"For land-based schemes, the mechanical energy required to grind
particles down to chemically-available sizes is a significant input. The
trade off between grinding and reaction speed is materially significant
to both the cost and efficacy of weathering programmes."
Very true. the optimum grain size seems to be about 0.1mm.
Mathematically, the energy of grinding is proportionate to the surface
area created, so as you get down to very small grains sizes the energy
input soars. If the weathering is purely chemical even at 0.1mm the
weathering away takes a long time. But weathering rates are hugely
enhanced by biological activity (animal guts, fungi, etc) so the actual
grain lifetime is typically < 10y. Mechanical abrasion also increases
weathering rates, for example wave action on beaches.
"I suspect that the vast majority of the mass will simply end up in
benthic sediments and will not impact ocean chemistry at all."
You may be right, but it would be good to know for sure. A promising
area of research perhaps? But before going too far down this route, is
there actually enough mineable pumice in the world for it to be a
significant solution?
--
Oliver Tickell
Kyoto2 - for an effective climate agreement.
w: www.kyoto2.org
e: [email protected]
p: +44 1865 728118
On 09/08/2012 15:12, Andrew Lockley wrote:
Oliver, Mike
I note from previous discussion of chemical weathering geoengineering
that the available surface area for weathering deposits was a critical
limitation. It would seem that, if residency times on the ocean
surface were significant, then wave-grinding could potentially address
this issue.
Likely the key issue at stake for chemical impacts is the same as that
for direct albedo impacts: the proportion of mass lost at the surface,
versus the flux to the deep ocean. I suspect that the vast majority
of the mass will simply end up in benthic sediments and will not
impact ocean chemistry at all.
For land-based schemes, the mechanical energy required to grind
particles down to chemically-available sizes is a significant input.
The trade off between grinding and reaction speed is materially
significant to both the cost and efficacy of weathering programmes.
(for a discussion of energy, see
http://www.geoengineering.ox.ac.uk/research/oxford-geoengineering-programme-research/enhanced-weathering/)
Whilst the energy supplied for this process is renewable in the case
of wave action, it is not 'free' and will potentially effect a
significant change in surface wave amplitude. This may have a
knock-on effect on climate via a number mechanisms:
1) Direct albedo change, via angle of incidence - see doi:10.1029/2004GL021180
2) Indirect albedo change at surface, via changes to the formation of
whitecaps or persistent bubble rafts - see doi above
3) Cloud albedo changes by the alteration of fluxes of CCN from
bursting bubbles. (see
http://www.ucar.edu/governance/meetings/oct08/followup/head_and_chairs/phil_rasch.pdf)
A
On 9 August 2012 14:55, Oliver Tickell <[email protected]> wrote:
Has anyone considered another attribute of pumice - that chemically it
surely includes a lot of Mg2SiO4 - which absorbs CO2 as it weathers to
bicarbonate? As such it will counter AGW by drawing down CO2, and will
counter ocean acidification by adding alkalinity to the ocean. It will
also add silicic acid to the ocean, the limiting nutrient for diatoms,
whose fall to the depths is also an important CO2 vector. The key
thing here is that pumice should remain on the ocean surface long
enough for the weathering reaction to take place. Typically the
reaction is quite slow but the constant abrasion of pumice against
pumice under wave action should speed it up considerably. Biotic
factors may also come into play, if the pumice pieces are colonised by
algae for example.
Oliver Tickell
--
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.
--
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.
