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  • 1
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    Bathymetry data reveal glaciers vulnerable to ice-ocean interaction in Uummannaq and Vaigat glacial fjords, West Greenland. (2016)
    Wiley-Blackwell
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    Publication Date: 2016-03-10
    Description: Marine-terminating glaciers play a critical role in controlling Greenland's ice sheet mass balance. Their frontal margins interact vigorously with the ocean but our understanding of this interaction is limited, in part, by a lack of bathymetry data. Here, we present a multi-beam echo sounding survey of 14 glacial fjords in the Uummannaq and Vaigat fjords, West Greenland, that extends from the continental shelf to the glacier fronts. The data reveal valleys with shallow sills, overdeepenings (〉1,300 m) from glacial erosion, and seafloor depths 100-1,000 m deeper than in existing charts. Where fjords are deep enough, we detect the pervasive presence of warm, salty Atlantic Water (AW) (〉2.5 o C) with high melt potential, but we also find numerous glaciers grounded on shallow (〈200 m) sills, standing in cold (〈1 o C) waters in otherwise deep fjords, i.e. with reduced melt potential. Bathymetric observations extending to the glacier fronts are critical to understand the glacier evolution.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 2
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    Associating ground magnetometer observations with current or voltage generators (2017)
    Wiley-Blackwell
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    Publication Date: 2017-06-24
    Description: A circuit analogy for Magnetosphere-Ionosphere current systems has two extremes for drivers of ionospheric currents: ionospheric electric fields/voltages constant while current/conductivity vary - the “voltage generator” - and current constant while electric field/conductivity vary - the “current generator”. Statistical studies of ground magnetometer observations associated with dayside Transient High Latitude Current Systems (THLCS) driven by similar mechanisms find contradictory results using this paradigm: some studies associate THLCS with voltage generators, others with current generators. We argue most of this contradiction arises from two assumptions used to interpret ground magnetometer observations: (1) measurements made at fixed position relative to the THLCS field-aligned current and (2) negligible auroral precipitation contributions to ionospheric conductivity. We use observations and simulations to illustrate how these two assumptions substantially alter expectations for magnetic perturbations associated with either a current or voltage generator. Our results demonstrate that before interpreting ground magnetometer observations of THLCS in the context of current/voltage generators, the location of a ground magnetometer station relative to the THLCS field-aligned current and the location of any auroral zone conductivity enhancements need to be taken into account.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 3
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    Spectroscopic properties of Tm,Ho:CaYAlO4 single crystal (2014)
    Wiley-Blackwell
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    Publication Date: 2014-06-21
    Description: A Tm,Ho:CaYAlO 4 single crystal was grown using the Czochralski (CZ) method. The absorption spectra, the fluorescence spectrum around 2 μm, the upconversion spectrum and energy-transfer (ET) schemes between Tm 3+ ions and Ho 3+ ions have been studied. The crystal boule was free from cracks, inclusions and scattering centers. The broad FWHM of the 797-nm absorption band (with E // c polarization is 19 nm and with E // a polarization is 18 nm), the large emission bandwidth (about 600 nm) and the intense ET from Tm 3+ ions to Ho 3+ ions make Tm,Ho:CaYAlO 4 a promising media for tunable and ultrashort pulses. Tm,Ho:CaYAlO 4 single crystal was grown using the Czochralski (CZ) method. Absorption spectra, fluorescence spectrum around 2 µm, upconversion spectrum and energy transfer (ET) schemes between Tm 3+ ions and Ho 3+ ions have been studied. The broad FWHM of 797 nm absorption band, large emission bandwidth (about 600 nm) and intense ET from Tm 3+ ions to Ho 3+ ions makes Tm,Ho:CaYAlO 4 a promising media for tunable and ultrashort pulses.
