Benthic foraminiferal biofacies, sediments and water masses of the southern Peru- Chile Trench area, southeastern Pacific Ocean.

Lowest species diversities and specimen abundance correlate with a shallow O₂ minimum zone at 150-400m where dissolved O₂ values are less than 1 ml/l. The most dramatic faunal change across the entire shelf-edge-to-abyssal gradient occurs at the base of this low O₂ parcel between 400 and 500m, where 35 species have their shallowest or deepest occurrences. Low diversity and abundances also characterize a deep O₂-minimum zone at 900-1700m. Alternately, highest species diversities and abundances are found at depths shallower than 150m and at 400-900m correlating with surface and intermediate oxygen maxima and associated salinity minima. A sharp increase in the relative abundance and diversity of agglutinated species at c3500m correlates with the CaCO₃ lysocline. -from Authors