Browsing by Author "Chamberlayne, BK"

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    Impact of salinity and carbonate saturation on stable Sr isotopes (δ88/86Sr) in a lagoon-estuarine system
    (Elsevier, 2021-01-15) Shao, YX; Farkaš, J; Mosely, LM; Tyler, JJ; Wong, HKY; Chamberlayne, BK; Raven, M; Samanta, M; Holmden, C; Gillanders, BG; Kolevica, A; Eisenhauer, A
    Local carbonate cycling in lagoon-estuarine systems, involving processes such as inorganic and biogenic carbonate precipitation/dissolution, represents an important but poorly constrained component of the coastal carbon budget. This study investigates the sensitivity of stable Sr isotope tracer (δ88/86Sr) with respect to carbonate saturation and salinity of local waters in the Coorong, Lower Lakes and Murray Mouth (CLLMM) estuary in South Australia. The CLLMM has an extensive range of salinity from fresh to hypersaline (from ∼0 to over 100 PSU), with corresponding variations in water chemistry and major ion composition that in turn controls mineral saturation states, and thus CaCO3 precipitation/dissolution in local waters. Here we use the novel δ88/86Sr tracer in tandem with the more established radiogenic Sr isotope ratio (87Sr/86Sr), where the latter is a robust proxy for Sr sources and thus water provenance. We also produced a geochemical (PHREEQC) model of calcium carbonate (CaCO3) saturation changes across this unique lagoon-estuarine system. The results indicate a systematically increasing trend of δ88/86Sr (from ∼0.25‰ to ∼0.45‰) with increasing salinity and CaCO3 (aragonite, calcite) saturation indices of the coastal waters, which in turn suggest an overall control of carbonate dissolution/precipitation processes on the stable Sr isotope composition in the CLLMM system. This was further corroborated by Ca isotope data (δ44/40Ca) published previously on the same samples from the Coorong, as well as a quantitative simulation of local carbonate removal in the lagoon based on Rayleigh modelling and Sr isotope data. Overall, our results confirm that a coupled Sr isotope approach (combining 87Sr/86Sr and δ88/86Sr) can be used to constrain not only the main water sources (continental versus marine Sr) but also local CaCO3 dissolution/precipitation processes, and thus inorganic carbon and coastal carbonate cycling in the CLLMM system. Finally, this coupled δ88/86Sr and 87Sr/86Sr approach can be potentially applied to fossil carbonate archives to reconstruct paleo-hydrology and salinity changes in the CLLMM and/or other carbonate-producing coastal systems. © 2020 Elsevier Ltd.
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    Palaeohydrology of the southern Coorong Lagoon, inferred from oxygen isotope ratios of the bivalve Arthritica helmsi
    (Australasian Quaternary Association, 2021-07-08) Chamberlayne, BK; Tyler, JJ; Gillanders, BM; Jacobsen, GE; Tibby, J; Haynes, D
    Understanding the resilience of aquatic ecosystems to climate and human impacts requires a long term perspective that is rarely attainable via standard monitoring programs. This is evident in the South Lagoon of the Coorong in South Australia where a history of ecosystem management has been based on limited knowledge of the range of natural variability. Here, we present a ~1750 year record of hydrological variability inferred from the oxygen isotope ratios of the bivalve Arthritica helmsi. Analysis of the controls of oxygen isotope fractionation in modern waters, and modern populations of A. helmsi inform the interpretation that the oxygen isotope ratios of shells preserved in the Coorong sediments reflect the precipitation/evaporation balance of lagoonal waters. Centennial scale variability in the oxygen isotope based hydroclimate record from the Coorong is consistent with other records in the region, contributing to a deeper understanding of the scale of natural hydrological variability in southeastern Australia during the last 2000 years. While the sedimentary bivalve data suggest that the lagoon was slightly less saline in pre-European times, the range of oxygen isotope variability within sedimentary bivalve shells is not statistically distinguishable from the range predicted by the hydrological conditions of the modern day Coorong South Lagoon, suggesting that present day hydrological conditions are not markedly unusual in the context of the past 1750 years. As a consequence, our bivalve oxygen isotope data suggest that major hydrological alterations to the Coorong South Lagoon – for example flushing the lagoon with sea water – could result in a departure from the natural hydrological state of the system over the last 2000 years.