Lake-sediment record of PAH, mercury, and fly-ash particle deposition near coal-fired power plants in Central Alberta, Canada

We report a historical record of atmospheric deposition in dated sediment cores from Hasse Lake, ideally located near both currently and previously operational coal-fired power plants in Central Alberta, Canada. Accumulation rates of spheroidal carbonaceous particles (SCPs), an unambiguous marker of high-temperature fossil-fuel combustion, in the early part of the sediment record (pre-1955) compared well with historical emissions from one of North America's earliest coal-fired power plants (Rossdale) located ∼43 km to the east in the city of Edmonton. Accumulation rates in the latter part of the record (post-1955) suggested inputs from the Wabamun region's plants situated ∼17–25 km to the west. Increasing accumulation rates of SCPs, polycyclic aromatic hydrocarbons (PAHs) and Hg coincided with the previously documented period of peak pollution in the Wabamun region during the late 1960s to early 1970s, although Hg deposition trends were also similar to those found in western North American lakes not directly affected by point sources. A noticeable reduction in contaminant inputs during the 1970s is attributed in part to technological improvements and stricter emission controls. The over one hundred-year historical record of coal-fired power plant emissions documented in Hasse Lake sediments has provided insight into the impact that both environmental regulations and changes in electricity output have had over time. This information is crucial to assessing the current and future role of coal in the world's energy supply

A log-normal spectral analysis of inorganic grain-size distributions from a Canadian boreal lake core: Towards refining depositional process proxy data from high latitude lakes

Better methods for interpreting grain size spectra will enhance current understanding of past transport–depositional processes. A high-resolution inorganic grain-size dataset has been measured from a freeze core extracted from ‘Alberta Lake E’ a boreal fresh water lake 40 km east of the Athabasca Oil Sands in north-eastern Alberta, Canada. The grain-size spectra are remarkably consistent throughout the core, exhibiting a structure comprising six persistent grain-size distributions below ca 250 μm, plus a rare medium-sand distribution. Automated deconvolution of the grain-size spectra produced poor results. Constraining the modes of two of the distributions produced deconvolution solutions that were statistically excellent and consistent with the structure of each spectrum. Statistical analysis of the ‘constrained’ solutions indicates that deconvolution successfully extracted independent grain-size populations. Conversely, the multimodal spectra generate traditional measures (for example, mean grain size) that are inconsistent combinations of different individual populations, and thus are poor proxies of transport–depositional processes. Alberta Lake E is situated in a boreal wetland landscape where sediment delivery is dominated by overland flow transport during spring melt. This context means that the Alberta Lake E grain-size spectra can be interpreted to reflect: (i) a bedload component transported during short-duration high discharge events that reflect the intensity of the melt; and (ii) a finer suspended load component representing material whose magnitude is controlled by the volume of the spring melt. Stratigraphically, bedload and suspended load populations demonstrate different short-wavelength and long-wavelength cyclicity, suggesting that spring melt is likely to be driven by cyclic external forcing factors. The links between the grain-size spectra and spring melt have potential for generating proxy records that better capture the external controls over spring melt in boreal systems, and the risks associated with these energetic hydrodynamics. This is exemplified by the coarsest Alberta Lake E distributions, which indicate that more intense spring melt dynamics occurred in pre-historical times

Highly Customizable Transaction Management For Systems Integration

Transactions are well-known and fundamental control abstractions that arose from the database community. In principle, programmers can now use transactions as units of encapsulation to structure any application. In practice, however, many distinct transactional systems have been defined. Therefore, each kind of application must be developed using different concepts of transaction. We have designed and implemented in the Java programming language a new, generic and customizable transactional system that allows to structure any application as a set of nested transactional units regardless, in the one hand, of the kind or of the type of data, and, in the other hand, of the behavior, including multithreaded one, applied on them. Our approach is based on a modular composition of transactional properties, some of them being assigned to objects or/and to external transactional systems. Thus, we provide a new and implicit transactional semantic that allows user to manage transactional units wi..

