Standard seawater comparison up to P129

Abstract

Batch to batch differences of IAPSO standard seawater (SSW) batches P103 to P129 were examined. Several comparison experiments, in which 2–23 batches of SSW were compared with each other, were carried out during the period from 1991 to 1997. Batch to batch differences for the KCl-labeled batches, P91 through P129 except for P113, P115, P117, P125 and P126, ranged from −2.2×10 −3 to 1.2×10 −3 in salinity with an average of −0.1×10 −3 in salinity. Within-batch differences were observed to be <0.3×10 −3 in salinity for recent batches except a few for which the differences were up to 0.6–0.9×10 −3 in salinity. The KCl-labeled batches generally agreed to within 1.0×10 −3 in salinity with the assumed reference. Applications of batch to batch differences of SSW for World Ocean Circulation Experiment (WOCE) expedition salinity data led to a significant reduction in salinity variance at crossovers both at the regional scale of the Philippine Sea and the basin scale of the Pacific Ocean and Atlantic Ocean. To obtain accuracy better than 2×10 −3 in salinity, within-batch differences were also considered before the standardization for several ampoules of SSW. It is prudent that we continue the monitoring of batch to batch differences of SSW by comparing new with previous batches, so that one may correct both future salinity data and the historical salinity data.