Research and Publications - Department of Geological Sciences

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    The Elusive Evidence of Volcanic Lightning
    (Nature Portfolio, 2017) Genareau, K.; Gharghabi, P.; Gafford, J.; Mazzola, M.; University of Alabama Tuscaloosa; Mississippi State University
    Lightning strikes are known to morphologically alter and chemically reduce geologic formations and deposits, forming fulgurites. A similar process occurs as the result of volcanic lightning discharge, when airborne volcanic ash is transformed into lightning-induced volcanic spherules (LIVS). Here, we adapt the calculations used in previous studies of lightning-induced damage to infrastructure materials to determine the effects on pseudo-ash samples of simplified composition. Using laboratory high-current impulse experiments, this research shows that within the lightning discharge channel there is an ideal melting zone that represents roughly 10% or less of the total channel radius at which temperatures are sufficient to melt the ash, regardless of peak current. The melted ash is simultaneously expelled from the channel by the heated, expanding air, permitting particles to cool during atmospheric transport before coming to rest in ash fall deposits. The limited size of this ideal melting zone explains the low number of LIVS typically observed in volcanic ash despite the frequent occurrence of lightning during explosive eruptions.
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    Use of ESI-FTICR-MS to Characterize Dissolved Organic Matter in Headwater Streams Draining Forest-Dominated and Pasture-Dominated Watersheds
    (PLOS, 2015) Lu, YueHan; Li, Xiaping; Mesfioui, Rajaa; Bauer, James E.; Chambers, R. M.; Canuel, Elizabeth A.; Hatcher, Patrick G.; University of Alabama Tuscaloosa; Old Dominion University; Ohio State University; William & Mary; Virginia Institute of Marine Science
    Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) has proven to be a powerful technique revealing complexity and diversity of natural DOM molecules, but its application to DOM analysis in grazing-impacted agricultural systems remains scarce. In the present study, we presented a case study of using ESI-FTICR-MS in analyzing DOM from four headwater streams draining forest-or pasture-dominated watersheds in Virginia, USA. In all samples, most formulas were CHO compounds (71.8-87.9%), with other molecular series (CHOS, CHON, CHONS, and CHOP (N, S)) accounting for only minor fractions. All samples were dominated by molecules falling in the lignin-like region (H/C = 0.7-1.5, O/C = 0.1-0.67), suggesting the predominance of allochthonous, terrestrial plant-derived DOM. Relative to the two pasture streams, DOM formulas in the two forest streams were more similar, based on Jaccard similarity coefficients and nonmetric multidimensional scaling calculated from Bray-Curtis distance. Formulas from the pasture streams were characterized by lower proportions of aromatic formulas and lower unsaturation, suggesting that the allochthonous versus autochthonous contributions of organic matter to streams were modified by pasture land use. The number of condensed aromatic structures (CAS) was higher for the forest streams, which is possibly due to the controlled burning in the forest-dominated watersheds and suggests that black carbon was mobilized from soils to streams. During 15-day biodegradation experiments, DOM from the two pasture streams was altered to a greater extent than DOM from the forest streams, with formulas with H/C and O/C ranges similar to protein (H/C = 1.5-2.2, O/C = 0.3-0.67), lipid (H/C = 1.5-2.0, O/C = 0-0.3), and unsaturated hydrocarbon (H/C = 0.7-1.5, O/C = 0-0.1) being the most bioreactive groups. Aromatic compound formulas including CAS were preferentially removed during combined light+bacterial incubations, supporting the contention that black carbon is labile to light alterations. Collectively, our data demonstrate that head-water DOM composition contains integrative information on watershed sources and processes, and the application of ESI-FTICR-MS technique offers additional insights into compound composition and reactivity unrevealed by fluorescence and stable carbon isotopic measurements.
