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Dear Jim,

>When you and I
>discussed this recently in Bern, I think we agreed that an inorganic model
>with C-14 and C-12 as separate tracers would do a good job. Such a
>2-tracer approach is slightly more complicated that that which you suggest
>now, (1-tracer "fractionation-corrected ratio" from Toggweiler et al.,
>1989).  However, since we are going to make the solubility pump run
>anyway, adding C-14 to that would be about the same amount of work, and
>would not require more CPU time.  Actually the 2-tracer run (for C-14 and
>C-12) would be more efficient (in CPU time) than the alternative (one run
>for the solubility pump plus another run for the C-14/C-12 ratio). 

Sorry, if I have produced some confusion. The single fractionation
corrected C-14/C-12 ratio
tracer and the full blown organic version are just what we have right
now to compare. Although, we hopefully will elaborate on this. 

In any case, I still agree with what you suggest above that 2
inorganic tracers are a good way to proceed. I would suggest to
simulate TOTAL C and not C-12, and to simulate FRACTIONATION CORRECTED
C-14, i.e. air-sea and other fractionation factors are set to 1. You probably wanted
to say this?

>A key issue is that results from inorganic and biotic runs should be the
>same, to within a few permil, if atmospheric CO2 is held to the same value
>(Bacastow and Maier-Reimer, Climate Dynamics, 1990). 

Olivier's results agree with that by Bob and Ernst.
Deviations are indeed small.

>I would be particularly interested in seeing your results for
>the industrial and postnuclear era. How will you model changes in surface
>ocean CO2?

I will see what we can do. 

With best wishes, Fortunat 

- -- 
- ----------------------------------------------------------------------------
Fortunat Joos
Physics Institute, KUP, Sidlerstr. 5, CH-3012 Bern

Phone:    ++41(0)31 631 44 61
Fax:      ++41(0)31 631 44 05
e-mail:   joos@climate.unibe.ch
Internet: http://www.climate.unibe.ch/~joos/