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Sample records for zorro gris pampeano

  1. The Caballero Revisited: Postmodernity in "The Cisco Kid", "The Mask of Zorro", and "Shrek II"

    ERIC Educational Resources Information Center

    Leen, Catherine

    2007-01-01

    This article discusses the achievement of the postmodern caballero films and the relevance of the social bandit myth for Chicano resistance. The continued relevance of the social bandit myth is clearly demonstrated by "The Cisco Kid" and "The Mask of Zorro." Both films show how initially flawed or directionless characters can…

  2. Mobility of Heavy Metals (Pb, Cd, Zn) in the Pampeano and Puelche Aquifers, Argentina: Partition and Retardation Coefficients.

    PubMed

    Jakomin, L M; Marbán, L; Grondona, S; Glok Galli, M; Martínez, D E

    2015-09-01

    The prediction about metals behaviour in soil requires knowledge on their solid-liquid partitioning. Usually it is expressed with an empirical distribution coefficient or Kd, which gives the ratio of the metal concentration in the solid phase to that in the solution. Kd values have been determined for Zn, Pb and Cd from samples representing the two most exploited aquifers in Argentina, Pampeano and Puelche, at three different locations in the province of Buenos Aires. The Pampeano aquifer presented higher Kd values than the Puelche aquifer. Comparing Kd values, different relationships could be observed: (a) Pampeano aquifer: Pb > Zn > Cd, and (b) Puelche aquifer: Pb > Cd > Zn. Kd for Cd seems to be linked to cationic exchange capacity, but solid phases precipitation can be more determining for Pb and Zn.

  3. The origin of groundwater composition in the Pampeano Aquifer underlying the Del Azul Creek basin, Argentina.

    PubMed

    Zabala, M E; Manzano, M; Vives, L

    2015-06-15

    The Pampean plain is the most productive region in Argentina. The Pampeano Aquifer beneath the Pampean plain is used mostly for drinking water. The study area is the sector of the Pampeano Aquifer underlying the Del Azul Creek basin, in Buenos Aires province. The main objective is to characterize the chemical and isotopic compositions of groundwater and their origin on a regional scale. The methodology used involved the identification and characterization of potential sources of solutes, the study of rain water and groundwater chemical and isotopic characteristics to deduce processes, the development of a hydrogeochemical conceptual model, and its validation by hydrogeochemical modelling with PHREEQC. Groundwater samples come mostly from a two-depth monitoring network of the "Dr. Eduardo J. Usunoff" Large Plains Hydrology Institute (IHLLA). Groundwater salinity increases from SW to NE, where groundwater is saline. In the upper basin groundwater is of the HCO3-Ca type, in the middle basin it is HCO3-Na, and in the lower basin it is ClSO4-NaCa and Cl-Na. The main processes incorporating solutes to groundwater during recharge in the upper basin are rain water evaporation, dissolution of CO2, calcite, dolomite, silica, and anorthite; cationic exchange with Na release and Ca and Mg uptake, and clay precipitation. The main processes modifying groundwater chemistry along horizontal flow at 30 m depth from the upper to the lower basin are cationic exchange, dissolution of silica and anorthite, and clay precipitation. The origin of salinity in the middle and lower basin is secular evaporation in a naturally endorheic area. In the upper and middle basins there is agricultural pollution. In the lower basin the main pollution source is human liquid and solid wastes. Vertical infiltration through the boreholes annular space during the yearly flooding stages is probably the pollution mechanism of the samples at 30 m depth. Copyright © 2015 Elsevier B.V. All rights reserved.

  4. Biomass Burning and the 2012 Greenland Ice Sheet (GrIS) melt

    NASA Astrophysics Data System (ADS)

    Choi, H. D.; Soja, A. J.; Polashenski, C.; Fairlie, T. D.; Winker, D. M.; Trepte, C. R.

    2017-12-01

    This study is the part of the Sunlight Absorption on the Greenland ice sheet Experiment (SAGE) project investigating the impact of light absorbing impurities (e.g., aerosols) on the Greenland Ice Sheet (GrIS). Satellite observations, [e.g. Oceansat-2 (OS2) and the Moderate-resolution Imaging Spectroradionmeter (MODIS)] discovered an unusually large melt event in July 2012. NASA sensors showed that nearly 98.6% of the GrIS experienced melting at or near surface [Nghiem et al., 2012]. In this study, we question the extent to which biomass burning derived aerosols enhanced melting across the GrIS. Random points [59 total, 13 coincident with snow pit sites and 46 gridded] are selected across the entire extent of the GrIS from April 1st to August 31st 2012, and then the NASA Langley Trajectory Model (LaTM) is used to simulate the transport of potentially smoke-filled air parcels backwards for 5 days form these points, evaluation the back trajectory for coincidence with active fire detections. The trajectory model is initialized for 24-hour sustained injection from each site, and air parcels are released from the surface to 2 km at 200m intervals. With the trajectory model outputs, we are able to identify trajectories that have coincidences with fires. We focus on events in April through July when the GrIS albedo was dramatically decreased. We also utilize Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data to verify smoke-aerosol signatures in boreal regions based on the NASA LaTM results. The results of this study will help us better understand the transport of biomass burning plumes and black carbon deposition that could lead to enhanced GrIS melting.

  5. "Gris Quintana": a Spanish granite from the Past into the Future.

    NASA Astrophysics Data System (ADS)

    José Tejado, Juan; Mota, M. Isabel; Pereira, Dolores

    2014-05-01

    "Gris Quintana" is a medium-grained, biotite and amphibole granodiorite extracted in the Pluton of Quintana de la Serena (Extremadura, Spain). It is a constant light grey granite from the Hercynian geologic with excellent physicomechanical and physicochemical properties. The granodiorite is composed of plagioclase, biotite, quartz and alkali feldspar, with accessory allanite, titanite, apatite, zircon and ilmenite, mostly as inclusions within the biotite crystals. This commercial variety is extracted from many quarries in the late Hercynian plutons located in the Iberian Massif in Spain period (transition between Central Iberian and Ossa-Moren Zones), having large reserves of granite. Many of the quarries have their own transformation factory (high production zone), with which the sector is offered an endless variety of finishes and constructive rock typologies. A wide range of solutions to architects and designers are offered. Gris Quintana granite is one of the materials with highest technological benefits that are used in arquitecture. "Gris Quintana" granite has been used since ancient times, not only at a regional, but also at national and international level: paving, building (structural, exterior façadas, interior uses), urban decoration and funeral art. It can be found in monuments and more recently, in buildings of different styles and uses, that stand out in beauty and splendor, lasting in time. Some singular works in "Gris Quintana" granite all over the world: extension to the "Congreso de Diputados" (Parliament) in Madrid, "Puerta de San Vicente" in Madrid, Andalucia Parliament columns in Sevilla, New Senate Buiding in Madird, "Gran Vía" pavement in Madrid, "Teatro Real façade" in Madrid… "Gris Quintana" granite accomplishes all the requirements for its nomination as Global Heritage Stone Resource, for both its use in construction and for artistic purposes.

  6. Opto-mechanical design of an image slicer for the GRIS spectrograph at GREGOR

    NASA Astrophysics Data System (ADS)

    Vega Reyes, N.; Esteves, M. A.; Sánchez-Capuchino, J.; Salaun, Y.; López, R. L.; Gracia, F.; Estrada Herrera, P.; Grivel, C.; Vaz Cedillo, J. J.; Collados, M.

    2016-07-01

    An image slicer has been proposed for the Integral Field Spectrograph [1] of the 4-m European Solar Telescope (EST) [2] The image slicer for EST is called MuSICa (Multi-Slit Image slicer based on collimator-Camera) [3] and it is a telecentric system with diffraction limited optical quality offering the possibility to obtain high resolution Integral Field Solar Spectroscopy or Spectro-polarimetry by coupling a polarimeter after the generated slit (or slits). Considering the technical complexity of the proposed Integral Field Unit (IFU), a prototype has been designed for the GRIS spectrograph at GREGOR telescope at Teide Observatory (Tenerife), composed by the optical elements of the image slicer itself, a scanning system (to cover a larger field of view with sequential adjacent measurements) and an appropriate re-imaging system. All these subsystems are placed in a bench, specially designed to facilitate their alignment, integration and verification, and their easy installation in front of the spectrograph. This communication describes the opto-mechanical solution adopted to upgrade GRIS while ensuring repeatability between the observational modes, IFU and long-slit. Results from several tests which have been performed to validate the opto-mechanical prototypes are also presented.

  7. GRIS observations of Al-26 gamma-ray line emission from two points in the Galactic plane

    NASA Technical Reports Server (NTRS)

    Teegarden, B. J.; Barthelmy, S. D.; Gehrels, N.; Tueller, J.; Leventhal, M.

    1991-01-01

    Both of the Gamma-Ray Imaging Spectrometer (GRIS) experiment's two observations of the Galactic center region, at l = zero and 335 deg respectively, detected Al-26 gamma-ray line emission. While these observations are consistent with the assumed high-energy gamma-ray distribution, they are consistent with other distributions as well. The data suggest that the Al-26 emission is distributed over Galactic longitude rather than being confined to a point source. The GRIS data also indicate that the 1809 keV line is broadened.

  8. MuSICa at GRIS: a prototype image slicer for EST at GREGOR

    NASA Astrophysics Data System (ADS)

    Calcines, A.; Collados, M.; López, R. L.

    2013-05-01

    This communication presents a prototype image slicer for the 4-m European Solar Telescope (EST) designed for the spectrograph of the 1.5-m GREGOR solar telescope (GRIS). The design of this integral field unit has been called MuSICa (Multi-Slit Image slicer based on collimator-Camera). It is a telecentric system developed specifically for the integral field, high resolution spectrograph of EST and presents multi-slit capability, reorganizing a bidimensional field of view of 80 arcsec^{2} into 8 slits, each one of them with 200 arcsec length × 0.05 arcsec width. It minimizes the number of optical components needed to fulfil this multi-slit capability, three arrays of mirrors: slicer, collimator and camera mirror arrays (the first one flat and the other two spherical). The symmetry of the layout makes it possible to overlap the pupil images associated to each part of the sliced entrance field of view. A mask with only one circular aperture is placed at the pupil position. This symmetric characteristic offers some advantages: facilitates the manufacturing process, the alignment and reduces the costs. In addition, it is compatible with two modes of operation: spectroscopic and spectro-polarimetric, offering a great versatility. The optical quality of the system is diffraction-limited. The prototype will improve the performances of GRIS at GREGOR and is part of the feasibility study of the integral field unit for the spectrographs of EST. Although MuSICa has been designed as a solar image slicer, its concept can also be applied to night-time astronomical instruments (Collados et al. 2010, Proc. SPIE, Vol. 7733, 77330H; Collados et al. 2012, AN, 333, 901; Calcines et al. 2010, Proc. SPIE, Vol. 7735, 77351X)

  9. Localization and subcellular association of Grapevine Pinot Gris Virus in grapevine leaf tissues.

    PubMed

    Tarquini, Giulia; Ermacora, Paolo; Bianchi, Gian Luca; De Amicis, Francesca; Pagliari, Laura; Martini, Marta; Loschi, Alberto; Saldarelli, Pasquale; Loi, Nazia; Musetti, Rita

    2018-05-01

    Despite the increasing impact of Grapevine Pinot gris disease (GPG-disease) worldwide, etiology about this disorder is still uncertain. The presence of the putative causal agent, the Grapevine Pinot Gris Virus (GPGV), has been reported in symptomatic grapevines (presenting stunting, chlorotic mottling, and leaf deformation) as well as in symptom-free plants. Moreover, information on virus localization in grapevine tissues and virus-plant interactions at the cytological level is missing at all. Ultrastructural and cytochemical investigations were undertaken to detect virus particles and the associated cytopathic effects in field-grown grapevine showing different symptom severity. Asymptomatic greenhouse-grown grapevines, which tested negative for GPGV by real time RT-PCR, were sampled as controls. Multiplex real-time RT-PCR and ELISA tests excluded the presence of viruses included in the Italian certification program both in field-grown and greenhouse-grown grapevines. Conversely, evidence was found for ubiquitous presence of Grapevine Rupestris Stem Pitting-associated Virus (GRSPaV), Hop Stunt Viroid (HSVd), and Grapevine Yellow Speckle Viroid 1 (GYSVd-1) in both plant groups. Moreover, in every field-grown grapevine, GPGV was detected by real-time RT-PCR. Ultrastructural observations and immunogold labelling assays showed filamentous flexuous viruses in the bundle sheath cells, often located inside membrane-bound organelles. No cytological differences were observed among field-grown grapevine samples showing different symptom severity. GPGV localization and associated ultrastructural modifications are reported and discussed, in the perspective of assisting management and control of the disease.

  10. Assessment of processes controlling the regional distribution of fluoride and arsenic in groundwater of the Pampeano Aquifer in the Del Azul Creek basin (Argentina)

    NASA Astrophysics Data System (ADS)

    Zabala, M. E.; Manzano, M.; Vives, L.

    2016-10-01

    Groundwater in the upper 50 m of the Pampeano Aquifer in the Del Azul Creek basin (Argentina) has F and As contents above the WHO safe drinking levels. This basin is situated to the SE of the Chaco-Pampean plain, in Buenos Aires Province. The Pampeano Aquifer is a major water source for all uses. The aim of the study is to assess the primary processes controlling the regional distribution of F and As in the most exploited part of the aquifer. The study involved sampling for chemical and isotopic analyses, interpretation of data with different methods (diagrams, bivariate analyses, mineral saturation states, Principal Component Analysis) and deduction of leading processes. Information about aquifer mineralogy and hydrogeochemical processes involved in F and As solubilization in the aquifer has been taken from previous works of the same and other authors. Groundwater salinity increases to the NE, in the direction of the regional groundwater flow. Chemical types evolve from Ca/Mg-HCO3 in the upper part of the basin, to Na-HCO3 in the middle part and to Na-ClSO4 and Na-Cl in the lower part. The regional distribution of F is controlled by hydrogeochemical processes. The distribution of As is controlled by two types of processes dominating in different areas: hydrogeochemical controls prevail in the low to moderately mineralized groundwater of the middle and lower parts of the basin; hydrogeological controls lead to the NE of the lower basin and beyond it. In the last zone there are abundant lagoons and seasonal flooding is frequent, making evapoconcentration an important process for groundwater mineralization. The main hydrogeochemical processes involved in both F and As distribution are cation exchange, with Na release and Ca uptake, carbonate dissolution and pH increase. Arsenic release induced by redox processes may play to the NE, but its results would be masked by the effect of evaporation.

  11. A novel specific duplex real-time RT-PCR method for absolute quantitation of Grapevine Pinot gris virus in plant material and single mites.

    PubMed

    Morán, Félix; Olmos, Antonio; Lotos, Leonidas; Predajňa, Lukáš; Katis, Nikolaos; Glasa, Miroslav; Maliogka, Varvara; Ruiz-García, Ana B

    2018-01-01

    Grapevine Pinot gris virus (GPGV) is a widely distributed grapevine pathogen that has been associated to the grapevine leaf mottling and deformation disease. With the aim of better understanding the disease epidemiology and providing efficient control strategies a specific and quantitative duplex TaqMan real-time RT-PCR assay has been developed. This method has allowed reliable quantitation of the GPGV titer ranging from 30 up to 3 x 108 transcript copies, with a detection limit of 70 viral copies in plant material. The assay targets a grapevine internal control that reduces the occurrence of false negative results, thus increasing the diagnostic sensitivity of the technique. Viral isolates both associated and non-associated to symptoms from Greece, Slovakia and Spain have been successfully detected. The method has also been applied to the absolute quantitation of GPGV in its putative transmission vector Colomerus vitis. Moreover, the viral titer present in single mites has been determined. In addition, in the current study a new polymorphism in the GPGV genome responsible for a shorter movement protein has been found. A phylogenetic study based on this genomic region has shown a high variability among Spanish isolates and points to a different evolutionary origin of this new polymorphism. The methodology here developed opens new possibilities for basic and epidemiological studies as well as for the establishment of efficient control strategies.

  12. Existing con el Lobo, Traversing la Frontera con Mis Nepantla Coyotes, y Buscando la Vida del Zorro: An Autoethnographic Exploration of a Chicano in Academia

    ERIC Educational Resources Information Center

    Ramirez, Ernesto Fidel

    2017-01-01

    This dissertation is the experience of my life, an evolution of platicas I have had con mis coyotes, my Nepantlero guides. I am one Chicano navigating through the mechanisms of a coercive and hegemonic system which limits our advancement in the academy. My ontology, epistemology, and axiology stem from my cultural and family foundations which I…

  13. Applications and benefits of technology in naturally fractured, low permeability reservoirs with special emphasis on results from GRI`s devonian shale and berea sand research in the appalachian basin

    SciT

    Jochen, J.E.; Hopkins, C.W.

    1993-12-31

    ;Contents: Naturally fractured reservoir description; Geologic considerations; Shale-specific log model; Stress profiles; Berea reasearch; Benefits analysis; Summary of technologies; Novel well test methods; Natural fracture identification; Reverse drilling; Production data analysis; Fracture treatment quality control; Novel core analysis methods; and Shale well cleanouts.

  14. Robust image alignment for cryogenic transmission electron microscopy.

    PubMed

    McLeod, Robert A; Kowal, Julia; Ringler, Philippe; Stahlberg, Henning

    2017-03-01

    Cryo-electron microscopy recently experienced great improvements in structure resolution due to direct electron detectors with improved contrast and fast read-out leading to single electron counting. High frames rates enabled dose fractionation, where a long exposure is broken into a movie, permitting specimen drift to be registered and corrected. The typical approach for image registration, with high shot noise and low contrast, is multi-reference (MR) cross-correlation. Here we present the software package Zorro, which provides robust drift correction for dose fractionation by use of an intensity-normalized cross-correlation and logistic noise model to weight each cross-correlation in the MR model and filter each cross-correlation optimally. Frames are reliably registered by Zorro with low dose and defocus. Methods to evaluate performance are presented, by use of independently-evaluated even- and odd-frame stacks by trajectory comparison and Fourier ring correlation. Alignment of tiled sub-frames is also introduced, and demonstrated on an example dataset. Zorro source code is available at github.com/CINA/zorro. Copyright © 2016 Elsevier Inc. All rights reserved.

  15. 76 FR 66625 - Approval of Grape Variety Names for American Wines

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-27

    ... commercial potential of the variety, such as the acreage planted and its location or market studies. Section... required to be marketed as ``Durif,'' a name he notes has little market presence. In response to the last... the names Sauvignon gris, Valvin Muscat, and Cabernet Diane are misleading. Sauvignon gris, a pink...

  16. The Sensitivity of the Greenland Ice Sheet to Glacial-Interglacial Oceanic Forcing

    NASA Astrophysics Data System (ADS)

    Tabone, I.; Blasco Navarro, J.; Robinson, A.; Alvarez-Solas, J.; Montoya, M.

    2017-12-01

    Up to now, the scientific community has mainly focused on the sensitivity of the Greenland Ice Sheet (GrIS) to atmospheric variations. However, several studies suggest that the enhanced ice mass loss experienced by the GrIS in the past decades is directly connected to the increasing North Atlantic temperatures. Melting of GrIS outlet glaciers triggers grounding-line retreat increasing ice discharge into the ocean. This new evidence leads to consider the ocean as a relevant driver to be taken into account when modeling the evolution of the GrIS. The ice-ocean interaction is a primary factor controling not only the likely future retreat of GrIS outlet glaciers, or the huge ice loss in past warming climates, but also, and more strongly, the past GrIS glacial expansion. The latter assumption is supported by reconstructions which propose the GrIS to be fully marine-based during glacials, and thus more exposed to the influence of the ocean. Here, for the first time, we investigate the response of the GrIS to past oceanic changes using a three-dimensional hybrid ice-sheet/ice-shelf model, which combines the Shallow Ice Approximation (SIA) for slow grounded ice sheets and the Shallow Shelf Approximation (SSA) in ice shelves and ice streams. The model accounts for a time-dependent parametrisation of the marine basal melting rate, which is used to reproduce past oceanic variations. In this work simulations of the last two glacial cycles are performed. Our results show that the GrIS is very sensitive to the ocean-triggered submarine melting (freezing). Mild oceanic temperature variations lead to a rapid retreat (expansion) of the GrIS margins, which, inducing a dynamic adjustment of the grounded ice sheet, drive the evolution of the whole ice sheet. Our results strongly suggest the need to consider the ocean as an active forcing in paleo ice sheet models.

  17. The sensitivity of the Greenland Ice Sheet to glacial-interglacial oceanic forcing

    NASA Astrophysics Data System (ADS)

    Tabone, Ilaria; Blasco, Javier; Robinson, Alexander; Alvarez-Solas, Jorge; Montoya, Marisa

    2018-04-01

    Observations suggest that during the last decades the Greenland Ice Sheet (GrIS) has experienced a gradually accelerating mass loss, in part due to the observed speed-up of several of Greenland's marine-terminating glaciers. Recent studies directly attribute this to warming North Atlantic temperatures, which have triggered melting of the outlet glaciers of the GrIS, grounding-line retreat and enhanced ice discharge into the ocean, contributing to an acceleration of sea-level rise. Reconstructions suggest that the influence of the ocean has been of primary importance in the past as well. This was the case not only in interglacial periods, when warmer climates led to a rapid retreat of the GrIS to land above sea level, but also in glacial periods, when the GrIS expanded as far as the continental shelf break and was thus more directly exposed to oceanic changes. However, the GrIS response to palaeo-oceanic variations has yet to be investigated in detail from a mechanistic modelling perspective. In this work, the evolution of the GrIS over the past two glacial cycles is studied using a three-dimensional hybrid ice-sheet-shelf model. We assess the effect of the variation of oceanic temperatures on the GrIS evolution on glacial-interglacial timescales through changes in submarine melting. The results show a very high sensitivity of the GrIS to changing oceanic conditions. Oceanic forcing is found to be a primary driver of GrIS expansion in glacial times and of retreat in interglacial periods. If switched off, palaeo-atmospheric variations alone are not able to yield a reliable glacial configuration of the GrIS. This work therefore suggests that considering the ocean as an active forcing should become standard practice in palaeo-ice-sheet modelling.

  18. Visceral leishmaniasis in captive wild canids in Brazil.

    PubMed

    Luppi, Marcela M; Malta, Marcelo C C; Silva, Teane M A; Silva, Fabiana L; Motta, Rafael O C; Miranda, Ildikó; Ecco, Roselene; Santos, Renato L

    2008-08-01

    Visceral leishmaniasis (VL) is endemic in Belo Horizonte (State of Minas Gerais, Brazil). Leishmania sp. can naturally infect several species of mammals, and the domestic dog is the most important reservoir of the disease in South America. This report describes five cases of visceral leishmaniasis in Brazilian canids. Among 15 animals kept in captivity in a zoo in Belo Horizonte (State of Minas Gerais, Brazil), two animals, a bush dog (Spheotos venaticos) and a hoary zorro (Lycalopex vetulus) were serologically positive and developed clinical signs of VL, whereas three other canids, including a crab-eating fox (Cerdocyon thous), a maned wolf (Chrysocyon brachyurus), and a hoary zorro (Lycalopex vetulus) had positive serological results without clinical signs.

  19. The United States Air Force in Southeast Asia: Interdiction in Southern Laos, 1960-1968

    DTIC Science & Technology

    1993-01-01

    Tactical Sorties in Northern and Southern Laos. December 1967 .................................... 245 Charts . Tables. Diagrams Page 272 276 278...aircraft, chiefly 0-1F Bird Dogs (used mostly as FACs), T-28Ds, C-123 Blindbats, and C-123 Candlesticks . Along the Ho Chi Minh Trail, the scope...Blindbats and C-123 Candlesticks teamed with BIG EAGLE A-26Ks or USAF T-28D ZORROS (or both) to conduct the nocturnal mission^.^’ The Seventh Air Force

  20. Transient ice mass variations over Greenland detected by the combination of GPS and GRACE data

    NASA Astrophysics Data System (ADS)

    Zhang, B.; Liu, L.; Khan, S. A.; van Dam, T. M.; Zhang, E.

    2017-12-01

    Over the past decade, the Greenland Ice Sheet (GrIS) has been undergoing significant warming and ice mass loss. Such mass loss was not always a steady process but had substantial temporal and spatial variabilities. Here we apply multi-channel singular spectral analysis to crustal deformation time series measured at about 50 Global Positioning System (GPS) stations mounted on bedrock around the Greenland coast and mass changes inferred from Gravity Recovery and Climate Experiment (GRACE) to detect transient changes in ice mass balance over the GrIS. We detect two transient anomalies: one is a negative melting anomaly (Anomaly 1) that peaked around 2010; the other is a positive melting anomaly (Anomaly 2) that peaked between 2012 and 2013. The GRACE data show that both anomalies caused significant mass changes south of 74°N but negligible changes north of 74°N. Both anomalies caused the maximum mass change in southeast GrIS, followed by in west GrIS near Jakobshavn. Our results also show that the mass change caused by Anomaly 1 first reached the maximum in late 2009 in the southeast GrIS and then migrated to west GrIS. However, in Anomaly 2, the southeast GrIS was the last place that reached the maximum mass change in early 2013 and the west GrIS near Jakobshavn was the second latest place that reached the maximum mass change. Most of the GPS data show similar spatiotemporal patterns as those obtained from the GRACE data. However, some GPS time series show discrepancies in either space or time, because of data gaps and different sensitivities of mass loading change. Namely, loading deformation measured by GPS can be significantly affected by local dynamical mass changes, which, yet, has little impact on GRACE observations.

  1. A Resilient Greenland Ice Sheet More Than 900,000 Years Old.

    NASA Astrophysics Data System (ADS)

    Dahl-Jensen, D.; Funder, S.; Schmidt, A. Z. M.; Solgaard, A.; Steffensen, J. P.; Willerslev, E.

    2014-12-01

    The Greenland Ice Sheet (GRIS) has the potential of causing a 7.36 m global sea level rise (GSLR) if it were to melt away. To properly assess risk of future melting, it is crucial to understand the formation and growth of the GRIS during past climate regimes. However, despite decades of research, it remains debated when and in what environment GRIS got established and to what extent GRIS changed in size during past warm interglacials, such as MIS 5e some 130 kyr BP. Here, we present results from analyses of environmental DNA, 10Be/36Cl, 234U/238U, single grain optically stimulated luminescence (OSL), palaeomagnetics, macrofossils and molecular clock dating of basal ice from the Camp Century ice core in north western Greenland and the Kap København Formation in North Greenland. We combine these with results from the DYE 3 and GRIP ice cores from southern and central Greenland to evaluate the evolution of the GRIS. We find evidence that the present GRIS formed quickly some time before 900 kyr BP in a largely forested Greenland and that it has changed by only 30-40% of its present volume since it was established. Our DNA findings of boreal forest imply that warming of more than 10oC is needed to have an ice-free Greenland. This threshold is higher than earlier predictions and the corresponding palaeo-calibration of the GRIS contribution to sea level changes suggests a sensitivity of 0.3-0.5 m GSLR per degree Celsius of warming over Greenland. Ice core data from the deep Greenland ice cores can be used to reconstruct the size of the ice sheet during the present interglacial (the Holocene) and the last interglacial (the Eemian). Reconstructions based on stable water isotopes and gas content is used to validate the resilience of the GRIS.

  2. Late glacial and Holocene history of the Greenland Ice Sheet margin, Nunatarssuaq, Northwestern Greenland

    NASA Astrophysics Data System (ADS)

    Farnsworth, L. B.; Kelly, M. A.; Axford, Y.; Bromley, G. R.; Osterberg, E. C.; Howley, J. A.; Zimmerman, S. R. H.; Jackson, M. S.; Lasher, G. E.; McFarlin, J. M.

    2015-12-01

    Defining the late glacial and Holocene fluctuations of the Greenland Ice Sheet (GrIS) margin, particularly during periods that were as warm or warmer than present, provides a longer-term perspective on present ice margin fluctuations and informs how the GrIS may respond to future climate conditions. We focus on mapping and dating past GrIS extents in the Nunatarssuaq region of northwestern Greenland. During the summer of 2014, we conducted geomorphic mapping and collected rock samples for 10Be surface exposure dating as well as subfossil plant samples for 14C dating. We also obtained sediment cores from an ice-proximal lake. Preliminary 10Be ages of boulders deposited during deglaciation of the GrIS subsequent to the Last Glacial Maximum range from ~30-15 ka. The apparently older ages of some samples indicate the presence of 10Be inherited from prior periods of exposure. These ages suggest deglaciation occurred by ~15 ka however further data are needed to test this hypothesis. Subfossil plants exposed at the GrIS margin on shear planes date to ~ 4.6-4.8 cal. ka BP and indicate less extensive ice during middle Holocene time. Additional radiocarbon ages from in situ subfossil plants on a nunatak date to ~3.1 cal. ka BP. Geomorphic mapping of glacial landforms near Nordsø, a large proglacial lake, including grounding lines, moraines, paleo-shorelines, and deltas, indicate the existence of a higher lake level that resulted from a more extensive GrIS margin likely during Holocene time. A fresh drift limit, characterized by unweathered, lichen-free clasts approximately 30-50 m distal to the modern GrIS margin, is estimated to be late Holocene in age. 10Be dating of samples from these geomorphic features is in progress. Radiocarbon ages of subfossil plants exposed by recent retreat of the GrIS margin suggest that the GrIS was at or behind its present location at AD ~1650-1800 and ~1816-1889. Results thus far indicate that the GrIS margin in northwestern Greenland

  3. Atmospheric river impacts on Greenland Ice Sheet surface melt and mass balance

    NASA Astrophysics Data System (ADS)

    Mattingly, K.; Mote, T. L.

    2017-12-01

    Mass loss from the Greenland Ice Sheet (GrIS) has accelerated during the early part of the 21st Century. Several episodes of widespread GrIS melt in recent years have coincided with intense poleward moisture transport by atmospheric rivers (ARs), suggesting that variability in the frequency and intensity of these events may be an important driver of the surface mass balance (SMB) of the GrIS. ARs may contribute to GrIS surface melt through the greenhouse effect of water vapor, the radiative effects of clouds, condensational latent heating within poleward-advected air masses, and the energy provided by liquid precipitation. However, ARs may also provide significant positive contributions to GrIS SMB through enhanced snow accumulation. Prior research on the role of ARs in Arctic climate has consisted of case studies of ARs associated with major GrIS melt events or examined the effects of poleward moisture flux on Arctic sea ice. In this study, a long-term (1979-2016) record of intense moisture transport events affecting Greenland is compiled using a conventional AR identification algorithm as well as a self-organizing map (SOM) classification applied to integrated water vapor transport (IVT) data from several atmospheric reanalysis datasets. An analysis of AR effects on GrIS melt and SMB is then performed with GrIS surface melt data from passive microwave satellite observations and the Modèle Atmosphérique Régional (MAR) regional climate model. Results show that meltwater production is above normal during and after AR impact days throughout the GrIS during all seasons, with surface melt enhanced most by strong (> 85th percentile IVT) and extreme (> 95th percentile IVT) ARs. This relationship holds at the seasonal scale, as the total amount of water vapor transported to the GrIS by ARs is significantly greater during above-normal melt seasons. ARs exert a more complex influence on SMB. Normal (< 85th percentile IVT) ARs generally do not have a substantial impact on

  4. The role of synoptic weather variability in Greenland ice sheet dynamics

    NASA Astrophysics Data System (ADS)

    Walker, J. M.; Radic, V.

    2017-12-01

    Much of the large uncertainty in predictions of future global sea level rise is due to our limited understanding of Greenland ice sheet (GrIS) motion and its interactions with climate. Over the next century, climate models predict that the GrIS will experience not only gradual warming, but also changes in atmospheric circulation, hydrology, and weather, including a northward shift of the North Atlantic storm track, with greater frequency and intensity of rain storms over the GrIS. Recent studies of GrIS dynamics have focused on the effects of increased seasonal mean meltwater on ice velocities, finding only a modest impact due to compensation by subglacial drainage systems, but subglacial hydraulic theory indicates that variability on shorter timescales is also relevant: short-term surges in meltwater or rainfall can overload drainage systems at rates faster than they can adjust, leading to water pressure spikes and ice acceleration. If the magnitude or frequency of these transient ice accelerations increase substantially as synoptic weather patterns change over the next century, there could be a significant cumulative impact on seasonal mean ice velocities. However, this issue has not been addressed in the literature and represents a major source of uncertainty. In this study, we investigate the role of synoptic weather variability in GrIS dynamics, with the ultimate goal of evaluating the relationships between extreme weather events and ice sheet flow in different seasons and regions of the GrIS. As a first step, we apply the machine learning technique of self-organizing maps to atmospheric reanalysis data to categorize the predominant synoptic weather systems over the GrIS domain, evaluating atmospheric moisture transport and rainfall to assess the impacts of each weather system on GrIS surface hydrology. The preliminary results presented here will be used in conjunction with ice velocity satellite measurements in future work, to identify any correlations

  5. Greenland ice sheet beyond 2100: Simulating its evolution and influence using the coupled climate-ice sheet model EC-Earth - PISM

    NASA Astrophysics Data System (ADS)

    Yang, S.; Christensen, J. H.; Madsen, M. S.; Ringgaard, I. M.; Petersen, R. A.; Langen, P. P.

    2017-12-01

    Greenland ice sheet (GrIS) is observed undergoing a rapid change in the recent decades, with an increasing area of surface melting and ablation and a speeding mass loss. Predicting the GrIS changes and their climate consequences relies on the understanding of the interaction of the GrIS with the climate system on both global and local scales, and requires climate model systems incorporating with an explicit and physically consistent ice sheet module. In this work we study the GrIS evolution and its interaction with the climate system using a fully coupled global climate model with a dynamical ice sheet model for the GrIS. The coupled model system, EC-EARTH - PISM, consisting of the atmosphere-ocean-sea ice model system EC-EARTH, and the Parallel Ice Sheet Model (PISM), has been employed for a 1400-year simulation forced by CMIP5 historical forcing from 1850 to 2005 and continued along an extended RCP8.5 scenario with the forcing peaking at 2200 and stabilized hereafter. The simulation reveals that, following the anthropogenic forcing increase, the global mean surface temperature rapidly rises about 10 °C in the 21st and 22nd century. After the forcing stops increasing after 2200, the temperature change slows down and eventually stabilizes at about 12.5 °C above the preindustrial level. In response to the climate warming, the GrIS starts losing mass slowly in the 21st century, but the ice retreat accelerates substantially after 2100 and ice mass loss continues hereafter at a constant rate of approximately 0.5 m sea level rise equivalence per 100 years, even as the warming rate gradually levels off. Ultimately the volume and extent of GrIS reduce to less than half of its preindustrial value. To understand the interaction of GrIS with the climate system, the characteristics of atmospheric and oceanic circulation in the warm climate are analyzed. The circulation patterns associated with the negative surface mass balance that leads to GrIS retreat are investigated

  6. Effect of specific pathways to 1.5°C global warming on the contribution of Greenland to sea level rise

    NASA Astrophysics Data System (ADS)

    Humbert, A.; Rückamp, M.; Falk, U.; Frieler, K.

    2017-12-01

    Sea level rise associated with changing climate is expected to pose a major challenge for societies. Here, we estimate the future contribution of the Greenland ice sheet (GrIS) to sea level change in terms of different emission scenarios. We investigate the effect of different pathways of global warming on the dynamics and mass balance of the GrIS with a focus on scenarios in line with limiting global warming to 2.0° or even 1.5° by the end of 2100 (Paris Agreement). We particularly address the issue of peak and decline scenarios temporarily exceeding a given temperature limit. This kind of overshooting might have strong effects on the evolution of the GrIS. Furthermore, we investigate the long-term effects of different levels of climate change to estimate the threshold for stabilizing the GrIS. For modeling the flow dynamics and future evolution of the GrIS, we apply the thermo-mechanical coupled Ice Sheet System Model (ISSM). The model is forced with anomalies for temperature and surface mass balance derived from different GCM data from the CMIP5 RCP2.6 scenario provided from the ISIMIP2b project. In order to obtain these anomalies from the GCM data, a surface energy balance model is applied.

  7. Coupled Long-Term Evolution of Climate and the Greenland Ice Sheet During the Last Interglacial and Implications for the Future

    NASA Astrophysics Data System (ADS)

    Otto-Bliesner, B. L.; Lofverstrom, M.; Lipscomb, W.; Fyke, J. G.; Marshall, S.; Sacks, B.

    2017-12-01

    The Greenland Ice Sheet (GrIS) is expected to contribute increasingly to global sea level rise by the end of this century, and potentially several meters in this millennium, but still with considerable uncertainty. The rate of Greenland melt will impact on regional sea levels. The Last Interglacial (LIG, 129 ka to 116 ka) is recognized as an important period for testing our knowledge of climate-ice sheet interactions in warm climate states. Although the LIG was discussed in the First Assessment Report of the IPCC, it gained more prominence in the IPCC Fourth and Fifth Assessment (AR4 and AR5) with reconstructions highlighting that global mean sea level was at least 5 m higher (but probably no more than 10 m higher) than present for several thousand years during the LIG. Model results assessed for the AR5 suggest a sea level contribution of 1.4 to 4.3 m from the GrIS. These model simulations, though, did not include all the feedbacks of the climate system and the GrIS. Here, we examine the response of the Arctic climate system and the GrIS in simulations with the Community Earth System Model (CESM) fully coupled to the Community Ice Sheet Model (CISM), using a surface energy balance scheme and without bias corrections. The analysis focuses on how the GrIS responds to the imposed high boreal summer insolation of the LIG and in addition, to the long-term feedbacks of high-latitude vegetation changes. Results will highlight the evolution of the ice sheet and the surface mass balance (patterns of ablation and accumulation) as compared to data-based reconstructions for the LIG. We conclude with a discussion on how the LIG may be informative as a potential process analogue for the GrIS response for future centuries to come.

  8. Changes in Greenland ice bed conditions inferred from seismology

    NASA Astrophysics Data System (ADS)

    Toyokuni, Genti; Takenaka, Hiroshi; Takagi, Ryota; Kanao, Masaki; Tsuboi, Seiji; Tono, Yoko; Childs, Dean; Zhao, Dapeng

    2018-04-01

    Basal conditions of the Greenland Ice Sheet (GrIS) are a key research topic in climate change studies. The recent construction of a seismic network has provided a new opportunity for direct, real-time, and continuous monitoring of the GrIS. Here we use ambient noise surface wave data from seismic stations all over Greenland for a 4.5-year period to detect changes in Rayleigh-wave phase velocity between seismic station pairs. We observe clear seasonal and long-term velocity changes for many pairs, and propose a plausible mechanism for these changes. Dominant factors driving the velocity changes might be seasonal and long-term pressurization/depressurization of the GrIS and shallow bedrock by air and ice mass loading/unloading. However, heterogeneity of the GrIS basal conditions might impose strong regionalities on the results. An interesting feature is that, even at adjacent two station pairs in the inland GrIS, one pair shows velocity decrease while another shows velocity increase as a response to the high air and snow pressure. The former pair might be located on a thawed bed that decreases velocity by increased meltwater due to pressure melting, whereas the latter pair might be located on a frozen bed that increases velocity by compaction of ice and shallow bedrock. The results suggest that surface waves are very sensitive to the GrIS basal conditions, and further observations will contribute to a more direct and quantitative estimation of water balance in the Arctic region.

  9. New constraints on the deglaciation chronology of the southeastern margin of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Levy, L.; Larsen, N. K.; Kjaer, K. H.; Bjork, A. A.; Kjeldsen, K. K.; Funder, S.; Kelly, M. A.; Howley, J. A.; Zimmerman, S. R. H.

    2015-12-01

    The Greenland Ice Sheet (GrIS) is responding rapidly to climate change. Marine terminating outlet glaciers that drain the GrIS have responded especially sensitively to present-day climate change by accelerating, thinning and retreating. In southeastern Greenland several outlet glaciers are undergoing rapid changes in mass balance and ice dynamics. To improve our understanding of the future, long-term response of these marine-terminating outlet glaciers to climate change, we focus on the response of three outlet glaciers to climate change since the Last Glacial Maximum. The timing and rates of late-glacial and early Holocene deglaciation of the southeastern sector of the GrIS are relatively unconstrained due to the inaccessibility of the region. Using a helicopter and a sailboat, we collected samples for 10Be surface exposure dating from three fjords in southeastern Greenland: Skjoldungen (63.4N), Uvtorsiutit (62.7N), and Lindenow (60.6N). These fjords drain marine terminating glaciers of the GrIS. Here we present 18 new 10Be ages from ~50 km long transects along these fjords that mark the timing of deglaciation from the outer coast inland to the present-day GrIS margin. Together with previously constrained deglaciation chronologies from Bernstorffs, Sermilik, and Kangerdlussuaq fjords in southeastern Greenland, these new chronologies offer insight into the late-glacial and early Holocene dynamics of the southeastern GrIS outlet glaciers. We compare the timing and rate of deglaciation in southeastern Greenland to climate records from the region to examine the mechanisms that drove deglaciation during late-glacial and early Holocene time. These new 10Be ages provide a longer-term perspective of marine terminating outlet glacier fluctuations in southeastern Greenland and can be used to model the ice sheet's response to late-glacial and early Holocene climate changes.

