Premium
Post‐mortem oxygen isotope exchange within cultured diatom silica
Author(s) -
Tyler Jonathan J.,
Sloane Hilary J.,
Rickaby Rosalind E.M.,
Cox Eileen J.,
Leng Melanie J.
Publication year - 2017
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.7954
Subject(s) - chemistry , isotopes of oxygen , oxygen , fractionation , oxygen isotope ratio cycle , isotope fractionation , isotope ratio mass spectrometry , biogenic silica , diatom , stable isotope ratio , isotope , analytical chemistry (journal) , environmental chemistry , mass spectrometry , mineralogy , chromatography , nuclear chemistry , geology , oceanography , organic chemistry , physics , quantum mechanics
Rationale Potential post‐mortem alteration to the oxygen isotope composition of biogenic silica is critical to the validity of palaeoclimate reconstructions based on oxygen isotope ratios (δ 18 O values) from sedimentary silica. We calculate the degree of oxygen isotope alteration within freshly cultured diatom biogenic silica in response to heating and storing in the laboratory. Methods The experiments used freshly cultured diatom silica. Silica samples were either stored in water or dried at temperatures between 20 °C and 80 °C. The mass of affected oxygen and the associated silica‐water isotope fractionation during alteration were calculated by conducting parallel experiments using endmember waters with δ 18 O values of −6.3 to −5.9 ‰ and −36.3 to −35.0 ‰. Dehydroxylation and subsequent oxygen liberation were achieved by stepwise fluorination with BrF 5 . The 18 O/ 16 O ratios were measured using a ThermoFinnigan MAT 253 isotope ratio mass spectrometer. Results Significant alterations in silica δ 18 O values were observed, most notably an increase in the δ 18 O values following drying at 40–80 °C. Storage in water for 7 days between 20 and 80 °C also led to significant alteration in δ 18 O values. Mass balance calculations suggest that the amount of affected oxygen is positively correlated with temperature. The estimated oxygen isotope fractionation during alteration is an inverse function of temperature, consistent with the extrapolation of models for high‐temperature silica‐water oxygen isotope fractionation. Conclusions Routinely used preparatory methods may impart significant alterations to the δ 18 O values of biogenic silica, particularly when dealing with modern cultured or field‐collected material. The significance of such processes within natural aquatic environments is uncertain; however, there is potential that similar processes also affect sedimentary diatoms, with implications for the interpretation of biogenic silica‐hosted δ 18 O palaeoclimate records.