Calibrations for benthic foraminiferal Mg/Ca paleothermometry and the carbonate ion hypothesis

Elderfield, H. and Yu, J. and Anand, P. and Kiefer, T. and Nyland, B. (2006) Calibrations for benthic foraminiferal Mg/Ca paleothermometry and the carbonate ion hypothesis. Earth and Planetary Science Letters, 250 (3-4). pp. 633-649. ISSN 0012-821X DOI 10.1016/j.epsl.2006.07.041

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Abstract

Benthic foraminiferal magnesium/calcium ratios were determined on one hundred and forty core-top samples from the Atlantic Ocean, the Norwegian Sea, the Indian Ocean, the Arabian Sea and the Pacific Ocean, mostly at sites with bottom water temperatures below 5 °C. Mg/Ca ratios are consistently lower, by not, vert, similar 0.2 mmol/mol, in samples cleaned using oxidative and reductive steps than using oxidative cleaning. Differences between Cibicidoides species have been identified: Mg/Ca of Cibicidoides robertsonianus > Cibicidoides kullenbergi > Cibicidoides wuellerstorfi. Comparison with bottom water temperatures support observations of lowered Mg/Ca of C. wuellerstorfi at temperature below not, vert, similar 3 °C compared with values predicted by published calibrations and from other Cibicidoides species. Hydrographic data shows that carbonate ion saturation (Δ[CO32−]) decreases rapidly below this temperature. An empirical sensitivity of Δ[CO32−] on Mg/Ca has been established for C. wuellerstorfi of 0.0086 ± 0.0006 mmol/mol/μmol/kg. A novel application using modern temperatures and Last Glacial Maximum temperatures derived via pore fluid modelling supports a carbonate ion saturation state effect on Mg incorporation. This may significantly affect calculated δ18Oseawater obtained from foraminiferal δ18O and Mg/Ca temperature.

Item Type:	Article
Uncontrolled Keywords:	2006 AREP IA52 2006 P
Subjects:	01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions:	01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title:	Earth and Planetary Science Letters
Volume:	250
Page Range:	pp. 633-649
Identification Number:	10.1016/j.epsl.2006.07.041
Depositing User:	Sarah Humbert
Date Deposited:	16 Feb 2009 13:02
Last Modified:	23 Jul 2013 10:06
URI:	http://eprints.esc.cam.ac.uk/id/eprint/269

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