  10. Assimilation of MODIS Ice Surface Temperature and Albedo into the Snow and Ice Model CROCUS Over the Greenland Ice Sheet Along the K-transect Stations

    NASA Astrophysics Data System (ADS)

    Navari, M.; Margulis, S. A.; Bateni, S. M.; Alexander, P. M.; Tedesco, M.

    2016-12-01

    Estimating the Greenland Ice Sheet (GrIS) surface mass balance (SMB) is an important component of current and future projections of sea level rise. In situ measurement provides direct estimates of the SMB, but are inherently limited by their spatial extent and representativeness. Given this limitation, physically based regional climate models (RCMs) are critical for understanding GrIS physical processes and estimating of the GrIS SMB. However, the uncertainty in estimates of SMB from RCMs is still high. Surface remote sensing (RS) has been used as a complimentary tool to characterize various aspects related to the SMB. The difficulty of using these data streams is that the links between them and the SMB terms are most often indirect and implicit. Given the lack of in situ information, imperfect models, and under-utilized RS data it is critical to merge the available data in a systematic way to better characterize the spatial and temporal variation of the GrIS SMB. This work proposes a data assimilation (DA) framework that yields temporally-continuous and physically consistent SMB estimates that benefit from state-of-the-art models and relevant remote sensing data streams. Ice surface temperature (IST) is the most important factor that regulates partitioning of the net radiation into the subsurface snow/ice, sensible and latent heat fluxes and plays a key role in runoff generation. Therefore it can be expected that a better estimate of surface temperature from a data assimilation system would contribute to a better estimate of surface mass fluxes. Albedo plays an important role in the surface energy balance of the GrIS. However, even advanced albedo modules are not adequate to simulate albedo over the GrIS. Therefore, merging remotely sensed albedo product into a physically based model has a potential to improve the estimates of the GrIS SMB. In this work a MODIS-derived IST and a 16-day albedo product are independently assimilated into the snow and ice model CROCUS

  11. Evidence for smaller extents of the northwestern Greenland Ice Sheet and North Ice Cap during the Holocene

    NASA Astrophysics Data System (ADS)

    Kelly, M. A.; Osterberg, E. C.; Axford, Y.; Bigl, M.; Birkel, S. D.; Corbett, L. B.; Roy, E. P.; Thompson, J. T.; Whitecloud, S.

    2013-12-01

    The Greenland Ice Sheet (GrIS) and local glaciers on Greenland are responding dynamically to warming temperatures with widespread retreat. GRACE satellite data (e.g., Kahn et al., 2010) and the Petermann Glacier calving events document the recent expansion of ice loss into northwestern Greenland. To improve the ability to estimate future ice loss in a warming climate, we are developing records of the response of the northwestern Greenlandic cryosphere to Holocene climatic conditions, with a focus on past warm periods. Our ongoing research includes analyses of glacial geology, sub-fossil vegetation, lake sediment cores, chironomid assemblages and ice cores combined with glaciological modeling. To constrain past ice extents that were as small as, or smaller than, at present, we recovered sub-fossil vegetation exposed at the receding margins of the GrIS and North Ice Cap (NIC) in the Nunatarssuaq region (~76.7°N, 67.4°W) and of the GrIS near Thule (~76.5°N, 68.7°W). We present vegetation types and radiocarbon ages of 30 plant samples collected in August 2012. In the Nunatarssuaq region, five ages of in situ (rooted) vegetation including Polytrichum moss, Saxifraga nathorstii and grasses located <5 m outboard of the GrIS margin are ~120-200 cal yr BP (range of medians of the 2-sigma calibrated age ranges). Nine ages of in situ Polytrichum, Saxifraga oppositafolia and grasses from ~1-5 m inboard of the NIC margin (excavated from beneath ice) range from ~50 to 310 cal yr BP. The growth of these plants occurred when the GrIS and NIC were at least as small as at present and their ages suggest that ice advances occurred in the last 50-120 yrs. In addition to the in situ samples, we collected plants from well-preserved ground material exposed along shear planes in the GrIS margins. In Nunatarssuaq, two Polytrichum mosses rooted in ground material and exposed along a shear plane in the GrIS margin date to 4680 and 4730 cal yr BP. Near Thule, three ages of Salix arctica

  12. Sensitivity of the Greenland Ice Sheet to Interglacial Climate Forcing: MIS 5e Versus MIS 11

    NASA Astrophysics Data System (ADS)

    Rachmayani, Rima; Prange, Matthias; Lunt, Daniel J.; Stone, Emma J.; Schulz, Michael

    2017-11-01

    The Greenland Ice Sheet (GrIS) is thought to have contributed substantially to high global sea levels during the interglacials of Marine Isotope Stage (MIS) 5e and 11. Geological evidence suggests that the mass loss of the GrIS was greater during the peak interglacial of MIS 11 than MIS 5e, despite a weaker boreal summer insolation. We address this conundrum by using the three-dimensional thermomechanical ice sheet model Glimmer forced by Community Climate System Model version 3 output for MIS 5e and MIS 11 interglacial time slices. Our results suggest a stronger sensitivity of the GrIS to MIS 11 climate forcing than to MIS 5e forcing. Besides stronger greenhouse gas radiative forcing, the greater MIS 11 GrIS mass loss relative to MIS 5e is attributed to a larger oceanic heat transport toward high latitudes by a stronger Atlantic meridional overturning circulation. The vigorous MIS 11 ocean overturning, in turn, is related to a stronger wind-driven salt transport from low to high latitudes promoting North Atlantic Deep Water formation. The orbital insolation forcing, which causes the ocean current anomalies, is discussed.

  13. A tipping point in refreezing accelerates mass loss of Greenland's glaciers and ice caps.

    PubMed

    Noël, B; van de Berg, W J; Lhermitte, S; Wouters, B; Machguth, H; Howat, I; Citterio, M; Moholdt, G; Lenaerts, J T M; van den Broeke, M R

    2017-03-31

    Melting of the Greenland ice sheet (GrIS) and its peripheral glaciers and ice caps (GICs) contributes about 43% to contemporary sea level rise. While patterns of GrIS mass loss are well studied, the spatial and temporal evolution of GICs mass loss and the acting processes have remained unclear. Here we use a novel, 1 km surface mass balance product, evaluated against in situ and remote sensing data, to identify 1997 (±5 years) as a tipping point for GICs mass balance. That year marks the onset of a rapid deterioration in the capacity of the GICs firn to refreeze meltwater. Consequently, GICs runoff increases 65% faster than meltwater production, tripling the post-1997 mass loss to 36±16 Gt -1 , or ∼14% of the Greenland total. In sharp contrast, the extensive inland firn of the GrIS retains most of its refreezing capacity for now, buffering 22% of the increased meltwater production. This underlines the very different response of the GICs and GrIS to atmospheric warming.

  14. A tipping point in refreezing accelerates mass loss of Greenland's glaciers and ice caps

    PubMed Central

    Noël, B.; van de Berg, W. J; Lhermitte, S.; Wouters, B.; Machguth, H.; Howat, I.; Citterio, M.; Moholdt, G.; Lenaerts, J. T. M.; van den Broeke, M. R.

    2017-01-01

    Melting of the Greenland ice sheet (GrIS) and its peripheral glaciers and ice caps (GICs) contributes about 43% to contemporary sea level rise. While patterns of GrIS mass loss are well studied, the spatial and temporal evolution of GICs mass loss and the acting processes have remained unclear. Here we use a novel, 1 km surface mass balance product, evaluated against in situ and remote sensing data, to identify 1997 (±5 years) as a tipping point for GICs mass balance. That year marks the onset of a rapid deterioration in the capacity of the GICs firn to refreeze meltwater. Consequently, GICs runoff increases 65% faster than meltwater production, tripling the post-1997 mass loss to 36±16 Gt−1, or ∼14% of the Greenland total. In sharp contrast, the extensive inland firn of the GrIS retains most of its refreezing capacity for now, buffering 22% of the increased meltwater production. This underlines the very different response of the GICs and GrIS to atmospheric warming. PMID:28361871

  15. Inter-annual Variations in Snow/Firn Density over the Greenland Ice Sheet by Combining GRACE gravimetry and Envisat Altimetry

    NASA Astrophysics Data System (ADS)

    Su, X.; Shum, C. K.; Guo, J.; Howat, I.; Jezek, K. C.; Luo, Z.; Zhou, Z.

    2017-12-01

    Satellite altimetry has been used to monitor elevation and volume change of polar ice sheets since the 1990s. In order to derive mass change from the measured volume change, different density assumptions are commonly used in the research community, which may cause discrepancies on accurately estimating ice sheets mass balance. In this study, we investigate the inter-annual anomalies of mass change from GRACE gravimetry and elevation change from Envisat altimetry during years 2003-2009, with the objective of determining inter-annual variations of snow/firn density over the Greenland ice sheet (GrIS). High positive correlations (0.6 or higher) between these two inter-annual anomalies at are found over 93% of the GrIS, which suggests that both techniques detect the same geophysical process at the inter-annual timescale. Interpreting the two anomalies in terms of near surface density variations, over 80% of the GrIS, the inter-annual variation in average density is between the densities of snow and pure ice. In particular, at the Summit of Central Greenland, we validate the satellite data estimated density with the in situ data available from 75 snow pits and 9 ice cores. This study provides constraints on the currently applied density assumptions for the GrIS.

  16. A model of the Greenland ice sheet deglaciation

    NASA Astrophysics Data System (ADS)

    Lecavalier, Benoit

    The goal of this thesis is to improve our understanding of the Greenland ice sheet (GrIS) and how it responds to climate change. This was achieved using ice core records to infer elevation changes of the GrIS during the Holocene (11.7 ka BP to Present). The inferred elevation changes show the response of the ice sheet interior to the Holocene Thermal Maximum (HTM; 9-5 ka BP) when temperatures across Greenland were warmer than present. These ice-core derived thinning curves act as a new set of key constraints on the deglacial history of the GrIS. Furthermore, a calibration was conducted on a three-dimensional thermomechanical ice sheet, glacial isostatic adjustment, and relative sea-level model of GrIS evolution during the most recent deglaciation (21 ka BP to present). The model was data-constrained to a variety of proxy records from paleoclimate archives and present-day observations of ice thickness and extent.

  17. A century of variation in the dependence of Greenland iceberg calving on ice sheet surface mass balance and regional climate change.

    PubMed

    Bigg, G R; Wei, H L; Wilton, D J; Zhao, Y; Billings, S A; Hanna, E; Kadirkamanathan, V

    2014-06-08

    Iceberg calving is a major component of the total mass balance of the Greenland ice sheet (GrIS). A century-long record of Greenland icebergs comes from the International Ice Patrol's record of icebergs (I48N) passing latitude 48° N, off Newfoundland. I48N exhibits strong interannual variability, with a significant increase in amplitude over recent decades. In this study, we show, through a combination of nonlinear system identification and coupled ocean-iceberg modelling, that I48N's variability is predominantly caused by fluctuation in GrIS calving discharge rather than open ocean iceberg melting. We also demonstrate that the episodic variation in iceberg discharge is strongly linked to a nonlinear combination of recent changes in the surface mass balance (SMB) of the GrIS and regional atmospheric and oceanic climate variability, on the scale of the previous 1-3 years, with the dominant causal mechanism shifting between glaciological (SMB) and climatic (ocean temperature) over time. We suggest that this is a change in whether glacial run-off or under-ice melting is dominant, respectively. We also suggest that GrIS calving discharge is episodic on at least a regional scale and has recently been increasing significantly, largely as a result of west Greenland sources.

  18. Greenland ice sheet retreat since the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Beitch, Marci J.

    Late 20th century and 21st century satellite imagery of the perimeter of the Greenland Ice Sheet (GrIS) provide high resolution observations of the ice sheet margins. Examining changes in ice margin positions over time yield measurements of GrIS area change and rates of margin retreat. However, longer records of ice sheet margin change are needed to establish more accurate predictions of the ice sheet's future response to global conditions. In this study, the trimzone, the area of deglaciated terrain along the ice sheet edge that lacks mature vegetation cover, is used as a marker of the maximum extent of the ice from its most recent major advance during the Little Ice Age. We compile recently acquired Landsat ETM+ scenes covering the perimeter of the GrIS on which we map area loss on land-, lake-, and marine-terminating margins. We measure an area loss of 13,327 +/- 830 km2, which corresponds to 0.8% shrinkage of the ice sheet. This equates to an averaged horizontal retreat of 363 +/- 69 m across the entire GrIS margin. Mapping the areas exposed since the Little Ice Age maximum, circa 1900 C.E., yields a century-scale rate of change. On average the ice sheet lost an area of 120 +/- 16 km 2/yr, or retreated at a rate of 3.3 +/- 0.7 m/yr since the LIA maximum.

  19. Mergers between Governmental Research Institutes and Universities in the Danish HE Sector

    ERIC Educational Resources Information Center

    Aagaard, Kaare; Hansen, Hanne Foss; Rasmussen, Jørgen Gulddahl

    2016-01-01

    This article presents an analysis of the mergers in the Danish Higher Education (HE)-sector with a particular emphasis on the 2007 mergers involving universities and Government Research Institutes (GRIs). Furthermore, it follows the post-merger processes up to 2014/2015 at two Danish universities and examines the consequences of the changes seen…

  20. A Comparison of Performance on Cloze Tests, Group Reading Inventories and Standardized Reading Achievement in Grades Seven, Eight and Nine.

    ERIC Educational Resources Information Center

    Rakes, Thomas A.; McWilliams, Lana J.

    A random sample of 300 seventh, eighth, and ninth grade students participated in a comparative study of performance on social studies cloze tests, social studies group reading inventories (GRI), and a popular standardized test (Gates-MacGinitie Reading Tests, Survey E). It was found that cloze tests and GRIs constructed from social studies content…

  1. A tipping point in refreezing accelerates mass loss of Greenland's glaciers and ice caps

    NASA Astrophysics Data System (ADS)

    Noël, B.; van de Berg, W. J.; Lhermitte, S.; Wouters, B.; Machguth, H.; Howat, I.; Citterio, M.; Moholdt, G.; Lenaerts, J. T. M.; van den Broeke, M. R.

    2017-03-01

    Melting of the Greenland ice sheet (GrIS) and its peripheral glaciers and ice caps (GICs) contributes about 43% to contemporary sea level rise. While patterns of GrIS mass loss are well studied, the spatial and temporal evolution of GICs mass loss and the acting processes have remained unclear. Here we use a novel, 1 km surface mass balance product, evaluated against in situ and remote sensing data, to identify 1997 (+/-5 years) as a tipping point for GICs mass balance. That year marks the onset of a rapid deterioration in the capacity of the GICs firn to refreeze meltwater. Consequently, GICs runoff increases 65% faster than meltwater production, tripling the post-1997 mass loss to 36+/-16 Gt-1, or ~14% of the Greenland total. In sharp contrast, the extensive inland firn of the GrIS retains most of its refreezing capacity for now, buffering 22% of the increased meltwater production. This underlines the very different response of the GICs and GrIS to atmospheric warming.

  2. Career Aspirations of Malaysian Research and Development Professionals in the Knowledge Economy

    ERIC Educational Resources Information Center

    Ismail, Maimunah; Ramly, Efizah Sofiah

    2011-01-01

    Purpose: This paper seeks to compare the influence of self-efficacy, organizational socialization and continuous improvement (CI) practices on the career aspirations of research and development (R&D) professionals in government research institutes (GRIs) and multinational corporations (MNCs) in Malaysia. R&D professionals in this study…

  3. 76 FR 27657 - Notice of Domestic Interested Party Petitioner's Desire To Contest the Tariff Classification...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-05-12

    ... by offering guidance in understanding the scope of the headings and GRIs. The wickless wax objects... Wickless Wax Objects AGENCY: U.S. Customs and Border Protection, Department of Homeland Security. ACTION... imported wickless wax objects identified in entry documents as ``wax cylinders'', ``wax pillars'', ``wax...

  4. Meltwater export of prokaryotic cells from the Greenland ice sheet.

    PubMed

    Cameron, Karen A; Stibal, Marek; Hawkings, Jon R; Mikkelsen, Andreas B; Telling, Jon; Kohler, Tyler J; Gözdereliler, Erkin; Zarsky, Jakub D; Wadham, Jemma L; Jacobsen, Carsten S

    2017-02-01

    Microorganisms are flushed from the Greenland Ice Sheet (GrIS) where they may contribute towards the nutrient cycling and community compositions of downstream ecosystems. We investigate meltwater microbial assemblages as they exit the GrIS from a large outlet glacier, and as they enter a downstream river delta during the record melt year of 2012. Prokaryotic abundance, flux and community composition was studied, and factors affecting community structures were statistically considered. The mean concentration of cells exiting the ice sheet was 8.30 × 10 4 cells mL -1 and we estimate that ∼1.02 × 10 21 cells were transported to the downstream fjord in 2012, equivalent to 30.95 Mg of carbon. Prokaryotic microbial assemblages were dominated by Proteobacteria, Bacteroidetes, and Actinobacteria. Cell concentrations and community compositions were stable throughout the sample period, and were statistically similar at both sample sites. Based on our observations, we argue that the subglacial environment is the primary source of the river-transported microbiota, and that cell export from the GrIS is dependent on discharge. We hypothesise that the release of subglacial microbiota to downstream ecosystems will increase as freshwater flux from the GrIS rises in a warming world. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

  5. Increasing runoff and sediment load from the Greenland ice sheet at kangerlussuaq (Sonder Stromfjord) in a 30-year perspective, 1979-2008

    SciT

    Mernild, Sebastian Haugard; Liston, Glen; Hasholt, Bent

    2009-01-01

    This observation and modeling study provides insights into runoff and sediment load exiting the Watson River drainage basin, Kangerlussuaq, West Greenland during a 30 year period (1978/79-2007/08) when the climate experienced increasing temperatures and precipitation. The 30-year simulations quantify the terrestrial freshwater and sediment output from part of the Greenland Ice Sheet (GrIS) and the land between the GrIS and the ocean, in the context of global warming and increasing GrIS surface melt. We used a snow-evolution modeling system (SnowModel) to simulate the winter accumulation and summer ablation processes, including runoff and surface mass balance (SMB), of the Greenland icemore » sheet. Observed sediment concentrations were related to observed runoff, producing a sediment-load time series. To a large extent, the SMB fluctuations could be explained by changes in net precipitation (precipitation minus evaporation and sublimation), with 8 out of 30 years having negative SMB, mainly because of relatively low annual net precipitation. The overall trend in net precipitation and runoff increased significantly, while 5MB increased insignificantly throughout the simulation period, leading to enhanced precipitation of 0.59 km{sup 3} w.eq. (or 60%), runoff of 0.43 km{sup 3} w.eq (or 54%), and SMB of 0.16 km3 w.eq. (or 86%). Runoff rose on average from 0.80 km{sup 3} w.eq. in 1978/79 to 1.23 km{sup 3} w.eq. in 2007/08. The percentage of catchment oudet runoff explained by runoff from the GrIS decreased on average {approx} 10%, indicating that catchment runoff throughout the simulation period was influenced more by precipitation and snowmelt events, and less by runoff from the GrIS. Average variations in the increasing Kangerlussuaq runoff from 1978/79 through 2007/08 seem to follow the overall variations in satellite-derived GrIS surface melt, where 64% of the variations in simulated runoff were explained by regional melt conditions on the GrIS. Throughout the

  6. Greenland Ice Sheet seasonal and spatial mass variability from model simulations and GRACE (2003-2012)

    NASA Astrophysics Data System (ADS)

    Alexander, Patrick M.; Tedesco, Marco; Schlegel, Nicole-Jeanne; Luthcke, Scott B.; Fettweis, Xavier; Larour, Eric

    2016-06-01

    Improving the ability of regional climate models (RCMs) and ice sheet models (ISMs) to simulate spatiotemporal variations in the mass of the Greenland Ice Sheet (GrIS) is crucial for prediction of future sea level rise. While several studies have examined recent trends in GrIS mass loss, studies focusing on mass variations at sub-annual and sub-basin-wide scales are still lacking. At these scales, processes responsible for mass change are less well understood and modeled, and could potentially play an important role in future GrIS mass change. Here, we examine spatiotemporal variations in mass over the GrIS derived from the Gravity Recovery and Climate Experiment (GRACE) satellites for the January 2003-December 2012 period using a "mascon" approach, with a nominal spatial resolution of 100 km, and a temporal resolution of 10 days. We compare GRACE-estimated mass variations against those simulated by the Modèle Atmosphérique Régionale (MAR) RCM and the Ice Sheet System Model (ISSM). In order to properly compare spatial and temporal variations in GrIS mass from GRACE with model outputs, we find it necessary to spatially and temporally filter model results to reproduce leakage of mass inherent in the GRACE solution. Both modeled and satellite-derived results point to a decline (of -178.9 ± 4.4 and -239.4 ± 7.7 Gt yr-1 respectively) in GrIS mass over the period examined, but the models appear to underestimate the rate of mass loss, especially in areas below 2000 m in elevation, where the majority of recent GrIS mass loss is occurring. On an ice-sheet-wide scale, the timing of the modeled seasonal cycle of cumulative mass (driven by summer mass loss) agrees with the GRACE-derived seasonal cycle, within limits of uncertainty from the GRACE solution. However, on sub-ice-sheet-wide scales, some areas exhibit significant differences in the timing of peaks in the annual cycle of mass change. At these scales, model biases, or processes not accounted for by models related

  7. Exploring the functional diversity of the supraglacial environment: Microbial degradation of the pesticide 2,4-D on the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Stibal, M.; Bælum, J.; Holben, W. E.; Jacobsen, C. S.

    2012-12-01

    The surface of the Greenland ice sheet (GrIS) harbours a diverse community of heterotrophic microorganisms. Organic compounds of anthropogenic origin, including pesticides, are deposited on the GrIS; however, the fate of these compounds in the ice is currently unknown. In this study we determine the potential of the microbial community from the surface of the GrIS to mineralise the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D). It is one of the most easily degraded compounds among the phenoxyacetic acid pesticides, and the ability to mineralise 2,4-D has been found to be widespread in microbial communities around the globe. Functional genes involved in the degradation pathway have also been characterised. Thus, 2,4-D represents a very suitable model compound to use in order to gain an insight into pollutant degradation dynamics in the rapidly changing Arctic region. We collected surface ice cores on the GrIS and incubated them for up to 529 days in microcosms simulating in situ conditions. We measured mineralisation of side-chain- and ring-labelled 14C-2,4-D in the samples and performed quantitative PCR targeting the tfdA gene, encoding an enzyme catalysing the first step in the degradation pathway of 2,4-D, in the DNA extracted from the ice after the experiments. We show that the microbial community on the surface of the GrIS is of low diversity, but contains microbes capable of degrading 2,4-D. The low diversity of the community and the similarity of the detected clones to those from other icy environment clones suggest that the bacterial community on the GrIS is selected from a pool of propagules deposited on the surface of the ice sheet, based on the level of adaptation to the conditions in the surface ice. The 2,4-D degraders are likely present in very low numbers, and they can mineralise 2,4-D at a rate of up to 1 nmol per m2 per day, equivalent to ~26 ng C m-2 d-1. We contend that the surface of the GrIS should not be considered to be a mere reservoir of

  8. A comparison of Holocene fluctuations of the eastern and western margins of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Levy, L.; Kelly, M. A.; Lowell, T. V.; Hall, B. L.; Applegate, P. J.; Howley, J.; Axford, Y.

    2013-12-01

    Determining how the Greenland Ice Sheet (GrIS) responded to past temperature fluctuations is important for assessing its future stability in a changing climate. We present a record of the Holocene extents of the western GrIS margin near Kangerlussuaq (67.0°N, 50.7°W) and compare this with the past fluctuations of Bregne ice cap (71°N, 25.6° W), a small ice cap in the Scoresby Sund region 90 km from the eastern GrIS margin, to examine the mechanisms that influenced past ice margin fluctuations. The past extents of the Bregne ice cap are a proxy for the climatic conditions that influenced the nearby GrIS margin. We used glacial geomorphic mapping, 10Be dating of boulders and bedrock, and sediment cores from proglacial and non-glacial lakes. In western Greenland, 10Be ages on the Keglen moraines, 13 km west of the current GrIS margin and the Ørkendalen moraines, ≤2 km west of the current ice margin date to 7.3 × 0.1 ka (n=6) and 6.8 × 0.3 ka (n=9), respectively. Fresh moraines, ≤50 m from the current ice margin date to AD 1830-1950 and are likely associated with advances during the Little Ice Age (LIA). In some areas, the LIA moraines lie stratigraphically above the Ørkendalen moraines, indicating the GrIS was inboard of the Ørkendalen limit from 6.8 ka to the 20th century. In eastern Greenland, 10Be ages show that Bregne ice cap retreated within its late Holocene limit by 10.7 ka. A lack of clastic sediment in a proglacial lake suggests the ice cap was smaller or completely absent from ~10-2.6 ka. A snowline analysis indicates that temperatures ~0.5°C warmer than present would render the entire ice cap into an ablation zone. Glacial silts in the proglacial lake at ~2.6 and ~1.9 cal kyr BP to present indicate advances of Bregne ice cap. Fresh moraines ≤200 m of Bregne ice cap were deposited ≤2.6 cal kyr BP and mark the largest advance of the Holocene. Both the western GrIS margin and Bregne ice cap were influenced by Northern Hemisphere summer

  9. Runoff simulations from the Greenland ice sheet at Kangerlussuaq from 2006-2007 to 2007/08. West Greenland

    SciT

    Mernild, Sebastian Haugard; Hasholt, Bent; Van Den Broeke, Michiel

    2009-01-01

    This study focuses on runoff from a large sector of the Greenland Ice Sheet (GrIS) - the Kangerlussuaq drainage area, West Greenland - for the runoff observation period 2006/07 to 2007/08. SnowModel, a state-of-the-art snow-evolution modeling system, was used to simulate winter accumulation and summer ablation processes, including runoff. Independent in situ end-of-winter snow depth and high-resolution runoff observations were used for validation of simulated accumulation and ablation processes. Runoff was modeled on both daily and hourly time steps, filling a data gap of runoff exiting part of the GrIS. Using hourly meteorological driving data instead of smoothed daily-averaged datamore » produced more realistic meteorological conditions in relation to snow and melt threshold surface processes, and produced 6-17% higher annual cumulative runoff. The simulated runoff series yielded useful insights into the present conditions of inter-seasonal and inter-annual variability of Kangerlussuaq runoff, and provided an acceptable degree of agreement between simulated and observed runoff. The simulated spatial runoff distributions, in some areas of the GrIS terminus, were as high as 2,750 mm w.eq. of runoff for 2006/07, while only 900 mm w.eq was simulated for 2007/08. The simulated total runoff from Kangerlussuaq was 1.9 km{sup 3} for 2006/07 and 1.2 km{sup 3} for 2007/08, indicating a reduction of 35-40% caused by the climate conditions and changes in the GrIS freshwater storage. The reduction in runoff from 2006/07 to 2007/08 occurred simultaneously with the reduction in the overall pattern of satellite-derived GrIS surface melt from 2007 to 2008.« less

  10. NHM-SMAP: spatially and temporally high-resolution nonhydrostatic atmospheric model coupled with detailed snow process model for Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Niwano, Masashi; Aoki, Teruo; Hashimoto, Akihiro; Matoba, Sumito; Yamaguchi, Satoru; Tanikawa, Tomonori; Fujita, Koji; Tsushima, Akane; Iizuka, Yoshinori; Shimada, Rigen; Hori, Masahiro

    2018-02-01

    To improve surface mass balance (SMB) estimates for the Greenland Ice Sheet (GrIS), we developed a 5 km resolution regional climate model combining the Japan Meteorological Agency Non-Hydrostatic atmospheric Model and the Snow Metamorphism and Albedo Process model (NHM-SMAP) with an output interval of 1 h, forced by the Japanese 55-year reanalysis (JRA-55). We used in situ data to evaluate NHM-SMAP in the GrIS during the 2011-2014 mass balance years. We investigated two options for the lower boundary conditions of the atmosphere: an offline configuration using snow, firn, and ice albedo, surface temperature data from JRA-55, and an online configuration using values from SMAP. The online configuration improved model performance in simulating 2 m air temperature, suggesting that the surface analysis provided by JRA-55 is inadequate for the GrIS and that SMAP results can better simulate physical conditions of snow/firn/ice. It also reproduced the measured features of the GrIS climate, diurnal variations, and even a strong mesoscale wind event. In particular, it successfully reproduced the temporal evolution of the GrIS surface melt area extent as well as the record melt event around 12 July 2012, at which time the simulated melt area extent reached 92.4 %. Sensitivity tests showed that the choice of calculation schemes for vertical water movement in snow and firn has an effect as great as 200 Gt year-1 in the GrIS-wide accumulated SMB estimates; a scheme based on the Richards equation provided the best performance.

  11. Atmospheric Drivers of Greenland Surface Melt Revealed by Self-Organizing Maps

    NASA Technical Reports Server (NTRS)

    Mioduszewski, J. R.; Rennermalm, A. K.; Hammann, A.; Tedesco, M.; Noble, E. U.; Stroeve, J. C.; Mote, T. L.

    2016-01-01

    Recent acceleration in surface melt on the Greenland ice sheet (GrIS) has occurred concurrently with a rapidly warming Arctic and has been connected to persistent, anomalous atmospheric circulation patterns over Greenland. To identify synoptic setups favoring enhanced GrIS surface melt and their decadal changes, we develop a summer Arctic synoptic climatology by employing self-organizing maps. These are applied to daily 500 hPa geopotential height fields obtained from the Modern Era Retrospective Analysis for Research and Applications reanalysis, 1979-2014. Particular circulation regimes are related to meteorological conditions and GrIS surface melt estimated with outputs from the Modèle Atmosphérique Régional. Our results demonstrate that the largest positive melt anomalies occur in concert with positive height anomalies near Greenland associated with wind, temperature, and humidity patterns indicative of strong meridional transport of heat and moisture. We find an increased frequency in a 500 hPa ridge over Greenland coinciding with a 63% increase in GrIS melt between the 1979-1988 and 2005-2014 periods, with 75.0% of surface melt changes attributed to thermodynamics, 17% to dynamics, and 8.0% to a combination. We also confirm that the 2007-2012 time period has the largest dynamic forcing relative of any period but also demonstrate that increased surface energy fluxes, temperature, and moisture separate from dynamic changes contributed more to melt even during this period. This implies that GrIS surface melt is likely to continue to increase in response to an ever warmer future Arctic, regardless of future atmospheric circulation patterns.

  12. Greenland ice sheet surface mass-balance modeling in a 131-year perspective, 1950-2080

    SciT

    Mernild, Sebastian Haugard; Liston, Glen; Hiemstra, Christopher

    2009-01-01

    Fluctuations in the Greenland Ice Sheet (GrIS) surface mass-balance (SMB) and freshwater influx to the surrounding oceans closely follow climate fluctuations and are of considerable importance to the global eustatic sea level rise. SnowModel, a state-of-the-art snow-evolution modeling system, was used to simulate variations in the GrIS melt extent, surface water balance components, changes in SMB, and freshwater influx to the ocean. The simulations are based on the IPCC scenario AlB modeled by the HIRHAM4 RCM (using boundary conditions from ECHAM5 AOGCM) from 1950 through 2080. In-situ meteorological station (GC-Net and WMO DMI) observations from inside and outside the GrISmore » were used to validate and correct RCM output data before it was used as input for SnowModel. Satellite observations and independent SMB studies were used to validate the SnowModel output and confirm the model's robustness. We simulated a {approx}90% increase in end-of-summer surface melt extent (0.483 x 10{sup 6} km{sup 2}) from 1950 to 2080, and a melt index (above 2,000-m elevation) increase of 138% (1.96 x 10{sup 6} km{sup 2} x days). The greatest difference in melt extent occured in the southern part of the GrIS, and the greatest changes in the number of melt days was seen in the eastern part of the GrIS ({approx}50-70%) and was lowest in the west ({approx}20-30%). The rate of SMB loss, largely tied to changes in ablation processes, lead to an enhanced average loss of 331 km{sup 3} from 1950 to 2080, an average 5MB level of -99 km{sup 3} for the period 2070-2080. GrIS surface freshwater runoff yielded an eustatic rise in sea level from 0.8 {+-} 0.1 (1950-1959) to 1.9 {+-} 0.1 mm (2070-2080) sea level equivalent (SLE) y{sup -1}. The accumulated GrIS freshwater runoff contribution from surface melting equaled 160 mm SLE from 1950 through 2080.« less

  13. Abrupt Greenland Ice Sheet runoff and sea water temperature changes since 1821, recorded by coralline algae

    NASA Astrophysics Data System (ADS)

    Kamenos, N.; Hoey, T.; Bedford, J.; Claverie, T.; Fallick, A. E.; Lamb, C. M.; Nienow, P. W.; O'Neill, S.; Shepherd, I.; Thormar, J.

    2012-12-01

    The Greenland Ice Sheet (GrIS) contains the largest store of fresh water in the northern hemisphere, equivalent to ~7.4m of eustatic sea level rise, but its impacts on current, past and future sea level, ocean circulation and European climate are poorly understood. Previous estimates of GrIS melt, from 26 years of satellite observations and temperature driven melt-models over 48 years, show a trend of increasing melt. There are however no runoff data of comparable duration with which to validate temperature-based runoff models, or relationships between the spatial extent of melt and runoff. Further, longer runoff records that extend GrIS melt records to centennial timescales will enable recently observed trends to be put into a better historical context. We measured Mg/Ca, δ18O and structural cell size in annual growth bands of red coralline algae to reconstruct: (1) near surface sea water temperature; and, (2) melt/runoff from the GrIS. (1) Temperature: we reconstructed the longest (1821-2009) sub-annual resolution record of water temperature in Disko Bugt (western Greenland) showing an abrupt change in temperature oscillation patterns during the 1920s which may be attributable to the interaction between atmospheric temperature and mass loss from Jakobshavn Isbrae glacier. (2) GrIS runoff: using samples from distal parts of Søndre Strømfjord we produced the first reconstruction of decadal (1939-2002) GrIS runoff. We observed significant negative relationships between historic runoff, relative salinity and marine summer temperature. Our reconstruction shows a trend of increasing reconstructed runoff since the mid 1980s. In situ summer marine temperatures followed a similar trend. We suggest that since 1939 atmospheric temperatures have been important in forcing runoff. Subject to locating in situ coralline algae samples, these methods can be applied across hundreds to thousands of years. These results show that our technique has significant potential to enhance

  14. Reconstructing Southern Greenland Ice Sheet History During the Plio-Pleistocene Intensification of Northern Hemisphere Glaciation: Insights from IODP Site U1307

    NASA Astrophysics Data System (ADS)

    Blake-Mizen, K. R.; Hatfield, R. G.; Carlson, A. E.; Walczak, M. H.; Stoner, J. S.; Xuan, C.; Lawrence, K. T.; Bailey, I.

    2017-12-01

    Should it melt entirely, the Greenland Ice Sheet (GrIS) has the potential to raise global sea-level by 7 metres. With the Arctic continuing to warm at a remarkable rate, to better understand how the GrIS will respond to future anthropogenically-induced climate change we must constrain its natural variability in the geological past. In this regard, much uncertainty exists surrounding its pre-Quaternary history; particularly during the mid-Piacenzian warm period (mPWP; 3.3-3.0 Ma) - widely considered an analogue for near-future equilibrium climate with modern atmospheric CO2 levels and elevated temperatures relative to today - and the late Pliocene/early Pleistocene onset of widespread Northern Hemisphere glaciation (NHG, 2.7 Ma). GrIS reconstructions for these intervals have been largely hampered by a lack of well-dated, high-resolution records from suitable sites. To address this, we present new high-resolution, multi-proxy records from IODP Site U1307, a North Atlantic marine sediment core recovered from the Eirik Drift just south of Greenland. Generation of a new high-resolution relative palaeointensity (RPI)-based age-model - representing the first of its kind for high-latitude sediments deposited during NHG - has enabled strong orbital age control. Our ice-rafted debris (IRD) record confirms a 2.72 Ma initiation of major southern GrIS marine-terminating glaciations, which appear to persist even through interglacial periods up to at least 2.24 Ma. XRF-scanning and IRD evidence suggests, however, that an ephemeral ice-cap of likely considerable size persisted on southern Greenland prior to the mPWP. These data, together with the analysed provenance of individual IRD, indicate marine-based GrIS margins extended southward over the NHG interval and only occurred on Greenland's southern tip from 2.7 Ma. Despite a large increase in the deposition of GrIS-derived IRD from this time, bulk sedimentation rates and magnetic grain-size dropped significantly, implying that

  15. Airborne geophysical investigations of basal conditions at flow transitions of outlet glaciers on the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Palmer, S. J.; Dowdeswell, J. A.; Christoffersen, P.; Siegert, M. J.; Blankenship, D. D.; Young, D. A.; Greenbaum, J.

    2011-12-01

    Recent observations have shown that the fast flowing marine-terminating outlet glaciers which drain the Greenland Ice Sheet (GrIS) have thinned in places at rates in excess of 10 m yr-1. The 21 largest outlet glaciers in Greenland accelerated by 57 % between 1996 and 2005, leading to a 100 Gt yr-1 increase in mass loss due to ice discharge over the same period and a 150 % increase of the GrIS's contribution to sea level. Observations that thinning rates are greater than those expected from changes in surface mass balance alone suggest thinning of some GrIS marine-terminating outlet glaciers can be attributed to changes in ice dynamics. An important question for both scientists and policy makers is how the GrIS will react to projected temperature increases, particularly in the context that the Arctic is likely to warm at a greater rate than the global average due to the ice-albedo feedback. As the combined width of all major marine-terminating glaciers draining the GrIS (as measured at the narrowest point in each case) is less 200 km, an understanding of their dynamics is crucial in predicting the effect of future warming on the ice sheet as a whole. During April 2011, we used a Basler BT-67 aircraft equipped with a suite of geophysical instruments to investigate three major glacier systems in Greenland. Data were acquired at the Sermeq Kujatdl and Rink Glacier systems in West Greenland; and Daugaard Jensen Glacier in East Greenland. The study areas were selected because they are major drainage basins (c. 103-105 km2) which provide a high ice flux to the sea (c. 10-20 km3 yr-1); and are located in different regions of the GrIS with correspondingly different atmospheric and oceanic settings. Here we present results from the High Capability Radar Sounder instrument, a phase coherent VHF ice-penetrating radar which operates in frequency-chirped mode from 52.5 to 67.5 MHz. We use these data to determine ice thickness along flightlines both parallel and perpendicular to

  16. Simulation of the Greenland Ice Sheet over two glacial-interglacial cycles: investigating a sub-ice-shelf melt parameterization and relative sea level forcing in an ice-sheet-ice-shelf model

    NASA Astrophysics Data System (ADS)

    Bradley, Sarah L.; Reerink, Thomas J.; van de Wal, Roderik S. W.; Helsen, Michiel M.