    Print ISSN: 0232-1300
    Electronic ISSN: 1521-4079
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell
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  • 4
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    Rates and radiocarbon content of summer ecosystem respiration in response to long-term deeper snow in the High Arctic of NW Greenland (2014)
    Wiley-Blackwell
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    Publication Date: 2014-05-02
    Description: The amount and timing of snow-cover control the cycling of carbon (C), water and energy in arctic ecosystems. The implications of changing snow-cover for regional C budgets, biogeochemistry, hydrology and albedo due to climate change are rudimentary, especially for the High Arctic. In a polar semi-desert of NW Greenland, we used a ~10-year-old snow manipulation experiment to quantify how deeper snow affects magnitude, seasonality and 14 C content of summer C emissions. We monitored ecosystem respiration (R eco ), soil CO 2 and their 14 C contents over three summers in vegetated and bare areas. Additional snowpack, elevated soil water content (SWC) and temperature throughout the growing-season in vegetated, but not in bare areas. Daily R eco was positively correlated to temperature, but negatively correlated to SWC; consequently we found no effect of increased snow on daily flux. Cumulative summertime R eco was not related to annual snowfall, but to water-year precipitation (winter snow plus summer rain). Experimentally increased snowpack shortened the growing-season length and reduced summertime R eco up to 40%. Soil CO 2 was older under increased snow. However, we found no effect of snow-depth on the R eco age because older C emissions were masked by younger CO 2 produced from the litter layer or plant respiration. In the High Arctic, anticipated changes in precipitation regime associated with warming are a key uncertainty for understanding future C cycling. In polar semi-deserts, water-year precipitation is an important driver of summertime R eco . Permafrost C is vulnerable to changes in snowpack, with a deeper snowpack promoting decomposition of older soil C.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 5
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    Effects of crop-straw biochar on crop growth and soil fertility over a wheat-millet rotation in soils of China (2014)
    Wiley-Blackwell
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    Publication Date: 2014-05-25
    Description: We conducted a pot experiment using a wheat-millet rotation to examine the effects of two successive rice-straw biochar applications on crop growth and soil properties in acidic oxisols and alkaline cambosols from China. Biochar was incorporated into soil at rates of 0, 2.25 or 22.5 Mg/ha at the beginning of each crop season with identical applications of NPK fertilizer. In the oxisols, the largest biochar treatment enhanced soil pH and cation exchange capacity, decreased soil bulk density, improved soil P, K, Ca and Mg availability and enhanced their uptake, and increased wheat and millet yields by 157 and 150% for wheat grain and straw, respectively, and 72.6% for millet straw. In the cambosols, biochar treatment decreased soil bulk density, improved P and K availability, increased N, P and K uptake by crops and increased wheat and millet straw yields by 19.6 and 60.6%, respectively. Total soil organic carbon increased in response to successive biochar applications over the rotation. No difference in water-soluble organic carbon was recorded between biochar-treated and control soils. Converting straw to biochar and treating soils with successive applications may be a viable option for improving soil quality, sequestering carbon and utilizing straw resources in China.
    Print ISSN: 0266-0032
    Electronic ISSN: 1475-2743
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley-Blackwell
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  • 6
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    Erratum to: Spectroscopic properties of Tm,Ho: CaYAlO4 single crystal [Cryst. Res. Technol. 49, 446–451 (2014)] (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2015-03-04
    Description:  We correct fit description from a previous paper [Cryst. Res. Technol. 49, 446–451 (2014)]. The a and c polarization absorption spectra of the crystals were incorrectly reported in our previous paper [Cryst. Res. Technol. 49, 446–451 (2014)] [1]. The rest of the figure and is identical to the published version. We apologize for this oversight and for any confusion that it has caused.
    Print ISSN: 0232-1300
    Electronic ISSN: 1521-4079
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell
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  • 7
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    Effects of seasonal grazing on soil respiration in alpine meadow on the Tibetan plateau (2014)
    Wiley-Blackwell
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    Publication Date: 2014-05-30
    Description: Little research has been conducted on how to balance plant production and soil respiration (Rs) under seasonal grazing patterns in alpine meadows. Our results from 2009 to 2012 showed that warm season grazing (WG) from June to September significantly increased aboveground net primary production compared with no-grazing (NG), except in 2010, and compared with cold season grazing (CG) except in 2012, while there were no significant differences between NG and CG except in 2009. In both WG and CG treatments, grazing increased root biomass at 0–40 cm depth compared with NG, except in 2011. WG and CG only significantly increased seasonal Rs in 2009. Daily Rs was mainly affected by soil temperature, which explained 40–49% of the variation in daily Rs for all grazing treatments. Seasonal Rs from July to September was significantly influenced by soil temperature and root biomass, which explained 55% of the variation in seasonal Rs for all grazing treatments. Therefore, relative to NG, regardless of WG and CG, moderate grazing significantly increased plant production and had little influence on soil respiration in this alpine region.
