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- Title
Comparison of ten packages that compute ocean carbonate chemistry.
- Authors
Orr, J. C.; Epitalon, J.-M.; Gattuso, J.-P.
- Abstract
Marine scientists often use two measured or modeled carbonate system variables to compute others. These carbonate chemistry calculations, based on well-known thermodynamic equilibria, are now available in a dozen public packages. Ten of those were compared using common input data and the set of equilibrium constants recommended for best practices. Current versions of all 10 packages agree within 0.2 µatm for pCO2, 0.0002 units for pH, and 0.1 µmol kg-1 for CO32- in terms of surface zonal-mean values. That represents more than a 10-fold improvement relative to outdated versions of the same packages. Differences between packages grow with depth for some computed variables but remain small. Discrepancies derive largely from differences in equilibrium constants. Analysis of the sensitivity of each computed variable to changes in each constant reveals the general dominance of K1 and K2 but also the comparable sensitivity to KB for the AT-CT input pair. Best-practice formulations for K1 and K2 are implemented consistently among packages. Yet with more recent formulations designed to cover a wider range of salinity, packages disagree by up to 8 µatm in pCO2, 0.006 units in pH, and 1 µmol kg-1 in CO32- under typical surface conditions. They use different proposed sets of coefficients for these formulations, all of which are inconsistent. Users would do well to use up-to-date versions of packages and the constants recommended for best practices.
- Subjects
CARBONATES; MARINE scientists; NUMERICAL calculations; THERMODYNAMIC equilibrium; PH effect
- Publication
Biogeosciences, 2015, Vol 12, Issue 5, p1483
- ISSN
1726-4170
- Publication type
Article
- DOI
10.5194/bg-12-1483-2015