= Name and subject of the action

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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 missing external source of Fe from iceberg and ice shelf in the PISCES model


=== Implementation

{{{#!box width=35em help
Describe flow chart of the changes in the code. \\
List the Fortran modules and subroutines to be created/edited/deleted. \\
Detailed list of new variables to be defined (including namelists), \\
give for each the chosen name and description wrt coding rules.
}}}

Fe is actualized according to the external sources of Fe from iceberg and ice shelf.
A sediment content associated to a solubility fraction of sediment Fe is added to the freshwater fluxes of iceberg and ice shelf. For ice shelf, the parameterization of Mathiot et al. (2017) is used for the distribution of Fe throughout the water column. For iceberg, a homogeneous distribution until 120 m of depth is applied.

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

This file dependency didn’t exist for ORCA2 grid. I have build one but roughly interpolated. Another issue with the ORCA2 configuration is that the grid is not extended in the Antarctic. There is no representation of ice shelf cavities which are needed to model the distribution of freshwater flux under ice shelves with the parameterization of Mathiot et al. (2017) used in the present development.

Consequently, this external of source Fe will be disabled in the ORCA2 configuration.

Two options are possible to implement the development of the AIS Fe source:
- Activation in PISCES: namelist_pisces (originally developed)
- Activation in TOP: namelist_top

We opt for the generic solution by creating a trc_ais routine controllable in the TOP module and allowing to adjust the concentration of Fe and of other nutrients as well as DIC and Alkalinity in icebergs and ice shelves through a loop over all the biogeochemical tracers. This AIS tracers source will be activated with a boolean in the namelist_top named, for instance, ln_aistrc.

Starting point to create the trc_ais routine (3 subroutines): 
- trc_sbc (trc_bc?) for the structure
- trc_ice for initialization, calling/reading of the 24 bgc tracers
- p4zsed for interpolation and read freshwater flux from icebergs and ice shelves

To be added in the namelist_top
- isffeinput: Fraction of bioavailable iron in ice shelves
- icbfeinput: Fraction of bioavailable iron in iceberg
- icbdepth: surface distribution (0) or throughout the water column until 120 m (1)

Do we use the same value fraction of bioavailable iron for both sources?

Warning: the isf source has to be activated in the namelist_cfg: parameter nn_isf >0 

Orginally (activated in namelist_pisces_cfg  with boolean ln_ironice)

Modified routines: p4zsed, p4zsbc

Intermediate variables created to compute ziron variable: 
- zironberg: iron from iceberg freshwater flux
- zironisf: iron from ice shelves freshwater flux


originally modified routines :
- p4zsbc.F90 
- p4zsed.F90

Intermediate variables to compute ziron variable in p4zsed:\\ 
- zironberg : "iron from iceberg freshwater flux"\\
- zironisf  : "iron from ice shelf freshwater flux"

In namelist_pisces, 3 parameters were added:\\
- isffeinput : "Fraction of bioavailable iron from ice shelves"\\
- icbfeinput : "Fraction of bioavailable iron from icebergs"\\
- icbdep : "Mean underwater depth of iceberg (level depth)"

=== Documentation updates

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Using previous parts, define the main changes to be done in the NEMO literature 
(manuals, guide, web pages, …).
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== Preview 

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[[Include(wiki:Developers/DevProcess#preview_)]]
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== Tests

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[[Include(wiki:Developers/DevProcess#tests)]]
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== Review

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[[Include(wiki:Developers/DevProcess#review)]]
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