die, and their cells will be decomposed by microbes. That decomposition process is what draws down oxygen levels. Too much phytoplankton = no oxygen.
Hypoxia was never observed off of the Oregon coast until the summer of 2002, and has been getting steadily worse over the last few years. In August 2006, hypoxia progressed to full anoxia, meaning that the water was completely devoid of oxygen. This anoxic area caused a huge die-off in macrofauna - the big stuff we can see, primarily crabs in this case. Researchers took video along a transect line off of Cape Perpetua during the summers of 2001 and 2006. The difference is quite dramatic.
Researchers are still trying to understand what is causing Oregon's hypoxia, as it's a very new feature of out ocean. It appears that it is linked to global climate change through changing wind patterns. Our summer winds are what control upwelling, and changing them will change the overall dynamic of the near-shore ecosystem.
If you're interested in learning more, the PISCO website on hypoxia is a great place to start.
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