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\subsection {DIC Package} |
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\label{sec:pkg:dic} |
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\subsubsection {Introduction} |
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This is one of the biogeochemical packages handled from the |
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pkg gchem. The main purpose of this package is to consider |
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the cycling of carbon in the ocean. It also looks at the |
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cycling of phosphorous and oxygen. There are five tracers |
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$DIC$, $ALK$, $PO4$, $DOP$ and $O2$. The air-sea exchange |
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of CO$_2$ and O$_2$ are handled as in the OCMIP experiments |
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(reference). The export of biological matter is computed |
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as a function of available light and PO$_4$. This export is |
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remineralized at depth according to a Martin curve (again, |
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this is the same as in the OCMIP experiments). There is |
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also a representation of the carbonate flux handled as in |
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the OCMIP experiments. The air-sea exchange on CO$_2$ |
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is affected by temperature, salinity and the pH of the |
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surface waters. The pH is determined following the |
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method of Follows et al. |
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\subsubsection {Key subroutines and parameters} |
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\noindent |
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{{\bf INITIALIZATION}} \\ |
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{\it DIC\_ABIOTIC.h} contains the common block for the |
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parameters and fields needed to calculate the air-sea |
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flux of $CO_2$ and $O_2$. The fixed parameters are set in |
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{\it dic\_abiotic\_param} which is called from {\it gchem\_init\_fixed.F}. |
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The parameters needed for the biotic part of the calculations |
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are initialized in {\it dic\_biotic\_param} and are stored |
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in {\it DIC\_BIOTIC.h}. The first guess of pH is calculated |
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in {\it dic\_surfforcing\_init.F}. |
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\vspace{.5cm} |
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\noindent |
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{{\bf LOADING FIELDS}}\\ |
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The air-sea exchange of $CO_2$ and $O_2$ need wind, atmospheric |
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pressure (although the current version has this hardwired to 1), |
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and sea-ice coverage. The calculation of pH needs silica fields. |
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These fields are read in in {\it dic\_fields\_load.F}. These |
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fields are initialized to zero in {\it dic\_ini\_forcing.F}. |
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The fields for interpolating are in common block in |
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{\it DIC\_LOAD.h}. |
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\vspace{.5cm} |
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\noindent |
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{{\bf FORCING}}\\ |
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The tracers are advected-diffused in {\it ptracers\_integrate.F}. |
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The updated tracers are passed to {\it dic\_biotic\_forcing.F} |
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where the effects of the air-sea exchange and biological |
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activity and remineralization are calculated and the tracers |
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are updated for a second time. Below we discuss the |
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subroutines called from {\it dic\_biotic\_forcing.F}. |
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Air-sea exchange of $CO_2$ is calculated in {\it dic\_surfforcing}. |
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Air-Sea Exchange of $CO_2$ depends on T,S and pH. The determination |
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of pH is done in {\it carbon\_chem.F}. There are three subroutines |
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in this file: {\it carbon\_coeffs} which determines the coefficients |
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for the carbon chemistry equations; {\it calc\_pco2} which calculates |
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the pH using a Newton-Raphson method; and {\it calc\_pco2\_approx} |
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which uses the much more efficient method of Follows et al. |
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The latter is hard-wired into this package, the former is kept |
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here for completeness. |
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Biological productivity is determined following |
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McKinely et al. and is calculated in {\it bio\_export.F} |
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The light in each latitude band is calculate in {\it insol.F}. |
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The formation of hard tissue (carbonate) is linked to |
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the biological productivity and has an effect on the |
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alkalinity - the flux of carbonate is calculated in |
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{\it car\_flux.F}. The flux of phosphate to depth where |
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it instantly remineralized is calculated in {\it phos\_flux.F}. |
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Alkalinity tendency comes from changes to the salinity from |
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addition/subtraction of freshwater in the surface. This |
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is handled in {\it alk\_surfforcing.F}. |
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Oxygen air-sea exchange is calculated in {\it o2\_surfforcing.F}. |
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\vspace{.5cm} |
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\noindent |
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{{\bf DIAGNOSTICS}}\\ |
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Averages of air-sea exchanges, biological productivity, |
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carbonate activity and pH are calculated. These are |
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initialized to zero in {\it dic\_biotic\_init} and |
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are stored in common block in {\it DIC\_BIOTIC.h}. |
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\subsubsection{Do's and Don'ts} |
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This package must be run with both ptracers and gchem enabled. |
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It is set up for 5 tracers, but there is the provision of |
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a 6th tracer (iron) that is not discussed here. |
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\subsubsection{Reference Material} |
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\subsubsection{Experiments and tutorials that use dic} |
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\label{sec:pkg:dic:experiments} |
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\begin{itemize} |
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\item{Global Ocean tutorial, in tutorial\_global\_oce\_biogeo verification directory, |
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described in section \ref{sect:eg-biogeochem_tutorial} } |
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\end{itemize} |
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