Salinity, chlorinity, conductivity, and density

Abstract

No convenient, inexpensive, and accurate techniques exist for determining the total salt content of seawater. Fofonoff 1985 When dealing with any sample of seawater, the primary information required is usually a measurement of the salinity. Many properties, such as the concentrations of the conservative elements, can be calculated directly from the salinity, and others are related to it. The density is obtained from the salinity and the temperature, as are the solubilities of gases and other substances. The special requirements for exceedingly high accuracy and precision of this measurement, and the technical difficulties associated with the chemical composition of seawater, have influenced the early history of oceanography and the degree of international cooperation in marine science. An understanding of present practice and even some of the terms used requires an appreciation of the historical developments. Need for accurate determination of salinity and density In the latter decades of the nineteenth century, the question of variability in fisheries began to be addressed by several naturalists. The stocks of herring in the North Sea and along the coasts of Scandinavia were extremely variable, with great abundance in some years, and great scarcity in others. The Swedish chemist, Gustav Ekman, investigating the distribution of temperature and salinity in the Skagerack (between Sweden and Denmark), found that there were layers of water which differed in these respects, and he observed that herring seemed to prefer one layer over the others. The idea took hold that tracking the layers of water would help discover what happened to the fish, but one person alone could not do it. In 1890, Ekman and another Swedish chemist, Otto Pettersson, organized the first in a series of surveys of the Skagerack, the Kattegat, and adjacent regions of the Baltic and North seas, that involved coordinated sampling by vessels from Sweden and Denmark, and later Norway, Germany, and Scotland.