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

Abstract

Virtually any study of natural waters relies at some point on knowledge of particular physical properties of the fluid. These physical properties depend on the temperature, pressure, and the chemical composition of dissolved matter in the solution. The amount of dissolved matter is often characterized using a single scalar, the salinity. Since the freshwater and saline inland waters typically studied by limnologists, which we denote "limnological" waters, include a wide range of relative compositions, the relationships between physical properties of different lakes and rivers and the salinity are also variable.Physical properties of particular limnological waters have been estimated by various means. These include direct measurements of the water in question (McManus et al. 1992;Jellison et al. 1999;Vollmer et al. 2002), empirical or semi-empirical "corrections" to known seawater relationships (Vollmer et al. 2002;Fisher and Lawrence 2006), direct numerical calculation based on an analysis of the composition and a chemical theory (Wüest et al. 1996;Millero 2000;Pawlowicz 2008; Boehrer et al. 2010), or for some thermodynamic properties, use of a generic set of "limnological" equations (Chen and Millero 1986). As one might expect for such a heterogeneous set of ad hoc approaches, little is known of the accuracy of the results or the degree to which they can be generalized. The generic equations in particular are the easiest to apply, but give results with the largest degree of uncertainty.Recently, a new international standard for the thermodynamic properties of seawater has been developed, the Ther- AbstractThe new Thermodynamic Equation of Seawater 2010 (TEOS-10) provides a highly accurate, thermodynamically consistent, and complete representation of all thermodynamic properties of seawater over a wide range in temperature and salinity. These properties include density, sound speed, heat capacity, enthalpy, chemical potential, and many others. Here we provide simple procedures by which limnological studies can take advantage of TEOS-10. These require replacing the TEOS-10 salinity argument, seawater Absolute Salinity S A , with a limnological salinity S a . In typical natural waters where anion concentrations are dominated by HCO 3 -or Cl -, S a can be approximated by the solution salinity S a soln , obtained by summing the concentrations of different dissolved constituents in a complete chemical analysis after multiplying by their molar masses. Slightly better results can be obtained, especially at very low salinities where silicic acid Si(OH) 4 is an important constituent, by using a density salinity S a dens carefully defined by dividing the solution salinity into an ionic and a nonionic part and changing the weighting factors for each in the summation. In cases where the dominant anion is HCO 3 -, which covers the majority of inland waters, measurements of electrical conductivity can be used to estimate the ionic salinity, which will be ≈60% greater than the Absolute Salinity of seawater of the same conduc...

Subglacial Lake Whillans microbial biogeochemistry: a synthesis of current knowledge

“…The casts were aligned at their lowest point (figure 1a), based on the assumption of a flat lake bottom and no change in water elevation in the borehole. Properties including absolute salinity, conservative temperature and density were derived using the TEOS-10 equations ([56,57], for a limnological setting [58]), resulting in salinity being approximately 50% higher than inferred initially [32]. Data collected with the CTD indicate that SLW is a cold, freshwater lake (figure 1a).…”

A practical approach to lake water density from electrical conductivity and temperature

“…In all other cases, the adaptation for limnic systems proposed by Pawlowicz and Feistel (2012) was used since all other systems are limnic. Because the only difference between both algorithms is the calculation of the so-called absolute salinity and the equation for density is the same, "TEOS-" was used in the legends of all diagrams in Fig.…”

“…Pawlowicz et al (2011) implemented the LIMBETA method that calculates density from composition. Another approach comes from Pawlowicz et al (2012) where the authors propose to use TEOS-10 but replace seawater salinity with specific salinities obtained and corrected for freshwaters. This limnic salinity can be calculated using the chemical composition by summing up all the dissolved solutes (Sa soln ) or by summing up only the dissolved ions (Sa ionic ) and correcting this value with the dissolved Si(OH) 4 , Sa dens = Sa ionic + 50.6 × [Si(OH) 4 ] (mol kg −1 ).…”

“…Jellison et al, 1999;Vollmer et al, 2002;Karakas et al, 2003). If the composition is constant and the main constituents are ions, electrical conductivity or salinity may be used as an easy-to-measure proxy for concentrations (Bührer and Ambühl, 1975;Chen and Millero, 1986;Pawlowicz and Feistel, 2012). Imboden and Wüest (1995) discussed the influence of dissolved substances on (potential) density because both the concentration and chemical composition of the total dissolved solids change considerably from lake to lake (see e.g.…”

“…However, as the composition of solutes differs greatly from the ocean, density calculation based on ocean conditions can only be of limited accuracy. Pawlowicz and Feistel (2012) have considered the application of TEOS-10 (IOC et al, 2010) in several cases different from seawater, correcting the salinity values depending on the composition before applying TEOS-10 (IOC et al, 2010). Bührer and Ambühl (1975) developed an equation to calculate density based on temperature and specific conductance at 20 • C for alpine lakes.…”