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    Recognition of a likely two phased extinction at the K-Pg boundary in Antarctica
    (Nature Portfolio, 2017) Tobin, Thomas S.; University of Alabama Tuscaloosa
    The southernmost Cretaceous-Paleogene (K-Pg) outcrop exposure is the well-studied exposure on Seymour Island, Antarctica. Deposition across the K-Pg boundary there is uninterrupted, and as a consequence the ammonite fossil record is commonly used to test statistical methods of evaluating mass extinctions to account for the incompleteness of the fossil record. Numerous detailed fossil data sets from Seymour Island, comprised dominantly of mollusks, have been published over the last 30 years, but in most cases have not received statistical treatment. Here a previously published statistical technique is modified, automated, and applied to all published macrofossil data sets available from Seymour Island. All data sets reveal likely evidence of two separate multi-species extinctions, one synchronous with bolide impact evidence at the K-Pg boundary, and another 45 +/- 15 meters (similar to 140-290 ky) below the boundary. The apparent earlier extinction primarily affects benthic mollusks, while the boundary extinction primarily affects ammonites. While there is no unique sedimentological change over the interval where the earlier extinction is identified, it is impossible to exclude the possibility that this pattern is stratigraphically controlled. The automation of this technique allows it to be applied easily to other large fossil data sets.
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    Effects of Lightning on the Magnetic Properties of Volcanic Ash
    (Nature Portfolio, 2019) Genareau, Kimberly; Hong, Yang-Ki; Lee, Woncheol; Choi, Minyeong; Rostaghi-Chalaki, Mojtaba; Gharghabi, Pedram; Gafford, James; Kluss, Joni; University of Alabama Tuscaloosa; Mississippi State University; University of North Carolina; University of North Carolina Charlotte
    High-current impulse experiments were performed on volcanic ash samples to determine the magnetic effects that may result from the occurrence of volcanic lightning during explosive eruptions. Pseudo-ash was manufactured through milling and sieving of eruptive deposits with different bulk compositions and mineral contents. By comparing pre- and post-experimental samples, it was found that the saturation (i.e., maximum possible) magnetization increased, and coercivity (i.e., ability to withstand demagnetization) decreased. The increase in saturation magnetization was greater for compositionally evolved samples compared to more primitive samples subjected to equivalent currents. Changes in remanent (i.e., residual) magnetization do not correlate with composition, and show wide variability. Variations in magnetic properties were generally more significant when samples were subjected to higher peak currents as higher currents affect a greater proportion of the subjected sample. The electrons introduced by the current impulse cause reduction and devolatilization of the ash grains, changing their structural, mineralogical, and magnetic properties.
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    Fractal nature of groundwater level fluctuations affected by riparian zone vegetation water use and river stage variations
    (Nature Portfolio, 2019) Sun, HongGuang; Gu, Xiufen; Zhu, Jianting; Yu, Zhongbo; Zhang, Yong; Hohai University; University of Wyoming; University of Alabama Tuscaloosa
    Groundwater systems affected by various factors can exhibit complex fractal behaviors, whose reliable characterization however is not straightforward. This study explores the fractal scaling behavior of the groundwater systems affected by plant water use and river stage fluctuations in the riparian zone, using multifractal detrended fluctuation analysis (MFDFA). The multifractal spectrum based on the local Hurst exponent is used to quantify the complexity of fractal nature. Results show that the water level variations at the riparian zone of the Colorado River, USA, exhibit multifractal characteristics mainly caused by the memory of time series of the water level fluctuations. The groundwater level at the monitoring well close to the river characterizes the season-dependent scaling behavior, including persistence from December to February and anti-persistence from March to November. For the site with high-density plants (Tamarisk ramosissima, which requires direct access to groundwater as its source of water), the groundwater level fluctuation becomes persistent in spring and summer, since the plants have the most significant and sustained influence on the groundwater in these seasons, which can result in stronger memory of the water level fluctuation. Results also show that the high-density plants weaken the complexity of the multifractal property of the groundwater system. In addition, the groundwater level variations at the site close to the river exhibit the most complex multifractality due to the influence of the river stage fluctuation.
