Radionuclide bioaccumulation in trees at an Australian legacy low-level waste site: concentration patterns in branches and foliage

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Late Holocene record of environmental changes, cyclones and tsunamis in a coastal lake, Mangaia, Cook Islands

A 4.3 m‐long peat sequence from the shore of Lake Tiriara, Mangaia, Cook Islands, was analyzed using an ITRAX core scanner equipped with a magnetic susceptibility meter. Variations in the elemental profiles, providing insights into long‐ and short‐term environmental changes over the last 3500 years, are supported by grain size data and diatom assemblages. The scattering ratio (Mo Inc/Mo Coh) was evaluated and found to represent a good proxy for organic matter in peat. X‐Ray Fluorescence (XRF) data were processed by principal component analysis that confirmed the distinction of biogenic and detrital phases, organic matter and elements of marine origin. The record preserved in the peat sequence includes a peatland infilling stage followed by alternating drier and wetter periods. A notable steady increase in clay associated with high counts of detrital elements from 2000–1700 cal yr BP is attributed to increased erosion, which is most probably linked with human colonization and/or more intense chemical weathering linked with a wetter climate. Freshwater gastropods (Melanoides sp. ), which were possibly introduced by humans, or are native, occupied the wetland during a period of lower water level about 1000–1100 cal yr BP. Short‐term changes in the elemental profiles are often linked with slight coarsening of the inorganic fraction that is, however, only revealed after grain size analysis. Peaks in marine indicators (Br, Cl, S, and/or Ca) associated with marine‐dominated diatom assemblages most probably represent marine incursions through the underground tunnel in the makatea, a fossilized, uplifted coral limestone rim. While none of the marine event units present characteristics typical of cyclone or tsunami deposits, the concurrent or absent peak of detrital elements (Fe, Si, Rb, Ti, K) attributed to increased erosion of the volcanic cone associated with a cyclone is used to distinguish both types of events, as also suggested by principal component analysis. © 1999-2020 John Wiley & Sons, Inc

Enhanced biocompatibility of PDMS (polydimethylsiloxane) polymer films by ion irradiation

PDMS films several microns thick deposited on polished Si wafers were irradiated with Mg, Ta, and Fe in the low energy range of 40 keV to 200 keV, and for doses of 1016–1018 ions/cm2. After irradiation the films surface is self-organised into 3D coherent and semi-coherent domains. As a consequence of the surface irradiation conditions and the surface boundary conditions, some domains are highly ordered in the form of parallel waves of approximately 1 μm in height, or the result can be semi-ordered regions or disordered regions. In addition, the surface energy of the irradiated polymer is increasing, as reflected in the decrease in its surface hydrophobicity, which is beneficial for cell adhesion. The irradiated samples were tested in vivo, and the results show an increase in viable cell count of up to 650%. © 2020 Elsevier B.

Groundwater isotopic record in southwest Australia: links to recharge variations and climatic conditions

Groundwater resources are a reliable and important source of water. Considering most large groundwater basins can contain ‘old’ groundwater where extraction exceeds groundwater recharge, knowledge of the past conditions and timing under which groundwater was recharged is needed to sustainably manage groundwater resources. Applying isotopic tools to groundwater contained in regional aquifer systems can provide low-resolution information on recharge intensity, recharge source and past climatic conditions for the region. Furthermore, an understanding of how groundwater recharge and climate have been connected in the past can be used to inform climate adaptation strategies for sustaining groundwater resources during climate change. Large regional groundwater systems, contained within the Perth Basin in southwest Australia were investigated in this study to provide information on groundwater recharge and climate over the past 35,000 years. Regional scale databases containing groundwater age and isotopic records are not commonly developed in Australia and are generally more site specific. Therefore, this Perth Basin database provides a unique opportunity to study and interpret a low-resolution palaeo-archive of groundwater recharge for southwest Australia. Groundwater ages (14CDIC) and stable O isotopes of water (δ18O) from two regional groundwater systems within the Perth Basin have been collated and groundwater ages calculated. The trends δ18O over time in the regional groundwater data are consistent with the groundwater flow line data supporting our hypothesis that groundwater δ18O is a proxy for palaeo-recharge. The Southern Perth Basin groundwater isotope record is interpreted to be a low resolution archive of recharge driven by changes in the relative intensity of past rainfall and recharge thresholds. This long-term stable isotopic recharge record provides a greater understanding of groundwater palaeo-recharge, as well as how recharge and climate have been connected in the past. © Author(s

Independent Bayesian age modelling in subtropical wetlands to assess the influence of global climate drivers across Australia

