Saturday, December 10, 2011

A Cause for Concern: De-Oxygenation of the Oceans

It is a serious cause for concern, of should be, that a recent article published in Eos: Transactions of the American Geophysical Union (Vol. 92, No. 46, Nov. 15, p. 409), reports world-wide de-oxygenation of the world's oceans on a scale never observed before. This is serious since ultimately all ocean life depends on getting enough oxygen, and if it doesn't that implies massive die off and subsequent food chain collapse. This is likely to commence with the phyto-plankton which also produce a good proportion of the planet's oxygen.

The article itself perhaps understates (in typical subdued, scientific fashion) the effects:

"The potential consequences of ocean oxygen loss are profound: long term declines could lead to reduced biological productivity and diversity, altered animal behavior, declines in fisheries, redistributions of communities, and altered bio-geochemical cycles. Environmental feedbacks may also result in increased production of greenhouse gases such as nitrous oxide and methane".

Of course, the preceding description assumes an underlying gradualism, i.e. leading to the "long term effects", but there is no given here that this need be so. A precipitous, cataclysmic decline is also possible, especially if we are unsure what has led to the current ocean oxygen status. If there is a nonlinear driver behind the decline, we need to ascertain what it is and sooner rather than later.

As the article notes, we already know asymmetric oxygen declines are occurring on continental margins in many regions and these can be traced to "anthropogenic nutrient loadings". In other words, traced to chemical such as plastics which decay over long times, as well as other (agro-chemicals) that incept de-oxygenated states and periodic breakouts of the "red tide".

But as the attached image from the article shows, oxygen also appears to be declining in both the expansive North Pacific Ocean and the tropical oceans worldwide. Could temperature increases of the oceans have something to do with this? We already know, for example, that the increased acidity (30% over that from the onset of the Industrial Age) from CO2 absorption by the oceans and the formation of carbonic acid (e.g. H2O + CO2 -> H2 CO3)

The article itself is open on the issue of greenhouse gas effects to cause the de-oxygenation, only noting that:

"Continental configuration and climate are clearly critical, insofar as these factors influence ocean circulation and hence the sites and extent of ventilation of the ocean interior. Indeed, most of the ocean anoxia events occurred during times when both the atmospheric carbon dioxide and inferred temperature were high. However, long term events leading to mass extinctions are often associated with additional triggers, most commonly large tectonic processes..such as volcanism".

However, as I already showed:

in the paper, Volcanic Versus Anthropogenic Carbon Dioxide in the journal Eos( Vol. 92, No. 24, June 14, 2011, p. 201), the anthropogenic carbon dioxide CO2 multiplier (ACM) calculated from time series data on anthopogenic CO2 emission rates shows the projected anthropogenic CO2 emission rate of 35 gigatons per year is 135 times greater than the 0.26 gigatons per year emission rate for volcanoes, plumes etc.

In other words, barring major planetary tectonic upheavals in very short times scales, say all the major volcanoes erupting at once, our primary concern still needs to be the slow, steady input of CO2 into the atmosphere. Indeed, the just referenced Eos paper puts the basic nails into the coffin of the "volcanoes did it" excuse, at least as a source over time! It is also worth mentioning how the ACM data show an astounding rise in the CO2 multiplier from about 18 in 1900, to roughly 38 in 1950, which parallels the vastly enhanced use of automobiles as a primary mode of personal transport - with the planet now saddled with nearly 600 million vehicles.

The more recent paper's authors are correct, however, in noting that we need much better methods of measurement to more precisely allocate the source(s) and we need the long records of observations to have equal quality to short records. There exist two such high quality long records for observations in the North Pacific spanning 50 years or more. We need the same now for the regions near the continental margins sinc de-oxygenation is much more dramatic there and emerges over far shorter periods.

Special attention surely needs to be paid to "upwelling systems" occurring near continental shelves, since at these points ther is already low O2 content and we know a high input of nutrients exists. For example this applies to the Benguala upwelling region on the Atlantic side of southern Africa and the Peruvian upwelling region off the west coast of South America.

This is critical because the interplay of these forces, and particularly the high flux of man-made nutrients from nitrogneous fertilizers, etc. can cause vast masses of phytoplankton to sink and then enormous fish kills. Collapse of whole local fisheries and ecosystems is possible.

Perhaps needed more than anything (as in the case of the ACM multiplier data cited earlier) are better time series analyses. As the authors note:

"Time series of reliable oxygen contentrations are suprisingly sparse in the contemporary ocean, and hence patterns are difficult to discern with certainty."

But is is exactly the patters of de-oygenation we need to know, before time runs out.

Fortunately, the Ocean Observing Network (a multi-institutional project sponsored by the National Science Foundation) is hard at work to remedy the time-data deficiencies using sensors mounted on fixed moorings as well as gliders.

This may well yield worthwhile insights....assuming the Republican House doesn't cut it during one of their austerity orgies!

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