Earth Sciences

Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/43

By virtue of our outstanding location in the scenic and rugged mountains of southwest Montana, Earth Science students have many opportunities to participate in field trips that will facilitate the study of earth processes, earth resources, earth history, and environments that people have modified. These field trips are an integral part of many courses, as well as extracurricular activities sponsored by the department. Fieldwork is a very important component of our instructional programs at both the undergraduate and graduate levels.Because of the research conducted by faculty in the department, an undergraduate student may have the opportunity to work on active research projects. In particular, we offer the opportunity to do a "Senior Thesis" to our top students in each senior class. The senior thesis enables a student to work on an actual research project under the supervision of a faculty member, write a research report (a mini-thesis), and present the results at a professional conference. This is excellent preparation for graduate school and/or the workplace. Our Master's theses frequently involve field-testing of state-of-the-art hypotheses proposed elsewhere, as well as formulation of the next generation of hypotheses, which will shape our disciplines in the decades to come. Most Master's thesis work in the Department is published in the peer-reviewed professional literature after presentation at regional or national professional meetings.

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A framework to link climate change, food security, and migration: unpacking the agricultural pathway
(Springer Science and Business Media LLC, 2024-03) Tuholske, Cascade; Di Landro, Maria Agustina; Anderson, Weston; van Duijne, Robbin Jan; de Sherbinin, Alex
Researchers have long hypothesized linkages between climate change, food security, and migration in low- and middle-income countries (LMICs). One such hypothesis is the “agricultural pathway,” which postulates that negative climate change impacts on food production harm livelihoods, which triggers rural out-migration, internally or abroad. Migration is thus an adaptation to cope with the impacts of climate change and bolster livelihoods. Recent evidence suggests that the agriculture pathway is a plausible mechanism to explain climate-related migration. But direct causal connections from climate impacts on food production to livelihood loss to rural out-migration have yet to be fully established. To guide future research on the climate-food-migration nexus, we present a conceptual framework that outlines the components and linkages underpinning the agricultural pathway in LMICs. We build on established environmental-migration conceptual frameworks that have informed empirical research and deepened our understanding of complex human-environmental systems. First, we provide an overview of the conceptual framework and its connection to the agricultural pathway hypothesis in the climate mobility literature. We then outline the primary components and linkages of the conceptual framework as they pertain to LMIC contexts, highlighting current research gaps and challenges relating to the agricultural pathway. Last, we discuss possible future research directions for the climate-food-migration nexus. By highlighting the complex, multiscale, interconnected linkages that underpin the agricultural pathway, our framework unpacks the multiple causal connections that currently lie hidden in the agricultural pathway hypothesis.
An accumulation of turtle eggs with embryos from the Campanian (Upper Cretaceous) Judith River Formation of Montana
(2017-01) Lawver, Daniel R.; Jackson, Frankie D.
A weathered accumulation of turtle eggs, interpreted as remnants of a single clutch composed of at least 16 turtle eggs (MOR 710) from the Campanian (Upper Cretaceous) Judith River Formation of north-central Montana, USA, represents a new oospecies Testudoolithus zelenitskyae. This ootaxon is diagnosed by the following unique combination of characters: spherical eggs 34â€“39 mm in diameter, 660â€“760 Î¼m thick eggshell, shell unit height-to-width ratio of 3.15:1â€“5.5:1, and domed shell units. Estimated egg mass indicates that the egg-laying adult likely possessed a carapace 35.0â€“54.4 cm in length. Similarities between T. zelenitskyae oosp. nov. and Adocus sp. eggs, along with comparable body size, suggest that this taxon might have produced MOR 710. One egg exhibits abnormal multilayered eggshell, likely resulting from prolonged egg retention by the female turtle. At least five of these eggs, including the multilayered specimen, preserve embryonic remains that demonstrate a late stage of embryonic development. This suggests that death occurred just prior to hatching.
Aerobic and Anaerobic Thiosulfate Oxidation by a Cold-Adapted, Subglacial Chemoautotroph
(2015-12) Harrold, Zoe R.; Skidmore, Mark L.; Hamilton, Trinity L.; Desch, Elizabeth; Kirina, Amada; van Gelder, Will; Glover, Kevin; Roden, Eric E.; Boyd, Eric S.