    2018-05-01

    Observational evidence, including offshore moraines and sediment cores, confirm that at the Last Glacial Maximum (LGM) the Greenland ice sheet (GrIS) expanded to a significantly larger spatial extent than seen at present, grounding into Baffin Bay and out onto the continental shelf break. Given this larger spatial extent and its close proximity to the neighbouring Laurentide Ice Sheet (LIS) and Innuitian Ice Sheet (IIS), it is likely these ice sheets will have had a strong non-local influence on the spatial and temporal behaviour of the GrIS. Most previous paleo ice-sheet modelling simulations recreated an ice sheet that either did not extend out onto the continental shelf or utilized a simplified marine ice parameterization which did not fully include the effect of ice shelves or neglected the sensitivity of the GrIS to this non-local bedrock signal from the surrounding ice sheets. In this paper, we investigated the evolution of the GrIS over the two most recent glacial-interglacial cycles (240 ka BP to the present day) using the ice-sheet-ice-shelf model IMAU-ICE. We investigated the solid earth influence of the LIS and IIS via an offline relative sea level (RSL) forcing generated by a glacial isostatic adjustment (GIA) model. The RSL forcing governed the spatial and temporal pattern of sub-ice-shelf melting via changes in the water depth below the ice shelves. In the ensemble of simulations, at the glacial maximums, the GrIS coalesced with the IIS to the north and expanded to the continental shelf break to the southwest but remained too restricted to the northeast. In terms of the global mean sea level contribution, at the Last Interglacial (LIG) and LGM the ice sheet added 1.46 and -2.59 m, respectively. This LGM contribution by the GrIS is considerably higher (˜ 1.26 m) than most previous studies whereas the contribution to the LIG highstand is lower (˜ 0.7 m). The spatial and temporal behaviour of the northern margin was highly variable in all simulations

  17. Spatial Variability of accumulation across the Western Greenland Ice Sheet Percolation Zone from ground-penetrating-radar and shallow firn cores

    NASA Astrophysics Data System (ADS)

    Lewis, G.; Osterberg, E. C.; Hawley, R. L.; Marshall, H. P.; Birkel, S. D.; Meehan, T. G.; Graeter, K.; Overly, T. B.; McCarthy, F.

    2017-12-01

    The mass balance of the Greenland Ice Sheet (GrIS) in a warming climate is of critical interest to scientists and the general public in the context of future sea-level rise. Increased melting in the GrIS percolation zone over the past several decades has led to increased mass loss at lower elevations due to recent warming. Uncertainties in mass balance are especially large in regions with sparse and/or outdated in situ measurements. This study is the first to calculate in situ accumulation over a large region of western Greenland since the Program for Arctic Regional Climate Assessment campaign during the 1990s. Here we analyze 5000 km of 400 MHz ground penetrating radar data and sixteen 25-33 m-long firn cores in the western GrIS percolation zone to determine snow accumulation over the past 50 years. The cores and radar data were collected as part of the 2016-2017 Greenland Traverse for Accumulation and Climate Studies (GreenTrACS). With the cores and radar profiles we capture spatial accumulation gradients between 1850-2500 m a.s.l and up to Summit Station. We calculate accumulation rates and use them to validate five widely used regional climate models and to compare with IceBridge snow and accumulation radars. Our results indicate that while the models capture most regional spatial climate patterns, they lack the small-scale spatial variability captured by in situ measurements. Additionally, we evaluate temporal trends in accumulation at ice core locations and throughout the traverse. Finally, we use empirical orthogonal function and correlation analyses to investigate the principal drivers of radar-derived accumulation rates across the western GrIS percolation zone, including major North Atlantic climate modes such as the North Atlantic Oscillation, Atlantic Multidecadal Oscillation, and Greenland Blocking Index.

  18. Quantifying ocean and ice sheet contributions to nutrient fluxes in Sermilik Fjord, Southeast Greenland

    NASA Astrophysics Data System (ADS)

    Cape, M. R.; Straneo, F.; Beaird, N.; Bundy, R.; Charette, M. A.

    2016-12-01

    Meltwater discharged at the margins of the Greenland Ice Sheet (GrIS) represents a potential source of nutrients to biological communities downstream. In Greenland's glacial fjords, this discharge occurs at depth below and along the face of deeply grounded marine-terminating glaciers. This process drives vigorous circulation and mixing between melt and ambient waters at the ice-ocean margins, giving rise to a new glacially modified water mass (GMW) which constitutes the primary vehicle for transport of meltwater in the marine environment. While previous field studies have noted nutrient enrichment in GMW with respect to unmodified waters along the shelf, the source of this enrichment, whether due to entrainment of deep ambient waters or input by meltwater, remains poorly understood. This knowledge is however critical in order to evaluate the current and future contributions of the GrIS to marine biogeochemical cycling. Here we shed light on the distribution, composition, and properties of GMW along the GrIS margin by analyzing integrated physical and chemical measurements collected in August 2015 in Sermilik Fjord, a major glacial freshwater export pathway. Our results document up to a doubling of nutrient concentrations (nitrate, silicate, phosphate, and iron) in GMW, which is distributed in the top 300 m of the water column throughout the fjord. Partitioning of ocean and ice sheet contributions to GMW nutrient load demonstrates that upwelled waters are the primary source of macro-nutrients to GMW. We expand on these results to discuss the magnitude of fluxes in context of previous observations along the GrIS margins, export pathways of GMW to the shelf, and knowledge gaps needed to be addressed to better constrain ice sheet contributions to marine ecosystem processes.

  19. Greenland's glacial fjords and their role in regional biogeochemical dynamics.

    NASA Astrophysics Data System (ADS)

    Crosby, J.; Arndt, S.

    2017-12-01

    Greenland's coastal fjords serve as important pathways that connect the Greenland Ice Sheet (GrIS) and the surrounding oceans. They export seasonal glacial meltwater whilst being significant sites of primary production. These fjords are home to some of the most productive ecosystems in the world and possess high socio-economic value via fisheries. A growing number of studies have proposed the GrIS as an underappreciated yet significant source of nutrients to surrounding oceans. Acting as both transfer routes and sinks for glacial nutrient export, fjords have the potential to act as significant biogeochemical processors, yet remain underexplored. Critically, an understanding of the quantitative contribution of fjords to carbon and nutrient budgets is lacking, with large uncertainties associated with limited availability of field data and the lack of robust upscaling approaches. To close this knowledge gap we developed a coupled 2D physical-biogeochemical model of the Godthåbsfjord system, a sub-Arctic sill fjord in southwest Greenland, to quantitatively assess the impact of nutrients exported from the GrIS on fjord primary productivity and biogeochemical dynamics. Glacial meltwater is found to be a key driver of fjord-scale circulation patterns, whilst tracer simulations reveal the relative nutrient contributions from meltwater-driven upwelling and meltwater export from the GrIS. Hydrodynamic circulation patterns and freshwater transit times are explored to provide a first understanding of the glacier-fjord-ocean continuum, demonstrating the complex pattern of carbon and nutrient cycling at this critical land-ocean interface.

  20. Increasing Freshwater Runoff and Tidal Action Influences on Spatial Mixing Patterns in Søndre Strømfjord, West Greenland

    NASA Astrophysics Data System (ADS)

    Smiley, C. R.; Kamenos, N.; Hoey, T.; Cottier, F.; Ellam, R. M.

    2014-12-01

    Greenland Ice Sheet melt has the potential to affect global sea levels and the strength of the thermohaline circulation (THC). Investigating spatial mixing patterns of seawater in Greenlandic fjords can help reveal characteristics of changes in runoff from the GrIS; for example higher runoff may be associated with lower salinity within GrIS fjords, which can be recorded by palaeoenvironmental proxies (Kamenos et al 2012). The Kangerlussuaq Drainage Basin mirrors melt patterns of the whole GrIS and drains into Søndre Strømfjord, a 170km long fjord on the west coast of Greenland. Temperature and salinity profiles to 40m depth were obtained at 11 stations along Søndre Strømfjord during the 2014 melt season. Each station was sampled twice once at high KDB runoff and once at low KDB runoff. With increasing freshwater runoff, salinity decreases by 1.65 - 2.91 at each station over a 7 hour time period. Higher salinities occur at low run-off. In addition, with increasing run-off, the disparity between surface and deeper water (30m) becomes greater with a 19.3 difference between the surface and 30m. With higher KDB runoff temperature increases by 0.47oC - 2.34oC. This information will be integrated with oxygen and deuterium isotope patterns to pinpoint the exact source of the runoff causing salinity reductions. Our data show a relationship between KDB runoff and salinity of Søndre Strømfjord, data that will enable further calibration of marine proxies of GrIS melt.

  1. Concepts for a global resources information system

    NASA Technical Reports Server (NTRS)

    Billingsley, F. C.; Urena, J. L.

    1984-01-01

    The objective of the Global Resources Information System (GRIS) is to establish an effective and efficient information management system to meet the data access requirements of NASA and NASA-related scientists conducting large-scale, multi-disciplinary, multi-mission scientific investigations. Using standard interfaces and operating guidelines, diverse data systems can be integrated to provide the capabilities to access and process multiple geographically dispersed data sets and to develop the necessary procedures and algorithms to derive global resource information.

  2. Geodetic measurements reveal similarities between post-Last Glacial Maximum and present-day mass loss from the Greenland ice sheet.

    PubMed

    Khan, Shfaqat A; Sasgen, Ingo; Bevis, Michael; van Dam, Tonie; Bamber, Jonathan L; Wahr, John; Willis, Michael; Kjær, Kurt H; Wouters, Bert; Helm, Veit; Csatho, Beata; Fleming, Kevin; Bjørk, Anders A; Aschwanden, Andy; Knudsen, Per; Munneke, Peter Kuipers

    2016-09-01

    Accurate quantification of the millennial-scale mass balance of the Greenland ice sheet (GrIS) and its contribution to global sea-level rise remain challenging because of sparse in situ observations in key regions. Glacial isostatic adjustment (GIA) is the ongoing response of the solid Earth to ice and ocean load changes occurring since the Last Glacial Maximum (LGM; ~21 thousand years ago) and may be used to constrain the GrIS deglaciation history. We use data from the Greenland Global Positioning System network to directly measure GIA and estimate basin-wide mass changes since the LGM. Unpredicted, large GIA uplift rates of +12 mm/year are found in southeast Greenland. These rates are due to low upper mantle viscosity in the region, from when Greenland passed over the Iceland hot spot about 40 million years ago. This region of concentrated soft rheology has a profound influence on reconstructing the deglaciation history of Greenland. We reevaluate the evolution of the GrIS since LGM and obtain a loss of 1.5-m sea-level equivalent from the northwest and southeast. These same sectors are dominating modern mass loss. We suggest that the present destabilization of these marine-based sectors may increase sea level for centuries to come. Our new deglaciation history and GIA uplift estimates suggest that studies that use the Gravity Recovery and Climate Experiment satellite mission to infer present-day changes in the GrIS may have erroneously corrected for GIA and underestimated the mass loss by about 20 gigatons/year.

  3. Microbial Degradation of 2,4-Dichlorophenoxyacetic Acid on the Greenland Ice Sheet

    PubMed Central

    Stibal, Marek; Bælum, Jacob; Holben, William E.; Sørensen, Sebastian R.; Jensen, Anders

    2012-01-01

    The Greenland ice sheet (GrIS) receives organic carbon (OC) of anthropogenic origin, including pesticides, from the atmosphere and/or local sources, and the fate of these compounds in the ice is currently unknown. The ability of supraglacial heterotrophic microbes to mineralize different types of OC is likely a significant factor determining the fate of anthropogenic OC on the ice sheet. Here we determine the potential of the microbial community from the surface of the GrIS to mineralize the widely used herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Surface ice cores were collected and incubated for up to 529 days in microcosms simulating in situ conditions. Mineralization of side chain- and ring-labeled [14C]2,4-D was measured in the samples, and quantitative PCR targeting the tfdA genes in total DNA extracted from the ice after the experiment was performed. We show that the supraglacial microbial community on the GrIS contains microbes that are capable of degrading 2,4-D and that they are likely present in very low numbers. They can mineralize 2,4-D at a rate of up to 1 nmol per m2 per day, equivalent to ∼26 ng C m−2 day−1. Thus, the GrIS should not be considered a mere reservoir of all atmospheric contaminants, as it is likely that some deposited compounds will be removed from the system via biodegradation processes before their potential release due to the accelerated melting of the ice sheet. PMID:22582066

  4. Evaluation of the Surface Representation of the Greenland Ice Sheet in a General Circulation Model

    NASA Technical Reports Server (NTRS)

    Cullather, Richard I.; Nowicki, Sophie M. J.; Zhao, Bin; Suarez, Max J.

    2014-01-01

    Simulated surface conditions of the Goddard Earth Observing System model, version 5 (GEOS 5) atmospheric general circulation model (AGCM) are examined for the contemporary Greenland Ice Sheet (GrIS). A surface parameterization that explicitly models surface processes including snow compaction, meltwater percolation and refreezing, and surface albedo is found to remedy an erroneous deficit in the annual net surface energy flux and provide an adequate representation of surface mass balance (SMB) in an evaluation using simulations at two spatial resolutions. The simulated 1980-2008 GrIS SMB average is 24.7+/-4.5 cm yr(- 1) water-equivalent (w.e.) at.5 degree model grid spacing, and 18.2+/-3.3 cm yr(- 1) w.e. for 2 degree grid spacing. The spatial variability and seasonal cycle of the simulation compare favorably to recent studies using regional climate models, while results from 2 degree integrations reproduce the primary features of the SMB field. In comparison to historical glaciological observations, the coarser resolution model overestimates accumulation in the southern areas of the GrIS, while the overall SMB is underestimated. These changes relate to the sensitivity of accumulation and melt to the resolution of topography. The GEOS-5 SMB fields contrast with available corresponding atmospheric models simulations from the Coupled Model Intercomparison Project (CMIP5). It is found that only a few of the CMIP5 AGCMs examined provide significant summertime runoff, a dominant feature of the GrIS seasonal cycle. This is a condition that will need to be remedied if potential contributions to future eustatic change from polar ice sheets are to be examined with GCMs.

  5. Response of the North Atlantic dynamic sea level and circulation to Greenland meltwater and climate change in an eddy-permitting ocean model

    NASA Astrophysics Data System (ADS)

    Saenko, Oleg A.; Yang, Duo; Myers, Paul G.

    2017-10-01

    The response of the North Atlantic dynamic sea surface height (SSH) and ocean circulation to Greenland Ice Sheet (GrIS) meltwater fluxes is investigated using a high-resolution model. The model is forced with either present-day-like or projected warmer climate conditions. In general, the impact of meltwater on the North Atlantic SSH and ocean circulation depends on the surface climate. In the two major regions of deep water formation, the Labrador Sea and the Nordic Seas, the basin-mean SSH increases with the increase of the GrIS meltwater flux. This SSH increase correlates with the decline of the Atlantic meridional overturning circulation (AMOC). However, while in the Labrador Sea the warming forcing and GrIS meltwater input lead to sea level rise, in the Nordic Seas these two forcings have an opposite influence on the convective mixing and basin-mean SSH (relative to the global mean). The warming leads to less sea-ice cover in the Nordic Seas, which favours stronger surface heat loss and deep mixing, lowering the SSH and generally increasing the transport of the East Greenland Current. In the Labrador Sea, the increased SSH and weaker deep convection are reflected in the decreased transport of the Labrador Current (LC), which closes the subpolar gyre in the west. Among the two major components of the LC transport, the thermohaline and bottom transports, the former is less sensitive to the GrIS meltwater fluxes under the warmer climate. The SSH difference across the LC, which is a component of the bottom velocity, correlates with the long-term mean AMOC rate.

  6. Regional Greenland accumulation variability from Operation IceBridge airborne accumulation radar

    NASA Astrophysics Data System (ADS)

    Lewis, Gabriel; Osterberg, Erich; Hawley, Robert; Whitmore, Brian; Marshall, Hans Peter; Box, Jason

    2017-03-01

    The mass balance of the Greenland Ice Sheet (GrIS) in a warming climate is of critical interest to scientists and the general public in the context of future sea-level rise. An improved understanding of temporal and spatial variability of snow accumulation will reduce uncertainties in GrIS mass balance models and improve projections of Greenland's contribution to sea-level rise, currently estimated at 0.089 ± 0.03 m by 2100. Here we analyze 25 NASA Operation IceBridge accumulation radar flights totaling > 17 700 km from 2013 to 2014 to determine snow accumulation in the GrIS dry snow and percolation zones over the past 100-300 years. IceBridge accumulation rates are calculated and used to validate accumulation rates from three regional climate models. Averaged over all 25 flights, the RMS difference between the models and IceBridge accumulation is between 0.023 ± 0.019 and 0.043 ± 0.029 m w.e. a-1, although each model shows significantly larger differences from IceBridge accumulation on a regional basis. In the southeast region, for example, the Modèle Atmosphérique Régional (MARv3.5.2) overestimates by an average of 20.89 ± 6.75 % across the drainage basin. Our results indicate that these regional differences between model and IceBridge accumulation are large enough to significantly alter GrIS surface mass balance estimates. Empirical orthogonal function analysis suggests that the first two principal components account for 33 and 19 % of the variance, and correlate with the Atlantic Multidecadal Oscillation (AMO) and wintertime North Atlantic Oscillation (NAO), respectively. Regions that disagree strongest with climate models are those in which we have the fewest IceBridge data points, requiring additional in situ measurements to verify model uncertainties.

  7. Geodetic measurements reveal similarities between post–Last Glacial Maximum and present-day mass loss from the Greenland ice sheet

    PubMed Central

    Khan, Shfaqat A.; Sasgen, Ingo; Bevis, Michael; van Dam, Tonie; Bamber, Jonathan L.; Wahr, John; Willis, Michael; Kjær, Kurt H.; Wouters, Bert; Helm, Veit; Csatho, Beata; Fleming, Kevin; Bjørk, Anders A.; Aschwanden, Andy; Knudsen, Per; Munneke, Peter Kuipers

    2016-01-01

    Accurate quantification of the millennial-scale mass balance of the Greenland ice sheet (GrIS) and its contribution to global sea-level rise remain challenging because of sparse in situ observations in key regions. Glacial isostatic adjustment (GIA) is the ongoing response of the solid Earth to ice and ocean load changes occurring since the Last Glacial Maximum (LGM; ~21 thousand years ago) and may be used to constrain the GrIS deglaciation history. We use data from the Greenland Global Positioning System network to directly measure GIA and estimate basin-wide mass changes since the LGM. Unpredicted, large GIA uplift rates of +12 mm/year are found in southeast Greenland. These rates are due to low upper mantle viscosity in the region, from when Greenland passed over the Iceland hot spot about 40 million years ago. This region of concentrated soft rheology has a profound influence on reconstructing the deglaciation history of Greenland. We reevaluate the evolution of the GrIS since LGM and obtain a loss of 1.5-m sea-level equivalent from the northwest and southeast. These same sectors are dominating modern mass loss. We suggest that the present destabilization of these marine-based sectors may increase sea level for centuries to come. Our new deglaciation history and GIA uplift estimates suggest that studies that use the Gravity Recovery and Climate Experiment satellite mission to infer present-day changes in the GrIS may have erroneously corrected for GIA and underestimated the mass loss by about 20 gigatons/year. PMID:27679819

  8. The diversity of ice algal communities on the Greenland Ice Sheet as revealed by oligotyping

    PubMed Central

    Lutz, Stefanie; McCutcheon, Jenine; McQuaid, James B.; Benning, Liane G.

    2018-01-01

    The Arctic is being disproportionally affected by climate change compared with other geographic locations, and is currently experiencing unprecedented melt rates. The Greenland Ice Sheet (GrIS) can be regarded as the largest supraglacial ecosystem on Earth, and ice algae are the dominant primary producers on bare ice surfaces throughout the course of a melt season. Ice-algal-derived pigments cause a darkening of the ice surface, which in turn decreases albedo and increases melt rates. The important role of ice algae in changing melt rates has only recently been recognized, and we currently know little about their community compositions and functions. Here, we present the first analysis of ice algal communities across a 100 km transect on the GrIS by high-throughput sequencing and subsequent oligotyping of the most abundant taxa. Our data reveal an extremely low algal diversity with Ancylonema nordenskiöldii and a Mesotaenium species being by far the dominant taxa at all sites. We employed an oligotyping approach and revealed a hidden diversity not detectable by conventional clustering of operational taxonomic units and taxonomic classification. Oligotypes of the dominant taxa exhibit a site-specific distribution, which may be linked to differences in temperatures and subsequently the extent of the melting. Our results help to better understand the distribution patterns of ice algal communities that play a crucial role in the GrIS ecosystem. PMID:29547098

  9. Continuous Estimates of Surface Density and Annual Snow Accumulation with Multi-Channel Snow/Firn Penetrating Radar in the Percolation Zone, Western Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Meehan, T.; Marshall, H. P.; Bradford, J.; Hawley, R. L.; Osterberg, E. C.; McCarthy, F.; Lewis, G.; Graeter, K.

    2017-12-01

    A priority of ice sheet surface mass balance (SMB) prediction is ascertaining the surface density and annual snow accumulation. These forcing data can be supplied into firn compaction models and used to tune Regional Climate Models (RCM). RCMs do not accurately capture subtle changes in the snow accumulation gradient. Additionally, leading RCMs disagree among each other and with accumulation studies in regions of the Greenland Ice Sheet (GrIS) over large distances and temporal scales. RCMs tend to yield inconsistencies over GrIS because of sparse and outdated validation data in the reanalysis pool. Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) implemented multi-channel 500 MHz Radar in multi-offset configuration throughout two traverse campaigns totaling greater than 3500 km along the western percolation zone of GrIS. The multi-channel radar has the capability of continuously estimating snow depth, average density, and annual snow accumulation, expressed at 95% confidence (+-) 0.15 m, (+-) 17 kgm-3, (+-) 0.04 m w.e. respectively, by examination of the primary reflection return from the previous year's summer surface.

  10. Cloning, sequencing, and analysis of the griseusin polyketide synthase gene cluster from Streptomyces griseus.

    PubMed Central

    Yu, T W; Bibb, M J; Revill, W P; Hopwood, D A

    1994-01-01

    A fragment of DNA was cloned from the Streptomyces griseus K-63 genome by using genes (act) for the actinorhodin polyketide synthase (PKS) of Streptomyces coelicolor as a probe. Sequencing of a 5.4-kb segment of the cloned DNA revealed a set of five gris open reading frames (ORFs), corresponding to the act PKS genes, in the following order: ORF1 for a ketosynthase, ORF2 for a chain length-determining factor, ORF3 for an acyl carrier protein, ORF5 for a ketoreductase, and ORF4 for a cyclase-dehydrase. Replacement of the gris genes with a marker gene in the S. griseus genome by using a single-stranded suicide vector propagated in Escherichia coli resulted in loss of the ability to produce griseusins A and B, showing that the five gris genes do indeed encode the type II griseusin PKS. These genes, encoding a PKS that is programmed differently from those for other aromatic PKSs so far available, will provide further valuable material for analysis of the programming mechanism by the construction and analysis of strains carrying hybrid PKS. Images PMID:8169211

  11. Modelling the climate and surface mass balance of polar ice sheets using RACMO2 - Part 1: Greenland (1958-2016)

    NASA Astrophysics Data System (ADS)

    Noël, Brice; van de Berg, Willem Jan; Melchior van Wessem, J.; van Meijgaard, Erik; van As, Dirk; Lenaerts, Jan T. M.; Lhermitte, Stef; Kuipers Munneke, Peter; Smeets, C. J. P. Paul; van Ulft, Lambertus H.; van de Wal, Roderik S. W.; van den Broeke, Michiel R.

    2018-03-01

    We evaluate modelled Greenland ice sheet (GrIS) near-surface climate, surface energy balance (SEB) and surface mass balance (SMB) from the updated regional climate model RACMO2 (1958-2016). The new model version, referred to as RACMO2.3p2, incorporates updated glacier outlines, topography and ice albedo fields. Parameters in the cloud scheme governing the conversion of cloud condensate into precipitation have been tuned to correct inland snowfall underestimation: snow properties are modified to reduce drifting snow and melt production in the ice sheet percolation zone. The ice albedo prescribed in the updated model is lower at the ice sheet margins, increasing ice melt locally. RACMO2.3p2 shows good agreement compared to in situ meteorological data and point SEB/SMB measurements, and better resolves the spatial patterns and temporal variability of SMB compared with the previous model version, notably in the north-east, south-east and along the K-transect in south-western Greenland. This new model version provides updated, high-resolution gridded fields of the GrIS present-day climate and SMB, and will be used for projections of the GrIS climate and SMB in response to a future climate scenario in a forthcoming study.

  12. Sustained High Basal Motion of the Greenland Ice Sheet Revealed by Borehole Deformation

    NASA Technical Reports Server (NTRS)

    Ryser, Claudia; Luthi, Martin P.; Andrews, Lauren C.; Hoffman, Matthew, J.; Catania, Ginny A.; Hawley, Robert L.; Neumann, Thomas A.; Kristensen, Steen S.

    2014-01-01

    Ice deformation and basal motion characterize the dynamical behavior of the Greenland ice sheet (GrIS). We evaluate the contribution of basal motion from ice deformation measurements in boreholes drilled to the bed at two sites in the western marginal zone of the GrIS. We find a sustained high amount of basal motion contribution to surface velocity of 44-73 percent in winter, and up to 90 percent in summer. Measured ice deformation rates show an unexpected variation with depth that can be explained with the help of an ice-flow model as a consequence of stress transfer from slippery to sticky areas. This effect necessitates the use of high-order ice-flow models, not only in regions of fast-flowing ice streams but in all temperate-based areas of the GrIS. The agreement between modeled and measured deformation rates confirms that the recommended values of the temperature-dependent flow rate factor A are a good choice for ice-sheet models.

  13. Assessing backscatter change due to backscatter gradient over the Greenland ice sheet using Envisat and SARAL altimetry

    NASA Astrophysics Data System (ADS)

    Su, Xiaoli; Luo, Zhicai; Zhou, Zebing

    2018-06-01

    Knowledge of backscatter change is important to accurately retrieve elevation change time series from satellite radar altimetry over continental ice sheets. Previously, backscatter coefficients generated in two cases, namely with and without accounting for backscatter gradient (BG), are used. However, the difference between backscatter time series obtained separately in these two cases and its impact on retrieving elevation change are not well known. Here we first compare the mean profiles of the Ku and Ka band backscatter over the Greenland ice sheet (GrIS), with results illustrating that the Ku-band backscatter is 3 ∼ 5 dB larger than that of the Ka band. We then conduct statistic analysis about time series of backscatter formed separately in the above two cases for both Ku and Ka bands over two regions in the GrIS. It is found that the standard deviation of backscatter time series becomes slightly smaller after removing the BG effect, which suggests that the method for the BG correction is effective. Furthermore, the impact on elevation change from backscatter change due to the BG effect is separately assessed for both Ku and Ka bands over the GrIS. We conclude that Ka band altimetry would benefit from a BG induced backscatter analysis (∼10% over region 2). This study may provide a reference to form backscatter time series towards refining elevation change time series from satellite radar altimetry over ice sheets using repeat-track analysis.

  14. Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics.

    PubMed

    Csatho, Beata M; Schenk, Anton F; van der Veen, Cornelis J; Babonis, Gregory; Duncan, Kyle; Rezvanbehbahani, Soroush; van den Broeke, Michiel R; Simonsen, Sebastian B; Nagarajan, Sudhagar; van Angelen, Jan H

    2014-12-30

    We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993-2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt ⋅ y(-1), equivalent to 0.68 mm ⋅ y(-1) sea level rise (SLR) for 2003-2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004-2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland's outlet glaciers.

  15. SciT

    Bakker, P.; Schmittner, A.; Lenaerts, J. T. M.

    The most recent Intergovernmental Panel on Climate Change assessment report concludes that the Atlantic Meridional Overturning Circulation (AMOC) could weaken substantially but is very unlikely to collapse in the 21st century. However, the assessment largely neglected Greenland Ice Sheet (GrIS) mass loss, lacked a comprehensive uncertainty analysis, and was limited to the 21st century. Here in a community effort, improved estimates of GrIS mass loss are included in multicentennial projections using eight state‐of‐the‐science climate models, and an AMOC emulator is used to provide a probabilistic uncertainty assessment. We find that GrIS melting affects AMOC projections, even though it is ofmore » secondary importance. By years 2090–2100, the AMOC weakens by 18% [−3%, −34%; 90% probability] in an intermediate greenhouse‐gas mitigation scenario and by 37% [−15%, −65%] under continued high emissions. Afterward, it stabilizes in the former but continues to decline in the latter to −74% [+4%, −100%] by 2290–2300, with a 44% likelihood of an AMOC collapse. This result suggests that an AMOC collapse can be avoided by CO2 mitigation.« less

  16. Northeast sector of the Greenland Ice Sheet to undergo the greatest inland expansion of supraglacial lakes during the 21st century

    NASA Astrophysics Data System (ADS)

    Ignéczi, Ádám.; Sole, Andrew J.; Livingstone, Stephen J.; Leeson, Amber A.; Fettweis, Xavier; Selmes, Nick; Gourmelen, Noel; Briggs, Kate

    2016-09-01

    The formation and rapid drainage of supraglacial lakes (SGL) influences the mass balance and dynamics of the Greenland Ice Sheet (GrIS). Although SGLs are expected to spread inland during the 21st century due to atmospheric warming, less is known about their future spatial distribution and volume. We use GrIS surface elevation model and regional climate model outputs to show that at the end of the 21st century (2070-2099) approximately 9.8 ± 3.9 km3 (+113% compared to 1980-2009) and 12.6 ± 5 km3 (+174%) of meltwater could be stored in SGLs under moderate and high representative concentration pathways (RCP 4.5 and 8.5), respectively. The largest increase is expected in the northeastern sector of the GrIS (191% in RCP 4.5 and 320% in RCP 8.5), whereas in west Greenland, where the most SGLs are currently observed, the future increase will be relatively moderate (55% in RCP 4.5 and 68% in RCP 8.5).

  17. Investigating the Impact of Aerosol Deposition on Snow Melt over the Greenland Ice Sheet Using a New Kernel

    NASA Astrophysics Data System (ADS)

    Li, Y.; Flanner, M.

    2017-12-01

    Accelerating surface melt on the Greenland Ice Sheet (GrIS) has led to a doubling of Greenland's contribution to global sea level rise during recent decades. The darkening effect due to black carbon (BC), dust, and other light absorbing impurities (LAI) enhances snow melt by boosting its absorption of solar energy. It is therefore important for coupled aerosol-climate and ice sheet models to include snow darkening effects from LAI, and yet most do not. In this study, we develop an aerosol deposition—snow melt kernel based on the Community Earth System Model (CESM) to investigate changes in melt flux due to variations in the amount and timing of aerosol deposition on the GrIS. The Community Land Model (CLM) component of CESM is driven with a large range of aerosol deposition fluxes to determine non-linear relationships between melt perturbation and deposition amount occurring in different months and location (thereby capturing variations in base state associated with elevation and latitude). The kernel product will include climatological-mean effects and standard deviations associated with interannual variability. Finally, the kernel will allow aerosol deposition fluxes from any global or regional aerosol model to be translated into surface melt perturbations of the GrIS, thus extending the utility of state-of-the-art aerosol models.

  18. Decreasing cloud cover drives the recent mass loss on the Greenland Ice Sheet

    PubMed Central

    Hofer, Stefan; Tedstone, Andrew J.; Fettweis, Xavier; Bamber, Jonathan L.

    2017-01-01

    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. PMID:28782014

  19. Relationship between dissolved organic matter quality and microbial community composition across polar glacial environments.

    PubMed

    Smith, H J; Dieser, M; McKnight, D M; SanClements, M D; Foreman, C M

    2018-05-14

    Vast expanses of Earth's surface are covered by ice, with microorganisms in these systems affecting local and global biogeochemical cycles. We examined microbial assemblages from habitats fed by glacial meltwater within the McMurdo Dry Valleys, Antarctica, and on the west Greenland Ice Sheet, (GrIS) evaluating potential physicochemical factors explaining trends in community structure. Microbial assemblages present in the different Antarctic dry valley habitats were dominated by Sphingobacteria and Flavobacteria, while Gammaproteobacteria and Sphingobacteria prevailed in west GrIS supraglacial environments. Microbial assemblages clustered by location (Canada Glacier, Cotton Glacier, west GrIS) and were separated by habitat type (i.e. ice, cryoconite holes, supraglacial lakes, sediment, and stream water). Community dissimilarities were strongly correlated with dissolved organic matter (DOM) quality. Microbial meltwater assemblages were most closely associated with different protein-like components of the DOM pool. Microbes in environments with mineral particles (i.e. stream sediments, cryoconite holes) were linked to DOM containing more humic-like fluorescence. Our results demonstrate the establishment of distinct microbial communities within ephemeral glacial meltwater habitats, with DOM-microbe interactions playing an integral role in shaping communities on local and polar spatial scales.

  20. Decreasing cloud cover drives the recent mass loss on the Greenland Ice Sheet.

    PubMed

    Hofer, Stefan; Tedstone, Andrew J; Fettweis, Xavier; Bamber, Jonathan L

    2017-06-01

    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.

  1. Ice Core Records of West Greenland Melt and Climate Forcing

    NASA Astrophysics Data System (ADS)

    Graeter, K. A.; Osterberg, E. C.; Ferris, D. G.; Hawley, R. L.; Marshall, H. P.; Lewis, G.; Meehan, T.; McCarthy, F.; Overly, T.; Birkel, S. D.

    2018-04-01

    Remote sensing observations and climate models indicate that the Greenland Ice Sheet (GrIS) has been losing mass since the late 1990s, mostly due to enhanced surface melting from rising summer temperatures. However, in situ observational records of GrIS melt rates over recent decades are rare. Here we develop a record of frozen meltwater in the west GrIS percolation zone preserved in seven firn cores. Quantifying ice layer distribution as a melt feature percentage (MFP), we find significant increases in MFP in the southernmost five cores over the past 50 years to unprecedented modern levels (since 1550 CE). Annual to decadal changes in summer temperatures and MFP are closely tied to changes in Greenland summer blocking activity and North Atlantic sea surface temperatures since 1870. However, summer warming of 1.2°C since 1870-1900, in addition to warming attributable to recent sea surface temperature and blocking variability, is a critical driver of high modern MFP levels.

  2. CdZnTe Background Measurements at Balloon Altitudes with PoRTIA

    NASA Technical Reports Server (NTRS)

    Parsons, A.; Barthelmy, S.; Bartlett, L.; Gehrels, N.; Naya, J.; Stahle, C. M.; Tueller, J.; Teegarden, B.

    2003-01-01

    Measurements of the CdZnTe internal background at balloon altitudes are essential to determine which physical processes make the most important background contributions. We present results from CdZnTe background measurements made by PoRTIA, a small CdZnTe balloon instrument that was flown three times in three different shielding configurations. PoRTIA was passively shielded during its first flight from Palestine, Texas and actively shielded as a piggyback instrument on the GRIS balloon experiment during its second and third flights from Alice Springs, Australia, using the thick GRIS Nal anticoincidence shield. A significant CdZnTe background reduction was achieved during the third flight with PoRTIA placed completely inside the GRIS shield and blocking crystal, and thus completely surrounded by 15 cm of Nal. A unique balloon altitude background data set is provided by CdZnTe and Ge detectors simultaneously surrounded by the same thick anticoincidence shield; the presence of a single coxial Ge detector inside the shield next to PoRTIA allowed a measurement of the ambient neutron flux inside the shield throughout the flight. These neutrons interact with the detector material to produce isomeric states of the Cd, Zn and Te nuclei that radiatively decay; calculations are presented that indicate that these decays may explain most of the fully shielded CdZnTe background.

  3. Biomarker signature of Greenland sediments: from modern rivers and soils to MIS 5e and 11 records

    NASA Astrophysics Data System (ADS)

    Lupker, M.; Anspach, J.; Haghipour, N.; Eglinton, T. I.

    2016-12-01

    Better constraining the evolution of the Greenland Ice Sheet (GrIS) is crucial for a broader understanding of past and future climate changes. Previous studies reported that the GrIS was significantly smaller during interglacial periods MIS 5e and MIS 11 than at present [1,2], which suggests that a bigger fraction of Greenland was covered by vegetation and soils. To investigate whether terrestrial biomarkers provide new constraints on the dynamics of the GrIS over the past interglacials, we characterised the biomarker composition (GDGTs and n-alkanes), as well as the bulk geochemistry (TOC, δ13C, C-14), of modern sediments from southwestern Greenland and of Eirik Drift core IODP-303-U1305 over MIS5e and 11. Rivers in southwestern Greenland constitute the main link between the Greenland Ice Sheet (GrIS) and the ocean. Understanding the composition of suspended river sediments gives insights into the source of organic carbon that is mobilised and further exported to the ocean. To address these questions, biomarkers in suspended sediments and soils coming from Kangerlussuaq, southwestern Greenland, were measured. Kangerlussuaq is located in the most sensitive region of Greenland with regard to climate change, and is a good analogue for interglacials. Preliminary results (e.g. biomarker concentrations, MAT, CPI, ACL) show that soils or lakes are not the only source of organic matter in these rivers, and suggest that part of the biomarker signature is inherited from older, presently subglacial, organic pools. The Eirik Drift accumulates material that is eroded from the eastern and southern Greenland margin, and it has been shown to record significant environmental changes of the GrIS over MIS 5e and MIS 11 [1,2,3]. However, the GDGT and n-alkane characterisation of drift sediments from IODP-303-U1305 do not show a significant response of the biomarker record to these interglacials. [1] Colville, E. J., et al., 2011 - Science 333, 620-623. [2] Reyes, A. V., et al., 2014

  4. A downscaled 1 km dataset of daily Greenland ice sheet surface mass balance components (1958-2014)

    NASA Astrophysics Data System (ADS)

    Noel, B.; Van De Berg, W. J.; Fettweis, X.; Machguth, H.; Howat, I. M.; van den Broeke, M. R.

    2015-12-01

    The current spatial resolution in regional climate models (RCMs), typically around 5 to 20 km, remains too coarse to accurately reproduce the spatial variability in surface mass balance (SMB) components over the narrow ablation zones, marginal outlet glaciers and neighbouring ice caps of the Greenland ice sheet (GrIS). In these topographically rough terrains, the SMB components are highly dependent on local variations in topography. However, the relatively low-resolution elevation and ice mask prescribed in RCMs contribute to significantly underestimate melt and runoff in these regions due to unresolved valley glaciers and fjords. Therefore, near-km resolution topography is essential to better capture SMB variability in these spatially restricted regions. We present a 1 km resolution dataset of daily GrIS SMB covering the period 1958-2014, which is statistically downscaled from data of the polar regional climate model RACMO2.3 at 11 km, using an elevation dependence. The dataset includes all individual SMB components projected on the elevation and ice mask from the GIMP DEM, down-sampled to 1 km. Daily runoff and sublimation are interpolated to the 1 km topography using a local regression to elevation valid for each day specifically; daily precipitation is bi-linearly downscaled without elevation corrections. The daily SMB dataset is then reconstructed by summing downscaled precipitation, sublimation and runoff. High-resolution elevation and ice mask allow for properly resolving the narrow ablation zones and valley glaciers at the GrIS margins, leading to significant increase in runoff estimate. In these regions, and especially over narrow glaciers tongues, the downscaled products improve on the original RACMO2.3 outputs by better representing local SMB patterns through a gradual ablation increase towards the GrIS margins. We discuss the impact of downscaling on the SMB components in a case study for a spatially restricted region, where large elevation

  5. Dark ice dynamics of the south-west Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Tedstone, Andrew J.; Bamber, Jonathan L.; Cook, Joseph M.; Williamson, Christopher J.; Fettweis, Xavier; Hodson, Andrew J.; Tranter, Martyn

    2017-11-01

    Runoff from the Greenland Ice Sheet (GrIS) has increased in recent years due largely to changes in atmospheric circulation and atmospheric warming. Albedo reductions resulting from these changes have amplified surface melting. Some of the largest declines in GrIS albedo have occurred in the ablation zone of the south-west sector and are associated with the development of dark ice surfaces. Field observations at local scales reveal that a variety of light-absorbing impurities (LAIs) can be present on the surface, ranging from inorganic particulates to cryoconite materials and ice algae. Meanwhile, satellite observations show that the areal extent of dark ice has varied significantly between recent successive melt seasons. However, the processes that drive such large interannual variability in dark ice extent remain essentially unconstrained. At present we are therefore unable to project how the albedo of bare ice sectors of the GrIS will evolve in the future, causing uncertainty in the projected sea level contribution from the GrIS over the coming decades. Here we use MODIS satellite imagery to examine dark ice dynamics on the south-west GrIS each year from 2000 to 2016. We quantify dark ice in terms of its annual extent, duration, intensity and timing of first appearance. Not only does dark ice extent vary significantly between years but so too does its duration (from 0 to > 80 % of June-July-August, JJA), intensity and the timing of its first appearance. Comparison of dark ice dynamics with potential meteorological drivers from the regional climate model MAR reveals that the JJA sensible heat flux, the number of positive minimum-air-temperature days and the timing of bare ice appearance are significant interannual synoptic controls. We use these findings to identify the surface processes which are most likely to explain recent dark ice dynamics. We suggest that whilst the spatial distribution of dark ice is best explained by outcropping of particulates from

  6. Recent Rise in West Greenland Surface Melt and Firn Density Driven by North Atlantic SSTs and Blocking Events

    NASA Astrophysics Data System (ADS)

    Osterberg, E. C.; Graeter, K.; Hawley, R. L.; Marshall, H. P.; Ferris, D. G.; Lewis, G.; Birkel, S. D.; Meehan, T.; McCarthy, F.