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    Two-step extinction of Late Cretaceous marine vertebrates in northern Gulf of Mexico prolonged biodiversity loss prior to the Chicxulub impact
    (Nature Portfolio, 2020) Ikejiri, Takehito; Lu, YueHan; Zhang, Bo; University of Alabama Tuscaloosa
    Recent studies on mass extinctions are often based on the global fossil record, but data from selected paleogeographic regions under a relatively constant paleoenvironmental setting can also provide important information. Eighty-nine marine vertebrate species, including cartilaginous and bony fish and marine reptiles, from northern Gulf of Mexico - located about 500km from the Chicxulub crater - offer a unique opportunity to determine an extinction process during the last 20 million years of the Late Cretaceous. Our diversity data show two separate extinction events: (i) the 'Middle Campanian Crisis' (about 77 Mya) and (ii) the end-Maastrichtian (66 Mya) events. Whether this stepwise pattern of extinctions occurred locally or globally cannot be determined at present due to the lack of a dataset of the marine vertebrate record for reliable comparison. However, this stepwise pattern including the Middle Campanian and end-Maastrichtian events for, at least, a 13 million-year interval indicates long-term global marine environmental changes (e.g., regression, ocean water chemistry change). Because most Cretaceous marine vertebrates already disappeared in the Gulf of Mexico prior to the latest Maastrichtian, the Chicxulub Impact may not be considered as the most devastating extinction event for the community.
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    Nitrogen Fertilization Restructured Spatial Patterns of Soil Organic Carbon and Total Nitrogen in Switchgrass and Gamagrass Croplands in Tennessee USA
    (Nature Portfolio, 2020) Li, Jianwei; Jian, Siyang; Lane, Chad S.; Guo, Chunlan; Lu, YueHan; Deng, Qi; Mayes, Melanie A.; Dzantor, Kudjo E.; Hui, Dafeng; Tennessee State University; University of North Carolina; University of North Carolina Wilmington; Jiangxi Agricultural University; University of Alabama Tuscaloosa; Chinese Academy of Sciences; South China Botanical Garden, CAS; United States Department of Energy (DOE); Oak Ridge National Laboratory
    Nitrogen (N) fertilizers can potentially alter spatial distribution of soil organic carbon (SOC) and total nitrogen (TN) concentrations in croplands such as switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.), but it remains unclear whether these effects are the same between crops and under different rates of fertilization. C-13 and N-15 are two important proxy measures of soil biogeochemistry, but they were rarely examined as to their spatial distributions in soil. Based on a three-year long fertilization experiment in Middle Tennessee, USA, the top mineral horizon soils (0-15cm) were collected using a spatially explicit design within two 15-m(2) plots under three fertilization treatments in SG and GG croplands. A total of 288 samples were collected based on 12 plots and 24 samples in each plot. The fertilization treatments were no N input (NN), low N input (LN: 84kgN ha(-1) in urea) and high N input (HN: 168kgN ha(-1) in urea). The SOC, TN, SOC/TN (C: N), delta C-13 and delta N-15 were quantified and their within-plot variations and spatial distributions were achieved via descriptive and geostatistical methods. Results showed that SG generally displayed 10 similar to 120% higher plot-level variations in all variables than GG, and the plot-level variations were 20 similar to 77% higher in NN plots than LN and HN plots in SG but they were comparable in unfertilized and fertilized plots in GG. Relative to NN, LN and HN showed more significant surface trends and spatial structures in SOC and TN in both croplands, and the fertilization effect appeared more pronounced in SG. Spatial patterns in C: N, delta C-13 and delta N-15 were comparable among different fertilization treatments in both croplands. The descending within-plot variations were also identified among variables (SOC>TN>delta N-15>C: N>delta C-13). This study demonstrated that N fertilizations generally reduced the plot-level variance and simultaneously re-established spatial structures of SOC and TN in bioenergy croplands, which little varied with fertilization rate but was more responsive in switchgrass cropland.
