Relationship between shell size, thickness and stable isotopes in individual planktonic foraminifera from two Equatorial Atlantic cores

• Published in: The Journal of Foraminiferal Research
• Main Authors: Billups, K., Spero, H. J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cushman Foundation for Foraminiferal Research 1995
• Subjects: Planktonic foraminifera
• Online Access: https://oceanrep.geomar.de/id/eprint/38738/; https://oceanrep.geomar.de/id/eprint/38738/1/Billups.pdf; https://doi.org/10.2113/gsjfr.25.1.24

We establish the relationship between shell oxygen(6le0) and carbon (S13C) isotopic composition and size and thickness for the planktonic foraminifers Orbulina universa and Neogloboquadrina dutertrei (size only). The degree to which the stable isotopic composition of individual shells correlates with shell size limits their applicability to paleoenvironmental reconstructions and must therefore be examined carefully. We selected shelis from four intervals from a western and an eastern equatorial Atlantic core corresponding to the glacialhnterglacial extremes of the last 150,000 years (isotope stages 1, 2, 5e, and 6). We estimate the shell thickness of 0, universa using a mathematical relationship between the geometry and physical properties of a calcite sphere. Thickness measurements on selected shells of this species confirm that the calculated thickness, once it has been corrected for shell porosity, is equivalent to the measured thickness. There are no consistent trends between 0. universa 6l80 or 613C values and shell size or thickness for the size range 450-900 pm. For N. dutertrei, there are no systematic fluctuations between shell 6l80 and size between 450-700 pm. N. dutertrei shells larger than 500 pm show no 613C : size relationship. We are confident that the stable isotopic variability contained in 0. universa (450-900 pm) and N. dutertrei (>500 pm) assemblages analyzed does not fluctuate with differences in shell morphology. The stable isotope data from these size ranges can thus be confidently used for paleoenvironmental reconstructions.