An analysis is presented of current, salinity, and temperature records obtained under ice cover near the mouth of the fjord Gullmaren, on the Sweden Skagerrak coast. Results are compared with an earlier analysis from spring and summer conditions (Shaffer and Djurfeldt, 1983). Large-amplitude vertical fluctuations of the density field of several week periods regularly occurring in the winter season appear to be associated with variations in the Baltic Sea outflow. The local alongshore wind seems to force motions of several day periods in the fjord, even under ice cover, through interaction with the coastal zone. Internal seiches, prominent features during spring and summer, are essentially absent under ice cover, which implies that these motions are forced most effectively by the direct action of the local wind on the fjord. A method is presented for the determination of significance levels in empirical orthogonal function analysis in the frequency domain. ¿American Geophysical Union 1987