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The game of radiocarbon dating and calibration
No full textArchaeologists and geoscientists rely on continuous improvement in radioisotopic chronological techniques to generate accurate and reliable calibration curves by which measured data can be converted into an absolute age scale.
Various archives are included in providing radiocarbon data sets for calibration – tree rings,
corals, marine and lake sediments, and possibly some speleothems. This has generated
a number of calibration curves and statistical age-depth models. The IntCal Radiocarbon
Working Group recently released a terrestrial and marine radiocarbon calibration curve
(IntCal09 and Marine09) from 0 to 50 ka which effectively spans the full sensitivity of the
AMS method.
However all archives other than tree rings (0-12 ka of calibration curve) do not reflect
contemporary atmospheric 14C content. Dissolved inorganic 14C in corals and forams varies
with CO2 exchange at the atmospheric-ocean interface and admixture of 14C depleted
carbon from deep upwelling waters. Total 14C in speleothems depends on the admixture
of 14C depleted CO2 from soil and/or rock carbonate. Hence a dead-carbon fraction
or reservoir correction (modelled or otherwise) must be included to convert measured
radiocarbon to atmospheric equivalent prior to inclusion into a universal calibration curve.
These complexities, the different calibration curves and web-based program will be discussed and presented
Burial dating in archaeology using 10Be and 26Al in-situ produced cosmogenic radioisotopes
No full textDating sediment associated with archaeological artefacts and hominid fossils over the Plio-Pleistocene is difficult due to the limited range of radiocarbon, U-series and OSL techniques, with magnetostratigraphy being the only dating tool to offer chronological constraints.
Recently a new innovative technique - in-situ cosmogenic burial dating – can provide burial ages from 0.5 to 5 Ma with errors of about 10%-15%. Galactic cosmic ray particles which interact with bedrock surfaces and boulders on the Earth’s surface result in producing a host of long-lived cosmogenic radionuclides (eg 10Be and 26Al). If we know the production rate of these radioisotopes, their half-life and can measure their minute concentration via AMS, we can estimate the time the bedrock or boulder has been exposed.
If this material after initial dosing is transported to depths a few meters below the surface, production will cease, and decay will reduce their concentrations. The change in concentration is a measure of the burial age. If burial depth is insufficient, post-burial production by deep penetrating muons can be estimated to correct the burial age. The method has been successfully applied at key sites of hominid evolution. Details of the technique will be presented with examples of burial dating hominid cave deposit. © ANST
Solar and volcanic forcing of the Southern Hemisphere climate over the past 1500 years
No full textThe past 1500 years provides a valuable opportunity to
study the role of external forcings in driving the global
climate. Significant changes have taken place within
the climate system over this period, and proxy data
that records these changes covers a wide geographical
area and has high temporal resolution. Natural and
anthropogenic forcings are also reasonably well
constrained. While previous detection and attribution
studies have found a significant role of volcanic eruptions
in driving the pre-industrial Northern Hemisphere climate,
the drivers of the Southern Hemisphere climate are much
less well understood.
Here, the CSIRO Mk3L climate system model is used
to simulate the global climate of the past 1500 years.
Different combinations of natural and anthropogenic
forcings are applied, including changes in the Earth’s
orbital parameters, solar irradiance, volcanic emissions
and anthropogenic greenhouse gases. The simulations
are then compared with a multi-proxy reconstruction of
Southern Hemisphere temperature. We find strong solar
and volcanic influences on the Southern Hemisphere
climate during the pre-industrial period, with the
anthropogenic signal becoming increasingly dominant
after 1850 CE. However, the results are sensitive to the
specific reconstructions of solar and volcanic activity
that are used to drive the model. The choice of volcanic
reconstruction is particularly critical, and we find that the
dating of major eruptions can impact significantly upon the agreement between the model and the proxy record.
If we are to learn all that we can from the climate of recent
millennia, a critical challenge is therefore to develop better
reconstructions of past climatic forcings − particularly
volcanic eruptions
A global database of Holocene paleotemperature records
Get PDFA 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
Predicted ionisation in mitochondria and observed acute changes in the mitochondrial transcriptome after gamma irradiation: A Monte Carlo simulation and quantitative PCR study
No full textIt is a widely accepted that the cell nucleus is the primary site of radiation damage while extra-nuclear radiation effects are not yet systematically included into models of radiation damage.
We performed Monte Carlo simulations assuming a spherical cell (diameter 11.5 μm) modelled after JURKAT cells with the inclusion of realistic elemental composition data based on published literature. The cell model consists of cytoplasm (density 1 g/cm3), nucleus (diameter 8.5 μm; 40% of cell volume) as well as cylindrical mitochondria (diameter 1 μm; volume 0.5 μm3) of three different densities (1, 2 and 10 g/cm3) and total mitochondrial volume relative to the cell volume (10, 20, 30%). Our simulation predicts that if mitochondria take up more than 20% of a cell's volume, ionisation events will be the preferentially located in mitochondria rather than in the cell nucleus.
