A bioavailable strontium isoscape of Australia. Initial contribution

Strontium isotopes (87Sr/86Sr) are useful in the earth sciences (e.g. recognising geological provinces, studying geological processes) as well as in archaeological (e.g. informing on past human migrations), palaeontological/ecological (e.g. investigating extinct and extant taxa’s dietary range and migrations) and forensic (e.g. validating the origin of drinks and foodstuffs) sciences. Recently, Geoscience Australia and the University of Wollongong have teamed up to determine 87Sr/86Sr ratios in fluvial sediments selected mostly from the low-density National Geochemical Survey of Australia (NGSA; www.ga.gov.au/ngsa). Three regional projects were focussed on: inland southeastern, northern, and southwestern Australia, together covering over 2.5 million km2 of catchment area. Whilst results on total Sr isotopic analyses have been reported previously (Caritat et al. 2022, 2023, 2024), a pilot study targeting the isotopic composition of bioavailable (or labile) Sr was conducted in parallel and this dataset is released here. In contrast to the total Sr isotope analyses, which were conducted mostly on NGSA Bottom Outlet Sediments (BOS; taken on average from ~60-80 cm depth), the bioavailable Sr work used Top Outlet Sediments (TOS; taken from 0-10 cm depth) to make the results more relevant to soil-, plant- and animal-focused applications. Approximately 1 g of air-dried, coarse-sieved (<2 mm) soil sample was reacted with 2.5 M ammonium acetate (buffered to pH 7) for 24 hr on a mixing table, to extract operationally defined plant-available cations (after Stewart et al. 1998). The solution was filtered at 0.45 µm and dried down to incipient dryness. The residue was re-dissolved in 2M nitric acid. The Sr was separated by chromatography and its 87Sr/86Sr ratio determined by multicollector-inductively coupled plasma-mass spectrometry. Results for 278 samples across all three regions demonstrate a wide range of bioavailable Sr isotopic values (0.7050 to 0.7812, median 0.7191) across Australia, reflecting a large diversity of source rock lithologies, geological, pedogenic and biogeochemical processes, and, ultimately, bedrock ages. Modelling and interpretation of this dataset will be presented elsewhere. The resulting bioavailable Sr isoscape for Australia, although sparse at the moment, and models to be derived therefrom, may have applications in archaeological, paleontological and ecological studies that aim to investigate past and modern animal (including humans) dietary habits and migrations.&nbsp;The new spatial dataset is publicly available through the Geoscience Australia portal (https://portal.ga.gov.au/).

References cited
Caritat, P. de, Dosseto, A., Dux, F., 2022. A strontium isoscape of inland southeastern Australia, Earth System Science Data, 14, 4271–4286, https://doi.org/10.5194/essd-14-4271-2022 
Caritat, P. de, Dosseto, A., Dux, F., 2023. A strontium isoscape of northern Australia, Earth System Science Data, 15, 1655–1673, https://doi.org/10.5194/essd-15-1655-2023 
Caritat, P. de, Dosseto, A., Dux, F., 2024. A strontium isoscape of southwestern Australia and progress toward a national strontium isoscape, Earth System Science Data Discussion [non peer-reviewed preprint], https://doi.org/10.5194/essd-2024-352 
Stewart, B. W., Capo, R. C., Chadwick, O. A., 1998. Quantitative strontium isotope models for weathering, pedogenesis and biogeochemical cycling, Geoderma, 82, 173–195, https://doi.org/10.1016/S0016-7061(97)00101-8 

Tags: Barkly-Isa-Georgetown, Darling-Curnamona-Delamerian, EFTF – Exploring for the Future, Isotopic Atlas of Australia, National Database of Archived Samples, Published_External, Regolith, Regolith and landscape evolution, Soil chemistry and soil carbon sequestration (excl. carbon sequestration science), Sr isotopes, Yilgarn
Organization: Geoscience Australia Data