Merge branch 'maltrud/ocean/seaice-melt-alkalinity' into next (PR #6236)

Assign alkalinity equals DIC in sea ice melt

Set alkalinity of sea ice melt flux into the ocean to be equal to DIC
flux, analogous to what is done with river runoff. Previously the flux
was zero, resulting in unphysical dilution.

Fixes #6210

[BFB] for all current tests

components/mpas-ocean/src/shared/mpas_ocn_tracer_ecosys.F

@@ -1975,6 +1975,8 @@ subroutine ocn_tracer_ecosys_surface_flux_compute(activeTracers, ecosysTracers,
                ecosysSurfaceFlux(fe_ind_MPAS,iCell) + iceFluxFeDissolved(iCell)/parm_Fe_bioavail
             ecosysSurfaceFlux(dic_ind_MPAS,iCell) =  &
                ecosysSurfaceFlux(dic_ind_MPAS,iCell) + iceFluxDIC(iCell)
+            ecosysSurfaceFlux(alk_ind_MPAS,iCell) =  &
+               ecosysSurfaceFlux(alk_ind_MPAS,iCell) + iceFluxDIC(iCell)
             ecosysSurfaceFlux(dic_alt_co2_ind_MPAS,iCell) =  &
                ecosysSurfaceFlux(dic_alt_co2_ind_MPAS,iCell) + iceFluxDIC(iCell)
             ecosysSurfaceFlux(doc_ind_MPAS,iCell) =  &