High‐Precision,High‐Accuracy Oxygen Isotope Measurements of Zircon Reference Materials with the SHRIMP‐SI

Analytical protocols for SHRIMP‐SI oxygen isotope analysis (δ¹⁸O) of a suite of zircon reference materials (RMs) are presented. Data reduction involved a robust estimate of uncertainties associated with the individual spot as well as for groups where the spot data are combined. The repeatability of δ¹⁸O measurements is dependent on both the analytical conditions and the choice of the primary reference material. Under optimised conditions, repeatability was often better than 0.4‰ (2s) allowing sample uncertainties to be obtained to better than 0.2‰ (at 95% confidence limit). Single spot uncertainty combined the within‐spot precision with the scatter associated with repeated measurements of the primary zircon reference material during a measurement session. The uncertainty for individual spots measured under optimised conditions was between 0.3 and 0.4‰ (at 95% confidence). The analytical protocols described were used to assess a variety of zircon RMs that have been used for geochronology and for which laser fluorination oxygen isotope data are available (Temora 2, FC1, R33, QGNG and Ple?ovice), as well as zircons that have been used as RMs for trace element or other types of determination (Mud Tank, Monastery, 91500, AS57, AS3, KIM‐5, OG1, SL13, CZ3 and several other Sri Lankan zircons). Repeated analyses over nine sessions and seven different mounts show agreement within analytical uncertainty for Temora 2, FC1, R33, QGNG, Ple?ovice and 91500, when normalised to Mud Tank. For existing ion microprobe mounts with these materials, an appropriate δ¹⁸O can be determined. However, care should be taken when using zircons from the Duluth Complex (i.e., FC1, AS57 and AS3) as reference materials as our data indicated an excess scatter on δ¹⁸O values associated with low‐U zircon grains.     

Patterns and drivers of peat topographic changes determined from Structure-from-Motion photogrammetry at field plot and laboratory scales

Little is known about the spatial and temporal variability of peat erosion nor some of its topographic and weather-related drivers. We present field and laboratory observations of peat erosion using Structure-from-Motion (SfM) photogrammetry. Over a 12 month period, 11 repeated SfM surveys were conducted on four geomorphological sites of 18–28 m² (peat hagg, gully wall, riparian area and gully head) in a blanket peatland in northern England. A net topographic change of –14 to +30 mm yr^–1 for the four sites was observed during the whole monitoring period. Cold conditions in the winter of 2016 resulted in highly variable volume change (net surface topographic rise first and lowering afterwards) via freeze–thaw processes. Long periods of dry conditions in the summer of 2017 led to desiccation and drying and cracking of the peat surface and a corresponding surface lowering. Topographic changes were mainly observed over short-term intervals when intense rainfall, flow wash, needle-ice production or surface desiccation was observed. In the laboratory, we applied rainfall simulations on peat blocks and compared the peat losses quantified by traditional sediment flux measurements with SfM derived topographic data. The magnitude of topographic change determined by SfM (mean value: 0.7 mm, SD: 4.3 mm) was very different to the areal average determined by the sediment yield from the blocks (mean value: –0.1 mm, SD: 0.1 mm). Topographic controls on spatial patterns of topographic change were illustrated from both field and laboratory surveys. Roughness was positively correlated to positive topographic change and was negatively correlated to negative topographic change at field plot scale and laboratory macroscale. Overall, the importance of event-scale change and the direct relationship between surface roughness and the rate of topographic change are important characteristics which we suggest are generalizable to other environments. © 2018 John Wiley & Sons, Ltd.     

