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Re: Nutrient Restoring model



Ernst, I'm guessing from your questions that you haven't had a chance to look
at the protocol.  If you're having a problem reading it, let us know.  But let
me answer your questions now.  I'm posting them to ocmip-all because you 
bring up some important points.  -Ray
>   
>   Question: Are "virtual" fluxes of salt, DIC and Alk still operating
>   in the MOM-groups, or are they abandoned by Alk normalized to salinity?

What we proposed was to explicitly model the effect of air-sea fresh water
fluxes on DIC and Alk using

F = (E-P)*[DIC]o

where F is the air-sea virtual flux of DIC (mol/m2/s), E-P is evap minus
precip (m/s) and [DIC]o is the mean observed surface [DIC] concentration
(mol/m3).  A similar formulation would be used for Alk.  Each model would have
its own E-P field, either explicitly from the forcing or derived from
restoring to salinity.  This is more realistic and straightforward than 
carrying salinity-normalized DIC and Alk in the model and adjusting them only
when computing pCO2 from DIC and Alk.
>   
>   Do we have any thoughts about CaCO3??
>   
>   The difference in treatment of PO4, Alk and DIC could provide a pitfall
>   which a nasty reviewer would enjoy to identify.

I'm not sure what you mean here.  Are you saying that restoring to PO4 and
not DIC and Alk is a problem?  If so, there is no way we can restore to DIC
and Alk, as you know.
>   
>   What about the following suggestion? (I have no experience with restoring
>   models except T and S)
>   
>   for each unit of PO4 we have in the Ocean:
>       -120 of DIC   and    +16   from organic parts
>       -30  of DIC   and    -60 (Alk)  from hard parts
>   
>   
>   as pCO2 is essentially a function of (Alk - DIC) We could subtract
>   the Alk removal from the DIC removal and come out with 150 - 44
>   = 106 (incidentially the classical Redfield number)
>
This is essentially what we proposed, except we used a different rain ratio,
the one suggested by Yamanaka and Tajika (0.07), not the classical value
of 0.25 that you use above.  

What troubles me is that the rain ratio is spatially constant in the model.
The sediment trap data synthesis by Tsonogai and Noriki (Tellus CO2 conference
issue, Hinterzarten) clearly shows that it varies dramatically, at least
between low and high latitudes (much greater in low latitudes).  I'm not sure
how to model this.  HAMOCC3 uses temperature and silica availability to
determine the rain ratio, but are these really the factors that are important?
I really don't know.  ANYONE OUT THERE HAVE ANY IDEAS?  This is really 
important for OCMIP!  The other issue is CaCO3 dissolution in the water
column.  The state of the art now is to have a constant e-folding depth for
dissolution, but clearly it is not this simple--there must be differences,
for example, between the North Atlantic and North Pacific, where the saturation
horizons are at very different depths.

Ray