Geochemical data indicate that protons released during pyrite (FeS2) oxidation are important drivers of mineral weathering in oxic and anoxic zones of many aquatic environments including those beneath glaciers. Oxidation of FeS2 under oxic, circumneutral conditions proceeds through the metastable intermediate thiosulfate (S2O32-), which represents an electron donor capable of supporting microbial metabolism. Subglacial meltwaters sampled from Robertson Glacier (RG), Canada over a seasonal melt cycle reveal concentrations of S2O32- that are typically below detection despite the presence of available pyrite and several orders of magnitude higher concentrations of the FeS2 oxidation product sulfate (SO42-). Here we report the physiological and genomic characterization of the chemolithoautotrophic facultative anaerobe Thiobacillus sp. RG5 isolated from the subglacial environment at RG. The RG5 genome encodes pathways for the complete oxidation of S2O32-, CO2 fixation, and aerobic and anaerobic respiration with nitrite or nitrate. Growth experiments indicate that the energy required to synthesize a cell under oxygen or nitrate reducing conditions with S2O32- as electron donor was lower at 5.1 °C than 14.4 °C, indicating that this organism is cold-adapted. RG sediment-associated soxB transcripts, which encode a component of the S2O32--oxidizing complex, were closely affiliated to soxB from RG5. Collectively, these results suggest an active sulfur cycle in the subglacial environment at RG mediated in part by populations closely affiliated with RG5. Microbial consumption of S2O32- by RG5-like populations may accelerate abiotic FeS2 oxidation thereby enhancing mineral weathering in the subglacial environment.
An analysis of fossil identification guides to improve data reporting in citizen science programs
(2020-04) Butler, Dava K.; Esker, Donald A.; Juntunen, Kristopher L.; Lawver, Daniel R.
An increasing number of organizations use untrained volunteers to gather scientific data. This citizen science movement builds enthusiasm for science by engaging the public, as well as providing a way to gather large amounts of data at little or no expense. The challenge of citizen science is obtaining accurate information from participants. Many citizen science programs encourage participants to use visual identification guides to ensure they provide correct data. Identifying an image style that increases correct identifications helps not only the citizen science movement but also scientific instruction in general. This study tests three image-based identification guides for identifying late Hemphillian (5–4.5 m.y.a.) fossils from Polk County, Florida. Each guide has identical layout and text, differing only in image style: color photos, grayscale photos, or illustrations. Untrained participants each use one guide to identify fossils. Geology and paleontology professionals also identify fossils for comparison. Comparing results reveals that color photographic images produce results most similar to data from professionals. In addition, participants provide data on their years of education, previous experience finding fossils, and enthusiasm about finding fossils. Analysis of this information reveals that participants with higher education and/or previous experience finding fossils produce data most similar to that from professionals. Paradoxically, participants with higher enthusiasm produce data less similar to that from professionals, while moderate interest levels correlated with greater similarity.
The Ancestral Lhasa River: A Late Cretaceous trans-arc river that drained the proto-Tibetan Plateau
(2019-09-19) Laskowski, Andrew K.; Orme, Devon A.; Cai, Fulong; Ding, Lin
Late Cretaceous trench basin strata were deposited in the subduction zone that consumed Neo-Tethyan oceanic lithosphere along the southern margin of the proto–Tibetan Plateau. We conducted detrital zircon (DZ) U-Pb geochronology on six trench basin samples (n = 1716) collected near Dênggar, Tibet (∼500 km west of Lhasa), to assess the provenance of these rocks and reconstruct Late Cretaceous sediment transport pathways. They contained DZ ages that point to a unique source around Lhasa city, north of the Late Cretaceous Gangdese magmatic arc. The modern Lhasa River catchment contains the requisite sources, and its main trunk transects the Gangdese magmatic arc, joining with the Yarlung River at a barbed junction at the India-Asia suture. We infer that the Lhasa River is an ancient feature that transported sediment to the subduction zone in Late Cretaceous time and persisted during India-Asia collision.
