Salinity

PIs

  • Susan Becker

  • James Swift

Technicians

  • John Calderwood

  • Patrick A’Hearn

Equipment and Techniques

Two Guildline Autosals were on board and operational, SIO-owned 8400B S/N 69-180, and UW-owned 8400B S/N 94-894. S/N 69-180 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. Both instruments were serviced prior to the cruise by their respective institutions and shipped to WHOI with other equipment in March. IAPSO Standard Seawater Batch P-164 was used for all calibrations: K15 =0.99985, salinity 34.994, expiration 2023-03-23. 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. 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. Between runs the water from the last standard was left in the cell. 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.

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 linear function of elapsed run time. The corrected salinity data was then incorporated into the cruise database.

Narrative

No major problems were encountered during this cruise. Minor problems:

There was a temperature excursion of the climate control chamber on the last day of analysis which had to be corrected before the last samples could be run.

Three bottles were broken during sampling; four had their rims chipped. In all, seven sample bottles were damaged and replaced.

2963 total salinity samples were taken from a test cast, 90 CTD casts, and some underway seawater samples. 11 boxes (110 vials) of std seawater were consumed.

UNESCO1981

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