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 at http://groups.google.com/group/geoengineering?hl=en.
