Carbon isotope offsets between benthic foraminifer species of the genus Cibicides (Cibicidoides) in the glacial sub-Antarctic Atlantic

• Published in: Paleoceanography
• Main Authors: Gottschalk, J., Vazquez Riveiros, N., Waelbroeck, C, Skinner, L. C., Michel, E, Duplessy, JC, Hodell, D., Mackensen, A
• Format: Article in Journal/Newspaper
• Language: English
• Published: AGU 2016
• Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems; Antarctic; Antarc*
• Online Access: http://eprints.esc.cam.ac.uk/4110/; http://eprints.esc.cam.ac.uk/4110/1/Gottschalk_et_al-2016-Paleoceanography.pdf; http://onlinelibrary.wiley.com/doi/10.1002/2016PA003029/abstract; https://doi.org/10.1002/2016PA003029

©2016. American Geophysical Union. All Rights Reserved. Epibenthic foraminifer δ 13 C measurements are valuable for reconstructing past bottom water dissolved inorganic carbon δ 13 C (δ 13 C DIC ), which are used to infer global ocean circulation patterns. Epibenthic δ 13 C, however, may also reflect the influence of 13 C-depleted phytodetritus, microhabitat changes, and/or variations in carbonate ion concentrations. Here we compare the δ 13 C of two benthic foraminifer species, Cibicides kullenbergi and Cibicides wuellerstorfi, and their morphotypes, in three sub-Antarctic Atlantic sediment cores over several glacial-interglacial transitions. These species are commonly assumed to be epibenthic, living above or directly below the sediment-water interface. While this might be consistent with the small δ 13 C offset that we observe between these species during late Pleistocene interglacial periods (Δδ 13 C = −0.19 ± 0.31‰, N = 63), it is more difficult to reconcile with the significant δ 13 C offset that is found between these species during glacial periods (Δδ 13 C = −0.76 ± 0.44‰, N = 44). We test possible scenarios by analyzing Uvigerina spp. δ 13 C and benthic foraminifer abundances: (1) C. kullenbergi δ 13 C is biased to light values either due to microhabitat shifts or phytodetritus effects and (2) C. wuellerstorfi δ 13 C is biased to heavy values, relative to long-term average conditions, for instance by recording the sporadic occurrence of less depleted deepwater δ 13 C DIC . Neither of these scenarios can be ruled out unequivocally. However, our findings emphasize that supposedly epibenthic foraminifer δ 13 C in the sub-Antarctic Atlantic may reflect several factors rather than being solely a function of bottom water δ 13 C DIC . This could have a direct bearing on the interpretation of extremely light South Atlantic δ 13 C values at the Last Glacial Maximum.