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

• Published in: Deep-sea research. Part I, Oceanographic research papers Vol. 47; no. 6; pp. 1035 - 1057
• Main Authors: Mork, Kjell Arne, Blindheim, Johan
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-06-2000; Elsevier; Pergamon Press Inc
• Subjects: Convection, turbulence, diffusion. Boundary layer structure and dynamics; Earth, ocean, space; Exact sciences and technology; External geophysics; Marine; Meteorology; Oceanography; Oceans; Arctic Ocean; Greenland Sea; North Atlantic; Norwegian Sea; Atlantic Ocean; ANE, North Sea; ANE, North Atlantic; Northeast Atlantic; Temperature distribution; North Atlantic oscillation; Sea current; Depth profile; Empirical orthogonal function; Ocean dynamics; Hydrography; Salinity
• ISSN: 0967-0637; 1879-0119
• DOI: 10.1016/S0967-0637(99)00091-6

Hydrographic observations on the Svinøy section, which runs NW from about 62°N on the Norwegian coast to 64°40′N on the prime meridian, have been used to investigate variations in the Atlantic inflow to the Nordic Seas. The data are from the winter 1955 to 1973 and from the spring and the summer 1978 to 1996. The observations show that in the summer there exist 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 kernels with northward currents in the Svinøy section: one over the inner part of the continental slope (over 600–800
m depths) and one further offshore (over 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 variations are considered. In the western part of the section the temperature and salinity are negatively correlated with the winter North Atlantic Oscillation index, but in the eastern part of the section they are weakly positively correlated. This is not found in the winter data from 1955 to 1973. The geostrophic volume transport in the summer through the Svinøy 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 transports west and east in the section seem to be in opposite phase. From the summer data 1978 to 1996 there is a positive linear trend for the eastern transport (+2.4
Sv), but there is a negative linear trend for the western transport (−2.0
Sv). The transport through the whole section has increased by 1.1
Sv during the same similar period. The atmospheric conditions were different in years with relatively low temperatures and salinities in the western part of the section compared to those years with relatively high temperatures and salinities. It is proposed that interannual variations of temperature, salinity and volume transport in the Svinøy section are controlled mostly by a large-scale variable pressure system (i.e. the North Atlantic Oscillation index).