BENTHIC FORAMINIFERA AS TRACERS OF OPEN OCEAN BIOPRODUCTIVITY, COMPARISON TO OTHER PROXIES

Much research over the past several decades has demonstrated that benthic foraminiferal assemblages are sensitive to the flux of organic carbon to the seabed, and to the variability, or seasonality, of that flux. Ultimately, in the open ocean, the organic carbon flux is controlled by surface ocean bioproductivity, so benthic assemblages can serve as a proxy for paleoproductivity. This proxy has been quantitatively calibrated using hundreds of samples from the world ocean. Application of the proxy to the late Pleistocene bioproductivity record of the Eastern Equatorial Pacific has revealed consistent regional patterns that can be explained in terms of known oceanographic features of the region. The most important outcome of this work is the demonstration that the southern ocean can exert a strong influence on Pacific tropical oceanography. The benthic foraminiferal proxy for bioproductivity can be compared to independent tracers as a test of its reliability. All those tracers not based on accumulation rates of biogenic particles (e.g. element ratios, radiogenic tracers) at the seabed support the benthic foraminiferal results. Proxies that are based on accumulation rates show different patterns in time and generally conflict with the foraminiferal and non-accumulation rate based tracers. The conflict between the two classes of proxies raises questions about what features of the bioproductivity system each tracer reflects. I suggest that benthic foraminifera reflect the flux of labile organic carbon to the seabed. Accumulation rate proxies reflect the generation of hard particles by the planktonic community, which may be more a function of community composition.