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  • 1
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    Noble gas signatures in Greenland – Tracing glacial meltwater sources (2015)
    Wiley
    Details
    Publication Date: 2015-10-22
    Description: This study represents the first comprehensive noble gas study in glacial meltwater (GMW) from the Greenland Ice Sheet (GrIS). It shows that most samples are in disequilibrium with surface collection conditions. A preliminary Ne and Xe analysis suggests that about half of the samples equilibrated at a temperature of ~0 °C and altitudes between 1000 m and 2000 m, with a few samples pointing to lower equilibration altitudes and temperatures between 2 °C and 5 °C. Two samples suggest an origin as melted ice and complete lack of equilibration with surface conditions. A helium component analysis suggests that this glacial meltwater was isolated from the atmosphere prior to the 1950's, with most samples yielding residence times ≤420 yrs. Most samples represent a mixture between a dominant atmospheric component originating as precipitation and basal meltwater or groundwater which has accumulated crustal 4 He over time.
    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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  • 2
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    An open source Bayesian Monte Carlo isotope mixing model with applications in Earth surface processes (2015)
    Wiley
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    Publication Date: 2015-03-28
    Description: The implementation of isotopic tracers as constraints on source contributions has become increasingly relevant to understanding Earth surface processes. Interpretation of these isotopic tracers has become more accessible with the development of Bayesian Monte Carlo (BMC) mixing models, which allow uncertainty in mixing end-members and provide methodology for systems with multi-component mixing. This study presents an open source multiple isotope BMC mixing model that is applicable to Earth surface environments with sources exhibiting distinct end-member isotopic signatures. Our model is first applied to new δ 18 O and δD measurements from the Athabasca Glacier, which showed expected seasonal melt evolution trends and vigorously assessed the statistical relevance of the resulting fraction estimations. To highlight the broad applicability of our model to a variety of Earth surface environments and relevant isotopic systems we expand our model to two additional case studies: deriving melt sources from δ 18 O, δD and 222 Rn measurements of Greenland Ice Sheet bulk water samples and assessing nutrient sources from ϵ Nd and 87 Sr/ 86 Sr measurements of Hawaiian soil cores. The model produces results for the Greenland Ice Sheet and Hawaiian soil datasets that are consistent with the originally published fractional contribution estimates. The advantage of this method is that it quantifies the error induced by variability in the end-member compositions, unrealized by the models previously applied to the above case studies. Results from all three case studies demonstrate the broad applicability of this statistical BMC isotopic mixing model for estimating source contribution fractions in a variety of Earth surface systems. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Sequential Separation of Uranium, Hafnium and Neodymium from Natural Waters Concentrated by Iron Co-precipitation (2014)
    Wiley
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    Publication Date: 2014-09-16
    Description: A new ion exchange chromatography method is presented for the isolation of high field-strength elements (HFSE) from freshwater and seawater samples that have undergone iron co-precipitation. Large volumes of water can be condensed through the application of iron co-precipitation, but clean separation of elements from the precipitate proves difficult. Our technique is a five-column process designed to separate the HFSE, including rare earth elements such as neodymium and hafnium, before removing the iron and isolating uranium. Subsequent isolation of Nd and Hf was achieved using established ion exchange chromatography methods. The efficacy of our chemistry was verified through measurements of analytical reference materials – both standard solutions and seawater samples – subjected to the chemical separation methods described. Elution results indicate high yields (〉 90%) determined by concentration measurements of a known reference material added to each column. Comparison of isotopic compositions for seawater (U, Nd), and standard solutions (NIST SRM 960, U) with previously published values are identical within uncertainty. Compositions were identical between solutions (Spex CLMS3, Spex PLND2) that underwent different iron co-precipitation procedures. Reference materials (JNdi-1, NIST SRM 960) run on the mass spectrometers for isotopic determinations were in agreement with universally accepted values for these materials and indicate high precision. This article is protected by copyright. All rights reserved.
