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Title: A snapshot of groundwater residence times and water stable isotope results across the Australian continent (2015 update)
Authors: Cendón, DI
Jasechko, S
Meredith, KT
Hughes, CE
Markowska, M
Hollins, SE
Keywords: Ground water
Stable isotopes
Sedimentary basins
Groundwater recharge
Quaternary period
Issue Date: 5-Jul-2015
Publisher: Geoloogia instituut, Tallinn University of Technology
Citation: Cendón D.I., Jasechko S., Meredith K., Hughes C., Markowska M., Hollins S. (2015). A snapshot of groundwater residence times and water stable isotope results across the Australian continent (2015 update). Paper presented to the 4th Annual Meeting of G@GPS IGCP 618 "Project Palaeogroundwater from past and present glaciated areas", Estonia, 5-9 July 2015, (pp.13-14). Retrieved from:
Abstract: The G@GPS (Groundwater@Global Paleoclimatic Signals) was setup to explore links between paleogroundwater climate-derived observations (low resolution) and other palaeoclimate archives (higher resolution) e.g. speleothemes, palynological reconstructions, etc. Initially, an emphasis was placed in large aquifers (e.g. Baltic Aquifer Basin, etc) and intercontinental comparisons. However, the addition of smaller groundwater basins has improved paleoclimatic interpretations and allowed intracontinental interpretations. Several reasons contribute to this: 1) better geographic distribution; 2) smaller basins are more likely to contain groundwater with residence times between 0 to ~30 ka, the gap where 14CDIC can obtain best results and better matching to other paleoclimate proxy records; 3) shorter flow paths minimize intense water-interaction processes, maximising residence time estimations; and 4) small systems are more likely to record local conditions while bigger counterparts (e.g. Great Artesian Basin, Australia) represent mixtures of several regional recharge zones in some cases thousands of kilometres away from the recharge zone. During the last 5 years several new datasets have been incorporated into our snapshot of Australia groundwater (Fig 1). The need to understand inter-aquifer connectivity, particularly within coal seam gas (CSG) exploitation zones, and regulatory assessments of aquifer sustainability, have driven most of the research in Australia. In the case of CSG studies, many groundwater samples are beyond 14C capabilities and occasionally 36Cl/Cl residence times have been suggested. In order to interpret the distribution of paleo-groundwater recharge across Australia, we have assembled a continent wide database comprising over 1300 groundwater samples. Information includes geographical, geological data as well as available geochemical information. Geochemical data include mostly 14CDIC, δ13CDIC and water stable isotopes (δ18O, δ2H) with other complementary information such as 3H activity or major ion composition available in some cases. In general, 14CDIC shows a wide spread of values (0 – 140 pmC) with an average of ~51 pmC. Radiocarbon values have been filtered so all “bomb-pulse” affected samples are considered modern, prior to building a chronological framework. Due to the uncertainties associated with hydrogeochemical 14C corrections and the difference of input data for each individual study, original corrections were maintained, if provided. Any other treatment was done on individual basis when data from neighbouring basins allowed better estimates for input parameters. Interestingly, there are observable patterns and distinctions in the frequency of pmC data over the last ~30 ka. The greatest frequency of observations occurred in the range of 0 – 10 pmC, which assuming no sampling bias, would suggest important late Pleistocene recharge. There also seems to be a slight ‘dip’ in pmC frequency during the period of 20–40 pmC. This may indicate a period of less recharge and/or an enhanced dryness with a diminished water cycle, roughly coinciding with the end of the last glacial. Water stable isotopes show the meteoric origin of groundwater across the continent and reveal important evaporation processes during recharge for some basins, including: Otway Basin (SA), Murchinson River Basin (WA), West Canning Basin (WA), Murray Basin (Lake Cooper, VIC) and Murray-Darling Basin (NSW, QLD). In general groundwater isotopic trends are more depleted from the coast to the interior, particularly in northern areas where major rainfall is dominated by the Australasian monsoon. The increasing aridity in the Holocene in most of the continent suggests only large, rainfall/flooding events produced effective recharge. On a general temporal scale, modern groundwater generally appears to be more isotopically enriched.
ISBN: 978-9949-430-88-8
Appears in Collections:Conference Publications

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