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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
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    American Association for the Advancement of Science (AAAS)
    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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  • 7
    Publication Date: 2017-06-11
    Description: Surface melt from the Greenland Ice Sheet (GrIS) collects particulate organic carbon (POC) as it drains into subglacial environments, and transports it downstream where it serves as a microbial substrate. We hypothesized that older POC is entrained by meltwaters as the subglacial drainage network expands upglacier over the summer. To test this, POC samples were collected from a meltwater river exiting the GrIS over an ablation season and 14 C-dated. Resulting values were compared with meltwater hydrochemistry and satellite observations of the catchment area. We found POC ages increased from ~5,000 to ~9,000 yr BP until peak discharge and catchment size. Afterwards, significant fluctuations in POC age were observed, interpreted to result from periods of high and low subglacial hydrological pressure, and sediment supply and subsequent exhaustion. These observations suggest a seasonal progression in the source of POC exported from the GrIS, and provide evidence for a seasonally-evolving subglacial drainage system.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    Publication Date: 2018-02-21
    Description: The freshwater budget of the Arctic and sub-polar North Atlantic Oceans has been changing due, primarily, to increased river runoff, declining sea ice and enhanced melting of Arctic land ice. Since the mid 1990s this latter component has experienced a pronounced increase. We use a combination of satellite observations of glacier flow speed and regional climate modeling to reconstruct the land ice freshwater flux from the Greenland ice sheet and Arctic glaciers and ice caps for the period 1958-2016. The cumulative freshwater flux anomaly exceeded 6300±316 km 3 by 2016. This is roughly twice the estimate of a previous analysis that did not include glaciers and ice caps outside of Greenland and which extended only to 2010. From 2010 onward, the total freshwater flux is about 1300 km 3 /yr, equivalent to 0.04 Sv, which is roughly 40% of the estimated total runoff to the Arctic for the same time period. Not all of this flux will reach areas of deep convection or Arctic and Sub-Arctic seas. We note, however, that the largest freshwater flux anomalies, grouped by ocean basin, are located in Baffin Bay and Davis Strait. The land ice freshwater flux displays a strong seasonal cycle with summer time values typically around five times larger than the annual mean. This will be important for understanding the impact of these fluxes on fjord circulation, stratification, and the biogeochemistry of, and nutrient delivery to, coastal waters.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
    Publication Date: 2016-10-01
    Description: Basal sliding is a main control on glacier flow primarily driven by water pressure at the glacier base. The ongoing increase in surface melting of the Greenland Ice Sheet warrants an examination of its impact on basal water pressure and in turn on basal sliding. Here, we examine the case of Russell Glacier, in West Greenland, where an extensive set of observations has been collected. These observations suggest that the recent increase in melt has had an equivocal impact on the annual velocity, with stable flow on the lower part of the drainage basin, but accelerated flow above the Equilibrium Line Altitude (ELA). These distinct behaviors have been attributed to different evolutions of the subglacial draining system during and after the melt season. Here, we use a high-resolution subglacial hydrological model forced by reconstructed surface runoff for the period 2008 to 2012 to investigate the cause of these distinct behaviors. We find that the increase in meltwater production at low elevation yields a more efficient drainage system compatible with the observed stagnation of the mean annual flow below the ELA. At higher elevation, the model indicates that the drainage system is mostly inefficient and is therefore strongly sensitive to an increase in meltwater availability, which is consistent with the observed increase in ice velocity.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
    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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