Summary of 2014 JCOMM Pilot Inter-Comparison Project for Seawater Salinity Measurements

Abstract

The inter-comparison project for seawater salinity measurements, in which 25 laboratories from 16 countries took part, was conducted by JCOMM (Joint WMO/IOC Technical Commission for Oceanography and Marine Meteorology) for the first time in 2014. Two seawater samples of different salinity values ranging from 30−35 and 20−25 for Sample A and Sample B respectively and which had sufficient homogeneity and stability were distributed to all participants. Participants measured the salinity in their own laboratories at least 3 times and reported the results. Statistical treatments were applied to the results to assess discrepancies among laboratories. 20 out of the 25 laboratories used laboratory salinometers and statistics for this group were denoted as belonging to group α; while 5 out of the 25 laboratories used hand-held measuring instruments and statistics for this group were denoted as belonging to group β. Bias described as discrepancy among laboratories in group α was within ± 0.001 and expanded uncertainty (k = 2) was in the vicinity of 0.002. The bias and the uncertainty of Korea Institute of Ocean Science and Technology (KIOST), in group α, were 0.000 and 0.002, respectively. The biases of group β were greater than group α because of constraints related to instrument accuracy. Biases from 3 laboratories in group β exceed the accuracy specification of the corresponding instruments. Considering that the uncertainty of Standard Seawater (SSW) is of the order 0.001 to 0.002, the inter-comparison results show that 16 laboratories among the 25 laboratories made high quality measurements, largely indistinguishable from one another.