Reconstructing the palaeo-hydrology of The Coorong south lagoon via Strontium isotope tracers: 87Sr/86Sr and δ88/86Sr

Ms Yuexiao Shao1, Dr Juraj Farkaš1, Prof John Tibby1, Ms Deborah  Haynes1, Mr Henri Wong2, Dr Jonathan Tyler1

1University of Adelaide, Adelaide, Australia, 2Australian Nuclear Science and Technology Organisation, Sydney, Australia

Abstract:

The Coorong Lagoon, as part of the wetland system at the terminus of the River Murray, is recognised for its unique geomorphology and salinity gradient that ranges from fresh/brackish (< 35 PSU) in the north lagoon to hypersaline (> 70 PSU) in the south lagoon. The lagoon hydrology is controlled by seawater-continental water mixing processes,that are traceable via the radiogenic Strontium (Sr) isotopes (87Sr/86Sr). The hypersaline south lagoon is a sink for dissolved inorganic carbon (DIC); local carbonate precipitation is caused by calcite and aragonite oversaturation linked to high rates of evaporation. These processes are traceable via the novel stable Sr isotope (δ88/86Sr), which is particularly sensitive to mass-dependent isotope fractionation processes such as carbonate precipitation/dissolution. Importantly, the south lagoon has seen dramatic hydrological and ecological changes over the last ~200 years, evident from geochemical and diatom records from sediment cores [1]. This study focuses on Sr isotope analyses (87Sr/86Sr and δ88/86Sr) of fossil shells (species Arthritica helmsi) from a sediment core in the south lagoon, and is complemented by elemental concentrations to better constrain (i) variability in the mixing of water sources over the last ~2500 years; and (ii) changing palaeo-salinity associated with changes in carbonate precipitation/dissolution. Preliminary data confirms significant continental water input into the south lagoon and indicates increased carbonate precipitation towards present time throughout the history of the sediment core, which contributed to an improved understanding of the paleo-hydrology of The Coorong south lagoon.

[1] McKirdy et al. (2010) Organic Geochemistry 41, 96-110.


Biography:

My project is mainly focused on developing and applying novel geochemical techniques to reconstruct paleo-hydrology in carbonate-producing coastal environments such as the Coorong. The acquired data in turn, is not only critical for the reconstruction of the local paleo-environment, but also for the prediction of future climate variability in this unique coastal ecosystem, which is particularly sensitive to anthropogenic and climatic perturbation.