Salinometers

Salz-schicht, /. layer of salt, -schmelze,/. salt melt, fused salt, -see, /. salt lake, -siede-pfanne, /. salt pan. -sieder, m. salt boiler, salt maker, -siederei, /. salt making salt works, -sole, -soole, f. brine, salt water salt spring, -speck, m. bacon, -stein, m. boiler scale rock salt, -stoffwechsel, m. salt metabolism, -ton, m. salt clay, saliferous clay. -wa(a)ge,/. brine gage, salinometer. 

Wilson [32] has described a portable flow-cell membrane salinometer. Although test solutions are normally passed through the cell, the electrodes can be connected to a remote membrane sensor head by means of salt bridges for measurement of the salinity of estuarine muds in situ. The error is within 1% over the salinity range 1 - 40%. 

The inductive salinometer has become the measurement technique of choice because of its ease of use, speed, and precision. The reason for this high precision lies in the inductive salinometer s ability to detect very small differences in the ratio of the conductivity of a seawater sample as compared to that of a standard. By international agreement, this standard is prepared by diluting filtered Atlantic ocean water to produce seawater of chlorinity 19 374%o. The International Association for Physical Sciences of the Ocean (lAPSO) has designated Ocean Scientific International Ltd. (OSH) in Wormley, UK, as the sole preparer and distributor of this standard, which is called lAPSO Standard Seawater. ... 

Salinometer The device used to measure the salinity of seawater by deterrmning its electrical conductivity. 

However, salinity values are easily obtained with a salinometer (which measures electrical conductivity and is appropriately calibrated with standard solutions and adjusted to account for T effects). The salinity of seawater increases if the loss of H2O (evaporation, formation of ice) exceeds the atmospheric input (rain plus rivers), and diminishes near deltas and lagoons. Salinity and temperature concur antithetically to define the density of seawater. The surface temperature of the sea reflects primarily the latitude and season of sampling. The vertical thermal profile defines three zones surface (10-100 m), where T is practically constant thermoclinal (100-1000 m), where T diminishes regularly with depth and abyssal... 

Salinometer instrument used to measure salinity, where the conductivity of water is measured in essence the electrical current is controlled by the movement and abundance of ions, the more dissolved salts, the greater the conductivity. 

Salinity samples were drawn from the flow and allov ed to equilibrate to the laboratory temperature for 24 h prior to analysis with a Guildline Autosal. Throughout the cruise the salinometer was calibrated against the... 

Salinity is presently determined by measuring the conductance of seawater by using a salinometer. The modem definition of salinity uses the practical salinity scale, which replaces the chlorinity-salinity relationship with a definition based on a conductivity ratio (Millero, 1996). A seawater sample of salinity S= 35 has a conductivity equal to that of a KCl solution containing a mass of 32.435 6g KCl in 1 kg of solution at 15 °C and 1 atm pressure. No units are necessary on the practical salinity scale however, in practice, one often sees parts per thousand, ppt, or the abbreviation psu. New salinometers using this method are capable of extremely high precision so that the salinity ratio can be determined to 1 part in 40 000. At a typical salinity near 35 this procedure enables salinities to be determined to an accuracy of 35.000 0.001. This is much better than most chemical titrations, which, at best, achieve routine accuracy of 0.5 parts per thousand. 

An online salinometer continuously analyses the salt content of the condensate. If it contains more than 50 ppm then it is rejected to sea again/used elsewhere on the ship. This can indicate some leak in the system which is investigated and attended immediately. 

In the early 1960s, bench salinometers were developed that allowed measurement of the electrical conductivity of a seawater sample relative to that of a standard with high precision. Cox et al. (1967) had related chlorinity and conductivity ratios of seawater to standard seawater at temperatures higher than 10 °C and tabulated their results (UNESCO, 1966). Following their work, the responsible international oceanographic organizations adopted a redefinition of salinity (Wooster et al, 1969). Firstly, it was assumed that salinity was proportional to chlorinity, to be consistent with the assumed constancy of the ionic composition. The constant was chosen so that for 5=35 %o, both the Knudsen formula (3-1) and the new relationship... 

The 1969 definition and the available corrections for temperatures higher than 10 °C were suitable for use with bench salinometers. However, for use with in situ measuring systems, it was insufficient because it did not cover the whole oceanic range of parameters. It was this severe lack of validity and the demand to define salinity solely from physical parameters that led to the definition of the Practical Salinity Scale of 1978. 

To determine salinity from bottle samples, bench salinometers have now replaced the chlorinity titration method almost completely, initially for practical reasons. Subsequently, as the 1978 Practical Salinity Scale has been adopted, consistent application of this scale requires the use of salinometers. 

To reduce costs, users sometimes replace standard seawater with substandards to calibrate their salinometer. The use of substandards will inevitably result in reduced accuracy, but under certain circumstances may be acceptable. Their usage is described in Section 3.5.7. 

Only lAPSO recognized SSW provides a reliable standard for conductivity ratio measurements. It should be used to standardize each bench salinometer before being used for sample salinity measurements and to detect and eventually trace any drift. The use of so-called substandards for standardization is not recommended, as it will significantly decrease accuracy (see Section 3.5.7 for exceptions if a decrease in accuracy is acceptable). 

After a saUnometer has been standardized, SSW measurements are required on a regular basis to detect any drift or malfunction. Small offsets of SSW measurements from its printed salinity value can be used for linear trend corrections. Large offsets usually indicate nonstable room temperatiure or a malfunction of the salinometer. 

Station salinity samples for analysis with a salinometer are taken from water samplers that are closed at desired depths or pressures. In many cases, a rosette sampler is used that carries Niskin or comparable water sampling bottles (see Chapter 1). Ihe bottles are mounted in one or more rings on a frame. Closing the bottles at desired pressure levels is triggered from the deck unit in the ship s laboratory. New s tems allow selection of bottles individually and not just in the order of their position on the frame. Most frequently, and necessary for WOCE standards, the rosette sampler is operated together with a CTD that is mounted on the rosette s frame. The CTD s on-line pressure information is then used for controlled closing of the water samplers. 

Samples for salinity measurements are transferred from water samplers to salinity sample bottles and stored in the laboratory before they are analysed with a salinometer. 

Sample bottles are kept in cases large enough to store all bottles from a deep-ocean station. The cases with the samples are stored in the temperature controlled laboratory where the salinometer is operated. Depending on the size of the sample bottles, the samples will have reached laboratory temperature between a few hours and one day. Good ventilation may speed up the equilibration. 

Before a major cruise, each salinometer needs all the checks and the maintenance recommended in the manual to be carried out including checks of the electric circuits. As an accurately controlled bath temperature is essential for high accuracy in salinity measurement. 

An experience to be kept in mind is that well maintained AUTOSAL salinometers are extremely stable under stable temperature conditions. Any salinity drift larger than 0.001 during a cruise is probably due either to non-stable laboratory conditions or to a malfunction of one of the salinometer s component. Under no circumstances should it simply be assumed that that the salinometer has drifted . 

The power cable and the connecting interface cable from the salinometer s digital output to a personal computer may act as antennae. Shielded power and data cables should therefore be used. Computers should be de-coupled electrically from the salinometer and therefore communicate with the salinometer through opto-coupling interfaces only. 

---