Sound speed contributions of solutes in water

Abstract

Understanding sound speed in natural waters is utilized in applications such as echo sounding, side scanning, temperature field tomography, evaluating compressibility and thermodynamic properties. While established approaches, such as the UNESCO formula and TEOS‐10 package, describe sound speed in oceanic waters, the information about the contributions of specific solutes in water environments, however, is very scarce. In this work, we present systematic experimental data on the contribution of various electrolytes to sound speed in water, covering a temperature range from 1°C to 30°C and concentrations up to 0.05 mol L ⁻¹ , which covers fully the freshwater range and goes slightly beyond it. We observed no evidence of nonlinearities both for temperature and concentration dependences within the studied range and our accuracy. Coefficients for calculating sound speed excess are provided for a range of salts containing all major ions commonly found in natural waters. Sound speed contributions in mixtures of salts can be directly added up and coefficients of the unmeasured ionic combinations can be numerically evaluated. Using our data, isothermal and adiabatic compressibility as well as in situ density can be calculated with an enhanced accuracy for any composition of common solutes. A numerical tool for evaluating sound speed at given ionic composition within the limnic pressure and temperature range has been developed.