Susan A. Welch

The current investigation aims to offer fundamental, molecular- to microscopic-level descriptions of methane gas inside natural source clay minerals. Texas montmorillonite (STx-1), Georgia kaolinite (KGa-2), and Ca²⁺-saturated Texas montmorillonite (Ca-STx-1, Ca-bentonite) were utilized as subsurface model clay minerals for elucidating nano-confinement behaviors of ¹³C-labeled methane gas. High-pressure magic angle spinning (MAS) nuclear magnetic resonance (NMR) was used to describe the interactions between methane and the clays by varying temperature and pressure. Proton-decoupled ¹³C-NMR spectra were acquired at 28.2 bar at 307 K, 32.6 bar at 346 K, 56.4 bar at 307 K, 65.1 bar at 346 K, 112.7 bar at 307 K, and 130.3 bar at 346 K. In the pure state, no significant thermal effect on the behavior of methane was observed. However, there was a perceptible variation in the chemical shift position of confined methane in the mixtures with the clays up to 346 K. Conversely, the ¹³C-NMR chemical shift of methane altered by varying pressure in a pure state, and the mixtures with clays, attributed to the interaction of methane with the clay surfaces or the nanopore network of the clay–silica mixed phase. Pressure-induced shifts in methane peak positions were observed: 0.25 ppm (28.2–56.4 bar) and 0.47 ppm (56.4–112.3 bar) at 307 K. For methane in a montmorillonite mixture, shifts were 0.32 ppm for bulk-like methane and 0.20 ppm for confined methane under similar conditions. At 346 K, increasing pressure from 65.1 to 130.3 bar caused shifts exceeding 0.50 ppm, with bulk-like methane showing a 0.64 ppm shift and confined methane a 0.57 ppm shift. There was only one ¹³C-NMR methane peak in the mixture with either kaolinite (KGa-2) or Ca-bentonite with line broadening compared to that of pure methane. Still, two peaks were observed in the mixture with STx-1, explained by the imbibition and mobility of methane in the pore network.

The present study aims to provide fundamental, molecular- to microscopic-level descriptions of methane gas within natural source clay minerals. Texas montmorillonite (STx-1), Georgia kao-linite (KGa-2), and Ca2+ saturated Texas montmorillonite (Ca-STx-1, Ca-bentonite) were used as subsurface model systems for elucidating nano-confinement behaviors of 13C labeled methane gas. High-pressure Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) was utilized to characterize the interactions between methane and the clays by varying temperature and pressure. In the pure state, no significant thermal effect on the behavior of methane was observed. However, there was a perceptible change in the chemical shift position of confined methane in the mixtures with the clays up to 346 K. Conversely, the 13C-NMR chemical shift of methane changed as a func-tion of pressure in a pure state, and the mixtures with clays, attributed to the interaction of me-thane with the clay surfaces or the nanopore network of the clay-silica mixed phase. There was only one 13C-NMR peak of methane in the mixture with either kaolinite (KGa-2) or Ca-bentonite with line-broadening compared to that of pure methane, but two peaks were observed in the mix-ture with STx-1, explained by the imbibition and mobility of methane in the pore network.

The Triglav Glacier in the Julian Alps and the Skuta Glacier in the Kamnik-Savinja Alps are among the south-easternmost glaciers in the Alps. Historical data show that ice masses are undergoing mass loss as the overall climate warms. Glacier ice and cave ice contain a wealth of paleoclimatic information, and rapid sampling is needed if any such information is to be saved before the ice is completely melted. We present the first comprehensive geochemical and water isotope data from glacier ice, meltwater, spring water, and cave ice in the Mount Triglav area and glacier ice from the Skuta Glacier. The samples primarily reflect the initial precipitation signal that has been greatly modified by the input of local CaCO3-rich dust with lesser amounts of marine aerosol and vegetation debris.

Geochemical characterisation of hypersaline waters is difficult as high concentrations of salts hinder the analysis of constituents at low concentrations, such as trace metals, and the collection of samples for trace metal analysis in natural waters can be easily contaminated. This is particularly the case if samples are collected by non-conventional techniques such as those required for aquatic subglacial environments. In this paper we present the first analysis of a subglacial brine from Taylor Valley, (~ 78°S), Antarctica for the trace metals: Ba, Co, Mo, Rb, Sr, V, and U. Samples were collected englacially using an electrothermal melting probe called the IceMole. This probe uses differential heating of a copper head as well as the probe’s sidewalls and an ice screw at the melting head to move through glacier ice. Detailed blanks, meltwater, and subglacial brine samples were collected to evaluate the impact of the IceMole and the borehole pump, the melting and collection process, filtration, and storage on the geochemistry of the samples collected by this device. Comparisons between melt water profiles through the glacier ice and blank analysis, with published studies on ice geochemistry, suggest the potential for minor contributions of some species Rb, As, Co, Mn, Ni, NH₄⁺, and NO₂⁻+NO₃⁻ from the IceMole. The ability to conduct detailed chemical analyses of subglacial fluids collected with melting probes is critical for the future exploration of the hundreds of deep subglacial lakes in Antarctica.

Blood Falls is a hypersaline, iron‐rich discharge at the terminus of the Taylor Glacier in the McMurdo Dry Valleys, Antarctica. In November 2014, brine in a conduit within the glacier was penetrated and sampled using clean‐entry techniques and a thermoelectric melting probe called the IceMole. We analyzed the englacial brine sample for filterable iron (fFe), total Fe, major cations and anions, nutrients, organic carbon, and perchlorate. In addition, aliquots were analyzed for minor and trace elements and isotopes including δD and δ¹⁸O of water, δ³⁴S and δ¹⁸O of sulfate, ²³⁴U, ²³⁸U, δ¹¹B, ⁸⁷Sr/⁸⁶Sr, and δ⁸¹Br. These measurements were made in order to (1) determine the source and geochemical evolution of the brine and (2) compare the chemistry of the brine to that of nearby hypersaline lake waters and previous supraglacially sampled collections of Blood Falls outflow that were interpreted as end‐member brines. The englacial brine had higher Cl⁻ concentrations than the Blood Falls end‐member outflow; however, other constituents were similar. The isotope data indicate that the water in the brine is derived from glacier melt. The H₄SiO₄ concentrations and U and Sr isotope suggest a high degree of chemical weathering products. The brine has a low N:P ratio of ~7.2 with most of the dissolved inorganic nitrogen in the form of NH₄⁺. Dissolved organic carbon concentrations are similar to end‐member outflow values. Our results provide strong evidence that the original source of solutes in the brine was ancient seawater, which has been modified with the addition of chemical weathering products.

Cave ice samples collected within karstic terrain have major ion and nutrient concentrations showing that the ice originates from local precipitation modified by the addition of Ca²⁺ and HCO₃⁻ from the dissolution of the local bedrock. Isotopic profiles of Paradana Cave ice are similar to those described in other ice caves in central and eastern Europe, where the profiles are developed through the freezing of cave pool or “lake” waters from the top downward during the onset of the cold portion of the year. Stable isotope data suggest future studies may yield a long-term paleo-environmental record for this location.