IAPSO batch-to-batch comparisons are necessary to determine whether IAPSO differences between batches may affect salinity data over time. In October 1995, duplicate salinity samples from the BATS (Bermuda Atlantic Time-Series) project were measured for comparison with HOT-67 salinity samples. The mean difference between the HOT-BATS duplicate salinity samples was 1.3 mpsu (Nosse 1996, "HOT-BATS Salinity Intercomparison," Appendix O). Nosse speculated that the only differences in these measurements were that IAPSO batch P127 was used by BATS for their measurement sessions, while IAPSO batch P123 was used by the HOT group for their measurement sessions. However, a recent study of IAPSO water comparison by Aoyama et al. (2002, Appendix P) stated that the difference between batches P123 and P127 is only 0.1 mpsu. Aoyama et al. (2002, Appendix P) suggests that within-batch comparisons are useful in indicating the presence of drift in Autosal electronics. Their study also determined correction values for IAPSO batches up to P129. Their batch-to-batch comparisons indicate an IAPSO shelf life of 5 years. In the future, we should continue monitoring IAPSO within-batch differences to detect possible Autosal drift. The corrections to IAPSO bottles suggested by Aoyama et al. (2002, Appendix P) should be applied to the HOT samples.

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