Christoph et al.,While the ocean does contain a lot of untapped energy and CO2
removal potential, I share your concerns about the difficulties of tapping into
photosynthetic energy to do this for the reasons you state. That's not to say
that there couldn't be clever ways of harnessing marine macro/micro flora, but
it would require careful management of N, P, Fe, Si, O2 etc to effect the
desired CO2 management while not disrupting existing surface ocean
ecosystems/biogeochemistry.
As for putting the deep ocean to use, in addition to a nutrient and CO2
source/sink it is also a very large heat sink. When coupled via OTEC to the
(growing) surface ocean heat source you've got something like 10TW of
continuous, potential, deliverable electrical power even considering a 3% OTEC
energy conversion efficiency. Ways of performing such OTEC that vertically move
only heat (not seawater) in a closed cycle have been proposed. When coupled
with a CO2-consuming method of generating H2, you've got a global scale
negative emissions energy delivery system whose CDR potential could be 50Gt
CO2/yr while delivering CO2-free fuel equivalent to >3X annual global gasoline
consumption. It also directly and beneficially cools and alkalizes the surface
ocean - https://agu.confex.com/agu/fm16/meetingapp.cgi/Paper/121574 ; I can
provide further details if interested. Nor are we restricted to OTEC since any
source of non-fossil electricity can make C-negative H2.
Anyway, the NYT's CDR model restriction of 12 Gt CO2/yr by 2100 would indeed
seem unduly pessimistic, esp if we allow ourselves to think beyond land-based
and biology-based methods of saving the planet. Now would seem a good time to
expand the search and find out what if any viable options we actually have,
considering the scale and urgency of the problem.
Greg
From: Christoph Voelker <[email protected]>
To: Robert Tulip <[email protected]>; "[email protected]"
<[email protected]>
Sent: Friday, September 8, 2017 12:14 AM
Subject: Re: [geo] Carbon budget/removal in NYTimes interactive
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 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
#yiv9662949173 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
e: [email protected]
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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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