Thanks, David, for the info. Certainly agree that limestone dissolution only works in undersaturated, sub-surface waters, which Harvey goes to some lengths to locate and model for carbonate dissolution. As for P, I doubt carbonate rain would have much of a effect on surface ocean P since there is precious little there anyway. What happens at depth could be a different story. Easy enough to test: take some seawater with measurable P, mix in calcite powder, and see what happens to dissolved P. As for P inhibition of calcite dissolution, sample or make calcite undersaturated seawater, add or remove P, add calcite, measure differences in resulting alkalinity or DIC in the preceding treatments. Even better, let's just rain calcite powder into a likely spot in the ocean and measure vertical profiles of P, DIC, alkalinity, etc and compare to Berner et al models (and Harvey's!). A paleo example: following the PETM event carbonate rain rate went from zero to huge numbers while there was not much change in organic C accumulation, so something in surface waters was getting enough P to make the OC despite high carbonate rain, if that is your concern. Another idea: certainly inhibition of carbonate precipitation in the ocean is a major player in setting ocean water column and atmospheric C levels. To what extent have these inhibitors (P, Mg, organics, etc) varied in the past, (how) have they affected C levels, and might we want to investigate purposely modulating these inhibitors to manage ocean/air C in the future? -Greg ________________________________________ From: geoengineering@googlegroups.com [geoengineering@googlegroups.com] On Behalf Of David Zhong [shaojun.zh...@gmail.com] Sent: Wednesday, September 28, 2011 11:23 AM To: geoengineering Subject: [geo] Re: Monbiot Claims SAI "already tested ... with catastrophic results"
Greg, Phosphate ions are known to have a strong affinity for the reactive sites of calcite and inhibit the dissolution (BERNER & MORSE, 1974; MORSE & BERNER, 1979) as well as precipitation (MUCCI, 1986) reactions of calcite in seawater. It is conceivable that the settling fine limestone (calcite) particles would scavenge the dissolved phosphate ions in the upwelling seawater. Furthermore, let’s not forget that calcite dissolution can only happen in seawater that is undersaturated with respect to calcite; and most surface seawaters are in fact supersaturated with respect to calcite. Adding limestone to a CaCO3-undersaturated upwelling seawater body may reduce its degree of undersaturation, it could not make it supersaturated with respect to calcite. Mixing with the CaCO3- supersaturated surface seawater and/or CO2 degassing and/or primary productivity (plus temperature and pressure change) will make it supersaturated with respect to calcite (and aragonite). In view of the slow calcite dissolution reaction rate in seawater (there are lots of studies and data on this), I doubt the effectiveness of this scheme. BERNER R. A. and MORSE J. W. (1974) Dissolution kinetics of calcium carbonate in seawater. IV. Theory of calcite dissolution. Amer. J. Sci. 274. 108-134. MORSE J. W. and BERNER R. A. (1979) The chemistry of calcium carbonate in the deep oceans. In Chemical Modeling-Speciation, Sorption. Solubility and Kinetics in Aqueous Systems (ed. E. JENNE), pp. 499-535. ACS Symposium Series 93. American Chemical Society, Washington, D.C. MUCCI A. (1986) Growth kinetics and composition of magnesian calcite overgrowths precipitated from seawater: Quantitative influence of orthophosphate ions. Gmchimica et Cosmochimica Acta Vol. 50, pp. 2255-2265. Cheers, David. On Sep 27, 1:00 pm, "Rau, Greg" <r...@llnl.gov> wrote: > Thanks David. I defer to Harvey's paper as to the particle size and rain rate > needed to effect limestone dissolution at depth. Slow kinetics can always be > countered by increased particle surface area (at a cost). I wasn't aware of > the P story - reprints? On the other hand elevating pH might reduce trace > metal solubility - good or bad for phytos? E.g., Cu vs Fe? The added > alkalinity might save coccoliths, pteropods, etc from an acidic grave. Let's > find out with a mesoscale live ocean test. In contrast to iron exps, perhaps > Greenpeace will supply the ship and cheering section this time. No? > Regards, > Greg > ________________________________________ > From: geoengineering@googlegroups.com [geoengineering@googlegroups.com] On > Behalf Of David Zhong [shaojun.zh...