WOMBAT: Add N wet and dry flux to ocean surface

[pearseb]

Need to add a wet and dry atmospheric source of NH4 and NO3 to the generic tracers NH4 and NO3 tracers. In the case of WOMBAT-lite, where there isn't an NH4 tracer, we would add both wet and dry fluxes of NH4 and NO3 to the NO3 tracer.

[pearseb]

Hi Dougie. I also just figure out where we want to pull NHx and NOy deposition rates from:

https://data.isimip.org/search/product/InputData/subcategory/n-deposition/tree/ISIMIP3b/

Details are here: https://www.isimip.org/gettingstarted/input-data-bias-adjustment/details/116/
and here: https://www.geo.fu-berlin.de/met/ag/strat/publikationen/docs/Eyring-et-al_SPARC-Newsletter40.pdf
Citation: Jia Yang, Hanqin Tian (2020): ISIMIP3b N-deposition input data (v1.0). ISIMIP Repository. https://doi.org/10.48364/ISIMIP.600567

Things to note:

1. We want to use the present day depositions for any runs with JRA55 normal year forcings (probably 2015, or we could make it inter-annually varying).
2. We want to use the preindustrial depositions (i.e., 1850) for things like the ESM1.6 control simulations.
3. I think for WOMBAT-lite, we combine the variables nhx and noy together and feed these into the NO3 tracer at the surface.
4. For WOMBAT-mid, which has NH4 and NO3 tracers, we would direct nhx to NH4 and noy to NO3.