Introduction

As a good first-order generalization, the noble gases found in natural waters are acquired from air and are present in concentrations approximately consistent with air equilibration. Solubility data (Tables 4.1–4.4 and Fig. 4.1) are thus of central importance in evaluating noble gas observations in water. A comprehensive review and data evaluation for the general phenomenon of gas solution in water is given by Wilhelm et al. (1977).

On the whole, noble gases exhibit about the same order of magnitude of solubility in water as do other gases that do not react chemically with the water. Ar, in particular, is approximately as soluble as the major atmospheric gases: its solubility (pure water at 0°C) is 2.26 times that of N2 and 1.09 times that of O2. As a group, however, the noble gases exhibit a fairly wide spread in solubilities, with the characteristic features of strongly increasing solubility and temperature dependence of solubility with increasing atomic weight. This signature, combined with the useful feature that (with exceptions discussed later) they are conservative – no sources or sinks in organisms or other material in sea water and unlikely to participate in complex chemical reactions – makes the noble gases useful in a variety of geochemical studies.

A noteworthy feature of such studies is that they frequently make the most stringent demands encountered in noble gas geochemistry for high-precision absolute elemental abundances.