Browsing by Author "Raven, M"
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- ItemHolocene sediment records from World Heritage-listed K'gari/Fraser Island lakes (subtropical eastern Australia) highlight their sensitivity to drying(International Union for Quaternary Research (INQUA), 2019-07-30) Tibby, J; Barr, C; McInerney, F; Murphy, C; Raven, M; Leng, MJ; Tyler, JJ; Marshall, JC; McGregor, GB; Gadd, PSLakes are some of the most biodiverse, yet vulnerable, ecosystems on the planet. In Australia, the driest inhabited continent on earth, permanent lakes are relatively rare. By contrast, K'gari or Fraser Island, the largest sand island in the world, has a large number of permanent lakes and represents one of the few lake districts on the continent. The lakes of K'gari/Fraser island are remarkable because many are perched above the regional water table where an impermeable layer separates them from the sand below. They are one of the reasons why the island is listed as a UNESCO World Heritage site. Holocene sediment sequences have now been analysed from at least six lakes on K'gari/Fraser Island. It appears that there was marked aridity on the island from c. 8000 to 5000 ka BP. Some lakes dried completely at a time previously thought to be characterised by humid climates in the Australian subtropics. Interestingly, in some sequences there is little to no physical evidence of drying which is recorded as a hiatus in the accumulation of highly organic, acidic, lake sediments. The mid-Holocene dry phase recorded on K'gari/Fraser Island contrasts with evidence from North Stradbroke Island, a similar sand island which also has perched lakes, approximately 150 km to the south. As a result, there is strong potential to infer the Holocene regional climatology of the Australian subtropics at small spatial scales from these records. Lastly, our study highlights a largely unrecognised vulnerability of lakes on K’gari to drying and indicates a need to better understand their hydrology and response to projected future climate change. © The Authors.
- ItemImpact 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, ALocal 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.
- ItemIron-monosulfide oxidation in natural sediments: resolving microbially mediated S transformations using XANES, electron microscopy, and selective extractions(American Chemical Society, 2009-05-01) Burton, ED; Bush, RT; Sullivan, LA; Hocking, RK; Mitchell, DRG; Johnston, SG; Fitzpatrick, RW; Raven, M; McClure, S; Jang, LYIron-monosulfide oxidation and associated S transformations in a natural sediment were examined by combining selective extractions, electron microscopy and S K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The sediment examined in this study was collected from a waterway receiving acid−sulfate soil drainage. It contained a high acid-volatile sulfide content (1031 μmol g−1), reflecting an abundance of iron-monosulfide. The iron-monosulfide speciation in the initial sediment sample was dominated by nanocrystalline mackinawite (tetragonal FeS). At near-neutral pH and an O2 partial pressure of 0.2 atm, the mackinawite was found to oxidize rapidly, with a half-time of 29 ± 2 min. This oxidation rate did not differ significantly (P < 0.05) between abiotic versus biotic conditions, demonstrating that oxidation of nanocrystalline mackinawite was not microbially mediated. The extraction results suggested that elemental S (S08) was a key intermediate S oxidation product. Transmission electron microscopy showed the S08 to be amorphous nanoglobules, 100−200 nm in diameter. The quantitative importance of S08 was confirmed by linear combination XANES spectroscopy, after accounting for the inherent effect of the nanoscale S08 particle-size on the corresponding XANES spectrum. Both the selective extraction and XANES data showed that oxidation of S08 to SO42− was mediated by microbial activity. In addition to directly revealing important S transformations, the XANES results support the accuracy of the selective extraction scheme employed here. © 2009, American Chemical Society