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Studies of pre-bomb mollusks live-collected around the Australian coastline have concluded that near-shore marine radiocarbon reservoir effects are small and relatively uniform. These studies are based on limited samples of sometimes dubious quality representing only selective parts of Australia's lengthy coastline. We systematically examine spatial variability in the marine radiocarbon reservoir effect (ΔR) through analysis of 292 live-collected mollusk samples across the Australian mainland coasts and near-shore islands subject to strict selection criteria. This study presents 233 new ΔR values combined with an evaluation of 59 previously published values. Results demonstrate significant spatial variability in marine radiocarbon reservoir effects across the study region. ΔR values range from 68 ± 24 14C years off the Pilbara region of Western Australia to –337 ± 46 14C years in the southern Gulf of Carpentaria in Queensland. Most sets of local values exhibit internal consistency, reflecting the dominant influence of regional oceanography, including depletion in ΔR values southwards along the eastern Australian coastline coincident with the East Australian Current. Anomalous values are attributed to inaccurate documentation, species-specific relationships with the carbon cycle and/or short-term fluctuations in marine radiocarbon activities. To account for the heterogeneous distribution of marine 14C, we recommend using a location specific ΔR value calculated using the Australian ΔR Calculator, available at: https://delta-r-calc.jcu.io/. [ABSTRACT FROM AUTHOR]

Lake sediments are important archives of past climate variability and lake responses to climate. In order to accurately infer past climates, it is necessary to understand, and account for, the ecological processes that affect the record of indicators preserved in lake sediment. This is particularly the case with respect to the concentration of carbon and nitrogen (TOC, TN, and calculated C:N), and the stable isotope composition of organic matter preserved in lake sediments. These are common, yet ambiguous, tracers of environmental change. Ideally, palaeoenvironmental reconstructions using the concentration and isotope composition of organic matter should be grounded in a detailed understanding of the sources of the organic material. This study documents the history and evolution of Blue Lake, an environmentally and culturally important oligotrophic, groundwater window lake on North Stradbroke Island, Queensland, Australia. We utilise organic matter δ13C, TOC, TN, and C:N from a 2.4 m sediment core with a basal age of 7.5 cal kyr BP, to investigate changing organic matter sources as a measure of the climate sensitivity of Blue Lake. This interpretation is supported by data from contemporary algae, aquatic and terrestrial plants, and catchment soils. We show that lake nutrient dynamics drove an increase in algal biomass at 4.2 cal kyr BP. This change coincides with a widely documented intensification of the El Niño-Southern Oscillation, which we infer to have influenced lake nutrient concentrations by reducing groundwater throughflow. Climatic changes resulted in marked changes in lake primary productivity, despite relatively little turnover of the lake diatom flora and catchment vegetation. This suggests that south-east Queensland dune lakes are sensitive to climate changes and helps to refine past and future palaeoclimate research using sediments from these lakes. It also indicates that increased nutrient concentrations in Blue Lake may result from projected changes in 21st Century climate. [ABSTRACT FROM AUTHOR]

Debate about the nature of climate and the magnitude of ecological change across Australia during the last glacial maximum (LGM; 26.5–19 ka) persists despite considerable research into the late Pleistocene. This is partly due to a lack of detailed paleoenvironmental records and reliable chronological frameworks. Geochemical and geochronological analyses of a 60 ka sedimentary record from Brown Lake, subtropical Queensland, are presented and considered in the context of climate-controlled environmental change. Optically stimulated luminescence dating of dune crests adjacent to prominent wetlands across North Stradbroke Island (Minjerribah) returned a mean age of 119.9 ± 10.6 ka; indicating relative dune stability soon after formation in Marine Isotope Stage 5. Synthesis of wetland sediment geochemistry across the island was used to identify dust accumulation and applied as an aridification proxy over the last glacial-interglacial cycle. A positive trend of dust deposition from ca. 50 ka was found with highest influx occurring leading into the LGM. Complexities of comparing sedimentary records and the need for robust age models are highlighted with local variation influencing the accumulation of exogenic material. An inter-site comparison suggests enhanced moisture stress regionally during the last glaciation and throughout the LGM, returning to a more positive moisture balance ca. 8 ka. [ABSTRACT FROM AUTHOR]

Radiocarbon-calibrated amino acid racemization ages of 250 individually dated Tellina shells from two sediment cores are used to quantify molluscan time averaging with increasing burial depth in the shallow-water carbonate lagoon of Rib Reef, central Great Barrier Reef, Australia. The top 20 cm of sediment contain a distinct, essentially modern assemblage with a median age of only 5 yr. Sediment between 20 and 125 cm are age-homogeneous and significantly older than the surface sediment (median age 189 yr). Shell age distributions within layers indicate that the top 125 cm of lagoonal sediment is thoroughly mixed on a subcentennial scale. Shell size is an important correlate of shell half-life and an important determinant of the inferred age of sedimentary layers. These results illustrate the importance of bioturbation in these environments, indicate that age estimates in this depositional setting are sensitive to specimen choice, and document a size-dependent bias in death assemblage formation. [ABSTRACT FROM AUTHOR]