    Print ISSN: 1639-4488
    Electronic ISSN: 1751-908X
    Topics: Geosciences
    Published by Wiley
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  • 4
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    Spatial and temporal variability of freshwater discharge into the Gulf of Alaska (2015)
    Wiley
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    Publication Date: 2015-01-12
    Description: A study of the freshwater discharge into the Gulf of Alaska (GOA) has been carried out. Using available streamgage data, regression equations were developed for monthly flows. These equations express discharge as a function of basin physical characteristics such as area, mean elevation, and land cover, and of basin meteorological characteristics such as temperature, precipitation, and accumulated water year precipitation. To provide the necessary input meteorological data, temperature and precipitation data for a 40 year hind-cast period were developed on high-spatial-resolution grids using weather station data, PRISM climatologies, and statistical downscaling methods. Runoff predictions from the equations were found to agree well with observations. Once developed, the regression equations were applied to a network of delineated watersheds spanning the entire GOA drainage basin. The region was divided into a northern region, ranging from the Aleutian Chain to the Alaska / Canada border in the southeast panhandle, and a southern region, ranging from there to the Fraser River. The mean annual runoff volume into the northern GOA region was found to be 792±120 km 3 yr – 1 . A water balance using MODIS-based evapotranspiration rates yielded seasonal storage volumes that were consistent with GRACE satellite-based estimates. The GRACE data suggest that an additional 57±11 km 3 yr –1 be added to the runoff from the northern region, due to glacier volume loss (GVL) in recent years. The ease of application of the derived regression equations provides an accessible tool for quantifying mean annual values, seasonal variation, and interannual variability of runoff in any ungaged basin of interest. This article is protected by copyright. All rights reserved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Rapid wastage of Alaska glaciers and their contribution to rising sea level (2002)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2002-07-20
    Description: We have used airborne laser altimetry to estimate volume changes of 67 glaciers in Alaska from the mid-1950s to the mid-1990s. The average rate of thickness change of these glaciers was -0.52 m/year. Extrapolation to all glaciers in Alaska yields an estimated total annual volume change of -52 +/- 15 km3/year (water equivalent), equivalent to a rise in sea level (SLE) of 0.14 +/- 0.04 mm/year. Repeat measurements of 28 glaciers from the mid-1990s to 2000-2001 suggest an increased average rate of thinning, -1.8 m/year. This leads to an extrapolated annual volume loss from Alaska glaciers equal to -96 +/- 35 km3/year, or 0.27 +/- 0.10 mm/year SLE, during the past decade. These recent losses are nearly double the estimated annual loss from the entire Greenland Ice Sheet during the same time period and are much higher than previously published loss estimates for Alaska glaciers. They form the largest glaciological contribution to rising sea level yet measured.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Arendt, Anthony A -- Echelmeyer, Keith A -- Harrison, William D -- Lingle, Craig S -- Valentine, Virginia B -- New York, N.Y. -- Science. 2002 Jul 19;297(5580):382-6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Geophysical Institute, University of Alaska, 903 Koyukuk Drive, Post Office Box 757320, Fairbanks, AK 99775, USA. arendta@gi.alaska.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/12130781" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    Geophysics. Assessing the status of Alaska's glaciers (2011)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2011-05-28
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Arendt, Anthony A -- New York, N.Y. -- Science. 2011 May 27;332(6033):1044-5. doi: 10.1126/science.1204400.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Geophysical Institute, University of Alaska, Fairbanks, Fairbanks, AK 99775, USA. anthony.arendt@gi.alaska.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21617066" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 7
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    A reconciled estimate of glacier contributions to sea level rise: 2003 to 2009 (2013)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2013-05-21
    Description: Glaciers distinct from the Greenland and Antarctic Ice Sheets are losing large amounts of water to the world's oceans. However, estimates of their contribution to sea level rise disagree. We provide a consensus estimate by standardizing existing, and creating new, mass-budget estimates from satellite gravimetry and altimetry and from local glaciological records. In many regions, local measurements are more negative than satellite-based estimates. All regions lost mass during 2003-2009, with the largest losses from Arctic Canada, Alaska, coastal Greenland, the southern Andes, and high-mountain Asia, but there was little loss from glaciers in Antarctica. Over this period, the global mass budget was -259 +/- 28 gigatons per year, equivalent to the combined loss from both ice sheets and accounting for 29 +/- 13% of the observed sea level rise.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gardner, Alex S -- Moholdt, Geir -- Cogley, J Graham -- Wouters, Bert -- Arendt, Anthony A -- Wahr, John -- Berthier, Etienne -- Hock, Regine -- Pfeffer, W Tad -- Kaser, Georg -- Ligtenberg, Stefan R M -- Bolch, Tobias -- Sharp, Martin J -- Hagen, Jon Ove -- van den Broeke, Michiel R -- Paul, Frank -- New York, N.Y. -- Science. 2013 May 17;340(6134):852-7. doi: 10.1126/science.1234532.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Graduate School of Geography, Clark University, Worcester, MA 01610, USA. agardner@clarku.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23687045" target="_blank"〉PubMed〈/a〉
