DEEP-DWELLING PLANKTONIC-FORAMINIFERA OF THE NORTHEASTERN PACIFIC-OCEAN REVEAL ENVIRONMENTAL-CONTROL OF OXYGEN AND CARBON ISOTOPIC DISEQUILIBRIA

We assess the utility of four species of living planktonic foraminifer a as tracers of thermocline and intermediate water masses in the north ern Pacific Ocean, based on their water-column distribution and shell isotopic composition. Assuming oxygen isotopic equilibria with the wat er column, we infer apparent calcification depths. This allows an esti mate of apparent carbon isotopic disequilibria. We then relax the assu mption of oxygen isotopic equilibrium to examine habitat effects on ki netic disequilibrium processes. In the California Current, left-coilin g Neogloboquadrina pachyderma and Globigerina calida calcify in the up per thermocline. Globorotalia scitula resides within the Shallow Salin ity Minumum (potential density sigma(theta) = 25.1-26.7), while Globoq uadrina hexagona is associated with the deeper, North Pacific Intermed iate Water (sigma(theta) = 26.7-26.9). Apparent carbon isotopic disequ ilibria corrected for oxygen isotopic disequilibria, range from 1.0-1. 9 parts per thousand in these asymbiotic species. The carbon isotopic disequilibrium can be modeled as a single exponential function of temp erature or a logarithmic function of potential food supply. We infer t hat carbon isotopic disequilibrium increases with metabolic rate, rela ted to temperature and/or food supply. Kinetic processes of oxygen and carbon isotopic disequilibria yields reasonable depth habitats if the slope of the oxygen:carbon isotopic shift is about 0.35, consistent w ith culture data. Our finding of a link between environment, metabolis m, and isotopic disequilibrium observed in oceanic settings suggests t he potential to better reconstruct the structure and biological proces ses of the upper water column from geologic data.