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Factors affecting carbon-14 activity of unsaturated zone CO2 and implications for groundwater dating
No full textUnsaturated zone processes may influence the carbon-14 (14C) activity of infiltrating groundwater and thus introduce error in derived groundwater residence times. However unsaturated zone 14C activities are rarely measured and there is little understanding of how they may vary spatially in a groundwater basin. In this study we measured 14C activity in unsaturated zone gas at five sites with different watertable depths (8.2–31.5 m) in the arid Ti Tree Basin, central Australia. We observed a relatively uniform decrease in 14C activity of unsaturated zone gas with depth at most sites, with variation in unsaturated zone depths leading to variation in 14C activities directly above the watertable at each site (ranging from 54 to 106 percent Modern Carbon (pMC)). Through modelling we show that the profiles are influenced by CO2 production at different depths from sources with different isotopic ratios, including production of ‘modern’ CO2 in the root zone and production of ‘old’ CO2 above the watertable. Scenario modelling showed that these processes are independent of recharge when recharge is low (0–10 mm y−1) but that higher recharge rates (>100 mm y−1) result in more advective transport of atmospheric CO2 to the watertable. The variation in 14C above the watertable was more sensitive to watertable depth and shallow and deep CO2 production rates. These findings offer insight into how unsaturated zone 14C activities may vary spatially and provide guidance as to when 14C depletion in unsaturated zone CO2 may become important for groundwater dating, particularly in arid settings. © 2014, Elsevier B.V
Lacustrine paleoseismometers reveal spatial and temporal patterns of rupture during the last ten large earthquakes on the Alpine Fault, New Zealand
No full textThe rarity of long, well-dated paleoseismic records from sites along plate boundary transform faults is a major constraint on the development and evaluation of conceptual models of fault rupture behaviour. This is the case for the 800 km long, high slip rate (27±5 mm yr-1), dextral strike-slip Alpine Fault at the boundary between the Pacific and Australian plates in southern New Zealand. We use lacustrine paleoseismology to evaluate the hypothesis that the Alpine Fault exhibits self-similar behaviour, that is, the fault always produces earthquakes at or near a maximum magnitude of Mw8. The hypothesis is tested using reconstructions of high intensity shaking from five lakes situated along 240 km of the Alpine Fault's Central section. Sedimentological investigation of lake cores shows that high intensity shaking events are recorded in the lake sediments as turbidites formed by subaqueous slumping. These turbidites are overlain by terrigenous sediment from co- and post-seismic landsliding on hillslopes in the lakes' mountainous catchments. Chronologies derived from Bayesian modelling of AMS 14C dates on terrestrial leaf macrofossils precisely constrain the timing of earthquakes at the lake sites, facilitating along-strike correlation. Shaking events correlate between the sites and with known ruptures of the Alpine Fault, confirming the seismic origin of the deposits and allowing thresholds of shaking intensity for deposit formation to be determined using isoseismal modelling. Modelled shaking intensities for the last two Alpine Fault earthquakes show that subaqueous slumping occurs when shaking intensities exceed Modified Mercalli scale (MM) VI-VII, and that increased fluvial sediment fluxes from earthquake-induced landslides occur when shaking intensities exceed MM IX. The record of synchronous MM IX shaking at the lake sites provides first order constraint on the rupture length of the last ten earthquakes on the central Alpine Fault. Rupture scenarios for these earthquakes are augmented by correlating event timing with long earthquake records from the South Westland section and geomorphic reconstructions of the slip distribution for the most recent ruptures to explore the best-fit model of fault behaviour and to test the hypothesis that the Alpine Fault always ruptures in great (Mw8) earthquakes
Neutron powder diffraction study of the magnetic structure of EuZrO3
No full textNeutron powder diffraction experiments on the orthorhombic perovskite EuZrO3 show it to have an antiferromagnetic G-type magnetic structure with the magnetic moments aligned parallel to the a-axis. The orthorhombic crystal structure is a consequence of cooperative rotations of the corner-sharing ZrO6 octahedra. The crystal structure does not change significantly below the Néel temperature, ~4.1 K, showing there to be only weak magnetoelastic coupling.
© 2014, IOP Publishing Ltd
New light through old windows – reaping the benefits of a palaeotsunami database.
