Journal Article

Using Kgen to Generate Cross‐Verified Apparent Equilibrium Constants (K∗’s) for Palaeoseawater Carbonate Chemistry

Whiteford, Ross, Branson, Oscar, Mayk, Dennis

2025

Overview

Quantification of palaeo pH and palaeo CO2 from marine proxies requires the use of apparent equilibrium constants (K∗’s). The K∗’s required to calculate seawater carbonate chemistry are described by empirically determined calibrations, and for palaeoseawater these calibrations must be adjusted to account for changes in seawater composition. There are a number of possible calibrations that can be used to calculate K∗’s, and each software package for calculating carbonate chemistry separately implements these K∗ calibrations, which are manually verified against previous implementations. Palaeo applications typically only implement a single calibration for each K∗, but have additional complexity from the need to adjust each calibration for changing seawater composition through time. The fragmented approach to K∗ calculation can result in unintended and difficult to resolve discrepancies between outputs calculated by different pieces of software. We present “Kgen,” a synchronised collection of three pieces of software to consistently calculate palaeoseawater K∗’s in Python, R, and Matlab. Kgen provides a simple, and nearly identical interface in each language. Through use of a Continuous Integration/Continuous Delivery (CI/CD) pipeline, Kgen guarantees consistent outputs between languages by automatically cross‐checking results from all three implementations. Unifying the approach to K∗ calculation in this way provides an extensible platform for verifiable K∗ generation for palaeoseawater, which can be integrated into existing carbon speciation calculators to improve the consistency of results. Plain Language Summary To calculate how various compounds in seawater behave (chemically speaking), it is necessary to calculate what are known as “apparent equilibrium constants” (denoted by the symbol K∗). These K∗’s are used to determine proportions of compounds which are present in seawater in a variety of forms. K∗’s are also sensitive to the chemical make‐up of seawater, which has changed through time. Before the work presented here, K∗ calculation was usually done as a necessary aside within other software. This is an issue, because different pieces of software can calculate them in subtly different ways (in particular the adjustment for changing chemical composition), which leads to differences in the outputs of these packages which are difficult to resolve. In this work, we present a software package called Kgen that is exclusively devoted to calculating K∗’s. The software is co‐written in three programming languages that are routinely used for seawater calculations, and we integrate an automatic testing procedure to guarantee that all three languages always produce the same results. Kgen provides a more coherent approach to K∗ generation that can be integrated into existing software. Key Points Kgen is a software package to calculate apparent equilibrium constants for palaeoseawater carbonate system calculations Kgen accounts for the influences of temperature, pressure, salinity, magnesium concentration, and calcium concentration We provide a new implementation of the MyAMI model (“pymyami”) to adjust apparent equilibrium constants for changing seawater composition

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Calculators / Calibration / Carbon dioxide / carbonate chemistry / Carbonates / Chemical equilibrium / Chemistry / equilibrium constants / K's / Seawater / Seawater composition