The latest batch-to-batch difference table of standard seawater and its application to the WOCE onetime sections

Abstract

An updated batch-to-batch difference table of IAPSO standard seawater (SSW) up to P145 is proposed. The batch-to-batch difference table is based on several recent SSW comparison experiments, including the experiments conducted independently at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and Woods Hole Institute of Oceanography (WHOI) at about the same time using the same procedure. Proposed batch-to-batch differences range from 1.2 × 10⁻³ to −1.9 × 10⁻³ with reference to the average of those from P91 to P102. Batch-to-batch differences from P29 to P145 with reference to the recent batches and this average over every 5 years since 1960 are also presented, together with standard deviation. This reveals that inconsistency among batches has improved since 1980s. In particular, the standard deviation was 0.3 × 10⁻³ in this decade, which is about one-half the value reported previously and almost equal to the modern measurement precision (0.2 × 10⁻³) and is within-batch difference (<0.3 × 10⁻³). Proposed batch-to-batch differences were applied to the observational results of the WOCE hydrographic onetime section (WHP onetime) in the Indian Ocean. Average absolute salinity differences at 14 crossover points in the Indian Ocean were slightly larger, from 1.2 × 10⁻³ to 1.5 × 10⁻³, when the batch-to-batch difference table was applied; however, when results from the Indian, Pacific, and Atlantic Oceans were combined, application of the batch-to-batch difference table yielded statistically acceptable salinity differences. The table was also applied to WHP sections P1 and P17 (revisited about 10 years after the original observations during the WOCE period) and sections I1, I7, and I8 (visited twice by different research vessels in the same year). In all cases, the table corrected unrealistically large salinity changes in space and time. The results suggest that the application of the batch-to-batch table to well-controlled salinity data such as WOCE datasets would be effective in making the datasets more consistent in space and time.