FORAMINIFERAL DISTRIBUTION PATTERNS ACROSS THE OXYGEN MINIMUM ZONE IN THE SOUTHERN CALIFORNIA BIGHT

As part of an effort to understand the responses of benthic foraminifera to changes in oxygen availability, living (Rose Bengal stained) specimens were examined from surface sediments (0-1 cm) of multicores taken along a depth transect (360-3000 meters) off the coast of southern California. Sites were chosen in areas where surface samples typically contain relatively coarse grained sediments. Concentrations of dissolved oxygen in bottom waters and sediment cores were determined onboard ship using amperometric microsensors. Bottom water oxygen varied from 0.47 ml/L at approximately 1000 meters to 3.63 ml/L at approximately 3000 meters. Analyses of the >150 micron size fraction revealed differences in foraminiferal assemblages between sites. At 1000 meters, Planulina wuellerstorfi was among the dominant calcareous taxa, and Uvigerina spp. were common at many sites The presence of epifaunal species such as Planulina wuellerstorfi at many oxygen-poor sites reconfirms the idea that the distributions of at least some epifaunal taxa are not controlled entirely by oxygen availability.