Previous salinity reports and records suggest that while Ted Walsh measured salinity samples on the Minisal, salt samples were collected in 250 ml high-density polyethylene plastic Nalgene bottles. Evaporation is the single most important factor that affects salinity samples in plastic bottles. Though parafilm was used as additional sealer for plastic bottles, evaporation still occurred through the sides of the bottles. Along with the switch to the Autosal 8400A, the group also started using 200 ml flint glass bottles. The glass bottles, equipped with screw caps and Poly-Seal caps to prevent leakage and evaporation, meet WOCE specifications more readily than the plastic bottles. The first record of glass bottles being used is on October 4, 1990 by Sean Kennan during his test of evaporation in plastic bottles using glass bottles as reference samples (Kennan 1991, "Evaporation of Plastic Bottles," Appendix D). Kennan reports that samples in plastic bottles not measured within 15 days after the cruise must be corrected by an evaporation rate of 1 mpsu/14 days or 0.071 mpsu/day. Thus, all samples collected in plastic bottles should have been corrected if measured on or later than the fifteenth day after the cruise (due to our own threshold of making corrections for differences >1 mpsu). A review of these corrections is presented below.
The first cruise that utilized glass bottles for some casts seems to be HOT-23 (February 1991). These samples were measured on both the Minisal and the Autosal 8400A and the results are summarized in a report by Sean Kennan (Kennan 1991, "Summary of Salinity Measurements from HOT-23 (2/1 to 2/6, 1991)," Appendix E). After switching to glass bottles during HOT-24, the bottles were numbered in sequential order from #1 to #408. When there were not enough glass bottles during a cruise, plastic bottles were used, mostly for thermosalinograph and duplicate samples. HOT-82 shows new glass bottles (#501 and up) being used; however, plastic bottles were still used for thermosalinograph samples. HOT-84 (June 1997) is the first cruise in which only glass bottles (#1 to about #700) were used for all casts and since then, only glass bottles have been used. Since bottles should be replaced every eight to ten years according to the WOCE Operations Manual, the group started using a second set of bottles (#501 to #980) during HOT-140 (September 2002). Table 1 below categorizes the bottle types used for sets of HOT cruises and whether evaporation corrections were applied to the respective sets of data.
| Table 1: Summary of Salinity Bottle Types and Evaporation Corrections |
||
| HOT
Cruise #
|
Bottle
Types Used
|
Evaporation
corrections
|
|
1-2, 5, 8, 10-11, 16, 18-19, 21 |
Plastic bottles |
Measured within 15 days after the cruise; no
corrections needed
|
|
3-4, 6-7, 9, 12-15, 17, 20, 22 |
Plastic bottles |
Measured
on or after the 15th day post cruise (see Appendix F); data corrected in November
2003.
|
|
23 |
Glass and plastic bottles |
See Kennan's report "Summary of Salinity Measurements from HOT-23" (Appendix E) |
|
24-28, 30, 33-34, 37-44, 46-48, 50, 52, 54, 56 |
All glass bottles (#1-408) |
No corrections needed
|
|
29, 31-32, 35-36, 49, 51, 55, 57 |
Glass bottles, plastic bottles used for duplicates when not enough glass bottles |
Measured within 15 days after the cruise; no
corrections needed
|
|
45 |
Glass bottles, plastic bottles used for Station 2 casts 3, 4, 6, 8, 10, 12, 14 |
Measured
about a month after the cruise; data corrected for plastic bottles
in November 2003.
|
|
53 |
Glass bottles, plastic bottles used for Station 1 cast 3 and Station 3 cast 1) |
Measured more than 3 months after the cruise; data corrected for plastic bottles in November 2003. |
|
64-67, 69-80, 83 |
Glass bottles, thermosalinograph and duplicate samples in plastic bottles |
Measured within 15 days after the cruise; no
corrections needed
|
|
63, 68, 81, 82 |
Glass bottles, thermosalinograph and duplicate samples in plastic bottles |
Measured on or after the 15th day post cruise; doesn't affect primary salinity data. No
corrections needed
|
|
84-139 |
All glass bottles (#1 to about #700) |
No
corrections needed
|
|
140-present |
All glass bottles (#501 to #980) |
No
corrections needed
|