Temperature sensitivity of planktic foraminifera and its influence on the oxygen isotope record

We used oxygen isotope measurements from Holocene surface sediments to infer optimum temperature and temperature sensitivity of the planktic foraminiferal species Globigerinoides ruber (pink) and Globigerinoides sacculifer. The (isotopic) optimum temperature of G. ruber (pink) is close to 27°C. G. sacculifer seems to have optimum vital conditions around 22°C and is less temperature sensitive than G. ruber (pink). Our estimations of optimum temperature and temperature sensitivity are in good accordance with laboratory and field investigations. Two simple experiments show that the temperature sensitivity of planktic foraminifera, determined from oxygen isotopes, can influence phase and amplitude of oxygen isotope records, if the temperature distribution at the sea surface changes through time. To use this distortion for paleoceanography, we suggest to derive an ‘isotopic transfer function’ which allows the calculation of average temperature, temperature variability and the isotopic composition of seawater if the oxygen-isotope differences between at least three species are known.