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

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

Urban point sources of nutrients were the leading cause for the historical spread of hypoxia across European lakes

Enhanced phosphorus (P) export from land into streams and lakes is a primary factor driving the expansion of deep-water hypoxia in lakes during the Anthropocene. However, the interplay of regional scale environmental stressors and the lack of long-term instrumental data often impede analyses attempting to associate changes in land cover with downstream aquatic responses. Herein, we performed a synthesis of data that link paleolimnological reconstructions of lake bottom-water oxygenation to changes in land cover/use and climate over the past 300 years to evaluate whether the spread of hypoxia in European lakes was primarily associated with enhanced P exports from growing urbanization, intensified agriculture, or climatic change. We showed that hypoxia started spreading in European lakes around CE 1850 and was greatly accelerated after CE 1900. Socioeconomic changes in Europe beginning in CE 1850 resulted in widespread urbanization, as well as a larger and more intensively cultivated surface area. However, our analysis of temporal trends demonstrated that the onset and intensification of lacustrine hypoxia were more strongly related to the growth of urban areas than to changes in agricultural areas and the application of fertilizers. These results suggest that anthropogenically triggered hypoxia in European lakes was primarily caused by enhanced P discharges from urban point sources. To date, there have been no signs of sustained recovery of bottom-water oxygenation in lakes following the enactment of European water legislation in the 1970s to 1980s, and the subsequent decrease in domestic P consumption

Isotopic Evidence for Oil Sands Petroleum Coke in the Peace–Athabasca Delta

The continued growth of mining and upgrading activities in Canada’s Athabasca oil sands (AOS) region has led to concerns about emissions of contaminants such as polycyclic aromatic hydrocarbons (PAHs). Whereas a recent increase in PAH emissions has been demonstrated within around 50 km of the main center of surface mining and upgrading operations, the exact nature of the predominant source(s) and the geographical extent of the deposition are still under debate. Here, we report a century-long source apportionment of PAHs using dual (δ²H, δ¹³C) compound-specific isotope analysis on phenanthrene deposited in a lake from the Athabasca sector of the Peace–Athabasca Delta situated ∼150 km downstream (north) of the main center of mining operations. The isotopic signatures in the core were compared to those of the main potential sources in this region (i.e., unprocessed AOS bitumen, upgrader residual coke, forest fires, coal, gasoline and diesel soot). A significant concurrent increase (∼55.0‰) in δ²H and decrease (∼1.5‰) in δ¹³C of phenanthrene over the last three decades pointed to an increasingly greater component of petcoke-derived PAHs. This study is the first to quantify long-range (i.e., >100 km) transport of a previously under-considered anthropogenic PAH source in the AOS region

Source Apportionment of Background PAHs in the Peace-Athabasca Delta (Alberta, Canada) Using Molecular Level Radiocarbon Analysis

The downstream accumulation of polycyclic aromatic hydrocarbons (PAHs) in the Peace-Athabasca Delta (PAD), an ecologically important landscape, is a key issue of concern given the rapid development of the oil sands industry in Northern Alberta, Canada. In addition to PAHs derived from <i>industrial</i> activity (i.e., oil sands mining) within the Athabasca watershed, however, forest fires and erosion of fossil fuel deposits within both the Athabasca and Peace watersheds are two potentially important <i>natural</i> sources of PAHs delivered to the PAD. Consequently, evaluating the environmental impact of mining activities requires a quantitative understanding of natural, background PAHs. Here, we utilize molecular-level natural-abundance radiocarbon measurements on an amalgamated sediment record from a Peace River flood-susceptible oxbow lake in the northern Peace sector of the PAD to quantitatively discriminate sources of naturally occurring alkylated PAHs (fossil and modern biomass). A radiocarbon mass balance quantified a predominantly natural petrogenic source (93% petrogenic, 7% forest fire) for alkylated PAHs during the past ∼50 years. Additionally, a significant petrogenic component determined for retene, a compound usually considered a biomarker for softwood combustion, suggests that its use as a unique forest fire indicator may not be suitable in PAD sediments receiving Peace watershed-derived fluvial inputs