Variability of foraminiferal stable isotope ratios in Caribbean shallow waters of Panama: A modern framework for Neogene studies

Abstract

Oxygen and carbon isotope analyses of the foraminifera Orbulina universa (planktic), Uvigerina peregrina (benthic) and Cibicides pachyderma (benthic) in 45 bottom samples from the archipelago of Bocas del Toro, Caribbean Panama, are used to address the reliability of stable isotope values in distinguishing differences among neritic surface water and middle neritic to upper bathyal depths. The significance of variation in isotope values within stations, between stations within depth-defined groups, and between depths was determined with Analysis of Variance. Isotope values differ significantly among stations with few exceptions; thus, within-station error is minimal. δ18O values of O. universa across the open shelf are the same. Oxygen isotope ratios of U. peregrina discriminate outer shelf to upper slope depths well. δ18O values of C. pachyderma from the inner middle shelf, outer middle shelf, and inner outer shelf are significantly different, and mean values from 33m to 240m are strongly correlated with water depth. Cibicides pachyderma from two stations shows strong δ18O evidence of downslope transport of 80 and 160m, corroborated by foraminiferal assemblages. δ13C can only differentiate middle shelf and outermost outer shelf to upper slope depths. Oxygen isotope values of O. universa and U. peregrina generally agree with predicted temperatures, and those of C. pachyderma are consistently low. Comparisons of δ18O values of benthic and planktic foraminifera, and neritic and deep-sea planktic foraminifera, enable qualitative and even quantitative estimates of paleodepth and paleosalinity, enabling their use in Neogene studies of sedimentary rocks within the region.