Living benthic foraminifera distributions on the continental slope and rise east of Newfoundland, Canada
Replicate box cores collected between 500 and 2,700 m on the continental slope of Newfoundland indicate that the most abundant living species are Adercotryma glomerata and Nonionellina labradorica at 500 m; Elphidium excavatum and variants, Nonionella atlantica , and Reophax difflugiformis at 1,500 m; and Oridorsalis umbonatus , Epistominella vitrea , and Trochammina bullata at ∼ 2,700 m. Within-core (centimetre- to decimetre-scale) assemblages show a graduation in correlation from relatively high values between subsamples in the upper-rise environment (2,700 m) to relatively low levels in the upper-slope environment (500 m); between-core (kilometre-scale) assemblage distributions yield a similar pattern. Among the ten most abundant species, the calcareous forms tend to have a relatively uniform distribution at the centimetre and kilometre scales on the upper and middle slope (1,500 m) compared to the arenaceous taxa. In contrast, arenaceous species have a comparatively uniform distribution in the upper-rise environment. The pattern of species in both the arenaceous and calcareous categories is distinctly uniform on the upper rise, compared to upper-slope species distribution patterns. With increasing water depth, species diversity ranges from 28 to 45, mean number of living specimens per cubic centimetre of wet sediment ranges from 1.6 to 136.8, mean percentage of calcareous specimens ranges from 39 to 77, mean species dominance ranges from 62% to 49%, and the mean percentage of living to total specimens ranges from 20 to 31. Except for the percentage of living parameter, all population indices show a direct relationship with respect to water depth. Percentage of living to total is highest for the middle-slope environment, a finding that apparently reflects both the size of the living population and the rate of sedimentation compared to the rise environment. Conversely, living specimens per unit area are highest on the rise.