Effect of Temperature and Salinity on Stable Isotopic Composition of Shallow Water Benthic Foraminifera: A Laboratory Culture Study

Abstract : Quantitative estimation of past climatic parameters from stable isotopic composition of foraminifera relies on estimating the precise relationship between stable isotopic composition of the species analyzed and the physico-chemical factors of the seawater. This relationship can be established either on species collected from surface sediments or in plankton tows. Another method to establish such relationships is by subjecting the foraminiferal species to known physico-chemical parameters in the laboratory. In the present work, shallow water benthic foraminiferal species, Rosalina sp. and Pararotalia nipponica were subjected to different combinations of seawater temperature (25°C to 35°C) and salinity (25 psu to 37 psu) in the laboratory to assess their stable oxygen isotopic composition and its applicability in determining seawater temperature and salinity. The stable isotopic ratio of the species shows no consistent relationship with salinity. The relationship between δ18O foraminifera and seawater temperature is more consistent for P. nipponica than for Rosalina sp. Salinity appears to have less control on δ18O foraminifera as compared to the seawater temperature, within the studied salinity and temperature range. The study shows that the changes in δ18O of P. nipponica can be used effectively to infer past seawater temperature changes.