Approaches and mechanisms for ecologically based pest management across multiple scales
(2016-08) Zhao, Zi-Hua; Reddy, Gadi V. P.; Hui, Cang; Li, Bai-Lian
The past 50 years have seen substantial change of agroecosystems in the world, including an intensified use of agrochemicals and expansion of cropland, resulting in a rapid loss of biodiversity and a reduction of ecosystem services. The effects of these changes, at both the field and landscape scale, on ecologically based pest management (EBPM) in agroecosystems have become increasingly important. Here, we review the theories, important approaches and mechanisms of habitat management practices (at multiple spatial scales) that can be applied to facilitate EBPM in crop fields and even over larger landscapes. In particular, we discuss links between pest outbreaks and rapid changes of habitat composition at local and regional scales. We also summarize recent progress of habitat management and their application to pest management, which is an activity that we believe must be implemented at multiple spatial scales to successfully conserve ecosystem services and address environmental issues related to crop pest control.
Après Nous, le Déluge: A Human‐Triggered Jökulhlaup From a Subglacial Lake
(American Geophysical Union, 2020-11) Gaidos, E.; Johannesson, T.; Einarsson, B.; Thorsteinsson, Th.; Amend, J.P.; Skidmore, M.
Glacial floods (jökulhlaups) are a phenomenon of some temperate ice masses; they are a significant natural hazard, but their complex hydrology is incompletely understood.We document a jökulhlaup from a subglacial lake in Iceland that was inadvertently triggered by a borehole drilled through the overlying ice.We propose that this borehole allowed an englacial water body to drain into the lake, inducing a transient rise in pressure that overwhelmed the lake's subglacial seal 5 days later. Runaway melting of a subglacial conduit by 4◦C lake water then initiated a flood to the outlet glacier margin. This incident suggests that draining of englacial water bodies via hydrofracturing crevasses and flooding of moulins by precipitation events are potential natural triggers of jökulhlaups and explains a correlation between surface melting and jökulhlaups. This hydraulic trigger could have wider implications for relations between meteorological conditions, drainage, and dynamics of some glaciers.
Aquatic Ecosystem Services Survey: Round One Results
(Montana State University, 2021-04) Gilbert, Ashlie; Kleindl, William; Chruch, Sarah P.
Wetlands, streams, and floodplains (hereafter called aquatic systems) are an important resource for social and ecological wellbeing. Since the early 1990s, Federal policy has required a no overall net loss (NNL) of wetland area (i.e. aquatic systems), functions, and values in the United States (US). Past efforts to build assessment tools have focused primarily on wetland structure and function, and less on inherent services provided by aquatic ecosystems that are valued by people (hereafter referred to as ecosystem services (ES)). Moreover, there has been little effort to develop assessment tools that measure wetland services in a rapid and repeatable manner. Our intent with this research is to develop a framework and generalized methodology for the rapid assessment of ES provided by wetlands, streams and their riparian buffers for use in permitting, compensatory mitigation, and preservation decisions. Moreover, we seek to understand aquatic systems decision-makers’ perceptions of planning and land use surrounding wetland protection and mitigation.
Aquatic Ecosystem Services Survey: Round Two Results
(Montana State University, 2022-05) Gilbert, Ashlie; Kleindl, William; Church, Sarah P.
Wetlands, streams, and floodplains (hereafter called aquatic systems) are an important resource for social and ecological wellbeing. Since the early 1990s, Federal policy has required a no overall net loss (NNL) of wetland area (i.e., aquatic systems), functions, and values in the United States (US). Past efforts to build assessment tools have focused primarily on wetland structure and function, and less on inherent services provided by aquatic ecosystems that are valued by people (hereafter referred to as ecosystem services (ES)). Moreover, there has been little effort to develop assessment tools that measure wetland services in a rapid and repeatable manner. Our intent with this research is to develop a framework and generalized methodology for the rapid assessment of ES provided by wetlands, streams, and their riparian buffers for use in permitting, compensatory mitigation, and preservation decisions. Moreover, we seek to understand aquatic systems decision-makers’ perceptions of planning and land use surrounding wetland protection and mitigation.
