Reconstructing Water Column Hydrography Using Individual Shell Stable Isotope Data From Multiple Planktic Foraminifera Species (Invited)

Oxygen and carbon isotope data from planktic foraminifera play an important role in reconstructing past ocean temperatures, salinity and nutrient content since they first appeared in a publication by Cesare Emiliani in 1955. For most of the next 5 decades, research focused on analyses of foraminifera shells from a few mixed layer and thermocline species. Such analyses have typically been conducted on multiple shell samples from an assemblage of foraminifera, pooled into a single analysis. It has long been recognized that significant depth-specific and seasonal information is contained within populations of shells and that analyses of single specimens and some underutilized species could provide novel information about water column processes and hydrography. Nevertheless, it has only been in the past decade that researchers have begun to explore this individual-shell multispecies paleoenvironmental archive for paleoceanographic applications. As a result of experiments with living foraminifera, our understanding of the mechanisms that contribute to the vital effect black box that governs inter- and intraspecific geochemical variability in foraminifera has attained a level of maturity that now allows us to reconcile foraminifera biology and ecology with the geochemical signals obtained from marine sediments. Within this context, we present individual shell carbon and oxygen isotope data from 11 species of planktonic foraminifera (G. ruber (pink & white var.), G. sacculifer, O. universa, G. siphonifera, S. dehiscens, G. conglobatus, G. menardii, N. dutertrei, P. obliquiloculata, G. truncatulinoides and G. tumida). We use these data to reconstruct late Holocene water column hydrography from cores in the Caribbean (ODP 999A; 12°45’N, 78°25’W; 2,827 m) and eastern equatorial Pacific (TR163-19; 2°16’N, 90°57’W, 2348 m). We show that interpretation of such complex data sets requires consideration of biological and environmental controls such as symbiont photosynthesis, ontogeny, and the depth-dependent variation of the carbonate ion effect, water column light levels, temperature and salinity. In the context of these variables, stable isotope datasets from multiple foraminifera species may be accurately interpreted for paleoceanographic reconstructions of upper water column structure