13C-18O isotope signatures and 'clumped isotope' thermometry in foraminifera and coccoliths

Tripati, A. K. and Eagle, Robert A. and Thiagarajan, Nivedita and Gagnon, Alexander C. and Bauch, Henning and Halloran, Paul R. and Eiler, John M. (2010) 13C-18O isotope signatures and 'clumped isotope' thermometry in foraminifera and coccoliths. Geochimica et Cosmochimica Acta, 74 (20). pp. 5697-5717. DOI 10.1016/j.gca.2010.07.006

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Abstract

Accurate constraints on past ocean temperatures and compositions are critical for documenting climate change and resolving its causes. Most proxies for temperature are not thermodynamically based, appear to be subject to biological processes, require regional calibrations, and/or are influenced by fluid composition. As a result, their interpretation becomes uncertain when they are applied in settings not necessarily resembling those in which they were empirically calibrated. Independent proxies for past temperature could provide an important means of testing and/or expanding on existing reconstructions. Here we report measurements of abundances of stable isotopologues of calcitic and aragonitic benthic and planktic foraminifera and coccoliths, relate those abundances to independently estimated growth temperatures, and discuss the possible scope of equilibrium and kinetic isotope effects. The proportions of 13C–18O bonds in these samples exhibits a temperature dependence that is generally similar to that previously been reported for inorganic calcite and other biologically precipitated carbonate-containing minerals (apatite from fish, reptile, and mammal teeth; calcitic brachiopods and molluscs; aragonitic coral and mollusks). Most species that exhibit non-equilibrium 18O/16O (δ18O) and 13C/12C (δ13C) ratios are characterized by 13C–18O bond abundances that are similar to inorganic calcite and are generally indistinguishable from apparent equilibrium, with possible exceptions among benthic foraminiferal samples from the Arctic Ocean where temperatures are near-freezing. Observed isotope ratios in biogenic carbonates can be explained if carbonate minerals generally preserve a state of ordering that reflects the extent of isotopic equilibration of the dissolved inorganic carbon species.

Item Type:	Article
Uncontrolled Keywords:	2010AREP; IA61
Subjects:	01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions:	01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title:	Geochimica et Cosmochimica Acta
Volume:	74
Page Range:	pp. 5697-5717
Identification Number:	10.1016/j.gca.2010.07.006
Depositing User:	Sarah Humbert
Date Deposited:	24 Sep 2010 17:17
Last Modified:	23 Jul 2013 10:00
URI:	http://eprints.esc.cam.ac.uk/id/eprint/1941

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