Ostracode Distribution and Biofacies, Newfoundland Continental Slope and Rise

Abstract

The spatial distribution, abundance and ecology of ostracods present on the continental slope and rise (400-3210 m) between 49.degree. and 50.degree.30''N were studied after collection by Van Veen grabs and replicate box-cores. Three biofacies are present in the study area. An upper slope biofacies, defined by living individuals of Muellinera canadensis and M. abyssicola, is found at depths from 300-1499 m. Few ostracods are present in the trasitional fauna which occurs between 1500 and 2399 m. Species known only as empty valves dominate a lower slope and rise biofacies between 2400 and 3210 m. This fauna may owe its origin to the transport of shells parallel to isobaths by rapid contour currents, or the uncovering and concentration of the sand fraction of a mid-Holocene (7000 million yr B.P.) stratigraphic unit by current erosion. The diversity of the living fauna increases slightly below 2800 m in response to decreasing current velocities. Significant faunal changes at .apprx. 1600 m coincide with the downslope transition from waters associated with Labrador Current to North Atlantic Bottom Water locally entrained in the Western Boundary Undercurrent. Environmental contrasts between these water masses, chiefly salinity and temperature, are thought to be primarily responsible for the ostracod depth zonation.