Depths of Depression – Dead Zones

By The Marine Detective on October 1, 2010

Added January 2022:
The Economist: January 6, 2022 Dead zones: how chemical pollution is suffocating the sea

Update December 2019 – See the International Union for Conservation of Nature’s  (IUCN) report “Ocean deoxygenation: everyone’s problem“. If the Ocean is warmer – there is less oxygen dissolved in it. If there is more runoff (sewage, fertilizers, fossil fuels), there are more algae using up the oxygen (eutrophication). Warmer surface layers mean less circulation of nutrients as well and less oxygen exchange with the atmosphere.

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Original post from October 2010:

Dear Readers,

There is currently an area of ocean in Hood Canal, Washington with very little oxygen (“hypoxic” = very low levels of oxygen; “anoxic” = no oxygen).  Too little oxygen means that marine life cannot breathe.

These ocean “dead zones” appear to becoming more common in the Pacific Northwest.  As I type there are fish and other marine life that have suffocated in Hood Canal.

The lack of oxygen in the ocean water is the result of increased winds and/or too much nitrogen.

The specific event now in Hood Canal is most likely caused by the accumulation of nutrients like nitrogen (from agricultural run-off and human sewage) “fertilizing” phytoplankton (plant-like plankton / algae).  The phytoplankton thrive, increase in number, causing a “bloom” and using up the oxygen. This is called eutrophication. In this case, wind could alleviate the situation as it would cause mixing and oxygenation of the water.

However, increased winds due to climate change can also cause “dead zones”. If the winds bring oxygen-poor and nutrient rich water from the ocean’s depths to the surface, this fertilizes phytoplankton at the surface, creating a bloom. The phytoplankton use up what little oxygen there is and when they die and decay at the ocean bottom, more oxygen is used up. The dynamic is very well illustrated in the Oregon State University image above.

The situation in Hood Canal was painfully captured in images by diver Janna Nichols at Sund Rock (Southern Hood Canal) on September 27th, 2010.

From Janna: “While some of this may appear normal to non-Pacific NW divers, it is most certainly NOT normal. Fish are out of their usual depth ranges (usually found deeper) and all clustered within 15 feet of the surface of the water. They are up so high in the water column because this is the only area that contains oxygen. There are also freakishly huge schools – we don’t usually see that many at once. Fish that normally hide were found out in the open, lethargic and “panting”.

Caption: “The top three feet under the surface are occupied by hundreds of small silvery Shiner Perch. Under them are hundreds of schooling Black and Copper Rockfish – densely packed and hardly moving. (to conserve energy). It is very unusual to see SO MANY of these fish together. All of this is in 9 feet of water or less. (The top number you see on my dive computer is the depth).”

She watched a Giant Pacific Octopus die; finds 4 Wolf-Eels and multiple Decorator Warbonnets out in the open, panting (these are cryptic species that are usually not out in the open and do not “breathe” like this); and she films dense schools of fish attempting to conserve energy to lower their oxygen demands. [I think these images may be all the more painful for fellow divers as you will fully know how aberrant these behaviours are.]

How to solve the problem? Don’t become despondent. Take this for what it is, an additional symptom of the same disease and therefore the solutions are the same – less fossil fuel use, less disposables, less consumerism.
Care more. Consume less. 

• See Janna Nichols video and photos. Janna provides annotations that explain what she witnessed.
• See the excellent video and text explaining the formation of dead zones off the coast of Oregon and Washington.

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