Using quantitative polymerase chain reaction, we substantiate in JURKAT cells that human mitochondria respond to gamma radiation with early (within 30 min) differential changes in the expression levels of 18 mitochondrially encoded genes, whereby the number of regulated genes varies in a dose-dependent but non-linear pattern (10 Gy: 1 gene; 50 Gy: 5 genes; 100 Gy: 12 genes).
The simulation data as well as the experimental observations suggest that current models of acute radiation effects, which largely focus on nuclear effects, might benefit from more systematic considerations of the early mitochondrial responses and how these may subsequently determine cell response to ionising radiation. © 2013 Elsevier B.V
Ferric iron geometry and coordination during hydrolysis and ferrihydrite precipitation
Get PDFDefinitive structural characterisation of ferrihydrite has challenged scientists primarily due to its nanosized particles
and inherent long-range structural disorder which challenges analytical methodology (and modelling) typically employed to determine the structure of minerals. Here we report on the application of a synchrotron quick-scanning X-ray absorption spectroscopy (XAS) approach, which allows the collection of
Extended X-ray Absorption Fine Structure (EXAFS) spectral data to k = 15 Å-1 in < 1 minute, to obtain unparalleled iron Kedge
data on the hydrolysis of FeIII(H2O)6 and ferrihydrite precipitation.
Modelling of the pre-edge and EXAFS data: 1) supports theoretical studies which have suggested the existence of a monomeric penta-coordinated FeIII hydrolysis species and;
2) corroborates recently proposed structural models of ferrihydrite that contain tetrahedral FeIII. Modelling results
indicate that ferrihydrite consists of 15 to 25 % tetrahedral FeIII and suggest that this geometry must be included in any comprehensive structural model of ferrihydrite and, furthermore, should be considered when evaluating the reactivity, stability and other structure-property relationships of this mineral. © The Authors
Groundwater residence time in the Kulnura-Mangrove Mountain Plateau (Gosford, NSW, Australia)
Get PDFThe Kulnura-Mangrove Mountain plateau consists of
the catchments of Mangrove, Narara, Mooney Mooney,
and Ourimbah Creeks, and Wyong River. Groundwater
plays a key role in sustaining stream flow within these
catchments. Estimates indicate up to 50% of annual
stream flow is derived from baseflow.
The local community water supply relies on the
groundwater within the elevated Hawkesbury-
Narrabeen sandstone plateau. Furthermore, the
Gosford-Wyong Councils’ Water Authority (WSA) is the
third largest in NSW and utilises many of the streams
flowing from the sandstone plateau for municipal water
supply. It is anticipated that the WSA will provide
municipal water for 319 000 persons by the year 2010.
The increasing volumes of groundwater being extracted
and changing land use have the potential to cause
damage to the fresh water aquifer through
contamination and aquifer depletion.
A hydrogeochemical survey (2006-2009) has been
conducted in NSW Dept of Water and Energy (DWE)
monitoring wells across the plateau in order to
determine groundwater residence times. Groundwater
was analysed for major ions, minor and trace elements,
H2O 18O and 2H, 13CDIC, 87Sr/86Sr, 14CDIC, and 3H,
and complemented with mineralogical and isotopic
information obtained from soil and drill chips collected
during well construction. Water stable isotopes confirm
the meteoric origin of the groundwater with most values
plotting on the local meteoric water line. Localised
evaporative trends suggest recharge with evaporated
groundwater stored in ponds.
Shallow groundwaters have 3H and 14C activities
consistent with modern recharge (Fig 1). Carbon “bomb
pulse” signatures of up to 116.8 pmC are found in the
central areas of the plateau. The thin soils, lack of
carbonates in the intensely weathered near-surface
Hawkesbury sandstone, and the shallow depth of the
water samples is consistent with the 3H results
measured, suggesting minimal dilution of the original
14C. Input of this data into a southern hemisphere bomb
pulse model [1] suggest potential recharge during the
1990´s, coinciding with sustained wet conditions and
above average rainfalls experienced during this period.
Fig. 1. 14C vs 3H plot of groundwater samples in the Kulnura-
Mangrove Mountain Plateau
Deeper groundwaters have lower 14C and 3H activities
in some cases close to background level (Fig. 1). The
quantifiable 3H suggests residence times of <70 a.
However, non-corrected 14C residence times are submodern
(>500 a). This apparent discrepancy can be
explained by either mixing with older waters or
dissolution of carbonates. The good correlation of total
dissolved inorganic carbon (TDIC) and Ca (R2=0.8),
13CTDIC in groundwater and mineralogy results from
drill chips suggest that dissolution of dispersed
carbonates is taking place.
