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more CaCO3 dissolution



>   From maier-reimer@dkrz.de Tue Jun 30 07:30 EDT 1998
>   From: maier-reimer@dkrz.de (E.Maier-Reimer)
>   Subject: Re: CaCO3 dissolution
>   To: najjar@essc.psu.edu (Ray Najjar)
>   Date: Tue, 30 Jun 1998 13:29:39 +0200 (MET DST)
>   MIME-Version: 1.0
>   Content-Transfer-Encoding: 7bit
>   
>   
>   Dear Ray,
>   of course, I did my suggestion against better knowledge.
>   The reason was for simplicity and reduction of fruitless
>   discussions. Do you have any evidence that the rain ratio
>   0.07 (I've seen the paper but now forgotten where) works
>   within the framework of our models with a reasonable
>   profile of alkalinity? I doubt. It could be for the wrong reasons.
>   If you do PO4 and alkalinity restoring you should be able
>   to compute the rainratio (depending, of course, from the assumed
>   rxponential profile). I would like to see the fig (number).
>   When Wally, long time ago, did the estimate of 0.25 he simply
>   overlooked the thermodynamical contribution ( pers. comm.).
>   He favours 0.2 now.
>   Cheers
>   Ernst
>

Ernst:

The paper I suggest looking at is

Yamanaka, Y. and E. Tajika. 1996. The role of the vertical fluxes of
particulate organic matter and calcite in the oceanic carbon cycle: studies
using an ocean biogeochemical circulation model. Global Biogeochem. Cycles, 10,
361-382.

They make the case, very nicely, I think, for a lower rain ratio.  The
important point is at what depth you define the rain ratio.  If it is at the
thermocline, as Wally did, then 0.2-0.25 is correct.  But clearly the rain
ratio will be smaller if you define it at the base of the euphotic zone
because of the smaller length scale for org C remineralization with respect
to CaCO3 dissolution.

Yamanaka and Tajika argue that 0.06-0.08 agrees well with sediment trap
data, though it is not terribly clear how the comparison is done. YASU,
CAN YOU COMMENT ON THIS?  But 0.06-0.08 and a dissolution length scale of
3500 m does give the best fit to the alkalinity distribution in their model.
Now you can certainly argue that this is a model-dependent result to some
extent, and I would agree.  It's the best we have, however, in my opinion.
These numbers also agree pretty well with the Anderson and Sarmiento (1994)
Redfield ratio calculations.

A related point with regard to CaCO3 dissolution is that the alkalinity data
do show shallower dissolution in the Indian and Pacific with respect to the
Atlantic, as pointed out by Anderson and Sarmiento (1994).  This tells
me that we ultimately need a more mechanistic approach to CaCO3 modeling.

Ray