Seasonal and spatial dynamics of234Th/238U disequilibria in southern Lake Michigan

[1] Measurements of 234Th/238U disequilibria were made on an approximately bimonthly basis over the course of a year in nearshore (10–40 m deep) and offshore (160 m deep) surface waters of the southern basin of Lake Michigan (18,100 km2). The mean activity of 238U in Lake Michigan measured 230 ± 20 dpm m−3, approximately 1 order of magnitude lower than what is typically found in marine systems. Measured median activities of dissolved (