title: An experiment to assess the effects of diatom dissolution on oxygen isotope ratios.
abstract: BACKGROUND
  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‰.
authors.affiliation: NERC Isotope Geosciences Facilities, British Geological Survey, Nottingham, NG12 5GG, UK.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Smith
authors.affiliation: NERC Isotope Geosciences Facilities, British Geological Survey, Nottingham, NG12 5GG, UK.|Centre for Environmental Geochemistry, University of Nottingham, Nottingham, NG7 2RD, UK.
authors.forename: Melanie J
authors.initials: MJ
authors.lastname: Leng
authors.affiliation: Centre for Environmental Geochemistry, University of Nottingham, Nottingham, NG7 2RD, UK.|School of Geography, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
authors.forename: George E A
authors.initials: GE
authors.lastname: Swann
authors.affiliation: Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK.
authors.forename: Philip A
authors.initials: PA
authors.lastname: Barker
authors.affiliation: Environmental Change Research Centre, Department of Geography, UCL, London, WC1E 6BT, UK.
authors.forename: Anson W
authors.initials: AW
authors.lastname: Mackay
authors.affiliation: Centre for Hydrological and Ecosystem Science (CHES), Department of Geography, Loughborough University, Loughborough, LE11 3TU, UK.
authors.forename: David B
authors.initials: DB
authors.lastname: Ryves
authors.affiliation: NERC Isotope Geosciences Facilities, British Geological Survey, Nottingham, NG12 5GG, UK.
authors.forename: Hilary J
authors.initials: HJ
authors.lastname: Sloane
authors.affiliation: British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK.
authors.forename: Simon R N
authors.initials: SR
authors.lastname: Chenery
authors.affiliation: Department of Geology, University of Leicester, Leicester, LE1 7RH, UK.
authors.forename: Mike
authors.initials: M
authors.lastname: Hems
mesh_terms: D017377:Diatoms / Q000737:chemistry*; D005580:Fossils; D019015:Geologic Sediments; D008855:Microscopy, Electron, Scanning; D010103:Oxygen Isotopes / Q000032:analysis*; D013997:Time Factors
chemical_list: D010103:Oxygen Isotopes