Fluxes of water and nutrients within and into the Skagerrak

Results from simultaneous velocity, salinity and nutrient measurements within the Southern Jutland Current and in the Skagerrak are presented. The measurements were undertaken during the 1990 and 1994 period along three sections perpendicular to the northwest coast of Denmark with the main purpose of estimating the importance of the Southern Jutland Current as a carrier of nutrients and contaminants from the continental rivers. Based on a total of 64 transects, we estimated the average cyclonic circulation in the outer Skagerrak at 0.8 Sv (1 Sv = 106·m3·s−1), half of which occurs in the upper 50–100 m (S<35 psu). The northward flow along the west coast of Denmark, at Tyborön, averaged 0.045 Sv within 100 km from the coast. Although this average flow is almost negligible, the northward flux of nutrients (mainly as DIN, inorganic N or TN, total N) along the coast is not a negligible contribution to the fluxes into the Skagerrak. Tidal currents and strong longshore nutrient gradients give rise to significant diffusive fluxes. Including some intermittent outflows of low-salinity water from the southern North Sea, we find an average northward DIN (TN) flux of 350 (600)·106 kg per year. While the diffusive component dominates, it seems that large outflows of southern North Sea water during winter or early spring, directly related to high freshwater discharge, is the only way in which the Kattegat nitrogen budget may be influenced. Such large outflows were recorded in the spring of 1988, 1989 and 1994. The last period is included in our measurements.