Thermophysical property anomalies of Baltic seawater

Abstract

Abstract. While the thermodynamic properties of Standard Seawater are very well known, the quantitative effect of sea salt composition anomalies on various properties is difficult to estimate since comprehensive lab experiments with the various natural waters are scarce. Coastal and estuarine waters exhibit significant anomalies which also influence to an unknown amount the routine salinity calculation from conductivity measurements.Recent numerical models of multi-component aqueous electrolytes permit the simulation of physical chemical properties of seawater with variable solute composition. In this paper, the FREZCHEM model is used to derive a Gibbs function for Baltic seawater, and the LSEA DELS model to provide estimates for the conductivity anomaly relative to Standard Seawater. From additional information such as direct density measurements or empirical salinity anomaly parameterisation, the quantitative deviations of properties between Baltic and Standard Seawater are calculated as functions of salinity and temperature. While several quantities show anomalies that are comparable with their measurement uncertainties and do not demand special improvement, others exhibit more significant deviations from Standard Seawater properties. In particular density and sound speed turn out to be significantly sensitive to the presence of anomalous solute. Suitable general correction methods are suggested to be applied to Baltic Sea samples with known Practical Salinity and, optionally, directly determined density.

Absolute Salinity, ''Density Salinity'' and the Reference-Composition Salinity Scale: present and future use in the seawater standard TEOS-10

“…Unfortunately, very little experimental work has been done on the influence of composition anomalies on the thermal expansion or compressibility of seawater. However, the FREZCHEM model (Marion and Kargel, 2008;Feistel and Marion, 2007;Feistel et al, 2010b), which is based on Pitzer equations for aqueous electrolyte solutions, can be used to estimate the magnitude of the errors indicated by Eq. (7).…”

“…Estimation of the influence of composition anomalies on other quantities is complicated by the almost complete lack of experimental results on the thermodynamic properties of seawater in the presence of known composition anomalies. Feistel et al (2010b) develop an approach that allows them to estimate the full range of thermophysical properties in the presence of small composition anomalies relative to SSW. Using the FREZCHEM model (Marion and Kargel, 2008), "data" is generated for the specific volume, heat capacity and activity potential of seawater that includes the composition anomaly of interest and this data is then used to determine the Gibbs function for the anomalous seawater (Feistel and Marion, 2007;Feistel et al, 2010b).…”

“…Feistel et al (2010b) develop an approach that allows them to estimate the full range of thermophysical properties in the presence of small composition anomalies relative to SSW. Using the FREZCHEM model (Marion and Kargel, 2008), "data" is generated for the specific volume, heat capacity and activity potential of seawater that includes the composition anomaly of interest and this data is then used to determine the Gibbs function for the anomalous seawater (Feistel and Marion, 2007;Feistel et al, 2010b). Note that although the FREZCHEM "data" is limited to only three properties, once the Gibbs function is obtained a much broader range of properties is easily considered.…”

Limnological applications of the Thermodynamic Equation of Seawater 2010 (TEOS‐10)

“…Then, temperature and pressure dependence of R, as well as concentration-dependent changes in the conductivity/salinity ratio is removed by the calculation of oceanographic Practical Salinity S P using the Practical Salinity Scale 1978 (UNESCO 1981b) with the addition of a low-salinity correction (Hill et al 1986), which extends its validity to dilute seawaters. Finally, a Reference Salinity S R , in units of grams solute per kilogram solution is estimated using (IOC et al 2010), (Meybeck 1987) and by continent (after Table 10-2 of Wetzel 2001), with two estimates of the world mean, as well as the major ion composition of a dilute seawater (Pawlowicz 2010) and saline lake Issyk-Kul (Vollmer et al 2002). Geological basin compositions (except for shale) were corrected for effects of seawater salts in rain by Meybeck (1987) Note that much of the technical complexity behind Eq.…”

“…Predicted conductivities are low by about 10% for typical seawaters with S A = 35 g kg -1 . However, in these cases, a perturbation approach has been successfully used to determine the effects on conductivity of small changes in the composition (Pawlowicz 2010).…”