Add MARBL to MOM6

[mnlevy1981]

I'm working on adding a new tracer module that calls MARBL, and I've reached a point where it might be useful for other people (e.g. @ashao) to look at the mods I'm making. There will also be a PR to ESCOMP/MOM_Interface necessary to get this running through CESM, and I'll link to that PR once it has been made.

[mnlevy1981]

@marshallward -- we (@alperaltuntas, @gustavo-marques, @klindsay28, and I) are starting the review process of this PR, and had a couple of questions that I hope you can answer:

1. I created src/tracer/tracer_forcing_utils.F90, a module that extends the interface to time_interp_external to allow things like "use the first time level of a forcing file until model year X" or "after model year Y, use the last time level of a forcing file." I put it in src/tracer/ thinking it would be useful for both the MARBL tracer module and the CFCs but it's not really tracer-specific. Do you have a recommendation for location and / or name? We were thinking maybe src/framework or src/core.
2. I made modifications to src/initialization/MOM_tracer_initialization_from_Z.F90 to make the default values of Z_INIT_ALE_REMAPPING and Z_INIT_REMAPPING_SCHEME match what is in MOM_state_initialization.F90. Should I be using do_not_log=.true. instead? (There are also get_param() calls in my MARBL-specific modules to things like INPUTDIR where I opted to repeat the existing default rather than use do_not_log.)

I'd welcome general feedback here as well, though we're still going through the detailed code review so it might make sense to wait until I've had a chance to fix the issues raised from that (or wait until we try to get this to main on mom-ocean/MOM6)

[marshallward]

1. I created src/tracer/tracer_forcing_utils.F90, a module that extends the interface to time_interp_external to allow things like "use the first time level of a forcing file until model year X" or "after model year Y, use the last time level of a forcing file." I put it in src/tracer/ thinking it would be useful for both the MARBL tracer module and the CFCs but it's not really tracer-specific. Do you have a recommendation for location and / or name? We were thinking maybe src/framework or src/core.

If its purpose is to provide some fine-grain control over time_interp_external(), then I would say it belongs in src/framework, possibly even move the content to MOM_interpolate.F90. I don't know exactly how the new function connects to time_interp_external, but I could see adding the new type as either an optional argument or as an alternative to the existing time_interp_external arguments (although maybe I'm being too creative here).

In any case, I agree it looks very general purpose and potentially useful to others, and it would be good to move outside of src/tracer, although there might need to be some discussion about the implementation.

2. I made modifications to src/initialization/MOM_tracer_initialization_from_Z.F90 to make the default values of Z_INIT_ALE_REMAPPING and Z_INIT_REMAPPING_SCHEME match what is in MOM_state_initialization.F90. Should I be using do_not_log=.true. instead? (There are also get_param() calls in my MARBL-specific modules to things like INPUTDIR where I opted to repeat the existing default rather than use do_not_log.)

do_not_log is generally only used when the parameter has already been read, and we don't want it appear twice in MOM_parameter_doc.*. I suppose it might need a just_read argument similar to MOM_temp_salt_initialize_from_Z, but it's hard for me to tell from just looking. I suppose if it appears twice in MOM_parameter_doc.all, then yes, you need do_not_log=.true. or something similar 😄 .

[mnlevy1981]

21529b9 addressed most of the concerns from code review. Still remaining

• Call MARBL_tracer_stocks from MOM_tracer_flow_control:call_tracer_stocks()
• Can of worms in MOM_tracer_flow_control:get_chl_from_model: need better logic for when to get chlorophyll from generic tracers vs getting it from MARBL_tracers (perhaps a CS flag get_chl_from_generic_tracers that defaults to True but gets set to False if MARBL is running with base biotic tracers?)
• I also haven't made any changes based on @marshallward's suggestions in Add MARBL to MOM6 #157 (comment)

I'll note that I ignored two suggestions from the review:

1. I wrote down that I should change FESEDFLUX units from conc m/s -> conc Z/T, but this is a forcing file that never gets converted from physical units to model units
2. There was a comment in MOM_forcing_type.F90 (!These fields should only be allocated when USE_MARBL is activated.) that I was going to remove, but in the context of the other calls to myAlloc() I think we want to leave it in.

Next steps:

• finish the checklist above
• update MARBL Support ESCOMP/MOM_interface#92 based on review so I can test solo_driver
• merge latest dev/ncar here and main in MOM_interface, and test in latest CESM tag

[mnlevy1981]

As of 97c0917 I've addressed all the concerns raised in code review, and only see expected test failures (MacOS-related). I'll leave this in draft mode while addressing the companion PR at MOM_interface.

[mnlevy1981]

(I may also need to merge in the latest dev/ncar; I wanted to address all the code review comments in my cesm2_3_alpha17f sandbox before moving to the cesm3_0 alpha / beta tags)

[alperaltuntas]

This line causes a memory leak. Any fix suggestions @mnlevy1981 ?