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    Effects of nitrogen fertilization and bioenergy crop type on topsoil organic carbon and total Nitrogen contents in middle Tennessee USA
    (PLOS, 2020) Li, Jianwei; Jian, Siyang; Lane, Chad S.; Lu, YueHan; He, Xiaorui; Wang, Gangsheng; Mayes, Melanie A.; Dzantor, Kudjo E.; Hui, Dafeng; Tennessee State University; University of North Carolina; University of North Carolina Wilmington; University of Alabama Tuscaloosa; University of Oklahoma - Norman; United States Department of Energy (DOE); Oak Ridge National Laboratory
    Nitrogen (N) fertilization affects bioenergy crop growth and productivity and consequently carbon (C) and N contents in soil, it however remains unclear whether N fertilization and crop type individually or interactively influence soil organic carbon (SOC) and total N (TN). In a three-year long fertilization experiment in switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.) croplands in Middle Tennessee USA, soil samples (0-15cm) were collected in plots with no N input (NN), low N input (LN: 84 kg N ha(-1) yr(-1) in urea) and high N input (HN: 168 kg N ha(-1) yr(-1) in urea). Besides SOC and TN, the aboveground plant biomass was also quantified. In addition to a summary of published root morphology data based on a separated mesocosm experiment, the root leachable dissolved organic matter (DOM) of both crops was also measured using archived samples. Results showed no significant interaction of N fertilization and crop type on SOC, TN or plant aboveground biomass (ABG). Relative to NN, HN (not LN) significantly increased SOC and TN in both crops. Though SG showed a 15-68% significantly higher ABG than GG, GG showed a 9.3-12% significantly higher SOC and TN than SG. The positive linear relationships of SOC or TN with ABG were identified for SG. However, GG showed structurally more complex and less readily decomposed root DOM, a larger root volume, total root length and surface area than SG. Collectively, these suggested that intensive N fertilization could increase C and N stocks in bioenergy cropland soils but these effects may be more likely mediated by the aboveground biomass in SG and root chemistry and morphology in GG. Future studies are expected to examine the root characteristics in different bioenergy croplands under the field fertilization experiment.
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    Observations of lightning in relation to transitions in volcanic activity during the 3 June 2018 Fuego Eruption
    (Nature Portfolio, 2020) Schultz, Christopher J.; Andrews, Virginia P.; Genareau, Kimberly D.; Naeger, Aaron R.; National Aeronautics & Space Administration (NASA); University of Alabama Tuscaloosa; University of Alabama Huntsville
    Satellite and ground-based remote sensing are combined to characterize lightning occurrence during the 3 June 2018 Volcan de Fuego eruption in Guatemala. The combination of the space-based Geostationary Lightning Mapper (GLM) and ground-based Earth Networks Total Lightning Network observed two distinct periods of lightning during this eruption totaling 75 unique lightning flash occurrences over five hours (57 in cloud, 18 cloud-to-ground). The first period of lightning coincided with the rapid growth of the ash cloud, while the second maxima occurred near the time of a deadly pyroclastic density current (PDC) and thunderstorm. Ninety-one percent of the lightning during the event was observed by only one of the lightning sensors, thus showing the importance of combining lightning datasets across multiple frequencies to characterize electrical activity in volcanic eruptions. GLM flashes during the event had a median total optical energy and flash length of 16 fJ, and 12 km, respectively. These median GLM flash energies and lengths observed in the volcanic plume are on the lower end of the flash spectrum because flashes observed in surrounding thunderstorms on 3 June had larger median total optical energy values (130 fJ) and longer median flash lengths (20 km). All 18 cloud-to-ground flashes were negative polarity, supportive of net negative charge within the plume. Mechanisms for the generation of the secondary lightning maxima are discussed based on the presence and potential interaction between ash plume, thunderstorm, and PDC transport during this secondary period of observed lightning.
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    Modeling COVID-19 spreading dynamics and unemployment rate evolution in rural and urban counties of Alabama and New York using fractional derivative models
    (Elsevier, 2021) Yu, Xiangnan; Zhang, Yong; Sun, HongGuang; Hohai University; University of Alabama Tuscaloosa
    The COVID-19 pandemic has been affecting the United States (U.S.) since the outbreak documented on 2/29/2020, and understanding its dynamics is critical for pandemic mitigation and economic recovery. This study proposed and applied novel time fractional derivative models (FDMs) to quantify the spatiotemporal dynamics of the COVID-19 pandemic spreading in the states of Alabama and New York, U.S., two states with quite different population compositions, urbanization, and industry structures. Model applications revealed that the pandemic evolving in the two states exhibited an overall similar time-dependent trend with subtle differences in propagation rates. Alabama may have more inter-county communications in rural areas than urban areas, while the opposite may be true for the New York State. Further analysis using the space FDM showed that the COVID-19 pandemic spread in rural/urban areas of the two states by following the tempered stable density distributions with different indexes, while the number of the state's pandemic epicenters affected the pattern of the COVID-19 pandemic spreading in space. Finally, applications of a novel time FDM revealed that the evolution of the economy, represented by the weekly unemployment insurance claims in the two states, exhibited different spreading and recovery rates, most likely due to their different exposures and responses to the pandemic. Therefore, COVID-19 spreading dynamics exhibited strong and subtly different spatiotemporal memories in rural and urban areas in the Alabama and New York States, motivating the application of FDMs.
