The isothermal compressibility of seawater near one atmosphere

Abstract The isothermal compressibility of artificial seawater has been measured by a piezometric technique from 0 to 40‰ S in 5‰ intervals and from 0 to 40°C in 5° intervals. The measurements were made at 17 bar increments to 34 bars and the data extrapolated to one atmosphere. Compressibility determinations on a Copenhagen seawater sample ( ∼35‰S ) over the same temperature and pressure range yielded results that agreed with the artificial seawater results (within our experimental error of ±0·05 × 10−6 bar−1). The isothermal compressibility results at one atmosphere and 35‰ are in excellent agreement with the values calculated from Wilson's (1960) sound velocity data; however, our results disagree with the P-V-T data of Ekman (1908), Newton and Kennedy (1965) and Wilson and Bradley (1968). The normalized compressibilities of Ekman show excellent agreement with Wilson's and our results. A theoretical equation for the compressibility of seawater as a function of chlorinity has been developed in terms of the apparent equivalent compressibility of the major ionic components of seawater. The theoretically calculated isothermal compressibilities of seawater at 25° agree very well with the experimental results (to within ±0·09 × 10−6 bar−1).

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