Are We Recording? Putting Embayment Speedometry to the Test Using High Pressure‐Temperature Decompression Experiments
(American Geophysical Union, 2023-06) Hosseini, Behnaz; Myers, Madison L.; Watkins, James M.; Harris, Megan A.
Despite its increasing application to estimate magma decompression rates for explosive eruptions, the embayment speedometer has long awaited critical experimental evaluation. We present the first experimental results on the fidelity of natural quartz-hosted embayments in rhyolitic systems as recorders of magma decompression. We conducted two high pressure-temperature isobaric equilibrium experiments and 13 constant-rate, continuous isothermal decompression experiments in a cold-seal pressure vessel where we imposed rates from 0.005 to 0.05 MPa s−1 in both H2O-saturated and mixed-volatile (H2O + CO2)-saturated systems. In both equilibrium experiments, we successfully re-equilibrated embayment melt to new fluid compositions at 780°C and 150 MPa, confirming the ability of embayments to respond to and record changing environmental conditions. Of the 32 glassy embayments recovered, seven met the criteria previously established for successful geospeedometry and were thus analyzed for their volatile (H2O ± CO2) concentrations, with each producing a good model fit and recovering close to the imposed decompression rate. In one H2O-saturated experiment, modeling H2O concentration gradients in embayments from three separate crystals resulted in best-fit decompression rates ranging from 0.012 to 0.021 MPa s−1, in close agreement with the imposed rate (0.015 MPa s−1) and attesting to the reproducibility of the technique. For mixed-volatile experiments, we found that a slightly variable starting fluid composition (2.4–3.5 wt.% H2O at 150 MPa) resulted in good fits to both H2O + CO2 profiles. Overall our experiments provide confidence that the embayment is a robust recorder of constant-rate, continuous decompression, with the model successfully extracting experimental conditions from profiles representing nearly an order of magnitude variation (0.008–0.05 MPa s−1) in decompression rate.
Assessment of L-band InSAR snow estimation techniques over a shallow, heterogeneous prairie snowpack
(Elsevier BV, 2023-10) Palomaki, Ross T.; Sproles, Eric A
Snow water equivalent (SWE) is a critical input for weather, climate, and water resource management models at local to global scales. Despite its importance, global SWE measurements that are accurate, consistent, and at sufficiently high spatiotemporal resolutions are not currently available. L-band interferometric synthetic aperture radar (InSAR) techniques have been used to measure SWE at local to regional scales, and two upcoming L-band SAR satellite missions have renewed interest in these techniques to provide regular SWE measurements at the global scale. However, previous research demonstrating the capabilities of L-band InSAR-SWE measurement has been limited to mountain or tundra snowpack regimes. Here we examine the feasibility of applying the same techniques over a prairie snowpack, which are typically characterized by shallow snow depths (mean snow depth of 0.22 m in this study), exposed agricultural vegetation, and high spatial variability over short distances. Our study area in central Montana, USA (47.060, -109.951) was a validation site for NASA SnowEx 2021, as part of the UAVSAR snow timeseries. Airborne L-band SAR imagery was acquired by the UAVSAR platform while concurrent snow measurements were collected using uncrewed aerial vehicle (UAV)-based LiDAR, UAV-based photogrammetry, and ground-based manual techniques. This validation dataset enables an investigation of the effects of sub-pixel snow cover heterogeneity and exposed agricultural vegetation stubble on SAR data and the resulting SWE estimations. Results based on repeated application of the Kolmogorov–Smirnov test show that UAVSAR VV phase change is sensitive to differences in snow cover but relatively unaffected by differences in agricultural stubble height. However, we did not find similarly definitive results when we used the same phase change data to estimate SWE. Although broad spatial patterns were similar in both LiDAR-derived and InSAR-derived SWE estimates, considerable differences in the two estimates were apparent in areas with large sub-pixel snow depth variability. Our results indicate that additional work is necessary to derive accurate SWE estimates in prairie environments. Regular measurements from L-band SAR satellites will provide an excellent opportunity to refine InSAR-based snow estimation techniques over shallow, heterogeneous snowpacks.