The deepest groundwaters show the most difference in
residence time across the study area. The eastern and
western plateaus yield old groundwater with 14C
corrected residence times of around 9 ka and 4 ka
respectively. However, the groundwater at equivalent
depths in the central plateau was found to be
considerably younger with residence times of <70 a
Deep meteoric leaching and its implications for groundwater residence time in a dissected Hawkesbury sandstone plateau (Kulnura-Mangrove Mountain Aquifier, NSW, Australia).
No full textIn the Kulnura-Mangrove region, groundwater extraction for potable water supply and for industrial activities such
as farming and mining, can co-exist provided the main recharge areas are protected, pumping does not exceed
recharge, and knowledge of the basic parameters within the aquifer are known through appropriate studies. In this
study, groundwater residence time in the Kulnura-Mangrove Mountain aquifers was assessed over multiple years
using environmental tracers (H2O stable isotopes, 13CDIC, 3H, 14C and 87Sr/86Sr) and general hydrogeochemistry.
The Kulnura-Mangrove Mountain aquifer is mostly hosted in its upper part by the Hawkesbury Sandstone, where
intense and deep sandstone weathering profiles have resulted in enhanced groundwater storage. Weathering
reactions favoured by the local geological setting has transformed the original Hawkesbury Sandstone quartz arenite
into a semisolid or friable sandstone with variable weathering depths where most of the original carbonate cements
have been leached, resulting in higher porosity and permeability. XRD analyses show an upper zone down to ~50 m
and even 90 m in some areas where all carbonates and probably feldspars have been dissolved and the derived
products goethite and kaolinite have formed. With depth, carbonates, mostly siderite, are present representing
fresher or less-weathered sandstone. Isotopic analysis of dispersed carbonates shows consistent values with their
depositional environment and devoid of 14C.
The study incorporated whole rock analysis from samples recovered during well construction at four sites to better
characterise water–rock interactions. Based on hydrogeochemistry, isotopic tracers and mineral phase distribution
from whole rock XRD analysis, two main groundwater zones are differentiated in areas not disturbed by
groundwater extraction. A shallow zone where oxidising Na–Cl-type waters with low pH and EC contain 3H and 14C
activities consistent with very modern groundwater affected by bomb pulse signatures (up to 116.9 pMC). In this
shallow zone the original Hawkesbury Sandstone has been deeply weathered, enhancing storage capacity for
groundwater down to ~50 m in most areas and up to ~90 m in the Peats Ridge zone. The deeper groundwater zone is
also relatively oxidising with a tendency towards Ca–HCO3 type waters, higher pH and EC, no 3H and 14C activities
consistent with residence times from 0.9 to 11.8 ka BP, depending on the specific areas. The original sandstone is less weathered with depth, favouring the dissolution of dispersed carbonates and a transition to a fractured-rock
flow type aquifer, both impacting on groundwater mean residence times
Sydney particle characterisation study PM2.5 source apportionment in the Sydney Region between 2000 and 2014
Get PDFThe Australian Nuclear Science and Technology Organisation (ANSTO) has been applying accelerator based nuclear techniques to the characterisation of fine PM2.5 ambient air pollution since the early 1990s. Over the decades large long-term databases have been acquired at dozens of sites both in Australia and internationally on the PM2.5 mass together with over 23 different elemental and chemical species that make up this fine particle pollution. In this study we used data previously collected by ANSTO from four of our long-term sampling sites covering the period from 1 January 2000 to 31 December 2014. Positive matrix factorisation (PMF) source apportionment techniques were applied to this data to identify seven different source components or fingerprints that make up the measured total PM2.5mass at each of these four sites. The primary aim of this study was to: convert the existing 15-year PM2.5 mass and elemental datasets for four given sites in the Sydney basin into identifiable source fingerprints quantify the absolute and the percentage contribution of each of these fingerprints to the total fine PM2.5 mass provide seasonal and annual variations for each of the source fingerprints provide a readily accessible database containing the daily source fingerprints and their contributions covering the 15-year period from 2000–2014 for four given sites in the Sydney basin if possible, identify and quantify the major contributors of fine particle pollution to the ambient air quality in Sydney. Typically fine particles were collected over 24-hour periods twice a week (104 filters per year) at Lucas Heights, Richmond, Mascot and Liverpool sites over a 15-year period from 2000 to 2014. In all, around 6000 sampling days are represented by this study. Each of these filters was analysed for the 23 elemental and chemical species: hydrogen (H), sodium (Na), al uminium (Al), silicon (Si), phosphorous (P), sulfur (S), chlorine (Cl), potassium (K), calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), selenium (Se), bromium (Br), lead (Pb), bl ack carbon (BC) and total nitrogen (TotN) to concentrations down to 1ngm–3 of air sampled. TotN is the total nitrogen from ammonium and nitrate ions. © 2016 ANST