Introducing the “Franken‐Kiel” Carbonate Device: First Application to Δ47‐T Calibrations of Calcite and Dolomite

Abstract Recent interlaboratory efforts have enabled methodological refinements in carbonate clumped isotope geochemistry, including the adoption of a carbonate‐based reference frame, the InterCarb Carbon Dioxide Equilibration Scale (I‐CDES). This calcite‐based standardization scheme aims at simplifying sample preparatory routines and ensuring identical treatment for all standards and unknowns. While the I‐CDES is a major step forward for the production of coherent results by laboratories for calcite, two aspects of this reference frame may only approximate but not ensure the principle of identical treatment of standards and unknowns because (a) the 90°C‐acid digestion temperature favored by I‐CDES is not achievable by all analytical setups and (b) the clumped isotope systematics of other carbonate minerals, if reported within a calcite reference frame only, may introduce uncertainties. We present an upgraded Kiel IV carbonate device—the “Franken‐Kiel”—performing acid digestions up to a theoretical 135°C, an enhancement over the factory‐default temperature of 70°C. The optimized setup considerably reduces the reaction time needed for digesting samples and yields good precision on Δ47 (i.e., long‐term standard deviations of 0.027 and 0.005‰ for calcite and dolomite standards, respectively). We further re‐evaluated the Δ47‐T relationship for calcite and dolomite directly in the I‐CDES and showed consistency between the produced temperature calibration and previous calibrations for calcite. We propose a mineralogy correction for dolomite in the I‐CDES that allows to partially reconcile theory with experimentation. Overall, the Franken‐Kiel showed excellent performance and warrants further tests on more recalcitrant carbonates, such as siderite and magnesite at higher acidification temperatures

Clumped isotope temperature calibration for calcite: Bridging theory and experimentation

Clumped isotopes (Delta(47)) analysis in carbonates is becoming widespread across the geochemical community as a geothermometer that also allows for the reconstruction of the precipitating fluid delta O-18 composition. While initial Delta(47)-temperature relationship discrepancies between laboratories have been considerably reduced over the past 10 years, theoretical temperature calibration and laboratory experimental efforts have still not converged to common ground. Moreover, a lack of high temperature anchor points has weakened its application to high temperature calcite formation. Here we present a temperature calibration for carbonate clumped isotopes between 5 and 726 degrees C, using synthetically precipitated and heated calcites, to extend the calcite Delta(47) -temperature calibration to higher temperatures. By showing a strong agreement between the empirical calibration proposed here, theoretical and all recently published T-calibrations made using a full carbonate referencing scheme, this study: (1) provides a calibration allowing more precise application in high temperature geological systems, (2) further supports the improvement of inter-laboratory comparison by using carbonate standards, (3) reconciles empirical temperature calibrations with theory.ISSN:2410-339XISSN:2410-340

Cosmogenic (un-)steadiness revealed by paired-nuclide catchment-wide denudation rates in the formerly half-glaciated Vosges Mountains (NE France)

International audienceAlthough catchment-wide denudation rates inferred from in situ cosmogenic nuclide concentrations measured in stream sediments has represented a ground-breaking progress in geomorphology over the last three decades, most of these studies rely on 10Be concentrations only. It seems that this current and routine one-nuclide approach to infer catchment-wide denudation rates has somehow overshadowed two key assumptions that are cosmogenic steady-state and short sediment transit time at the catchment scale. Although a paired-nuclide approach allow testing these assumptions, it is rarely performed on stream sediments and this can become highly problematic in slow-eroding, formerly glaciated contexts. In this study, we thus measure both 10Be and 26Al in stream sediments pertaining to twenty-one rivers draining an entire low mountain range: the Vosges Massif (NE France). The latter exhibits a sharp gradient between its southern and northern part in terms of lithology, morphometry and climate. Moreover, if its northern part remained void of glacial cover during Quaternary cold stages, its southern part was significantly and repeatedly glaciated. We aim to assess the factors that control the denudation of the Vosges Mountains and to quantitatively explore the impact of both repeated glacial cover and storage of glacially derived sediments on 26Al/10Be ratios, hence cosmogenic (un-)steadiness in modern river samples. Our results first show that elevation, slope, channel steepness and precipitation are primarily organised along a N-S increasing trend. 10Be- and 26Al-derived catchment-wide denudation rates accordingly range from 34±1 to 66±2, and 41±3 to 73±7 mm/ka, respectively, in thirteen investigated catchments that are in cosmogenic equilibrium. Lithological contrasts may control the pattern of denudation with a higher erodibility of the sandstone-dominated catchment to the north compared to the crystalline-dominated catchments to the south. Our results also show that catchments in strong cosmogenic disequilibrium (26Al/10Be ratios from 1.4 to 5.2) spatially cluster in the SW part of the Vosges Mountains that was the most intensively glaciated during Quaternary cold stages. If this precludes any conclusion about controlling factors at the whole massif scale, this study is the first to quantify the impact of past glaciations on cosmogenic (un-)steadiness measured in stream sediments. A statistically significant relationship between the degree of depletion of the 26Al/10Be ratios and the spatial pattern of glaciation is found: the larger the former glacial cover in each catchment, the lower the 26Al/10Be ratio. Equally important is the significant correlation reported between the degree of depletion of the 26Al/10Be ratios and the proportion of glacial and fluvio-glacial deposits within each catchment. These two relationships underline the link between cosmogenic unsteadiness in the stream cosmogenic signal and long-lasting and repetitive ice shielding, and complex sediment routing systems in glacial environments, respectively. We thus argue to systematically measure 26Al in complement to 10Be and to test the steady-state assumption when it comes to infer catchment-wide denudation rates from modern stream sediments, especially in slow eroding, formerly glaciated landscapes

