Effect of Sediment Suspensions on Seawater Salinity Assessments
Journal of Water Resources and Ocean Science
Volume 6, Issue 2, April 2017, Pages: 23-34
Received: Jan. 3, 2017; Accepted: Jan. 20, 2017; Published: Apr. 28, 2017
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Marc Le Menn, Metrology and Chemical Oceanography Department, French Hydrographic and Oceanographic Service (Shom), Brest, France
Laurent Pacaud, Metrology and Chemical Oceanography Department, French Hydrographic and Oceanographic Service (Shom), Brest, France
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The absolute salinity of seawater can be assessed by conductivity measurements and the calculation of a practical salinity, or by density measurements. The effect of low concentrations of suspended particulate matter on these measurements has never been documented, but the theories developed to explain and predict the conductivity of sediments show clearly that, under an electrical field, they interact with the ionic composition of seawater. Moreover, it can be easily shown that adding any quantity of particles has an effect on the measured density of a seawater sample. This publication describes a measurement method settled to measure the effect of sediment particles on seawater conductivity and proposes relations for explaining and predicting the observed phenomena. It also describes the effects of particles on density measurements. The results obtained show that the errors on the measured conductivities (and practical salinities) caused by sand in suspensions, are less than 0.001 mS cm-1 (on average) with concentrations encountered in oceans fields, but that these cannot be neglected in some coastal areas. The amplitude of the measurement noise leaded by particles circulation in the conductivity cell exceeds 0.002 in salinity beyond 200 mg l-1. For density measurements, the threshold for keeping the error inferior to the uncertainty of 0.004 kg m-3 usually obtained with vibrating tube densimeters, is much lower, 9 mg l-1, and close to the concentrations encountered in the open ocean.
Seawater, Salinity, Conductivity, Density, Sediment, Formation Factor, Limnology
To cite this article
Marc Le Menn, Laurent Pacaud, Effect of Sediment Suspensions on Seawater Salinity Assessments, Journal of Water Resources and Ocean Science. Vol. 6, No. 2, 2017, pp. 23-34. doi: 10.11648/j.wros.20170602.11
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