An experiment to assess the effects of diatom dissolution on oxygen isotope ratios. (14th December 2015)

• Record Type: Journal Article
• Authors: Smith, Andrew C.; Leng, Melanie J.; Swann, George E. A.; Barker, Philip A.; Mackay, Anson W.; Ryves, David B.; Sloane, Hilary J.; Chenery, Simon R. N.; Hems, Mike
• Is Part Of: Rapid communications in mass spectrometry. Volume 30:Number 2(2016)
• Page Start: 293
• Page End: 300
• Publication Date: 2015-12-14
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.7446
• Languages: English
• ISSNs: 0951-4198

Abstract

Abstract : Rationale: Current studies which use the oxygen isotope composition from diatom silica (δ 18 Odiatom ) as a palaeoclimate proxy assume that the δ 18 Odiatom 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 δ 18 Odiatom 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 δ 18 O 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 δ 18 Odiatom 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 δ 18 Odiatom 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 δ 18 Odiatom values, especially when interpreting variations in these values of <1‰. Copyright © 2015 John Wiley & Sons, Ltd.