THE ECOLOGY OF BENTHIC FORAMINIFERA LIVING IN AN OXYGEN MINIMUM ZONE ON THE EASTERN PACIFIC MARGIN

In an effort to evaluate benthic foraminiferal abundances and assemblages within an oxygen minimum zone, multicore samples were collected along a depth transect (360-3000m) within the Southern California Bight. In this study area, bottom water oxygen values varied from 0.38 ml/L to 3.63 ml/L, temperatures ranged from 2.9^oC-7.1^oC, and mean grain size ranged from 23.9-105.7 µm. Living (Rose Bengal stained) specimens of the >150µm fraction were examined from 0-2cm and the 63-150µm fraction were examined from the surface sediments (0-1cm) of multicore tubes. Abundant taxa in the >150µm fraction included Uvigerina spp., Cassidulina spp., Hoeglundina elegans., Nonionella sp., Hanzawaia nipponica, and Cibicidoides wuellerstorfi. Vertical distributions of Cassidulina sp., H. nipponica and H. elegans in the >150µm fraction indicate epifaunal microhabitat preference at all depths from 690m to 1050m, with greatest abundances at the 360 m site. Globobulimina spp., Uvigerina spp., and Chilostomella oolina in the >150µmportion, were relatively abundant in surface sediments. Standing stock values of the >150µm assemblage (primarily calcareous taxa) ranged from 55 individuals/50cm² at 1050m to 831 individuals/50cm². Comparisons of the >150µm fraction assemblages with those of the 63-150µm fraction will yield additional insight into the ecology and distribution patterns of dominant species, and provide modern analogs to assess fossil assemblages.