Calibration of δsup18/supO of cultured benthic foraminiferal calcite as a function of temperature

摘要

The geochemical composition of deep-sea benthic foraminiferal calcite iswidely used to reconstruct sea floor paleoenvironments. The calibration ofthe applied proxy methods has until now been based on field observations incomplex natural ecosystems where multiple factors are interfering. However,laboratory experiments with stable physico-chemical conditions appear to bethe ideal way to evaluate the influence of a single parameter. In thispaper, we present the oxygen isotopic composition of deep-sea benthicforaminiferal shells entirely calcified under controlled experimentalconditions over a large temperature range (4 to 19 °C). The newlaboratory protocols developed for this study allowed us to produce largequantities of shells in stable conditions, so that also the shell sizeeffect could be investigated. It appears that when considering a narrow testsize range, the curve describing the temperature dependency of δ18O in Bulimina marginata is parallel to the thermodynamicallydetermined curve observedin inorganically precipitated calcite (−0.22‰ °C−1). Thisobservation validates the use of δ18O of this benthic speciesin paleoceanographical studies. Over the studied size range (50 to 300 μm),the effect of test size was 0.0014‰ μm−1, confirming previoussuggestions of a substantial test size effect on δ18O ofbenthic foraminifera. This study opens new perspectives for future proxycalibrations in laboratory set-ups with deep-sea benthic foraminifera (e.g. quantification of the influence of the carbonate chemistry).