Salinity

PIs

  • Todd Martz (SIO)

  • Susan Becker (SIO)

Technicians

  • John Calderwood (SIO)

  • Royhon Agostine (SIO)

Equipment and Techniques

Two Guildline Autosals were on board and operational, SIO-owned 8400A S/N 57-526 and 8400B S/N 69-180. S/N 57-526 was used for all salinity measurements during this cruise. The salinity analysis was run in the ship’s Climate Controlled Chamber, a refrigerator port and amidships between the Computer Lab and Bioanalytical Lab. The chamber temperature varied between about 21 and 25 degrees Celcius around 3 times each hour, with an average (based on measuring temperatures of items in the chamber) of about 23°C.

IAPSO Standard Seawater Batch P-165 was used for all calibrations: K15 = 0.99986, salinity 34.994, expiration 2024-04-15. A LabView program developed by Carl Mattson was used for monitoring temperatures, logging data and prompting the operator. Salinity analyses were performed after samples had equilibrated to laboratory temperature of 23°C, usually 8 hours or more after collection. Samples were placed under fans to speed their acclimatization to the set room temperature.

The salinometer was standardized for each group of samples analyzed (normally 1 or 2 casts, up to 72 samples) using two bottles of standard seawater: one at the beginning and one at the end of each set of measurements. For each calibration standard and sample reading, the salinometer cell was initially flushed at least 2 times before a set of conductivity ratio readings was recorded. Standardization conductivity offsets did not exceed 0.00005 mS/cm for all casts. Between runs the water from the last standard was left in the cell.

Sampling and Data Processing

The salinity samples were collected in 200 ml Kimax high-alumina borosilicate bottles that had been rinsed at least three times with sample water prior to filling. The bottles were sealed with plastic insert thimbles and Nalgene screw caps. This assembly provides very low container dissolution and sample evaporation. Prior to sample collection, inserts were inspected for proper fit and loose inserts replaced to insure an airtight seal. Laboratory temperature was also monitored electronically throughout the cruise. PSS-78 salinity [UNESCO1981] was calculated for each sample from the measured conductivity ratios. The offset between the initial standard seawater value and its reference value was applied to each sample. Then the difference (if any) between the initial and final vials of standard seawater was applied to each sample as a function of elapsed run time. The corrected salinity data was then incorporated into the cruise database.

Narrative

3955 salinity samples were taken during P02W-2022, including 22 samples from test cast 00102. Due to ambient electrical noise, the 8400A Autosal was used over the 8400B Autosal for all samples and practice. 8 samples were used for practice prior to arrival at the test station and are not reported. One sample bottle (#2) was broken and replaced during sampling, but the cast number was not recorded. One sample bottle (#34) was broken and replaced during sampling of cast 05701.

UNESCO1981

UNESCO 1981. Background papers and supporting data on the Practical Salinity Scale, 1978. UNESCO Technical Papers in Marine Science, No. 37 144.