The upper water column structure of the BG is as follows. Immediately beneath the summer BG mixed layer, a local temperature maximum is often observed, believed the result of locally absorbed solar heat (4, 6, 7). This layer is subject to strong seasonal variability. Below, at depths between roughly 50 and 150 m, is a second layer of relatively warm water within a large vertical salinity gradient (Fig. 1). These warm halocline waters, believed to originate from the Pacific Ocean via the Chukchi Sea and Alaskan Coastal Current (8), exhibit little seasonal variability (they are too deep to be influenced by local penetrative solar radiation) but significant interannual change (Fig. 1) (9). In a region of the central Canada Basin,