    2017-12-01

    The Greenland Ice Sheet (GrIS) has been losing mass since at least the early 2000s, mostly due to enhanced surface melt. Approximately 40% of the surface melt currently generated on the GrIS percolates into the snow/firn and refreezes, where it has no immediate impact on GrIS mass balance or sea-level rise. However, in situ observations of surface melt are sparse, and thus it remains unclear how melt water percolation and refreezing are modifying the GrIS percolation zone under recent warming. In addition, understanding the climatic drivers behind the recent increase in melt is critical for accurately predicting future GrIS surface melt rates and contributions to sea-level rise. Here we show that there have been significant increases in melt refreeze and firn density over the past 30-50 years along a 250 km-long region of the Western Greenland percolation zone (2137 - 2218 m elevation). We collected seven shallow firn cores as part of the 2016 Greenland Traverse for Accumulation and Climate Studies (GreenTrACS), analyzed each for melt layer stratigraphy and density, and developed timescales for each based on annual layer counting of seasonal chemical oscillations (e.g. δ18O, dust, and biogenic sulfur). The cores indicate that refrozen melt layers have increased 2- to 9-fold since 1970, with statistically significant (p < 0.05) linear trends at the five southernmost core sites. Comparisons of two GreenTrACS cores to co-located PARCA cores collected in 1998 reveal significant (p < 0.05) increases in density averaged over the top 10 m of firn ranging from 32-42 kg/m3. Recent density increases closely correspond with the locations of refrozen melt water. We use output from the MARv3.7 Regional Climate Model to assess climatic forcing of surface melt at GreenTrACS sites, and find significant summer-to-summer correlations between melt generation and the frequency of blocking high pressure centers over Greenland (represented by the Greenland Blocking Index; GBI), and

  7. Modelling the Climate - Greenland Ice Sheet Interaction in the Coupled Ice-sheet/Climate Model EC-EARTH - PISM

    NASA Astrophysics Data System (ADS)

    Yang, S.; Madsen, M. S.; Rodehacke, C. B.; Svendsen, S. H.; Adalgeirsdottir, G.

    2014-12-01

    Recent observations show that the Greenland ice sheet (GrIS) has been losing mass with an increasing speed during the past decades. Predicting the GrIS changes and their climate consequences relies on the understanding of the interaction of the GrIS with the climate system on both global and local scales, and requires climate model systems with an explicit and physically consistent ice sheet module. A fully coupled global climate model with a dynamical ice sheet model for the GrIS has recently been developed. The model system, EC-EARTH - PISM, consists of the EC-EARTH, an atmosphere, ocean and sea ice model system, and the Parallel Ice Sheet Model (PISM). The coupling of PISM includes a modified surface physical parameterization in EC-EARTH adapted to the land ice surface over glaciated regions in Greenland. The PISM ice sheet model is forced with the surface mass balance (SMB) directly computed inside the EC-EARTH atmospheric module and accounting for the precipitation, the surface evaporation, and the melting of snow and ice over land ice. PISM returns the simulated basal melt, ice discharge and ice cover (extent and thickness) as boundary conditions to EC-EARTH. This coupled system is mass and energy conserving without being constrained by any anomaly correction or flux adjustment, and hence is suitable for investigation of ice sheet - climate feedbacks. Three multi-century experiments for warm climate scenarios under (1) the RCP85 climate forcing, (2) an abrupt 4xCO2 and (3) an idealized 1% per year CO2 increase are performed using the coupled model system. The experiments are compared with their counterparts of the standard CMIP5 simulations (without the interactive ice sheet) to evaluate the performance of the coupled system and to quantify the GrIS feedbacks. In particular, the evolution of the Greenland ice sheet under the warm climate and its impacts on the climate system are investigated. Freshwater fluxes from the Greenland ice sheet melt to the Arctic

  8. Stable isotope hydrology in fractured and detritic aquifers at both sides of the South Atlantic Ocean: Mar del Plata (Argentina) and the Rawsonville and Sandspruit river catchment areas (South Africa)

    NASA Astrophysics Data System (ADS)

    Glok Galli, Melisa; Damons, Matthew E.; Siwawa, Sitembiso; Bocanegra, Emilia M.; Nel, Jacobus M.; Mazvimavi, Dominic; Martínez, Daniel E.

    2017-01-01

    The aim of this work is to characterize the isotope composition of water (2H and 18O) in order to establish the relationship between fractured and detritic aquifers in similar hydrological environments located at both sides of the Atlantic Ocean. The Mar del Plata zone, placed in the Argentine Buenos Aires province in South America, and the Rawsonville and Sandspruit river catchment areas, situated in the Western Cape province in South Africa were compared. Rainwater and groundwater samples from fractured and detritic aquifers were analyzed through laser spectroscopy. In both Argentina and South African study sites, stable isotopes data demonstrate an aquifers recharge source from rainfall. For the Mar del Plata region, two different groups of detritic aquifer's samples with distinct recharge processes can be identified due to the close relationship existing between the present hydrogeological environments, the aquifer's grain size sediments and the isotopes contents: one representing rapid infiltration in aquifer sediments of the creeks' palaeobeds and hills zones (sandy or silt sandy sediments) and the other with slow infiltration of evaporated water in plain zones with an aquitard behavior. In the last group, the evaporation process occurs previous infiltration or in the aquifer's non-saturated zone, because of the existence of very low topographic gradients and fine-grained sediments. The evaporation phenomenon is not evident in the Sandspruit river catchment site's detritic aquifer, because its sandy composition allows a faster infiltration rate than in the loess that compounds the Pampeano aquifer in the interfluves zones of the Argentinian study area.

  9. The present-day climate of Greenland : a study with a regional climate model

    NASA Astrophysics Data System (ADS)

    Ettema, J.

    2010-04-01

    Present-day climate of Greenland Over the past 20 years, the Greenland ice sheet (GrIS) has warmed. This temperature increase can be explained by an increase in downwelling longwave radiation due to a warmer overlying atmosphere. These temperature changes are strongly correlated to changes in the large scale circulation over the ice sheet. Since 1990, the melt has also strongly increased along the ice margins, inducing significant increase in runoff. With no significant change found in the total precipitation, the GrIS surface mass balance (SMB) decreased by 12 Gt yr-1 or 7 kg m-2 yr-1 since 1990. Locally, the SMB trend reaches -90 kg m-2 yr-1 at the western and eastern ice margins. These conclusions are drawn from a modelling study by Janneke Ettema, which discusses the present-day climate and surface mass balance of the GrIS. The emphasis of this research is on understanding the underlying physical processes. Using the regional atmospheric climate model RACMO2/GR at high horizontal resolution (11km) has resulted in unprecedented detail in the ice sheet climatology and SMB. By incorporating processes such as percolation, retention and refreezing of meltwater in the surface parameterisation, the model explicitly calculates how these processes affect snow pack temperature, density and surface albedo. RACMO2/GR shows that the GrIS climate is spatially very variable. Characteristic for the ice sheet climate are the persistent katabatic winds and a quasi-permanent surface temperature deficit. Due to strong radiative cooling and turbulent heat transport towards the surface, the atmospheric boundary layer cools, providing optimal conditions for strong katabatic winds to occur. The strongest temperature deficit and wind speeds are found in the northeastern part of the ice sheet, whereas in the lower ablation zone the temperatures are more moderate due to surface melt and warm air advection. The high-resolution climate model revealed that the surface mass balance of the GrIS

  10. Re-emergence of rabies virus maintained by canid populations in Paraguay.

    PubMed

    Amarilla, A C F; Pompei, J C A; Araujo, D B; Vázquez, F A; Galeano, R R; Delgado, L M; Bogado, G; Colman, M; Sanabria, L; Iamamoto, K; Garcia, R; Assis, D; Recalde, R; Martorelli, L F; Quiñones, E; Cabello, A; Martini, M; Cosivi, O; Durigon, E L; Favoretto, S R

    2018-02-01

    Paraguay has registered no human cases of rabies since 2004, and the last case in dogs, reported in 2009, was due to a variant maintained in the common vampire bat "Desmodus rotundus". In 2014, a dog was diagnosed as positive for rabies with aggression towards a boy and all required measures of control were successfully adopted. Epidemiological investigation revealed that the dog was not vaccinated and had been attacked by a crab-eating fox, "zorro" (Cerdocyon thous). The sample was diagnosed by the Official Veterinary Service of the Country and sent to the Center on Rabies Research from the University of São Paulo, Brazil, for antigenic and genetic characterization. A second sample from a dog positive for rabies in the same region in 2015 and 11 samples from a rabies outbreak from Asuncion in 1996 were also characterized. The antigenic profile of the samples, AgV2, was compatible with one of the variants maintained by dogs in Latin America. In genetic characterization, the samples segregated in the canine (domestic and wild species)-related group in an independent subgroup that also included samples from Argentina. These results and the epidemiology of the case indicate that even with the control of rabies in domestic animals, the virus can still circulate in wildlife and may be transmitted to domestic animals and humans, demonstrating the importance of continuous and improved surveillance and control of rabies, including in wild species, to prevent outbreaks in controlled areas. © 2017 Blackwell Verlag GmbH.

  11. Greenland Ice Sheet exports labile organic carbon to the Arctic oceans

    NASA Astrophysics Data System (ADS)

    Lawson, E. C.; Wadham, J. L.; Tranter, M.; Stibal, M.; Lis, G. P.; Butler, C. E. H.; Laybourn-Parry, J.; Nienow, P.; Chandler, D.; Dewsbury, P.

    2014-07-01

    Runoff from small glacier systems contains dissolved organic carbon (DOC) rich in protein-like, low molecular weight (LMW) compounds, designating glaciers as an important source of bioavailable carbon for downstream heterotrophic activity. Fluxes of DOC and particulate organic carbon (POC) exported from large Greenland catchments, however, remain unquantified, despite the Greenland Ice Sheet (GrIS) being the largest source of global glacial runoff (ca. 400 km3 yr-1). We report high and episodic fluxes of POC and DOC from a large (>600 km2) GrIS catchment during contrasting melt seasons. POC dominates organic carbon (OC) export (70-89% on average), is sourced from the ice sheet bed, and contains a significant bioreactive component (9% carbohydrates). A major source of the "bioavailable" (free carbohydrate) LMW-DOC fraction is microbial activity on the ice sheet surface, with some further addition of LMW-DOC to meltwaters by biogeochemical processes at the ice sheet bed. The bioavailability of the exported DOC (26-53%) to downstream marine microorganisms is similar to that reported from other glacial watersheds. Annual fluxes of DOC and free carbohydrates during two melt seasons were similar, despite the approximately two-fold difference in runoff fluxes, suggesting production-limited DOC sources. POC fluxes were also insensitive to an increase in seasonal runoff volumes, indicating a supply limitation in suspended sediment in runoff. Scaled to the GrIS, the combined DOC (0.13-0.17 Tg C yr-1 (±13%)) and POC fluxes (mean = 0.36-1.52 Tg C yr-1 (±14%)) are of a similar order of magnitude to a large Arctic river system, and hence may represent an important OC source to the near-coastal North Atlantic, Greenland and Labrador seas.

  12. Greenland Ice Sheet exports labile organic carbon to the Arctic oceans

    NASA Astrophysics Data System (ADS)

    Lawson, E. C.; Wadham, J. L.; Tranter, M.; Stibal, M.; Lis, G. P.; Butler, C. E. H.; Laybourn-Parry, J.; Nienow, P.; Chandler, D.; Dewsbury, P.

    2013-12-01

    Runoff from small glacier systems contains dissolved organic carbon (DOC), rich in protein-like, low molecular weight (LMW) compounds, designating glaciers as an important source of bioavailable carbon for downstream heterotrophic activity. Fluxes of DOC and particulate organic carbon (POC) exported from large Greenland catchments, however, remain unquantified, despite the Greenland Ice Sheet (GrIS) being the largest source of global glacial runoff (ca. 400 km3 yr-1). We report high and episodic fluxes of POC and DOC from a large (1200 km2) GrIS catchment during contrasting melt seasons. POC dominates organic carbon (OC) export (70-89% on average), is sourced from the ice sheet bed and contains a significant bioreactive component (9% carbohydrates). A major source for the "bioavailable" (free carbohydrates) LMW-DOC fraction is microbial activity on the ice sheet surface, with some further addition of LMW-DOC to meltwaters by biogeochemical processes at the ice sheet bed. The bioavailability of the exported DOC (30-58%) to downstream marine microorganisms is similar to that reported from other glacial watersheds. Annual fluxes of DOC and free carbohydrates during two melt seasons were similar, despite the ~ 2 fold difference in runoff fluxes, suggesting production-limited DOC sources. POC fluxes were also insensitive to an increase in seasonal runoff volumes, indicating supply-limitation of suspended sediment in runoff. Scaled to the GrIS, the combined DOC and POC fluxes (0.13-0.17 Tg C yr-1 DOC, 0.36-1.52 Tg C yr-1 mean POC) are of a similar order of magnitude to a large Arctic river system, and hence represent an important OC source to the North Atlantic, Greenland and Labrador Seas.

  13. Continuous, Pulsed Export of Methane-Supersaturated Meltwaters from the Bed of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Lamarche-Gagnon, G.; Wadham, J.; Beaton, A.; Fietzek, P.; Stanley, K. M.; Tedstone, A.; Sherwood Lollar, B.; Lacrampe Couloume, G.; Telling, J.; Liz, B.; Hawkings, J.; Kohler, T. J.; Zarsky, J. D.; Stibal, M.; Mowlem, M. C.

    2016-12-01

    Both past and present ice sheets have been proposed to cap large quantities of methane (CH4), on orders of magnitude significant enough to impact global greenhouse gas concentrations during periods of rapid ice retreat. However, to date most evidence for sub-ice sheet methane has been indirect, derived from calculations of the methanogenic potential of basal-ice microbial communities and biogeochemical models; field-based empirical measurements are lacking from large ice sheet catchments. Here, we present the first continuous, in situ record of dissolved methane export from a large catchment of the Greenland Ice Sheet (GrIS) in South West Greenland from May-July 2015. Our results indicate that glacial runoff was continuously supersaturated with methane over the observation period (dissolved CH4 concentrations of 30-700 nM), with total methane flux rising as subglacial discharge increased. Periodic subglacial drainage events, characterised by rapid changes (i.e. pulses) in meltwater hydrochemistry, also coincided with a rise in methane concentrations. We argue that these are likely indicative of the flushing of subglacial reservoirs of CH4 beneath the ice sheet. Total methane export was relatively modest when compared to global methane budgets, but too high to be explained by previously determined methanogenic rates from Greenland basal ice. Discrepancies between estimated Greenland methane reserves and observed fluxes stress the need to further investigate GrIS methane fluxes and sources, and suggest a more biogeochemically active subglacial environment than previously considered. Results indicate that future warming, and a coincident increase in ice melt rates, would likely make the GrIS, and by extension the Antarctic Ice Sheet, more significant sources of atmospheric methane, consequently acting as a positive feedback to a warming climate.

  14. Bimodal albedo distributions in the ablation zone of the southwestern Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Moustafa, S. E.; Rennermalm, A. K.; Smith, L. C.; Miller, M. A.; Mioduszewski, J. R.

    2014-09-01

    Surface albedo is a key variable controlling solar radiation absorbed at the Greenland Ice Sheet (GrIS) surface, and thus, meltwater production. Recent decline in surface albedo over the GrIS has been linked to enhanced snow grain metamorphic rates and amplified ice-albedo feedback from atmospheric warming. However, the importance of distinct surface types on ablation zone albedo and meltwater production is still relatively unknown, and excluded in surface mass balance models. In this study, we analyze albedo and ablation rates using in situ and remotely-sensed data. Observations include: (1) a new high-quality in situ spectral albedo dataset collected with an Analytical Spectral Devices (ASD) spectroradiometer measuring at 325-1075 nm, along a 1.25 km transect during three days in June 2013; (2) broadband albedo at two automatic weather stations; and (3) daily MODerate Resolution Imaging Spectroradiometer (MODIS) albedo (MOD10A1) between 31 May and 30 August. We find that seasonal ablation zone albedos have a bimodal distribution, with two alternate states. This suggests that an abrupt switch from high to low albedo can be triggered by a modest melt event, resulting in amplified surface ablation rates. Our results show that such a shift corresponds to an observed melt rate percent difference increase of 51.6% during peak melt season (between 10-14 and 20-24 July 2013). Furthermore, our findings demonstrate that seasonal changes in GrIS ablation zone albedo are not exclusively a function of a darkening surface from ice crystal growth, but rather are controlled by changes in the fractional coverage of snow, bare ice, and impurity-rich surface types. As the climate continues to warm, regional climate models should consider the seasonal evolution of ice surface types in Greenland's ablation zone to improve projections of mass loss contributions to sea level rise.

  15. Bimodal Albedo Distributions in the Ablation Zone of the Southwestern Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Moustafa, S.; Rennermalm, A. K.; Smith, L. C.; Miller, M. A.; Mioduszewski, J.; Koenig, L.

    2014-12-01

    Surface albedo is a key variable controlling solar radiation absorbed at the Greenland Ice Sheet (GrIS) surface, and thus meltwater production. Recent decline in surface albedo over the GrIS has been linked to enhanced snow grain metamorphic rates and amplified ice-albedo feedback from atmospheric warming. However, the importance of distinct surface types on ablation zone albedo and meltwater production is still relatively unknown, and excluded in surface mass balance models. In this study, we analyze albedo and ablation rates (m d-1) using in situ and remotely-sensed data. Observations include: 1) a new high-quality in situ spectral albedo dataset collected with an Analytical Spectral Devices (ASD) spectroradiometer measuring at 325-1075 nm, along a 1.25 km transect during three days in June 2013; 2) broadband albedo at two automatic weather stations; and 3) daily MODerate Resolution Imaging Spectroradiometer (MODIS) albedo (MOD10A1) between 31 May and 30 August. We find that seasonal ablation zone albedos have a bimodal distribution, with two alternate states. This suggests that an abrupt switch from high to low albedo can be triggered by a modest melt event, resulting in amplified ablation rates. Our results show that such a shift corresponds to an observed melt rate percent difference increase of 51.6% during peak melt season (between 10-14 July and 20-24 July, 2013). Furthermore, our findings demonstrate that seasonal changes in GrIS ablation zone albedo are not exclusively a function of a darkening surface from ice crystal growth, but rather are controlled by changes in the fractional coverage of snow, bare ice, and impurity-rich surface types. As the climate continues to warm, regional climate models should consider the seasonal evolution of ice surface types in Greenland's ablation zone to improve projections of mass loss contributions to sea level rise.

  16. Greenland uplift and regional sea level changes from ICESat observations and GIA modelling

    NASA Astrophysics Data System (ADS)

    Spada, G.; Ruggieri, G.; Sørensen, L. S.; Nielsen, K.; Melini, D.; Colleoni, F.

    2012-06-01

    We study the implications of a recently published mass balance of the Greenland ice sheet (GrIS), derived from repeated surface elevation measurements from NASA's ice cloud and land elevation satellite (ICESat) for the time period between 2003 and 2008. To characterize the effects of this new, high-resolution GrIS mass balance, we study the time-variations of various geophysical quantities in response to the current mass loss. They include vertical uplift and subsidence, geoid height variations, global patterns of sea level change (or fingerprints), and regional sea level variations along the coasts of Greenland. Long-wavelength uplifts and gravity variations in response to current or past ice thickness variations are obtained solving the sea level equation, which accounts for both the elastic and the viscoelastic components of deformation. To capture the short-wavelength components of vertical uplift in response to current ice mass loss, which is not resolved by satellite gravity observations, we have specifically developed a high-resolution regional elastic rebound (ER) model. The elastic component of vertical uplift is combined with estimates of the viscoelastic displacement fields associated with the process of glacial-isostatic adjustment (GIA), according to a set of published ice chronologies and associated mantle rheological profiles. We compare the sensitivity of global positioning system (GPS) observations along the coasts of Greenland to the ongoing ER and GIA. In notable contrast with past reports, we show that vertical velocities obtained by GPS data from five stations with sufficiently long records and from one tide gauge at the GrIS margins can be reconciled with model predictions based on the ICE-5G deglaciation model and the ER associated with the new ICESat-derived mass balance.

  17. Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics

    PubMed Central

    Csatho, Beata M.; Schenk, Anton F.; van der Veen, Cornelis J.; Babonis, Gregory; Duncan, Kyle; Rezvanbehbahani, Soroush; van den Broeke, Michiel R.; Simonsen, Sebastian B.; Nagarajan, Sudhagar; van Angelen, Jan H.

    2014-01-01

    We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993–2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt⋅y−1, equivalent to 0.68 mm⋅y−1 sea level rise (SLR) for 2003–2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004–2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland’s outlet glaciers. PMID:25512537

  18. Influence of glacial meltwater on global seawater δ234U

    NASA Astrophysics Data System (ADS)

    Arendt, Carli A.; Aciego, Sarah M.; Sims, Kenneth W. W.; Das, Sarah B.; Sheik, Cody; Stevenson, Emily I.

    2018-03-01

    We present the first published uranium-series measurements from modern Greenland Ice Sheet (GrIS) runoff and proximal seawater, and investigate the influence of glacial melt on global seawater δ234U over glacial-interglacial (g-ig) timescales. Climate reconstructions based on closed-system uranium-thorium (U/Th) dating of fossil corals assume U chemistry of seawater has remained stable over time despite notable fluctuations in major elemental compositions, concentrations, and isotopic compositions of global seawater on g-ig timescales. Deglacial processes increase weathering, significantly increasing U-series concentrations and changing the δ234U of glacial meltwater. Analyses of glacial discharge from GrIS outlet glaciers indicate that meltwater runoff has elevated U concentrations and differing 222Rn concentrations and δ234U compositions, likely due to variations in subglacial residence time. Locations with high δ234U have the potential to increase proximal seawater δ234U. To better understand the impact of bulk glacial melt on global seawater δ234U over time, we use a simple box model to scale these processes to periods of extreme deglaciation. We account for U fluxes from the GrIS, Antarctica, and large Northern Hemisphere Continental Ice Sheets, and assess sensitivity by varying melt volumes, duration and U flux input rates based on modern subglacial water U concentrations and compositions. All scenarios support the hypothesis that global seawater δ234U has varied by more than 1‰ through time as a function of predictable perturbations in continental U fluxes during g-ig periods.

  19. Assessing spatio-temporal variability and trends in modelled and measured Greenland Ice Sheet albedo (2000-2013)

    NASA Astrophysics Data System (ADS)

    Alexander, P. M.; Tedesco, M.; Fettweis, X.; van de Wal, R. S. W.; Smeets, C. J. P. P.; van den Broeke, M. R.

    2014-12-01

    Accurate measurements and simulations of Greenland Ice Sheet (GrIS) surface albedo are essential, given the role of surface albedo in modulating the amount of absorbed solar radiation and meltwater production. In this study, we assess the spatio-temporal variability of GrIS albedo during June, July, and August (JJA) for the period 2000-2013. We use two remote sensing products derived from data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS), as well as outputs from the Modèle Atmosphérique Régionale (MAR) regional climate model (RCM) and data from in situ automatic weather stations. Our results point to an overall consistency in spatio-temporal variability between remote sensing and RCM albedo, but reveal a difference in mean albedo of up to ~0.08 between the two remote sensing products north of 70° N. At low elevations, albedo values simulated by the RCM are positively biased with respect to remote sensing products by up to ~0.1 and exhibit low variability compared with observations. We infer that these differences are the result of a positive bias in simulated bare ice albedo. MODIS albedo, RCM outputs, and in situ observations consistently indicate a decrease in albedo of -0.03 to -0.06 per decade over the period 2003-2013 for the GrIS ablation area. Nevertheless, satellite products show a decline in JJA albedo of -0.03 to -0.04 per decade for regions within the accumulation area that is not confirmed by either the model or in situ observations. These findings appear to contradict a previous study that found an agreement between in situ and MODIS trends for individual months. The results indicate a need for further evaluation of high elevation albedo trends, a reconciliation of MODIS mean albedo at high latitudes, and the importance of accurately simulating bare ice albedo in RCMs.

  20. Modeled Response of Greenland Climate to the Presence of Biomass Burning-Based Absorbing Aerosols in the Atmosphere and Snow

    NASA Astrophysics Data System (ADS)

    Ward, J. L.; Flanner, M.; Bergin, M. H.; Courville, Z.; Dibb, J. E.; Polashenski, C.; Soja, A. J.; Strellis, B. M.; Thomas, J. L.

    2016-12-01

    Combustion of biomass material results in the emission of microscopic particles, some of which absorb incoming solar radiation. Including black carbon (BC), these absorbing species can affect regional climate through changes in the local column energy budgets, cloud direct and indirect effects, and atmospheric dynamical processes. The cryosphere, which consists of both snow and ice, is unusually susceptible to changes in radiation due to its characteristically high albedo. As the largest element of the cryosphere in the Northern Hemisphere, the Greenland Ice Sheet (GrIS) covers most of Greenland's terrestrial surface and, if subjected to the increased presence of light-absorbing impurities, could experience enhanced melt. A particularly enhanced melt episode of the GrIS occurred during July 2012; at the same time, large-scale biomass burning events were observed in Eurasia and North America. Observations showed that, at the same time, single-scattering albedo (SSA) was lower than average while aerosol optical depth (AOD) was high for the Greenland region. In this study, we apply idealized climate simulations to analyze how various aspects of Greenland's climate are affected by the enhanced presence of particulate matter in the atmospheric and on the surface of the GrIS. We employ the Community Earth System Model (CESM) with prescribed sea surface temperatures and active land and atmospheric components. Using four sets of modeling experiments, we perturb 1) only AOD, 2) only SSA, 3) mass mixing ratios of BC and dust in snow, and 4) both AOD and in-snow impurity concentrations. The chosen values for each of these modeling experiments are based on field measurements taken in 2011 (AOD, SSA) and the summers of 2012-2014 (mass mixing ratios of BC and dust). Comparing the results of these experiments provides information on how the overall climate of Greenland could be affected by large biomass burning events.

  1. Increasing freshwater runoff and tidal action influences on spatial mixing patterns in Søndre Strømfjord, West Greenland.

    NASA Astrophysics Data System (ADS)

    Smiley, Crystal; Kamenos, Nick; Hoey, Trevor; Cottier, Finlo; Ellam, Rob

    2015-04-01

    Greenland Ice Sheet melt has the potential to affect global sea levels and the strength of the thermohaline circulation (THC). Investigating spatial mixing patterns of seawater in Greenlandic fjords can help reveal characteristics of changes in runoff from the GrIS; for example higher runoff may be associated with lower salinity within GrIS fjords, which can be recorded by palaeoenvironmental proxies (Kamenos et al 2012). The Kangerlussuaq Drainage Basin mirrors melt patterns of the whole GrIS and drains into Søndre Strømfjord, a 170km long fjord on the west coast of Greenland. Temperature and salinity profiles to 40m depth were obtained at 11 stations along Søndre Strømfjord during the 2014 melt season. Each station was sampled twice once at high KDB runoff and once at low KDB runoff. With increasing freshwater runoff, salinity decreased by 1.65 - 2.91 and temperature increased by 0.47oC- 2.34oC at each station over a 7 hour time period. Higher salinities occurred at low run-off. In addition, with increasing run-off, the disparity between surface and deeper water (30m) salinity became greater with a 19.3 difference between the surface and 30m. This information was integrated with oxygen and deuterium isotopic signatures collected at 10 m depth from each station to pinpoint the exact source of the runoff causing salinity reductions. With increasing freshwater runoff, the chemistry of the fjord exhibits an enrichment of the heavier isotope. δ18Ovsmow values enrich by 7.40 permil while δDvsmow enrich 53.26 permil. Our data shows a relationship between KDB runoff, salinity, and oxygen, hydrogen isotopic chemistry of Søndre Strømfjord, data that will enable further calibration of marine proxies of GrIS melt. References Kamenos, N.A, Hoey, T.B, Nienow, P., Fallick, A.E., & Claverie, T., 2012: Reconstructing Greenland Ice Sheet runoff using coralline algae; Geological Society of America, Geology, doi: 10.1130/G33405.1

  2. The Darkening of the Greenland Ice Sheet: Trends, Drivers and Projections (1981-2100)

    NASA Technical Reports Server (NTRS)

    Tedesco, Marco; Doherty, Sarah; Fettweis, Xavier; Alexander, Patrick; Jeyaratnam, Jeyavinoth; Stroeve, Julienne

    2016-01-01

    The surface energy balance and meltwater production of the Greenland ice sheet (GrIS) are modulated by snow and ice albedo through the amount of absorbed solar radiation. Here we show, using space-borne multispectral data collected during the 3 decades from 1981 to 2012, that summertime surface albedo over the GrIS decreased at a statistically significant (99 %) rate of 0.02 decade(sup -1) between 1996 and 2012. Over the same period, albedo modelled by the Modele Atmospherique Regionale (MAR) also shows a decrease, though at a lower rate (approximately -0.01 decade(sup -1)) than that obtained from space-borne data. We suggest that the discrepancy between modelled and measured albedo trends can be explained by the absence in the model of processes associated with the presence of light-absorbing impurities. The negative trend in observed albedo is confined to the regions of the GrIS that undergo melting in summer, with the dry snow zone showing no trend. The period 1981-1996 also showed no statistically significant trend over the whole GrIS. Analysis of MAR outputs indicates that the observed albedo decrease is attributable to the combined effects of increased near-surface air temperatures, which enhanced melt and promoted growth in snow grain size and the expansion of bare ice areas, and to trends in light-absorbing impurities (LAI) on the snow and ice surfaces. Neither aerosol models nor in situ and remote sensing observations indicate increasing trends in LAI in the atmosphere over Greenland. Similarly, an analysis of the number of fires and BC emissions from fires points to the absence of trends for such quantities. This suggests that the apparent increase of LAI in snow and ice might be related to the exposure of a "dark band" of dirty ice and to increased consolidation of LAI at the surface with melt, not to increased aerosol deposition. Albedo projections through to the end of the century under different warming scenarios consistently point to continued

  3. Brief communication: Getting Greenland's glaciers right - a new data set of all official Greenlandic glacier names

    NASA Astrophysics Data System (ADS)

    Bjørk, A. A.; Kruse, L. M.; Michaelsen, P. B.

    2015-12-01

    Place names in Greenland can be difficult to get right, as they are a mix of Greenlandic, Danish, and other foreign languages. In addition, orthographies have changed over time. With this new data set, we give the researcher working with Greenlandic glaciers the proper tool to find the correct name for glaciers and ice caps in Greenland and to locate glaciers described in the historic literature with the old Greenlandic orthography. The data set contains information on the names of 733 glaciers, 285 originating from the Greenland Ice Sheet (GrIS) and 448 from local glaciers and ice caps (LGICs).

  4. Effect of repeated Ribavirin treatment on grapevine viruses.

    PubMed

    Komínek, P; Komínková, M; Jandová, B

    The effect of Ribavirin treatment for the chemotherapy of several grapevine viruses was evaluated. Four grapevine cultivars were repeatedly treated with Ribavirin in two different concentrations and with three different lengths of treatment. Repeating the Ribavirin treatment always had a significant effect on the number of healthy grapevine plants obtained. Ribavirin concentration and length of exposure showed a significant difference in sanitation of the Grapevine rupestris stem pitting-associated virus. During sanitation of the Grapevine Pinot gris virus and Grapevine fleck virus, those two factors did not show significant differences in the elimination of grapevine viruses.

  5. Recent thinning of Bowdoin Glacier, a marine terminating outlet glacier in northwestern Greenland

    NASA Astrophysics Data System (ADS)

    Tsutaki, S.; Sugiyama, S.; Sakakibara, D.; Sawagaki, T.; Maruyama, M.

    2014-12-01

    Ice discharge from calving glaciers has increased in the Greenland ice sheet (GrIS), and this increase plays important roles in the volume change of GrIS and its contribution to sea level rise. Thinning of GrIS calving glaciers has been studied by the differentiation of digital elevation models (DEMs) derived by satellite remote-sensing (RS). Such studies rely on the accuracy of DEMs, but calibration of RS data with ground based data is difficult. This is because field data on GrIS calving glaciers are few. In this study, we combined field and RS data to measure surface elevation change of Bowdoin Glacier, a marine terminating outlet glacier in northwestern Greenland (77°41'18″N, 68°29'47″W). The fast flowing part of the glacier is approximately 3 km wide and 10 km long. Ice surface elevation within 6 km from the glacier terminus was surveyed in the field in July 2013 and 2014, by using the global positioning system. We also measured the surface elevation over the glacier on August 20, 2007 and September 4, 2010, by analyzing Advanced Land Observing Satellite (ALOS), Panchromatic remote-sensing Instrument for Stereo Mapping (PRISM) images. We calibrated the satellite derived elevation data with our field measurements, and generated DEM for each year with a 25 m grid mesh. The field data and DEMs were compared to calculate recent glacier elevation change. Mean surface elevation change along the field survey profiles were -16.3±0.2 m (-5.3±0.1 m yr-1) in 2007-2010 and -10.8±0.2 m (-3.8±0.1 m yr-1) in 2010-2013. These rates are much greater than those observed on non-calving ice caps in the region, and similar to those reported for other calving glaciers in northwestern Greenland. Loss of ice was greater near the glacier terminus, suggesting the importance of ice dynamics and/or interaction with the ocean.

  6. Organic carbon export from the Greenland Ice Sheet: sources, sinks and downstream fluxes

    NASA Astrophysics Data System (ADS)

    Wadham, J. L.; Lawson, E.; Tranter, M.; Stibal, M.; Telling, J.; Lis, G. P.; Nienow, P. W.; Anesio, A. M.; Butler, C. E.

    2012-12-01

    Runoff from small glacier systems has been shown to contain dissolved organic carbon (DOC) rich in low molecular weight (LMW), and hence more labile forms, designating glaciers as an important source of carbon for downstream heterotrophic activity. Here we assess glacier surfaces as potential sources of labile DOC to downstream ecosystems, presenting data from a wide range of glacier systems to determine sources and sinks of DOC in glacial and proglacial systems. We subsequently focus upon the Greenland Ice Sheet (GrIS) which is the largest source of glacial runoff at present (400 km3 yr-1), with predicted increases in future decades. We report high fluxes of particulate organic carbon (POC), DOC and LMW labile fractions from a large GrIS catchment during two contrasting melt seasons. POC dominates OC export, is sourced from the ice sheet bed and contains a significant bioreactive component (~10% carbohydrates). The LMW-DOC "labile" fraction derives almost entirely from microbial activity on the ice sheet surface, which is supported by data from glacier systems also presented here. Annual fluxes of DOC, POC and labile components were lower in 2010 than 2009, despite a ~2 fold increase in runoff fluxes in 2010, suggesting production-limited DOC/POC sources. Scaled to the entire ice sheet, combined DOC and POC fluxes are of a similar order of magnitude to other large Arctic river systems and may represent an important source of organic carbon to the North Atlantic, Greenland and Labrador Seas.

  7. MuSICa image slicer prototype at 1.5-m GREGOR solar telescope

    NASA Astrophysics Data System (ADS)

    Calcines, A.; López, R. L.; Collados, M.; Vega Reyes, N.

    2014-07-01

    Integral Field Spectroscopy is an innovative technique that is being implemented in the state-of-the-art instruments of the largest night-time telescopes, however, it is still a novelty for solar instrumentation. A new concept of image slicer, called MuSICa (Multi-Slit Image slicer based on collimator-Camera), has been designed for the integral field spectrograph of the 4-m European Solar Telescope. This communication presents an image slicer prototype of MuSICa for GRIS, the spectrograph of the 1.5-m GREGOR solar telescope located at the Observatory of El Teide. MuSICa at GRIS reorganizes a 2-D field of view of 24.5 arcsec into a slit of 0.367 arcsec width by 66.76 arcsec length distributed horizontally. It will operate together with the TIP-II polarimeter to offer high resolution integral field spectropolarimetry. It will also have a bidimensional field of view scanning system to cover a field of view up to 1 by 1 arcmin.

  8. Changes in bacterioplankton community structure during early lake ontogeny resulting from the retreat of the Greenland Ice Sheet

    PubMed Central

    Peter, Hannes; Jeppesen, Erik; De Meester, Luc; Sommaruga, Ruben

    2018-01-01

    Retreating glaciers and ice sheets are among the clearest signs of global climate change. One consequence of glacier retreat is the formation of new meltwater-lakes in previously ice-covered terrain. These lakes provide unique opportunities to understand patterns in community organization during early lake ontogeny. Here, we analyzed the bacterial community structure and diversity in six lakes recently formed by the retreat of the Greenland Ice Sheet (GrIS). The lakes represented a turbidity gradient depending on their past and present connectivity to the GrIS meltwaters. Bulk (16S rRNA genes) and putatively active (16S rRNA) fractions of the bacterioplankton communities were structured by changes in environmental conditions associated to the turbidity gradient. Differences in community structure among lakes were attributed to both, rare and abundant community members. Further, positive co-occurrence relationships among phylogenetically closely related community members dominate in these lakes. Our results show that environmental conditions along the turbidity gradient structure bacterial community composition, which shifts during lake ontogeny. Rare taxa contribute to these shifts, suggesting that the rare biosphere has an important ecological role during early lakes ontogeny. Members of the rare biosphere may be adapted to the transient niches in these nutrient poor lakes. The directionality and phylogenetic structure of co-occurrence relationships indicate that competitive interactions among closely related taxa may be important in the most turbid lakes. PMID:29087379

  9. High resolution (1 km) positive degree-day modelling of Greenland ice sheet surface mass balance, 1870–2012 using reanalysis data

    SciT

    Wilton, David J.; Jowett, Amy; Hanna, Edward

    Here, we show results from a positive degree-day (PDD) model of Greenland ice sheet (GrIS) surface mass balance (SMB), 1870–2012, forced with reanalysis data. The model includes an improved daily temperature parameterization as compared with a previous version and is run at 1 km rather than 5 km resolution. The improvements lead overall to higher SMB with the same forcing data. We also compare our model with results from two regional climate models (RCMs). While there is good qualitative agreement between our PDD model and the RCMs, it usually results in lower precipitation and lower runoff but approximately equivalent SMB:more » mean 1979–2012 SMB (± standard deviation), in Gt a –1, is 382 ± 78 in the PDD model, compared with 379 ± 101 and 425 ± 90 for the RCMs. Comparison with in situ SMB observations suggests that the RCMs may be more accurate than PDD at local level, in some areas, although the latter generally compares well. Dividing the GrIS into seven drainage basins we show that SMB has decreased sharply in all regions since 2000. Finally we show correlation between runoff close to two calving glaciers and either calving front retreat or calving flux, this being most noticeable from the mid-1990s.« less

  10. Impact of MODIS Sensor Calibration Updates on Greenland Ice Sheet Surface Reflectance and Albedo Trends

    NASA Technical Reports Server (NTRS)

    Casey, Kimberly A.; Polashenski, Chris M.; Chen, Justin; Tedesco, Marco

    2017-01-01

    We evaluate Greenland Ice Sheet (GrIS) surface reflectance and albedo trends using the newly released Collection 6 (C6) MODIS (Moderate Resolution Imaging Spectroradiometer) products over the period 2001-2016. We find that the correction of MODIS sensor degradation provided in the new C6 data products reduces the magnitude of the surface reflectance and albedo decline trends obtained from previous MODIS data (i.e., Collection 5, C5). Collection 5 and 6 data product analysis over GrIS is characterized by surface (i.e., wet vs. dry) and elevation (i.e., 500-2000 m, 2000 m and greater) conditions over the summer season from 1 June to 31 August. Notably, the visible-wavelength declining reflectance trends identified in several bands of MODIS C5 data from previous studies are only slightly detected at reduced magnitude in the C6 versions over the dry snow area. Declining albedo in the wet snow and ice area remains over the MODIS record in the C6 product, albeit at a lower magnitude than obtained using C5 data. Further analyses of C6 spectral reflectance trends show both reflectance increases and decreases in select bands and regions, suggesting that several competing processes are contributing to Greenland Ice Sheet albedo change. Investigators using MODIS data for other ocean, atmosphere and/or land analyses are urged to consider similar re-examinations of trends previously established using C5 data.

  11. Holocene ice marginal fluctuations of the Qassimiut lobe in South Greenland

    PubMed Central

    Larsen, Nicolaj K.; Find, Jesper; Kristensen, Anders; Bjørk, Anders A.; Kjeldsen, Kristian K.; Odgaard, Bent V.; Olsen, Jesper; Kjær, Kurt H.