No full textThe New Zealand palaeotsunami database was first established in 2008 and has continued to grow in a somewhat ad hoc manner since then. While ostensibly a geological database, it has grown markedly through the addition of geomorphological, archaeological, anthropological and ecological data. The main tsunami research focus in New Zealand has tended to be along those coastlines either adjacent to a local subduction zone or exposed to events generated by similar distant sources; in this case - the eastern shores of New Zealand. Examining the database, we unexpectedly identified at least two large events within the past 700 years on the western shores. Event 1 occurred between 1470 and 1510AD and Event 2 between 1320 and 1450AD. Once the probable extent of these events was defined we were able to then propose a range of potential tsunamigenic sources including non-subduction fault ruptures and several slope failure mechanisms.
While numerous sites with contemporaneously-aged evidence along the eastern shores point to significant probable subduction zone tsunamis, at least one anomalously high elevation data point stands out. The ~60 masl site at Korapuke Island fits comfortably within the timing of a probable 15th century palaeotsunami but evidence from neighbouring sites along 10s of kms of coastline range from only 0-10 masl. A subsequent reassessment of the site identified no unusual characteristics that might amplify runup and no local tsunamigenic source. However, a similar nearby site has high elevation (~45 m) deposits laid down in 1996 by a waterspout and it seems increasing likely that Korapuke Island may have the first reported palaeo-waterspout deposit. This adds an interesting wrinkle to the palaeotsunami-palaeostorm deposit debate, but also reveals the value of a palaeotsunami database. There are probably similar anomalies (and errors) in the database, but without the context of related data it is unlikely that they would be exposed to such scrutiny. © 2014, American Geophysical Unio
Identifying nitrogen limitations to organic sediments accumulation in various vegetation types of arctic tundra (Hornsund, Svalbard)
No full textArctic and subarctic regions play important roles in the global carbon balance. However, nitrogen (N) deficiency is a major constraint for organic carbon sequestration in the High Arctic. Hence, the identification of the relative contributions from different N-sources is critical for understanding the constraints that limit tundra growth.
The stable nitrogen composition of the three main N-sources and numerous plants were analyzed in ten tundra types in the Fuglebekken catchment (Hornsund Fjord, Svalbard, 77°N 15°E). The percentage of the total tundra N-pool provided by seabirds’ feces (colonially breeding, planktivorous Alle alle), ranged from 0–21% in Patterned-ground tundra to 100% in Ornithocoprophilous tundra. The total N-pool utilized by tundra plants in the studied catchment was built in 36% by birds, 38% by atmospheric deposition, and 26% by N2-fixation. The results clearly show that N-pool in the tundra is significantly supplemented by nesting seabirds. Thus, if they experienced substantial negative environmental pressure associated with climate change, it would adversely influence the tundra N-budget [1].
The growth rates and the sediment thickness (<15 cm) in different tundra types varied considerably but the tundra age was similar, <450 cal BP. The only exception was Ornithocoprophilous tundra with very diverse ages ranging from 235 to 2300 cal BP and thickness up to 110cm. The growth rates for this tundra (62 cm core, 18 AMS 14C dates) were high (1.5-3.0 mm/yr) between 1568 and 1804 AD and then substantially declined for the period between 1804 and 1929 AD (0.2 mm/yr). These findings deliver an additional argument, that the organic matter accumulation is driven not only directly by climatic conditions but also by birds’ contribution to the tundra N-pool. © 2014, American Geophysical Union
History of human impact on Lake Kutubu, Papua New Guinea: The geochemical signatures of oil and gas mining activities in sediments
No full textLake Kutubu, a large tropical lake in Papua New Guinea, is well known for its ecological importance; however, there have been recent changes to the pristine nature of this lake due to activities associated with the largest oil and gas project in PNG. The aim of this study was to determine the geochemical profile of sediment cores of Lake Kutubu and to comprehend the contamination changes undergone in this lake due to mining activities utilising the hydraulic fracturing method. Sediment core profiles of Na, Mg, Al, Si, P, Ca, Ti, Cr, Fe, Mn, Ni, Cu, Zn, As, Se, Sr, Cd, Ba, Ce, Pb and U, grain size and dating analyses were conducted for five sites in the lake. Grain size and dating demonstrated that the northwest side of Lake Kutubu has sediments of allocthonous origin while the southeast sediments are of autochthonous origin. Ba was the element with the largest changes in concentrations since 1990 and the best tracer of mining activities near the lake. Sites KTB 02 and KTB 10 northwest of the lake showed the most distinct changes in element concentrations. Element enrichment factors (EF = 2.8, 4.2 and 3.2 respectively) demonstrated that Mn, Se and Ba have undergone a moderate enrichment in the lake since mining activities started. Ni, Cd and Se concentrations exceed sediment guidelines in some samples. No guideline is available for Ba, and special attention should be given to this element in this lake. This study demonstrated that Lake Kutubu oil/gas extraction activities are significant sources of elements to this lake and highlights the need for studies on the partitioning and speciation of elements to understand organism metal exposure. © 2016, Elsevier Ltd
The IAEA/RCA fine and coarse PMF receptor fingerprint database
Get PDFThis document accompanies the IAEA Master Positive Matrix Factorisation (PMF) Databases (fine and coarse). These databases have been generated from the 14 member state RCA Project RAC/07/015, “Characterization and Source Identification of Particulate Air Pollution in the Asia Region”. It fulfils the obligation under an IAEA contract to provide a fine and coarse ambient air PMF database with explanatory notes by February 2016 to the IAEA.
