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.