Heat capacity of seawater solutions from 5° to 35°C and 0.5 to 22‰ chlorinity

Abstract

The specific heat of seawater solutions from 0.5 to 22‰ chlorinity has been determined at 5°, 15°, 25°, and 35°C by using a new precision heat capacity calorimeter (Picker et al., 1971). The concentration dependence Cl (‰) of the specific heats cp has been fit to cp = cp° + ACp Cl (‰) + BCp Cl (‰)3/2, where cp° is the specific heat of pure water and ACp and BCp are temperature-dependent constants. The specific heats fit this equation with an average deviation of ±0.0002 joule deg−1 g−1 between 15° and 25°C and ±0.0005 joule deg−1 g−1 at 5°C. The specific heats determined in this study are in excellent agreement (±0.002 joule deg−1 g−1) with the results of Cox and Smith (1959) and Bromley et al. (1967, 1970). The apparent equivalent heat capacity ΦCp for sea salt has been determined from these heat capacities, and the concentration dependence (Im is the molal ionic strength) has been analyzed by ΦCp = ΦCp° + SCpIm1/2 + bCpIm, where ΦCp° is the infinite dilution equivalent heat capacity of sea salt (related to ion-water interactions), SCp is the Debye-Huckel limiting law slope (related to ideal ion-ion interactions), and bCp is an empirical constant (related to deviations from the Debye-Huckel limiting law). The relative apparent equivalent heat capacity ΦJ = ΦCp − ΦCp° calculated from our results is in good agreement with the temperature dependence of the enthalpy of seawater ΦJ = ∂ΦL/∂T calculated from the apparent equivalent enthalpy data ΦL of Millero et al. (1973). Young's (1954) rule, ΦCp = ∑EiφCp(i), has been used at 25°C to estimate the ΦCp of sea salt by using data on the major components of seawater in pure water. The estimated ΦCp and cp are in excellent agreement with the measured values.