Variations in the Atlantic inflow to the Nordic Seas, 1955-1996

Hydrographic observations on the Svinoy section, which runs NW from about 6 2 degrees N on the Norwegian coast to 64 degrees 40'N on the prime meridian , have been used to investigate variations in the Atlantic inflow to the No rdic Seas. The data are from the winter 1955 to 1973 and from the spring an d the summer 1978 to 1996. The observations show that in the summer there e xist two cores of water with salinity above 35.25 at about 100 m depth, but in the spring and the winter the core furthest offshore is less distinct. Geostrophic calculations show that, for all data sets, there are two kernel s with northward currents in the Svinoy section: one over the inner part of the continental slope lover 600-800 m depths) and one further offshore lov er 1400-2500 m depth). The mean volume transports of Atlantic water in the section are 4.5, 5.0 and 5.6 Sv in spring, summer and winter, respectively. Results from an Empirical Orthogonal Function analysis of the summer data indicate that there is a dual structure in the section when interannual var iations are considered. In the western part of the section the temperature and salinity are negatively correlated with the winter North Atlantic Oscil lation index, but in the eastern part of the section they are weakly positi vely correlated. This is not found in the winter data from 1955 to 1973. Th e geostrophic volume transport in the summer through the Svinoy section is positively correlated with the NAO indices for winter and spring, where the March NAO index gave the best correlation. Also, the summer volume transpo rts west and east in the section seem to be in opposite phase. From the sum mer data 1978 to 1996 there is a positive linear trend for the eastern tran sport ( +2.4 Sv), but there is a negative linear trend for the western tran sport ( - 2.0 Sv). The transport through the whole section has increased by 1.1 Sv during the same similar period. The atmospheric conditions were dif ferent in years with relatively low temperatures and salinities in the west ern part of the section compared to those years with relatively high temper atures and salinities. It is proposed that interannual variations of temper ature, salinity and volume transport in the Svinoy section are controlled m ostly by a large-scale variable pressure system (i.e, the North Atlantic Os cillation index). (C) 2000 Elsevier Science Ltd. All rights reserved.