Establishing standardised growth curves (SGCs) for OSL signals from individual grains of quartz: A continental-scale case study

The standardised growth curve (SGC) procedure is a technique that can facilitate rapid De estimation. In this study, we apply a least-squares (LS) normalisation procedure to single grains of quartz from multiple sites across Australia to test its applicability for establishing common SGCs for individual quartz grains from the same continent. Seventy-two samples from 18 sites were divided into two groups: (1) forty samples were used to construct common SGCs for Australian quartz, and (2) thirty-two samples were used to blind test the reliability of single-grain dating, based on the continental SGCs. Individual grains of quartz from different sites exhibit significant variability in their OSL decay curves, inherent signal intensities and dose response curves (DRCs) constructed using the single-aliquot regenerative dose (SAR) procedure. Application of a LS-normalisation procedure can largely reduce between-grain variability in the shape of the DRCs, allowing for the establishment of a suite of continental SGCs for Australian quartz. For radiation doses below 50 Gy, all investigated grains share a single, common SGC. At higher doses, the DRCs can be divided into six groups, with each group represented by a common SGC. The proportion of grains belonging to each group shows no discernable dependence on OSL properties, but varies significantly among the different sites. The single-grain De values determined using the continental SGCs are consistent at 2σ with those obtained from their individual DRCs. Likewise, the single-grain De distributions obtained using the SGCs and the individual DRCs are similar for most of the blind-test samples. Discrepancies for a small number of samples can be explained by the inclusion in the SGC De dataset of a few outlying values associated with aberrant or saturated grains. Our results show that the establishment of a group of continental SGCs can significantly reduce the machine time required for single-grain OSL measurements, enabling more samples and/or more grains to be measured per unit time. Continental SGCs also yield single-grain De estimates with comparable accuracy and precision to those obtained from individual DRCs constructed using the full SAR procedure.</p

Australian subtropical vegetation and wetland response to fire, climate and nutrient availability during the Holocene

The iconic sand dune systems of Minjerribah (North Stradbroke Island), in southeastern Queensland, Australia, host numerous lakes and swamps containing organic-rich sediment deposits that record changes in climate, fire and surrounding vegetation. Palaeoenvironmental reconstructions from individual locations can provide insights into changes in the environment, but determining the regional extent of these changes is seldom possible from a single site. Multi-site compilations help elucidate the geographical nature of environmental changes and determine if they are driven by local or regional forces. Here, a synthesis of palynological records from six Minjerribah wetlands using a muti-tiered Monte Carlo empirical orthogonal function (EOF) analysis allows island-wide patterns of vegetation change to be identified. Coherent changes in vegetation were recorded, with first-order changes (EOF1) indicating a long-term shift in vegetation composition from closed forests towards woodland and heath vegetation. A compilation of macroscopic and microscopic charcoal from the same sites shares coherent patterns of change with a rainfall record from the island, suggesting that regional fire occurrence between 7000 and 2000 cal a bp was driven primarily by long-term variations in rainfall and its influence on biomass. Comparison with fire activity, rainfall, sedimentary carbon, nitrogen and dust records from Minjerribah suggests that regional vegetation changes occur primarily in response to long-term changes in nutrients and increasing rainfall variability. This analysis highlights the multi-millennial connection between vegetation composition, climate, nutrients and fire occurrence across the Holocene in subtropical environments.</p

OCTOPUS Database v.2.2: Sedimentary Charcoal Records Sahul & NZ

An open database of sedimentary charcoal and black carbon records from Australia, New Guinea, and New Zealand. The data uses the WGS84/Pseudo-Mercator (EPSG: 3857) projected coordinate reference system. Sample metadata is comprehensive and includes bibliographic, contextual, and sample preparation and measurement related information

OCTOPUS Database v.2.2: Sedimentary Charcoal Records Sahul & NZ (units only)

An open database of sedimentary charcoal and black carbon records from Australia, New Guinea, and New Zealand. This collection contains unit-level information only. The data uses the WGS84/Pseudo-Mercator (EPSG: 3857) projected coordinate reference system. Sample metadata is comprehensive and includes bibliographic, contextual, and sample preparation and measurement related information