This is hardly conclusive, but the information seems to suggest that some of
the deep water exiting the GOM just goes around in a circle, with some of it
eventually reaching the Atlantic and the coldwater part of the THC. Thus,
the lifetime of CO2 that was released from biomass deposited on the floor of
the GOM must be much longer than the 250-years it would take to leave the
GOM, perhaps approaching the 1000-year time given for the overall ocean.
Even with some of the CO2 returned to surface waters by uwpelling, this
still keeps most of the carbon out of the atmosphere for hundreds of years,
time enough to perfect air capture and lower atmospheric CO2 levels so that
regardless of the fate of the biomass, it won't have an impact on future CO2
levels. If I remember correctly, your maximum use of CROPS would only
remove the equivalent of about 10% of present day emissions, decreasing
annually with increases in fossil fuel emissions. Thus, CROPS could offset
a significant portion of CO2 from the emission inventory, but not enough to
change the outcome of a BAU approach to emissions. If 3 billion tons of
CO2eq were removed annually to the deep ocean in the GOM by CROPS or by
using wood or some combination, then after 100 years, 300 billion tons would
be on the bottom of the Gulf or present as dissolved CO2, about 10 years of
present day emissions, not enough to cause a catastrophe if it were to be
slowly vented to the atmosphere. The impact of depositing the biomass
elsewhere would need to be studied to see if upwelling would hasten the
transport to the surface.
http://www.myroms.org/applications/ias/intro/circulation.php
"Much less is known about the deep circulation of the region. To the east of
the Antilles, a Deep Western Boundary Current (DWBC) forms part of the North
Atlantic thermohaline circulation. From timeseries of DWBC observations at
26.5°N just east of Abaco, Bahamas, Lee et al. (1996) found that the mean
DWBC transport was ~ 40 Sv, some 2-3 times larger than the accepted value,
indicating that a significant fraction of DWBC flow must recirculate in the
North Atlantic. Model studies suggest that this occurs primarily along f/h
contours associated with local bathymetric features. Lee et al. (1996) also
found significant variations in DWBC transport as large as 60 Sv associated
with offshore excursions and meanders of the current. The local transport
variability in this region is well correlated with the strength of the
Bermuda High. The deep flows in this region are also dominated by eddies,
perhaps a result of baroclinic instability, as evidenced by float data
(Leaman and Vertes, 1996). The deepest island passages are Anegada (1900 m)
and Windward Passage (1700 m), and ventilation of the Venezuelan, Colombian,
Cayman and Yucatan basins occurs via these passages (~ 0.2 Sv). In the
central Caribbean Sea, the deep flow is apparently dominated by a cyclonic
circulation as inferred from inverse calculations (Roemmich, 1981; Joyce et
al., 2001), and is perhaps to be expected based on dynamical arguments (Sou
et al., 1996). There is also observational evidence for deep eastward flow
along the entire southern boundary of the Caribbean Sea (Andrade et al.,
2003), and numerous estimates of ventilation, deep flow pathways and
transports have appeared in the literature (e.g. Morrison and Nowlin, 1982;
Joyce et al., 2001)."
----- Original Message -----
From: "Stuart Strand" <[email protected]>
To: "Alvia Gaskill" <[email protected]>; <[email protected]>;
"geoengineering" <[email protected]>;
<[email protected]>
Cc: <[email protected]>
Sent: Saturday, September 11, 2010 3:48
Subject: RE: [clim] Re: [geo] Carbon sequestration workshop Sep 9-10, Heinz
Center, Washington DC
Thanks, Alvia, for pointing this out. On second examination of the paper, I
was in error in thinking that the deep Gulf of Mexico is ventilated to
surface waters. I confused the deep flow with the Yucatan and Loop Currents
of the upper water and got the impression that deep waters rose and exited
to the Atlantic through the Straits of Florida. That is not correct. As
the Rivas paper shows, deep waters from the Gulf exit back through the
Yucatan Strait into the Carribean, which is deeper that the GoM, but where
it goes from there I am uncertain; the Anegada-Jungfern Passage, perhaps.
It looks like I have more homework to do...
= Stuart =
Stuart E. Strand
490 Ben Hall IDR Bldg.
Box 355014, Univ. Washington
Seattle, WA 98195
voice 206-543-5350, fax 206-685-9996
skype: stuartestrand
http://faculty.washington.edu/sstrand/
-----Original Message-----
From: Alvia Gaskill [mailto:[email protected]]
Sent: Friday, September 10, 2010 12:10 PM
To: Stuart Strand; [email protected]; geoengineering;
[email protected]
Cc: [email protected]
Subject: Re: [clim] Re: [geo] Carbon sequestration workshop Sep 9-10, Heinz
Center, Washington DC
I think there is some confusion about the term "ventilation rate" as it is
used here. The work that apparently forms the basis for the 250-year
ventilation rate for the GOM discusses it in terms of how long the deep
water in the Gulf stays there before being carried back out into the
Caribbean Sea. If you look at Figure 15 from the linked reference, it shows
that the deepest water exits over the Yucatan Sill at 2040 meters. What
happens to it after that is unclear. The ventilation rate referred to here
is how long it takes the water to make it out of the Gulf, not how long it
would take CO2 from decomposing bales of crop waste to re-enter the
atmosphere. The relatively high oxygen levels at the bottom, around 5 mg/L
could accelerate oxidation of the waste, but over long periods of time it
would probably become buried in sediment and would be in an anoxic
environment, also limiting any transport of CO2 to the surface. So I would
encourage you to research this a little more before giving up on the Gulf of
Mexico.
http://oceanografia.cicese.mx/personal/jochoa/PDFS/Rivas_etal_JPO_2005.pdf
----- Original Message -----
From: "Stuart Strand" <[email protected]>
To: <[email protected]>; <[email protected]>; "geoengineering"
<[email protected]>; <[email protected]>
Cc: <[email protected]>
Sent: Friday, September 10, 2010 12:50
Subject: RE: [clim] Re: [geo] Carbon sequestration workshop Sep 9-10, Heinz
Center, Washington DC
After our publication it was pointed out to me that the ventilation rate of
the Gulf of Mexico is such that the half life of water there is about 250
years. One of the major advantages of CROPS over terrestrial burial options
is that the biomass carbon separated from the atmosphere by the ocean
thermocline, so that if CO2 is released from the biomass it will not be
released to the atmosphere for 1000 years (the ventilation rate of the world
ocean). Thus we no longer view burial in the GoM as desirable (except
perhaps in hypersaline pools in the western gulf). As it happens the carbon
cost of transport to the Atlantic abyss is not much greater than our
previous estimates.
= Stuart =
Stuart E. Strand
490 Ben Hall IDR Bldg.
Box 355014, Univ. Washington
Seattle, WA 98195
voice 206-543-5350, fax 206-685-9996
skype: stuartestrand
http://faculty.washington.edu/sstrand/
Alvia Gaskill wrote
You might also consider the use of deep ocean disposal as Strand and Benford
did for crop waste. Wood chips can be sluiced and compressed together might
sink without any weights. Of course, this is probably not a good time to be
recommending doing this in the Gulf of Mexico.
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