The salinity of hypersaline brines: Concepts and misconceptions |
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Authors: | David A Anati |
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Institution: | (1) Institute of Earth Sciences, Hebrew University in Jerusalem, Givat Ram, 91904 Jerusalem, Israel |
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Abstract: | Some widespread misconceptions about salinity are pointed out, explained and commented on. Definitions, units, and methods
of salinity determination recommended for brines of moderate salinities may become unsuitable for highly saline brines. Various
salinity units are examined and commented on, and density at a precisely monitored temperature is chosen as the preferable
“substitute parameter” for salinity determination of hypersaline brines. It is shown that ambient air density during pycnometric
measurements must be known as accurately as required of the brine's density, and that its value must be added to the direct
pycnometric measurement. Variations of atmospheric pressure at the time of pycnometry must be taken into account if greater
than 15 mB. For a salinity accuracy of ±0.02 per mille, as required for some physical and chemical studies, the temperature
of the sample during salinity measurement must be monitored with an accuracy of at least 0.04°C. A definite curve in the ρ-S
plane, corresponding to the conversion of salinity to density at a fixed temperature, andvice-versa, does not exist if the brine is saturated in one of its salts. Non-linearity in the equation of state is shown to affect
the surface level drop due to evaporation; the effect is negligible at low salinities, but a 10 per cent correction is already
required at the salinity found in the northern Red Sea (41 per mille). Reliable reference points for the conversion of absolute
salinity to density of highly saline brines are not known, at present, as accurately as desirable; pending the accurate determination
of such reference points, a substantial dilution of hypersaline brines (for the purpose of adapting them to conductivity measurements)
would multiply the error range by more than a hundred fold. On the other hand, a minute dilution of hypersaline brine samples
to prevent salt crystal formation is possible and would not bring about any major increase of the error range in their density
(salinity) determination. |
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Keywords: | Dead Sea equation of state pycnometry salinity saturation |
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