

The ocean absorbs about a quarter of the anthropogenic carbon dioxide ( CO 2) currently emitted each year ( Friedlingstein et al., 2020).
#Request a software carbonate code
The code for P圜O2SYS is distributed via GitHub (, last access: 23 December 2021) under the GNU General Public License v3, archived on Zenodo ( Humphreys et al., 2021), and documented online (, last access: 23 December 2021).

Finally, we consider potential future developments to P圜O2SYS and discuss the outlook for this and other software for solving the marine carbonate system. We discuss insights that guided the development of P圜O2SYS: for example, the fact that the marine carbonate system cannot be unambiguously solved from certain pairs of parameters. We validate P圜O2SYS with internal consistency tests and comparisons against other software, showing that P圜O2SYS produces results that are either virtually identical or different for known reasons, with the differences negligible for all practical purposes. For example, P圜O2SYS uses automatic differentiation to solve the marine carbonate system and calculate chemical buffer factors, ensuring that the effect of every modelled solute and reaction is accurately included in all its results. We describe the elements of P圜O2SYS that have been inherited from the existing CO2SYS family of software and explain subsequent adjustments and improvements. Here, we present P圜O2SYS, a Python package intended to fill this capability gap. Several software tools exist to carry out these calculations, but no fully functional and rigorously validated tool written in Python, a popular scientific programming language, was previously available. To investigate these processes, at least two of the marine carbonate system's parameters are typically measured – most commonly, two from T C, total alkalinity ( A T), pH, and seawater CO 2 fugacity ( f CO 2 or its partial pressure, p CO 2, or its dry-air mole fraction, x CO 2 ) – from which the remaining parameters can be calculated and the equilibrium state of seawater solved.

Both the exchange of CO 2 between the ocean and atmosphere and the pH response are governed by a set of parameters that interact through chemical equilibria, collectively known as the marine carbonate system. Oceanic T C is increasing through uptake of anthropogenic carbon dioxide ( CO 2), and seawater pH is decreasing as a consequence. Oceanic dissolved inorganic carbon ( T C) is the largest pool of carbon that substantially interacts with the atmosphere on human timescales.
