Abstract
The western Beaufort Sea polychaete fauna may be divided into sublittoral and bathyal components. Sublittoral species occur mainly at depths less than 300 m, but may be stenobathic or eurybathic. Bathyal species are found exclusively below 300 m; a separate abyssal fauna could not be recognized. A dominance of Amphi-boreal-arctic species, a near absence of endemic species, and a relatively low number of species in the sublittoral environment is attributed to invasion of the sublittoral environment during interglacial intervals. Lower sea-level, grounded ice, and low nutrient supply during glacial intervals of the Pliocene and Pleistocene are suggested agents of faunal extinction. Within the bathyal polychaete fauna the-prevalence of endemic and Atlantic-boreoarctic species and the absence of Pacific-boreoarctic species reflect the relative isolation of the bathyal Arctic Ocean. The bathyal depth of the deepest portion of the North Atlantic Transversal Ridge (830 m) has permitted some exchange of Arctic and North Atlantic bathyal faunas since the Miocene, while the shallowness of the Bering Strait (70 m) has prevented a similar exchange of Arctic and Pacific bathyal faunas since the Late Cretaceous. Isolation of the basin below 830 m for approximately 65 m.y. has permitted the evolution of a strongly endemic fauna