Calibration of the dual clumped isotope thermometer for carbonates

International audienceTheD47(paleo)thermometer has opened a new avenue to determine carbonate formation temperatures independent of theoxygen isotopic composition of the fluid from which the carbonate crystallized. A major limitation of this thermometer isrelated to kinetic effects if homogeneous isotopic equilibrium is not attained during carbonate precipitation. Dual clumpedisotope thermometry – the high-precision analysis ofD48along withD47in CO2evolved from phosphoric acid digestion ofcarbonates – makes it possible to resolve temperature from the kinetic information recorded in an individual carbonate phase.Therefore, it provides a new opportunity to identify (bio)mineralization pathways and to determine carbonate formation tem-peratures devoid of a kinetic bias, based solely on isotopic analysis of a single carbonate phase.Identification of the nature and extent of kinetic effects as well as the reconstruction of accurate formation temperaturesrequires knowledge of the position of equilibrium inD47vsD48space. Here, we presentD47andD48data of carbonates thatwere previously considered as having crystallized closest to equilibrium in a temperature range of 8 to 1100°C. Across thisrange, the temperature dependences ofD47andD48are best expressed by the following fourth order polynomials of 1/T:D47(CDES 90) (‰) = 1.038 (5.897 1/T3.521 1031/T2+ 2.391 1071/T33.541 1091/T4) + 0.1856D48(CDES 90) (‰) = 1.028 (6.002 1/T1.299 1041/T2+ 8.996 1061/T37.423 1081/T4) + 0.1245with CDES 90 representing the Carbon Dioxide Equilibrium Scale at a reaction temperature of 90°C. In its entire tem-perature range, ourD47(CDES 90) - T - relationship agrees within 2 ppm with two previousD47(I-CDES) - T - relationshipsreported by Jautzy et al. (2020) and Anderson et al. (2021). Accuracy of our proposedD47(CDES 90)D48(CDES 90)equilibrium relationship is independently confirmed by additional dual clumped isotope data of experimental and geothermalcarbonates which precipitated from potentially equilibrated dissolved inorganic carbon pools at a temperature range of25–100°C. Furthermore, we reprocessed original dual clumped isotope data of natural carbonates (Bajnai et al., 2020)and compared their composition to the position of equilibrium inD47vsD48space. These results corroborate preliminaryevidence that the hydration/hydroxylation reactions became rate-limiting during the calcification of a speleothem-like sample,a warm water coral, a cold water coral and a brachiopod, finally evoking significant departures of carbonate-D47and -D48from dual clumped isotope equilibrium

Clumped isotope geothermometry of an Ordovician carbonate mound, Hudson Bay Basin

The Hudson Bay sedimentary basin remained geologically overlooked until two decades ago. Recent efforts in understanding the paleogeothermal history of this basin has led to the evaluation of fluid inclusion microthermometry, apatite fission track, organic matter reflectance as well as Rock-Eval analyses. While apatite fission tracks and organic maturity indicators tend to show relatively low maximum burial temperatures (60 to 80°C), evidence of potential oil slicks on the sea surface and oil and gas shows in offshore wells are reported across the Hudson Bay. Moreover, fluid inclusion microthermometry suggests homogenization temperatures for recrystallized syn-sedimentary marine calcite and late pore-filling burial calcite of 118 ± 25°C and 93 ± 10°C, respectively, in a carbonate mound sequence. This sequence provides an interesting geological framework to test the application of clumped isotope thermometry against independent geothermometers. Here, we present clumped isotope data acquired on the late calcite cements and diagenetically altered early marine phases. The integration of clumped isotopic data with other thermal indicators allows for reconstruction and refinement of the thermal-diagenetic history of these carbonates by confirming an episode of heating, likely of hydrothermal origin and prior to normal burial diagenesis, resetting both fluid inclusions and the clumped isotope indicators, without recrystallisation