Saturday, March 3, 2012

Large areas of open ocean starved of oxygen

“The water is getting warmer, and warm water holds substantially less oxygen than cold water . . . Off southern California over the past 22 years we’ve lost about 30% of the oxygen at depths of around 200 to 300 metres,” said Professor Lisa Levin of the Scripps Institution of Oceanography in La Jolla, California.

Deep-water temperature gauges off Spitsbergen in the Arctic and in the Southern Ocean near the Antarctic have recorded temperature increases of between 0.03°C and 0.5°C, and as much as 1°C, which is highly significant for a stable environment that does not change at all from one century to the next, she said.

“Those are significant numbers. The warming is more intense at the sea surface but it reaching the deep water,” Professor Levin said.

Above from: Report by Steve Conner in the Independent, February 21, 2012.

Why oxygen depletion is a problem

The above report is particularly relevant in regard to methane hydrates, as illustrated by the text below, which is partly from: Oxygenating the Arctic, by Sam Carana.

When methane is released from hydrates in underwater sediments, much of it can still be oxidized in the water. This would not be the case for large releases of methane, which would cause oxygen depletion, resulting in much of the methane entering the atmosphere. Furthermore, global warming makes the situation worse, as warmer water holds substantially less oxygen.

A two-part study by Berkeley Lab and Los Alamos National Laboratory shows that, as global temperature increases and oceans warm, methane releases from clathrates would over time cause depletion of oxygen, nutrients, and trace metals needed by methane-eating microbes, resulting in ever more methane escaping into the air unchanged, to further accelerate climate change.

In many ways, global warming sets the scene for catastrophic releases of methane in the Arctic. To avoid such scenarios, or even more worrying scenarios in the Arctic, it may be helpful to artificially add oxygen to the water. This has been done before, e.g. in lakes in Finland.

Oxygenating the Arctic

On the one hand, oxygenating Arctic waters seems beneficial, as this could enhance oxidation of methane in the water. Also, oxygen bubbles could form an insulating layer in between an ice-cap and warming water underneath the cap. Thirdly, bubbles could brighten the water, changing albedo and reflect more sunlight back into space. Where oxygen enters the atmosphere, this may help with the formation of hydroxyl and subsequent oxidation of atmospheric methane.

On the other hand, though, some processes could be counter-productive. As an example, bubbles could disturb a hydrate and accelerate release of methane. Rising bubbles could take more methane along upwards than they help oxidize. Experience in Finland shows that adding oxygen could also increase concentrations of nitrous oxide, a greenhouse gas with tremendous global warming potential. Also, producing oxygen locally through electrolysis could result in the release of hydrogen that could bind with oxygen or result in hydroxyl and stratospheric ozone depletion.

From: Nutrient reductions through engineering approaches, 2009
Tests are therefore recommended, in order to research what kind of impacts and side-effects can be expected. Proposals have been around for years to ventilate bottom waters by stimulating mixing with waters from mid- or upper-levels, as depicted in the above image from a study by Daniel Conley, or by adding air to the waters locally.

Transporting oxygen to the Arctic

Offshore Wind Turbines on Floating Bases
Wind turbines on
floating bases
Producing large amounts of oxygen from water locally may result in large amounts of surplus hydrogen, for which there is may not be enough local demand to make this process economic. This wouldn't be such a problem when producing the oxygen at lower latitudes. Wind turbines on bases, floating offshore the coast of, say, California, New York or the U.K., could supply electricity for use on land during the day, while at night powering electrolysis of seawater (possibly preceded by distillation), to produce oxygen and hydrogen.

The hydrogen could then be used to power transportation, in particular shipping, since the oxygen would be transported by ship, either liquefied or as compressed gas, to the Arctic. On arrival, a hose could be lowered from the ship into the water to release oxygen, or - in another application - a balloon could be launched, raising a hose to the desired height, and oxygen could be pumped up the hose for release into the atmosphere, in efforts to oxidize methane in the atmosphere.

Space Hose
Space Hose
If wanted, the same hose could also be used to release aerosols into the atmosphere, in further efforts to keep the Arctic from overheating. Finally, such hoses could carry devices to monitor composition of water and atmosphere, temperatures, currents and winds at various altitudes, etc.

Funding for the project could be provided in part by the electricity sold by the offshore turbines. To further fund the project, fees could be imposed on international shipping and aviation, e.g. on departures from U.S. seaports or airports, or on bunker fuel and jet fuel taken on board such ships or airplanes. The revenues of these fees could be used partly to fund the Arctic oxygenation project, and partly to fund rebates on hydrogen that is produced at the floating bases and sold to ships anchoring there. Such feebates could also satisfy calls by the European Union for airlines to join in with action on climate change.

Alternatively, such feebates could be imposed on international shipping only. Other types of feebates could then be imposed on international aviation, e.g. to fund air capture of carbon dioxide and the production of biofuel either in algae bags or as a result of pyrolysis of organic waste. More generally, feebates are the most effective way to facilitate the shift towards a sustainable economy.

Another approach: diatoms

Another approach is suggested by who propose to add iron and other trace metals/micro nutrients to the water in order to stimulate growth of a specific type of phytoplankton called diatom algae, which through photosynthesis absorb carbon dioxide in the water and add oxygen. The oxygen is then used by methanotroph bacteria to oxidize methane. 

The image below pictures a range of Arctic geoengineering methods that could be used as part of a comprehensive plan of action to deal with climate change. 

(click on image to enlarge)


  1. >...methane releases from clathrates
    would over time cause depletion of oxygen, nutrients, and trace metals ...

    Oxygen loss in oceans is a symptom and not a cause. So using mechanical means to add oxygen would only treat the symptom and not the root cause.

    trace metals depletion or nutrient : trace metal imbalance is the problem.

    The right balance results in a healthy environment.

    Human action has resulted in increase in nutrient (Nitrogen and Phosphorus0 input into water, due to increase in agriculture production.

    However the trace metal input has not increased or has actually declined.

    Damming of rivers reduces water and silt flow down rivers. Silt contains trace metals and silica.

    Therefore adding trace metals is a better solution than adding oxygen.

    Iron and other trace metals / micro nutrients cause a healthy bloom of Diatom in oceans. These give huge amounts of oxygen.

    About 40 to 50% of the oxygen produced in oceans is due to diatoms, there are reports of decline in diatoms in the oceans. Restoring them is the right solution.

  2. I understand that methane is venting offshore on both coasts of North America. It is said that this methane will not reach the atmosphere. But what exactly happens to sea water when methane is continuously dissolved in it?