Determination of salinity

Since the end of the 19th century it has been known that the composition of seawater is almost constant in space and time (the concept of conservatism , see Chapter 11). Therefore, to a good first approximation, oceanographers assume that seawater consists of just two components, the first one being pure water and the second one representing all dissolved ions that contribute to the mass of seawater, namely salinity. By this two-component assumption, three thermodynamic parameters are needed to derive the state of seawater. Besides salinity, it is convenient to choose temperature (T) and pressure (P) since they are relatively easy to measure at the required accuracies and, together with salinity, are also valuable for water mass analysis. 

The methods to determine salinity have changed with time. From the beginning of the 20th century until 1978, the constituent selected to represent and estimate the salinity was chlorinity (see Sections 11.1 and 11.2.4 for definition). Salinity then, together with the other two basic parameters, served to calculate density. 

With the introduction of electrical measurement methods and shipboard computers into oceanography in the 1960s, electrical conductivity replaced chlorinity as the third basic parameter. Two reasons were responsible for this change. Firstly, conductivity can be measured electrically in situ along with pressure and temperature, and salinity and density can be derived on-line once the fundamental determinations needed for such calculations have been made. Secondly, it turned out that based on electrical conductivity, the accuracy in density that could be achieved is an order of magnitude better than that based on chlorinity. 

In this chapter, a brief overview of the early definitions of salinity based on the chlorinity concept is given. It is followed by a description of the definition of the Practical Salinity Scale 1978 (PSS78), which is based on the measurement of electrical conductivity. Finally, methods are described that are used to derive salinity (and thus density) with modern instrumentation, both from bottle samples on a bench and in situ. 

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Although diverse electronic systems are available on the market that measure salinity in situ, the determination of salinity from bottle samples is still important. The main reason is that despite the expectation of early constructors, experience has shown that high accuracy (better than 0.002) of in situ derived salinity can only be achieved with an almost station-bystation calibration using salinity values from bottle samples. 

M.-J. Chen, Y.-T. Hsieh, Y.-M. Weng, and R.Y.Y. Chiou. Flame photometric determination of salinity in processed foods. Food Chemistry 91 765-770,2005. 

IL DETERMINATION OF SALINITY BY TTTRA nON (HIGH PRECISION METHOD)... 

The determination of salinity can be simplified by esq ressing it in grams per liter of seawater. 

Data gathering in the water column should not be overlooked at the appraisal stage of the field life. Assessing the size and flow properties of the aquifer are essential in predicting the pressure support which may be provided. Sampling of the formation water is necessary to assess the salinity of the water for use in the determination of hydrocarbon saturations. 

Determination of total mud salinity. The total pounds of soluble salts per barrel of mud are calculated as... 

Determination of water phase salinity. By entering the graph in Figure 4-110 with total soluble salts, Ib/bbl of mud, at the correct volume percent of water line, the water phase salinity can be read from the left-hand scale. 

Farquhar, G.D., Ball, M.C., von Laemmer, S. and Roksandic, Z. 1982 Effect of salinity and humidity on 5 C values of halophytes. Evidence for diffusional isotope fractionation determined by the ratio of intercellular atmospheric COj under different environmental conditions. 

An important issue that influences estuarine behavior is the determination of the riverine component. Variations in the riverine endmember may occur over timescales that are short compared to the residence times of water in the estuary, which result in nonlinear relationships between salinity and trace elements across the estuary as different riverine compositions progress through the estuary (Loder and Reichard 1981 Officer... 

The saltiness of the ocean is defined in terms of salinity. In theory, this term is meant to represent the total number of grams of dissolved inorganic ions present in a kilogram of seawater. In practice, salinity is determined by measuring the conductivity of a sample and by calibration through empirical relationships to the International Association of Physical Sciences of the Ocean (IAPSO) Standard Sea Water. With this approach, salinity can be measured with a precision of at least 0.001 parts per thousand. This is fortunate, considering that 75% of all of the water in the ocean falls neatly between a salinity of 34 and 35. Obviously, these high-precision measurements are required to observe the small salinity variations in the ocean. 

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