This calculator requires the use of Javascript enabled and capable browsers. This calculator determines the freezing point of seawater for given salinity and pressure. The default calculation uses the pressure, 1 decibars and 35PSU for salinity. Surface pressure is 0 dbars. For this calculator, we assume that value 10 kPa = 1 dbar is valid, and is approximately the pressure increase that corresponds to an ocean depth increase of about 1 meter (3.2808398950131234 feet). Entering a pressure value (kPa) equal to the depth in meters will give a very close approximate result. You may also enter a PSI vale that is converted in the calculator to kPa. In our calculator, temperature uses IPTS-68 standards and definitions and salinity uses PSS-78 standards and definitions. They are referenced below. Though all measurements and references to this sort of measurement are normally in degrees C, our result is in degrees C, F and K. You may also wish to reference the table below the calculator for relationships in pressure.
The International Practical Temperature Scale of 1968 (IPTS-68)
In 1968 the International Committee of Weights and Measures created and approved the
International Practical Temperature Scale of 1968, having been empowered to do so by the
thirteenth General Conference of 1967 - 1968. The IPTS-68 incorporated very extensive
changes from the previous standard, IPTS-48. These included numerical changes, designed to bring to more
nearly in accord with thermodynamic temperatures, that were sufficiently large to be
apparent to many users. There were other changes also. The lower limit of the scale was
extended down to 13.81 K; at even lower temperatures (0.5 K to 5.2 K), the use of two
helium vapor pressure scales was recommended; six new defining fixed points were
introduced - the triple point of equilibrium hydrogen (13.81 K), an intermediate
equilibrium hydrogen point (17.042 K), the normal boiling point of equilibrium hydrogen
(20.28 K), the boiling point of neon (27.102 K), the triple point of oxygen (54.361 K),
and the freezing point of tin (231.9681 șC) which became a permitted alternative to the
boiling point of water; the boiling point of sulfur was deleted; the values assigned to
four fixed points were changed - the boiling point of oxygen (90.188 K), the freezing
point of zinc (419.58 șC), the freezing point of silver (961.93 șC), and the freezing
point of gold (1064.43 șC): the interpolating formulae for the resistance thermometer
range became much more complex; the value assigned to the second radiation constant c2
became 1.4388 x 10-2 m · K; the permitted ranges of the constants for the
interpolation formulae for the resistance thermometer and thermocouple were again
modified, as examples.
The International Practical Temperature Scale of 1968 (Amended Edition of 1975)
(IPTS-68)
The International Practical Temperature Scale of 1968, amended edition of 1975, was
adopted by the fifteenth General Conference in 1975. As was the case for the IPTS-48 with
respect to the ITS-48, the IPTS-68 (75) introduced no numerical changes. Most of the
extensive textural changes were; the oxygen point was defined as the condensation point
rather than the boiling point; the triple point of argon (83.798 K) was introduced as a
permitted alternative to the condensation point of oxygen; new values of the isotopic
composition of naturally occurring neon were adopted; the recommendation to use values of
T given by the 1958 4He and 1962 3He vapor-pressure scales was
rescinded.
Practical Salinity Scale of 1978 (PSS-78)
The modern oceanographic definition of salinity is the Practical Salinity Scale of 1978 (PSS-78). It yields a practical salinity from new equations, smooth expansions of conductivity ratio, which were carefully fit to the real salinity of diluted North Atlantic seawater. The numeric unit from PSS-78 is PSU (practical salinity unit) and is distinct from the previous physical quantity ppt (kg salt per kg water in parts per thousand). The primary motivation for PSU was consistency; it focused on a trace to a primary conductivity standard (K15) and recognition that ocean ion ratios were not identical. Salinometer work was plagued by an inconsistent standard and the PPT equations included ion ratios from different oceans. So, the trade was a consistent standard and equation that works for a single ion mix instead of exact salinity in other ocean basins. G. Siedler and H. Peters highlighted where PSS-78 and EOS-80 formulas deviate from real salinity and density (e.g., Baltic Sea is difficult, but the deep Pacific has EOS-80 deviations of up to 0.02 kg/m3, implying salinity errors of order 0.02 PSU).
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