Carbon isotope composition in modern brachiopod calcite: A case of equilibrium with seawater?

Author(s): Uwe Brand, K. Azmy, E. Griesshaber, M.A. Bitner, Alan Logan, Martin Zuschin, E. Ruggiero, P.L. Colin
Abstract: We examined a large number of modern, shallow-water articulated brachiopods representing the orders Terebratulida, Rhynchonellida, Thecideida and one inarticulated brachiopod of the order Craniida from polar to tropical regions for their carbon isotope compositions. Based on our detailed investigation, we recommend avoiding fast growth areas such as the youngest shell increments; in addition, the primary layer and transition zone calcites of brachiopods must be avoided because they are in carbon and oxygen isotope disequilibrium with ambient seawater. After adjusting isotope compositions for the Mg effect, we observed no significant difference (p>0.05) in δ¹³C values between dorsal and ventral valves of our articulated brachiopods. Using the calcite-bicarbonate enrichment factor (ε) in conjunction with δ¹³C values of dissolved inorganic carbon of habitat seawater, we conclude that modern shallow-water articulated and some inarticulated brachiopods incorporate oxygen (Brand et al., 2013) and carbon isotopes into shell calcite of secondary and/or tertiary layers in apparent equilibrium with ambient seawater. Within the general concept of equilibrium incorporation, with seawater, shell δ¹³C values are an excellent recorder of local/global seawater environments and water mass circulation. Thus, application of the Mg-effect permits brachiopods to be an extremely powerful archive, and δ¹³C values more precise proxy and tracer of past changes in marine productivity, evolution of seawater carbon chemistry and variation in the global carbon cycle.
Organisation(s): Department of Palaeontology
External organisation(s): University of New Brunswick (UNB), Brock University, Memorial University of Newfoundland, Ludwig-Maximilians-Universität München, Polish Academy of Sciences (PAS), Università degli studi di Napoli Federico II, Coral Reef Research Foundation
Journal: Chemical Geology
Volume: 411
Pages: 81-96
No. of pages: 16
ISSN: 0009-2541
DOI: https://doi.org/10.1016/j.chemgeo.2015.06.021
Publication date: 09-2015
Peer reviewed: Yes
Austrian Fields of Science 2012: 105118 Palaeontology
Keywords
ASJC Scopus subject areas: Geochemistry and Petrology, Geology
Portal url: https://ucrisportal.univie.ac.at/en/publications/carbon-isotope-composition-in-modern-brachiopod-calcite-a-case-of-equilibrium-with-seawater(21c73d1d-1e33-40d3-9fe9-2ccddc2cd18e).html

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