Long-term hydrographic variation in the Skagerrak based on the section Torungen-Hirtshals

Abstract

Measurements of temperature and salinity taken about once a month across the Skagerrak between Norway and Denmark have been analysed for long-term variations in the seasonal cycle in the surface water masses from 1962 onwards. Since most of the southern and central North Sea water passes through the Skagerrak before leaving the North Sea along the Norwegian coast, the results are expected to indicate possible variations in the hydrographical conditions of the North Sea. There is a persistent seasonal pattern in the upper layer across the section. Higher salinities are observed at the Danish shelf break during winter which is attributed to the intensification of direct inflow from the North Sea. During summer, salinity on the Danish side is always lower than during winter. However, the opposite situation exists in the centre of the Skagerrak with lower salinities in winter than during the summer. A long-term anomaly beginning in the late 1970s with a decrease in both temperature and salinity was coupled to the 'Great Salinity Anomaly' in the North Atlantic. A second anomaly started in the late 1980s with an increase in both temperature and salinity.