A timeline shows the salinity measurement instrument used for each HOT cruise (Figure 1).
Figure 1. Instruments used to measure salinity samples during the HOT project cruises 1 through 149. The horizontal axis indicates the cruise number.
During HOT-1 through HOT-26, salinity samples were measured by Ted Walsh at the Analytical Services Lab on the 5th floor of MSB using an AGE Minisal 2100 salinometer. The “Salinity Measurements” section in the World Ocean Circulation Experiment (WOCE) Operations Manual (Stalcup 1991, Appendix A) recommends Guildline Autosal salinometers as being the only type of instrument that is capable of achieving the required WOCE accuracy for salinity measurements.
The HOT project, originally a part of WOCE, purchased the Guildline Autosal 8400A salinometer (SN: 58296, UH Decal: 065QV) in 1990. Prior to switching over to the Autosal 8400A, comparisons were conducted between Autosal 8400A and Minisal measurements using substandards and duplicate salinity samples from HOT-22 through HOT-26. From HOT-27 through HOT-107, Autosal 8400A was used to measure primary salinity samples. For the first six cruises (HOT-27 to HOT-32), the Minisal was used to measure duplicate salinity samples for further comparison (Kennan 1992, “Summary of Comparisons between Guildline Autosal and AGE Minisal,” Appendix B). Around 1993, an older model of the Autosal 8400A (Autosal 8400, UH Decal: 916RF) was purchased by the Joint Institution of Marine and Atmospheric Research (JIMAR) and was given to the Roger Lukas group. This Autosal 8400 was used to rummage for parts and as a troubleshooting guide when the Autosal 8400A encountered problems. The Autosal 8400 was formally disposed of and removed from inventory in June 2001. After HOT-80 (March 1997), an adjustment was made on the Autosal 8400A to reset the standardization knob, which reached its minimum setting value and could not turn any further. After the standardization knob was reset, we continued to use the Autosal 8400A until HOT-107
The Autosal 8400B (SN: 63903, UH Decal: 924SP) was purchased in February 1999 using NSF shipboard equipment funding and has been used to measure primary and duplicate salinity samples since HOT-108 until present day. On September 19, 2002, a comparison experiment between Autosal instruments 8400A and 8400B was conducted by Daniel S. Fitzgerald (see his experiment notes, Appendix C) after Autosal 8400A was repaired in the lab by the Electronics Technician. He concluded that the Autosal 8400A is functioning correctly and that it is possible to utilize the Autosal 8400A in case of an emergency with the Autosal 8400B.