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  • 1
    ISSN: 0303-7207
    Keywords: Brown adipose tissue ; Ciglitazone ; Energy balance ; Insulin ; Thermogenesis
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2019-01-10
    Description: Ice sheets are currently ignored in global methane budgets1,2. Although ice sheets have been proposed to contain large reserves of methane that may contribute to a rise in atmospheric methane concentration if released during periods of rapid ice retreat3,4, no data exist on the current methane footprint of ice sheets. Here we find that subglacially produced methane is rapidly driven to the ice margin by the efficient drainage system of a subglacial catchment of the Greenland ice sheet. We report the continuous export of methane-supersaturated waters (CH4(aq)) from the ice-sheet bed during the melt season. Pulses of high CH4(aq) concentration coincide with supraglacially forced subglacial flushing events, confirming a subglacial source and highlighting the influence of melt on methane export. Sustained methane fluxes over the melt season are indicative of subglacial methane reserves that exceed methane export, with an estimated 6.3 tonnes (discharge-weighted mean; range from 2.4 to 11 tonnes) of CH4(aq) transported laterally from the ice-sheet bed. Stable-isotope analyses reveal a microbial origin for methane, probably from a mixture of inorganic and ancient organic carbon buried beneath the ice. We show that subglacial hydrology is crucial for controlling methane fluxes from the ice sheet, with efficient drainage limiting the extent of methane oxidation5 to about 17 per cent of methane exported. Atmospheric evasion is the main methane sink once runoff reaches the ice margin, with estimated diffusive fluxes (4.4 to 28 millimoles of CH4 per square metre per day) rivalling that of major world rivers6. Overall, our results indicate that ice sheets overlie extensive, biologically active methanogenic wetlands and that high rates of methane export to the atmosphere can occur via efficient subglacial drainage pathways. Our findings suggest that such environments have been previously underappreciated and should be considered in Earth’s methane budget.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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  • 3
    ISSN: 1573-4935
    Keywords: CGRP ; IAPP/amylin ; glucose removal ; insulin release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The effect of intravenous infusion of islet amyloid polypeptide (IAPP/amylin) and calcitonin gene-related peptide (CGRP) on blood glucose and plasma insulin in the basal and glucose-stimulated state was investigated in the anaesthetized rat. Both peptides had no effect on basal blood glucose or plasma insulin but following an intravenous bolus of glucose, CGRP-treated rats were hyperglycaemic and hyperinsulinaemic compared with control animals which were similar to IAPP-treated rats. IAPP had no effect on glucose-stimulated islet insulin secretion. These results suggest that CGRP, but not IAPP, alters glucose removalin vivo.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rotary forging has been used to produce high-density bonded magnets from rapidly quenched Nd-Fe-B based ribbons [MQP-D, of nominal composition 28%Nd-56%Fe-15%Co-1%B (wt %)]. Polytetrafluoroethylene (PTFE), when used as an additive (5%–15% by volume) has been found to act as an effective binder and greatly enhances the forgeability of the MQI, allowing higher forging pressures to be used. Densities of up to 98% of the fully dense composite have been achieved. The forging process can be undertaken in air at room temperature. Magnetically, the compacts are comparable to conventional epoxy resin bonded MQI, with energy products of up to 84 kJ/m3. Equivalent volume fractions of MQI (∼83.5 vol %) have been achieved in the compacts with increased PTFE content due to the displacement of pores by the PTFE. The effect of PTFE content on the mechanical strength of the compacts has been assessed and it has been found that strength increases with increasing PTFE content, consistent with the reduction in porosity.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 2017-04-20
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Earth and Planetary Science Letters 462 (2017): 180-188, doi:10.1016/j.epsl.2016.12.039.
    Description: Water flow beneath the Greenland Ice Sheet (GrIS) has been shown to include slow-inefficient (distributed) and fast-efficient (channelized) drainage systems, in response to meltwater delivery to the bed via both moulins and surface lake drainage. This partitioning between channelized and distributed drainage systems is difficult to quantify yet it plays an important role in bulk meltwater chemistry and glacial velocity, and thus subglacial erosion. Radon-222, which is continuously produced via the decay of 226Ra, accumulates in meltwater that has interacted with rock and sediment. Hence, elevated concentrations of 222Rn should be indicative of meltwater that has flowed through a distributed drainage system network. In the spring and summer of 2011 and 2012, we made hourly 222Rn measurements in the proglacial river of a large outlet glacier of the GrIS (Leverett Glacier, SW Greenland). Radon-222 activities were highest in the early melt season (10–15 dpm L−1), decreasing by a factor of 2–5 (3–5 dpm L−1) following the onset of widespread surface melt. Using a 222Rn mass balance model, we estimate that, on average, greater than 90% of the river 222Rn was sourced from distributed system meltwater. The distributed system 222Rn flux varied on diurnal, weekly, and seasonal time scales with highest fluxes generally occurring on the falling limb of the hydrograph and during expansion of the channelized drainage system. Using laboratory based estimates of distributed system 222Rn, the distributed system water flux generally ranged between 1–5% of the total proglacial river discharge for both seasons. This study provides a promising new method for hydrograph separation in glacial watersheds and for estimating the timing and magnitude of distributed system fluxes expelled at ice sheet margins.
