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" <[email protected]> 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" <[email protected]> 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" <[email protected]> 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 [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.
