Abstract
AbstractWe expanded the batch-to-batch offsets of The International Association for the Physical Sciences of the Oceans (IAPSO) Standard Seawater (SSW) batches P145–P163 by intercomparison measurements using salinometers. On the basis of our results, we recommend using the correction factors instead of the offsets to correct the batch-to-batch differences, especially for salinity data outside the range of 30–40 g kg−1. We evaluated the expanded batch-to-batch correction factors by applying them to time series salinity data collected in the northwestern North Pacific Ocean and found that they are effective for detecting recent freshening (−0.6 ± 0.1 × 10−3 g kg−1 decade−1) in the deep North Pacific, which might be related to a reduction of the formation rate of Antarctic Bottom Water. We also evaluated the SSW linearity pack by applying the batch-to-batch correction factors. Linearity errors of the salinometers estimated from decade resistance substituters were consistent with the results of the linearity pack measurements. To correct the linearity errors of a salinometer, it might be suitable to use the more detailed distribution of those estimated from the decade resistance substituter than the linearity pack measurements. Since the cause of large batch-to-batch differences is still unclear, a reference seawater that is more robust and stable than SSW might be necessary to establish a high-level of international comparability of salinity measurements; the Multiparametric Standard Seawater (MSSW) currently under development might be a candidate for such reference seawater, because MSSW is expected to be more stable than SSW not only in practical salinity but also in absolute salinity.
Highlights
The salinity of the ocean is an important indicator ofEarth’s climate change
Since we can only evaluate the batch-tobatch offset of a target batch relative to a known estimated ‘‘true value,’’ we referred to the batch-to-batch offset-corrected salinities proposed by Kawano et al (2006) with reference to the average of the batch-tobatch offsets for batches P130–P145, taking the comparability into consideration
We expanded the batch-to-batch salinity offset table of the IAPSO Standard Seawater (SSW) proposed by Kawano et al (2006) for recent batches P145–P163 by intercomparison measurements using salinometers (Autosal model 8400B)
Summary
The salinity of the ocean is an important indicator ofEarth’s climate change. For example, the Southern Ocean has freshened and warmed over the past several decades primarily as a result of human-induced greenhouse gas increases (Swart et al 2018). The salinity of the ocean is an important indicator of. The Southern Ocean has freshened and warmed over the past several decades primarily as a result of human-induced greenhouse gas increases (Swart et al 2018). Denotes content that is immediately available upon publication as open access. Unauthenticated | Downloaded 11/02/21 04:41 PM UTC. VOLUME 37 it moves northward from Antarctica. Monitoring long-term changes in the deep-sea environment, such as freshening of abyssal waters, requires salinity measurements of the highest possible quality (Levin et al 2019)
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