The concentration and isotopic fractionation of gases dissolved in freshwater in equilibrium with the atmosphere. 1. Oxygen

Abstract

Equations and tables are presented from which accurate values can be obtained, in any of several sets of units, for the concentration of oxygen dissolved in freshwater in equilibrium with the atmosphere from 0° to 40°C and 0.5 to 1.1 atm. The y are based on values for the Henry coefficient of oxygen, ko, which have an estimated accuracy of 0.02%. Equations are derived which relate ko to equilibrium concentrations in natural waters. The equations include corrections for molecular interactions in the vapor phase. Uncertainty about the best way to correct for these interactions limits the estimated accurracy of the derived values to about ± 0.07% at 0°C and 0.04% at 40°C, but the new results are much more accurate than values from the UNESCO tables. Within their random errors, previous measurements agree very well with the new results. Under equilibrium conditions, and between 0° and 60°C, the per mil difference between the 34 O 2:32 O 2 abundance ratio in the dissolved gas and the air is given by δ = −0.730 + (427/T), where T is in kelvin and the standard deviation is <0.02‰.