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    Abundance and morphology of charcoal in sediments provide no evidence of massive slash-and-burn agriculture during the Neolithic Kuahuqiao culture, China
    (PLOS, 2020) Hu, YuanFeng; Zhou, Bin; Lu, YueHan; Zhang, JianPing; Min, SiYu; Dai, MingZhe; Xu, SiYu; Yang, Qing; Zheng, HongBo; Nanjing University; University of Alabama Tuscaloosa; Chinese Academy of Sciences; Institute of Geology & Geophysics, CAS; Yunnan University
    It remains debatable whether slash-and-burn practices were adopted in rice cultivation by the Neolithic Kuahuqiao culture in the Ningshao Plain, one of the birthplaces of rice farming. Here, we established charcoal-based indices to reconstruct the history of fire and vegetation in the Ningshao Plain since the last glacial period. We collected representative modern vegetation and conducted combustion and fragmentation experiments to simulate fire and depositional processes, respectively. Charcoals from modern vegetation show clear morphological differences between herbaceous and woody plants. In particular, the length to width ratios (L/W) of herbaceous charcoals were systematically higher than those of woody charcoals, and the associated end-member values were 4.50 and 1.94, respectively. These values were then applied to sediment cores (KHQ-14/15) collected in proximity to the Kuahuqiao archaeological site. Results show that the amount of combusted herbaceous plants increased sharply after the Holocene, and the most remarkable rise occurred around 8550 yr B.P. This observation may reflect local environment (sedimentary and/or climatic) changes or small-scale early human activities. During the Kuahuqiao cultural period (8250-7450 yr B.P.), the relative abundance of woody charcoals increased, but the overall fire intensity decreased. This finding suggests that the Kuahuqiao farming was restricted to a small geographic area and large-scale slash-and-burn farming activities were not adopted.
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    Microbial community composition across a coastal hydrological system affected by submarine groundwater discharge (SGD)
    (PLOS, 2020) Adyasari, Dini; Hassenrueck, Christiane; Montiel, Daniel; Dimova, Natasha; Leibniz Zentrum fur Marine Tropenforschung (ZMT); University of Alabama Tuscaloosa
    Mobile Bay, the fourth largest estuary in the USA located in the northern Gulf of Mexico, is known for extreme hypoxia in the water column during dry season caused by NH4+-rich and anoxic submarine groundwater discharge (SGD). Nutrient dynamics in the coastal ecosystem point to potentially elevated microbial activities; however, little is known about microbial community composition and their functional roles in this area. In this study, we investigated microbial community composition, distribution, and metabolic prediction along the coastal hydrological compartment of Mobile Bay using 16S rRNA gene sequencing. We collected microbial samples from surface (river and bay water) and subsurface water (groundwater and coastal pore water from two SGD sites with peat and sandy lithology, respectively). Salinity was identified as the primary factor affecting the distribution of microbial communities across surface water samples, while DON and PO(4)(3-)were the major predictor of community shift within subsurface water samples. Higher microbial diversity was found in coastal pore water in comparison to surface water samples.Gammaproteobacteria,Bacteroidia, andOxyphotobacteriadominated the bacterial community. Among the archaea, methanogens were prevalent in the peat-dominated SGD site, while the sandy SGD site was characterized by a higher proportion of ammonia-oxidizing archaea.Cyanobium PCC-6307and unclassifiedThermodesulfovibrioniawere identified as dominant taxa strongly associated with trends in environmental parameters in surface and subsurface samples, respectively. Microbial communities found in the groundwater and peat layer consisted of taxa known for denitrification and dissimilatory nitrate reduction to ammonium (DNRA). This finding suggested that microbial communities might also play a significant role in mediating nitrogen transformation in the SGD flow path and in affecting the chemical composition of SGD discharging to the water column. Given the ecological importance of microorganisms, further studies at higher taxonomic and functional resolution are needed to accurately predict chemical biotransformation processes along the coastal hydrological continuum, which influence water quality and environmental condition in Mobile Bay.
