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Subsections
6.7.2 DIC Package
This is one of the biogeochemical packages handled from the
pkg gchem. The main purpose of this package is to consider
the cycling of carbon in the ocean. It also looks at the
cycling of phosphorous and oxygen. There are five tracers
 ,  ,  ,  and  . The air-sea exchange
of CO and O are handled as in the OCMIP experiments
(reference). The export of biological matter is computed
as a function of available light and PO . This export is
remineralized at depth according to a Martin curve (again,
this is the same as in the OCMIP experiments). There is
also a representation of the carbonate flux handled as in
the OCMIP experiments. The air-sea exchange on CO
is affected by temperature, salinity and the pH of the
surface waters. The pH is determined following the
method of Follows et al.
INITIALIZATION
DIC_ABIOTIC.h contains the common block for the
parameters and fields needed to calculate the air-sea
flux of  and  . The fixed parameters are set in
dic_abiotic_param which is called from gchem_init_fixed.F.
The parameters needed for the biotic part of the calculations
are initialized in dic_biotic_param and are stored
in DIC_BIOTIC.h. The first guess of pH is calculated
in dic_surfforcing_init.F.
LOADING FIELDS
The air-sea exchange of and need wind, atmospheric
pressure (although the current version has this hardwired to 1),
and sea-ice coverage. The calculation of pH needs silica fields.
These fields are read in in dic_fields_load.F. These
fields are initialized to zero in dic_ini_forcing.F.
The fields for interpolating are in common block in
DIC_LOAD.h.
FORCING
The tracers are advected-diffused in ptracers_integrate.F.
The updated tracers are passed to dic_biotic_forcing.F
where the effects of the air-sea exchange and biological
activity and remineralization are calculated and the tracers
are updated for a second time. Below we discuss the
subroutines called from dic_biotic_forcing.F.
Air-sea exchange of is calculated in dic_surfforcing.
Air-Sea Exchange of depends on T,S and pH. The determination
of pH is done in carbon_chem.F. There are three subroutines
in this file: carbon_coeffs which determines the coefficients
for the carbon chemistry equations; calc_pco2 which calculates
the pH using a Newton-Raphson method; and calc_pco2_approx
which uses the much more efficient method of Follows et al.
The latter is hard-wired into this package, the former is kept
here for completeness.
Biological productivity is determined following
McKinely et al. and is calculated in bio_export.F
The light in each latitude band is calculate in insol.F.
The formation of hard tissue (carbonate) is linked to
the biological productivity and has an effect on the
alkalinity - the flux of carbonate is calculated in
car_flux.F. The flux of phosphate to depth where
it instantly remineralized is calculated in phos_flux.F.
Alkalinity tendency comes from changes to the salinity from
addition/subtraction of freshwater in the surface. This
is handled in alk_surfforcing.F.
Oxygen air-sea exchange is calculated in o2_surfforcing.F.
DIAGNOSTICS
Averages of air-sea exchanges, biological productivity,
carbonate activity and pH are calculated. These are
initialized to zero in dic_biotic_init and
are stored in common block in DIC_BIOTIC.h.
This package must be run with both ptracers and gchem enabled.
It is set up for 5 tracers, but there is the provision of
a 6th tracer (iron) that is not discussed here.
6.7.2.5 Experiments and tutorials that use dic
- Global Ocean tutorial, in tutorial_global_oce_biogeo verification directory,
described in section 3.17
Next: 7. Diagnostics and I/O
Up: 6.7 Biogeochemistry Packages
Previous: 6.7.1 GCHEM Package
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