A critical evaluation of calcium isotope ratios in tests of planktonic foraminifers

Gussone, Nikolaus, Hönisch, B., Heuser, A., Eisenhauer, Anton, Spindler, Michael and Hemleben, C. (2009) A critical evaluation of calcium isotope ratios in tests of planktonic foraminifers Geochimica et Cosmochimica Acta, 73 (24). pp. 7241-7255. DOI 10.1016/j.gca.2009.08.035.

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Abstract

We critically evaluate the applicability of Ca-isotope ratios in planktonic foraminifers as proxy for past sea surface temperatures (SST) and isotope composition of paleo-seawater (δ44Casw) reconstructions. Previous studies have shown discrepancies regarding the temperature sensitivity of Ca isotope fractionation in foraminifers of more than one order of magnitude. We present new data from the planktonic foraminifer species Orbulina universa, Globigerinoides sacculifer and Neogloboquadrina pachyderma (sinistral) from culture experiments, multinet deployments and coretop samples. Specimens of G. sacculifer cultured at low salinities (33–34.5) show predominantly no major temperature dependent Ca isotope fractionation, in contrast to previous individuals cultured at higher salinities of 34.5–36. The new data of O. universa are consistent with previously published results, revealing a small but significant temperature sensitivity. Calcium isotope fractionation in tests of N. pachyderma shows a significant variation with temperature, which is not uniform over the total investigated temperature range (−1.6 °C to +10 °C), possibly reflecting the influence of additional controlling factors besides temperature. Controlled dissolution experiments in the laboratory indicate that the Ca-isotope composition of G. sacculifer and N. pachyderma is relatively insensitive to partial dissolution of their tests.

Calcium isotope ratios in the planktonic foraminifers G. sacculifer and N. pachyderma (s) reveal a complex Ca isotope fractionation behaviour, which is not yet fully understood. Additional validation studies are crucial to enhance the basic understanding of the calcium isotope systematics in planktic foraminifer shells, and the potential for applying Ca-isotope ratios as proxies for seawater temperature and the oceanic Ca budget.

Document Type: Article
Keywords: calcium isotope ratios, planktonic foraminifers
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
DOI etc.: 10.1016/j.gca.2009.08.035
ISSN: 0016-7037
Projects: Future Ocean
Date Deposited: 07 Dec 2009 10:50
Last Modified: 27 Sep 2017 09:59
URI: http://eprints.uni-kiel.de/id/eprint/3588

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