It's serious. Oceanic Dead Zones Continue to Spread (2008 Scientific American)
And "in the summer, northerly summer winds work together with the Earth's rotation to push oxygenated surface water offshore; this coastal water is replaced by low-oxygen but nutrient-rich waters from the depths of the continental shelf in a process known as upwelling. (See illustration.) Once this nutrient-rich water reaches the ocean's sunlit layers, it fertilizes blooms of phytoplankton. Resulting phytoplankton blooms feed the food chain and thereby help make the Pacific Northwest one of the nation's most productive fisheries. But the decomposition of unconsumed, sunken phytoplankton promotes the formation of deep pools of low-oxygen water.
Periods of upwelling-favorable northerly winds may be interrupted by relatively short periods of southerly winds during the summer and by longer periods during the fall. These southerly winds work together with the Earth's rotation to drive oxygenated surface waters back towards the shore and to drive low-oxygen bottom waters away from the shore in a process known as downwelling. Periods of strong downwelling have traditionally occurred frequently enough to flush the low-oxygen pools from the continental shelf, and thereby prevent them from expanding all the way to the shore.
But underwater surveys conducted by the research team of waters off the Pacific Northwest have identified the following new phenomenon:
Pools of low-oxygen water have expanded from the continental shelf to near-shore waters off Oregon and Washington every summer since 2002; the close proximity of these dead zones to the shore had never been reported before that year.
Coastal dead zones have been more hypoxic than the low-oxygen pools located on the continental shelf, with some coastal areas periodically completely stripped of their oxygen.
Areas of hypoxia that have seasonally dotted the Pacific Northwest coast, "have been connected to one another by a ribbon of low-oxygen water that runs along the coastal sea floor," says Barth. So far, the most hypoxic year for the Pacific Northwest was 2006, when the research team discovered a dead zone off Newport, Oregon that sprawled over almost 1,200 square miles, and pressed so close to the shore that "a baseball hit from Highway 101 during the summer could land in it," says Barth. Covering up to 80 percent of the water column and lasting for an unusually long time (four months), "this dead zone transformed a teeming habitat into a fish-free zone that was carpeted with dead crabs, worms, severely stressed anemones and sea stars, and what looked like potentially noxious bacterial mats," says Barth." Is Climate Change Suffocating Our Seas?