The sound speed anomaly of Baltic seawater

Abstract

Abstract. The effect of the anomalous chemical composition of Baltic seawater on the speed of sound relative to seawater with quasi-standard composition was quantified at atmospheric pressure and temperatures of 1 to 46 °C. Three modern oceanographic time-of-flight sensors were applied in a laboratory setup for measuring the speed-of-sound difference δw in a pure water diluted sample of North Atlantic seawater and a sample of Baltic seawater of the same conductivity, i.e., the same practical salinity (SP = 7.766). The average δw amounts to 0.069 ± 0.014 m s−1, which is significantly larger than the resolution and reproducibility of the sensors and independent of temperature. This magnitude for the anomaly effect was verified with offshore measurements conducted at different sites in the Baltic Sea using one of the sensors. The results from both measurements show values up to 1 order of magnitude smaller than existing predictions based on chemical models.

Reply to the short comments of Hannes Schmidt of 04 Apr 2018

“…First, the validity of a new density equation (Feistel, 2010) at atmospheric pressure could be extended to temperatures up to 90 • C and absolute salinities up to 70 g kg −1 using new measurements of . Second, for an industrial seawater standard the "scientific" Helmholtz function forming the pure-water part was replaced by an "indus-trial" IAPWS Gibbs function for liquid water (Wagner and Kretzschmar, 2008;Kretzschmar et al, 2015;IAPWS AN5-13, 2016).…”