    2016-01-01

    Knowledge about the Holocene evolution of the Greenland ice sheet (GrIS) is important to put the recent observations of ice loss into a longer-term perspective. In this study, we use six new threshold lake records supplemented with two existing lake records to reconstruct the Holocene ice marginal fluctuations of the Qassimiut lobe (QL) – one of the most dynamic parts of the GrIS in South Greenland. Times when the ice margin was close to present extent are characterized by clastic input from the glacier meltwater, whereas periods when the ice margin was behind its present day extent comprise organic-rich sediments. We find that the overall pattern suggests that the central part of the ice lobe in low-lying areas experienced the most prolonged ice retreat from ~9–0.4 cal. ka BP, whereas the more distal parts of the ice lobe at higher elevation re-advanced and remained close to the present extent during the Neoglacial between ~4.4 and 1.8 cal. ka BP. These results demonstrate that the QL was primarily driven by Holocene climate changes, but also emphasises the role of local topography on the ice marginal fluctuations. PMID:26940998

  12. Greenland ice sheet mass balance: a review.

    PubMed

    Khan, Shfaqat A; Aschwanden, Andy; Bjørk, Anders A; Wahr, John; Kjeldsen, Kristian K; Kjær, Kurt H

    2015-04-01

    Over the past quarter of a century the Arctic has warmed more than any other region on Earth, causing a profound impact on the Greenland ice sheet (GrIS) and its contribution to the rise in global sea level. The loss of ice can be partitioned into processes related to surface mass balance and to ice discharge, which are forced by internal or external (atmospheric/oceanic/basal) fluctuations. Regardless of the measurement method, observations over the last two decades show an increase in ice loss rate, associated with speeding up of glaciers and enhanced melting. However, both ice discharge and melt-induced mass losses exhibit rapid short-term fluctuations that, when extrapolated into the future, could yield erroneous long-term trends. In this paper we review the GrIS mass loss over more than a century by combining satellite altimetry, airborne altimetry, interferometry, aerial photographs and gravimetry data sets together with modelling studies. We revisit the mass loss of different sectors and show that they manifest quite different sensitivities to atmospheric and oceanic forcing. In addition, we discuss recent progress in constructing coupled ice-ocean-atmosphere models required to project realistic future sea-level changes.

  13. Isostasy as a Driver of Paleo Retreat of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Robinson, A.; Tabone, I.; Alvarez-Solas, J.; Montoya, M.

    2016-12-01

    During glacial times, the Greenland ice sheet (GrIS) extended onto the continental shelf, and thus was much more directly affected by changing ocean temperatures through basal melt of the marine ice margins than it is today. The larger glacial ice sheet also induced lithospheric depression of several hundred meters in regions that are near sea level today. As the ice sheet retreated inland under interglacial climatic forcing, the regions significantly affected by local isostatic changes in elevation were exposed to much higher basal melt rates than they would have been given the present-day topography. Here we explore this effect using a hybrid ice sheet model that represents both grounded and floating ice, as well as local isostatic effects, and is driven by both atmospheric and oceanic temperature anomalies. We find that when transient oceanic forcing is included in the model, isostasy plays an important role in allowing oceanic melting to drive GrIS retreat in some regions. During the last interglacial, for example, this effect can account for a significant additional sea-level contribution, as well as an increase in the rate of sea-level rise. Our results highlight the importance of accounting for ice-ocean-lithosphere interactions in the past, in order to be able to properly reconstruct the evolution of the ice sheet, and for estimating its sensitivity to potential changes in climate in the future.

  14. Rational Design of Glucose-Responsive Insulin Using Pharmacokinetic Modeling.

    PubMed

    Bakh, Naveed A; Bisker, Gili; Lee, Michael A; Gong, Xun; Strano, Michael S

    2017-11-01

    A glucose responsive insulin (GRI) is a therapeutic that modulates its potency, concentration, or dosing of insulin in relation to a patient's dynamic glucose concentration, thereby approximating aspects of a normally functioning pancreas. Current GRI design lacks a theoretical basis on which to base fundamental design parameters such as glucose reactivity, dissociation constant or potency, and in vivo efficacy. In this work, an approach to mathematically model the relevant parameter space for effective GRIs is induced, and design rules for linking GRI performance to therapeutic benefit are developed. Well-developed pharmacokinetic models of human glucose and insulin metabolism coupled to a kinetic model representation of a freely circulating GRI are used to determine the desired kinetic parameters and dosing for optimal glycemic control. The model examines a subcutaneous dose of GRI with kinetic parameters in an optimal range that results in successful glycemic control within prescribed constraints over a 24 h period. Additionally, it is demonstrated that the modeling approach can find GRI parameters that enable stable glucose levels that persist through a skipped meal. The results provide a framework for exploring the parameter space of GRIs, potentially without extensive, iterative in vivo animal testing. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. High resolution (1 km) positive degree-day modelling of Greenland ice sheet surface mass balance, 1870–2012 using reanalysis data

    DOE PAGES

    Wilton, David J.; Jowett, Amy; Hanna, Edward; ...

    2016-12-15

    Here, we show results from a positive degree-day (PDD) model of Greenland ice sheet (GrIS) surface mass balance (SMB), 1870–2012, forced with reanalysis data. The model includes an improved daily temperature parameterization as compared with a previous version and is run at 1 km rather than 5 km resolution. The improvements lead overall to higher SMB with the same forcing data. We also compare our model with results from two regional climate models (RCMs). While there is good qualitative agreement between our PDD model and the RCMs, it usually results in lower precipitation and lower runoff but approximately equivalent SMB:more » mean 1979–2012 SMB (± standard deviation), in Gt a –1, is 382 ± 78 in the PDD model, compared with 379 ± 101 and 425 ± 90 for the RCMs. Comparison with in situ SMB observations suggests that the RCMs may be more accurate than PDD at local level, in some areas, although the latter generally compares well. Dividing the GrIS into seven drainage basins we show that SMB has decreased sharply in all regions since 2000. Finally we show correlation between runoff close to two calving glaciers and either calving front retreat or calving flux, this being most noticeable from the mid-1990s.« less

  16. Continuous summer export of nitrogen-rich organic matter from the Greenland Ice Sheet inferred by ultrahigh resolution mass spectrometry.

    PubMed

    Lawson, Emily C; Bhatia, Maya P; Wadham, Jemma L; Kujawinski, Elizabeth B

    2014-12-16

    Runoff from glaciers and ice sheets has been acknowledged as a potential source of bioavailable dissolved organic matter (DOM) to downstream ecosystems. This source may become increasingly significant as glacial melt rates increase in response to future climate change. Recent work has identified significant concentrations of bioavailable carbon and iron in Greenland Ice Sheet (GrIS) runoff. The flux characteristics and export of N-rich DOM are poorly understood. Here, we employed electrospray ionization (ESI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to determine the elemental compositions of DOM molecules in supraglacial water and subglacial runoff from a large GrIS outlet glacier. We provide the first detailed temporal analysis of the molecular composition of DOM exported over a full melt season. We find that DOM pools in supraglacial and subglacial runoff are compositionally diverse and that N-rich material is continuously exported throughout the melt season, as the snowline retreats further inland. Identification of protein-like compounds and a high proportion of N-rich DOM, accounting for 27-41% of the DOM molecules identified by ESI FT-ICR MS, may suggest a microbial provenance and high bioavailability of glacially exported DOM to downstream microbial communities.

  17. Multi-channel Ice Penetrating Radar Traverse for Estimates of Firn Density in the Percolation Zone, Western Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Meehan, T.; Osterberg, E. C.; Lewis, G.; Overly, T. B.; Hawley, R. L.; Bradford, J.; Marshall, H. P.

    2016-12-01

    To better predict the response of the Greenland Ice Sheet (GrIS) to future warming, leading edge Regional Climate Models (RCM) must be calibrated with in situ measurements of recent accumulation and melt. Mass balance estimates averaged across the entire Greenland Ice Sheet (GrIS) vary between models by more than 30 percent, and regional comparisons of mass balance reconstructions in Greenland vary by 100 percent or more. Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) is a multi-year and multi-disciplinary 1700 km science traverse from Raven/Dye2 in SW Greenland, to Summit Station. Multi-offset radar measurements can provide high accuracy electromagnetic (EM) velocity estimates of the firn to within (+-) 0.002 to 0.003 m/ns. EM velocity, in turn, can be used to estimate bulk firn density. Using a mixing equation such as the CRIM Equation we use the measured EM velocity, along with the known EM velocity in air and ice, to estimate bulk density. During spring 2016, we used multi-channel 500MHz radar in a multi-offset configuration to survey more than 800 km from Raven towards summit. Preliminary radar-derived snow density estimates agree with density estimates from a firn core measurement ( 50 kg/m3), despite the lateral heterogeneity of the firn across the length of the antenna array (12 m).

  18. A daily, 1 km resolution data set of downscaled Greenland ice sheet surface mass balance (1958-2015)

    NASA Astrophysics Data System (ADS)

    Noël, Brice; van de Berg, Willem Jan; Machguth, Horst; Lhermitte, Stef; Howat, Ian; Fettweis, Xavier; van den Broeke, Michiel R.

    2016-10-01

    This study presents a data set of daily, 1 km resolution Greenland ice sheet (GrIS) surface mass balance (SMB) covering the period 1958-2015. Applying corrections for elevation, bare ice albedo and accumulation bias, the high-resolution product is statistically downscaled from the native daily output of the polar regional climate model RACMO2.3 at 11 km. The data set includes all individual SMB components projected to a down-sampled version of the Greenland Ice Mapping Project (GIMP) digital elevation model and ice mask. The 1 km mask better resolves narrow ablation zones, valley glaciers, fjords and disconnected ice caps. Relative to the 11 km product, the more detailed representation of isolated glaciated areas leads to increased precipitation over the southeastern GrIS. In addition, the downscaled product shows a significant increase in runoff owing to better resolved low-lying marginal glaciated regions. The combined corrections for elevation and bare ice albedo markedly improve model agreement with a newly compiled data set of ablation measurements.

  19. Changes in bacterioplankton community structure during early lake ontogeny resulting from the retreat of the Greenland Ice Sheet.

    PubMed

    Peter, Hannes; Jeppesen, Erik; De Meester, Luc; Sommaruga, Ruben

    2017-10-31

    Retreating glaciers and ice sheets are among the clearest signs of global climate change. One consequence of glacier retreat is the formation of new meltwater-lakes in previously ice-covered terrain. These lakes provide unique opportunities to understand patterns in community organization during early lake ontogeny. Here, we analyzed the bacterial community structure and diversity in six lakes recently formed by the retreat of the Greenland Ice Sheet (GrIS). The lakes represented a turbidity gradient depending on their past and present connectivity to the GrIS meltwaters. Bulk (16S rRNA genes) and putatively active (16S rRNA) fractions of the bacterioplankton communities were structured by changes in environmental conditions associated to the turbidity gradient. Differences in community structure among lakes were attributed to both, rare and abundant community members. Further, positive co-occurrence relationships among phylogenetically closely related community members dominate in these lakes. Our results show that environmental conditions along the turbidity gradient structure bacterial community composition, which shifts during lake ontogeny. Rare taxa contribute to these shifts, suggesting that the rare biosphere has an important ecological role during early lakes ontogeny. Members of the rare biosphere may be adapted to the transient niches in these nutrient poor lakes. The directionality and phylogenetic structure of co-occurrence relationships indicate that competitive interactions among closely related taxa may be important in the most turbid lakes.The ISME Journal advance online publication, 31 October 2017; doi:10.1038/ismej.2017.191.

  20. Multi-millennia simulation of Greenland deglaciation from the Max-Plank-Institute Model (MPI-ISM) 2xCO2 simulation

    NASA Astrophysics Data System (ADS)

    Cabot, Vincent; Vizcaino, Miren; Mikolajewicz, Uwe

    2016-04-01

    Long-term ice sheet and climate coupled simulations are of great interest since they assess how the Greenland Ice Sheet (GrIS) will respond to global warming and how GrIS changes will impact on the climate system. We have run the Max-Plank-Institute Earth System Model coupled with an Ice Sheet Model (SICOPOLIS) over a time period of 10500 years under two times CO2 forcing. This is a coupled atmosphere (ECHAM5T31), ocean (MPI-OM), dynamic vegetation (LPJ), and ice sheet (SICOPOLIS, 10 km horizontal resolution) model. Given the multi-millennia simulation, the horizontal spatial resolution of the atmospheric component is relatively coarse (3.75°). A time-saving technique (asynchronous coupling) is used once the global climate reaches quasi-equilibrium. In our doubling-CO2 simulation, the GrIS is expected to break up into two pieces (one ice cap in the far north on one ice sheet in the south and east) after 3000 years. During the first 500 simulation years, the GrIS climate and surface mass balance (SMB) are mainly affected by the greenhouse effect-forced climate change. After the simulated year 500, the global climate reaches quasi-equilibrium. Henceforth Greenland climate change is mainly due to ice sheet decay. GrIS albedo reduction enhances melt and acts as a powerful feedback for deglaciation. Due to increased cloudiness in the Arctic region as a result of global climate change, summer incoming shortwave radiation is substantially reduced over Greenland, reducing deglaciation rates. At the end of the simulation, Greenland becomes green with forest growing over the newly deglaciated regions. References: Helsen, M. M., van de Berg, W. J., van de Wal, R. S. W., van den Broeke, M. R., and Oerlemans, J. (2013), Coupled regional climate-ice-sheet simulation shows limited Greenland ice loss during the Eemian, Climate of the Past, 9, 1773-1788, doi: 10.5194/cp-9-1773-2013 Helsen, M. M., van de Wal, R. S. W., van den Broeke, M. R., van de Berg, W. J., and Oerlemans, J

  1. Magnetic Characterization of Stream-Sediments From Buenos Aires Province, Argentina, Affected by Pollution

    NASA Astrophysics Data System (ADS)

    Chaparro, M. A.; Sinito, A. M.; Bidegain, J. C.; Gogorza, C. S.; Jurado, S.

    2001-12-01

    A wide urban area from Northeast of Buenos Aires Province is exposed to an important anthropogenic influence, mainly due to industrial activity. In this two water streams were chosen: one of them (Del Gato stream, G) next to La Plata City and the another one (El Pescado stream, P) on the outskirts of the city. Both streams have similar characteristics, although the first one (G) has a higher input of pollutants (fluvial effluents, fly ashes, solid wastes, etc.) than the last one (P). Sediments analyzed in this work are limes from continental origin of PostPampeano (Holocene). Although, some cores were affected by sandy-limy sediments with mollusc valves from Querandino Sea (Pleistocene - later Holocene) and limy sediments of chestnut color with calcareous concretions from the Ensenadense. Magnetic measurements and geochemical studies were carried out on the samples. Among the magnetic parameters, specific susceptibility (X), X frequency-dependence (Xfd%), X temperature-dependence, Natural Remanent Magnetization (NRM), Isothermal Remanent Magnetization (IRM), Saturation IRM (SIRM), coercivity of remanence (Bcr), S ratio and SIRM/X ratio, Anhysteric Remanent Magnetization (ARM), Magnetic and Thermal Demagnetization were studied. The magnetic characteristics for both sites indicate the predominance of magnetically soft minerals on G site and relatively hard minerals on P site. Magnetite is the main magnetic carrier, Pseudo Single Domain and Single Domain grains were found. Chemical studies show (in some cases) a high concentration for some heavy metals (Pb, Cu, Zn, Ni and Fe) on the upper 22-cm. Contents of heavy metals and ARM were correlated. Very good correlation (R> 0.81) is found for Cu, Zn, Ni, Fe and the sum (of Pb, Cu, Zn and Ni), and a weaker correlation for Pb.

  2. Temporal analysis of genetic structure to assess population dynamics of reintroduced swift foxes.

    PubMed

    Cullingham, Catherine I; Moehrenschlager, Axel

    2013-12-01

    Reintroductions are increasingly used to reestablish species, but a paucity of long-term postrelease monitoring has limited understanding of whether and when viable populations subsequently persist. We conducted temporal genetic analyses of reintroduced populations of swift foxes (Vulpes velox) in Canada (Alberta and Saskatchewan) and the United States (Montana). We used samples collected 4 years apart, 17 years from the initiation of the reintroduction, and 3 years after the conclusion of releases. To assess program success, we genotyped 304 hair samples, subsampled from the known range in 2000 and 2001, and 2005 and 2006, at 7 microsatellite loci. We compared diversity, effective population size, and genetic connectivity over time in each population. Diversity remained stable over time and there was evidence of increasing effective population size. We determined population structure in both periods after correcting for differences in sample sizes. The geographic distribution of these populations roughly corresponded with the original release locations, which suggests the release sites had residual effects on the population structure. However, given that both reintroduction sites had similar source populations, habitat fragmentation, due to cropland, may be associated with the population structure we found. Although our results indicate growing, stable populations, future connectivity analyses are warranted to ensure both populations are not subject to negative small-population effects. Our results demonstrate the importance of multiple sampling years to fully capture population dynamics of reintroduced populations. Análisis Temporal de la Estructura Genética para Evaluar la Dinámica Poblacional de Zorros (Vulpes velox) Reintroducidos. © 2013 Society for Conservation Biology.

  3. Multi-modal albedo distributions in the ablation area of the southwestern Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Moustafa, S. E.; Rennermalm, A. K.; Smith, L. C.; Miller, M. A.; Mioduszewski, J. R.; Koenig, L. S.; Hom, M. G.; Shuman, C. A.

    2015-05-01

    Surface albedo is a key variable controlling solar radiation absorbed at the Greenland Ice Sheet (GrIS) surface and, thus, meltwater production. Recent decline in surface albedo over the GrIS has been linked to enhanced snow grain metamorphic rates, earlier snowmelt, and amplified melt-albedo feedback from atmospheric warming. However, the importance of distinct surface types on ablation area albedo and meltwater production is still relatively unknown. In this study, we analyze albedo and ablation rates using in situ and remotely sensed data. Observations include (1) a new high-quality in situ spectral albedo data set collected with an Analytical Spectral Devices Inc. spectroradiometer measuring at 325-1075 nm along a 1.25 km transect during 3 days in June 2013; (2) broadband albedo at two automatic weather stations; and (3) daily MODerate Resolution Imaging Spectroradiometer (MODIS) albedo (MOD10A1) between 31 May and 30 August 2012 and 2013. We find that seasonal ablation area albedos in 2013 have a bimodal distribution, with snow and ice facies characterizing the two peaks. Our results show that a shift from a distribution dominated by high to low albedos corresponds to an observed melt rate increase of 51.5% (between 10-14 July and 20-24 July 2013). In contrast, melt rate variability caused by albedo changes before and after this shift was much lower and varied between ~10 and 30% in the melting season. Ablation area albedos in 2012 exhibited a more complex multimodal distribution, reflecting a transition from light to dark-dominated surface, as well as sensitivity to the so called "dark-band" region in southwest Greenland. In addition to a darkening surface from ice crystal growth, our findings demonstrate that seasonal changes in GrIS ablation area albedos are controlled by changes in the fractional coverage of snow, bare ice, and impurity-rich surface types. Thus, seasonal variability in ablation area albedos appears to be regulated primarily as a function

  4. Sensitivity of the marine-terminating margins to Holocene climate change in south and southeast Greenland

    NASA Astrophysics Data System (ADS)

    Levy, L.; Larsen, N. K.; Kjaer, K. H.; Bjork, A. A.; Kjeldsen, K. K.; Funder, S.; Kelly, M. A.; Howley, J. A.

    2016-12-01

    The marine-terminating glaciers of the Greenland Ice Sheet (GrIS) are responding rapidly to present-day climate change. More than one-third of the GrIS's discharge flows to the ocean through the marine-terminating outlet glaciers of southeastern Greenland, making it a potentially important region of the ice sheet. Documenting how these outlet glaciers have responded to longer-term past climate change (i.e. the Holocene) allows for more accurate predictions of their response to future climate changes. Here, we present 36 new 10Be ages on boulders perched on bedrock and on bedrock that record the timing of ice marginal fluctuations in several fjords in southeast and south Greenland, a region where little is known about past ice fluctuations due to its relative inaccessibility. We show that at Skjoldungen Sund (63.4N), deglaciation was rapid, beginning by 10.1 ± 0.4 ka. Deglaciation occurred concurrently at Timmiarmiut Fjord (62.7N), 100 km to the south, at 10.3 ± 0.4 ka. We suggest that this was in response to the warming ocean and air temperatures of the early Holocene. Additionally, 10Be ages on boulders perched on bedrock just distal to the historic­ moraines in Timmiarmiut Fjord date to 1.7 ± 0.1 ka, indicating the presence of a late Holocene advance prior to the Little Ice Age. In southern Greenland, deglaciation at Lindenow Fjord (60.6N), which drains the Julienhåb ice cap, occurred at 11.2 ± 0.4 ka. The ice then retreated up-fjord at a rate of 70-100 m yr-1, comparable with modern retreat rates of 30-100 m yr-1. We hypothesize that the earlier deglaciation at Lindenow Fjord by 1 ka may indicate that the Julienhåb ice cap was more sensitive to early Holocene warming than the GrIS. Additional 10Be ages from Prins Christen Fjord and near Qaqortoq are forthcoming. These new 10Be ages provide a longer-term perspective of marine-terminating outlet glacier fluctuations in Greenland and show that the ice sheet responded sensitively to Holocene climate change.

  5. Sensitivity of Pliocene ice sheets to orbital forcing

    Dolan, A.M.; Haywood, A.M.; Hill, D.J.; Dowsett, H.J.; Hunter, S.J.; Lunt, D.J.; Pickering, S.J.

    2011-01-01

    The stability of the Earth's major ice sheets is a critical uncertainty in predictions of future climate and sea level change. One method of investigating the behaviour of the Greenland and the Antarctic ice sheets in a warmer-than-modern climate is to look back at past warm periods of Earth history, for example the Pliocene. This paper presents climate and ice sheet modelling results for the mid-Pliocene warm period (mPWP; 3.3 to 3.0 million years ago), which has been identified as a key interval for understanding warmer-than-modern climates (Jansen et al., 2007). Using boundary conditions supplied by the United States Geological Survey PRISM Group (Pliocene Research, Interpretation and Synoptic Mapping), the Hadley Centre coupled ocean–atmosphere climate model (HadCM3) and the British Antarctic Survey Ice Sheet Model (BASISM), we show large reductions in the Greenland and East Antarctic Ice Sheets (GrIS and EAIS) compared to modern in standard mPWP experiments. We also present the first results illustrating the variability of the ice sheets due to realistic orbital forcing during the mid-Pliocene. While GrIS volumes are lower than modern under even the most extreme (cold) mid-Pliocene orbit (losing at least 35% of its ice mass), the EAIS can both grow and shrink, losing up to 20% or gaining up to 10% of its present-day volume. The changes in ice sheet volume incurred by altering orbital forcing alone means that global sea level can vary by more than 25 m during the mid-Pliocene. However, we have also shown that the response of the ice sheets to mPWP orbital hemispheric forcing can be in anti-phase, whereby the greatest reductions in EAIS volume are concurrent with the smallest reductions of the GrIS. If this anti-phase relationship is in operation throughout the mPWP, then the total eustatic sea level response would be dampened compared to the ice sheet fluctuations that are theoretically possible. This suggests that maximum eustatic sea level rise does not

  6. Evaluation of the SMAP model calculated snow albedo at the SIGMA-A site, northwest Greenland, during the 2012 record surface melt event

    NASA Astrophysics Data System (ADS)

    Niwano, M.; Aoki, T.; Matoba, S.; Yamaguchi, S.; Tanikawa, T.; Kuchiki, K.; Motoyama, H.

    2015-12-01

    The snow and ice on the Greenland ice sheet (GrIS) experienced the extreme surface melt around 12 July, 2012. In order to understand the snow-atmosphere interaction during the period, we applied a physical snowpack model SMAP to the GrIS snowpack. In the SMAP model, the snow albedo is calculated by the PBSAM component explicitly considering effects of snow grain size and light-absorbing snow impurities such as black carbon and dust. Temporal evolution of snow grain size is calculated internally in the SMAP model, whereas mass concentrations of snow impurities are externally given from observations. In the PBSAM, the (shortwave) snow albedo is calculated from a weighted summation of visible albedo (primarily affected by snow impurities) and near-infrared albedo (mainly controlled by snow grain size). The weights for these albedos are the visible and near-infrared fractions of the downward shortwave radiant flux. The SMAP model forced by meteorological data obtained from an automated weather station at SIGMA-A site, northwest GrIS during 30 June to 14 July, 2012 (IOP) was evaluated in terms of surface (optically equivalent) snow grain size and snow albedo. Snow grain size simulated by the model was compared against that retrieved from in-situ spectral albedo measurements. Although the RMSE and ME were reasonable (0.21 mm and 0.17 mm, respectively), the small snow grain size associated with the surface hoar could not be simulated by the SMAP model. As for snow albedo, simulation results agreed well with observations throughout the IOP (RMSE was 0.022 and ME was 0.008). Under cloudy-sky conditions, the SMAP model reproduced observed rapid increase in the snow albedo. When cloud cover is present the near-infrared fraction of the downward shortwave radiant flux is decreased, while it is increased under clear-sky conditions. Therefore, the above mentioned performance of the SMAP model can be attributed to the PBSAM component driven by the observed near-infrared and

  7. Assessing modeled Greenland surface mass balance in the GISS Model E2 and its sensitivity to surface albedo

    NASA Astrophysics Data System (ADS)

    Alexander, Patrick; LeGrande, Allegra N.; Koenig, Lora S.; Tedesco, Marco; Moustafa, Samiah E.; Ivanoff, Alvaro; Fischer, Robert P.; Fettweis, Xavier

    2016-04-01

    The surface mass balance (SMB) of the Greenland Ice Sheet (GrIS) plays an important role in global sea level change. Regional Climate Models (RCMs) such as the Modèle Atmosphérique Régionale (MAR) have been employed at high spatial resolution with relatively complex physics to simulate ice sheet SMB. Global climate models (GCMs) incorporate less sophisticated physical schemes and provide outputs at a lower spatial resolution, but have the advantage of modeling the interaction between different components of the earth's oceans, climate, and land surface at a global scale. Improving the ability of GCMs to represent ice sheet SMB is important for making predictions of future changes in global sea level. With the ultimate goal of improving SMB simulated by the Goddard Institute for Space Studies (GISS) Model E2 GCM, we compare simulated GrIS SMB against the outputs of the MAR model and radar-derived estimates of snow accumulation. In order to reproduce present-day climate variability in the Model E2 simulation, winds are constrained to match the reanalysis datasets used to force MAR at the lateral boundaries. We conduct a preliminary assessment of the sensitivity of the simulated Model E2 SMB to surface albedo, a parameter that is known to strongly influence SMB. Model E2 albedo is set to a fixed value of 0.8 over the entire ice sheet in the initial configuration of the model (control case). We adjust this fixed value in an ensemble of simulations over a range of 0.4 to 0.8 (roughly the range of observed summer GrIS albedo values) to examine the sensitivity of ice-sheet-wide SMB to albedo. We prescribe albedo from the Moderate Resolution Imaging Spectroradiometer (MODIS) MCD43A3 v6 to examine the impact of a more realistic spatial and temporal variations in albedo. An age-dependent snow albedo parameterization is applied, and its impact on SMB relative to observations and the RCM is assessed.

  8. Estimating the impact of internal climate variability on ice sheet model simulations

    NASA Astrophysics Data System (ADS)

    Tsai, C. Y.; Forest, C. E.; Pollard, D.

    2016-12-01

    Rising sea level threatens human societies and coastal habitats and melting ice sheets are a major contributor to sea level rise (SLR). Thus, understanding uncertainty of both forcing and variability within the climate system is essential for assessing long-term risk of SLR given their impact on ice sheet evolution. The predictability of polar climate is limited by uncertainties from the given forcing, the climate model response to this forcing, and the internal variability from feedbacks within the fully coupled climate system. Among those sources of uncertainty, the impact of internal climate variability on ice sheet changes has not yet been robustly assessed. Here we investigate how internal variability affects ice sheet projections using climate fields from two Community Earth System Model (CESM) large-ensemble (LE) experiments to force a three-dimensional ice sheet model. Each ensemble member in an LE experiment undergoes the same external forcings but with unique initial conditions. We find that for both LEs, 2m air temperature variability over Greenland ice sheet (GrIS) can lead to significantly different ice sheet responses. Our results show that the internal variability from two fully coupled CESM LEs can cause about 25 35 mm differences of GrIS's contribution to SLR in 2100 compared to present day (about 20% of the total change), and 100m differences of SLR in 2300. Moreover, only using ensemble-mean climate fields as the forcing in ice sheet model can significantly underestimate the melt of GrIS. As the Arctic region becomes warmer, the role of internal variability is critical given the complex nonlinear interactions between surface temperature and ice sheet. Our results demonstrate that internal variability from coupled atmosphere-ocean general circulation model can affect ice sheet simulations and the resulting sea-level projections. This study highlights an urgent need to reassess associated uncertainties of projecting ice sheet loss over the next few

  9. Integrating tree-ring and wine data from the Palatinate (Germany)

    NASA Astrophysics Data System (ADS)

    Konter, Oliver

    2017-04-01

    Tree-ring growth of conifer trees originating from central European low mountain ranges often reveal indistinct growth-climate relationships. Temperature variations can play a crucial role, whereas water availability can also control the annual growth and become the main dominating factor. The low mountain range Pfälzerwald in the Palatinate region represents the largest contiguous forested area in Germany and features at its most eastern limitation a unique ecological setting due to its sandy soils and reduced water availability. In addition, its north-south orientation and associated lee-effects due to predominating westerlies together with altitudinal differences of more than 300 m lead to higher temperatures, lower precipitation amounts, and, as a forest management consequence, to a proportion of up to 80 % of pine trees. Despite these exceptional ecological and climatological prerequisites, calibrating tree-ring width data from 487 Pinus sylvestris core samples against regional meteorological stations (1950-2011) and gridded data (1901-2011) confirm alternating climate control mechanisms. Comparison with drought-related indices (scPDSI), combining precipitation and temperature, unfolds highest correlations with May-July conditions (r=0.34, p<0.05), however, lacking temporal robustness in the early 20th century. The vegetation outside the forested areas in the plain can be characterized as agricultural croplands with vineyards, representing one of the largest wine-growing regions in Germany. We collected and analyzed a 24 datasets of 57 consecutive years (1959-2015) of must sugar content, acidity, alcohol content, and sugar-free extracts in Riesling, Pinot Gris, Pinot Blanc, and Silvaner wines, originating from 15 wineries adjoining the forested area into the plain. Correlation of Riesling must sugar content against regional April-August temperature data reveals a highly significant signal (r=0.73, p<0.01; high-pass filtered r=0.49, p<0.01). Sugar-free extract

  10. Chemical composition of essential oils from needles and twigs of balkan pine (Pinus peuce grisebach) grown in Northern Greece.

    PubMed

    Koukos, P K; Papadopoulou, K I; Patiaka, D T; Papagiannopoulos, A D

    2000-04-01

    The composition of essential oils from twigs and needles of Balkan pine (Pinus peuce Gris.) grown in northern Greece was investigated. The compounds were identified by using GC-MS analysis. The twig oil was rich in alpha-pinene (7.38%), beta-pinene (12.46%), beta-phellandrene (26.93%), beta-caryophyllene (4.48%), and citronellol (12.48%), and the needle oil was rich in alpha-pinene (23.07%), camphene (5.52%), beta-pinene (22.00%), beta-phellandrene (6.78%), bornyl acetate (9.76%), beta-caryophyllene (3.05%), and citronellol (13.42%). The mean oil yield was 2.85% for twigs and 0. 57% for needles.

  11. Antioxidant White Grape Seed Phenolics: Pressurized Liquid Extracts from Different Varieties

    PubMed Central

    Garcia-Jares, Carmen; Vazquez, Alberto; Lamas, Juan P.; Pajaro, Marta; Alvarez-Casas, Marta; Lores, Marta

    2015-01-01

    Grape seeds represent a high percentage (20% to 26%) of the grape marc obtained as a byproduct from white winemaking and keep a vast proportion of grape polyphenols. In this study, seeds obtained from 11 monovarietal white grape marcs cultivated in Northwestern Spain have been analyzed in order to characterize their polyphenolic content and antioxidant activity. Seeds of native (Albariño, Caiño, Godello, Loureiro, Torrontés, and Treixadura) and non-native (Chardonnay, Gewurtzträminer, Pinot blanc, Pinot gris, and Riesling) grape varieties have been considered. Low weight phenolics have been extracted by means of pressurized liquid extraction (PLE) and further analyzed by LC-MS/MS. The results showed that PLE extracts, whatever the grape variety of origin, contained large amounts of polyphenols and high antioxidant activity. Differences in the varietal polyphenolic profiles were found, so a selective exploitation of seeds might be possible. PMID:26783956

  12. Dissolved black carbon in the global cryosphere: Concentrations and chemical signatures

    NASA Astrophysics Data System (ADS)

    Khan, Alia L.; Wagner, Sasha; Jaffe, Rudolf; Xian, Peng; Williams, Mark; Armstrong, Richard; McKnight, Diane