Autonomous Aerial Vehicles (AAVs) as a Tool for Improving the Spatial Resolution of Snow Albedo Measurements in Mountainous Regions
(MDPI, 2020-07) Sproles, Eric A.; Mullen, Andrew; Hendrikx, Jordy; Gatebe, Charles; Taylor, Suzi
We present technical advances and methods to measure effective broadband physical albedo in snowy mountain headwaters using a prototype dual-sensor pyranometer mounted on an Autonomous Aerial Vehicle (an AAV). Our test flights over snowy meadows and forested areas performed well during both clear sky and snowy/windy conditions at an elevation of ~2650 m above mean sea level (MSL). Our AAV-pyranometer platform provided high spatial (m) and temporal resolution (sec) measurements of effective broadband (310–2700 nm) surface albedo. The AAV-based measurements reveal spatially explicit changes in landscape albedo that are not present in concurrent satellite measurements from Landsat and MODIS due to a higher spatial resolution. This AAV capability is needed for validation of satellite snow albedo products, especially over variable montane landscapes at spatial scales of critical importance to hydrological applications. Effectively measuring albedo is important, as annually the seasonal accumulation and melt of mountain snowpack represent a dramatic transformation of Earth’s albedo, which directly affects headwaters’ water and energy cycles.
Biogeochemical Responses to Mixing of Glacial Meltwater and Hot Spring Discharge in the Mount St. Helens Crater
(Wiley, 2022-09) Dubnick, A.; Faber, Q.; Hawkings, J. R.; Bramiall, N.; Christner, B. C.; Doran, P. T.; Nadeau, J.; Snyder, C.; Kellerman, A. M.; Spencer, R. G. M.; Skidmore, M. L.
Environments where geothermal waters and glacier meltwater mix are common on Earth yet little is known about the biogeochemical processes that occur when hot, reduced geothermal water mixes with cold, oxidized glacial meltwater in natural systems. Mount St. Helens provides an ideal location to study the interaction between geothermal and glacier waters since the water sources, and their mixing environment in Step Creek, are exposed in the volcanic crater. We find that the two water sources contain distinct major ion, trace element, dissolved organic matter (DOM), and biological signatures. The hot spring contains high concentrations of biogeochemically reactive components (e.g., siderophile and chalcophile trace elements and DOM) compared to the glacier discharge but a large fraction of these solutes do not remain in solution after the waters mix. In contrast, glacier discharge contains fewer solutes but most of these solutes remain in solution after the waters mix. The mixing of glacier and hot spring water in Step Creek supports seston and benthic ecosystems that have higher phototrophic and microbial biomass than those in the source waters, suggesting that the mixing environment in this high-gradient stream provide a more comprehensive suite of soluble and essential nutrients that promote primary production and DOM cycling.
Broad-Scale Surface and Atmospheric Conditions during Large Fires in South-Central Chile
(2021-05) McWethy, David B.; Garreaud, Rene D.; Holz, Andres; Pederson, Gregory T.
The unprecedented size of the 2017 wildfires that burned nearly 600,000 hectares of central Chile highlight a need to better understand the climatic conditions under which large fires develop. Here we evaluate synoptic atmospheric conditions at the surface and free troposphere associated with anomalously high (active) versus low (inactive) months of area burned in south-central Chile (ca. 32–41° S) from the Chilean Forest Service (CONAF) record of area burned from 1984–2018. Active fire months are correlated with warm surface temperatures, dry conditions, and the presence of a circumpolar assemblage of high-pressure systems located ca. 40°–60° S. Additionally, warm surface temperatures associated with active fire months are linked to reduced strength of cool, onshore westerly winds and an increase in warm, downslope Andean Cordillera easterly winds. Episodic warm downslope winds and easterly wind anomalies superimposed on long-term warming and drying trends will continue to create conditions that promote large fires in south-central Chile. Identifying the mechanisms responsible for easterly wind anomalies and determining whether this trend is strengthening due to synoptic-scale climatic changes such as the poleward shift in Southern Hemisphere westerly winds will be critical for anticipating future large fire activity in south-central Chile.
Burial and exhumation history of the Xigaze Forearc, Yarlung Suture Zone, Tibet
(2017-12) Orme, Devon A.
