Abstract:Optic refractive index is a good proxy for in situ salinity measurement of seawateraccording to TEOS-10. Currently, salinity of seawater is estimated by practical salinity (Sp).which is calculated by measuring electric conductivity, temperature and pressure usingConductivity-Temperature-Depth (CTD) sensors. However, the electric conductivitymethod only takes into account the conductive compositions to seawater salinity andignores the contribution of non-ionic components. However, non-ionic components inseawater affect seawater salinity according to the definition of salinity of seawater.but they could not be measured by conductivity sensor, Optical refractive index issensitive to all dissolved matters of seawater including ionic and non-ioniccomponents. Here, we take the dissolved organic matter (DOM) extracted fromAoshan Bay seawater as the representative sample to experimentally study thecontribution of the non-ionic component to the refractive index of the standardseawater. Seawater refractive indices with different DOM concentrations weremeasured by a home-made V-shaped groove refractometer. The experimental resultsshow that refractive index of seawater increases linearly with increasing DOMconcentration at rate of 1.19 x 10-/1(g/kg) DOM