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| Titel |
Improved routines to model the ocean carbonate system: mocsy 2.0 |
| VerfasserIn |
J. C. Orr, J.-M. Epitalon |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 8, no. 3 ; Nr. 8, no. 3 (2015-03-09), S.485-499 |
| Datensatznummer |
250116173
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| Publikation (Nr.) |
 copernicus.org/gmd-8-485-2015.pdf |
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| Zusammenfassung |
| Modelers compute ocean carbonate chemistry often based on code from
the Ocean Carbon Cycle Model Intercomparison Project (OCMIP), last
revised in 2005. Here we offer improved publicly available Fortran 95
routines to model the ocean carbonate system (mocsy 2.0). Both codes
take as input dissolved inorganic carbon CT and total
alkalinity AT, tracers that are conservative with respect
to mixing and changes in temperature and salinity. Both use the same
thermodynamic equilibria to compute surface-ocean pCO2 and
simulate air–sea CO2 fluxes, but mocsy 2.0 uses a faster
and safer algorithm (SolveSAPHE) to solve the alkalinity-pH equation,
applicable even under extreme conditions. The OCMIP code computes
only surface pCO2, while mocsy computes all other
carbonate system variables throughout the water column. It also
avoids three common model approximations: that density is constant,
that modeled potential temperature is equal to in situ temperature,
and that depth is equal to pressure. Errors from these approximations
grow with depth, e.g., reaching 3% or more for pCO2,
H+, and ΩA at 5000 m. The mocsy
package uses the equilibrium constants recommended for best
practices. It also offers two new options: (1) a recently reassessed
total boron concentration BT that is 4% larger and (2) new
K1 and K2 formulations designed to include
low-salinity waters. Although these options enhance surface
pCO2 by up to 7 μatm, individually, they should
be avoided until (1) best-practice equations for K1 and
K2 are reevaluated with the new BT and (2)
formulations of K1 and K2 for low salinities
are adjusted to be consistent among pH scales. The common modeling
practice of neglecting alkalinity contributions from inorganic
P and Si leads to substantial biases that could easily
be avoided. With standard options for best practices, mocsy agrees
with results from the CO2SYS package within 0.005% for the three
inorganic carbon species (concentrations differ by less than
0.01 μmol kg−1). Yet by default, mocsy's deep-water
fCO2 and pCO2 are many times larger than those
from older packages, because they include pressure corrections for
K0 and the fugacity coefficient. |
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