Dr. Wigley, By "But won't the bugs just work harder to keep the soil PCO2 about the same?", are you referring to the rate of soil organic matter degradation?
Regards, David. On Sep 30, 1:06 am, Tom Wigley <[email protected]> wrote: > It's a long time since I did anything in this field, so this is some ad > hoc thinking. > > Soil PCO2 is much higher than in the atmosphere. An old paper on this is ... > > Drake, J.J. and Wigley, T.M.L., 1975: The effect of climate on the > > chemistry of carbonate groundwater. Water Resources Research 11, 958 962. > > Adding CaCO3 will add Ca++ and HCO3- to the soil/groundwater. The > dissolution will reduce soil PCO2. So the flux of CO2 from soil to > atmosphere will decrease. But won't the bugs just work harder to keep > the soil PCO2 about the same? The climate/soilPCO2 relationship in the > above paper suggests that this is what will happen. > > So the net effect is probably small. > > Tom. > > +++++++++++++++++++++ > > On 9/29/2011 5:14 PM, Rau, Greg wrote: > > > > > > > > > There's a large literature on and practice of crop soil limestoning. In the > > context of CO2, my concerns would be added CO2 release from reaction of > > limestone with soil or precipt strong acids, and added downstream and > > groundwater hardness via dissolved Ca(HCO3)2 addition. The latter can be a > > big deal for communities that have to use the water, the potential for CaCO3 > > reprecipitation and scaling will go up, above that naturally present in the > > water, esp in limestone regions. For this reason it would be important to > > somehow keep the water below CaCO3 saturation. This goes away with disposal > > in seawater, which is why doing this close to a river mouth might be the > > best thing. Anyway, we eagerly await the results of your (backyard?) > > experiments. > > G > > > On 9/29/11 3:29 PM, "David Zhong"<[email protected]> wrote: > > >> Greg, > > >> This might not be a bad idea. > > >> CO2 emission to the atmosphere through soil respiration is estimated > >> at about 60 GtC/a. Cutting down 10% of this natural emission will give > >> us about 6 GtC/a. For comparison, current anthropogenic carbon > >> emission to the atmosphere is about 8 GtC/a. > > >> To capture 6 GtC/a of carbon emission from soil respiration requires > >> mining and grinding a minimum of 50 Gt of CaCO3 per year (i.e., > >> 6/12X100). For comparison, current coal mining is estimated at about > >> 25 Gt/a. Limestone is certainly more abundant and wide spread than > >> coal. Using your estimate of limestone mining and grinding and > >> transportation cost of about $5/ton, the annual total cost would be > >> about $250 billion. > > >> Spreading 50 Gt of limestone to 10% to 20% of the land (or about 15-30 > >> million km2, about 0.3 to 0.15 kg CaCO3 per m2 per year) where soil > >> respiration is most intensive would probably be sufficient to > >> capture 6 GtC/a. > > >> Compared to limestoning the ocean scheme, this limestoning the > >> soil" scheme would cut CO2 emission to the atmosphere immediate, > >> instead of waiting for years or tens or hundreds of years. > > >> As for your two concerns, I am sure that if the soil system is > >> overloaded with limestone, the end product of limestone dissolution > >> would be dissolved bicarbonate ions instead of carbon dioxide. > >> Limestone landscapes are found all over the continents and people have > >> been living happily in limestone regions for generations. I doubt that > >> the hardness of the resulting runoff of a limestoning the soil" > >> scheme will be any worse than that of the watershed of a limestone > >> region. > > >> I am sure that there will be some other environmental and/or > >> ecological side effects or risks. But I am also sure that any or > >> every solution to such a planetary scale problem will carry risks. > >> The question is, are these risks manageable? > > >> What