Variability in calcitic Mg/Ca and Sr/Ca ratios in clones of the benthic foraminifer Ammonia tepida

de Nooijer, L. J. and Hathorne, E. C. and Reichart, G. J. and Langer, G. and Bijma, J. (2014) Variability in calcitic Mg/Ca and Sr/Ca ratios in clones of the benthic foraminifer Ammonia tepida. Marine Micropaleontolog, 107. pp. 32-43. ISSN 0377-8398 DOI 10.1016/j.marmicro.2014.02.002

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Abstract

Biological activity introduces variability in element incorporation during calcification and thereby decreases the precision and accuracy when using foraminifera as geochemical proxies in paleoceanography. This so-called ‘vital effect’ consists of organismal and environmental components. Whereas organismal effects include uptake of ions from seawater and subsequent processing upon calcification, environmental effects include migration- and seasonality-induced differences. Triggering asexual reproduction and culturing juveniles of the benthic foraminifer Ammonia tepida under constant, controlled conditions allow environmental and genetic variability to be removed and the effect of cell-physiological controls on element incorporation to be quantified. Three groups of clones were cultured under constant conditions while determining their growth rates, size-normalized weights and single-chamber Mg/Ca and Sr/Ca using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Results show no detectable ontogenetic control on the incorporation of these elements in the species studied here. Despite constant culturing conditions, Mg/Ca varies by a factor of ~ 4 within an individual foraminifer while intra-individual Sr/Ca varies by only a factor of 1.6. Differences between clone groups were similar to the intra-clone group variability in element composition, suggesting that any genetic differences between the clone-groups studied here do not affect trace element partitioning. Instead, variability in Mg/Ca appears to be inherent to the process of bio-calcification itself. The variability in Mg/Ca between chambers shows that measurements of at least 6 different chambers are required to determine the mean Mg/Ca value for a cultured foraminiferal test with a precision of ≤ 10%.

Item Type: Article
Uncontrolled Keywords: 2013AREP; IA67;
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
04 - Palaeobiology
Divisions: 04 - Palaeobiology
Journal or Publication Title: Marine Micropaleontolog
Volume: 107
Page Range: pp. 32-43
Identification Number: 10.1016/j.marmicro.2014.02.002
Depositing User: Sarah Humbert
Date Deposited: 11 Apr 2014 13:53
Last Modified: 15 Apr 2014 20:30
URI: http://eprints.esc.cam.ac.uk/id/eprint/3021

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