Move MOM_generic_tracer.F90 to ocean_BGC?

[yichengt900]

Following #790, the MOM_generic_tracer.F90 file has been relocated from MOM6/src/tracer to MOM6/config_src/external/GFDL_ocean_BGC as a reference and archive. For COBALTv3, a copy of MOM_generic_tracer.F90 has been added to the CEFI ocean_BGC repository to ensure it does not impact the build process.

It might be worthwhile to also include a COBALTv2-compatible version of MOM_generic_tracer.F90 in the main branch of ocean_BGC. This would help users still working with COBALTv2 avoid disruptions. @nikizadehgfdl, if this seems like a good approach, I can open a PR to implement it. Let me know your thoughts. CC @theresa-morrison

[dougiesquire]

@yichengt900, @theresa-morrison we use generic tracers in a few of our models and maintain our own fork of this repository. Unfortunately I missed the recent MOM developer meetings where NOAA-GFDL/MOM6#790 was discussed as I was on parental leave.

Could you clarify the differences between the COBALTv2- and COBALTv3-compatible MOM_generic_tracer.F90 so that we can decide on the right way forward for our fork?

[yichengt900]

@dougiesquire, the main updates to the MOM_generic_tracer.F90 file for COBALTv3 compatibility, compared to COBALTv2, include the addition of two new optional arguments: geolat and photo_acc_dpth (mixed layer depth for phytoplankton photoacclimation) in the generic_tracer_source subroutine. The calculation of photo_acc_dpth has also been added to MOM_generic_tracer.F90, which is essential for the enhanced phytoplankton photoacclimation dynamics introduced in COBALTv3. This improvement enables a better representation of observed chlorophyll patterns. Additionally, we’ve introduced an optional tracer sponge feature, allowing users to nudge specific BGC tracers. All other aspects remain largely unchanged.

[dougiesquire]

Great, thanks for those details @yichengt900. Some of those changes sound very relevant to our plans. Do you know whether the changes will eventually make it back to this repo (NOAA-GFDL/ocean_BGC)? Or is the intention to keep them only in NOAA-CEFI-Regional-Ocean-Modeling/ocean_BGC. If the latter, it may make more sense for us to have NOAA-CEFI-Regional-Ocean-Modeling/ocean_BGC as our upstream.

[yichengt900]

@dougiesquire, we do plan to bring all our new enhancements in COBALTv3 back to NOAA-GFDL/ocean_BGC for GFDL ESM4.5 as well as CMIP7. In fact, we are currently in the middle of the cleanup process. Once it’s complete, those changes will be pushed here.