Influence of suspended particulate matter on salinity measurements

• The influence of SPM on salinity measurements was investigated in laboratory study.
• Conductivity-based salinity measurements are disturbed in turbid waters.
• The measurements were distorted by a “blinding effect” of the conductivity sensor.
• The effect of SPM is negligible for concentrations up to 10 g l−1.
• Ion adsorption by clay minerals accounted for a small part of the deviations.

Salinity is a very important parameter in marine science, which is normally measured via the electrical conductivity of sea water. Suspended Particular Matter (SPM) can influence salinity measurements but so far there had been no experimental studies to test this.In this paper a new laboratory study about the influence of SPM on conductivity based salinity measurements is presented. Different sensor types were deployed to investigate the influence of the conductivity sensor design on the observed salinity deviations. The role of clay minerals was additionally analysed. Two natural mud samples of different origins were used to set up various SPM concentrations. The results have shown that high suspended sediment concentrations (up to 300 g l−1) can distort salinity measurements up to 30%. On average only 22% of the observed salinity deviation could be explained by the adsorption of ions by clay minerals. The CTD cell geometry had no verifiable effect, in the resolution limits of the instruments.The observed salinity deviations were caused by a “blinding effect” of the sensor due to the dissolved particles.