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Re: CaCO3 dissolution


I agree that CaCO3 plays essentially no role in fossil CO2 neutralization and
that circulation changes are probably the most important factor in determining
NA-NP difference.

I also agree that, for now, the best thing to do is for everyone to do some-
thing similar and simple, such as what was proposed for the nutrient restoring
model: spatially and temporally constant values of (1) the ratio of CaCO3/Corg
at the base of the euphotic zone and (2) exponential dissolution length scale.
I proposed values of 0.07 and 3500 m, respectively, as suggested by Yamanaka
and Tajika.  I think it is a mistake to adopt your suggestion of using the same
length scale for organic C and CaCO3--as you know, it is awfully clear from all
sorts of data that CaCO3 dissolution occurs much deeper than remineralization.

Part of OCMIP's goals is to improve marine carbon cycle models so that they can
be used for future prediction.  I think that simulating the alkalinity 
distribution is important in this regard--we want to be able to estimate how
the rain ratio and the dissolution length scale might change in response to
physical forcing.  This means we need something more mechanistic than what is
in hand now, such as the suggestions of Feely and Caldeira to model dissolution
as a function of saturation state.

It would be wasteful for everyone to experiment with a new scheme.  One idea
we came up with at the February meeting was "distibuted sensitivity studies."
This would allow one group to explore certain parameterizations--gas exchange,
remineralization, etc--and report back to the group as a whole.  CaCO3 cycling
could be one of those studies.