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Re: Returned mail: Private list 'ocmip-all'
Thanks for the feedback on our routines. You have brought up an
point in that the functions we generated include the full carbon chemistry to
consistent with the measured carbon parameters. There are a number of shortcuts
take to simplify these equations, but there are finite errors associated with
the simplifications. For example, I gather that you ignore all of the secondary
that contribute to total alkalinity except for borate. Borate is by far the
the secondary species and I think you agree that it needs to be included. As
and fluoride, their contribution is very small (<0.1 uatm in calculated fco2)
could probably be ignored without a problem. I guess it comes down to a trade
between being chemically correct versus the computer time for the 4 extra
(bt, ft, kb and and kf). Phosphate and Silicate are somewhere in the middle. I
disagree with your statement that the phosphate and silicate are "far below any
precision of measurements"). Obviously in warm, low latitude surface waters
concentrations are near 0 they are not significant, but they do certainly make
measurable difference in the Southern Ocean. If we take an example from the
layer in the South Pacific with:
alk=2275, TCO2=2150, Temp=1.5, Sal=34, phosphate=2, silicate=50
With the full chemistry you would calculate an fCO2 of 384 uatm.
If you ignore the phosphate and silicate, fco2=377, a difference of 7 uatm.
5 uatm of that error results from ignoring phosphate. The remaining 2 uatm
from the silicate. Since silicate can get as high as 200 umol/kg in the ocean
contribution can be larger. I can't say whether a 7 uatm error is significant
the model calculations. That is a decision you guys need to make. If you would
us to remove some or all of the secondary species just let me know.
As for using CO3-- and hydrogen to calculate the chemistry, I am not
I follow. Unfortunately, I was not able to completely follow the code you
without knowing the definitions for some of the variables you use. With our
I believe you can easily converge on an htotal with only 4 iterations if you
a little thought into your choice of ph ranges. I am not sure what the
are in our approach without a better understanding of your code. One thing to
remember is that the dissociation constants are strongly dependent on
and salinity, so the CO3-- can vary widely simply because of changes in
or salinity. The only carbon parameters that are not a function of temperature
salinity are total CO2 and total alkalinity (in mass units). Note that with the
accepted definition, carbonate alkalinity is not independent of Temp and Sal.
I hope this makes some sense. If you have further questions or would
us to modify the functions just let me know.
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