Sediment and fluvial particulate carbon flux from an eroding peatland catchment

Erosion and the associated loss of carbon is a major environmental concern in many peatlands and remains difficult to accurately quantify beyond the plot scale. Erosion was measured in an upland blanket peatland catchment (0.017 km²) in northern England using structure-from-motion (SfM) photogrammetry, sediment traps and stream sediment sampling at different spatial scales. A net median topographic change of –27 mm yr^–1 was recorded by SfM over the 12-month monitoring period for the entire surveyed area (598 m²). Within the entire surveyed area there were six nested catchments where both SfM and sediment traps were used to measure erosion. Substantial amounts of peat were captured in sediment traps during summer storm events after two months of dry weather where desiccation of the peat surface occurred. The magnitude of topographic change for the six nested catchments determined by SfM (mean value: 5.3 mm, standard deviation: 5.2 mm) was very different to the areal average derived from sediment traps (mean value: –0.3 mm, standard deviation: 0.1 mm). Thus, direct interpolation of peat erosion from local net topographic change into sediment yield at the catchment outlet appears problematic. Peat loss measured at the hillslope scale was not representative of that at the catchment scale. Stream sediment sampling at the outlet of the research catchment (0.017 km²) suggested that the yields of suspended sediment and particulate organic carbon were 926.3 t km^–2 yr^–1 and 340.9 t km^–2 yr^–1, respectively, with highest losses occurring during the autumn. Both freeze–thaw during winter and desiccation during long periods of dry weather in spring and summer were identified as important peat weathering processes during the study. Such weathering was a key enabler of subsequent fluvial peat loss from the catchment. © 2019 John Wiley & Sons, Ltd.     

Watershed morphometric analysis of Wadi Baish Dam catchment area using integrated GIS-based approach

The integration of Remote Sensing (RS) and Geographic Information Systems (GIS) constitutes a powerful tool for the evaluation of watershed morphometric parameters. The benefits of this integration include saving time and effort as well as improving the accuracy of the analysis. Moreover, this technique is appropriate for describing the watershed and its streams. In this study, a detailed morphometric analysis of the Wadi Baish catchment area has been performed using the Shuttle Radar Topography Mission (SRTM). The performed morphometric analysis includes linear, areal, and relief aspects. The results of the morphometric analysis reveal that the catchment can be described as of eighth stream order and consists of an area of 4741.07 km². Additionally, the basin is characterized by a relatively high mean value of bifurcation (4.012), indicative of the scarcity of permeable rocks with high slope in the area. This value of bifurcation ratio is consistent with the high drainage density value of 2.064 km/km² and confirms the impermeability of the subsurface material and mountainous relief. The hypsometric integral of the catchment is 47.4%, and the erosion integral of the catchment is 52.6%, both were indications of a mature catchment area.     

Evaluating the use of 3'-(p-Aminophenyl) fluorescein for determining the formation of highly reactive oxygen species in particle suspensions

Background  

Given the importance of highly reactive oxygen species (hROS) as reactants in a wide range of biological, photochemical, and environmental systems there is an interest in detection and quantification of these species. The extreme reactivity of the hROS, which includes hydroxyl radicals, presents an analytical challenge. 3'-(p-Aminophenyl) fluorescein (APF) is a relatively new probe used for measuring hROS. Here, we further evaluate the use of APF as a method for the detection of hydroxyl radicals in particle suspensions.     

Combining in situ isotopic, trace element and textural analyses of quartz from four magmatic-hydrothermal ore deposits

