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 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]>
To: geoengineering <[email protected]>
Sent: Thursday, 7 September 2017, 3:13
Subject: [geo] Carbon budget/removal in NYTimes interactive
#yiv1081158045 body{font-family:Helvetica, Arial;font-size:13px;}
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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Christoph Voelker
Alfred Wegener Institute for Polar and Marine Research
Am Handelshafen 12
27570 Bremerhaven, Germany
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