Development of a cosmogenic 14C extraction line at Dalhousie University
Abstract
Applications of cosmogenic 14C produced in minerals or ice on Earth are providing a new frontier in exposure dating and landscape erosion rate studies. In particular, the isotope can avoid problems facing longer-lived, lower production rate isotopes. The Dalhousie C-14 Extraction Line Laboratory (DCELL), the first cosmogenic 14C extraction line in Canada, was completed in January 2017 and is undergoing background and blank tests. Up to 8 g of quartz is melted using LiBO2 flux in an alumina boat to extract cosmogenic 14C. After removal of meteoric CO2 from the boat, flux, and quartz at low temperature (500˚ C), ultrapure O2 is flowed over the melting quartz aliquot at 1050˚ C to capture the in situ 14C as 14CO2. The 14CO2 is then purified using temperature-specific Liquid Nitrogen-slush traps to remove SOx, NOx, and other condensable gases, and a high temperature Ag-Cu mesh oxidation. The purified CO2 has been analysed for 14C/12C on the MICADAS gas-source accelerator at ETH Zurich, eliminating a need to graphitize the CO2. The first blank measurement of 1.96 x105 atoms was obtained using operating procedures developed to minimize flux mass and volatility while still achieving complete 14C extraction. The blank result is comparable to other extraction lines that use LiBO2 flux in alumina boats. The inter-laboratory comparison sample, CRONUS-A, was calculated to be 5.22x105 atoms/g which is within the concentration range presented by other 14C labs. In the upcoming year the DCELL will be used to determine erosion rates over the past 35 ka on alluvial fans used as strain markers in Panamint Valley, California, by measuring 14C saturation concentrations in amalgamated samples from just below the soil mixing zone. Those erosion rates are used to constrain 10Be and 36Cl depth profiles in order to improve the precision of the exposure age and slip rates. Furthermore, in situ 14C measured in quartz sand in till will be used to improve our knowledge of the erosional dynamics of ice sheets in the Canadian Arctic where mineral exploration is complicated by their polythermal basal thermal regime.
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2018
- Bibcode:
- 2018EGUGA..2011489P