Geography Seminar: Clumped isotope palaeothermometry: method development and application to terrestrial palaeoenvironmental archives

Free Public Lecture

Geography Seminar: Clumped isotope palaeothermometry: method development and application to terrestrial palaeoenvironmental archives

Theatre 2
Building No. 379
207 Bouverie Street

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T: 8344 9395

jmcook@unimelb.edu.au

Clumped isotope geochemistry builds upon conventional light-element gas-source stable-isotope mass spectrometry. Where CO2 is liberated from carbonate minerals, measuring cardinal masses 44, 45 and 46 to deduce 13C/12C and 18O/16O ratios (i.e. 13C and 18O values). In addition, mass 47 (largely 13C18O16O), 48 and 49 are measured providing information about the temperature of carbonate formation. The measurement of mass 47 examines the affinity of heavy isotopes of carbon dioxide (13C18O16O = 47CO2) bonding together in favour of the lighter isotopes (12C16O16O = 44CO2) in CO2 evolved from the reaction of carbonates with phosphoric acid. This process of “clumping” is reported as a deviation of the abundance of mass 47 (largely 13C18O16O) or Δ47 (in per mill ‰) relative to the natural random stochastic distribution. This deviation is sensitive to ambient temperature at the time of carbonate precipitation, so can be used to determine palaeotemperatures. Δ47 can be measured to a precision of ± 0.01 ‰, implying a resolution, at Earth-surface conditions, of about ±2°C from a sensitivity of about 0.004 per mil per degree Celsius. Furthermore, Δ47 is independent of the 18O/16O ratio of the water from which inorganic or biogenic carbonate minerals precipitate. Accordingly, palaeotemperatures can be deduced without knowledge of the past 18O/16O (as δ18O) of the water. The stable isotope laboratory at the University of Melbourne (UoM) operates a Nu Instruments Perspective-IS mass spectrometer, coupled to a Nu Instruments NuCarb sample preparation unit allowing for fully automated sample reaction, purification and analysis, increasing the increasing the analytical productivity of clumped isotope palaeothermometry greatly, compared to previous manual methods. This seminar will provide an overview and introduction to the clumped isotope method and instrument, its current performance (i.e. stability and precision) and the first reference material (ETH and Carrara Marble) and sample data (speleothem) data produced by the UoM clumped isotope facility as well as other current ongoing projects incorporating clumped isotope absolute temperature determinations.

Presenter

  • Dr Florian Dux
    Dr Florian Dux, School of Geography, the University of Melbourne