Dear Robert,
I am a physicist, not an engineer, so I can't really judge how feasible
it is to pump half a percent of the total volume of the ocean (this is
what I got from my nutrient calculations, and I think they are correct)
from a depth of 1000m or more up to the surface every year by tidal
pumping, but I have to admit that I am sceptical.
I also cannot fully follow your argument about the concentration of
nutrients, but I think your numbers are not correct. The average
concentration of nitrate in the deep ocean is around 30 micromol/L (not
3 ppm, which is neither correct in mol/mol, nor in volume/volume); and
that of phosphate is not the same, but around 15 times less, i.e. around
2 micromol/L.
Anyway, there is a much more fundamental problem with the approach that
you are suggesting that is independent of its scale: When you pump up
deep ocean water to get at the nutrients therein, you also pump up water
that contains more dissolved inorganic carbon than surface ocean water.
On average deep ocean water contains as much more dissolved carbon as
you can fix with the nitrogen/phosphorus contained in it (again assuming
a constant Redfield C:N:P ratio); this is because the higher carbon
content in the deep ocean has been brought there mostly by the sinking
and subsequent remineralisation of organic matter. Of course, with the
nutrients that you bring up, most of that carbon will again be fixed in
your algal biomass and can then be disposed of (whereever, maybe as
biochar). But: That then leaves almost no room for using the algae to
fix additional carbon from power plants, as you suggest.
So in effect what you do with that approach is: You pump up the carbon
that has been stored in the deep ocean by the natural biological pump,
which without anything else would increase CO2 in the surface. Then you
fix this carbon in biomass and store it on land. In the end you have
only shifted carbon from the deep ocean to the storage on land, and have
achieved very little, if anything at all in terms of fixing the
fossil-fuel-generated carbon. The only way out of this that I see is to
use algae with an elevated C:N and C:P ratio compared to the Redfield
ratio, because then you can fix more carbon than you bring up.
But then again, I would be sceptical about the possible scale that you
mention, from my back-of-the-envelope calculation of the nutrient
requirements from my last email.
Best regards, Christoph
On 08.09.17 01:15, Robert Tulip wrote:
Thanks Cristoph.
Deep Ocean Water, with volume about a billion cubic kilometres below
the thermocline, has about three ppm nitrate and phosphate, about 3000
cubic kilometres of each, as I understand the numbers. Tidal pumping
arrays along the world's continental shelves could raise enough DOW to
the surface, mimicking natural algae blooms, to fuel controlled algae
production at the scale required for seven million square kilometres
of factories. Piping CO2 from power plants etc out to ocean algae
farms could clean up all the polluted air of the world.
Robert Tulip
------------------------------------------------------------------------
*From:* Christoph Voelker <[email protected]>
*To:* [email protected]
*Sent:* Friday, 8 September 2017, 8:43
*Subject:* Re: [geo] Carbon budget/removal in NYTimes interactive
I must admit that I am getting skeptical when I hear numbers in that
order of magnitude:
The total net primary production in the oceans presently is about 50
Gt carbon, and 80% of that is converted back into inorganic carbon
(and nutrients) by heterotrophs before it gets a chance to sink out
from the sunlit upper layer of the ocean. The roughly 10 Gt carbon
(some newer works even estimate just 6 Gt carbon) that sink out have
to be balanced by the upward mixing of nutrients (and a little bit by
atmospheric deposition of bioavailable nitrogen and phosphorus) in the
Redfield ratio of about 106:16:1 of C:N:P.
So, if you want to remove 20 Gt carbon per year from the atmosphere,
you'd have to increase the nutrient supply to the total surface ocean
by a factor of three, maybe four. Maybe I am a bit too pessimistic
here, because there are species like Sargassum which have a higher
C:N:P ratio than the average phytoplankton, so you get somewhat more
carbon per nitrogen/phosphorus. But even if it is just doubling, I
can't imagine that you can sustain such a nutrient consumption by
fertilizing from outside the ocean (especially since phosphorus is
scarce already now), you'd have to tap into the inorganic nutrients
stored in the deep ocean. How long can you do that?
If we assume that we harvest all the 20 Gt carbon in algae from these
factories and do something durable with them (to minimize lossed
through heterotrophy and problems with creating oxygen minimum zones),
we effectively remove nitrogen/phosphorus from the ocean. How much is
that per year?
Let us for simplicity assume Redfield ratios, I grant errors by a
factor of two or so. 20 Gt carbon then corresponds to (20
g/12(g/mol)/6.625(molC/molN))*1.0e15 or about 2.5e14 mol nitrogen. The
ocean has a volume of 1.33e18 m^3, and the average concentration of
available nitrogen (mostly nitrate) is 30 micromol/L or mmol/m^3
(calculated from the world ocean atlas), most of that is in the deep
ocean. This gives a total inventory of 4.0e16 mol nitrogen. 2.5e14
mol/year is thus more than half of a percent of the total available
nitrogen in the world oceans, which means you could try that for about
150 years, then everything is gone At that pace, nitrogen fixers are
unlikely to resupply the loss (nowaday, the residence time of nitrogen
is roughly 5000 years), and they can do that only for nitrogen, not
for phosphorus anyway. Letting technological problems aside (like: How
do you move 2.5% of the total nitrogen in the world oceans evry year
up to an area 2% of the ocean surface) I would call the whole idea -
at least that the scale suggested - a prime example of an
unsustainable process.
Best regards,
Christoph Voelker
On 07.09.17 23:37, 'Robert Tulip' via geoengineering wrote:
The assumption behind the NYT interactive model
<https://www.nytimes.com/interactive/2017/08/29/opinion/climate-change-carbon-budget.html?action=click&pgtype=Homepage&clickSource=story-heading&module=opinion-c-col-right-region®ion=opinion-c-col-right-region&WT.nav=opinion-c-col-right-region>
that the upper bound for carbon removal is 12 GT CO2 by 2080 is too
slow and small. We should think five times as much and five times as
fast.
Immediate aggressive investment to build industrial algae factories at
sea could remove twenty gigatons of carbon (50 GT CO2) from the air
per year by 2030, using 2% of the ocean surface, funded by use of the
produced algae.
That would stabilise the climate and enable no change in emission
trajectories, a policy result that would satisfy both the needs of the
climate and the traditional economy.
Robert Tulip
------------------------------------------------------------------------
*From:* Eric Durbrow <[email protected]> <mailto:[email protected]>
*To:* geoengineering <[email protected]>
<mailto:[email protected]>
*Sent:* Thursday, 7 September 2017, 3:13
*Subject:* [geo] Carbon budget/removal in NYTimes interactive
FYI There is a slick interactive graphic at the NYTimes that lets
people see if they can meet the world’s carbon budget restriction but
a combination of reduced emissions AND achieving Carbon Removal.
At
https://www.nytimes.com/interactive/2017/08/29/opinion/climate-change-carbon-budget.html?action=click&pgtype=Homepage&clickSource=story-heading&module=opinion-c-col-right-region®ion=opinion-c-col-right-region&WT.nav=opinion-c-col-right-region
I failed after clicking on Reduce in all geographic areas and Achieve
in Carbon Removal.
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Alfred Wegener Institute for Polar and Marine Research
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Christoph Voelker
Alfred Wegener Institute for Polar and Marine Research
Am Handelshafen 12
27570 Bremerhaven, Germany
e: [email protected]
t: +49 471 4831 1848
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