This study couples in situ ¹⁶O, ¹⁷O and ¹⁸O isotope and in situ trace element analyses to investigate and characterize the geochemical and textural complexity of magmatic-hydrothermal quartz crystals. Euhedral quartz crystals contemporaneous with mineralization were obtained from four magmatic-hydrothermal ore deposits: El Indio Au–Ag–Cu deposit; Summitville Au–Ag–Cu deposit; North Parkes Cu–Au deposit and Kingsgate quartz-Mo–Bi–W deposit. The internal features of the crystals were imaged using cathodoluminescence and qualitative electron microprobe maps. Quantitative isotopic data were collected in situ using 157 nm laser ablation inductively coupled plasma mass spectrometry (for 40 trace elements in quartz) and sensitive high-resolution ion microprobe (for 3 isotopes in quartz). Imaging revealed fine oscillatory zoning, sector zoning, complex “macromosaic” textures and hidden xenocrystic cores. In situ oxygen isotope analyses revealed a δ¹⁸O range of up to 12.4 ± 0.3 ‰ in a single crystal—the largest isotopic range ever ascribed to oscillatory zonation in quartz. Some of these crystals contain a heavier δ¹⁸O signature than expected by existing models. While sector-zoned crystals exhibited strong trace element variations between faces, no evidence for anisotropic isotope fractionation was found. We found: (1) isotopic heterogeneity in hydrothermal quartz crystals is common and precludes provenance analysis (e.g., δD–δ¹⁸O) using bulk analytical techniques, (2) the trace element signature of quartz is not an effective pathfinder toward noble metal mineralization and (3) in three of the four samples, both textural and isotopic data indicate non-equilibrium deposition of quartz.     

The dynamics of natural pipe hydrological behaviour in blanket peat

Natural soil pipes are found in peatlands, but little is known about their hydrological role. This paper presents the most complete set of pipe discharge data to date from a deep blanket peatland in Northern England. In a 17.4‐ha catchment, we identified 24 perennially flowing and 60 ephemerally flowing pipe outlets. Eight pipe outlets along with the catchment outlet were continuously gauged over an 18‐month period. The pipes in the catchment were estimated to produce around 13.7% of annual streamflow, with individual pipes often producing large peak flows (maximum peak of 3.8 l s^?1). Almost all pipes, whether ephemerally or perennially flowing, shallow or deep (outlets > 1 m below the peat surface), showed increased discharge within a mean of 3 h after rainfall commencement and were dominated by stormflow, indicating good connectivity between the peatland surface and the pipes. However, almost all pipes had a longer period between the hydrograph peak and the return to base flow compared with the stream (mean of 23.9 h for pipes, 19.7 h for stream). As a result, the proportion of streamflow produced by the pipes at any given time increased at low flows and formed the most important component of stream discharge for the lowest 10% of flows. Thus, a small number of perennially flowing pipes became more important to the stream system under low‐flow conditions and probably received water via matrix flow during periods between storms. Given the importance of pipes to streamflow in blanket peatlands, further research is required into their wider role in influencing stream water chemistry, water temperature and fluvial carbon fluxes, as well as their role in altering local hydrochemical cycling within the peat mass itself. Enhanced piping within peatlands caused by environmental change may lead to changes in the streamflow regime with larger low flows and more prolonged drainage of the peat. Copyright © 2012 John Wiley & Sons, Ltd.     

Abiotic ammonium formation in the presence of Ni-Fe metals and alloys and its implications for the Hadean nitrogen cycle

Experiments with dinitrogen-, nitrite-, nitrate-containing solutions were conducted without headspace in Ti reactors (200°C), borosilicate septum bottles (70°C) and HDPE tubes (22°C) in the presence of Fe and Ni metal, awaruite (Ni₈₀Fe₂₀) and tetrataenite (Ni₅₀Fe₅₀). In general, metals used in this investigation were more reactive than alloys toward all investigated nitrogen species. Nitrite and nitrate were converted to ammonium more rapidly than dinitrogen, and the reduction process had a strong temperature dependence. We concluded from our experimental observations that Hadean submarine hydrothermal systems could have supplied significant quantities of ammonium for reactions that are generally associated with prebiotic synthesis, especially in localized environments. Several natural meteorites (octahedrites) were found to contain up to 22 ppm N_tot. While the oxidation state of N in the octahedrites was not determined, XPS analysis of metals and alloys used in the study shows that N is likely present as nitride (N^3-). This observation may have implications toward the Hadean environment, since, terrestrial (e.g., oceanic) ammonium production may have been supplemented by reduced nitrogen delivered by metal-rich meteorites. This notion is based on the fact that nitrogen dissolves into metallic melts.