Comparison between measured and calculated density salinity for standard seawaters and real seawater

Density salinity of IAPSO Standard Seawater (SSW, Ocean Scientific International Ltd., UK) batches from P144 to P152 and Reference Materials for Nutrients in Seawater (RMNS, KANSO Technos Co., Ltd., Japan) lot BF were measured with an oscillation-type density meter (DMA 5000M, Anton-Paar GmbH, Austria). Practical salinity, nutrients, and total alkalinity for the standard seawaters were also measured. For the IAPSO SSW, as the date of manufacture was older, more silicate was dissolved. Measured density salinity were compared with calculated density salinity from two models by using measured Practical Salinity, silicate, nitrate and total alkalinity. Density salinity calculated from one model (Pawlowicz et al., Ocean Sci. Discuss., 7, 773-836, 2010) using Practical Salinity, silicate, nitrate and total alkalinity except for dissolved inorganic carbon agree well with the measured density salinity. However, the density salinity of IAPSO SSW calculated from another model (McDougall et al., Ocean Sci. Discuss., 6, 215-242, 2009) using simple relationship with silicate were overestimated probably due to difference in composition from real seawater, such as dissolution of silicate from glass bottle. The results suggest that RMNS has a significant potential as a reference liquid for density measurements. Comparison between measured and calculated density salinity for real seawater obtained in the western North Pacific and the Arctic Ocean will also be presented.