    Description: U.S. National Science Foundation Arctic Natural Sciences Program (ANS-1256669); Woods Hole Oceanographic Institution Arctic Research Initiative, Ocean Ventures Fund, and Ocean Climate Change Institute; United Kingdom Natural Environment Research Council studentship (NE/152830X/1); the Carnegie Trust, Edinburgh University Development Trust.
    Keywords: Radon ; Greenland ; Glacier ; Proglacial river ; Meltwater
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
    Publication Date: 2019-08-29
    Description: The cumulative Greenland freshwater flux anomaly has exceeded 5,000 km3 since the 1990s. The volume of this surplus freshwater is expected to cause substantial freshening in the North Atlantic. Analysis of hydrographic observations in the subpolar seas reveals freshening signals in the 2010s. The sources of this freshening are yet to be determined. In this study, the relationship between the surplus Greenland freshwater flux and this freshening is tested by analyzing the propagation of the Greenland freshwater anomaly and its impact on salinity in the subpolar North Atlantic based on observational data and numerical experiments with and without the Greenland runoff. A passive tracer is continuously released during the simulations at freshwater sources along the coast of Greenland to track the Greenland freshwater anomaly. Tracer budget analysis shows that 44% of the volume of the Greenland freshwater anomaly is retained in the subpolar North Atlantic by the end of the simulation. This volume is sufficient to cause strong freshening in the subpolar seas if it stays in the upper 50–100 m. However, in the model the anomaly is mixed down to several hundred meters of the water column resulting in smaller magnitudes of freshening compared to the observations. Therefore, the simulations suggest that the accelerated Greenland melting would not be sufficient to cause the observed freshening in the subpolar seas and other sources of freshwater have contributed to the freshening. Impacts on salinity in the subpolar seas of the freshwater transport through Fram Strait and precipitation are discussed.
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Dukhovskoy, D. S., Yashayaev, I., Proshutinsky, A., Bamber, J. L., Bashmachnikov, I. L., Chassignet, E. P., Lee, C. M., & Tedstone, A. J. Role of Greenland freshwater anomaly in the recent freshening of the subpolar North Atlantic. Journal of Geophysical Research-Oceans, 124(5), (2019): 3333-3360, doi:10.1029/2018JC014686.
    Keywords: Greenland ice sheet melting ; freshwater anomaly ; subpolar North Atlantic ; subpolar gyre ; passive tracer numerical experiment ; freshwater budget
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 7
    Publication Date: 2017-01-26
    Description: Ice sheets as a missing source of silica to the polar oceans Nature Communications, Published online: 25 January 2017; doi:10.1038/ncomms14198 Glacial runoff often has relatively low dissolved silica concentrations and therefore ice sheets have been thought insignificant in the global silicon cycle. Here, the authors show that ice sheets likely play an important role in the production and export of dissolved and dissolvable amorphous silica downstream.
    Electronic ISSN: 2041-1723
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 8
    Publication Date: 2017-05-19
    Description: Nature Geoscience 10, 360 (2017). doi:10.1038/ngeo2920 Authors: Michaela Musilova, Martyn Tranter, Jemma Wadham, Jon Telling, Andrew Tedstone & Alexandre M. Anesio
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 9
    Publication Date: 2017-05-03
    Description: Nature Geoscience 10, 360 (2017). doi:10.1038/ngeo2920 Authors: Michaela Musilova, Martyn Tranter, Jemma Wadham, Jon Telling, Andrew Tedstone & Alexandre M. Anesio
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 10
    Publication Date: 2017-06-29
    Description: The Greenland Ice Sheet (GrIS) has been losing mass at an accelerating rate since the mid-1990s. This has been due to both increased ice discharge into the ocean and melting at the surface, with the latter being the dominant contribution. This change in state has been attributed to rising temperatures and a decrease in surface albedo. We show, using satellite data and climate model output, that the abrupt reduction in surface mass balance since about 1995 can be attributed largely to a coincident trend of decreasing summer cloud cover enhancing the melt-albedo feedback. Satellite observations show that, from 1995 to 2009, summer cloud cover decreased by 0.9 ± 0.3% per year. Model output indicates that the GrIS summer melt increases by 27 ± 13 gigatons (Gt) per percent reduction in summer cloud cover, principally because of the impact of increased shortwave radiation over the low albedo ablation zone. The observed reduction in cloud cover is strongly correlated with a state shift in the North Atlantic Oscillation promoting anticyclonic conditions in summer and suggests that the enhanced surface mass loss from the GrIS is driven by synoptic-scale changes in Arctic-wide atmospheric circulation.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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