More on those pumps (hoisted from comments)
An interesting contribution from the comments thread on Lovelock and Rapley propose cure for global warming by Peter Williams which I thought I'd hoist up here for wider circulation. -- Oliver
Lovelock and Rapley (Nature, 449,403, 2007) put forward the idea that by pumping up nutrient rich deep oceanic water, the subsequent stimulation of planktonic photosynthetic production would give rise to a very significant drawdown atmospheric CO2. The concept is flawed scientifically on two accounts. Planktonic photosynthesis results in the assimilation of inorganic nitrogen and CO2 in a ratio which has a modal value in the region of 6.6 – the so-called Redfield ratio. A fraction of the organic particles that arise as a consequence of photosynthetic production, sink into the deeper parts of the ocean. The C/N ratio of these particles is somewhat higher than the Redfield ratio, as there is some fast decomposition of the nitrogen (and phosphorus) rich organic components before the particles reach deep water. The particles are eventually decomposed in the deeps, with the production in inorganic nutrients, along with CO2. If this water, now enriched in inorganic nitrogen (and phosphorus), were brought to the surface, it would indeed stimulate planktonic photosynthesis and result in the assimilation of CO2. However, the upwelled water is not only enriched in inorganic nitrogen but also CO2 produced at the same time, the latter being slightly in excess of the Redfield requirement due to the elevated C/N ratio of the settling particles. Thus, rather than drawing down atmospheric CO2 from the atmosphere, there would be export of CO2. The situation in fact would be worse, as the upwelled water would need to warm up (otherwise it would simply sink back again) this would reduce the solubility of CO2, resulting in further export of oceanic CO2 into the atmosphere.Further, from the engineering point of view the concept is infeasible – to lift up a 10m diameter column of dense (cold) to the surface would require a net lift of a number of tonnes and would almost certainly collapse a flexible tube or would cause a ribbed tube to concertina.
Even if the engineering problems could be solved, and the system made cost effective, both of which seem very doubtful, the proposal would have the reverse effect of that claimed.
Comments
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Posted by: Holly Hoar | October 11, 2007 10:28 AM
In coastal regions, mills could fit better than pipes.
There is a recent debate about the possibility of pumping waters from deep waters to the surface of the Ocean to face up the anthropogenic increase of atmospheric CO2. It was in some courses in the 90's when I learned from Dr. Margalef that one way to fertilize the relative low nutrient Mediterranean Sea could be by pumping deep waters to the surface. I was astonished when I saw the proposal of Lovelock and Rapley (Nature 449: 403) because it involves the same idea. During last summer, with the Margalef proposal in mind, I was thinking if there was not possible to build aerogenerators with an Arquimedes' screw inside to pump rich waters into the surface of coastal areas. If it is true that the addition of external nutrients to the system could change the succession and composition of planktonic species; thus, giving pass to uncertainties in the benefits of the drawn of CO2 by the changes produced in the ecosystem (see Shepherd et al., Nature 449: 781). It is also true that the pumping of internal nutrients to the system is a motor of primary production, as it happens every year in upwelling systems. At the same time, if the nutrients are pumped just after the phytoplankton bloom, they could maintain a longer lasting bloom followed by a "natural" phytoplankton succession with higher production rates linked to the higher nutrient concentrations.
The principal problem of the original idea of Lovelock and Rapley, as suggested by Peter Williams and posted by Oliver Morton (http://blogs.nature.com/climatefeedback/2007/10/more_on_those_pumps_hoisted_fr.html#c89878), is that the incoming of deep waters to the surface may lead to both a out-gassing due to warming and a net production of CO2 linked to the relatively high C:N of the incoming particulate organic matter. This is what happens every year in some upwelling regions (i.e. eastern Pacific), where there is an important pumping of CO2 to the atmosphere but, at the same time, an important fraction of this CO2 is harvested by diatoms that sediment to the bottom. In coastal regions the drawdown of CO2 could be higher than in deep sea because, on the one hand, phytoplankton reaches the sediment more quickly and, on the other hand, shelled filter feeders can use CO2 to produce CO3Ca. Besides, if the difference of temperature between the surface and the nutricline is not very high, the net balance between the losses (i.e. sedimentation) and out-gassing could be negative or zero.
Since my point of view, there are several advantages of mills over pipes: they do not have problems of collapse, the depth of withdraw and spill could be adjusted, and they can be switched off if there is an unexpected effect of mixing into the system. Moreover, as for the pipes described by Lovelock and Rapley, mills don't need an additional source of energy because they are propelled by wind.
I think that try to do some fertilization experiments in a small scale could not be worst than all the iron fertilization cruises performed during the last decades, and can bring also a valuable amount of knowledge about how marine ecosystems function.
Yours sincerely,
Evaristo Vázquez-Domínguez
Institut de Ciències del Mar. (CSIC)
Passeig Marítim de la Barceloneta, 37-49.
E-08003 Barcelona (Spain)
Posted by: Evaristo Vazquez-Domiguez | November 6, 2007 11:03 AM
I'm sorry, I commited an error in my previous apreciation. Calcification may lead to CO2 production not consumption. However, there are some studies showing that the rapid sedimentation of calcifyers in coastal waters could produce harvesting of organic and inorganic carbon instead of CO2 production.
Yours sincerely,
Evaristo Vázquez-Domínguez
Posted by: Evaristo Vazquez-Dominguez | November 22, 2007 07:56 PM
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Posted by: 水泵 | April 1, 2008 06:25 AM