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    Voluntary consensus based geospatial data standards for the global illegal trade in wild fauna and flora
    (Nature Portfolio, 2022) Gore, Meredith L.; Schwartz, Lee R.; Amponsah-Mensah, Kofi; Barbee, Emily; Canney, Susan; Carbo-Penche, Maria; Cronin, Drew; Hilend, Rowan; Laituri, Melinda; Luna, David; Maina, Faith; Mey, Christian; Mumford, Kathleena; Mugo, Robinson; Nduguta, Redempta; Nyce, Christopher; McEvoy, John; McShea, William; Mandimbihasina, Angelo; Salafsky, Nick; Smetana, David; Tait, Alexander; Wittig, Tim; Wright, Dawn; Naess, Leah Wanambwa; University of Maryland College Park; University of Ghana; University of Alabama Tuscaloosa; University of Oxford; Michigan State University; Colorado State University; Smithsonian Institution; Smithsonian National Zoological Park & Conservation Biology Institute; National Geographic Society; African Union (AU)
    We have more data about wildlife trafficking than ever before, but it remains underutilized for decision-making. Central to effective wildlife trafficking interventions is collection, aggregation, and analysis of data across a range of source, transit, and destination geographies. Many data are geospatial, but these data cannot be effectively accessed or aggregated without appropriate geospatial data standards. Our goal was to create geospatial data standards to help advance efforts to combat wildlife trafficking. We achieved our goal using voluntary, participatory, and engagement-based workshops with diverse and multisectoral stakeholders, online portals, and electronic communication with more than 100 participants on three continents. The standards support data-to-decision efforts in the field, for example indictments of key figures within wildlife trafficking, and disruption of their networks. Geospatial data standards help enable broader utilization of wildlife trafficking data across disciplines and sectors, accelerate aggregation and analysis of data across space and time, advance evidence-based decision making, and reduce wildlife trafficking.
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    Mercury's Northern Rise Core-Field Magnetic Anomaly
    (American Geophysical Union, 2021) Plattner, Alain M.; Johnson, Catherine L.; University of Alabama Tuscaloosa; University of British Columbia
    We use magnetic field data collected in orbit around Mercury by the MErcury Surface, Space ENvironment, GEochemistry and Ranging satellite, to detect a regional magnetic field anomaly that is spatially associated with Mercury's Northern Rise topographic signature. Regional spectral analysis indicates a source depth at or below the core-mantle boundary, and hence the anomaly is of core, not crustal, origin. This observation supports previous studies linking the Northern Rise to a deep-seated gravity anomaly and reveals connections among core, mantle, and crustal dynamics, likely enabled by Mercury's thin mantle.
