Seasonal water mixing and carbonate cycling in the Coorong lagoon, South Australia constrained via Sr isotope tracers (87Sr/86Sr and δ88/86Sr)

Shao Y1, Farkaš J1, Mosley L1, Tyler J1, Wong H2, Priestley S1, Gillanders B1

1University Of Adelaide,

2Australian Nuclear Science and Technology Organisation

Abstract:

The Coorong lagoon in South Australia, located at the end of the River Murray system, exhibits extensive ranges in salinity, carbonate saturation states, and thus CaCO3 dynamics (i.e., dissolution vs precipitation), which is an important but poorly constrained component of the global carbon cycle. In This study presents data of radiogenic and stable Sr isotope tracers (87Sr/86Sr and δ88/86Sr) from water samples collected from the Coorong region during 2018-2019, coupled with elemental concentration data and carbonate mineral saturation states to constrain the seasonal and spatial variations of water sources and CaCO3 dynamics in the lagoon, which in turn, is beneficial to future water management of the Coorong. Overall, 87Sr/86Sr and Mg/Na data (i.e., conservative tracers) indicate that most of the Coorong lagoon waters were mixtures of Southern Ocean seawater and various sources of continental waters. Coupled 87Sr/86Sr and δ88/86Sr data suggest that the Coorong South Lagoon acts as a net sink of dissolved inorganic carbon to form calcium carbonate (mainly aragonite). The interplay of salinity and alkalinity caused the largest increase in δ88/86Sr (from 0.41‰ to 0.48‰) for studied South Lagoon sites from August to December 2018, which accounts for ~25-30% of total Sr removal in the lagoon via aragonite precipitation based on a Rayleigh fractionation modelling.


Biography:

3rd year PhD student in University of Adelaide, mainly interested in alkaline metal isotopes in coastal systems as tracers of water source mixing, carbonate dynamics, and redox states, and further application of these tracers in reconstructing the paleo-climate of the local coastal system.