Spectrophotometric determination of bicarbonate dissociation constants (K2) for freshwater, estuarine, and marine waters over a wide range of temperatures

Le résumé fourni par la source

This study presents the first spectrophotometric determination of K 2 at estuarine conditions (0 ≤ S p ≤ 20; where S p is practical salinity) and over a broad range of temperatures (275.15 ≤ T ≤ 308.15 K; where T is temperature in Kelvin). Spectrophotometric data from Schockman and Byrne (2021) and Schockman et al. (2024) were combined with data obtained in the present study to produce a set of pK 2 (i.e., –log K 2 ) values for the salinity range 0 ≤ S p ≤ 41 and temperature range 275.15 ≤ T ≤ 308.15 K. The resulting set of pK 2 values was fitted as a function of S P and T to obtain a new pK 2 parameterization on the total pH scale: p K 2 = 5.1703 + 2136.77 T −1 – 177788 T −2 – 0.4457 S p 0.5 /(1 + 1.11* S p 0.5 ) + 0.0674 S p /ln T. – 0.0008238 S p 0.5 * T. The random uncertainty in this work is 0.0071 based on the standard deviation of the best-fit p K 2 parameterization. Residuals in the fit (i.e., measured minus parameterized p K 2 values) are approximately two times smaller in magnitude than the residuals obtained in past studies for similar S p and T ranges. The total combined standard uncertainty of p K 2 in this work is 0.0145. Assessments of high-quality total dissolved inorganic carbon ( C T ), total alkalinity ( A T ), and pH data obtained on oceanic research cruises indicate that internal consistency of CO 2 system calculations (comparing measured and calculated values; i.e., comparing measured pH with pH calculated from C T and A T ) is improved when calculations use this K 2 parameterization, especially for the Coastal Ocean Data Analysis Product in North America (CODAP-NA) data set (0.117 ≤ S p ≤ 36.980). As such, this new p K 2 parameterization provides an improved characterization of bicarbonate dissociation constant behavior that encompasses freshwater, estuarine, and open ocean conditions.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.