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Title: Radiocarbon analysis of bulk and fractionated dissolved organic carbon from ground and surface waters in remote NW Queensland
Authors: Van der Ley, M
Cendón, DI
Graham, IT
Keywords: Carbon 14
Ground water
Surface waters
Issue Date: 5-Aug-2012
Publisher: Australian Geosciences Council
Citation: van der Ley, M., Cendón, D., & Graham, I. (2012). Radiocarbon analysis of bulk and fractionated dissolved organic carbon from ground and surface waters in remote NW Queensland. Paper presented to the 34th International Geological Congress 2012, "Unearthing our Past and Future - Resourcing Tomorrow", Brisbane, Australia, 5-10 August 2012. (pp. 922).
Abstract: Radiocarbon analysis of dissolved inorganic carbon (DIC) is prone to dilution by radiocarbon-free DIC from older hosts, particularly in carbonate-rich areas. Dissolved organic carbon (DOC) can provide a source of carbon less affected by water-rock interactions, but is rarely utilised due to more complex sample processing and potential residence time differences for specific fractions. We have developed and applied 14C methods of bulk and fractionated DOC to waters in the Lawn Hill region, remote NW Queensland. As groundwater chemistry here is largely controlled by interactions with Cambrian carbonates, analysis of 14CDIC required uncertain geochemical corrections. Additional samples were analysed from the Greater Sydney region, NSW, with greater variety of residence times and chemistries, to test the methodology. Bulk DOC was pre-concentrated in the field using a weak and non-selective resin, followed by extraction in the lab and fractionation into different DOC groups based on ultrafiltration and selective resin adsorption techniques. All samples were characterised using liquid chromatography and fluorescence to monitor the characteristics of different fractions. Comparisons of 14C activities of DIC and DOC highlight the effect of carbonate dissolution and the usefulness of DOC in radiocarbon analyses. DIC activities were consistently lower than those of DOC, particularly in carbonate-rich regions. Additionally, comparison of fractionated DOC samples showed varying 14C activities, indicating that fractionation may be required for reliable residence times.
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