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conserving global alk

Dear Ray and OCMIP modelers,

We have some questions regarding the conservation of the global
inventories of alkalinity and total phosphorus (DOP+PO4). They arose from
considerations related to the discussion of fresh water fluxes in section
4 of the design document.

As the biological model is now described, the global inventory of DOP+PO4
is conserved, but not necessarily either separately. Since Alk is coupled
to PO4 via nitrate, the global inventory of Alk is not necessarily
conserved. However, the inventory of Alk + r_{N:P} PO4 is conserved.

So one option for compensate for global P-E imbalances, and other
numerical artifacts as described below, is to periodically adjust Alk so
that Alk + r_{N:P} PO4 is actually conserved.

Another option is to modify the biological model so that PO4 is conserved,
but maintain the coupling of Alk to PO4. Then, to compensate for global
P-E imbalances, one could periodically adjust Alk so that Alk itself is

What are your thoughts on these options?

With respect to the conservation of DOP+PO4, our model uses acceleration
in the deep ocean, which prevents exact global conservation. We intend to
occasionally (annually) rescale DOP & PO4 to correct for this. Is this
acceptable in the OCMIP framework?


Keith Lindsay                              phone: 303-497-1722
Climate and Global Dynamics                fax:   303-497-1700
National Center for Atmospheric Research   email: klindsay@cgd.ucar.edu
P.O. Box 3000
Boulder, CO  80307-3000