You're conflating two things Andrew, the limitation on growth and the consequences (usually on heterotrophs) of its decomposition / remineralization. Free oxygen is never limiting on photosynthesis, since it is not consumed in the process, but rather produced.
Anoxia or hypoxia as a result of phytoplankton growth are issues primarily in coastal enviornments when excess or continuous algal production in shallow environments leads to the depletion of oxygen in proximity to marine populations as that biomass decomposes. The question in the open ocean, where any kind of climate mitigation via phytoplankton would be done-- i.e. in 4-6km of water column vs. 100m-- is... what has happened in past climates when we know primary productivity was much higher over long time periods, and what might happen in today's ocean if productivity were increased by various degrees... obviously there is more water column for remineralization to be distributed through and advective currents will distribute the effects over a larger area. This is both a potential benefit as well as a potential concern. Cao and Caldeira have looked at the effects of acidification at depth (and also at the surface) based on taking phosphate to zero in the southern ocean. More models and observations need to be made for a variety of effects, including oxygen, N2O and methane, downstream nutrient depletion, DMS cooling in addition to CO2 reduction (and to Oliver's point, what kind of deployment would be appropriate for what kind of intended scenario)-- and looking at other kinds of limiting factors like silicate-- to get a better understanding of the processes there. Observational programs should both be driven by and feed modeling throughout. D On Mon, Dec 28, 2009 at 11:06 AM, Andrew Lockley <[email protected]>wrote: > The more you remove the micro and macro nutrient limitations from > phytoplankton growth, the more you make it likely that oxygen becomes the > limiting factor - ie. that all the available oxygen has been used up. This > is likely to lead to the creation or extension of 'dead zones' or anoxic > regions in the ocean, together with consequential disruption to the > ecosystem, and potential methane creation. > > It's this kind of effect which, I understand, worries ETC group and others. > (See Chan et al, 2008) > > I'm far from a marine biologist myself, and I'm raising the issue simply to > encourage caution, rather than to claim expertise. > > A > > 2009/12/28 Dan Whaley <[email protected]> > > Steve, >> >> In talking to Dave Karl a few years ago who was testing Phil Kithil's >> tube, it seemed like a core problem was trying to select for a depth where >> you had more nutrients (P, N) than CO2, so there was a net gain... since >> carbon is also greater at depth. Also-- Phil seemed to think he would keep >> the tubes equidistant from each other with a huge network of underwater >> cables... which seemed logistically (as well as aesthetically) problematic. >> >> Curious as to your thoughts in these areas... >> >> D >> >> >> On Mon, Dec 28, 2009 at 10:17 AM, Stephen Salter <[email protected]>wrote: >> >>> Hi All >>> >>> The oceans are a big thermal store so the scheme would give us time for >>> a quiet think. However we can bring nutrients up to the photic layers >>> and grow more phytoplankton giving more dimethyl sulphide for cloud >>> nuclei and converting lots of CO2 to non acidic biomass, some of which >>> we can eat. >>> >>> There is a paper called /Hurricanes carbon and fish and a picture called >>> /MacNeill downtube in the /Hurricanes folder at the site below my >>> signature. /Chlorophyll comparison shows how empty most of the oceans >>> are for most of the time. Click through at about one a second for a >>> month-by-month animation. We need lots of permanent, private la Nina >>> events. >>> >>> Stephen >>> >>> >>> Emeritus Professor of Engineering Design >>> School of Engineering and Electronics >>> University of Edinburgh >>> Mayfield Road >>> Edinburgh EH9 3JL >>> Scotland >>> tel +44 131 650 5704 >>> fax +44 131 650 5702 >>> Mobile 07795 203 195 >>> [email protected] >>> http://www.see.ed.ac.uk/~shs <http://www.see.ed.ac.uk/%7Eshs> >>> >>> >>> >>> Mike MacCracken wrote: >>> > Just a note that while pumping