Exploring sediment dynamics from source to sink in the Murray-Darling basin using cosmogenic 14C, 10Be, and 26Al

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Australasian Quaternary Association Inc.
The relatively short half-life of 14C, namely, 5730 years, means that, compared to the other cosmogenic nuclides, it is substantially more sensitive to short term variations in process rates. Both the erosion of steep mountains and the dynamics of sediment transport, storage and recycling occur over timescales that are too short to be detectable by the cosmogenic nuclides that are currently used routinely, namely 10Be and 26Al. In situ 14C on the other hand is ideally suited for these short timescales, and used in combination with 26Al and 10Be, it will allow for rapid fluctuations in process rates and/or the relatively short timescales that characterise sediment transfer and storage to be measured accurately. The above make in situ 14C an important addition to the cosmogenic radionuclide toolkit. We present results of in situ cosmogenic 14C system blank and calibration sample measurements obtained with the recently established ANSTO/UOW in situ 14C extraction system. The 14C extraction scheme follows the design of the University of Cologne, which exploits the phase transformation of quartz to crystobalite to quantitatively extract the carbon as CO2. Offline high-temperature furnace extraction allows a relative rapid sample throughput and can accommodate samples ranging between 0.5 to 4 grams of clean quartz. Following extraction and isolation, the CO2gas is graphitised using a micro-furnace and then measured using AMS similarly to routine small radiocarbon samples. We also present results of 14C, 26Al, and 10Be analyses from sediment samples collected from Australia’s largest river system, the Murray-Darling basin. We use the downstream changes in the ratios of the three radionuclides in samples collected at key locations along the rivers to quantify sediment mixing and sediment storage times in the river basin. Substantial 26Al/10Be ‘burial’ signal is observed in downstream Murray and Darling samples, while in situ 14C suggests complex burial-exposure histories in these samples. This could have implication of interpreting geochemical proxies at the outlet of Murray-Darling Basin for identification of paleoclimate driven sediment sources (i.e. Monsoon vs. Westerlies). © The Authors
Settling ponds, Sedimentation, Runoff, Water, Rivers, Carbon 14, Beryllium 10, Aluminium 26, Isotopes, Storage, Water reservoirs, Environmental transport, Carbon dioxide
Fülöp, R. H., Codilean, A. T., Marx, S., Cohen, T., Fink, D., Yang, B., Smith, A., Wilcken, K., Fujioka, T., & Wacker, L. (2018). Exploring sediment dynamics from source to sink in the Murray-Darling basin using cosmogenic 14C, 10Be, and 26Al. Paper presented at the AQUA Biennial Conference, Canberra, 10-14 December 2018, (pp. 35). https://aqua.org.au/wp-content/uploads/2019/10/AQUA-2018-Program.pdf