Corroborating ecological depth preferences of planktonic foraminifera in the tropical Atlantic with the stable oxygen isotope ratios of core top specimens

Abstract

Past variability in upper ocean thermocline depth is commonly estimated from the abundance of different species of planktonic organisms or the difference in oxygen isotopic composition between two species of planktonic foraminifera, one that lives in the mixed layer and one that lives in or near the thermocline. To test the latter relationships, we measured the oxygen isotopic composition of eight species of planktonic foraminifera (pink and white varieties of Globigerinoides ruber, Globigerinoides sacculifer without the final chamber, Orbulina universa, Pulleniatina obliquiloculata, Globorotalia menardii, Neogloborotalia dutertrei, and Globorotalia tumida) in surface sediment samples from 31 tropical Atlantic deep‐sea sediment cores. Bayesian analysis was used to compare measured oxygen isotopic compositions with their predictions based on modern data sets of annual temperatures and oxygen isotopic composition of ocean water in the upper 500 m at the core sites. Posterior probability densities for predictive model parameters were computed. Probability distributions of calcification depth for analyzed species corroborated their ecological preferences inferred from net tow and sediment trap data. Robustness of the habitat signals in core top specimens suggests that reconstructions of the entire upper ocean temperature profiles, not just their thermocline depth or temperature, might be possible.