IAPSO Standard Seawater: Definition of the Uncertainty in the Calibration Procedure, and Stability of Recent Batches

Abstract

Standard seawater (SSW) has been employed by oceanographers as a reference material in the determination of salinity for over a century. In all that time, this is the first study to determine the uncertainty of the SSW manufacturing process. SSW is calibrated in reference to carefully prepared solutions of potassium chloride (KCl). All uncertainties in the preparation and measurement of KCl solutions and of new SSW are calculated. The expanded uncertainty of the SSW conductivity ratio is found to be 1 ϫ 10 Ϫ5 , based on a coverage factor of 2, at the time of manufacture. There is no discernible "within batch" variability. No significant variability of quality within or between batches of KCl is found. Measurement of SSW "offsets" from the label conductivity ratio as long as 5 yr after the SSW batch manufacture are reported, and no significant change in label conductivity ratio for SSW batches P130 through P144 outside the expanded uncertainty of 1 ϫ 10 Ϫ5 is found. This last result is in contrast to some other studies, and herein are suggestions as to why this may be the case.

A model for predicting changes in the electrical conductivity, practical salinity, and absolute salinity of seawater due to variations in relative chemical composition

“…the scaled S P ) lie somewhere between a chlorinity-based measure and the true absolute salinity, although much closer to the former. This also accounts for the stability of conductivity in SSW (Bacon et al, 2007), in spite of the known variations in DIC that occur within samples.…”

“…The effects of pressure, which can lead to small changes in the chemical equilibria of the carbonate system, can also be investigated. Finally, there are possible uncertainties in the reliability of SSW for highest precision measurements (Kawano et al, 2006), although it is unclear why these variations arise (Bacon et al, 2007). Again, the model developed here may be useful in resolving some of these technical issues.…”

Decadal Freshening of the Antarctic Bottom Water Exported from the Weddell Sea

“…The accuracy and reliability of the SSW has been investigated by several independent groups (Mantyla 1980(Mantyla , 1987(Mantyla , 1994Kawano et al 2006;Bacon et al 2000Bacon et al , 2007. The accuracy and consistency of the different batch of SSW is important as they are used to calibrate the salinometer and thus help calibrate both the bottle and CTD salinity.…”

Hydrography in the Mediterranean Sea during a cruise with RV <i>Poseidon</i> in April 2014

“…of the standard seawater samples is 38H11 and they have a K15-factor of 1.07631 (24 • C). An explanation of standard seawater definitions can be found in Bacon et al (2007).…”