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An experiment to assess the effects of diatom dissolution on oxygen isotope ratios

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posted on 14.06.2016 by Andrew C. Smith, Melanie J. Leng, George E.A. Swann, Philip A. Barker, Anson W. Mackay, David Ryves, Hilary J. Sloane, Simon R.N. Chenery, Michael Hems
RATIONALE. Current studies which use the oxygen isotope composition from diatom silica (δ18O diatom) as a palaeoclimate proxy assume that the δ18O diatom value reflects the isotopic composition of the water in which the diatom formed. However, diatoms dissolve post mortem, preferentially losing less silicified structures in the water column and during/after burial into sediments. The impact of dissolution on δ18O diatom values and potential misinterpretation of the palaeoclimate record are evaluated. METHODS. Diatom frustules covering a range of ages (6 samples from the Miocene to the Holocene), environments and species were exposed to a weak alkaline solution for 48 days at two temperatures (20 °C and 4 °C), mimicking natural dissolution post mucilage removal. Following treatment, dissolution was assessed using scanning electron microscope images and a qualitative diatom dissolution index. The diatoms were subsequently analysed for their δ18O values using step-wise fluorination and isotope ratio mass spectrometry. RESULTS. Variable levels of diatom dissolution were observed between the six samples; in all cases higher temperatures resulted in more frustule degradation. Dissolution was most evident in younger samples, probably as a result of the more porous nature of the silica. The degree of diatom dissolution does not directly equate to changes in the isotope ratios; the δ18O diatom value was, however, lower after dissolution, but in only half the samples was this reduction outside the analytical error (2σ analytical error = 0.46‰). CONCLUSIONS. We have shown that dissolution can have a small negative impact on δ18O diatom values, causing reductions of up to 0.59‰ beyond analytical error (0.46‰) at natural environmental temperatures. These findings need to be considered in palaeoenvironmental reconstructions using δ18O diatom values, especially when interpreting variations in these values of <1‰.

Funding

The original data from this study was obtained by Michael Hems as part of his MGeol dissertation at Leicester University and was also supported by NERC Isotope Geosciences Facilities Steering Committee award IP-1533-0515.

History

School

  • Social Sciences

Department

  • Geography and Environment

Published in

RAPID COMMUNICATIONS IN MASS SPECTROMETRY

Volume

30

Issue

2

Pages

293 - 300 (8)

Citation

SMITH, A. ... et al., 2016. An experiment to assess the effects of diatom dissolution on oxygen isotope ratios. Rapid Communications in Mass Spectrometry, 30 (2), pp.293-300.

Publisher

© John Wiley & Sons

Version

AM (Accepted Manuscript)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Publication date

2015-12-14

Notes

This is the peer reviewed version of the following article: SMITH, A. ... et al., 2016. An experiment to assess the effects of diatom dissolution on oxygen isotope ratios. Rapid Communications in Mass Spectrometry, 30 (2), pp.293-300., which has been published in final form at http://dx.doi.org/10.1002/rcm.7446. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."

ISSN

0951-4198

eISSN

1097-0231

Language

en

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