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    A multi-proxy assessment of the impact of environmental instability on Late Holocene (4500-3800 BP) Native American villages of the Georgia coast
    (PLOS, 2022) Garland, Carey J.; Thompson, Victor D.; Sanger, Matthew C.; Smith, Karen Y.; Andrus, Fred T.; Lawres, Nathan R.; Napora, Katharine G.; Colaninno, Carol E.; Compton, J. Matthew; Jones, Sharyn; Hadden, Carla S.; Cherkinsky, Alexander; Maddox, Thomas; Deng, Yi-Ting; Lulewicz, Isabelle H.; Parsons, Lindsey; University of Georgia; University of Alabama Tuscaloosa; University of West Georgia; University of Kentucky; Southern Illinois University Edwardsville; Georgia Southern University; Northern Kentucky University
    Circular shell rings along the South Atlantic Coast of North America are the remnants of some of the earliest villages that emerged during the Late Archaic (5000-3000 BP). Many of these villages, however, were abandoned during the Terminal Late Archaic (ca 3800-3000 BP). We combine Bayesian chronological modeling with mollusk shell geochemistry and oyster paleobiology to understand the nature and timing of environmental change associated with the emergence and abandonment of circular shell ring villages on Sapelo Island, Georgia. Our Bayesian models indicate that Native Americans occupied the three Sapelo shell rings at varying times with some generational overlap. By the end of the complex's occupation, only Ring III was occupied before abandonment ca. 3845 BP. Ring III also consists of statistically smaller oysters harvested from less saline estuaries compared to earlier occupations. Integrating shell biochemical and paleobiological data with recent tree ring analyses shows a clear pattern of environmental fluctuations throughout the period in which the rings were occupied. We argue that as the environment became unstable around 4300 BP, aggregation at villages provided a way to effectively manage fisheries that are highly sensitive to environmental change. However, with the eventual collapse of oyster fisheries and subsequent rebound in environmental conditions ca. post-3800 BP, people dispersed from shell rings, and shifted to non-marine subsistence economies and other types of settlements. This study provides the most comprehensive evidence for correlations between large-scale environmental change and societal transformations on the Georgia coast during the Late Archaic period.
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    Holocene melting of the West Antarctic Ice Sheet driven by tropical Pacific warming
    (Nature Portfolio, 2022) Sproson, Adam D.; Yokoyama, Yusuke; Miyairi, Yosuke; Aze, Takahiro; Totten, Rebecca L.; University of Tokyo; Japan Agency for Marine-Earth Science & Technology (JAMSTEC); Australian National University; University of Alabama Tuscaloosa
    Ice loss from the Amundsen Sea sector of West Antarctica is rapidly accelerating. Here, the authors reveal that this region also underwent thinning and retreat from 9 to 6 thousand years ago, due to atmospheric connections with a warming tropical Pacific. The primary Antarctic contribution to modern sea-level rise is glacial discharge from the Amundsen Sea sector of the West Antarctic Ice Sheet. The main processes responsible for ice mass loss include: (1) ocean-driven melting of ice shelves by upwelling of warm water onto the continental shelf; and (2) atmospheric-driven surface melting of glaciers along the Antarctic coast. Understanding the relative influence of these processes on glacial stability is imperative to predicting sea-level rise. Employing a beryllium isotope-based reconstruction of ice-shelf history, we demonstrate that glaciers flowing into the Amundsen Sea Embayment underwent melting and retreat between 9 and 6 thousand years ago. Despite warm ocean water influence, this melting event was mainly forced by atmospheric circulation changes over continental West Antarctica, linked via a Rossby wave train to tropical Pacific Ocean warming. This millennial-scale glacial history may be used to validate contemporary ice-sheet models and improve sea-level projections.
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    Crystal orientation fabric anisotropy causes directional hardening of the Northeast Greenland Ice Stream
    (Nature Portfolio, 2023) Gerber, Tamara Annina; Lilien, David A.; Rathmann, Nicholas Mossor; Franke, Steven; Young, Tun Jan; Valero-Delgado, Fernando; Ershadi, M. Reza; Drews, Reinhard; Zeising, Ole; Humbert, Angelika; Stoll, Nicolas; Weikusat, Ilka; Grinsted, Aslak; Hvidberg, Christine Schott; Jansen, Daniela; Miller, Heinrich; Helm, Veit; Steinhage, Daniel; O'Neill, Charles; Paden, John; Gogineni, Siva Prasad; Dahl-Jensen, Dorthe; Eisen, Olaf; University of Copenhagen; Niels Bohr Institute; University of Manitoba; Helmholtz Association; Alfred Wegener Institute, Helmholtz Centre for Polar & Marine Research; University of Cambridge; University of St Andrews; Eberhard Karls University of Tubingen; University of Bremen; University of Kansas; University of Alabama Tuscaloosa
    This study uses radio-echo sounding measurements, ice-core data and models to map the spatial variation in ice-crystal orientation in the northeast Greenland Ice Stream and shows how it potentially affects the ice-flow dynamics in this region. The dynamic mass loss of ice sheets constitutes one of the biggest uncertainties in projections of ice-sheet evolution. One central, understudied aspect of ice flow is how the bulk orientation of the crystal orientation fabric translates to the mechanical anisotropy of ice. Here we show the spatial distribution of the depth-averaged horizontal anisotropy and corresponding directional flow-enhancement factors covering a large area of the Northeast Greenland Ice Stream onset. Our results are based on airborne and ground-based radar surveys, ice-core observations, and numerical ice-flow modelling. They show a strong spatial variability of the horizontal anisotropy and a rapid crystal reorganisation on the order of hundreds of years coinciding with the ice-stream geometry. Compared to isotropic ice, parts of the ice stream are found to be more than one order of magnitude harder for along-flow extension/compression while the shear margins are potentially softened by a factor of two for horizontal-shear deformation.
