Dead Zones in the Ocean

Posted on February 17, 2008  Comments (2)

Oceanic Dead Zones Off West Coast are the ‘New Normal’

Ever since it was first noticed by crab fishermen who hauled up hundreds of dead and dying crabs in 2002, the “dead zone” that popped up in the waters along the northwestern coastal shelf just off the coast of Oregon has claimed unknown millions of lives. This oxygen-depleted region has transformed formerly rich seafloor communities teeming with life into vast graveyards filled with the bodies of crabs, echinoderms, molluscs, sea worms and other creatures.

a low-oxygen zone appears each spring off the coast of Louisiana due to fertilizers in farm runoff and sewage present in the Mississippi River. When the Mississippi flows into the sea, it creates a nutrient-rich area that triggers huge but short-lived algal blooms that soon die, sink to the seafloor and are decomposed by bacteria that produce toxic sulfide gases.

the dead zone off the West Coast of North America has another cause: global warming. Here’s how it works: Winds cause the oceanic rivers of nutrients, such as the California Current in this case, to flow upwards from the deep, carrying nutrients and phyoplankton into the sunlight, which triggers the phytoplankton to reproduce, to “bloom”. This is the normal state of things, but since global warming has been causing land temperatures to increase, these winds have become stronger and more persistent. This is not normal because it prolongs the oceanic upwelling, producing a surplus of phytoplankton that isn’t consumed and subsequently dies, and sinks to the seafloor to decay. As the bacterial-mediated breakdown occurs, dissolved oxygen in the surrounding water is depleted to dangerously low levels

Related: Dead zones off Oregon and Washington likely tied to global warmingVast Garbage Float in the Pacific OceanAffect of Ocean Warming on Phytoplanktonthe Crisis at SeaFishy FutureSelFISHing

2 Responses to “Dead Zones in the Ocean”

  1. Randolph Femmer
    September 2nd, 2008 @ 2:53 pm

    A recent article in the journal science (Diaz, 15 August 2008) addresses approximately 400 known dead zones in the sea. Many of these result from pollution of near-shore regions with nutrient run-offs from fertilizers and animal wastes, etc. These nutrients stimulate growth of phytoplankton at the sea’s surface and as portions of this biomass sink to the sea floor, they stimulate populations of heterotrophic microbes which can quickly consume the deep-sea’s limited supplies of dissolved oxygen. The resulting anoxia produces a dead zone. (These same anoxic conditions and events have also long been produced in over-fertilized eutrophic ponds and lakes.)

    Given the above facts, it should be disturbing that an assortment of recent “geoengineering” scenarios contemplate deliberate, large-scale fertilization of the ocean under the premise that dying phytoplankton sinking to the depths of the sea might be used to transport atmospheric CO2 to the deep sea. These proposals erroneously envision the deep-sea as some sort of “carbon sink” where humanity’s CO2 excesses can be profitably locked away. Unfortunately, such scenarios show no cognition of the anoxia, and resulting dead zones (and likely extinctions) that they invite.

    One set of such proposals, for example, contemplate “fertilizing” the world’s oceans (with a dusting of iron, for example) to enhance the production of phytoplankton. The economic premise is that the phytoplankton would help combat or offset global warming by removing CO2 from the atmosphere – and private companies (such as Planktos, for example, and Climos) could then sell “carbon credits” to polluters for a profit by simply sailing out to sea and dusting the oceans with untold tons of powdered iron.

    A second fertilization scenario envisions vertical plastic pipes that would pump nutrient-rich waters from the ocean depths to the surface where, again, fertilized phytoplankton would prosper and eventually export tons of organic biomass to the floor of the sea. (Somewhat like the mentality of the dinosauria, right? Out of sight, out of mind…)

    While assorted policymakers, offset brokers, and industries are attracted to such adventures, the passage below suggests that the results of any such large-scale projects could trigger a deep-sea extinction event of unimaginable proportions.

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    January 5th, 2010 @ 10:19 pm

    […] Dead Zones in the Ocean – Vast Garbage Float in the Pacific Ocean – Sharpshinned Hawk – Biodegradable […]

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