Anomalous salinity-density relations of seawater in the eastern central Atlantic

Abstract

In the context of the recent oceanographic standard TEOS-10, the Thermodynamic Equation of Seawater – 2010, a new Reference-Composition Salinity Scale was introduced in 2008. For IAPSO Standard Seawater, values of this Reference Salinity are related to 1978 Practical Salinity by a definite factor, however, regional seawater samples may deviate from this equation. Over the past decade, various such salinity anomalies were investigated by direct density measurements and published in several studies. Typically, anomalies arise from non-dissociated solutes such as silicate which increase seawater density but not electrical conductivity. In contrast, negative density anomalies cannot be explained by added, electrically neutral salts, and their chemical or metrological origins remain elusive. In this paper, densities and Practical Salinities of seawater of the central eastern Atlantic Ocean in the region 18 °S to 33 °N, 22 °W to 12 °E are reported, measured between 2008 and 2013. Density anomalies in the range from 0 to –13 g m-3 were observed, consistent in magnitude with negative anomalies found by other authors elsewhere. No significant spatial or temporal trends of the anomalies could be observed.