VERTICAL DISTRIBUTIONS AND STABLE ISOTOPIC COMPOSITIONS OF LIVE (STAINED) BENTHIC FORAMINIFERA FROM THE NORTH-CAROLINA AND CALIFORNIA CONTINENTAL MARGINS

The vertical distributions of live (Rose Bengal stained) benthic foram inifera were determined in Soutar box cores from six sites on the Nort h Carolina continental margin (337-1477 m) and three sites on the Cali fornia continental margin (786-3705 m). Stained specimens of the most abundant taxa were analyzed for their carbon and oxygen isotopic compo sitions. Bottom water delta(13)C values and pore water delta(13)C prof iles were determined at seven of the sites to aid in interpretation of the live benthic foraminiferal delta(13)C data. The abundance profile s of most benthic foraminiferal species show consistent patterns withi n the sediments al each site. These patterns enable us to characterize taxa as epifaunal and shallow, intermediate, and deep infaunal. The v ertical range of the living assemblage is small (2-4 cm) in several of the cores, presumably as a consequence of the relatively high organic carbon fluxes and correspondingly small oxygen penetration depths in these continental margin environments. At each site, species with deep er within-sediment microhabitats have lower average delta(13)C values than do shallow-dwelling species. The delta(13)C offset from bottom wa ter for each species is larger at high bottom water oxygen sites (Nort h Carolina) than at low bottom water oxygen sites (California). Both o f these observations are consistent with a pore water influence on ben thic foraminiferal delta(13)C. Th, Atlantic-Pacific differences rule o ut a constant species-specific fractionation as the explanation for th e delta(13)C values of these foraminifera. Despite substantial downcor e changes in pore water delta(13)C, foraminiferal delta(13)C values fo r most species change very little over the entire depth range of stain ed individuals within each core. This lack of vertical delta(13)C vari ation may imply that calcification takes place in a relatively small s ub-zone of the microhabitat range suggested by the distribution data. (C) 1997 Published by Elsevier Science Ltd.