Carbon and oxygen isotope geochemistry of live (stained) benthic foraminifera from the Aleutian Margin and the Southern Australian Margin |
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Authors: | Chandranath Basak Anthony E. Rathburn M. Elena Pérez Jonathan B. Martin Jared W. Kluesner Lisa A. Levin Patrick De Deckker Joris M. Gieskes Michelle Abriani |
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Affiliation: | 1. Indiana State University, Geology Program, Science Building 179, Terre Haute, IN 47809, USA;2. Department of Palaeontology, The Natural History Museum, Cromwell Rd., London, SW7 5BD, UK;3. Department of Geological Sciences, University of Florida, Gainesville, Florida 32611, USA;4. Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093-0218, USA;5. Department of Earth and Marine Sciences, The Australian National University, Canberra 0200, Australia |
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Abstract: | Comparisons of ambient bottom-water geochemistry and stable isotopic values of the tests of living (stained) calcareous benthic foraminifera from the North Pacific (on the Aleutian Margin, water depth 1988 m) and Murray Canyons group in the Southern Indian Ocean (Australian Margin, water depths 2476 m and 1634 m) provide modern environmental analogs to calibrate paleoenvironmental assessments. Consistent with the hypothesis that microhabitat preferences influence foraminiferal isotopic values, benthic foraminifera from both margins were depleted in 13C with respect to bottom-water dissolved inorganic carbon (DIC). The carbon isotope values of deep infaunal foraminifera (Chilostomella oolina, Globobulimina pacifica) showed greater differences from estimates of those of DIC than shallow benthic foraminifera (Bulimina mexicana, Bolivinita quadrilatera, Pullenia bulloides). This study provides new isotopic and ecological information for B. quadrilatera. The mean Δδ13C value, defined as foraminiferal δ13C values minus estimated ambient δ13C values from the Aleutian Margin, is 0.97‰ higher for G. pacifica than the mean from the Murray Canyon. This difference may result either from genetic or biological differences between the populations or from differences in environmental isotopic influences (such as pore water differences) that were not accounted for in the equilibrium calculations. These analyses provide calibration information for the evaluation of bottom water conditions and circulation patterns of ancient oceans based on fossil foraminiferal geochemistry. |
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