    2017-06-01

    Black carbon (BC) is derived from the incomplete combustion of biomass and fossil fuels and can enhance glacial recession when deposited on snow and ice surfaces. Here we explore the influence of environmental conditions and the proximity to anthropogenic sources on the concentration and composition of dissolved black carbon (DBC), as measured by benzenepolycaroxylic acid (BPCA) markers, across snow, lakes, and streams from the global cryosphere. Data are presented from Antarctica, the Arctic, and high alpine regions of the Himalayas, Rockies, Andes, and Alps. DBC concentrations spanned from 0.62 μg/L to 170 μg/L. The median and (2.5, 97.5) quantiles in the pristine samples were 1.8 μg/L (0.62, 12), and nonpristine samples were 21 μg/L (1.6, 170). DBC is susceptible to photodegradation when exposed to solar radiation. This process leads to a less condensed BPCA signature. In general, DBC across the data set was composed of less polycondensed DBC. However, DBC from the Greenland Ice Sheet (GRIS) had a highly condensed BPCA molecular signature. This could be due to recent deposition of BC from Canadian wildfires. Variation in DBC appears to be driven by a combination of photochemical processing and the source combustion conditions under which the DBC was formed. Overall, DBC was found to persist across the global cryosphere in both pristine and nonpristine snow and surface waters. The high concentration of DBC measured in supraglacial melt on the GRIS suggests that DBC can be mobilized across ice surfaces. This is significant because these processes may jointly exacerbate surface albedo reduction in the cryosphere.Plain Language SummaryHere we present dissolved black carbon (DBC) results for snow and glacial melt systems in Antarctica, the Arctic, and high alpine regions of the Himalayas, Rockies, Andes, and Alps. Across the global cryosphere, DBC composition appears to be a result of photochemical processes occurring</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.7094S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.7094S"><span>Investigating connections between local-remote atmospheric variability and Greenland outlet glacier behavior</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sobolowski, Stefan; Chen, Linling; Miles, Victoria</p> <p>2016-04-01</p> <p>The outlet glaciers along the margins of the Greenland Ice Sheet (<span class="hlt">GrIS</span>) exhibit a range of behaviors, which are crucial for understanding <span class="hlt">GrIS</span> mass changes from a dynamical point of view. However, the drivers of this behavior are still poorly understood. Arguments (counter-arguments) have been made for a strong (weak) local oceanic influence on marine terminating outlet glaciers while decadal-scale drivers linked to fluctuations in the Ice sheet itself and the North Atlantic ocean (e.g. Atlantic Multidecadal Variability) have also been posited as drivers. Recently there have also been studies linking (e.g. seasonal to interannual) atmospheric variability, synoptic activity and the Ice Sheet variability. But these studies typically investigate atmospheric links to the large-scale behavior of the Ice Sheet itself and do not go down to the scale of the outlet glaciers. Conversely, investigations of the outlet glaciers often do not include potential links to non-local atmospheric dynamics. Here the authors attempt to bridge the gap and investigate the relationship between atmospheric variability across a range of scales and the behavior of three outlet glaciers on Greenland's southeast coast over a 33-year period (1980-2012). The glaciers - Helheim, Midgard and Fenris - are near Tasiilaq, are marine terminating and exhibit varying degree of connection to the <span class="hlt">GrIS</span>. ERA-Interim reanalysis, sea-ice data and glacier observations are used for the investigation. Long records of mass balance are unavailable for these glaciers and front position is employed as a measure of glacier atmosphere interactions across multiple scales, as it exhibits robust relationships to atmospheric variability on time scales of seasons to many years, with the strongest relationships seen at seasonal - interannual time scales. The authors do not make the argument that front position is a suitable proxy for mass balance, only that it is indicative of the role of local and remote atmospheric</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C13B0956K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C13B0956K"><span>Dissolved black carbon in the global cryosphere: concentrations and chemical signatures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Khan, A. L.; Wagner, S.; Jaffe, R.; Xian, P.; Williams, M. W.; Armstrong, R. L.; McKnight, D. M.</p> <p>2017-12-01</p> <p>Black carbon (BC) is derived from the incomplete combustion of biomass and fossil fuels and can enhance glacial recession when deposited on snow and ice surfaces. Here we explore the influence of environmental conditions and the proximity to anthropogenic sources on the concentration and composition of dissolved black carbon (DBC), as measured by benzenepolycaroxylic acid (BPCA) markers, across snow, lakes, and streams from the global cryosphere. Data are presented from Antarctica, the Arctic, and high alpine regions of the Himalayas, Rockies, Andes, and Alps. DBC concentrations spanned from 0.62 μg/L to 170 μg/L. The median and (2.5, 97.5) quantiles in the pristine samples were 1.8 μg/L (0.62, 12), and non-pristine samples were 21 μg/L (1.6, 170). DBC is susceptible to photodegradation when exposed to solar radiation. This process leads to a less condensed BPCA signature. In general, DBC across the dataset was comprised of less-polycondensed DBC. However, DBC from the Greenland Ice Sheet (<span class="hlt">GRIS</span>) had a highly-condensed BPCA molecular signature. This could be due to recent deposition of BC from Canadian wildfires. Variation in DBC appears to be driven by a combination of photochemical processing and the source combustion conditions under which the DBC was formed. Overall, DBC was found to persist across the global cryosphere in both pristine and non-pristine snow and surface waters. The high concentration of DBC measured in supra-glacial melt on the <span class="hlt">GRIS</span> suggests DBC can be mobilized across ice surfaces. This is significant because these processes may jointly exacerbate surface albedo reduction in the cryosphere.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.462..180L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.462..180L"><span>Utility of 222Rn as a passive tracer of subglacial distributed system drainage</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Linhoff, Benjamin S.; Charette, Matthew A.; Nienow, Peter W.; Wadham, Jemma L.; Tedstone, Andrew J.; Cowton, Thomas</p> <p>2017-03-01</p> <p>Water flow beneath the Greenland Ice Sheet (<span class="hlt">GrIS</span>) 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 <span class="hlt">GrIS</span> (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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5687855','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5687855"><span>Should coastal planners have concern over where land ice is melting?</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Larour, Eric; Ivins, Erik R.; Adhikari, Surendra</p> <p>2017-01-01</p> <p>There is a general consensus among Earth scientists that melting of land ice greatly contributes to sea-level rise (SLR) and that future warming will exacerbate the risks posed to human civilization. As land ice is lost to the oceans, both the Earth’s gravitational and rotational potentials are perturbed, resulting in strong spatial patterns in SLR, termed sea-level fingerprints. We lack robust forecasting models for future ice changes, which diminishes our ability to use these fingerprints to accurately predict local sea-level (LSL) changes. We exploit an advanced mathematical property of adjoint systems and determine the exact gradient of sea-level fingerprints with respect to local variations in the ice thickness of all of the world’s ice drainage systems. By exhaustively mapping these fingerprint gradients, we form a new diagnosis tool, henceforth referred to as gradient fingerprint mapping (GFM), that readily allows for improved assessments of future coastal inundation or emergence. We demonstrate that for Antarctica and Greenland, changes in the predictions of inundation at major port cities depend on the location of the drainage system. For example, in London, GFM shows LSL that is significantly affected by changes on the western part of the Greenland Ice Sheet (<span class="hlt">GrIS</span>), whereas in New York, LSL change predictions are greatly sensitive to changes in the northeastern portions of the <span class="hlt">GrIS</span>. We apply GFM to 293 major port cities to allow coastal planners to readily calculate LSL change as more reliable predictions of cryospheric mass changes become available. PMID:29152565</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.B43B2115K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.B43B2115K"><span>Compositionally heterogeneous dissolved organic matter reflects changing flowpaths in a large ice sheet catchment over the course of the melt season at Leverett Glacier, southwest Greenland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kellerman, A.; Hawkings, J.; Marshall, M.; Spencer, R.; Wadham, J.</p> <p>2017-12-01</p> <p>The Greenland Ice Sheet (<span class="hlt">GrIS</span>) is losing mass at a remarkable rate. This loss of mass coincides with the export of dissolved organic matter (DOM) and other nutrients from the ice sheet and exerts a primary control on secondary production in downstream ecosystems. However, little is known about the source and composition of DOM exported from these dilute, yet immense, systems. Samples were collected from May 11, 2015 to July 29, 2015 from the outflow of Leverett Glacier, a large, land-terminating glacier of the southwest <span class="hlt">GrIS</span>. Dissolved organic carbon (DOC) concentrations were measured and the optical properties of DOM were characterized using absorbance and fluorescence spectroscopy. At the beginning of the season, when discharge is <5 m3 sec-1, red-shifted fluorescence suggests terrestrial inputs from either overridden soils or proglacial inputs dominate the DOM pool. With the onset of melt, after an initial pulse in both DOC quantity and red-shifted fluorescence intensity, the DOC concentration and fluorescence intensity is diluted, with little change in DOM composition. The terrestrial signal is lost with the first outburst event in late June, and a single protein-like fluorophore is exhibited for three weeks. On July 10th, a fourth outburst event introduces a second protein-like fluorophore, indicative of production on the ice sheet, and this signature is maintained until the end of the July. These results suggest that subglaical drainage flowpaths and water source influence the exported DOC concentration and DOM composition over a summer melt season. As glacial outflow shifts from higher DOC concentrations early in the season to low DOC concentrations later in the summer, these results impact estimates of carbon export from glaciers. Furthermore, as composition is related to reactivity, the compositional changes observed may indicate shifts in the bioavailability of the DOM upon delivery to coastal systems, a result of changing DOM sources over the course of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014TCry....8.1457C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014TCry....8.1457C"><span>Ice-ocean interaction and calving front morphology at two west Greenland tidewater outlet glaciers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chauché, N.; Hubbard, A.; Gascard, J.-C.; Box, J. E.; Bates, R.; Koppes, M.; Sole, A.; Christoffersen, P.; Patton, H.</p> <p>2014-08-01</p> <p>Warm, subtropical-originating Atlantic water (AW) has been identified as a primary driver of mass loss across the marine sectors of the Greenland Ice Sheet (<span class="hlt">GrIS</span>), yet the specific processes by which this water mass interacts with and erodes the calving front of tidewater glaciers is frequently modelled and much speculated upon but remains largely unobserved. We present a suite of fjord salinity, temperature, turbidity versus depth casts along with glacial runoff estimation from Rink and Store glaciers, two major marine outlets draining the western sector of the <span class="hlt">GrIS</span> during 2009 and 2010. We characterise the main water bodies present and interpret their interaction with their respective calving fronts. We identify two distinct processes of ice-ocean interaction which have distinct spatial and temporal footprints: (1) homogenous free convective melting which occurs across the calving front where AW is in direct contact with the ice mass, and (2) localised upwelling-driven melt by turbulent subglacial runoff mixing with fjord water which occurs at distinct injection points across the calving front. Throughout the study, AW at 2.8 ± 0.2 °C was consistently observed in contact with both glaciers below 450 m depth, yielding homogenous, free convective submarine melting up to ~200 m depth. Above this bottom layer, multiple interactions are identified, primarily controlled by the rate of subglacial fresh-water discharge which results in localised and discrete upwelling plumes. In the record melt year of 2010, the Store Glacier calving face was dominated by these runoff-driven plumes which led to a highly crenulated frontal geometry characterised by large embayments at the subglacial portals separated by headlands which are dominated by calving. Rink Glacier, which is significantly deeper than Store has a larger proportion of its submerged calving face exposed to AW, which results in a uniform, relatively flat overall frontal geometry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4203507','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4203507"><span>Identification of gravitropic response indicator genes in Arabidopsis inflorescence stems</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Taniguchi, Masatoshi; Nakamura, Moritaka; Tasaka, Masao; Morita, Miyo Terao</p> <p>2014-01-01</p> <p>Differential organ growth during gravitropic response is caused by differential accumulation of auxin, that is, relative higher auxin concentration in lower flanks than in upper flanks of responding organs. Auxin responsive reporter systems such as DR5::GUS and DR5::GFP have usually been used as indicators of gravitropic response in roots and hypocotyls of Arabidopsis. However, in the inflorescence stems, the reporter systems don’t work well to monitor gravitropic response. Here, we aim to certify appropriate gravitropic response indicators (<span class="hlt">GRIs</span>) in inflorescence stems. We performed microarray analysis comparing gene expression profiles between upper and lower flanks of Arabidopsis inflorescence stems after gravistimulation. Thirty genes showed > 2-fold differentially increased expression in lower flanks at 30 min, of which 19 were auxin response genes. We focused on IAA5 and IAA2 and verified whether they are appropriate <span class="hlt">GRIs</span> by real-time qRT-PCR analyses. Transcript levels of IAA5 and IAA2 were remarkably higher in lower flanks than in upper flanks after gravistimulation. The biased IAA5 or IAA2 expression is disappeared in sgr2–1 mutant which is defective in gravity perception, indicating that gravity perception process is essential for formation of the biased gene expression during gravitropism. IAA5 expression was remarkably increased in lower flanks at 30 min after gravistimulation, whereas IAA2 expression was gradually decreased in upper flanks in a time-dependent manner. Therefore, we conclude that IAA5 is a sensitive GRI to monitor asymmetric auxin signaling caused by gravistimulation in Arabidopsis inflorescence stems. PMID:25763694</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015TCD.....9.4865M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015TCD.....9.4865M"><span>Glacier dynamics over the last quarter of a century at Jakobshavn Isbræ</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Muresan, I. S.; Khan, S. A.; Aschwanden, A.; Khroulev, C.; Van Dam, T.; Bamber, J.; van den Broeke, M. R.; Wouters, B.; Kuipers Munneke, P.; Kjær, K. H.</p> <p>2015-09-01</p> <p>Observations over the past two decades show substantial ice loss associated with the speedup of marine terminating glaciers in Greenland. Here we use a regional 3-D outlet glacier model to simulate the behaviour of Jakobshavn Isbræ (JI) located in west Greenland. Using atmospheric and oceanic forcing we tune our model to reproduce the observed frontal changes of JI during 1990-2014. We identify two major accelerations. The first occurs in 1998, and is triggered by moderate thinning prior to 1998. The second acceleration, which starts in 2003 and peaks in summer 2004, is triggered by the final breakup of the floating tongue, which generates a reduction in buttressing at the JI terminus. This results in further thinning, and as the slope steepens inland, sustained high velocities have been observed at JI over the last decade. As opposed to other regions on the Greenland Ice Sheet (<span class="hlt">GrIS</span>), where dynamically induced mass loss has slowed down over recent years, both modelled and observed results for JI suggest a continuation of the acceleration in mass loss. Further, we find that our model is not able to capture the 2012 peak in the observed velocities. Our analysis suggests that the 2012 acceleration of JI is likely the result of an exceptionally long melt season dominated by extreme melt events. Considering that such extreme surface melt events are expected to intensify in the future, our findings suggest that the 21st century projections of the <span class="hlt">GrIS</span> mass loss and the future sea level rise may be larger than predicted by existing modelling results.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_11");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_7 --> <div id="page_8" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="141"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JGRC..123.2570O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JGRC..123.2570O"><span>Exploring the Potential Impact of Greenland Meltwater on Stratification, Photosynthetically Active Radiation, and Primary Production in the Labrador Sea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Oliver, Hilde; Luo, Hao; Castelao, Renato M.; van Dijken, Gert L.; Mattingly, Kyle S.; Rosen, Joshua J.; Mote, Thomas L.; Arrigo, Kevin R.; Rennermalm, Åsa K.; Tedesco, Marco; Yager, Patricia L.</p> <p>2018-04-01</p> <p>In July 2012, the surface of the Greenland Ice Sheet (<span class="hlt">GrIS</span>) melted to an extent unprecedented over the last 100 years; we questioned the potential for such an extreme melt event to impact marine phytoplankton offshore. We hypothesized that stratification from meltwater could reduce light limitation for phytoplankton, and used a suite of numerical models to quantify the impact for 2003-2012. Because much of the 2012 meltwater discharged from southern Greenland, our study focused on the southwestern and southeastern coasts of Greenland, and the Labrador Sea. A 1-D phytoplankton model used output from a Regional Ocean Modeling System (ROMS) coupled with a Regional Climate Model and a hydrological model of meltwater from runoff sources on the ice sheet, peripheral glaciers, and tundra. ROMS was run with and without meltwater to test the sensitivity of phytoplankton photosynthetic rates to the meltwater input. With meltwater, the pycnocline was shallower during late summer and early fall and thus light limitation on photosynthesis was reduced. Averaged over all years, added meltwater had the potential to increase gross primary production by 3-12% in the summer (July-August), and 13-60% in the fall (September-October). This meltwater effect was amplified when light was more limiting, and thus was greatest in the fall, under cloudier conditions, with higher self-shading, and with more light-sensitive phytoplankton groups. As the <span class="hlt">GrIS</span> melt is projected to increase, late summer primary production in this region has the potential to increase as well, which could constitute an important biosphere response to high-latitude climate change.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.B21F..02W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.B21F..02W"><span>The geomicrobiology of the Greenland Ice Sheet: impact on DOC export (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wadham, J. L.; Stibal, M.; Lawson, E. C.; Barnett, M. J.; Hasan, F.; Telling, J.; Anesio, A.; Lis, G.; Cullen, D.; Butler, C.; Tranter, M.; Nienow, P. W.</p> <p>2010-12-01</p> <p>The Greenland Ice Sheet (<span class="hlt">GrIS</span>) is the largest mass of ice in the northern hemisphere, and contributes ~370 km3 in runoff annually to the Arctic Ocean. While recent work has highlighted runoff increases of up to 100% from the <span class="hlt">GrIS</span> over the next century, very little is known about the associated impacts upon rates of sediment-bound and dissolved organic carbon export from the ice sheet to the coastal ocean. This is relevant given recent work that has suggested that the high proportion of labile dissolved organic carbon (DOC) present in glacial runoff may be important in sustaining the productivity of ecosystems downstream. Here we report the phylogenetic and functional diversity of micro-organisms inhabiting the surface and basal regions of the Greenland Ice Sheet (at Leverett Glacier, SW Greenland), and whose activity influences the biogeochemical composition of runoff. Real time PCR data on runoff, together with 16S-rRNA bacterial clone libraries on sediments, demonstrate a subglacial microbial community that contrasts phylogenetically and functionally with the ice sheet surface ecosystem. We envisage that large sectors of the subglacial environment are microbially active, with overridden paleosols and in-washed surface organic matter providing a carbon substrate for a range of metabolic pathways. This includes methanogenesis which proceeds at rates similar to deep ocean sediments and via a CO2/H2 pathway. These subglacial microbial communities serve to chemically modify the DOC composition of meltwater inputs from the ice sheet surface and modulate the reactivity of bulk DOC exported in runoff. Evidence for subglacial microbial influences on DOC in runoff includes elevated concentrations of dissolved carbohydrates (e.g. glucose and fructose of up to 1 μmol/L), which are preferentially exported during subglacial outburst events. We examine the temporal changes in DOC export in runoff from the ice sheet over a full melt season, and consider how changes in total</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21898102','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21898102"><span>Environmental controls on microbial abundance and activity on the greenland ice sheet: a multivariate analysis approach.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Stibal, Marek; Telling, Jon; Cook, Joe; Mak, Ka Man; Hodson, Andy; Anesio, Alexandre M</p> <p>2012-01-01</p> <p>Microbes in supraglacial ecosystems have been proposed to be significant contributors to regional and possibly global carbon cycling, and quantifying the biogeochemical cycling of carbon in glacial ecosystems is of great significance for global carbon flow estimations. Here we present data on microbial abundance and productivity, collected along a transect across the ablation zone of the Greenland ice sheet (<span class="hlt">GrIS</span>) in summer 2010. We analyse the relationships between the physical, chemical and biological variables using multivariate statistical analysis. Concentrations of debris-bound nutrients increased with distance from the ice sheet margin, as did both cell numbers and activity rates before reaching a peak (photosynthesis) or a plateau (respiration, abundance) between 10 and 20 km from the margin. The results of productivity measurements suggest an overall net autotrophy on the <span class="hlt">GrIS</span> and support the proposed role of ice sheet ecosystems in carbon cycling as regional sinks of CO(2) and places of production of organic matter that can be a potential source of nutrients for downstream ecosystems. Principal component analysis based on chemical and biological data revealed three clusters of sites, corresponding to three 'glacier ecological zones', confirmed by a redundancy analysis (RDA) using physical data as predictors. RDA using data from the largest 'bare ice zone' showed that glacier surface slope, a proxy for melt water flow, accounted for most of the variation in the data. Variation in the chemical data was fully explainable by the determined physical variables. Abundance of phototrophic microbes and their proportion in the community were identified as significant controls of the carbon cycling-related microbial processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18..440W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18..440W"><span>Local and synoptic controls on rapid supraglacial lake drainage in West Greenland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Williamson, Andrew; Banwell, Alison; Arnold, Neil; Willis, Ian</p> <p>2016-04-01</p> <p>Many supraglacial lakes within the ablation zone of the Greenland Ice Sheet (<span class="hlt">GrIS</span>) are known to drain rapidly (in <1 day) in the mid- to late melt season, delivering large meltwater pulses to the subglacial drainage system, thus affecting basal water pressures and ice-sheet dynamics. Although it is now generally recognised that rapid lake drainage is caused by hydrofracture, the precise controls on hydrofracture initiation remain poorly understood: they may be linked to a local critical water-volume threshold, or they may be associated with synoptic-scale factors, such as ice thickness, driving stresses, ice velocities and strain rates. A combination of the local water-volume threshold and one or more synoptic-scale factors may explain the overall patterns of rapid lake drainage, but this requires verification using targeted field- and remotely-based studies that cover large areas of the <span class="hlt">GrIS</span> and span long timescales. Here, we investigate a range of potential controls on rapid supraglacial lake drainage in the land-terminating Paakitsoq region of the ice sheet, northeast of Jakobshavn Isbræ, for the 2014 melt season. We have analysed daily 250-m Moderate Resolution Imaging Spectroradiometer (MODIS) imagery in order to calculate lake areas, depths and volumes, and have developed an automatic lake-tracking algorithm to determine the dates on which all rapid lake drainage events occur. For each rapidly draining lake, the water volumes immediately prior to drainage are compared with other local factors, notably lake-filling rate and ice thickness, and with a variety of synoptic-scale features, such as slope angles, driving stresses, surface velocities, surface strain rates and the incidence of nearby lake-drainage events. We present the outcomes of our statistical analysis to elicit the statistically significant controls on hydrofracture beneath supraglacial lakes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12..971K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12..971K"><span>Modelling seasonal meltwater forcing of the velocity of land-terminating margins of the Greenland Ice Sheet</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koziol, Conrad P.; Arnold, Neil</p> <p>2018-03-01</p> <p>Surface runoff at the margin of the Greenland Ice Sheet (<span class="hlt">GrIS</span>) drains to the ice-sheet bed, leading to enhanced summer ice flow. Ice velocities show a pattern of early summer acceleration followed by mid-summer deceleration due to evolution of the subglacial hydrology system in response to meltwater forcing. Modelling the integrated hydrological-ice dynamics system to reproduce measured velocities at the ice margin remains a key challenge for validating the present understanding of the system and constraining the impact of increasing surface runoff rates on dynamic ice mass loss from the <span class="hlt">GrIS</span>. Here we show that a multi-component model incorporating supraglacial, subglacial, and ice dynamic components applied to a land-terminating catchment in western Greenland produces modelled velocities which are in reasonable agreement with those observed in GPS records for three melt seasons of varying melt intensities. This provides numerical support for the hypothesis that the subglacial system develops analogously to alpine glaciers and supports recent model formulations capturing the transition between distributed and channelized states. The model shows the growth of efficient conduit-based drainage up-glacier from the ice sheet margin, which develops more extensively, and further inland, as melt intensity increases. This suggests current trends of decadal-timescale slowdown of ice velocities in the ablation zone may continue in the near future. The model results also show a strong scaling between average summer velocities and melt season intensity, particularly in the upper ablation area. Assuming winter velocities are not impacted by channelization, our model suggests an upper bound of a 25 % increase in annual surface velocities as surface melt increases to 4 × present levels.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016HESS...20.1197Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016HESS...20.1197Y"><span>Stable oxygen isotope variability in two contrasting glacier river catchments in Greenland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yde, Jacob C.; Knudsen, Niels T.; Steffensen, Jørgen P.; Carrivick, Jonathan L.; Hasholt, Bent; Ingeman-Nielsen, Thomas; Kronborg, Christian; Larsen, Nicolaj K.; Mernild, Sebastian H.; Oerter, Hans; Roberts, David H.; Russell, Andrew J.</p> <p>2016-03-01</p> <p>Analysis of stable oxygen isotope (δ18O) characteristics is a useful tool to investigate water provenance in glacier river systems. In order to attain knowledge on the diversity of δ18O variations in Greenlandic rivers, we examined two contrasting glacierised catchments disconnected from the Greenland Ice Sheet (<span class="hlt">GrIS</span>). At the Mittivakkat Gletscher river, a small river draining a local temperate glacier in southeast Greenland, diurnal oscillations in δ18O occurred with a 3 h time lag to the diurnal oscillations in run-off. The mean annual δ18O was -14.68 ± 0.18 ‰ during the peak flow period. A hydrograph separation analysis revealed that the ice melt component constituted 82 ± 5 % of the total run-off and dominated the observed variations during peak flow in August 2004. The snowmelt component peaked between 10:00 and 13:00 local time, reflecting the long travel time and an inefficient distributed subglacial drainage network in the upper part of the glacier. At the Kuannersuit Glacier river on the island Qeqertarsuaq in west Greenland, the δ18O characteristics were examined after the major 1995-1998 glacier surge event. The mean annual δ18O was -19.47 ± 0.55 ‰. Despite large spatial variations in the δ18O values of glacier ice on the newly formed glacier tongue, there were no diurnal oscillations in the bulk meltwater emanating from the glacier in the post-surge years. This is likely a consequence of a tortuous subglacial drainage system consisting of linked cavities, which formed during the surge event. Overall, a comparison of the δ18O compositions from glacial river water in Greenland shows distinct differences between water draining local glaciers and ice caps (between -23.0 and -13.7 ‰) and the <span class="hlt">GrIS</span> (between -29.9 and -23.2 ‰). This study demonstrates that water isotope analyses can be used to obtain important information on water sources and the subglacial drainage system structure that is highly desired for understanding glacier hydrology.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.C43C0628B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.C43C0628B"><span>Assessing the Extent of Influence Subglacial Hydrology Has on Dynamic Ice Sheet Behavior</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Babonis, G. S.; Csatho, B. M.</p> <p>2012-12-01</p> <p>Numerous recent studies have done an excellent job capturing and quantifying the complex pattern of dynamic changes of the Greenland Ice Sheet (<span class="hlt">GrIS</span>) over the past several decades. The timing of changes in ice velocities and mass balance indicate that the mechanisms controlling these behaviors, both external and internal, act over variable spatial and temporal regimes, can change in rapid and complex fashion, and have significant effect on ice sheet behavior as well as sea level rise. With roughly half of the estimated ice loss from the <span class="hlt">GrIS</span> attributed to dynamic processes, these changes account for about 250 Gt/yr (2003-2008), equivalence to 0.6 mm/yr sea level rise. One of the primary influences of dynamic ice behavior is ice sheet hydrology, including the storage and transport of water from the supraglacial to subglacial environment, and the subsequent development of water transport pathways, thus demonstrating the need for further characterization of the subglacial environment. Enhanced dynamic flow of ice due to the influence of meltwater distribution on the subglacial environment has been reported, including In-SAR observations of large velocity increases over short periods of time, suggesting regions where dynamic changes are likely being caused by changes in hydrology. Additionally, building upon the 1993-2011 laser altimetry record, analyzed by our Surface Elevation Reconstruction And Change detection (SERAC) procedure, we have detected complex patterns of rapid thickening and thinning patterns over several outlet glaciers. This study presents a comprehensive investigation of hydrologic control on dynamic glacier behavior for several key sites in Greenland. We combine a high resolution surface digital elevation model (DEM) derived by fusing space- and airborne laser altimetry observations and SPIRIT SPOT DEMs, with a high resolution, hydrologically-corrected bedrock DEM derived from a combination of CResIS and Operation Icebridge ice penetrating radar data</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.3940M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.3940M"><span>Tracking surface and subsurface lakes on the Greenland Ice Sheet using Sentinel-1 SAR and Landsat-8 OLI imagery</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miles, Katie; Willis, Ian; Benedek, Corinne; Williamson, Andrew; Tedesco, Marco</p> <p>2017-04-01</p> <p>Supraglacial lakes (SGLs) on the Greenland Ice Sheet (<span class="hlt">GrIS</span>) are an important component of the ice sheet's mass balance and hydrology, with their drainage affecting ice dynamics. This study uses imagery from the recently launched Sentinel-1A Synthetic Aperture Radar (SAR) to investigate SGLs in West Greenland. SAR can image through cloud and in darkness, overcoming some of the limitations of commonly used optical sensors. A semi automated algorithm is developed to detect surface lakes from Sentinel images during the 2015 summer. It generally detects water in all locations where a Landsat-8 NDWI classification (with a relatively high threshold value) detects water. A combined set of images from Landsat-8 and Sentinel-1 is used to track lake behaviour at a comparable temporal resolution to that which is possible with MODIS, but at a higher spatial resolution. A fully automated lake drainage detection algorithm is used to investigate both rapid and slow drainages for both small and large lakes through the summer. Our combined Landsat-Sentinel dataset, with a temporal resolution of three days, could track smaller lakes (mean 0.089 km2) than are resolvable in MODIS (minimum 0.125 km2). Small lake drainage events (lakes smaller than can be detected using MODIS) were found to occur at lower elevations ( 200 m) and slightly earlier in the melt season than larger events, as were slow lake drainage events compared to rapid events. The Sentinel imagery allows the analysis to be extended manually into the early winter to calculate the dates and elevations of lake freeze-through more precisely than is possible with optical imagery (mean 30 August, 1270 m mean elevation). Finally, the Sentinel imagery allows subsurface lakes (which are invisible to optical sensors) to be detected, and, for the first time, their dates of appearance and freeze-through to be calculated (mean 9 August and 7 October, respectively). These subsurface lakes occur at higher elevations than the surface</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19..161W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19..161W"><span>A Fully Automated Supraglacial lake area and volume Tracking ("FAST") algorithm: development and application using MODIS imagery of West Greenland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Williamson, Andrew; Arnold, Neil; Banwell, Alison; Willis, Ian</p> <p>2017-04-01</p> <p>Supraglacial lakes (SGLs) on the Greenland Ice Sheet (<span class="hlt">GrIS</span>) influence ice dynamics if draining rapidly by hydrofracture, which can occur in under 24 hours. MODerate-resolution Imaging Spectroradiometer (MODIS) data are often used to investigate SGLs, including calculating SGL area changes through time, but no existing work presents a method that tracks changes in individual (and total) SGL volume in MODIS imagery over a melt season. Here, we present such a method. First, we tested three automated approaches to derive SGL areas from MODIS imagery by comparing calculated areas for the Paakitsoq and Store Glacier regions in West Greenland with areas derived from Landsat-8 (LS8) images. Second, we applied a physically-based depth-calculation algorithm to the pixels within the SGL boundaries from the best performing method, and validated the resultant depths with those calculated using the same method applied to LS8 imagery. Our results indicated that SGL areas are most accurately generated using dynamic thresholding of MODIS band 1 (red) with a 0.640 threshold value. Calculated SGL area, depth and volume values from MODIS were closely comparable to those derived from LS8. The best performing area- and depth-detection methods were then incorporated into a Fully Automated SGL Tracking ("FAST") algorithm that tracks individual SGLs between successive MODIS images. It identified 43 (Paakitsoq) and 19 (Store Glacier) rapidly draining SGLs during 2014, representing 21% and 15% of the respective total SGL populations, including some clusters of rapidly draining SGLs. We found no relationship between the water volumes contained within these rapidly draining SGLs and the ice thicknesses beneath them, indicating that a critical water volume linearly related to ice thickness cannot explain the incidence of rapid drainage. The FAST algorithm, which we believe to be the most comprehensive SGL tracking algorithm developed to date, has the potential to investigate statistical</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.C51B0712B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.C51B0712B"><span>Over-wintering of Supraglacial Lakes on the Greenland Ice Sheet from Sentinel-1 and Landsat-8 Data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Benedek, C. L.; Tedesco, M.</p> <p>2015-12-01</p> <p>Supra-glacial lakes on the <span class="hlt">GrIS</span> have become a focus of research relating to the contribution of the <span class="hlt">GrIS</span> to sea level rise. Lakes have been observed to appear during the summer melt season. Though it appears that the quantity of water collected on the surface is small, it is thought that the fracture and drainage of these lakes delivers significant pulses of water to the ice sheet bed, influencing the dynamic movement of glaciers towards the sea. The pattern of this transport mechanism may be a central driver of its influence over dynamic losses, as the flow of the viscoelastic ice sheet will differ if the water is delivered in a short pulse or a slower constant supply. A number of studies have catalogued the traits of lakes with an aim to quantify lake areas, depths, and timing of formation and cessation using visible and near infrared remote sensing instruments mostly focused on the summer melt season. Little is known about the behaviour of the surface lakes over the winter. A recent examination of the over-wintering of surface lakes has been conducted by Koenig et al. [2015] using airborne radar. While the study is extensive in area covered, it is limited in its temporal resolution by the availability of Operation IceBridge data, typically at one pass per year. This study seeks to observe the development of lakes over the winter period. Sentinel-1A radar images are used to track the presence of surface lakes and their variation in three study sites on the Greenland ice sheet. The sites are as follows: upstream of Ryder glacier, upstream of Petermann glacier, and upstream of Jakobshavn glacier. Water masks are created based on summer Landsat-8 images following NDWIice and then compared to Sentinel images at monthly temporal resolution through the winter of 2014-2015. These radar images show persistence of liquid water through the winter in agreement with previous research as well as variation in the buried lake area over the span of the year studied.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.5537R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.5537R"><span>Reconstruction of the Greenland ice sheet dynamics in a fully coupled Earth System Model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rybak, Oleg; Volodin, Evgeny; Huybrechts, Philippe</p> <p>2016-04-01</p> <p> cloudiness) after applying spline interpolation. EWBM-G calculates annual surface mass balance, SMB, (further transferred as an external forcing to the GrISM) and fresh water flux (transferred to the oceanic block of the INMCM32). After receiving SMB, <span class="hlt">GrIS</span> is integrated and returns update surface topography back to the INMCM32. The aim of the current research is to establish equilibration time of climate and <span class="hlt">GrIS</span> in the transient coupled run and to elaborate optimum methodology for performing numerical experiments simulating glacial/interglacial transitions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMPP24A..04C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMPP24A..04C"><span>New marine geophysical and sediment record of the Northeast Greenland Ice Stream.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Callard, L.; Roberts, D. H.; O'Cofaigh, C.; Lloyd, J. M.; Smith, J. A.; Dorschel, B.</p> <p>2017-12-01</p> <p>The NE Greenland Ice Stream (NEGIS) drains 16% of the Greenland Ice Sheet (<span class="hlt">GrIS</span>) and has a sea-level equivalent of 1.1-1.4 m. Stabilised by two floating ice shelves, 79N and Zachariae Isstrom, until recently it has shown little response to increased atmospheric and oceanic warming. However, since 2010 it has experienced an accelerated rate of grounding line retreat ( 4 km) and significant ice shelf loss that indicates that this sector of the <span class="hlt">GrIS</span> is now responding to current oceanic and/or climatic change and has the potential to be a major contributor to future global sea-level rise. The project `NEGIS', a collaboration between Durham University and AWI, aims to reconstruct the history of the NE Greenland Ice Stream from the Last Glacial Maximum (LGM) to present using both onshore and offshore geological archives to better understand past ice stream response to a warming climate. This contribution presents results and interpretations from an offshore dataset collected on the RV Polarstern, cruises PS100 and PS109 in 2016 and 2017. Gravity and box cores, supplemented by swath bathymetric and sub-bottom profiler data, were acquired and initial core analysis including x-radiographs and MSCL data logging has been performed. Data collection focused principally in the Norske Trough and the area directly in front of the 79N ice shelf, a sub-ice shelf environment as recently as two years ago. On the outer shelf streamlined subglacial bedforms, grounding-zone wedges and moraines as well as overconsolidated subglacial tills, record an extensive ice sheet advance to the shelf edge. On the inner shelf and in front of the 79N ice shelf, deep, glacially-eroded bedrock basins are infilled with stratified sediment. The stratified muds represent deglacial and Holocene glacimarine sedimentation, and capture the recent transition from sub-ice shelf to shelf free conditions. Multiproxy palaeoenvironmental reconstructions, including foraminifera and diatom analysis, and radiocarbon</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003PhDT.......135R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003PhDT.......135R"><span>Reconnaissance invariante d'objets 3-D et correlation SONG</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roy, Sebastien</p> <p></p> <p>Cette these propose des solutions a deux problemes de la reconnaissance automatique de formes: la reconnaissance invariante d'objets tridimensionnels a partir d'images d'intensite et la reconnaissance robuste a la presence de bruit disjoint. Un systeme utilisant le balayage angulaire des images et un classificateur par trajectoires d'espace des caracteristiques permet d'obtenir la reconnaissance invariante d'objets tridimensionnels. La reconnaissance robuste a la presence de bruit disjoint est realisee au moyen de la correlation SONG. Nous avons realise la reconnaissance invariante aux translations, rotations et changements d'echelle d'objets tridimensionnels a partir d'images d'intensite segmentees. Nous utilisons le balayage angulaire et un classificateur a trajectoires d'espace des caracteris tiques. Afin d'obtenir l'invariance aux translations, le centre de balayage angulaire coincide avec le centre geometrique de l'image. Le balayage angulaire produit un vecteur de caracteristiques invariant aux changements d'echelle de l'image et il transforme en translations du signal les rotations autour d'un axe parallele a la ligne de visee. Le classificateur par trajectoires d'espace des caracteristiques represente une rotation autour d'un axe perpendiculaire a la ligne de visee par une courbe dans l'espace. La classification se fait par la mesure de la distance du vecteur de caracteristiques de l'image a reconnaitre aux trajectoires stockees dans l'espace. Nos resultats numeriques montrent un taux de classement atteignant 98% sur une banque d'images composee de 5 vehicules militaires. La correlation non-lineaire generalisee en tranches orthogonales (SONG) traite independamment les niveaux de <span class="hlt">gris</span> presents dans une image. Elle somme les correlations lineaires des images binaires ayant le meme niveau de <span class="hlt">gris</span>. Cette correlation est equivalente a compter le nombre de pixels situes aux memes positions relatives et ayant les memes intensites sur deux images. Nous presentons</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C13A0944M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C13A0944M"><span>Evaluation of changes in atmospheric and oceanic fluxes during continental ice sheet retreat</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Martin, J.; Martin, E. E.; Deuerling, K. M.</p> <p>2017-12-01</p> <p>Extensive land areas were exposed across North America, Eurasia, and to a lesser extent Greenland as continental ice sheets retreated following the last glacial maximum. A transect of watersheds from the coast to the western Greenland Ice Sheet (<span class="hlt">GrIS</span>) provides an opportunity to evaluate possible changes in oceanic solute fluxes and atmospheric CO2 exchange as ice sheets retreat. We evaluate these fluxes in one proglacial watershed (draining ice sheet runoff) and four deglaciated watersheds (draining local precipitation and permafrost melt). Sr isotope ratios indicate bedrock near the coast has experienced greater weathering than near the ice sheet. A mass balance model of the major element composition of stream water indicates weathering in deglaciated watersheds is dominated by carbonic acid dissolution of carbonate minerals near the ice sheet that switches to carbonic acid alteration of silicate minerals near the coast. In addition, weathering by sulfuric acid, derived from oxidative dissolution of sulfide minerals, increases from the ice sheet to the coast. These changes in the weathered minerals and weathering acids impact CO2 sequestration associated with weathering. Weathering consumes 350 to 550 µmol CO2/L in watersheds near the ice sheet, but close to the coast, consumes only 15 µmol CO2/L in one watershed and sources 140 µmol CO2/L to the atmosphere at another coastal watershed. The decreasing CO2 weathering sink from the <span class="hlt">GrIS</span> to coast reflects decreased carbonic acid weathering and increased sulfuric acid weathering of carbonate minerals. The proglacial stream shows downstream variations in composition from mixing of two water sources, with only minor in-stream weathering, which consumes < 0.1 µmol CO2/L. Discharge from the deglaciated watersheds is currently unknown but their higher solute concentrations and CO2 exchange than proglacial systems suggest deglaciated watersheds dominate atmospheric fluxes of CO2 and oceanic solute fluxes. These results</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C13F1014L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C13F1014L"><span>The Effect of Topographic Shadowing by Ice on Irradiance in the Greenland Ice Sheet Ablation Zone</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Leidman, S. Z.; Rennermalm, A. K.; Ryan, J.; Cooper, M. G.; Smith, L. C.</p> <p>2017-12-01</p> <p>Accurately predicting runoff contributions to global sea level rise requires more refined surface mass balance (SMB) models of the Greenland Ice Sheet (<span class="hlt">GrIS</span>). Topographic shadowing has shown to be important in the SMB of snow-covered regions, yet SMB models for the <span class="hlt">GrIS</span> generally ignore how surface topography affects spatial variability of incoming solar radiation on a surface. In the ablation zone of Southwest Greenland, deeply incised supraglacial drainage features, fracturing, and large-scale bed deformation result in extensive areas of rough surface topography. This topography blocks direct radiation such that shadowed areas receive less energy for melting while other topographic features such as peaks recieve more energy. In this study, we quantify how shadowing from local topography features changes incoming solar radiation. We apply the ArcGIS Pro Solar Radiation Toolset to calculate the direct and diffuse irradiance in sunlit and shadowed areas by determining the sun's movement for every half hour increment of 2016. Multiple digital elevation models (DEMs) with spatial resolutions ranging from 0.06 to 5m were derived from fixed wing and quadcopter UAV imagery collected in summer 2016 and the ArcticDEM dataset. Our findings show that shadowing significantly decreases irradiance compared to smoothed surfaces where local topography is removed. This decrease is exponentially proportional to the DEM pixel sized with 5m DEMs only able to capture a small percentage of the effect. Applying these calculations to the ArcticDEM to cover a larger study area indicates that decreases in irradiance are nonlinearly proportional to elevation with highly crevassed areas showing a larger effect from shadowing. Even so, shading at higher elevations reduces irradiance enough to result in several centimeters snow water equivalence (SWE) per year of over-prediction of runoff in SMB models. Furthermore, analysis of solar radiation products shows that shadowing predicts albedo</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013TCD.....7.5579C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013TCD.....7.5579C"><span>Ocean properties, ice-ocean interactions, and calving front morphology at two major west Greenland glaciers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chauché, N.; Hubbard, A.; Gascard, J.-C.; Box, J. E.; Bates, R.; Koppes, M.; Sole, A.; Patton, H.