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Re: Biotic HOWTO

Hi Ann,

Thanks for your comments about the positivity.  I cc'd your message to the
OCMIP mailing list since others may want to try your approach and contact you
for the details and any questions.  I prefer to let individual modeling 
groups to solve numerical problems (such as positivity) as they see fit, since
different groups employ different numerical schemes.

About the CaCO3, no, not all of the CaCO3 precipitated is dissolved in the
bottom grid box.  The dissolution has a length scale of 3500 m.  Any flux
that reaches the bottom is dissolved there.  In this way, Ca2+ is conserved
since all that is removed above 75 m is instantaneously redistributed below.

Just to be clear, "compensation depth" does not refer to the CCD!  It refers
to, essentially, the euphotic zone depth, and maybe I should have used that
term to avoid confusion. 

Hope that helps.


>   From mouchet@astro.ulg.ac.be Fri Feb  5 02:38 EST 1999
>   Date: Fri, 5 Feb 1999 08:38:37 +0100 (MET)
>   From: Anne Mouchet <mouchet@astro.ulg.ac.be>
>   Subject: Biotic HOWTO
>   To: najjar@essc.psu.edu
>   Cc: orr@lsce.saclay.cea.fr, mouchet@astro.ulg.ac.be
>   MIME-Version: 1.0
>   Content-MD5: xdq2pCnj+FGKwpAVnFUzUw==
>   Ray,
>   Here are some remarks related to the biotic HowTo:
>   -  Positivity of DOP can be easily achieved by calculating the -k.[DOP] term
>      in an implicit way.
>      If one does solve the whole system at once (that is source/sinks are
>      solved together with transport) then the equations for PO4 and DOP are
>      to be solved together in order to achieve conservation but there is no
>      other problem than a little headache the first time one tries it (and 
>      nothing that aspirin can't help). That's how I do it.
>      If source/sinks terms are evaluated at some intermediate
>      stage then it is straightforward to include that formulation in the code.
>      I tried to find a similar way of solving PO4 so as to ensure positivity
>      but the only solution I found looks quite complicated due to the requirement
>      of conservation.
>      When using the nutrient-restoring formulation did you notice a link between
>      tau value and positivity? I guess that parameter has some influence.
>   -  One aspect in the description of CaCO3 related processes is not clear to me.
>      Does all the CaCO3 that is precipitated has to dissolve in the deepest mesh   
>      or only if that mesh is below the compensation depth?
>      In that case what does happen to the lost DIC and Alk?
>   Have a nice day,
>   Anne