CALIBRATION OF A NEW BENTHIC FORAMINIFERAL PROXY TO ASSESS BOTTOM WATER OXYGEN LEVELS

Marine oxygen concentrations often co-vary with other environmental factors, and proxies for dissolved oxygen concentrations in deep-sea settings remain equivocal. By examining epifaunal benthic foraminiferal test pore characteristics that are directly linked with ambient bottom-water oxygen levels, problems with co-varying environmental factors and exposure to potentially variable sediment pore water can be avoided. We conducted an investigation of test pore characteristics of epifaunal taxa collected alive or recently living (Rose Bengal stained) from different bottom water oxygen conditions (ranging from 0.04 to 6.20 ml/L) at 20 locations. Scanning electron micrographs were made of the umbilical side of calcareous epifaunal taxa (Cibicides, Cibidicoides, Planulina), and percentages of pore surface areas of chambers were determined using ArcGIS image analyses. A strong relationship is shown between dissolved oxygen in bottom waters and pore surface area of test chambers (R2= 0.729; p < 0.001). The direct relationship between test pores of epifaunal foraminifera and ambient oxygen provides a new, quantitative proxy to assess bottom water oxygen of ancient oceans.