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Re: More on alkalinity

Hi Jonathan,

        The decision to use global mean alkalinity for the solubility pump
was made by Rick Murnane and I in the study first reported in our 1995
paper in the Proceedings of the Royal Society.  We wanted the difference
between the combined and solubility models to represent the FULL effect of
biological processes, including the reduction of surface alkalinity due to
CaCO3 formation.  Thus we fixed the mean solubility pump alkalinity to the
mean observed alkalinity, NOT correcting for the surface reduction due to
biological removal to the deep ocean.  Obviously, it does not make sense to
use the solubility model defined this way to estimate anthropogenic CO2
uptake, although, as Rick pointed out, the effect is not very large.

        The choice of how to proceed from this point onwards should depend
on what one is trying to achieve.  If you want to use the solubility model
to estimate the anthropogenic CO2 uptake, then you should indeed use the
mean surface alkalinity, not the mean global alkalinity.  However, I would
be opposed to using the solubility model to estimate oceanic uptake.  That
should be done with the combined model.  In that case, the value of the
solubility model is as a contrast to the combined model to illustrate what
biology does.  We may decide that the way Rick and I defined the solubility
model is not ideal for this latter purpose, but I would suggest that if we
want to change the definition of the solubility model, we should do it with
the idea that we want to use it as a contrast to the combined model in
order to identify the contribution of the biological pump.

Best regards, Jorge

>Hello OCMIP people,
>Thanks to everyone who replied to my alkalinity query.
>It would seem that 2311*S/34.78 ueq/kg is a more reasonable expression
>to use for surface alk than 2374*S/34.78.
>As high latitude alkalinities are significantly higher than lower latitudes
>does this imply a strong alkalinity component to the solubility pump?
>From some very simple calculations using:
>High latitude  T=5C S=35o/oo ALK=2370ueq/kg
>Low latitude   T=25 S=35o/oo ALK=2285ueq/kg
>I find that the potential surface TCO2 high-low lat difference is enhanced
>by 40% over the case where both high and low lat alkalinities are 2310ueq/kg.
>Hence getting the surface alkalinity distribution right could significantly
>affect solubility pump calculations.
>Any comments?
>                        JONATHAN PALMER
>Room H013,                      Internet:  JRPalmer@meto.gov.uk
>Hadley Centre,
>Met. Office, London Road,       Tel:       +44 (0)1344 854478
>Bracknell, RG12 2SZ, UK         Fax:       +44 (0)1344 854898

Jorge L. Sarmiento
AOS Program, Princeton U.
Sayre Hall
P.O. Box CN710
Princeton, NJ 08544-0710

Tel. (609) 258-6585
Fax. (609) 258-2850
E-mail: jls@splash.princeton.edu