Rigorously dated, continuous sedimentological records capturing multiple glacial/interglacial cycles are important for evaluating the magnitude and range of drivers influencing ecosystem change in Australia. Multi-proxy palaeoenvironmental reconstructions are commonly used to identify changes in long-term environmental conditions, particularly when exploring the climatic backdrop to Australia’s large scale faunal extinctions. However, interpretations of these records may not be straightforward as local and regional climate signals are often mixed in proxy records. In order to evaluate whether improved temporal constraint can help with differentiating such convoluted signals, thereby increasing the confidence placed in the role of teleconnections across the Southern Hemisphere, we present a comprehensively dated 12.7 m (basal age ~130 ka) wetland core consisting of 21 optically stimulated luminescence and seven radiocarbon ages from North Stradbroke Island. The amalgamation of stratigraphic information and independent age constraints within a Bayesian framework, highlights the complex depositional history of Welsby Lagoon between late MIS 5 and MIS 2. ITRAX core scanning data reveals fluctuations in elemental abundance through time, in particular the decrease in the amount of aeolian sediment following MIS 3. Variability is attributed to regional environmental regime changes controlled by global drivers, including Heinrich events, and the influence of moisture across mainland Australia. The comprehensive dating approach undertaken at Welsby Lagoon highlights the role that the terrestrial palaeoenvironmental records of North Stradbroke Island can play in assessing long-term climate drivers across continental Australia, without relying exclusively on isotopic tuning of remote (ice core or marine) records. © The Author

A global database of Holocene paleotemperature records

A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format. © 2020 The Author

Atmospheric carbondisulfide and dimethylsulfide measurements at Cape Grim Australia, Marine, Terrestrial and Anthropogenic Contributions

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A new continuum regression model and its application to climate and rainfall isotope relationships

Climate field reconstruction using networks of rainfall-isotope proxies is an example of a problem that requires the estimation of a model that aims to predict one field (Y) using another field (X). The general problem is to estimate a subspace of X that retains useful information for predicting Y. Methods to estimate such subspaces include principal components regression (PCR), partial least squares (PLS), redundancy analysis (RDA), and canonical correlation analysis (CCA), but these methods typically do not estimate the same subspace. One solution is to treat these different methods as end members of a continuous manifold of regression subspaces. By weighting the end member solutions in some way, we can search for the best regression subspace over the manifold. In this study, a new continuum regression model is developed by extending an earlier method known as Principal Covariates Regression (PCovR). PCovR has two end members: PCR and RDA. Here, PCovR is extended by shrinking the covariance matrix of X. As a result, our new method regPCovR includes three end members (PCR, RDA and PLS) and is particularly suited to climate data, where the spatial dimension is larger than the temporal dimension, and where there are missing values in the response field (Y). regPCovR includes both a weighting parameter and shrinkage parameter, which are estimated using crossvalidation. The benefits of regPCovR are illustrated using two examples. In the first example, the problem of predicting the southern Australian winter rainfall (P) field from the regional winter sea level pressure (SLP) field is investigated. The best rank two regression subspace found by regPCovR explains over 50% of the variance in the rainfall field. This subspace thus estimates the relationship between SLP and P better than the end member subspaces. In the second example, PCovR is used to investigate the relationships between the winter SLP and P fields, and rainfall isotope (d18O) data from Australia and New Zealand. Two main patterns are identified, which explain about half the variance in the southern GNIP d18O sites. Subspace projection is used to relate these patterns to various regional and Southern Hemisphere climate indices. regPCovR will be useful for finding subspaces that better capture the relationships between climate and rainfall isotopes, which is a necessary step for quantitative palaeoclimatology. © The Author

Orakei maar paleolake (Auckland, NZ):A multi-method approach to the composite stratigraphy of a long sediment core

The development of records of Quaternary environmental and –climatic changes relies largely on long, complete sediment sequences. However, coring techniques do not allow extraction of one continuous record of sedimentation to be recovered from a single drill hole. In order to reconstruct a complete record, it is common practice to drill two or more overlapping cores with a depth offset to overcome coring-induced loss and disturbance and then stitch these records together using stratigraphic markers to produce a master stratigraphy. However, details of the process used and critical uncertainties are rarely reported despite the fact that spurious correlations may alter subsequent paleoenvironmental interpretations. Here we detail the procedure employed to build a composite stratigraphy from three overlapping long lake sediment cores from Orakei maar paleolake (Auckland). Orakei maar was created by a phreato-magmatic eruption to forming a lake basin of a low surface-to-depth ratio and virtually no catchment. The accumulated sediment can be considered a direct recorder of climatic and environmental changes over the Last Glacial Cycle in the Southern Hemisphere mid-latitudes, a crucial but under-studied part of the global climatic system. Finely laminated sediment in the Orakei record can be aligned and correlated along visually distinct marker horizons, as well as tephra layers (Fig. 1), with sub-cm to mm resolution, supplemented by μ- XRF core scanning elemental and X-ray density variability. Complications arise from lateral inhomogeneities in sedimentation along the lake bottom and hence, larger differences between the three cores. These sections, usually of coarser grain size, likely caused by local landslides from the crater rim, are correlated based on: visual logging, common pattern in μ-XRF elemental and Xray density variation, and typical depth offset between the observed debris flows in the cores. Figure 1: Composite stratigraphy and lithology of Orakei maar paleo-lake record built from three overlapping sediment cores. © The Author

Time history of a human kidney stone determined by bomb-pulse dating

An in vivo grown human kidney stone was dated using the atmospheric bomb pulse. The growth period was found to be 17.6 yr for a sample size of 6 mm across. The step dissolution method was used, as one of several possibilities, to produce depositional subsamples. A noticeable dead carbon presence is detected in the modern industrialized diet, and as a consequence in human metabolites. The importance for correction when applying bomb-pulse dating is noted. © 2016 by the Arizona Board of Regents on behalf of the University of Arizon