    Keywords: Arctic Regions ; Greenland ; *Ice Cover ; *Seawater
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 8
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    High-resolution modeling of coastal freshwater discharge and glacier mass balance in the Gulf of Alaska watershed (2016)
    Wiley
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    Publication Date: 2016-04-28
    Description: A comprehensive study of the Gulf of Alaska (GOA) drainage basin was carried out to improve understanding of the coastal freshwater discharge (FWD) and glacier volume loss (GVL). Hydrologic processes during the period 1980-2014 were modeled using a suite of physically based, spatially distributed weather, energy-balance snow/ice melt, soil water balance, and runoff routing models at a high resolution (1 km horizontal grid; daily time step). Meteorological forcing was provided by the North American Regional Reanalysis (NARR), Modern Era Retrospective Analysis for Research and Applications (MERRA), and Climate Forecast System Reanalysis (CFSR) datasets. Streamflow and glacier mass balance modeled using MERRA and CFSR compared well with observations in four watersheds used for calibration in the study domain. However, only CFSR produced regional seasonal and long term trends in water balance that compared favorably with independent Gravity Recovery and Climate Experiment (GRACE) and airborne altimetry data. Mean annual runoff using CFSR was 760 km 3 yr −1 , 8% of which was derived from the long-term removal of stored water from glaciers (glacier volume loss). The annual runoff from CFSR was partitioned into 63% snowmelt, 17% glacier ice melt, and 20% rainfall. Glacier runoff, taken as the sum of rainfall, snow and ice melt occurring each season on glacier surfaces, was 38% of the total seasonal runoff, with the remaining runoff sourced from non-glacier surfaces. Our simulations suggests that existing GRACE solutions, previously reported to represent glacier mass balance alone, are actually measuring the full water budget of land and ice surfaces. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Hydrologic Impacts of changes in climate and glacier extent in the Gulf of Alaska watershed (2017)
    Wiley
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    Publication Date: 2017-07-21
    Description: High-resolution regional-scale hydrologic models were used to quantify the response of late 21st century runoff from the Gulf of Alaska (GOA) watershed to changes in regional climate and glacier extent. NCEP Climate Forecast System Reanalysis data were combined with five Coupled Model Intercomparison Project Phase 5 General Circulation Models (GCM) for two representative concentration pathway (RCP) scenarios (4.5 and 8.5) to develop meteorological forcing for the period 2070–2099. A hypsographic model was used to estimate future glacier extent given assumed equilibrium line altitude (ELA) increases of 200 and 400 m. GCM predictions show an increase in annual precipitation of 12% for RCP 4.5 and 21% for RCP 8.5, and an increase in annual temperature of 2.5°C for RCP 4.5 and 4.3°C for RCP 8.5, averaged across the GOA. Scenarios with perturbed climate and glaciers predict annual GOA-wide runoff to increase by 9% for RCP4.5/ELA200 case and 14% for the RCP8.5/ELA400 case. The glacier runoff decreased by 14% for RCP4.5/ELA200 and by 34% for the RCP8.5/ELA400 case. Inter-model variability in annual runoff was found to be approximately twice the variability in precipitation input. Additionally, there are significant changes in runoff partitioning and increases in snowpack runoff are dominated by increases in rain-on-snow events. We present results aggregated across the entire GOA and also for individual watersheds to illustrate the range in hydrologic regime changes, and explore the sensitivities of these results by independently perturbing only climate forcings and only glacier cover.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 10
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    Site of G protein binding to rhodopsin mapped with synthetic peptides from the alpha subunit (1988)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1988-08-12
    Description: The interaction between receptors and guanine nucleotide binding (G) proteins leads to G protein activation and subsequent regulation of effector enzymes. The molecular basis of receptor-G protein interaction has been examined by using the ability of the G protein from rods (transducin) to cause a conformational change in rhodopsin as an assay. Synthetic peptides corresponding to two regions near the carboxyl terminus of the G protein alpha subunit, Glu311-Val328 and Ile340-Phe350, compete with G protein for interaction with rhodopsin. Amino acid substitution studies show that Cys321 is required for this effect. Ile340-Phe350 and a modified peptide, acetyl-Glu311-Lys329-amide, mimic G protein effects on rhodopsin conformation, showing that these peptides bind to and stabilize the activated conformation of rhodopsin.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hamm, H E -- Deretic, D -- Arendt, A -- Hargrave, P A -- Koenig, B -- Hofmann, K P -- EY06062/EY/NEI NIH HHS/ -- EY06225/EY/NEI NIH HHS/ -- RP05369/PHS HHS/ -- etc. -- New York, N.Y. -- Science. 1988 Aug 12;241(4867):832-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physiology and Biophysics, University of Illinois College of Medicine, Chicago 60680.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/3136547" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Antibodies, Monoclonal ; Antigen-Antibody Complex ; Binding Sites ; GTP-Binding Proteins/*metabolism ; Kinetics ; Macromolecular Substances ; Membrane Proteins/*metabolism ; Peptides/metabolism ; Protein Binding ; Protein Conformation ; Retinal Pigments/*metabolism ; Rhodopsin/analogs & derivatives/*metabolism ; Transducin
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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