The Cretaceous–Eocene Xigaze forearc basin is a crucial data archive for understanding the tectonic history of the Asian continental margin prior to and following collision with India during the early Cenozoic Era. This study reports apatite and zircon (U–Th)/He thermochronologic data from fourteen samples from Albian-Ypresian Xigaze forearc strata to determine the degree and timing of heating (burial) and subsequent cooling (exhumation) of two localities along the Yarlung suture zone (YSZ) near the towns of Saga and Lazi. Thirty-seven individual zircon He ages range from 31.5 ± 0.8 Ma to 6.06 ± 0.18 Ma, with the majority of grains yielding ages between 30 Ma and 10 Ma. Twenty apatite He ages range from 12.7 ± 0.5 Ma to 3.9 ± 0.3 Ma, with the majority of grains yielding ages between 9 Ma and 4 Ma. These ages suggest that the Xigaze forearc basin was heated to 140–200 °C prior to cooling in Oligocene–Miocene time. Thermal modeling supports this interpretation and shows that the samples were buried to maximum temperatures of ∼140–200 °C by 35–21 Ma, immediately followed by the onset of exhumation. The zircon He and apatite He dataset and thermal modeling results indicate rapid exhumation from ∼21 Ma to 15 Ma, and at ∼4 Ma. The 21–15 Ma thermochronometric signal appears to be regionally extensive, affecting all the lithotectonic units of the YSZ, and coincides with movement along the north-vergent Great Counter Thrust system. Thrusting, coupled with enhanced erosion possibly related to the paleo-Yarlung River, likely drove Early Miocene cooling of the Xigaze forearc basin. In contrast, the younger phase of rapid exhumation at ∼4 Ma was likely driven by enhanced rock uplift in the footwall of north-striking rifts that cross-cut the YSZ.
Can the Adoption of Desalination Technology Lead to Aquifer Preservation? A Case Study of a Sociotechnical Water System in Baja California Sur, Mexico
(2015-09) McEvoy, Jamie
There is growing concern about the sustainability of groundwater supplies worldwide. In many regions, desalination—the conversion of saline water to freshwater—is viewed as a way to increase water supplies and reduce pressure on overdrawn aquifers. Using data from reports, articles, interviews, a survey, and a focus group, this paper examines if, and how, the adoption of desalination technology can lead to aquifer preservation in Baja California Sur (BCS), Mexico. The paper outlines existing institutional arrangements (i.e., laws, rules, norms, or organizations) surrounding desalination in BCS and concludes that there are currently no effective mechanisms to ensure aquifer preservation. Four mechanisms that could be implemented to improve groundwater management are identified, including: 1) integrated water-and land-use planning; 2) creation of an institute responsible for coordinated and consistent planning; 3) improved groundwater monitoring; and 4) implementation of water conservation measures prior to the adoption of desalination technology. This paper concludes that viewing water technologies, including desalination, as sociotechnical systems—i.e., a set of technological components that are embedded in complex social, political, and economic contexts—has the potential to create a more sustainable human–environment–technology relationship. By assessing desalination technology as a sociotechnical system, this study highlights the need to focus on institutional development and capacity building, especially within local water utilities and urban planning agencies.
Capturing the complexity of soil evolution: Heterogeneities in rock cover and chemical weathering in Montana's Rocky Mountains
(Elsevier BV, 2022-05) Benjaram, Sarah S.; Dixon, Jean L.; Wilcox, Andrew C.