The aim of this document is to provide instructional steps and related information necessary for navigating and utilising the IAEA Master Positive Matrix Factorisation (PMF) databases. It is important to note that interpretation of the PMF fingerprints and apportionment contained in either the coarse or fine databases are beyond the scope of this document. However, several countries have already published peer-reviewed papers related to their sites PMF source fingerprinting and source apportionment results. Comprehensive lists of publications are provided in Appendix 2
Spatial variation in carbon storage: a case study for Currambene Creek, NSW, Australia
No full textQuantifying carbon storage in coastal wetland environments is important for identifying areas of high carbon
sequestration value that could be targeted for conservation. This study combines remote sensing and sediment
analysis to identify spatial variation in soil carbon storage for Currambene Creek, New South Wales, Australia to
establish whether vegetation structure influences soil carbon storage in the upper 30 cm. Wetland vegetation was
delineated to capture structural complexity within vegetation communities using Light detection and ranging (Lidar)
point cloud data and aerial imagery with an object-based image analysis approach. Sediment cores were collected
and analysed for soil carbon content to quantify below-ground carbon storage across the site. The total soil carbon
storage in the upper 30 cm for the wetland (59.6 ha) was estimated to be 3933 ± 444 Mg C. Tall mangrove were
found to have the highest total carbon storage (1420 ± 198 Mg C), however are particularly sensitive to changes in
sea-level as they are positioned lowest in the intertidal frame. Conservation efforts targeted at protecting areas of
high carbon sequestration, such as the tall mangrove, will lead to a greater contribution to carbon mitigation efforts
Predicting solar-cell dyes for cosensitization
No full textA major limitation of using organic dyes for dye-sensitized solar cells (DSCs) has been their lack of broad optical absorption. Cosensitization, in which two complementary dyes are incorporated into a DSC, offers a route to combat this problem. Here we construct and implement a design route for materials discovery of new dyes for cosensitization, beginning with a chemically compatible series of existing laser dyes which are without an anchor group necessary for DSC use. We determine the crystal structures for this dye series and use their geometries to establish the DSC molecular design prerequisites aided by density-functional theory and time-dependent density-functional theory calculations. Based on insights gained from these existing dyes, modified sensitizers are computationally designed to include a suitable anchor group. A DSC cosensitization strategy for these modified sensitizers is predicted, using the central features of highest-occupied and lowest-unoccupied molecular orbital positioning, optical absorption properties, intramolecular charge-transfer characteristics, and steric effects as selection criteria. Through this molecular engineering of a series of existing non-DSC dyes, we predict new materials for DSC cosensitization. © 2014, American Chemical Society
Can the ZoMBieS method be used to characterise scintillator non-linearity?.
No full textMeasurements of the detection efficiency as a function of deposited electron energy in a liquid scintillation cocktail between 4 keV and 49 keV are obtained using the ZoMBieS method. Comparison is made between the measured data and the Poisson–Birks detection efficiency model. Measurements of the Birks non-linearity parameter, kB, and the linearised scintillation response of each photomultiplier, ωi, were made using these data. However, the value of kB that best linearises the scintillator response is found to vary depending upon which photomultiplier is used in its determination, and the measured kB and ωi vary depending on the external source geometry. The cause of this behaviour is unknown. The triple-coincident detection efficiency appears to be unaffected by any systematic errors. © 2013,Elsevier Ltd