[MITgcm-support] Phosphate (PO4) concentration deviates in Offline mode

[Manfredi Manizza]

Hi Kaushai,

I would say that if your PO4 conc. increases it means that your sink term
in the equation is either zero or almost zero.

One possibility  could be that there is a problem in the term of PO4
equation of biological
drawdown of PO4 (that mimics the uptake by phytoplankton).
In this case first  you might want to check if the model reads correctly
the light fields from surface to
depth (top 200 m). Normally the seasonal cycle of PO4 at the surface
should follow the the opposite of light availability
especially in the polar oceans (I assume you work in that environment if
you use shelfice...)

Furthermore, normally the buildup of nutrients is at depth where the POP
gets remineralized and then it gets
converted into inorganic PO4 and then winter convection replenished the
values in the top boxes of the model.


At which depth do you see this problem? At all the depths? Surface ? Bottom?

> Somehow the parametrization for remineralization of particulate organic
matter (POP) does not work well in the offline mode (MITgcm/
pkg/dic/phos_flux.F)
IF you have no remineralization of POP you could not have an increase in
PO4, for instance.

I hope this helps to make some progress on your debugging.

Cheers
Manfredi






On Tue, Aug 11, 2020 at 1:19 PM Kaushal Gianchandani <
Kaushal.G at mail.huji.ac.il> wrote:

> Hello everyone
>
> I am currently using MITgcm to model the biogeochemistry in the context of
> paleoclimate. For the same, I have created an offline 2d model that uses
> the packages: dic, gchem, ptracers in conjunction with shelfice.
>
> I am facing a problem with the concentration of the nutrient (phosphate -
> PO4) in the model --- the concentration does not reach a steady-state.
> After just a few years of integration, the concentration deviates
> significantly from what it should be. In fact, the initial concentration of
> PO4 increases well beyond what I initially start with.
>
> I have gone through many threads provided in [MITgcm-support] dealing with
> similar problems but none of the solutions listed there worked for my
> problem. I have already tried the following:
> 1. Used the model with only dissolved organic phosphorus (DOP) and PO4 ---
> no problem in this case. The net Phosphorus is conserved and both PO4 and
> DOP concentrations reach a steady-state. Somehow the parametrization
> for remineralization of particulate organic matter (POP) does not work well
> in the offline mode (MITgcm/pkg/dic/phos_flux.F)
> 2. Running the model without the shelfice package --- the problem
> persists.
> 3. Verified that the PTRACERS_EvPrRn is unset.
>
> Please note that the online model with the same configuration works well.
> I'd really appreciate any help in this regard.
>
> Thank you,
>
> Regards,
> Kaushal.
>
> --
>
> *Kaushal Gianchandani*Ph.D. Student in Oceanography
> Fredy & Nadine Herrmann Institute of Earth Sciences
> Hebrew University of Jerusalem, Israel
> Phone: +972-50-471-4621
> web: https://kaushalgianchandani.github.io
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-- 

Dr. Manfredi Manizza
Geosciences Research Division
Scripps Institution of Oceanography
University of California San Diego
9500 Gilman Drive La Jolla, CA 92093-0244
email : mmanizza at ucsd.edu
tel   : +1-858-534-7094
web   : http://bluemoon.ucsd.edu/mmanizza/
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