MEAN CURRENTS AND CURRENT VARIABILITY IN THE ICELAND BASIN

Long-term (>6 months) current measurements from five moorings in the I celand Basin have been analysed for the mean currents and the structur e of the variable current components. The time-averaged flow at all fi ve moorings had a strong baroclinic character. The mean circulation in the upper layers with relatively warm Sub Polar Mode Water appears to have a general north-eastward direction with maximum mean velocities of 6 to 7 cm . s(-1). In the bottom layer south of Iceland, where the cold Iceland-Scotland Overflow Water flows westwards along the topogra phy in a Deep Northern Boundary Current, mean velocities of the order of 10 to 20 cm . s(-1) have been observed. Over the deep slope of the Hatton Bank, water enters the Iceland Basin in a branch of the Deep No rthern Boundary Current which has a cyclonic rotation sense in the Ice land Basin. The variable part of the current has been analysed by mean s of principal-component analysis. The current variations in the centr al Iceland Basin appear to have a mainly barotropic character while va riations in the baroclinic flow of Iceland-Scotland Over-flow Water co ntributed 10% or less to the total energy of the variable deep flow. O ver the slope of the Hatton Bank the variable currents had a mainly ba roclinic character with shear in both current speed and direction. Com parison of the geostrophic velocity with the mean Eulerian velocity ha s revealed that the sigma(T)heta=27.725 kg . m(-3) surface can be used adequately as level of no-motion for the geostrophic modelling of the flow along the Icelandic and Hatton slopes. The mean westward geostro phic transport of ISOW south of Iceland relative to this reference sur face amounted to 3.5 Sv, in agreement with existing independent estima tes.