@gmail.com] > Sent: Tuesday, September 27, 2011 11:43 AM > To: geoengineering > Subject: [geo] Re: Monbiot Claims SAI "already tested ... with catastrophic > results" > > Hi Greg, > > Two comments here: > > Limestone dissolution can be a very slow reaction, even in CaCO3- > undersaturated > upwelling seawaters. (Much slower than the rate of limestone > dissolution in normal > rainwater, for example) > > Adding limestone powders to the upwelling seawaters may in fact take > away > a significant portion of phosphorus through adsorption, therefore > reduce the > availability of a critical nutrient for surface ocean primary > production. > > David. > > On Sep 26, 10:49 am, "Rau, Greg" <r...@llnl.gov> wrote: > > > > > > > > > > > There is a delay if air capture is the objective - limestone dissolution > > takes place in the subsurface waters and alkalinity is generated, which can > > effect air capture only when upwelling finally brings it in contact with > > air. Gas diffusion rate and CO2 dissolution rate will then also affect the > > air capture rate. Alternatively, I'm suggesting let's use limestone, > > silicates, or some other cheap base to mop up some of the excess CO2 > > naturally present in surface/subsurface upwelling water before it degasses, > > thus reducing ocean CO2 emission to the atmosphere. This at least avoids > > the air-->ocean CO2 uptake rate limitations. It would seem easier/faster to > > chemically mop up excess CO2 in solution prior to degassing (ocean CO2 > > emissions reduction) than to chemically enhance CO2 transfer from gas to > > liquid (air capture). A detailed comparison of the two concepts re air CO2 > > stabilization under realistic ocean physics and starting chemistry would be > > an interesting paper. For starters, assuming an air pCO2 of 390 uatms and > > upwelling ocean pCO2 of 450 uatms, one would need to chemically drive ocean > > pCO2 to below 390 before net air capture is effected. In contrast one has to > > only chemically reduce ocean pCO2 to below 450 to reduce some ocean CO2 > > emissions (over natural) and to 390 to have zero net CO2 emissions from that > > ocean parcel. > > -G > > > On 9/26/11 9:25 AM, "Oliver Tickell" <oliver.tick...@kyoto2.org> wrote: > > > > Actually this option does not look too bad on first sight - low cost, > > > low tech, so that's a good start, and the chemistry looks right too. > > > Biggest problem is the delay of approx 100y before the results come > > > through, if I read the paper right. That's a long time for us to have > > > to wait. Also if we change our minds, its a long lead time for > > > reversal. > > > > Go for Mg silicate weathering on land / intertidal zones, and the CO2 > > > drawdown is immediate, operating on a decadal time scale. > > > > Re the kinetics of Mg silicate, they are unfavourable if carried out > > > in a chemistry lab. Carried out in nature and enhanced by activity of > > > fungi, bacteria, roots, digestive systems of worms and higher animals, > > > etc, it's a great deal faster - the biospheric enhancement factor > > > speeds it up by several orders of magnitude. > > > > Oliver. > > > > On Sep 26, 4:09 pm, "Rau, Greg" <r...@llnl.gov> wrote: > > >> And to round out the options, let¹s not forget Harvey¹s > > >> limestone-rain-in-the-ocean > > >> method:http://iod.ucsd.edu/courses/sio278/documents/harvey_08_co2_mitigation. > > >> .. > > >> While billed as (eventual) air capture, I view this as ocean CO2 capture > > >> > > >> bomb upwelling areas with limestone to consume the excess CO2(aq) prior > > >> to > > >> degassing to air. Don¹t forget that the ocean emits in gross >300 GT > > >> CO2/yr. > > >> If we can cut that by 1% it would have a huge effect on air CO2. No? > > >> Humbly, > > >> Greg > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To post to this group, send email to geoengineering@googlegroups.com. > To unsubscribe from this group, send email to > geoengineering+unsubscr...@googlegroups.com. > For more options, visit this group > athttp://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 geoengineering@googlegroups.com. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com. 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 geoengineering@googlegroups.com. 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