We investigate the relationship between chemical weathering, persistence of soil cover, and topography in two neighboring mountain ranges in the northern Rockies of western Montana, USA. We augment existing tools for measuring chemical weathering with adjustments for both local and landscape-scale contributions from unweathered rock fragments, boulders, and bedrock exposure. Adjusted weathering intensities recognize that quantifying weathering in mountainous systems should account for rock exposure, rather than focusing solely on fine-grained soil mantles. Our study systems' distinct morphologies are shaped by their unique climate histories. The previously glaciated Bitterroot Mountains consist of steep hillslopes with abundant rock cover, while the neighboring unglaciated Sapphire Mountains display convex, soil-mantled hillslopes. Over 380 soil thickness measurements, 118 analyses of soil and rock geochemistry, and digital terrain analysis reveal that patchy soils in the bedrock-rich system are roughly half as thick as those in the continuously-soil-mantled landscape, and ~45% less weathered, despite wetter conditions that would be expected to enhance weathering. These disparities increase when accounting for coarse rock fragments in soils and bedrock cover across the study catchments. The near continuously soil-mantled Sapphire system experiences ~1.5 times greater weathering intensity at a catchment scale compared to the bedrock-rich Bitterroot system. Rock exposure across the mountainous study system increases with increasing slope gradient. However, we find no clear threshold at which soils decrease in abundance or weathering intensity, and soils are surprisingly resilient even at the steepest hillslopes (comprising ~60% of the landscape area at slopes >30°). Our new data quantify soil abundance and chemical weathering intensity at both local and landscape scales. This work highlights how measurements of soil and rock cover need to be incorporated into studies quantifying chemical weathering, as traditional approaches may significantly overestimate and mischaracterize weathering regimes in mountain environments.
CHANGE: Climate and Hydrology Academic Network for Governance and the Environment
(American Meteorological Society, 2011-08) Garfin, Gregg; Gregg, Nancy; Magaña, Victor; Stewart, Ronald; Rolfe, J. Terry; McEvoy, Jamie
Chemolithotrophic primary production in a subglacial ecosystem
(2014-10) Boyd, Eric S.; Hamilton, Trinity L.; Havig, Jeff R.; Skidmore, Mark L.; Shock, Everett L.
Glacial comminution of bedrock generates fresh mineral surfaces capable of sustaining chemotrophic microbial communities under the dark conditions that pervade subglacial habitats. Geochemical and isotopic evidence suggests that pyrite oxidation is a dominant weathering process generating protons that drive mineral dissolution in many subglacial systems. Here, we provide evidence correlating pyrite oxidation with chemosynthetic primary productivity and carbonate dissolution in subglacial sediments sampled from Robertson Glacier (RG), Alberta, Canada. Quantification and sequencing of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) transcripts suggest that populations closely affiliated with Sideroxydans lithotrophicus, an iron sulfide-oxidizing autotrophic bacterium, are abundant constituents of microbial communities at RG. Microcosm experiments indicate sulfate production during biological assimilation of radiolabeled bicarbonate. Geochemical analyses of subglacial meltwater indicate that increases in sulfate levels are associated with increased calcite and dolomite dissolution. Collectively, these data suggest a role for biological pyrite oxidation in driving primary productivity and mineral dissolution in a subglacial environment and provide the first rate estimate for bicarbonate assimilation in these ecosystems. Evidence for lithotrophic primary production in this contemporary subglacial environment provides a plausible mechanism to explain how subglacial communities could be sustained in near-isolation from the atmosphere during glacial-interglacial cycles.
Chthonic severance: dinosaur eggs of the Mesozoic, the significance of partially buried eggs and contact incubation precursors
(The Royal Society, 2023-07) Hogan, Jason D.; Varricchio, David J.
For most dinosaurs, clutches consisted of a single layer of spherical to sub-spherical, highly porous eggs that were probably fully buried. Both eggs and clutch form change drastically with pennaraptoran theropods, the clade that includes birds. Here, far less porous, more elongate eggs are arranged with additional complexity, and only partially buried. While partial egg burial seems to be effective for an extremely small group of modern birds, the behaviour's overall rarity complicates our understanding of Mesozoic analogies. Recent experimental examination of pennaraptoran nesting thermodynamics suggests that partial egg burial, combined with contact incubation, may be more efficacious than has been presumed. We propose that nest guarding behaviour by endothermic archosaurs may have led to an indirect form of contact incubation using metabolic energy to affect temperature change in a buried clutch through a barrier of sediment, which in turn may have selected for shallower clutch burial to increasingly benefit from adult-generated energy until partial egg exposure. Once partially exposed, continued selection pressure may have aided a transition to fully subaerial eggs. This hypothesis connects the presence of partially buried dinosaurian clutches with the transition from basal, crocodile-like nesting (buried clutches guarded by adults) to the dominant avian habit of contact incubating fully exposed eggs.