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    Frost for the trees: Did climate increase erosion in unglaciated landscapes during the late Pleistocene?
    (American Association for the Advancement of Science, 2015) Marshall, Jill A.; Roering, Joshua J.; Bartlein, Patrick J.; Gavin, Daniel G.; Granger, Darryl E.; Rempel, Alan W.; Praskievicz, Sarah J.; Hales, Tristram C.; University of Oregon; University of California Berkeley; Purdue University West Lafayette Campus; Purdue University; University of Alabama Tuscaloosa; Cardiff University
    Understanding climatic influences on the rates and mechanisms of landscape erosion is an unresolved problem in Earth science that is important for quantifying soil formation rates, sediment and solute fluxes to oceans, and atmospheric CO2 regulation by silicate weathering. Glaciated landscapes record the erosional legacy of glacial intervals throughmoraine deposits and U-shaped valleys, whereas more widespread unglaciated hillslopes and rivers lack obvious climate signatures, hampering mechanistic theory for how climate sets fluxes and form. Today, periglacial processes in high-elevation settings promote vigorous bedrock-to-regolith conversion and regolith transport, but the extent to which frost processes shaped vast swaths of low-tomoderate-elevation terrain during past climate regimes is not well established. By combining a mechanistic frost weathering model with a regional Last Glacial Maximum (LGM) climate reconstruction derived from a paleo-Earth System Model, paleovegetation data, and a paleoerosion archive, we propose that frost-driven sediment production was pervasive during the LGM in our unglaciated Pacific Northwest study site, coincident with a 2.5 times increase in erosion relative to modern rates. Our findings provide a novel framework to quantify how climate modulates sediment production over glacial-interglacial cycles in midlatitude unglaciated terrain.
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    Size limits for rounding of volcanic ash particles heated by lightning
    (American Geophysical Union, 2017) Wadsworth, Fabian B.; Vasseur, Jeremie; Llewellin, Edward W.; Genareau, Kimberly; Cimarelli, Corrado; Dingwell, Donald B.; University of Munich; Durham University; University of Alabama Tuscaloosa
    Volcanic ash particles can be remelted by the high temperatures induced in volcanic lightning discharges. The molten particles can round under surface tension then quench to produce glass spheres. Melting and rounding timescales for volcanic materials are strongly dependent on heating duration and peak temperature and are shorter for small particles than for large particles. Therefore, the size distribution of glass spheres recovered from ash deposits potentially record the short duration, high-temperature conditions of volcanic lightning discharges, which are hard to measure directly. We use a 1-D numerical solution to the heat equation to determine the timescales of heating and cooling of volcanic particles during and after rapid heating and compare these with the capillary timescale for rounding an angular particle. We define dimensionless parameterscapillary, Fourier, Stark, Biot, and Peclet numbersto characterize the competition between heat transfer within the particle, heat transfer at the particle rim, and capillary motion, for particles of different sizes. We apply this framework to the lightning case and constrain a maximum size for ash particles susceptible to surface tension-driven rounding, as a function of lightning temperature and duration, and ash properties. The size limit agrees well with maximum sizes of glass spheres found in volcanic ash that has been subjected to lightning or experimental discharges, demonstrating that the approach that we develop can be used to obtain a first-order estimate of lightning conditions in volcanic plumes.