heat down into the ocean can lead to >>> > local cooling, storing heat in the ocean is adding and retaining >>> > energy, so will eventually emerge as warming. And, of course, it will >>> > contribute to sea level rise. Thus, while a local effort of this type >>> > to help limit hurricane intensification may be a good trade, it is not >>> > likely to be a global cure for the system (unless one can really pull >>> > the GHG concentrations down in other ways so heat from the ocean would >>> > moderate the rate of cooling—as it does now during winter). >>> > >>> > Mike MacCracken >>> > >>> > >>> > On 12/28/09 1:34 AM, "[email protected]" <[email protected]> wrote: >>> > >>> > Hello, I'm new here and I expect to make a few blunders until I am >>> > better acquainted with previous discussions. I am a retired >>> > physicist and have some leadership role in the Sierra Club. >>> > >>> > The Salter Sink is an excellent concept for raising cold water to >>> > the surface. the area that needs design attention is the injection >>> > system at the bottom of the tube. With careful design, it will >>> > raise probably ten times as much cold water as is pumped down. >>> > This design work is quite easy. >>> > >>> > Next, I had never considered the advantage of the wave-driven pump >>> > as a way to cool the ocean, rather as a way to raise nutrients to >>> > the surface to increase biological production. Most of the ocean >>> > surface world-wide is limited in production by inadequate nitrate >>> > and phosphate rather than iron. Some good places for hurricane >>> > control are also good for placement of "ocean farms" fed by wave >>> > pumps. For example, the North Atlantic Gyre region, also known as >>> > the Sargasso Sea. >>> > >>> > I believe if somebody will check the economic potential of >>> > pump-fed sea farms in some areas such as the horse latitudes, it >>> > will be found that the Salter pumps will pay for themselves and >>> > return a handsome profit. >>> > >>> > My thought-- it isn't necessary to remove the pump structures >>> > before they encounter storms--if they are lowered below the >>> > surface by about 100 meters, then they are completely sheltered >>> > from the storm above. >>> > >>> > I can imagine a Salter pump connected to a lattice structure that >>> > spreads over an area of sea around the pump. Kelp or other >>> > suitable plants are anchored to the lattice. The "farm" provides a >>> > sea pasture in which farm animals are grown and harvested for >>> market. >>> > >>> > Ernie Rogers >>> > Pleasant Grove, Utah >>> > Phone 801-368-4902 >>> > >>> > In a message dated 12/27/2009 6:02:04 P.M. Mountain Standard Time, >>> > [email protected] writes: >>> > >>> > John and list: >>> > >>> > I agree that this was an important interview for advancing >>> > geoengineering (Fareed Zakaria is one of my favorite >>> > writers/analysts/interviewers). My main objection was that >>> > Fareed or >>> > his show producers seemed to not be aware of the limitations >>> > of SRM. By >>> > this I mean that the fundamental causation agent - excess CO2 >>> > - was >>> > ignored, not mentioned once. Greg Lau's message to the list >>> just >>> > earlier on the need to protect against ocean acidification was >>> > never >>> > hinted at. (More tomorrow on that.) >>> > >>> > The end of the twenty minutes was on Myrhvold's firms focus on >>> > investing in inventions - which he says only his new firm is >>> > doing >>> > (emphasizing this is not the same as venture capital - which >>> > he also >>> > claimed has revolutionized modern American (world?) business). >>> > >>> > I wish I knew whether Myrhvold himself was working on CO2 >>> > removal as >>> > well as his SO2 approach. The site also has quite a bit on the >>> > Salton >>> > Sink concept (see >>> > >>> http://www.intvenlab.com/wp-content/uploads/2009/10/Salter-Sink-white-paper-300dpi1.pdf >>> ). >>> > >>> > Also see http://intellectualventureslab.com/?p=338 for added >>> > material on >>> > geoengineering. >>> > >>> > Ron >>> > >>> > >>> > John Nissen wrote: >>> > > Hi all >>> > > >>> > > Have you seen this? Best case for SRM in Arctic I've seen! >>> > > >>> > > Inventor Nathan Myhrvold describes "space hose" for getting >>> > aerosols >>> > > into stratosphere - and he's done the modelling to show it >>> > could be used >>> > > at the Arctic, to cool whole hemisphere, without disrupting >>> > weather (see >>> > > about 9 minutes in). "Cooling the Arctic shuts of a whole lot >>> of >>> > > tipping points." It shows incredible promise, but governments >>> > aren't >>> > > running to him - so far. >>> > > >>> > > >>> http://www.cnn.com/video/#/video/podcasts/fareedzakaria/site/2009/12/20/gps.podcast.12.20.cnn >>> > >>> > > >>> > > >>> > > "Suppressing the only technology that could get us out of >>> this >>> > > pickle..." would be plain silly. >>> > > >>> > > He argues (as nobody I've seen to argue before), that even >>> > emissions >>> > > reduction to zero overnight, would not solve the problem of >>> > global >>> > > warming, because about 20% CO2 stays in atmosphere for >>> > thousands of years. >>> > > >>> > > "Geoengineering has to be part of the debate". "We have to >>> > examine the >>> > > options". "You can't rule these things out." >>> > > >>> > > Cheers, >>> > > >>> > > John >>> > > >>> > > >>> > > -- >>> > > >>> > > You received this message because you are subscribed to the >>> > Google Groups "geoengineering" group. >>> > > To post to this group, send email to >>> > [email protected]. >>> > > To unsubscribe from this group, send email to >>> > >>> > [email protected]<geoengineering%[email protected]> >>> . >>> > > For more options, visit this group at >>> > http://groups.google.com/group/geoengineering?hl=en. >>> > > >>> > > >>> > > >>> ------------------------------------------------------------------------ >>> > > >>> > > >>> > > No virus found in this incoming message. >>> > > Checked by AVG - www.avg.com >>> > > Version: 9.0.722 / Virus Database: 270.14.121/2589 - Release >>> > Date: 12/27/09 02:18:00 >>> > > >>> > > >>> > >>> > -- >>> > >>> > You received this message because you are subscribed to the >>> > Google Groups "geoengineering" group. >>> > To post to this group, send email to >>> > [email protected]. >>> > To unsubscribe from this group, send email to >>> > >>> > [email protected]<geoengineering%[email protected]> >>> . >>> > For more options, visit this group at >>> > http://groups.google.com/group/geoengineering?hl=en. >>> > >>> > >>> > >>> > -- >>> > You received this message because you are subscribed to the Google >>> > Groups "geoengineering" group. >>> > To post to this group, send email to >>> [email protected]. >>> > To unsubscribe from this group, send email to >>> > >>> > [email protected]<geoengineering%[email protected]> >>> . >>> > For more options, visit this group at >>> > http://groups.google.com/group/geoengineering?hl=en. >>> > >>> > -- >>> > >>> > You received this message because you are subscribed to the Google >>> > Groups "geoengineering" group. >>> > To post to this group, send email to [email protected]. >>> > To unsubscribe from this group, send email to >>> > [email protected]<geoengineering%[email protected]> >>> . >>> > For more options, visit this group at >>> > http://groups.google.com/group/geoengineering?hl=en. >>> >>> -- >>> The University of Edinburgh is a charitable body, registered in >>> Scotland, with registration number SC005336. >>> >>> -- >>> >>> You received this message because you are subscribed to the Google Groups >>> "geoengineering" group. >>> To post to this group, send email to [email protected]. >>> To unsubscribe from this group, send email to >>> [email protected]<geoengineering%[email protected]> >>> . >>> For more options, visit this group at >>> http://groups.google.com/group/geoengineering?hl=en. >>> >>> >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "geoengineering" group. >> To post to this group, send email to [email protected]. >> To unsubscribe from this group, send email to >> [email protected]<geoengineering%[email protected]> >> . >> For more options, visit this group at >> http://groups.google.com/group/geoengineering?hl=en. >> > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]<geoengineering%[email protected]> > . > For more options, visit this group at > http://groups.google.com/group/geoengineering?hl=en. > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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