Borehole-Based Characterization of Deep Mixed-Mode Crevasses at a Greenlandic Outlet Glacier

Funder: Aberystwyth University Capital Equipment FundAbstract: Optical televiewer borehole logging within a crevassed region of fast‐moving Store Glacier, Greenland, revealed the presence of 35 high‐angle planes that cut across the background primary stratification. These planes were composed of a bubble‐free layer of refrozen ice, most of which hosted thin laminae of bubble‐rich “last frozen” ice, consistent with the planes being the traces of former open crevasses. Several such last‐frozen laminae were observed in four traces, suggesting multiple episodes of crevasse reactivation. The frequency of crevasse traces generally decreased with depth, with the deepest detectable trace being 265 m below the surface. This is consistent with the extent of the warmer‐than‐modeled englacial ice layer in the area, which extends from the surface to a depth of ∼400 m. Crevasse trace orientation was strongly clustered around a dip of 63° and a strike that was offset by 71° from orthogonal to the local direction of principal extending strain. The traces’ antecedent crevasses were therefore interpreted to have originated upglacier, probably ∼8 km distant involving mixed‐mode (I and III) formation. We conclude that deep crevassing is pervasive across Store Glacier, and therefore also at all dynamically similar outlet glaciers. Once healed, their traces represent planes of weakness subject to reactivation during subsequent advection through the glacier. Given their depth, it is highly likely that such traces—particularly those formed downglacier—survive surface ablation to reach the glacier terminus, where they may represent foci for fracture and iceberg calving

Polythermal structure of a Himalayan debris-covered glacier revealed by borehole thermometry

Runoff from high-elevation debris-covered glaciers represents a crucial water supply for millions of people in the Hindu Kush-Himalaya region, where peak water has already passed in places. Knowledge of glacier thermal regime is essential for predicting dynamic and geometric responses to mass balance change and determining subsurface drainage pathways, which ultimately influence proglacial discharge and hence downstream water availability. Yet, deep internal ice temperatures of these glaciers are unknown, making projections of their future response to climate change highly uncertain. Here, we show that the lower part of the ablation area of Khumbu Glacier, a high-elevation debris-covered glacier in Nepal, may contain ~56% temperate ice, with much of the colder shallow ice near to the melting-point temperature (within 0.8 °C). From boreholes drilled in the glacier’s ablation area, we measured a minimum ice temperature of −3.3 °C, and even the coldest ice we measured was 2 °C warmer than the mean annual air temperature. Our results indicate that high-elevation Himalayan glaciers are vulnerable to even minor atmospheric warming

Rapid development and persistence of efficient subglacial drainage under 900 m-thick ice in Greenland

Intensive study of the Greenland Ice Sheet's (GrIS) subglacial drainage has been motivated by its importance for ice dynamics and for nutrient/sediment export to coastal ecosystems. This has revealed consistent seasonal development of efficient subglacial drainage in the lower ablation area. While some hydrological models show qualitative agreement with field data, conflicting evidence (both field- and model-based) maintains uncertainty in the extent and rate of efficient drainage development under thick (∼1 km) ice. Here, we present the first simultaneous time series of directly-observed subglacial drainage evolution, supraglacial hydrology and ice dynamics over 11 weeks in a large GrIS catchment. We demonstrate development of a fast/efficient subglacial drainage system extending from the margin to beneath ice >900 m thick, which then persisted with little response to highly variable moulin inputs including extreme melt events and extended periods (2 weeks) of low melt input. This efficient system evolved within ∼3 weeks at a moulin initiated when a fracture intersected a supraglacial river (rather than hydrofracture and lake drainage). Ice flow response to surface melt inputs at this site follows a pattern commonly observed in the lower GrIS ablation area, and by assuming a strong relationship between ice dynamics and subglacial hydrology, we infer that efficient subglacial drainage evolution is widespread under 900 m-thick ice in west Greenland. This time series of tracer transit characteristics through a developing and then persistent efficient drainage system provides a unique data set with which to validate and constrain existing numerical drainage system models, extending their capability for simulating drainage system evolution under current and future conditionspublishedVersio

Thermodynamics of a fast-moving Greenlandic outlet glacier revealed by fiber-optic distributed temperature sensing

