= Name and subject of the action

Last edition: '''[[Wikinfo(changed_ts)]]''' by '''[[Wikinfo(changed_by)]]'''

The PI is responsible to closely follow the progress of the action, 
and especially to contact NEMO project manager if 
the delay on preview (or review) are longer than the 2 weeks expected.

[[PageOutline(2, , inline)]]

== Summary

||=Action       || Implementation of iceberg and ice shelf Fe source in PISCES ||
||=PI(S)        || Renaud Person                                               ||
||=Digest       || see person et al. (2019), doi: 10.5194/bg-16-3583-2019      ||
||=Dependencies || coupling with feshwater fluxes from ice shelf and iceberg   ||
||=Branch       || source:/NEMO/branches/2020/dev_r{REV}_{ACTION_NAME}         ||
||=Previewer(s) || O.Aumont, C. Éthe                                                    ||
||=Reviewer(s)  || O.Aumont, C. Éthe                                                    ||
||=Ticket       || #2443                                                 ||

=== Description


Based on the development done with NEMO 3.6 of the representation of the external source of Fe from iceberg and ice shelf missing in the PISCES model.


=== Implementation

Representation of the external source of biogeochemical tracers from iceberg and ice shelf.
For instance, for dissoved Fe, a sediment content associated to a solubility fraction of sediment Fe is added to the freshwater fluxes of iceberg and ice shelf. For icebergs, a homogeneous distribution of biogeochemical tracers is applied from the surface to a depth that can be selected in the namelist_top. For the time being, a distribution down to a depth of 120 m is recommended. For ice shelf, the biogeochemical tracer content is distributed homogeneously following the representation of the isf freshwater flux of Mathiot et al. (2017) whether the under ice shelf cavities are open or not. 

File dependency: feshwater fluxes from ice shelf and iceberg:
- runoff-icb_DaiTrenberth_Depoorter_eORCA1_JD.nc
- runoff-icb_DaiTrenberth_Depoorter_eORCA025_JD.nc

This file dependency didn’t exist for ORCA2 configuration as the grid is not extended in Antarctica. As a consequence, there is no representation of ice shelf cavities which are needed to model the distribution of freshwater flux under ice shelves with the parameterizations of Mathiot et al. (2017). Thus, this module can not be activated in ORCA2, the external source of BGC tracers from the Antarctic Ice Sheet is consequently disabled in this configuration.

- Activation in TOP:

Creation of the trcais routine controllable in TOP module, which allows to adjust the concentration of Fe, for now, and of other biogeochemical tracers (potentially later) associated with iceberg and ice shelf freshwater fluxes through a loop over all the biogeochemical tracers. The AIS tracers source can be activated with a boolean in the namelist_top:

ln_trcais     =  .false. !  Antarctic Ice Sheet nutrient supply

!-----------------------------------------------------------------------

&namtrc_ais      !  Representation of Antarctic Ice Sheet tracers supply

!-----------------------------------------------------------------------
   rn_trafac(14) =  4.476e-07   !  (  0.5e-3 / 55.85 * 0.05 )
!
   nn_ais_tr     =  1      !  tracer concentration in iceberg and ice shelf

- 0 is for null concentrations
- 1 for prescribed concentrations

   rn_icbdep     =  120.   ! Mean underwater depth of iceberg (m)

Warning: the isf source has to be activated in the namelist_cfg:
 ln_isf = .true.
then chose one of the two options for isf melt:

 ln_isfcav_mlt = .false. (resolved cavities) 

 or ln_isfpar_mlt = .true. (parameterized)

and activate runoff from icebergs

 ln_rnf_icb  = .true.    ! freshwater flux from icebergs

created routine:
- trcais.F90

List of modified routines:

- nemogcm.F90
- sbcrnf.F90
- trc.F90
- trcini.F90
- trcnam.F90
- trctrp.F90

=== Documentation updates

The documentation describing the implementation and activation of the external source of biogeochemical tracers from the Antarctic ice sheet is currently being drafted. This documentation will be an extension of the above written description.

== Preview 

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== Tests

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Sette tests succesfully passed. See attachment report.

There is no test case associated with this development, for the time being. It is only functional in the eORCA1 and eORCA025 configurations, i.e. configurations with a grid extended in the Southern hemisphere to represent the cavities of ice shelves.

In addition to the Sette tests, validation runs with the eORCA1 configuration (i.e. branch merged with trunk) and with regridded inputs have been performed with this development enabled or disabled. Inputs, namelists, and outputs can be found on the Jean Zay supercomputer (IDRIS) at:

/gpfswork/rech/omr/romr014/eORCA1_Valid_AIS_nutrient_r13541_merged_with_trunk/

== Review

I reviewed the code. The different aspects and processes have been properly coded according to my review. The choices make sense and the different tests have been successfully passed. I don't have any significant comments or changes to suggest. This branch is ready to be merged in the trunk.