</p> <p>2013-11-01</p> <p>Warm sub-polar mode water (SPMW) has been identified as a primary driver of mass loss of marine terminating glaciers draining the Greenland Ice Sheet (<span class="hlt">GrIS</span>) yet, the specific mechanisms by which SPMW interacts with these tidewater termini remain uncertain. We present oceanographic data from Rink Glacier (RG) and Store Glacier (SG) fjords, two major marine outlets draining the western sector of the <span class="hlt">GrIS</span> into Baffin Bay over the contrasting melt-seasons of 2009 and 2010. Submarine melting occurs wherever ice is in direct contact with warmer water and the consistent presence of 2.8 °C SPMW adjacent to both ice fronts below 400 m throughout all surveys indicates that melting is maintained by a combination of molecular diffusion and large scale, weak convection, diffusional (hereafter called ubiquitous) melting. At shallower depths (50-200 m), cold, brine-enriched water (BEW) formed over winter appears to persist into the summer thereby buffering this melt by thermal insulation. Our surveys reveal four main modes of glacier-ocean interaction, governed by water depth and the rate of glacier runoff water (GRW) injected into the fjord. Deeper than 200 m, submarine melt is the only process observed, regardless of the intensity of GRW or the depth of injection. However, between the surface and 200 m depth, three further distinct modes are observed governed by the GRW discharge. When GRW is weak (≲1000 m3 s-1), upward motion of the water adjacent to the glacier front is subdued, weak forced or free convection plus diffusional submarine melting dominates at depth, and seaward outflow of melt water occurs from the glacier toe to the base of the insulating BEW. During medium intensity GRW (∼1500 m3 s-1), mixing with SPMW yields deep mixed runoff water (DMRW), which rises as a buoyant plume and intensifies local submarine melting (enhanced buoyancy-driven melting). In this case, DMRW typically attains hydrostatic equilibrium and flows seaward at an intermediate depth of </p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1711613R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1711613R"><span>The role of the microfissuration of the rock matrix in the abrasion resistance of ornamental granitic rocks</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rodríguez-Rey, Angel; Sanchez-Delgado, Nuria; Camino, Clara; Calleja, Lope; Ruiz de Argandoña, Vicente G.; Setien, Alexia</p> <p>2015-04-01</p> <p>The microcrack density and the abrasion resistance of five ornamental granites (Albero, <span class="hlt">Gris</span> Alba, Mondariz, Rosa Porriño and Traspieles) from Galicia (NW Spain) have been quantified as part of a research aimed to interpret the cuttability of the rocks in relation to the petrophysical properties of the rock matrix. Large blocks from the quarries have been cut with an industrial saw and the microcrack density and the abrasion resistance have been measured in two surfaces: H, parallel to the cut surface; T, perpendicular both to the cut surface and the cutting direction. Both planes are perpendicular to the rift plane, as it is known in quarry works. The microcrack density has been quantified following an stereological procedure applied to polished sections imaged under scanning electron microscopy. The magnification of the images allowed the study of microcracks as narrow as 2 microns in aperture. The density has been quantified in terms of length of microcrack traces per surface unit so possible anisotropies of the microcrack network could be detected. The obtained values are in the typical range for this type of rocks although the Traspieles granite shows a higher value due to its weathering degree (H: 5.11, T: 5.37 mm/mm2). The values measured in the two surfaces (H and T) are quite similar in four of the rocks; only the Albero granite shows a marked anisotropy (H: 2.76 T: 3.53 mm/mm2). The abrasion resistance of the rocks has been measured following the european standard EN 14157:2004 using the capon method. The rocks can be classified in two groups according to their abrasion resistance. Rosa Porriño, <span class="hlt">Gris</span> Alba and Mondariz granites are the more resistant to abrasion with values around 16-17 mm. Albero and Traspieles granites are less resistant with values higher than 19 mm. The results show a good correlation between the microcrack density and the abrasion resistance. As can be expected the rocks with high microcrack density show low abrasion resistance. The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1815241S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1815241S"><span>Refreezing on the Greenland ice sheet: a model comparison</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Steger, Christian; Reijmer, Carleen; van den Broeke, Michiel; Ligtenberg, Stefan; Kuipers Munneke, Peter; Noël, Brice</p> <p>2016-04-01</p> <p>Mass loss of the Greenland ice sheet (<span class="hlt">GrIS</span>) is an important contributor to global sea level rise. Besides calving, surface melt is the dominant source of mass loss. However, only part of the surface melt leaves the ice sheet as runoff whereas the other part percolates into the snow cover and refreezes. Due to this process, part of the meltwater is (intermediately) stored. Refreezing thus impacts the surface mass balance of the ice sheet but it also affects the vertical structure of the snow cover due to transport of mass and energy. Due to the sparse availability of in situ data and the demand of future projections, it is inevitable to use numerical models to simulate refreezing and related processes. Currently, the magnitude of refrozen mass is neither well constrained nor well validated. In this study, we model the snow and firn layer, and compare refreezing on the <span class="hlt">GrIS</span> as modelled with two different numerical models. Both models are forced with meteorological data from the regional climate model RACMO 2 that has been shown to simulate realistic conditions for Greenland. One model is the UU/IMAU firn densification model (FDM) that can be used both in an on- and offline mode with RACMO 2. The other model is SNOWPACK; a model originally designed to simulate seasonal snow cover in alpine conditions. In contrast to FDM, SNOWPACK accounts for snow metamorphism and microstructure and contains a more physically based snow densification scheme. A first comparison of the models indicates that both seem to be able to capture the general spatial and temporal pattern of refreezing. Spatially, refreezing occurs mostly in the ablation zone and decreases in the accumulation zone towards the interior of the ice sheet. Below the equilibrium line altitude (ELA) where refreezing occurs in seasonal snow cover on bare ice, the storage effect is only intermediate. Temporal patterns on a seasonal range indicate two peaks in refreezing; one at the beginning of the melt season where</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70170667','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70170667"><span>Characterizing supraglacial meltwater channel hydraulics on the Greenland Ice Sheet from in situ observations</span></a></p> <p><a target="_blank" href=""></a></p> <p>Gleason, Colin J.; Smith, Laurence C.; Chu, Vena W.; Legleiter, Carl; Pitcher, Lincoln H.; Overstreet, Brandon T.; Rennermalm, Asa K.; Forster, Richard R.; Yang, Kang</p> <p>2016-01-01</p> <p>Supraglacial rivers on the Greenland ice sheet (<span class="hlt">GrIS</span>) transport large volumes of surface meltwater toward the ocean, yet have received relatively little direct research. This study presents field observations of channel width, depth, velocity, and water surface slope for nine supraglacial channels on the southwestern <span class="hlt">GrIS</span> collected between 23 July and 20 August, 2012. Field sites are located up to 74 km inland and span 494-1485 m elevation, and contain measured discharges larger than any previous in situ study: from 0.006 to 23.12 m3/s in channels 0.20 to 20.62 m wide. All channels were deeply incised with near vertical banks, and hydraulic geometry results indicate that supraglacial channels primarily accommodate greater discharges by increasing velocity. Smaller streams had steeper water surface slopes (0.74-8.83%) than typical in terrestrial settings, yielding correspondingly high velocities (0.40-2.60 m/s) and Froude numbers (0.45-3.11) with supercritical flow observed in 54% of measurements. Derived Manning's n values were larger and more variable than anticipated from channels of uniform substrate, ranging from 0.009 to 0.154 with a mean value of 0.035 +/- 0.027 despite the absence of sediment, debris, or other roughness elements. Ubiquitous micro-depressions in shallow sections of the channel bed may explain some of these roughness values. However, we find that other, unobserved sources of flow resistance likely contributed to these elevated n values: future work should explicitly consider additional sources of flow resistance beyond bed roughness in supraglacial channels. We conclude that hydraulic modelling for these channels must allow for both sub- and supercritical flow, and most importantly must refrain from assuming that all ice-substrate channels exhibit similar hydraulic behavior, especially for Froude numbers and Manning's n. Finally, this study highlights that further theoretical and empirical work on supraglacial channel hydraulics is</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.C51E..07C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.C51E..07C"><span>Investigation of Controls on Ice Dynamics in Northeast Greenland from Ice-Thickness Change Record Using Ice Sheet System Model (ISSM)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Csatho, B. M.; Larour, E. Y.; Schenk, A. F.; Schlegel, N.; Duncan, K.</p> <p>2015-12-01</p> <p>We present a new, complete ice thickness change reconstruction of the NE sector of the Greenland Ice Sheet for 1978-2014, partitioned into changes due to surface processes and ice dynamics. Elevation changes are computed from all available stereoscopic DEMs, and laser altimetry data (ICESat, ATM, LVIS). Surface Mass Balance and firn-compaction estimates are from RACMO2.3. Originating nearly at the divide of the Greenland Ice Sheet (<span class="hlt">GrIS</span>), the dynamically active North East Ice Stream (NEGIS) is capable of rapidly transmitting ice-marginal forcing far inland. Thus, NEGIS provides a possible mechanism for a rapid drawdown of ice from the ice sheet interior as marginal warming, thinning and retreat continues. Our altimetry record shows accelerating dynamic thinning of Zachariæ Isstrom, initially limited to the deepest part of the fjord near the calving front (1978-2000) and then extending at least 75 km inland. At the same time, changes over the Nioghalvfjerdsfjorden (N79) Glacier are negligible. We also detect localized large dynamic changes at higher elevations on the ice sheet. These thickness changes, often occurring at the onset of fast flow, could indicate rapid variations of basal lubrication due to rerouting of subglacial drainage. We investigate the possible causes of the observed spatiotemporal pattern of ice sheet elevation changes using the Ice Sheet System Model (ISSM). This work build on our previous studies examining the sensitivity of ice flow within the Northeast Greenland Ice Stream (NEGIS) to key fields, including ice viscosity, basal drag. We assimilate the new altimetry record into ISSM to improve the reconstruction of basal friction and ice viscosity. Finally, airborne geophysical (gravity, magnetic) and ice-penetrating radar data is examined to identify the potential geologic controls on the ice thickness change pattern. Our study provides the first comprehensive reconstruction of ice thickness changes for the entire NEGIS drainage basin during</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_8 --> <div id="page_9" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_11");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="161"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4523781','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4523781"><span>Proteomic and metabolic traits of grape exocarp to explain different anthocyanin concentrations of the cultivars</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Negri, Alfredo S.; Prinsi, Bhakti; Failla, Osvaldo; Scienza, Attilio; Espen, Luca</p> <p>2015-01-01</p> <p>The role of grape berry skin as a protective barrier against damage by physical injuries and pathogen attacks requires a metabolism able to sustain biosynthetic activities such as those relating to secondary compounds (i.e., flavonoids). In order to draw the attention on these biochemical processes, a proteomic and metabolomic comparative analysis was performed among Riesling Italico, Pinot <span class="hlt">Gris</span>, Pinot Noir, and Croatina cultivars, which are known to accumulate anthocyanins to a different extent. The application of multivariate statistics on the dataset pointed out that the cultivars were distinguishable from each other and the order in which they were grouped mainly reflected their relative anthocyanin contents. Sorting the spots according to their significance 100 proteins were characterized by LC-ESI-MS/MS. Through GC-MS, performed in Selected Ion Monitoring (SIM) mode, 57 primary metabolites were analyzed and the differences in abundance of 16 of them resulted statistically significant to ANOVA test. Considering the functional distribution, the identified proteins were involved in many physiological processes such as stress, defense, carbon metabolism, energy conversion and secondary metabolism. The trends of some metabolites were related to those of the protein data. Taken together, the results permitted to highlight the relationships between the secondary compound pathways and the main metabolism (e.g., glycolysis and TCA cycle). Moreover, the trend of accumulation of many proteins involved in stress responses, reinforced the idea that they could play a role in the cultivar specific developmental plan. PMID:26300900</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003A%26A...411L.451D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003A%26A...411L.451D"><span>SPI measurements of Galactic 26Al</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Diehl, R.; Knödlseder, J.; Lichti, G. G.; Kretschmer, K.; Schanne, S.; Schönfelder, V.; Strong, A. W.; von Kienlin, A.; Weidenspointner, G.; Winkler, C.; Wunderer, C.</p> <p>2003-11-01</p> <p>The precision measurement of the 1809 keV gamma-ray line from Galactic 26Al is one of the goals of the SPI spectrometer on INTEGRAL with its Ge detector camera. We aim for determination of the detailed shape of this gamma-ray line, and its variation for different source regions along the plane of the Galaxy. Data from the first part of the core program observations of the first mission year have been inspected. A clear detection of the 26Al line at =~ 5-7 sigma significance demonstrates that SPI will deepen 26Al studies. The line intensity is consistent with expectations from previous experiments, and the line appears narrower than the 5.4 keV FWHM reported by <span class="hlt">GRIS</span>, more consistent with RHESSI's recent value. Only preliminary statements can be made at this time, however, due to the multi-component background underlying the signal at =~ 40 times higher intensity than the signal from Galactic 26Al.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017MS%26E..263d2121M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017MS%26E..263d2121M"><span>Estimation of parameters of constant elasticity of substitution production functional model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mahaboob, B.; Venkateswarlu, B.; Sankar, J. Ravi</p> <p>2017-11-01</p> <p>Nonlinear model building has become an increasing important powerful tool in mathematical economics. In recent years the popularity of applications of nonlinear models has dramatically been rising up. Several researchers in econometrics are very often interested in the inferential aspects of nonlinear regression models [6]. The present research study gives a distinct method of estimation of more complicated and highly nonlinear model viz Constant Elasticity of Substitution (CES) production functional model. Henningen et.al [5] proposed three solutions to avoid serious problems when estimating CES functions in 2012 and they are i) removing discontinuities by using the limits of the CES function and its derivative. ii) Circumventing large rounding errors by local linear approximations iii) Handling ill-behaved objective functions by a multi-dimensional grid search. Joel Chongeh et.al [7] discussed the estimation of the impact of capital and labour inputs to the <span class="hlt">gris</span> output agri-food products using constant elasticity of substitution production function in Tanzanian context. Pol Antras [8] presented new estimates of the elasticity of substitution between capital and labour using data from the private sector of the U.S. economy for the period 1948-1998.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JESS..127...28R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JESS..127...28R"><span>Incorporation of ice sheet models into an Earth system model: Focus on methodology of coupling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rybak, Oleg; Volodin, Evgeny; Morozova, Polina; Nevecherja, Artiom</p> <p>2018-03-01</p> <p>Elaboration of a modern Earth system model (ESM) requires incorporation of ice sheet dynamics. Coupling of an ice sheet model (ICM) to an AOGCM is complicated by essential differences in spatial and temporal scales of cryospheric, atmospheric and oceanic components. To overcome this difficulty, we apply two different approaches for the incorporation of ice sheets into an ESM. Coupling of the Antarctic ice sheet model (AISM) to the AOGCM is accomplished via using procedures of resampling, interpolation and assigning to the AISM grid points annually averaged meanings of air surface temperature and precipitation fields generated by the AOGCM. Surface melting, which takes place mainly on the margins of the Antarctic peninsula and on ice shelves fringing the continent, is currently ignored. AISM returns anomalies of surface topography back to the AOGCM. To couple the Greenland ice sheet model (GrISM) to the AOGCM, we use a simple buffer energy- and water-balance model (EWBM-G) to account for orographically-driven precipitation and other sub-grid AOGCM-generated quantities. The output of the EWBM-G consists of surface mass balance and air surface temperature to force the GrISM, and freshwater run-off to force thermohaline circulation in the oceanic block of the AOGCM. Because of a rather complex coupling procedure of <span class="hlt">GrIS</span> compared to AIS, the paper mostly focuses on Greenland.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20000050471','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000050471"><span>On the Spatial Distribution of High Velocity Al-26 Near the Galactic Center</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sturner, Steven J.</p> <p>2000-01-01</p> <p>We present results of simulations of the distribution of 1809 keV radiation from the decay of Al-26 in the Galaxy. Recent observations of this emission line using the Gamma Ray Imaging Spectrometer (<span class="hlt">GRIS</span>) have indicated that the bulk of the AL-26 must have a velocity of approx. 500 km/ s. We have previously shown that a velocity this large could be maintained over the 10(exp 6) year lifetime of the Al-26 if it is trapped in dust grains that are reaccelerated periodically in the ISM. Here we investigate whether a dust grain velocity of approx. 500 km/ s will produce a distribution of 1809 keV emission in latitude that is consistent with the narrow distribution seen by COMPTEL. We find that dust grain velocities in the range 275 - 1000 km/ s are able to reproduce the COMPTEL 1809 keV emission maps reconstructed using the Richardson-Lucy and Maximum Entropy image reconstruction methods while the emission map reconstructed using the Multiresolution Regularized Expectation Maximization algorithm is not well fit by any of our models. The Al-26 production rate that is needed to reproduce the observed 1809 keV intensity yields in a Galactic mass of Al-26 of approx. 1.5 - 2 solar mass which is in good agreement with both other observations and theoretical production rates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AN....333..796S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AN....333..796S"><span>The 1.5 meter solar telescope GREGOR</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.; Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.; Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Waldmann , T. A.</p> <p>2012-11-01</p> <p>The 1.5 m telescope GREGOR opens a new window to the understanding of solar small-scale magnetism. The first light instrumentation includes the Gregor Fabry Pérot Interferometer (GFPI), a filter spectro-polarimeter for the visible wavelength range, the GRating Infrared Spectro-polarimeter (<span class="hlt">GRIS</span>) and the Broad-Band Imager (BBI). The excellent performance of the first two instruments has already been demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest solar telescope and number 3 in the world. Its all-reflective Gregory design provides a large wavelength coverage from the near UV up to at least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR is equipped with a high-order adaptive optics system, with a subaperture size of 10 cm, and a deformable mirror with 256 actuators. The science goals are focused on, but not limited to, solar magnetism. GREGOR allows us to measure the emergence and disappearance of magnetic flux at the solar surface at spatial scales well below 100 km. Thanks to its spectro-polarimetric capabilities, GREGOR will measure the interaction between the plasma flows, different kinds of waves, and the magnetic field. This will foster our understanding of the processes that heat the chromosphere and the outer layers of the solar atmosphere. Observations of the surface magnetic field at very small spatial scales will shed light on the variability of the solar brightness.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20546418','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20546418"><span>The impact of grape skin bioactive functionality information on the acceptability of tea infusions made from wine by-products.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Cheng, Vern Jou; Bekhit, Alaa El-Din A; Sedcole, Richard; Hamid, Nazimah</p> <p>2010-05-01</p> <p>The effect of information on the health benefits of bio-active compounds on the acceptability of 5 tea infusions made from grape skins generated from wine processing waste (from Vitis vinifera var. Pinot Noir and Pinot <span class="hlt">Gris</span>) was investigated. Samples of tea infusions with natural additives (PNHGT25 and PGGT50) and without additives (control PN, control PG, and PNPG50) were evaluated by 45 in-home consumer panels (30 female, 15 male) before and after information on the health benefits of grape skins were provided. Information significantly increased the overall acceptability, overall aroma, flavor, and aftertaste of the infusions. The results obtained showed a clear tendency toward increased purchase intention (by 29%) when information on the health benefits of the tea infusion samples was provided to consumers. Interactions existed between gender/infusion samples and stage of information on the purchase intention. Females recorded a significant increase (by 53%) in purchase intention, whereas no change in the males' purchase intention was found after information was provided.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ISPAr41B8..531S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ISPAr41B8..531S"><span>Fusion of Laser Altimetry Data with Dems Derived from Stereo Imaging Systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schenk, T.; Csatho, B. M.; Duncan, K.</p> <p>2016-06-01</p> <p>During the last two decades surface elevation data have been gathered over the Greenland Ice Sheet (<span class="hlt">GrIS</span>) from a variety of different sensors including spaceborne and airborne laser altimetry, such as NASA's Ice Cloud and land Elevation Satellite (ICESat), Airborne Topographic Mapper (ATM) and Laser Vegetation Imaging Sensor (LVIS), as well as from stereo satellite imaging systems, most notably from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Worldview. The spatio-temporal resolution, the accuracy, and the spatial coverage of all these data differ widely. For example, laser altimetry systems are much more accurate than DEMs derived by correlation from imaging systems. On the other hand, DEMs usually have a superior spatial resolution and extended spatial coverage. We present in this paper an overview of the SERAC (Surface Elevation Reconstruction And Change detection) system, designed to cope with the data complexity and the computation of elevation change histories. SERAC simultaneously determines the ice sheet surface shape and the time-series of elevation changes for surface patches whose size depends on the ruggedness of the surface and the point distribution of the sensors involved. By incorporating different sensors, SERAC is a true fusion system that generates the best plausible result (time series of elevation changes) a result that is better than the sum of its individual parts. We follow this up with an example of the Helmheim gacier, involving ICESat, ATM and LVIS laser altimetry data, together with ASTER DEMs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3528R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3528R"><span>New insights into West Greenland ice sheet/stream dynamics during the last glacial cycle.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roberts, David; Lane, Tim; Rea, Brice; Cofaigh, Colm O.; Jamieson, Stewart; Vieli, Andreas; Rodes, Angel</p> <p>2015-04-01</p> <p>Onshore and offshore geomorphological mapping and deglacial chronologies from West Greenland constrain the nature and magnitude of ice advance and decay of the Greenland Ice Sheet (<span class="hlt">GrIS</span>) during the last glacial cycle. Several ice stream troughs are known to have fed ice to the shelf edge during the last glacial cycle. Their offshore expression suggests that many were coalescent systems fed by smaller outlet glaciers and ice streams onshore but their central flow pathways were also controlled by geology and preglacial topography. The bed morphology of these large ice streams shows they operated over soft, deforming beds with drumlins, mega-scale glacial lineations and grounding zone wedges marking an offshore transition from predominant areal scour onshore. Records of offshore deglacial chronology remain sparse but the Uummannaq and Disko Bugt ice stream corridors are now well constrained. The Uummannaq ice stream (UIS) completely deglaciated from the continental shelf between 14.8 ka and 11.0 ka in response to rising air temperatures, increasing JJA solar radiation and sea-level rise, but temporary standstills and the asynchronous retreat history of its feeder zones suggest that topography/bathymetry strongly modulated retreat rates as ice became 'locked' back into the coastal fjord system. Initial reconstructions of behaviour UIS discounted an oceanic role in early deglaciation and favoured retreat from the mid-shelf and inner-shelf prior to the Younger Dryas but both these concepts remain under investigation. In Disko Bugt, Jakobshavn Isbrae deglaciated later than the UIS and remained on the outer shelf during the Younger Dyras stadial (12.8 - 11.7 cal. kyrs BP) only reaching in the inner coast fjords at approximately 10.0 ka. The later deglaciation of the Disko system (despite similar external forcing mechanisms) was controlled by regional topographic/bathymetric contrasts in their respective trough morphologies. This hypothesis is supported by recent model</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3047F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3047F"><span>The region of the Piedra Berroqueña: A potencial Global Heritage Stone Province.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Freire-Lista, David Martin; Fort, Rafael</p> <p>2015-04-01</p> <p>, Crema Valdemanco. In Cadalso de los Vidrios it is marketed under the commercial name of <span class="hlt">Gris</span> Cadalso and Rosa Cadalso. Biotite granites without cordierite or amphibole and the most representative historic quarries are in San Lorenzo del Escorial, Valdemorillo, Robledo de Chavela, Colmenar de Arroyo, Chapinería and Navas del Rey. In Zarzalejo is marketed under the commercial name of <span class="hlt">Gris</span> Escorial. Leucogranites in Manzanares el Real, San Martín de Valdeiglesias or La Cabrera there are historical quarries. In the Cadalso de los Vidrios is exported under the commercial name Blanco Ártico, Blanco Cristal and Oro Cristal. The Piedra Berroqueña province meets the requirements proposed to be nominated for GHSP. This nomination will contribute to better understanding and dissemination of an area with attractive economic aspects that focuses on the use of its resources. Thus, the Piedra Berroqueña remains part of the heritage of the province, whether used as a replacement stone for restoration of heritage buildings or when used for new buildings. Acknowledgements This study was funded by the Community of Madrid under the GEOMATERIALS 2 project (S2013/MIT-2914). The authors are members of the Complutense University of Madrid's Research Group: "Alteración y Conservación de los Materiales Pétreos del Patrimonio" (ref. 921349).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017TCry...11.1015F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017TCry...11.1015F"><span>Reconstructions of the 1900-2015 Greenland ice sheet surface mass balance using the regional climate MAR model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fettweis, Xavier; Box, Jason E.; Agosta, Cécile; Amory, Charles; Kittel, Christoph; Lang, Charlotte; van As, Dirk; Machguth, Horst; Gallée, Hubert</p> <p>2017-04-01</p> <p>With the aim of studying the recent Greenland ice sheet (<span class="hlt">GrIS</span>) surface mass balance (SMB) decrease relative to the last century, we have forced the regional climate MAR (Modèle Atmosphérique Régional; version 3.5.2) model with the ERA-Interim (ECMWF Interim Re-Analysis; 1979-2015), ERA-40 (1958-2001), NCEP-NCARv1 (National Centers for Environmental Prediction-National Center for Atmospheric Research Reanalysis version 1; 1948-2015), NCEP-NCARv2 (1979-2015), JRA-55 (Japanese 55-year Reanalysis; 1958-2014), 20CRv2(c) (Twentieth Century Reanalysis version 2; 1900-2014) and ERA-20C (1900-2010) reanalyses. While all these forcing products are reanalyses that are assumed to represent the same climate, they produce significant differences in the MAR-simulated SMB over their common period. A temperature adjustment of +1 °C (respectively -1 °C) was, for example, needed at the MAR boundaries with ERA-20C (20CRv2) reanalysis, given that ERA-20C (20CRv2) is ˜ 1 °C colder (warmer) than ERA-Interim over Greenland during the period 1980-2010. Comparisons with daily PROMICE (Programme for Monitoring of the Greenland Ice Sheet) near-surface observations support these adjustments. Comparisons with SMB measurements, ice cores and satellite-derived melt extent reveal the most accurate forcing datasets for the simulation of the <span class="hlt">GrIS</span> SMB to be ERA-Interim and NCEP-NCARv1. However, some biases remain in MAR, suggesting that some improvements are still needed in its cloudiness and radiative schemes as well as in the representation of the bare ice albedo. Results from all MAR simulations indicate that (i) the period 1961-1990, commonly chosen as a stable reference period for Greenland SMB and ice dynamics, is actually a period of anomalously positive SMB (˜ +40 Gt yr-1) compared to 1900-2010; (ii) SMB has decreased significantly after this reference period due to increasing and unprecedented melt reaching the highest rates in the 120-year common period; (iii) before 1960, both ERA</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12...39B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12...39B"><span>Influence of temperature fluctuations on equilibrium <br class="break"/>ice sheet volume</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bøgeholm Mikkelsen, Troels; Grinsted, Aslak; Ditlevsen, Peter</p> <p>2018-01-01</p> <p>Forecasting the future sea level relies on accurate modeling of the response of the Greenland and Antarctic ice sheets to changing temperatures. The surface mass balance (SMB) of the Greenland Ice Sheet (<span class="hlt">GrIS</span>) has a nonlinear response to warming. Cold and warm anomalies of equal size do not cancel out and it is therefore important to consider the effect of interannual fluctuations in temperature. We find that the steady-state volume of an ice sheet is biased toward larger size if interannual temperature fluctuations are not taken into account in numerical modeling of the ice sheet. We illustrate this in a simple ice sheet model and find that the equilibrium ice volume is approximately 1 m SLE (meters sea level equivalent) smaller when the simple model is forced with fluctuating temperatures as opposed to a stable climate. It is therefore important to consider the effect of interannual temperature fluctuations when designing long experiments such as paleo-spin-ups. We show how the magnitude of the potential bias can be quantified statistically. For recent simulations of the Greenland Ice Sheet, we estimate the bias to be 30 Gt yr-1 (24-59 Gt yr-1, 95 % credibility) for a warming of 3 °C above preindustrial values, or 13 % (10-25, 95 % credibility) of the present-day rate of ice loss. Models of the Greenland Ice Sheet show a collapse threshold beyond which the ice sheet becomes unsustainable. The proximity of the threshold will be underestimated if temperature fluctuations are not taken into account. We estimate the bias to be 0.12 °C (0.10-0.18 °C, 95 % credibility) for a recent estimate of the threshold. In light of our findings it is important to gauge the extent to which this increased variability will influence the mass balance of the ice sheets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C13F1007T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C13F1007T"><span>The Role of the North Atlantic Oscillation (NAO) on Recent Greenland Surface Mass Loss and Mass Partitioning</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tedesco, M.; Alexander, P.; Porter, D. F.; Fettweis, X.; Luthcke, S. B.; Mote, T. L.; Rennermalm, A.; Hanna, E.</p> <p>2017-12-01</p> <p>Despite recent changes in Greenland surface mass losses and atmospheric circulation over the Arctic, little attention has been given to the potential role of large-scale atmospheric processes on the spatial and temporal variability of mass loss and partitioning of the <span class="hlt">GrIS</span> mass loss. Using a combination of satellite gravimetry measurements, outputs of the MAR regional climate model and reanalysis data, we show that changes in atmospheric patterns since 2013 over the North Atlantic region of the Arctic (NAA) modulate total mass loss trends over Greenland together with the spatial and temporal distribution of mass loss partitioning. For example, during the 2002 - 2012 period, melting persistently increased, especially along the west coast, as a consequence of increased insulation and negative NAO conditions characterizing that period. Starting in 2013, runoff along the west coast decreased while snowfall increased substantially, when NAO turned to a more neutral/positive state. Modeled surface mass balance terms since 1950 indicate that part of the GRACE-period, specifically the period between 2002 and 2012, was exceptional in terms of snowfall over the east and northeast regions. During that period snowfall trend decreased to almost 0 Gt/yr from a long-term increasing trend, which presumed again in 2013. To identify the potential impact of atmospheric patterns on mass balance and its partitioning, we studied the spatial and temporal correlations between NAO and snowfall/runoff. Our results indicate that the correlation between summer snowfall and NAO is not stable during the 1950 - 2015 period. We further looked at changes in patterns of circulation using self organizing maps (SOMs) to identify the atmospheric patterns characterizing snowfall during different periods. We discuss potential implications for past changes and future GCM and RCM simulations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C23C..03S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C23C..03S"><span>Surface water hydrology and the Greenland Ice Sheet</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smith, L. C.; Yang, K.; Pitcher, L. H.; Overstreet, B. T.; Chu, V. W.; Rennermalm, A. K.; Cooper, M. G.; Gleason, C. J.; Ryan, J.; Hubbard, A.; Tedesco, M.; Behar, A.</p> <p>2016-12-01</p> <p>Mass loss from the Greenland Ice Sheet now exceeds 260 Gt/year, raising global sea level by >0.7 mm annually. Approximately two-thirds of this total mass loss is now driven by negative ice sheet surface mass balance (SMB), attributed mainly to production and runoff of meltwater from the ice sheet surface. This new dominance of runoff as a driver of <span class="hlt">GrIS</span> total mass loss will likely persist owing to anticipated further increases in surface melting, reduced meltwater storage in firn, and the waning importance of dynamical mass losses (ice calving) as the ice sheets retreat from their marine-terminating margins. It also creates the need and opportunity for integrative research pairing traditional surface water hydrology approaches with glaciology. As one example, we present a way to measure supraglacial "runoff" (i.e. specific discharge) at the supraglacial catchment scale ( 101-102 km2), using in situ measurements of supraglacial river discharge and high-resolution satellite/drone mapping of upstream catchment area. This approach, which is standard in terrestrial hydrology but novel for ice sheet science, enables independent verification and improvement of modeled SMB runoff estimates used to project sea level rise. Furthermore, because current SMB models do not consider the role of fluvial watershed processes operating on the ice surface, inclusion of even a simple surface routing model materially improves simulations of runoff delivered to moulins, the critical pathways for meltwater entry into the ice sheet. Incorporating principles of surface water hydrology and fluvial geomorphology and into glaciological models will thus aid estimates of Greenland meltwater runoff to the global ocean as well as connections to subglacial hydrology and ice sheet dynamics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.6661Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.6661Z"><span>Holocene evolution of Hans Tausen Iskappe (Greenland): merging constraints and models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zekollari, Harry; Lecavalier, Benoit S.; Huybrechts, Philippe</p> <p>2017-04-01</p> <p>In this study the Holocene evolution of Hans Tausen Iskappe (western Peary Land, Greenland) is investigated. Constraints on the ice cap evolution are combined with climatic records in a numerical ice flow - surface mass balance (SMB) model to better understand the palaeoenvironmental and climatic evolution of this region. Our simulations suggest that after disconnecting from the Greenland Ice Sheet (<span class="hlt">GrIS</span>) the ice cap had roughly its present-day size and geometry around 8.5-9 ka ago. An ice core drilled to the bed indicates that the southern part of the ice cap subsequently disappeared during the Holocene Thermal Maximum (HTM) and this collapse can be reproduced, but the model suggests that the northern part of the ice cap most likely survived this warmer period. The late Holocene growth of the ice cap to its Little Ice Age (LIA) maximum neoglacial extent can be reproduced from the temperature reconstruction. The simulations suggest that over the last millennia the local precipitation may have been up to 70-80% higher than at present. By coupling the pre-industrial temperature forcing to a post-LIA warming trend, it is concluded that the warming between the end of the LIA and the period 1961-1990 was between 1 and 2°C. In all experiments the ice flow model complexity and horizontal resolution have only a minor effect on the long-term evolution of the ice cap, which is largely driven by SMB changes. On the other hand the glacial isostatic adjustments (GIA) need to be accounted for in a detailed manner, as this has a large impact on the modelled Holocene ice cap evolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920012692','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920012692"><span>The gamma ray continuum spectrum from the galactic center disk and point sources</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gehrels, Neil; Tueller, Jack</p> <p>1992-01-01</p> <p>A light curve of gamma-ray continuum emission from point sources in the galactic center region is generated from balloon and satellite observations made over the past 25 years. The emphasis is on the wide field-of-view instruments which measure the combined flux from all sources within approximately 20 degrees of the center. These data have not been previously used for point-source analyses because of the unknown contribution from diffuse disk emission. In this study, the galactic disk component is estimated from observations made by the Gamma Ray Imaging Spectrometer (<span class="hlt">GRIS</span>) instrument in Oct. 1988. Surprisingly, there are several times during the past 25 years when all gamma-ray sources (at 100 keV) within about 20 degrees of the galactic center are turned off or are in low emission states. This implies that the sources are all variable and few in number. The continuum gamma-ray emission below approximately 150 keV from the black hole candidate 1E1740.7-2942 is seen to turn off in May 1989 on a time scale of less than two weeks, significantly shorter than ever seen before. With the continuum below 150 keV turned off, the spectral shape derived from the HEXAGONE observation on 22 May 1989 is very peculiar with a peak near 200 keV. This source was probably in its normal state for more than half of all observations since the mid-1960's. There are only two observations (in 1977 and 1979) for which the sum flux from the point sources in the region significantly exceeds that from 1E1740.7-2942 in its normal state.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26608668','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26608668"><span>Intraspecific variation in essential oil composition of the medicinal plant Lippia integrifolia (Verbenaceae). Evidence for five chemotypes.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Marcial, Guillermo; de Lampasona, Marina P; Vega, Marta I; Lizarraga, Emilio; Viturro, Carmen I; Slanis, Alberto; Juárez, Miguel A; Elechosa, Miguel A; Catalán, César A N</p> <p>2016-02-01</p> <p>The aerial parts of Lippia integrifolia (incayuyo) are widely used in northwestern and central Argentina for their medicinal and aromatic properties. The essential oil composition of thirty-one wild populations of L. integrifolia covering most of its natural range was analyzed by GC and GC-MS. A total of one hundred and fifty two terpenoids were identified in the essential oils. Sesquiterpenoids were the dominant components in all but one of the collections analyzed, the only exception being a sample collected in San Juan province where monoterpenoids amounted to 51%. Five clearly defined chemotypes were observed. One possessed an exquisite and delicate sweet aroma with trans-davanone as dominant component (usually above 80%). Another with an exotic floral odour was rich in oxygenated sesquiterpenoids based on the rare lippifoliane and africanane skeletons. The trans-davanone chemotype is the first report of an essential oil containing that sesquiterpene ketone as the main constituent. The absolute configuration of trans-davanone from L. integrifolia was established as 6S, 7S, 10S, the enantiomer of trans-davanone from 'davana oil' (Artemisia pallens). Wild plants belonging to trans-davanone and lippifolienone chemotypes were propagated and cultivated in the same parcel of land in Santa Maria, Catamarca. The essential oil compositions of the cultivated plants were essentially identical to the original plants in the wild, indicating that the essential oil composition is largely under genetic control. Specimens collected near the Bolivian border that initially were identified as L. boliviana Rusby yielded an essential oil practically identical to the trans-davanone chemotype of L. integrifolia supporting the recent view that L. integrifolia (<span class="hlt">Gris</span>.) Hieron. and L. boliviana Rusby are synonymous. Copyright © 2015 Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/10104161','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/10104161"><span>Comparison and verification of two models which predict minimum principal in situ stress from triaxial data</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciT</a></p> <p>Harikrishnan, R.; Hareland, G.; Warpinski, N.R.</p> <p></p> <p>This paper evaluates the correlation between values of minimum principal in situ stress derived from two different models which use data obtained from triaxial core tests and coefficient for earth at rest correlations. Both models use triaxial laboratory tests with different confining pressures. The first method uses a vcrified fit to the Mohr failure envelope as a function of average rock grain size, which was obtained from detailed microscopic analyses. The second method uses the Mohr-Coulomb failure criterion. Both approaches give an angle in internal friction which is used to calculate the coefficient for earth at rest which gives themore » minimum principal in situ stress. The minimum principal in situ stress is then compared to actual field mini-frac test data which accurately determine the minimum principal in situ stress and are used to verify the accuracy of the correlations. The cores and the mini-frac stress test were obtained from two wells, the Gas Research Institute`s (<span class="hlt">GRIs</span>) Staged Field Experiment (SFE) no. 1 well through the Travis Peak Formation in the East Texas Basin, and the Department of Energy`s (DOE`s) Multiwell Experiment (MWX) wells located west-southwest of the town of Rifle, Colorado, near the Rulison gas field. Results from this study indicates that the calculated minimum principal in situ stress values obtained by utilizing the rock failure envelope as a function of average rock grain size correlation are in better agreement with the measured stress values (from mini-frac tests) than those obtained utilizing Mohr-Coulomb failure criterion.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26729526','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26729526"><span>Thermal Processing of PVP- and HPMC-Based Amorphous Solid Dispersions.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>LaFountaine, Justin S; Prasad, Leena Kumari; Brough, Chris; Miller, Dave A; McGinity, James W; Williams, Robert O</p> <p>2016-02-01</p> <p>Thermal processing technologies continue to gain interest in pharmaceutical manufacturing. However, the types and grades of polymers that can be utilized in common thermal processing technologies, such as hot-melt extrusion (HME), are often limited by thermal or rheological factors. The objectives of the present study were to compare and contrast two thermal processing methods, HME and KinetiSol® Dispersing (KSD), and investigate the influence of polymer type, polymer molecular weight, and drug loading on the ability to produce amorphous solid dispersions (ASDs) containing the model compound griseofulvin (<span class="hlt">GRIS</span>). Dispersions were analyzed by a variety of imaging, solid-state, thermal, and solution-state techniques. Dispersions were prepared by both HME and KSD using polyvinylpyrrolidone (PVP) K17 or hydroxypropyl methylcellulose (HPMC) E5. Dispersions were only prepared by KSD using higher molecular weight grades of HPMC and PVP, as these could not be extruded under the conditions selected. Powder X-ray diffraction (PXRD) analysis showed that dispersions prepared by HME were amorphous at 10% and 20% drug load; however, it showed significant crystallinity at 40% drug load. PXRD analysis of KSD samples showed all formulations and drug loads to be amorphous with the exception of trace crystallinity seen in PVP K17 and PVP K30 samples at 40% drug load. These results were further supported by other analytical techniques. KSD produced amorphous dispersions at higher drug loads than could be prepared by HME, as well as with higher molecular weight polymers that were not processable by HME, due to its higher rate of shear and torque output.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C12B..05S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C12B..05S"><span>Surface mass balance model evaluation from satellite and airborne lidar mapping</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sutterley, T. C.; Velicogna, I.; Fettweis, X.; van den Broeke, M. R.</p> <p>2016-12-01</p> <p>We present estimates of Greenland Ice Sheet (<span class="hlt">GrIS</span>) surface elevation change from a novel combination of satellite and airborne laser altimetry measurements. Our method combines measurements from the Airborne Topographic Mapper (ATM), the Land, Vegetation and Ice Sensor (LVIS) and ICESat-1 to generate elevation change rates at high spatial resolution. This method allows to extend the records of each instrument, increases the overall spatial coverage compared to a single instrument, and produces high-quality, coherent maps of surface elevation change. In addition by combining the lidar datasets, we are able to investigate seasonal and interannual surface elevation change for years where Spring and Fall Operation IceBridge campaigns are available. We validate our method by comparing with the standard NSIDC elevation change product calculated using overlapping Level-1B ATM data. We use the altimetry-derived mass changes to evaluate the uncertainty in surface mass balance, particularly in the runoff component, from two Regional Climate Models (RCM's), the Regional Atmospheric Climate Model (RACMO) and the Modéle Atmosphérique Régional (MAR), and one Global Climate Model (GCM), MERRA2/GEOS-5. We investigate locations with low ice sheet surface velocities that are within the estimated ablation zones of each regional climate model. We find that the surface mass balance outputs from RACMO and MAR show good correspondence with mass changes derived from surface elevation changes over long periods. At two sites in Northeast Greenland (NEGIS), the MAR model has better correspondence with the altimetry estimate. We find that the differences at these locations are primarily due to the characterization of meltwater refreeze within the ice sheet.