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

Gottschalk, J. and Vazquez Riveiros, N. and Waelbroeck, C and Skinner, L. C. and Michel, E and Duplessy, JC and Hodell, D. and Mackensen, A (2016) Carbon isotope offsets between benthic foraminifer species of the genus Cibicides (Cibicidoides) in the glacial sub-Antarctic Atlantic. Paleoceanography, 31. pp. 1583-1602. ISSN 1944-9186 | 0883-8305 DOI https://doi.org/10.1002/2016PA003029

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Abstract

©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.

Item Type: Article
Uncontrolled Keywords: 2016AREP; IA70
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
08 - Green Open Access
Journal or Publication Title: Paleoceanography
Volume: 31
Page Range: pp. 1583-1602
Identification Number: https://doi.org/10.1002/2016PA003029
Depositing User: Sarah Humbert
Date Deposited: 19 Feb 2018 12:01
Last Modified: 19 Feb 2018 12:01
URI: http://eprints.esc.cam.ac.uk/id/eprint/4110

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