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minor corrections


Oceanographers can now routinely measure pCO2 in surface waters to within a few
microatmospheres, DIC to a few umol/kg and oxygen with even better precision.
I have been using the guideline that if a process affects something by more
than typical measurement precision, we should include it in OCMIP simulations.
The reason is that we want to be able to *evaluate* our models with
measurements, not just intercompare the models.

Sea level pressure varies from about 1020 mb at 30S to about 990 mb at 60S,
a 3% difference.  This translates into a pCO2 difference of about 10 uatm and
a corresponding DIC difference of about 6 umol/kg  (using a buffer factor of
10 and a mean surface DIC of 2000 umol/kg.  The O2 differnce would be
about 10 umol/kg.  These adjustments are just large enough, I think, that
pressure effects should be included in O2 and CO2 gas transfer. 

For CFCs the pressure effect is effectively much smaller because of the large
dynamic range in CFC concentrations due to the rapid increase from zero in the
past few decades.

With regard to the carbonate chemistry, it is important to include phosphate
and silicate equilibria because it will impact pCO2 by more than 5 uatm, as
Chris and I noted in our protocol description and as Bob reiterated in a
recent email.

These modifications are not going to make or break OCMIP, but they are not
trivial, they are systematic corrections, and are easily included in
calculations, so let's do them.

One could argue that cool-skin corrections and bubble-induced supersaturation
should be included as well, but the problem is that these effects are not well
characterized and easy to model.  So I suggest we not include these effects
until good parameterizations are developed.