Eddy formation on the coast of North Norway – evidenced by synoptic sampling

Abstract

Abstract In order to resolve advection, migration, and in situ population dynamics of zooplankton and capelin larvae in a mesoscale physical setting on the coast of North Norway, an extensive field survey was conducted. This paper reports on the physical conditions in the area and lays the basic environmental understanding for the analysis of vital rates of the biological components studied. We used a towed wing (SCANFISH) equipped with sensors and Objective Analysis for interpolation of hydrographic data into continuous fields. We show the importance of the mixing process along the coast of Norway, and identify the weakening of the signatures of Atlantic Water (AW). We also described the presence of a distinct and isolated water mass that is neither Norwegian Coastal Water (NCW) nor AW. This water mass had intermediate salinity but was significantly colder than NCW and AW. Several distinct non-linear mesoscale eddies were observed during a 12-day period. Anticyclonic eddies had lower salinity, while cyclonic eddies were relatively saline. We also observed meanders further offshore. Elongated eddies with the principle axis parallel to the shelf break developed into relatively larger isotropic eddies. The evolution of the eddy field was examined by cross-correlation between different periods of the survey. The most significant observation is the indication of eddy transport along the shelf. The translation speed was approximately 7 km day−1. We propose that the observed features are formed by baroclinic instabilities of the Norwegian Coastal Current (NCC) and that they play a crucial role as transport agents for biota.