Carbon isotopic fractionation in multiple species of planktonic foraminifera from core-tops in the tropical Atlantic

• Published in: The Journal of Foraminiferal Research
• Main Authors: Ravelo, A. C., Fairbanks, R. G.
• 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/38885/; https://oceanrep.geomar.de/id/eprint/38885/1/scan_2017-07-14_13-00-08r.1.pdf; https://doi.org/10.2113/gsjfr.25.1.53

Fifteen species and morphotypes of planktonic foraminifera from three core-tops in the tropical Atlantic were chosen for 6' 80 and 613C analyses. For each species several size fractions were analyzed. 6' 80 values are used to predict calcification temperature. Since temperature varies linearly with 6' 3C of IC02 of sea water due to mixing of upwelling waters with surface waters, it can be used to predict the 6'3C of IC02 of sea water. Measured d13C values are compared lo the predicted 613C of IC02 of sea water in order to determine the offsets of each size fraction of each species from the sea water values. Spinose species, and Neogloboquadri11a dutertrei have d13C offsets that vary as a function of size due to changing biological or kinetic fractionation effects as the foraminifera increases in size. For species measured from more than one site, the size-dependent fractionation is consistent between the sites which are located in regions with extremely different hydrographic conditions. Little to no size-dependent fractionation is found in Globorotalia menardii, G. tumida, G. injlata, G. crassaformis, G. truncatulinoides, and Pulleniatina obliquiloculata. Temperature dependenl kinetic fractionation of oxygen and carbon is found in G. menardii, G. crassaformis, G. trwrcatulinoides, and possibly G. injlata. No temperature dependent fractionation is apparent in G. tumida and P. obliquiloculata. lnter-core differences in the 613C offsets from sea water composition for each species may be due to inadequate constraints on sea water chemistry.