A Primer on Global Warming-Caused Marine Dead Zones

dead zone primer photo

Photo via BBC

Over the past couple years, biologists and fishermen have noticed an increase in marine dead zones off the West Coast—shellfish, starfish, rockfish, and other marine life have been washing up on shore in astonishing numbers. According to the Contra Coast Times, a dead zone discovered recently off the Oregon coast lead a California climatologist to examine coastlines there, with a specific culprit in mind: climate change.

And while dead zones have been covered in TreeHugger before, here's a primer on how dead zones come about, using the current case off the Oregon and California coast as a case study--and why the fact that tropical ones are set to increase by 50 percent worldwide is alarming news indeed.
Not-so Swell Upswells
It's been posited that global warming is causing harsher coastal winds, which in turn is responsible for and increased upswelling of ocean waters. A healthy upswelling leads to an abundance of marine life, but there's a delicate balance (as there so often is in nature). Too-strong upswelling may lead to boom-and-bust cycles that usurp all or most of the oxygen in the area, which creates the dead zones—any creatures that can't evacuate the zone essentially end up suffocating.

According to the Contra Costa Times:

In normal years, winds blowing from north to south drive upwelling in the spring and summer months off the Pacific Coast. These strengthened winds drive surface waters offshore, making room for deeper, nutrient-rich waters to surface, where sunlight triggers a heavy growth of phytoplankton, the bottom rung of the marine food chain.

But when the winds don't slacken and upwelling persists, excess phytoplankton blooms. When the uneaten plankton dies and sinks to the ocean floor, bacteria consuming it deplete the oxygen in the water.

Sea Life Imperiled by Global Warming
And while the theory remains in its initial stages of development, there's ample reason to pursue this line of thinking: California coastal winds have been increasing steadily over the last 30 years, and dead zones have been showing up with alarming frequency off the Oregon and Washington coasts. Fishermen have reported a surfeit of dead or sickly crabs and shellfish in their catch, and dead starfish and other marine life washed up on Oregon shores en masse in 2006, the worst year for dead zones yet recorded there.

More on Dead Zones:
Corn Ethanol Worsens Gulf of Mexico ' Dead Zone '
Could Large-Scale Oxygen Pumps Fix the Baltic Sea's Dead Zones

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