Sediment resuspension and transport in Lake Michigan during the unstratified period

Instrumented moorings were deployed during the winter of 1994-95 at three d epths (28, 58 and 101 m) in southern Lake Michigan. Storms during the obser vation period were not unusually severe, so the processes observed are typi cal of those that occur during an average winter. Time series observations of water temperature, beam attenuation coefficient (a measure of water tran sparency) and current velocity show that local resuspension of bottom sedim ent occurred frequently after the breakdown of the thermocline. Resuspension was most frequent close to the shore but was also observed at the 58 m station, Local resuspension did not occur at the 101 m station, bu t advection to the site of material resuspended at shallower sites was obse rved. These observations do not support the hypothesis proposed by previous investigators that local resuspension at depths of 100 m or greater occurs during the unstratified period. It is more likely that fine-grained materi al resuspended by storm action in intermediate water depths (approximate to 30-60 m) is transported into the deeper parts of the lake by the general l ake circulation.