Origin of the salinity minimum at intermediate depths of the Pacific ocean

Abstract

Uncertainty in concepts of the origin of the salinity minimum at intermediate depths [1] poses the question of its actual nature: is it water mass or a phenomenon in the continuously changing vertical salinity distribution? In some works, the existence of salinity extremes (minimums and maximums) in the water column is explained by changes in the sign of the freshwater balance on seasonal and synoptic time scales. Their characteristics (occurrence depth, salinity value, and excess of the surface salinity value over the salinity minimum or maximum) are changing continually up to its complete disappearance under the influence of variations in the freshwater balance [2, 3]. The long-lived (climatic) salinity minimum can also be related to changes in the freshwater balance, although on a larger time scale. In the ocean, long-period (climatic) changes in the freshwater balance are associated with regions with an annual cycle characterized by one of its phases: prevalence of either atmospheric precipitation ( P ) or evaporation ( E ) (arid zones). This communication is dedicated to within-year variability in the vertical distribution of salinity in the North Pacific. Particular attention is paid to changes in signs of the freshwater balance. Oceanographic databases compiled by Levitus et al. [4], VNIIGMII-MTsD [4, 5], and the Pacific Institute of Oceanology served as a basis for this study.