    Print ISSN: 0266-0032
    Electronic ISSN: 1475-2743
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley-Blackwell
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  • 8
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    Martian Magnetic Storms (2017)
    Wiley-Blackwell
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    Publication Date: 2017-03-02
    Description: The response of Mars to the major space weather events called Interplanetary Coronal Mass Ejections (ICMEs) is of interest for both general planetary solar wind interaction studies and related speculations on their evolutionary consequences-especially with respect to atmosphere escape. Various particle and field signatures of ICMEs have been observed on Phobos-2, Mars Global Surveyor (MGS), Mars Express (MEX), and now MAVEN. Of these, MAVEN's combined instrumentation and orbit geometry is particularly well-suited to characterize both the event drivers and their consequences. However, MAVEN has detected only moderate disturbances at Mars due in large part to the general weakness of the present solar cycle. Nevertheless, the strongest event observed by MAVEN in March 2015 provides an example illustrating how further insights can be gained from available models. Here we first look more closely at what previously run BATS-R-US MHD simulations of the combined MAVEN observations tell us about the March 2015 event consequences. We then use analogous models to infer those same responses, including magnetic field topology changes and ionospheric consequences, to a hypothetical extreme ICME at Mars based on STEREO-A measurements in July 2012. The results suggest how greatly enhanced, yet realistic, solar wind pressure, magnetic field, and convection electric field combine to produce strong magnetospheric coupling with important consequences for upper atmosphere and ionosphere energization.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 9
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    Acclimation of bloom-forming and perennial seaweeds to elevated pCO2 conserved across levels of environmental complexity (2017)
    Wiley-Blackwell
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    Publication Date: 2017-03-28
    Description: Macroalgae contribute approximately 15% of the primary productivity in coastal marine ecosystems, fix up to 27.4 Tg of carbon per year, and provide important structural components for life in coastal waters. Despite this ecological and commercial importance, direct measurements and comparisons of the short-term responses to elevated p CO 2 in seaweeds with different life-history strategies are scarce. Here, we cultured several seaweed species (bloom-forming/non-bloom-forming/perennial/annual) in the laboratory, in tanks in an in-door mesocosm facility, and in coastal mesocosms under p CO 2 levels ranging from 400 μatm to 2000 μatm. We find that, across all scales of the experimental set-up, ephemeral species of the genus Ulva increase their photosynthesis and growth rates in response to elevated p CO 2 the most, whereas longer-lived perennial species show a smaller increase or a decrease. These differences in short-term growth- and photosynthesis rates are likely to give bloom-forming green seaweeds a competitive advantage in mixed communities, and our results thus suggest that coastal seaweed assemblages in eutrophic waters may undergo an initial shift toward communities dominated by bloom-forming, short-lived seaweeds. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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  • 10
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    Introduction to CAUSES: Description of weather and climate models and their near-surface temperature errors in 5-day hindcasts near the Southern Great Plains (2018)
    Wiley-Blackwell
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    Publication Date: 2018-02-17
    Description: We introduce the Clouds Above the United States and Errors at the Surface (CAUSES) project with its aim of better understanding the physical processes leading to warm screen-temperature biases over the American Midwest in many numerical models. In this first of four companion papers, 11 different models, from 9 institutes, perform a series of 5-day hindcasts, each initialised from reanalyses. After describing the common experimental protocol and detailing each model configuration, a gridded temperature data set is derived from observations and used to show that all the models have a warm bias over parts of the Midwest. Additionally, a strong diurnal cycle in the screen-temperature bias is found in most models. In some models the bias is largest around midday, while in others it is largest during the night. At the Department of Energy Atmospheric Radiation Measurement Southern Great Plains (SGP) site, the model biases are shown to extend several kilometers into the atmosphere. Finally, to provide context for the companion papers, in which observations from the SGP site are used to evaluate the different processes contributing to errors there, it is shown that there are numerous locations across the Midwest where the diurnal cycle of the error is highly correlated with the diurnal cycle of the error at SGP. This suggests that conclusions drawn from detailed evaluation of models using instruments located at SGP will be representative of errors that are prevalent over a larger spatial scale.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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