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_11");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_9 --> <div id="page_10" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_11");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="181"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.8016N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.8016N"><span>The Macael landscape in the context of a possible candidate as Global Heritage Stone Province (Almería, SE of Spain)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Navarro Domínguez, Rafael; Pereira Gómez, Dolores; Carrillo, Gloria; Cruz, Anasol</p> <p>2017-04-01</p> <p>The beginning of the marble extraction activity in the Macael Area (Almería, South of Spain) date back 4000 years ago, and since then, it has been used in several and important monuments, principally, in Spain. The quality of the works carried out is more than proven. During this time, the extraction has alternated periods of activity with others of lesser or none-activity, ruling both the lives of the inhabitants of the region, and its landscape. The most well-known material extracted in the region, with international recognition, is marble "Blanco Macael" (White Macael), traditionally compared with "Carrara marble". But there are other marbles such as "Amarillo Macael", "<span class="hlt">Gris</span> Macael" or "Anasol", as well as serpentinites that are referred as "Verde Macael" or "Verde Almería". All of them have been employed in many recent important buildings, at national and international level. The problem of this intensive activity through the years, from the point of view of the preservation of the old landscapes, is that the modern quarries have replaced the old ones, leaving few remains of the old quarries. In some cases it is possible to see Muslim vestiges (e.g. "Puntilla"), but this is an exception. Notwithstanding, the landscape of the region has a high value due to the combination of high mountains, high faces with a lot of banks, waste dumps and full restored areas. Nowadays, the surface occupied by mining exploitation, only in the closer area to Macael village, is more 8.5 km2, with more than forty active quarries and many abandoned ones. These features have helped to configure a singular and beautiful landscape, possibly unique in Spain, in relation with an historic mining activity. This is an important added value to the possible candidature of the "Blanco Macael" as a "Global Heritage Stone Resource" and the "Macael Region" as a "Global Heritage Stone Province", mostly if we consider that these designations must take into consideration the social importance of the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29187140','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29187140"><span>Somatic embryogenesis from seeds in a broad range of Vitis vinifera L. varieties: rescue of true-to-type virus-free plants.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>San Pedro, Tània; Gammoudi, Najet; Peiró, Rosa; Olmos, Antonio; Gisbert, Carmina</p> <p>2017-11-29</p> <p>Somatic embryogenesis is the preferred method for cell to plant regeneration in Vitis vinifera L. However, low frequencies of plant embryo conversion are commonly found. In a previous work we obtained from cut-seeds of a grapevine infected with the Grapevine leafroll associated viruses 1 and 3 (GLRaV-1 and GLRaV-3), high rates of direct regeneration, embryo plant conversion and sanitation. The aim of this study is to evaluate the usefulness of this procedure for regeneration of other grapevine varieties which include some infected with one to three common grapevine viruses (GLRaV-3, Grapevine fanleaf virus (GFLV) and Grapevine fleck virus (GFkV)). As grapevine is highly heterozygous, it was necessary to select from among the virus-free plants those that regenerated from mother tissues around the embryo, (true-to-type). Somatic embryogenesis and plant regeneration were achieved in a first experiment, using cut-seeds from the 14 grapevine varieties Airén, Cabernet Franc, Cabernet Sauvignon, Mencía, Merlot, Monastrell, Petit Verdot, Pinot Blanc (infected by GFLV and GFkV), Pinot <span class="hlt">Gris</span>, Pinot Meunier, Pinot Noir, Syrah, Tempranillo (infected by GFLV), and Verdil. All regenerated plants were confirmed to be free of GFkV whereas at least 68% sanitation was obtained for GFLV. The SSR profiles of the virus-free plants showed, in both varieties, around 10% regeneration from mother tissue (the same genetic make-up as the mother plant). In a second experiment, this procedure was used to sanitize the varieties Cabernet Franc, Godello, Merlot and Valencí Blanc infected by GLRaV-3, GFkV and/or GFLV. Cut-seeds can be used as explants for embryogenesis induction and plant conversion in a broad range of grapevine varieties. The high regeneration rates obtained with this procedure facilitate the posterior selection of true-to-type virus-free plants. A sanitation rate of 100% was obtained for GFkV as this virus is not seed-transmitted. However, the presence of GLRaV-3 and GFLV in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20170005818&hterms=Remote+sensing&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DRemote%2Bsensing','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20170005818&hterms=Remote+sensing&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DRemote%2Bsensing"><span>Evaluation of Satellite Remote Sensing Albedo Retrievals over the Ablation Area of the Southwestern Greenland Ice Sheet</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Moustafa, Samiah E.; Rennermalm, Asa K.; Roman, Miguel O.; Wang, Zhuosen; Schaaf, Crystal B.; Smith, Laurence C.; Koenig, Lora S.; Erb, Angela</p> <p>2017-01-01</p> <p>MODerate resolution Imaging Spectroradiometer (MODIS) albedo products have been validated over spatially uniform, snow-covered areas of the Greenland ice sheet (<span class="hlt">GrIS</span>) using the so-called single 'point-to-pixel' method. This study expands on this methodology by applying a 'multiple-point-to-pixel' method and examination of spatial autocorrelation (here using semivariogram analysis) by using in situ observations, high-resolution World- View-2 (WV-2) surface reflectances, and MODIS Collection V006 daily blue-sky albedo over a spatially heterogeneous surfaces in the lower ablation zone in southwest Greenland. Our results using 232 ground-based samples within two MODIS pixels, one being more spatial heterogeneous than the other, show little difference in accuracy among narrow and broad band albedos (except for Band 2). Within the more homogenous pixel area, in situ and MODIS albedos were very close (error varied from -4% to +7%) and within the range of ASD standard errors. The semivariogram analysis revealed that the minimum observational footprint needed for a spatially representative sample is 30 m. In contrast, over the more spatially heterogeneous surface pixel, a minimum footprint size was not quantifiable due to spatial autocorrelation, and far exceeds the effective resolution of the MODIS retrievals. Over the high spatial heterogeneity surface pixel, MODIS is lower than ground measurements by 4-7%, partly due to a known in situ undersampling of darker surfaces that often are impassable by foot (e.g., meltwater features and shadowing effects over crevasses). Despite the sampling issue, our analysis errors are very close to the stated general accuracy of the MODIS product of 5%. Thus, our study suggests that the MODIS albedo product performs well in a very heterogeneous, low-albedo, area of the ice sheet ablation zone. Furthermore, we demonstrate that single 'point-to-pixel' methods alone are insufficient in characterizing and validating the variation of surface</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1712768T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1712768T"><span>Between and within-field variation in physico-chemical soil properties of vineyards: implications for terroir zoning and management in Heuvelland, Belgium</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tavernier, Emma; Verdoodt, Ann; Cornelis, Wim; Delbecque, Nele; Tiebergijn, Lynn; Seynnaeve, Marleen; Gabriels, Donald</p> <p>2015-04-01</p> <p>The 'Heuvelland' region with a surface area of 94 km² is situated in the Province of West Flanders, Belgium, bordering with France. The region comprises a number of hills ("heuvel") on which a fast growing 'wine culture' is developing. Both professional as well as non-professional wine makers together cultivate about 19 ha of vineyards, and are still expanding. Grapes cultivated include Chardonnay, Pinot <span class="hlt">gris</span> and Pinot noir among others. The small-scale, strongly dispersed vineyards are located in different landscape positions of variable aspect. The objective of our preliminary study was to assess the between-field and within-field variation in physico-chemical soil properties of these vineyards with the aim to better characterise the terroir(s) in Heuvelland and provide guidelines for soil management. Fourteen vineyards from five different wineries were selected for detailed soil sampling. Twenty-five sampling sites were chosen according to the topography, soil map units and observed variability in grape growth. The soil was sampled using 15 cm depth increments up to a depth of 60 cm or a shallower lithic contact. Composite samples of 5 sampling locations along the contour lines were taken per within-field zone. Besides the texture, pH, organic carbon, total nitrogen, available phosphorous and exchangeable base cations (Ca, Mg, K), also some micronutrients (Fe, B, Cu, Mn) were determined using standard laboratory procedures. The soils developed on Quaternary niveo-eolian sandy loam and loamy sediments of variable thickness covering marine sandy and clayey sediments of the Tertiary. Where the Tertiary clayey sediments occur at shallow depth, they can strongly influence the internal drainage. At higher positions in the landscape, iron-rich sandstone layers are found at shallow depth. Fragments of this iron-rich sandstone can also be found at lower positions (colluvial material). This iron sandstone is claimed to contribute to the unique character of this wine</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.H53F1590C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.H53F1590C"><span>An Emerging Wine Region in Nova Scotia, Canada: Terroir Trials and Tribulations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cameron, B. I.; Ketter, B. S.; Karakis, S.</p> <p>2012-12-01</p> <p>Nova Scotia, strategically located on Canada's east coast, is an emerging wine region, whose distinctive wines are garnering international acclaim. Nova Scotia has a long and rich tradition of growing grapes for wine dating back as far as 1611. Nova Scotia's mesoclimates, glacial soils, and proximity to the Atlantic Ocean form a complex alliance to create a unique and expressive terroir. Tidal Bay is a new appellation wine for Nova Scotia stylistically defined as a fresh, crisp and high-acid blend of white grapes. There are four main wine-growing regions in Nova Scotia, all influenced by the warming effects of the Bay of Fundy and Atlantic Ocean: Malagash Peninsula, Annapolis Valley, Bear River Valley and the South Shore. Nova Scotia currently has 14 producing wineries with many more in the development stage. Nova Scotia grape growers not only have had success developing mature and consistent hybrids, but in recent years several vinifera have flourished in this cool climate area. The white hybrids include L'Acadie Blanc, New York Muscat, Seyval Blanc, and Vidal Blanc. The white vinifera include chardonnay, riesling, pinot <span class="hlt">gris</span>, and sauvignon blanc. Red hybrids are Baco Noir, Leon Millet, Lucie Kuhlmann, and Marechal Foch, whereas the only red vinifera is pinot noir. Nova Scotia has nearly perfect climatic conditions for making world class icewines and sparkling wines. A preliminary GIS analysis of climate, topographic, geology and soil data helps to define Nova Scotia's terroir. Annual precipiatation varies from 10 to 21.6 cm/year with a vast majority of the wineries located in regions with the lowest rainfall. Daily average temperature ranges from 5.5 to 7.5°C, degree growing days above 5°C from 1382 to 1991, and mean August temperature from 15.6 to 19.3 °C. Wineries cluster in the warmest regions based on these temperature measures to assist grape ripening. Soils in these diverse wine regions can range from silty, sandy and clay loams to more gravel-rich sandy</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1615566M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1615566M"><span>Monitoring meteorological spatial variability in viticulture using a low-cost Wireless Sensor Network</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Matese, Alessandro; Crisci, Alfonso; Di Gennaro, Filippo; Primicerio, Jacopo; Tomasi, Diego; Guidoni, Silvia</p> <p>2014-05-01</p> <p>In a long-term perspective, the current global agricultural scenario will be characterize by critical issues in terms of water resource management and environmental protection. The concept of sustainable agriculture would become crucial at reducing waste, optimizing the use of pesticides and fertilizers to crops real needs. This can be achieved through a minimum-scale monitoring of the crop physiologic status and the environmental parameters that characterize the microclimate. Viticulture is often subject to high variability within the same vineyard, thus becomes important to monitor this heterogeneity to allow a site-specific management and maximize the sustainability and quality of production. Meteorological variability expressed both at vineyard scale (mesoclimate) and at single plant level (microclimate) plays an important role during the grape ripening process. The aim of this work was to compare temperature, humidity and solar radiation measurements at different spatial scales. The measurements were assessed for two seasons (2011, 2012) in two vineyards of the Veneto region (North-East Italy), planted with Pinot <span class="hlt">gris</span> and Cabernet Sauvignon using a specially designed and developed Wireless Sensor Network (WSN). The WSN consists of various levels: the Master/Gateway level coordinates the WSN and performs data aggregation; the Farm/Server level takes care of storing data on a server, data processing and graphic rendering. Nodes level is based on a network of peripheral nodes consisting of a sensor board equipped with sensors and wireless module. The system was able to monitor the agrometeorological parameters in the vineyard: solar radiation, air temperature and air humidity. Different sources of spatial variation were studied, from meso-scale to micro-scale. A widespread investigation was conducted, building a factorial design able to evidence the role played by any factor influencing the physical environment in the vineyard, such as the surrounding climate</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/971307','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/971307"><span>Meltwater flux and runoff modeling in the abalation area of jakobshavn Isbrae, West Greenland</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciT</a></p> <p>Mernild, Sebastian Haugard; Chylek, Petr; Liston, Glen</p> <p>2009-01-01</p> <p>The temporal variability in surface snow and glacier melt flux and runoff were investigated for the ablation area of lakobshavn Isbrae, West Greenland. High-resolution meteorological observations both on and outside the Greenland Ice Sheet (<span class="hlt">GrIS</span>) were used as model input. Realistic descriptions of snow accumulation, snow and glacier-ice melt, and runoff are essential to understand trends in ice sheet surface properties and processes. SnowModel, a physically based, spatially distributed meteorological and snow-evolution modeling system was used to simulate the temporal variability of lakobshavn Isbrre accumulation and ablation processes for 2000/01-2006/07. Winter snow-depth observations and MODIS satellite-derived summer melt observations weremore » used for model validation of accumulation and ablation. Simulations agreed well with observed values. Simulated annual surface melt varied from as low as 3.83 x 10{sup 9} m{sup 3} (2001/02) to as high as 8.64 x 10{sup 9} m{sup 3} (2004/05). Modeled surface melt occurred at elevations reaching 1,870 m a.s.l. for 2004/05, while the equilibrium line altitude (ELA) fluctuated from 990 to 1,210 m a.s.l. during the simulation period. The SnowModel meltwater retention and refreezing routines considerably reduce the amount of meltwater available as ice sheet runoff; without these routines the lakobshavn surface runoff would be overestimated by an average of 80%. From September/October through May/June no runoff events were simulated. The modeled interannual runoff variability varied from 1.81 x 10{sup 9} m{sup 3} (2001/02) to 5.21 x 10{sup 9} m{sup 3} (2004/05), yielding a cumulative runoff at the Jakobshavn glacier terminus of {approx}2.25 m w.eq. to {approx}4.5 m w.eq., respectively. The average modeled lakobshavn runoff of {approx}3.4 km{sup 3} y{sup -1} was merged with previous estimates of Jakobshavn ice discharge to quantify the freshwater flux to Illulissat Icefiord. For both runoff and ice discharge the average trends</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.1403P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.1403P"><span>A millennial-scale record of tidewater glacier advance and retreat, SW Greenland.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pearce, Danni; Mair, Doug; Rea, Brice; Schofield, Ed; Lea, James; Barr, Iestyn; Kamenos, Nick; Schoenrock, Kate</p> <p>2017-04-01</p> <p>Tidewater glaciers (TWGs) exert a major control on the short- and long-term mass balance of the Greenland Ice Sheet (<span class="hlt">GrIS</span>) and have experienced widespread retreat over the last century. However, in many cases inferences on their dynamics, prior to this, are poorly constrained due to a lack of observations and paucity of mapped or mappable deglacial geomorphology. Especially lacking is evidence associated with TWG advance during the Little Ice Age (LIA, AD c. 1300 to 1850). Such data are crucial for numerical model calibration and validation in order to more confidently forward model ice sheet dynamics and projection future sea-level rise. Therefore, empirical data constraints from the palaeo-record, that span such timescales (decadal to millennial), are essential. Kangiata Nunaata Sermia (KNS) is the most dynamic TWG in SW Greenland, located c. 100 km inland from Nuuk, at the head of Godthabsfjord. KNS has received considerable research attention over the last decade but glacial geomorphological and numerical dating investigations have been limited. However, the adjacent topography and geomorphology presents a unique opportunity to reconstruct the advance and retreat dynamics over the LIA. We present detailed glacial geomorphological mapping for KNS, which followed a morphostratigraphic approach, using a combination of aerial photos, Landsat, a DEM and field mapping. This identified a three landsystems, which are associated with the LIA, pre-LIA and neoglacial. From the mapping inferences on rapid changes in meltwater routing have been inferred. When KNS reached its LIA maximum (c. 1761), the calving front was c. >22 km further along the fjord than present and a number of ice-dammed lakes were formed. We present new 14C dating from peat underlying lake sediments associated with an ice-dammed lake and buried palaeosols resulting from meltwater re-routing over topographic spillways. The ages support an early and rapid LIA advance phase, with advance rates being</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20160011338&hterms=510&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3D510','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20160011338&hterms=510&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3D510"><span>Derivation and Validation of Supraglacial Lake Volumes on the Greenland Ice Sheet from High-Resolution Satellite Imagery</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Moussavi, Mahsa S.; Abdalati, Waleed; Pope, Allen; Scambos, Ted; Tedesco, Marco; MacFerrin, Michael; Grigsby, Shane</p> <p>2016-01-01</p> <p>Supraglacial meltwater lakes on the western Greenland Ice Sheet (<span class="hlt">GrIS</span>) are critical components of its surface hydrology and surface mass balance, and they also affect its ice dynamics. Estimates of lake volume, however, are limited by the availability of in situ measurements of water depth,which in turn also limits the assessment of remotely sensed lake depths. Given the logistical difficulty of collecting physical bathymetric measurements, methods relying upon in situ data are generally restricted to small areas and thus their application to largescale studies is difficult to validate. Here, we produce and validate spaceborne estimates of supraglacial lake volumes across a relatively large area (1250 km(exp 2) of west Greenland's ablation region using data acquired by the WorldView-2 (WV-2) sensor, making use of both its stereo-imaging capability and its meter-scale resolution. We employ spectrally-derived depth retrieval models, which are either based on absolute reflectance (single-channel model) or a ratio of spectral reflectances in two bands (dual-channel model). These models are calibrated by usingWV-2multispectral imagery acquired early in the melt season and depth measurements from a high resolutionWV-2 DEM over the same lake basins when devoid of water. The calibrated models are then validated with different lakes in the area, for which we determined depths. Lake depth estimates based on measurements recorded in WV-2's blue (450-510 nm), green (510-580 nm), and red (630-690 nm) bands and dual-channel modes (blue/green, blue/red, and green/red band combinations) had near-zero bias, an average root-mean-squared deviation of 0.4 m (relative to post-drainage DEMs), and an average volumetric error of b1%. The approach outlined in this study - image-based calibration of depth-retrieval models - significantly improves spaceborne supraglacial bathymetry retrievals, which are completely independent from in situ measurements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.4931H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.4931H"><span>A 70-year record of outlet glacier retreat in northern Greenland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hill, Emily; Carr, Rachel; Stokes, Chris; Gudmundsson, Hilmar</p> <p>2017-04-01</p> <p>Over the past two decades, the Greenland Ice Sheet (<span class="hlt">GrIS</span>) has undergone accelerated mass loss increasing its contribution to sea level rise. This is partly attributed to increased mass loss from dynamic marine-terminating outlet glaciers. Despite marine-terminating outlet glaciers in northern Greenland draining 40% of the ice sheet by area, they are comparatively less well-studied than other regions of the ice sheet (e.g. central west or south-east). This region could be susceptible to marine-ice sheet instability due to large proportions of the bedrock rested below sea level and is also unique in the presence of large floating ice tongues. Here, we use a range of satellite imagery sources, accompanied by historical maps, to examine multi-decadal front position changes at 21 outlet glaciers in northern Greenland between 1948 and 2016. We accompany these terminus changes, with annual records of ice velocity, climate-ocean forcing data, and glacier-specific factors (e.g. fjord-width and basal topography) to understand the dominant forcing on glacier dynamics in the region. Over the last 70 years, there has been a clear pattern of glacier retreat in northern Greenland. This is particularly notable during the last two decades, where 62% of our study glaciers showed accelerated retreat. This was most notable at Humboldt, Tracy, Hagen Brae, C. H. Ostenfeld and Petermann Glaciers, and in the case of the latter three glaciers, this involved substantial retreat of their floating ice tongues (> 10 km). Alongside retreat, several study glaciers underwent simultaneous velocity increases. However, the collapse of floating ice tongues did not always result in increased velocity. Similar to other regions of the ice sheet, recent glacier retreat in the northern regions of the Greenland Ice Sheet could be linked to climatic-oceanic forcing, but at this stage this remains largely unknown. This response to external forcing is further complicated by the presence of glacier</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017MsT.........21W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017MsT.........21W"><span>Determining and Interpreting Detailed Ice Surface Elevation Changes of the Glaciers in Upernavik Isstrom, Northwest Greenland, 1985-2016</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wendler, Lindsay</p> <p></p> <p>The several distinct glaciers of Upernavik Isstrom, which drain a portion of the northwest margin of the Greenland Ice Sheet (<span class="hlt">GrIS</span>), exhibit variable thinning, retreat, and velocity behaviors, despite being in such close proximity, draining into the same fjord, and experiencing similar climatic conditions. The goal of this study was to reconstruct, in as much detail as possible, a 1985-2016 surface elevation change history for each Upernavik glacier. Surface elevation datasets used in these reconstructions included laser altimetry data collected by several NASA systems (ATM, LVIS, ICESat) and digital elevation models (DEMs) derived from various sources (1985 aerial photographs; ASTER, SPOT, and Worldview-1 and 2 satellite stereo imagery). The Surface Elevation Reconstruction and Change detection (SERAC) program was used to combine the data and correct the DEMs for use in final reconstructions. The spatiotemporal pattern of ice surface change was analyzed and compared with other data sets, such as bed elevation, SMB anomalies, runoff, as well as marginal retreat derived from satellite imagery corresponding to the ASTER DEMs, to investigate possible forcings that may have influenced the variable behavior of the glaciers. We detected rapid thinning on glaciers 1, 2, and 5 and determined the timing of these thinning events. Major findings included detection of rapid dynamic thinning of glacier 1 between 2005 and 2006, during a period of a stable calving front position. Continued thinning and speed-up led to a loss of contact with a pinning point causing a major retreat between 2007 and 2008. This sequence of events contradicts previously held hypotheses that major thinning was caused by reduced backstress when a long-lived floating tongue disintegrated. Also, our results show a period of large thinning on glacier 2 between 2010 and 2011, after the retreat of the front resulted in a loss of contact between the glacier and one of its flanking outcrops, suggesting that</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.6657V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.6657V"><span>Wine from the Netherlands: investigating the effect of soil-type on taste</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vis, Geert-Jan; Maljers, Denise; Beurskens, Stan</p> <p>2016-04-01</p> <p>During the last decade professional viticulture has seen a strong increase in the Netherlands, reaching 270 ha in 2015. Although on a European scale this is a small area, the number of prize-winning quality wines is steadily growing. This growth can largely be ascribed to new grape varieties from Germany and Switzerland, that are better adapted to the cooler and moister climate at the northern fringe of the viticultural zone, as well as to increasing viticultural expertise. The distribution of vineyards across the Netherlands shows that they occur on a plethora of substrates. Dutch substrate is dominated by typical lowland deposits such as fluvial and marine sands and clays and aeolian sands. Unlike many European countries, bedrock is scarce. Only in the south-eastern extremity and in the east of the country, carbonate bedrock is present at or near the surface. This wide variety of substrate triggered our interest in the effect of the various soil-types on the smell and taste characteristics of wines. An effect which is often mentioned concerning well-known foreign wines. We wondered whether an Auxerrois wine from carbonate rocks tastes significantly different from a wine from the same grape variety from loess. And how about a Johanniter wine from fluvial deposits versus windblown sands? And what happens if you make wine in exactly the same way with the same grape variety and from the same vineyard, but with three different yeast types? To answer our questions, we selected ten Dutch vineyards with varying soil-types and the grape varieties Auxerrois and Johanniter. In October 2014 we harvested the grapes and wine was made under controlled identical conditions (in a double setup). The wines were scientifically tested at the institute of Viticulture and Oenology in Neustadt, Germany. The results show no significant effect of soil-type on the smell and taste of Dutch wines in our experiment. Varying yeast types (Cryarome, 3079, VL2) used on Souvignier <span class="hlt">Gris</span> grapes from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23728829','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23728829"><span>Clinical outcomes, health resource use, and cost in patients with early versus late dual or triple anti-platelet treatment for acute coronary syndrome.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Friedman, Howard; Mollon, Patrick; Lian, Jean; Navaratnam, Prakash</p> <p>2013-08-01</p> <p>Acute coronary syndrome (ACS) guidelines recommend early dual anti-platelet therapy (thienopyridines + acetylsalicylic acid [aspirin]). However, triple therapy (thienopyridines + aspirin + glycoprotein IIb/IIIa receptor inhibitors [<span class="hlt">GRIs</span>]) has shown benefit in clinical trials. This study assessed real-world ACS treatment patterns and outcomes in the acute care setting. A retrospective analysis of patients admitted to hospital with ACS (index event) from January 2007 to December 2009 was conducted (Thomson's MarketScan Hospital Drug Database). Eligible patients were ≥18 years of age, of either sex, and had primary admission and discharge diagnoses of ACS. Cohorts were defined by anti-platelet treatment and then by the timing of treatment initiation (early initiation: within ≤2 days of admission; late initiation: ≥2 days post-admission). Patient characteristics, clinical outcomes, resource utilization, and costs were assessed using descriptive statistics. A total of 249,907 eligible patients were placed into four treatment cohorts (aspirin assumed for all patients): aspirin only; clopidogrel only (dual therapy); GRI only (dual therapy); and clopidogrel + GRI (triple therapy). Patients in the 'clopidogrel-only' cohort were more likely to be older, female, and have more co-morbidities than those in other cohorts; stroke (6.2 %) and re-hospitalization (15.4 %) rates were higher than in the 'GRI-only' and 'triple therapy' cohorts. The GRI-only cohort had higher major bleeding rates (3.3 %), mortality (7.6 %), and costs ($US21,975 [year 2010 values]) than the clopidogrel-only and triple-therapy cohorts. Late initiation cohorts were more likely to be older, female, and have more co-morbidities than early initiation cohorts. Major bleeding was more likely with GRI-only patients (regardless of initiation timing) than with other cohorts. Late-treated clopidogrel-only patients had higher rates of stroke (6.9 %), ACS-related re-admissions (6.1 %), and all</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.170..157S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.170..157S"><span>Exposure age and climate controls on weathering in deglaciated watersheds of western Greenland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scribner, C. A.; Martin, E. E.; Martin, J. B.; Deuerling, K. M.; Collazo, D. F.; Marshall, A. T.</p> <p>2015-12-01</p> <p>Fine-grained sediments deposited by retreating glaciers weather faster than the global average and this weathering can impact the global carbon cycle and oceanic fluxes of nutrients and radiogenic isotopes. Much work has focused on subglacial and proglacial weathering of continental ice sheets, but little is known about weathering and resulting fluxes from deglacial watersheds, which are disconnected from the ice sheets and discharge only annual precipitation and permafrost melt. We investigate the effects of exposure age and precipitation on weathering intensity in four deglacial watersheds on Greenland that form a transect from the coast near Sisimiut toward the Greenland Ice Sheet (<span class="hlt">GrIS</span>) near Kangerlussuaq based on evaluations of major ion compositions, Sr isotope ratios, and mineral saturation states of waters and sediments. The transect is underlain by Archean orthogneiss and is characterized by gradients in moraine ages (∼7.5-8.0 ky inland to ∼10 ky at the coast) and water balance (-150 mm/yr inland to +150 mm/yr at the coast). Anion compositions are generally dominated by HCO3, but SO4 becomes increasingly important toward the coast, reflecting a switch from trace carbonate dissolution to sulfide mineral oxidation. Coastal watersheds have a higher proportion of dissolved silica, higher Na/Cl, Si/Ca, and lower Ca/Sr ratios than inland watersheds, indicating an increase in the relative proportion of silicate weathering and an increase in the extent of weathering toward the coast. More extensive weathering near the coast is also apparent in differences in the 87Sr/86Sr ratios of stream water and bedload (Δ87Sr/86Sr), which decreases from 0.017 inland to 0.005 at the coast, and in increased saturation states relative to amorphous SiO2 and quartz. The steep weathering gradient from inland to coastal watersheds reflects enhanced weathering compared to that expected from the 2 to 3 ky difference in exposure age caused by elevated coastal precipitation. The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12.1851H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12.1851H"><span>Seasonal monitoring of melt and accumulation within the deep percolation zone of the Greenland Ice Sheet and comparison with simulations of regional climate modeling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Heilig, Achim; Eisen, Olaf; MacFerrin, Michael; Tedesco, Marco; Fettweis, Xavier</p> <p>2018-06-01</p> <p>Increasing melt over the Greenland Ice Sheet (<span class="hlt">GrIS</span>) recorded over the past several years has resulted in significant changes of the percolation regime of the ice sheet. It remains unclear whether Greenland's percolation zone will act as a meltwater buffer in the near future through gradually filling all pore space or if near-surface refreezing causes the formation of impermeable layers, which provoke lateral runoff. Homogeneous ice layers within perennial firn, as well as near-surface ice layers of several meter thickness have been observed in firn cores. Because firn coring is a destructive method, deriving stratigraphic changes in firn and allocation of summer melt events is challenging. To overcome this deficit and provide continuous data for model evaluations on snow and firn density, temporal changes in liquid water content and depths of water infiltration, we installed an upward-looking radar system (upGPR) 3.4 m below the snow surface in May 2016 close to Camp Raven (66.4779° N, 46.2856° W) at 2120 m a.s.l. The radar is capable of quasi-continuously monitoring changes in snow and firn stratigraphy, which occur above the antennas. For summer 2016, we observed four major melt events, which routed liquid water into various depths beneath the surface. The last event in mid-August resulted in the deepest percolation down to about 2.3 m beneath the surface. Comparisons with simulations from the regional climate model MAR are in very good agreement in terms of seasonal changes in accumulation and timing of onset of melt. However, neither bulk density of near-surface layers nor the amounts of liquid water and percolation depths predicted by MAR correspond with upGPR data. Radar data and records of a nearby thermistor string, in contrast, matched very well for both timing and depth of temperature changes and observed water percolations. All four melt events transferred a cumulative mass of 56 kg m-2 into firn beneath the summer surface of 2015. We find that</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29867702','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29867702"><span>Basic Color Terms (BCTs) and Categories (BCCs) in Three Dialects of the Spanish Language: Interaction Between Cultural and Universal Factors.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lillo, Julio; González-Perilli, Fernando; Prado-León, Lilia; Melnikova, Anna; Álvaro, Leticia; Collado, José A; Moreira, Humberto</p> <p>2018-01-01</p> <p>Two experiments were performed to identify and compare the Basic Color Terms (BCTs) and the Basic Color Categories (BCCs) included in three dialects (Castilian, Mexican, and Uruguayan) of the Spanish language. Monolexemic Elicited lists were used in the first experiment to identify the BCTs of each dialect. Eleven BCTs appeared for the Spanish and the Mexican, and twelve did so for the Uruguayan. The six primary BCTs ( rojo "red," verde "green," amarillo "yellow," azul "blue," negro "black," and blanco "white") appeared in the three dialects. This occurred for only three derived BCTs ( <span class="hlt">gris</span> "gray," naranja "orange," and rosa "pink") but not for the other five derived BCTs ( celeste "sky blue," marrón "brown," café "brown," morado "purple," and violeta "purple"). Color transitions were used in the second experiment for two different tasks. Extremes naming task was used to determine the relation between two different dialects' BCTs: equality, equivalence or difference. The results provided the first evidence for marrón "brown" and café "brown" being equivalent terms for the same BCC (brown in English) as is the case of morado "purple" and violeta "purple." Uruguayan celeste "sky blue" had no equivalent BCT in the other two dialects. Boundary delimitation task required the selection of the color in the boundary between two categories. The task was used to reasonably estimate the volume occupied by each BCC in the color space considering its chromatic area and lightness range. Excluding sky blue ( celeste "sky blue") and blue ( azul "blue"), the other BCCs color volumes were similar across the three dialects. Uruguayan sky blue and blue volumes conjointly occupied the portion of the color space corresponding to the Castilian and Mexican blue BCC. The fact that the BCT celeste "sky blue" only appeared in Uruguayan very probably derived from specific cultural factors (the use of the color in the flags and the arrival of an important number of Italian immigrants</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5968181','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5968181"><span>Basic Color Terms (BCTs) and Categories (BCCs) in Three Dialects of the Spanish Language: Interaction Between Cultural and Universal Factors</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Lillo, Julio; González-Perilli, Fernando; Prado-León, Lilia; Melnikova, Anna; Álvaro, Leticia; Collado, José A.; Moreira, Humberto</p> <p>2018-01-01</p> <p>Two experiments were performed to identify and compare the Basic Color Terms (BCTs) and the Basic Color Categories (BCCs) included in three dialects (Castilian, Mexican, and Uruguayan) of the Spanish language. Monolexemic Elicited lists were used in the first experiment to identify the BCTs of each dialect. Eleven BCTs appeared for the Spanish and the Mexican, and twelve did so for the Uruguayan. The six primary BCTs (rojo “red,” verde “green,” amarillo “yellow,” azul “blue,” negro “black,” and blanco “white”) appeared in the three dialects. This occurred for only three derived BCTs (<span class="hlt">gris</span> “gray,” naranja “orange,” and rosa “pink”) but not for the other five derived BCTs (celeste “sky blue,” marrón “brown,” café “brown,” morado “purple,” and violeta “purple”). Color transitions were used in the second experiment for two different tasks. Extremes naming task was used to determine the relation between two different dialects' BCTs: equality, equivalence or difference. The results provided the first evidence for marrón “brown” and café “brown” being equivalent terms for the same BCC (brown in English) as is the case of morado “purple” and violeta “purple.” Uruguayan celeste “sky blue” had no equivalent BCT in the other two dialects. Boundary delimitation task required the selection of the color in the boundary between two categories. The task was used to reasonably estimate the volume occupied by each BCC in the color space considering its chromatic area and lightness range. Excluding sky blue (celeste “sky blue”) and blue (azul “blue”), the other BCCs color volumes were similar across the three dialects. Uruguayan sky blue and blue volumes conjointly occupied the portion of the color space corresponding to the Castilian and Mexican blue BCC. The fact that the BCT celeste “sky blue” only appeared in Uruguayan very probably derived from specific cultural factors (the use of the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.1290L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.1290L"><span>Evaluation of three methods of different levels of complexity to represent the interactions between the Greenland ice sheet and the atmosphere at the century time scale.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Le clec'h, Sébastien; Fettweis, Xavier; Quiquet, Aurelien; Dumas, Christophe; Kageyama, Masa; Charbit, Sylvie; Ritz, Catherine</p> <p>2017-04-01</p> <p> increase the spatial variability of the surface mass balance changes through time. Our results also indicate that differences between the two coupling methods increase with time, which suggests that the choice of the method should depend on the timescale considered. Beyond century scale projections the fully coupled method is necessary in order to avoid underestimation of the ice sheet volume reduction, whilst the one-way method seems to be sufficient to represent the interactions between the atmosphere and the <span class="hlt">GrIS</span> for projections by the end of the century.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.C41A0692S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.C41A0692S"><span>A Newly Updated Database of Elevation-changes of the Greenand Ice Sheet to Study Surface Processes and Ice Dynamics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schenk, A. F.; Csatho, B. M.; van den Broeke, M.; Kuipers Munneke, P.</p> <p>2015-12-01</p> <p>This paper reports about important upgrades of the Greenland Ice Sheet (<span class="hlt">GrIS</span>) surface elevation and elevation-change database obtained with our Surface Elevation And Change detection (SERAC) software suite. We have developed SERAC to derive information from laser altimetry data, particularly time series of elevation changes and their partitioning into changes caused by ice dynamics. This allows direct investigation of ice dynamic processes that is much needed for improving the predictive power of ice sheet models. SERAC is different from most other change detection methods. It is based on detecting changes of surface patches, about 1 km by 1 km in size, rather than deriving elevation changes from individual laser points. The current database consists of ~100,000 time series with satellite laser altimetry data from ICESat, airborne laser observations obtained by NASA's Airborne Topographic Mapper (ATM) and the Land, Vegetation and Ice Sensor (LVIS). The upgrade is significant, because not only new observations from 2013 and 2014 have been added but also a number of improvements lead to a more comprehensive and consistent record of elevation-changes. First, we used the model that gives in addition to ice sheet also information about ice caps and glaciers (Rastner et al., 2012) for deciding if a laser point is on the ice sheet or ice cap. Then we added small gaps that exist in the ICESat GLA12 data set because the ice sheet mask is not wide enough. The new database is now more complete and will facilitate more accurate comparisons of mass balance studies obtained from the Gravity Recovery and Climate Experiment system (GRACE). For determining the part of a time series caused by ice dynamics we used the new firn compaction model and Surface Mass Balance (SMB) estimates from RACMO2.3. The new database spans the time period from 1993 to 2014. Adding new observations amounts to a spatial densification of the old record and at the same time extends the time domain by two</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3049F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3049F"><span>Zarzalejo granite (Spain). A nomination for 'Global Heritage Stone Resource'</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Freire Lista, David Martin; Fort, Rafael; José Varas-Muriel, María</p> <p>2015-04-01</p> <p> Escorial Monastery, which shows the building material used during its construction. There is currently an active quarry of this dimension stone which continues to be sold under the commercial name of "<span class="hlt">Gris</span> Escorial". Zarzalejo granite is mainly exported to Turkey, Italy and Saudi Arabia. Today this stone is used primarily in flooring. Other uses include cobblestones, funeral art, and building and monument restoration and rehabilitation. Sculptures have also built in recent years, notably the great monoliths in Salvador Dalí Square (1989) in Madrid. There are also small historic family-run quarries intermittently continuing this dimension stone carving tradition. Given its characteristics, Zarzalejo granite meets the requisites proposed to be nominated as a GHSR. This nomination will contribute to raising awareness and disseminate key aspects for conservation and thus ensure its use as a replacement stone in restoring heritage buildings where it was used as a building stone. Acknowledgements This study was funded by the Community of Madrid under the GEOMATERIALS 2 project (S2013/MIT-2914). The authors are members of the Complutense University of Madrid's Research Group: "Alteración y Conservación de los Materiales Pétreos del Patrimonio" (ref. 921349).</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_11");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_11");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016A%26A...587A..67L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016A%26A...587A..67L"><span>FORS2 observes a multi-epoch transmission spectrum of the hot Saturn-mass exoplanet WASP-49b</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lendl, M.; Delrez, L.; Gillon, M.; Madhusudhan, N.; Jehin, E.; Queloz, D.; Anderson, D. R.; Demory, B.-O.; Hellier, C.</p> <p>2016-03-01</p> <p>Context. Transmission spectroscopy has proven to be a useful tool for the study of exoplanet atmospheres, because the absorption and scattering signatures of the atmosphere manifest themselves as variations in the planetary transit depth. Several planets have been studied with this technique, leading to the detection of a small number of elements and molecules (Na, K, H2O), but also revealing that many planets show flat transmission spectra consistent with the presence of opaque high-altitude clouds. Aims: We apply this technique to the MP = 0.40MJ, Rp = 1.20RJ, P = 2.78 d planet WASP-49b, aiming to characterize its transmission spectrum between 0.73 and 1 ¯m and search for the features of K and H2O. Owing to its density and temperature, the planet is predicted to possess an extended atmosphere and is thus a good target for transmission spectroscopy. Methods: Three transits of WASP-49b have been observed with the FORS2 instrument installed at the VLT/UT1 telescope at the ESO Paranal site. We used FORS2 in MXU mode with grism <span class="hlt">GRIS</span>_600z, producing simultaneous multiwavelength transit light curves throughout the I' and z' bands. We combined these data with independent broadband photometry from the Euler and TRAPPIST telescopes to obtain a good measurement of the transit shape. Strong correlated noise structures are present in the FORS2 light curves, which are due to rotating flat-field structures that are introduced by inhomogeneities of the linear atmospheric dispersion corrector's transparency. We accounted for these structures by constructing common noise models from the residuals of light curves bearing the same noise structures and used them together with simple parametric models to infer the transmission spectrum. Results: We present three independent transmission spectra of WASP-49b between 0.73 and 1.02 ¯m, as well as a transmission spectrum between 0.65 and 1.02 ¯m from the combined analysis of FORS2 and broadband data. The results obtained from the three</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28902932','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28902932"><span>Non-pharmacological interventions to promote the sleep of patients after cardiac surgery: a systematic review.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Machado, Fernanda de Souza; Souza, Regina Claudia da Silva; Poveda, Vanessa Brito; Costa, Ana Lucia Siqueira</p> <p>2017-09-12</p> <p> foram incluídos na revisão. Constatou-se que as intervenções não farmacológicas agruparam-se em três categorias principais, a saber: técnicas de relaxamento, dispositivos ou equipamentos para minimizar a interrupção do sono e/ou induzir o sono e estratégias educacionais. Houve melhoria significativa nos escores de avaliação do sono entre os estudos que testaram intervenções como tampões de ouvidos, máscara de olhos, relaxamento muscular, treinamento de postura e relaxamento, produção sonora e estratégia educacional. Em relação à qualidade metodológica dos estudos, não foram encontrados estudos considerados de alta qualidade pelo escore de Jadad. houve melhora significativa nos escores de avaliação do sono em estudos que avaliaram intervenções como tampões de ouvidos, máscara de olhos, relaxamento muscular, treinamento de postura e relaxamento, produção sonora e estratégia educacional. analizar las evidencias disponibles en la literatura sobre las intervenciones no farmacológicas, eficientes para el tratamiento de la alteración del patrón del sueño en pacientes sometidos a una cirugía cardíaca. revisión sistemática realizada mediante búsqueda en las bases de datos de la Librería Nacional de Medicina (National Library of Medicine), de los Institutos Nacionales de la Salud (National Institutes of Health), del Registro Central Cochrane de Ensayos Controlados (Cochrane Central Register of Controlled Trials), de la literatura latinoamericana y del Caribe, en Ciencias de la Salud, Scopus, Embase, Índice Acumulado de Enfermería y Literatura en Ciencias de la Salud, CINAHL (Cumulative Index to Nursing and Allied Health Literature) y PsycINFO, y en la literatura <span class="hlt">gris</span>. se incluyeron en la revisión diez ensayos clínicos controlados y aleatorizados. Se constató que las intervenciones no farmacológicas se agruparon en tres categorías principales: técnicas de relajación, dispositivos o equipos para minimizar la interrupción del sue</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..11.2378F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..11.2378F"><span>MicroCT vs. Hg porosimetry: microporosity in commercial stones</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fusi, N.; Martinez-Martinez, J.; Barberini, V.; Galimberti, L.</p> <p>2009-04-01</p> <p>Decay of rocks, due both to extrinsic and intrinsic factors, can show up in several different forms, such as neoformation of minerals, decohesion of grains and/or crystals, magnification of previous defects, new discontinuities, etc. Intrinsic factors include the type of material, its properties and microstructure, in particular porosity and microporosity. Extrinsic factors relate to atmosphere and usage of the material itself. Rock degradation has several heavy consequences for commercial stones, such as increase of permeability, loss of material, loss of mechanical strength; these consequences are of crucial importance for conservation of historical buildings. Aim of this study is to compare microporosity of some massive commercial stones by means of X ray microtomography, a non destructive technique, and Hg porosimetry. Nine of the most used Spanish limestones and dolostones have been analysed. The lithotypes have been chosen for their homogeneous mineralogical composition (calcitic or dolomitic) and for their low porosity; some of them have been widely used in Spain for historical buildings. Different lithotypes have been described in thin section: Ambarino (A) and Beige Serpiente (BS): brecciated dolostone, composed by microcrystalline dolomitic clasts, in a dolomitic and/or calcitic microcrystalline matrix. Amarillo Triana (AT): yellow dolomitic marble, with fissures filled up by calcite and Fe oxides. Blanco Alconera (BA): a white-pink homogeneous limestone, with veins. Blanco Tranco (BT): a homogeneous white calcitic marble, without any fissures and/or fractures. Crema Valencia (CV): a pinkish limestone, characterized by abundant stilolythes, filled mainly by quartz (80%) and kaolin (11%). <span class="hlt">Gris</span> Macael (GM): a calcitic marble wiht darker and lighter beds, conferring a strong anisotropy. Rojo Cehegin (RC): a red fossiliferous limestone with white calcitic veins. Travertino Blanco (TB): a massive white calcitic travertine. Prismatic samples of about 2x1x1 cm</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_11");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <center> <div class="footer-extlink text-muted"><small>Some links on this page may take you to non-federal websites. 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