Funding: This research was funded by the European Research Council as part of the RESPONDER project under the European Union’s Horizon 2020 research and innovation program (grant 683043). R.L. and T.R.C. were supported by Natural Environment Research Council Doctoral Training Partnership studentships (grant NE/ L002507/1). B.H. was supported by a HEFCW/Aberystwyth University Capital Equipment Grant.Measurements of ice temperature provide crucial constraints on ice viscosity and the thermodynamic processes occurring within a glacier. However, such measurements are presently limited by a small number of relatively coarse-spatial-resolution borehole records, especially for ice sheets. Here, we advance our understanding of glacier thermodynamics with an exceptionally high-vertical-resolution (~0.65 m), distributed-fiber-optic temperature-sensing profile from a 1043-m borehole drilled to the base of Sermeq Kujalleq (Store Glacier), Greenland. We report substantial but isolated strain heating within interglacial-phase ice at 208 to 242 m depth together with strongly heterogeneous ice deformation in glacial-phase ice below 889 m. We also observe a high-strain interface between glacial- and interglacial-phase ice and a 73-m-thick temperate basal layer, interpreted as locally formed and important for the glacier's fast motion. These findings demonstrate notable spatial heterogeneity, both vertically and at the catchment scale, in the conditions facilitating the fast motion of marine-terminating glaciers in Greenland.Publisher PDFPeer reviewe

Derivation of High Spatial Resolution Albedo from UAV Digital Imagery:Application over the Greenland Ice Sheet

Measurements of albedo are a prerequisite for modeling surface melt across the Earth's cryosphere, yet available satellite products are limited in spatial and/or temporal resolution. Here, we present a practical methodology to obtain centimeter resolution albedo products with accuracies of ?5% using consumer-grade digital camera and unmanned aerial vehicle (UAV) technologies. Our method comprises a workflow for processing, correcting and calibrating raw digital images using a white reference target, and upward and downward shortwave radiation measurements from broadband silicon pyranometers. We demonstrate the method with a set of UAV sorties over the western, K-sector of the Greenland Ice Sheet. The resulting albedo product, UAV10A1, covers 280 km2, at a resolution of 20 cm per pixel and has a root-mean-square difference of 3.7% compared to MOD10A1 and 4.9% compared to ground-based broadband pyranometer measurements. By continuously measuring downward solar irradiance, the technique overcomes previous limitations due to variable illumination conditions during and between surveys over glaciated terrain. The current miniaturization of multispectral sensors and incorporation of upward facing radiation sensors on UAV packages means that this technique could become increasingly common in field studies and used for a wide range of applications. These include the mapping of debris, dust, cryoconite and bioalbedo, and directly constraining surface energy balance models.publishersversionPeer reviewe

Hospital trajectories and early predictors of clinical outcomes differ between SARS-CoV-2 and influenza pneumonia

BACKGROUND: A comparison of pneumonias due to SARS-CoV-2 and influenza, in terms of clinical course and predictors of outcomes, might inform prognosis and resource management. We aimed to compare clinical course and outcome predictors in SARS-CoV-2 and influenza pneumonia using multi-state modelling and supervised machine learning on clinical data among hospitalised patients. METHODS: This multicenter retrospective cohort study of patients hospitalised with SARS-CoV-2 (March-December 2020) or influenza (Jan 2015-March 2020) pneumonia had the composite of hospital mortality and hospice discharge as the primary outcome. Multi-state models compared differences in oxygenation/ventilatory utilisation between pneumonias longitudinally throughout hospitalisation. Differences in predictors of outcome were modelled using supervised machine learning classifiers. FINDINGS: Among 2,529 hospitalisations with SARS-CoV-2 and 2,256 with influenza pneumonia, the primary outcome occurred in 21% and 9%, respectively. Multi-state models differentiated oxygen requirement progression between viruses, with SARS-CoV-2 manifesting rapidly-escalating early hypoxemia. Highly contributory classifier variables for the primary outcome differed substantially between viruses. INTERPRETATION: SARS-CoV-2 and influenza pneumonia differ in presentation, hospital course, and outcome predictors. These pathogen-specific differential responses in viral pneumonias suggest distinct management approaches should be investigated. FUNDING: This project was supported by NIH/NCATS UL1 TR002345, NIH/NCATS KL2 TR002346 (PGL), the Doris Duke Charitable Foundation grant 2015215 (PGL), NIH/NHLBI R35 HL140026 (CSC), and a Big Ideas Award from the BJC HealthCare and Washington University School of Medicine Healthcare Innovation Lab and NIH/NIGMS R35 GM142992 (PS)

Who Invited You? The Complex Story Of Aquatic Invasive Species

Invasive species represent a global threat to ecosystems, human health, and the economy. A basic knowledge of invasive species biology is crucial to understand current and future impacts and implications. The purpose of this book is to provide a broad background on invasive species, and also details on specific examples through case studies. The students in the course Aquatic Invasive Species (MAR 442) at the University of New England in Biddeford, Maine, have researched and reviewed scientific literature to educate readers about these issues. The class, comprised of fifteen junior and senior Marine Science, Marine Affairs, Animal Behavior, and Environmental Sciences students, selected the different topics, presented the material, wrote the chapters, and assembled the final versions into this book. This book cannot be all inclusive, but we think this book will provide an excellent broad overview of the most important aspects of Invasive Species Biology and might stimulate the reader to dive deeper into the material.https://dune.une.edu/marinesci_studproj/1003/thumbnail.jp