do you think? > > >> David > > >> On Sep 29, 11:14 am, "Rau, Greg"<[email protected]> wrote: > >>> That would work for me a la crop liming IF: 1) soil acids other than > >>> carbonic acid are such that CO2 is not emitted to the air from the acid > >>> limestone reaction, and 2) the hardness of the resulting runoff is within > >>> environmental standards. How about limestoning the mouths of rivers to > >>> mop > >>> up excess dissolved CO2 - there are no hardness standards for discharge to > >>> the ocean. Then again, by the time rivers discharge to the ocean they've > >>> probably pretty much degassed and equilibrated with air pCO2. > >>> -Greg > > >>> On 9/29/11 10:35 AM, "David Zhong"<[email protected]> wrote: > > >>>> Would it be more effective (and perhaps simpler) if the limestone is > >>>> distributed to a large area of land (ideally in regions with heavy wet > >>>> precipitation and with organic matter rich soil) instead of the > >>>> upwelling > >>>> regions of the ocean? > > >>>> After all, limestone dissolution in normal rainwater (pH< 5.6, ionic > >>>> strength ~ 0) is much faster than in seawater (pH> 7.6, ionic > >>>> strength ~ 0.7) and natural CO2 exchange (or flux) between soil > >>>> and atmosphere is on the same order as that between ocean and > >>>> atmosphere? > > >>>> Just a thought. > > >>>> David. > > >>>> On Sep 29, 9:12 am, "Rau, Greg"<[email protected]> wrote: > >>>>> Thanks, Tom. I think we all can agree that the volume of CaCO3 > >>>>> undersaturation in the subsurface ocean is vast, it is a very effective > >>>>> consumer (60-80%) of natural carbonate rain, and hence is a massive > >>>>> (re)generator of carbonate alkalinity that can in turn consume ocean and > >>>>> atmospheric CO2. It follows that adding additional CaCO3 to the > >>>>> undersaturated regions of the ocean, especially particles of high > >>>>> surface > >>>>> area/volume, will generate additional (new) alkalinity and CO2 consuming > >>>>> potential. The only question then is can this occur in shallow enough > >>>>> water > >>>>> (e.g., upwelling areas) such that its communication with and effect on > >>>>> the > >>>>> atmosphere occurs on a time scale shorter than the usual 1kyr involved > >>>>> in > >>>>> thermohaline ventilation of deep water. In this regard the subsurface > >>>>> N > >>>>> Pacific Ocean, being first up for such ventilation, would seem to hold > >>>>> the > >>>>> most promise. Then there is the CaCO3-challenged Southern Ocean. > >>>>> Or am I off base? > >>>>> Anyway, if you don't like the rates afforded by natural seawater > >>>>> carbonate > >>>>> undersaturation, there is a relatively straightforward way to change > >>>>> this:http://pubs.acs.org/doi/abs/10.1021/es102671x > >>>>> Regards, > >>>>> Greg > > >>>>> On 9/28/11 6:18 PM, "[email protected]"<[email protected]> wrote: > > >>>>>> Regardless of possible inhibiters, I think that kinetic limitations > >>>>>> make > >>>>>> this an unlikely possibility. > > >>>>>> See ... > > >>>>>> Plummer, L.N. and Wigley, T.M.L., 1976: The dissolution of calcite in > >>>>>> CO2-saturated solutions at 25 C and 1 atmosphere total pressure. > >>>>>> Geochimica et Cosmochimica Acta 40, 191 202. > > >>>>>> Plummer, L.N., Wigley, T.M.L. and Parkhurst, D.L., 1978: The kinetics > >>>>>> of calcite dissolution in CO2-water systems at 5 60 C and 0.0 1.0 atm > >>>>>> CO2. American Journal of Science 278, 179 216. > > >>>>>> Tom. > > >>>>>> ++++++++++++++++++++++++++++ > > >>>>>> On 9/28/2011 1:44 PM, Rau, Greg wrote: > >>>>>>> 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: [email protected] > >>>>>>> [[email protected]] > >>>>>>> On > >>>>>>> Behalf Of David Zhong [[email protected]] > >>>>>>> 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 > > ... > > read more » -- 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]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
