WorldWideScience

Sample records for greenland ice investigating

  1. Greenland Ice Sheet Mass Balance

    Science.gov (United States)

    Reeh, N.

    1984-01-01

    Mass balance equation for glaciers; areal distribution and ice volumes; estimates of actual mass balance; loss by calving of icebergs; hydrological budget for Greenland; and temporal variations of Greenland mass balance are examined.

  2. (CH4)-C-14 Measurements in Greenland Ice: Investigating Last Glacial Termination CH4 Sources

    DEFF Research Database (Denmark)

    Petrenko, V. V.; Smith, A. M.; Brook, E. J.

    2009-01-01

    by direct cosmogenic C-14 production in ice. C-14 of CO was measured to better understand this process and correct the sample (CH4)-C-14. Corrected results suggest that wetland sources were likely responsible for the majority of the Younger Dryas-Preboreal CH4 rise.......The cause of a large increase of atmospheric methane concentration during the Younger Dryas-Preboreal abrupt climatic transition (similar to 11,600 years ago) has been the subject of much debate. The carbon-14 (C-14) content of methane ((CH4)-C-14) should distinguish between wetland and clathrate...... contributions to this increase. We present measurements of (CH4)-C-14 in glacial ice, targeting this transition, performed by using ice samples obtained from an ablation site in west Greenland. Measured (CH4)-C-14 values were higher than predicted under any scenario. Sample (CH4)-C-14 appears to be elevated...

  3. Hydrologic Outlets of the Greenland Ice Sheet

    Data.gov (United States)

    National Aeronautics and Space Administration — The Hydrologic Outlets of the Greenland Ice Sheet data set contains GIS point shapefiles that include 891 observed and potential hydrologic outlets of the Greenland...

  4. Polar Ice Caps: a Canary for the Greenland Ice Sheet

    Science.gov (United States)

    Honsaker, W.; Lowell, T. V.; Sagredo, E.; Kelly, M. A.; Hall, B. L.

    2010-12-01

    changes in ELA where you can track an “on-off” type of mass balance switch. To place these ELA changes into temporal context, we propose to investigate proglacial lake environments below the various catchments. We intend to take rock flour as an indicator that the individual catchment is above the ELA. By contrasting the chronology from different catchments we can assemble minor ELA changes. Such an approach could be applied for other ice caps in Greenland and other areas, such as the Quelccaya Ice Cap, Peru.

  5. Ice flow Modelling of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Nielsen, Lisbeth Tangaa

    Models of ice flow have a range of application in glaciology, including investigating the large-scale response of ice sheets to changes in climate, assimilating data to estimate unknown conditions beneath the ice sheet, and in interpreting proxy records obtained from ice cores, among others. In t...... a steady state with respect to the reference climate at the end of the simulation and that the mass balance of the ice sheet at this time was more sensitive to recent climate fluctuations than the temperature forcing in the early or mid-Holocene.......Models of ice flow have a range of application in glaciology, including investigating the large-scale response of ice sheets to changes in climate, assimilating data to estimate unknown conditions beneath the ice sheet, and in interpreting proxy records obtained from ice cores, among others....... In this PhD project, the use of ice flow models for the interpretation of the age-structure of the Greenland ice sheet, i.e. the depth within the ice, at which ice deposited at given times are found at present day. Two different observational data sets of this archive were investigated. Further, paleo...

  6. Greenland Radar Ice Sheet Thickness Measurements

    Data.gov (United States)

    National Aeronautics and Space Administration — Two 150-MHz coherent radar depth sounders were developed and flown over the Greenland ice sheet to obtain ice thickness measurements in support of PARCA...

  7. Balance velocities of the Greenland ice sheet

    DEFF Research Database (Denmark)

    Joughin, I.; Fahnestock, M.; Ekholm, Simon

    1997-01-01

    We present a map of balance velocities for the Greenland ice sheet. The resolution of the underlying DEM, which was derived primarily from radar altimetery data, yields far greater detail than earlier balance velocity estimates for Greenland. The velocity contours reveal in striking detail......, the balance map is useful for ice-sheet modelling, mass balance studies, and field planning....

  8. 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

    Directory of Open Access Journals (Sweden)

    S. L. Bradley

    2018-05-01

    Full Text Available 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

  9. Mountain building and the initiation of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Solgaard, Anne Munck; Bonow, Johan; Langen, Peter Lang

    2013-01-01

    The effects of a new hypothesis about mountain building in Greenland on ice sheet initiation are investigated using an ice sheet model in combination with a climate model. According to this hypothesis, low-relief landscapes near sea level characterised Greenland in Miocene times until two phases...... superimposed by cold and warm excursions. The modelling results show that no ice initiates in the case of the low-lying and almost flat topography prior to the uplifts. However, the results demonstrate a significant ice sheet growth in response to the orographically induced increase in precipitation....... Under conditions that are colder than the present, the ice can overcome the Föhn effect, flow into the interior and form a coherent ice sheet. The results thus indicate that the Greenland Ice Sheet of today is a relict formed under colder conditions. The modelling results are consistent...

  10. Balance Velocities of the Greenland Ice Sheet

    Science.gov (United States)

    Joughin, Ian; Fahnestock, Mark; Ekholm, Simon; Kwok, Ron

    1997-01-01

    We present a map of balance velocities for the Greenland ice sheet. The resolution of the underlying DEM, which was derived primarily from radar altimetry data, yields far greater detail than earlier balance velocity estimates for Greenland. The velocity contours reveal in striking detail the location of an ice stream in northeastern Greenland, which was only recently discovered using satellite imagery. Enhanced flow associated with all of the major outlets is clearly visible, although small errors in the source data result in less accurate estimates of the absolute flow speeds. Nevertheless, the balance map is useful for ice-sheet modelling, mass balance studies, and field planning.

  11. Destabilization of the Northeast Greenland Ice Stream

    DEFF Research Database (Denmark)

    Korsgaard, N. J.; Khan, Shfaqat Abbas; Kjaer, K. H.

    . Here, we reveal that the Northeast Greenland Ice Stream (NEGIS), which extends more than 600 km into the interior of the ice sheet, is now undergoing dynamic thinning after more than a quarter of a century of stability. This sector of the GrIS is of particular interest in sea level projections, because...... the glacier flows into a large submarine basin with a negative bed slope near the grounding line. Our findings unfold the next step in mass loss of the GrIS as we show a heightened risk of rapid sustained loss from Northeast Greenland on top of the thinning in Southeast and Northwestern Greenland....

  12. Ice age plant refugia in East Greenland

    DEFF Research Database (Denmark)

    Funder, Svend Visby

    1979-01-01

    From the distribution of plants it has been inferred by some botanists that ice-free areas existed in East Greenland accommodating a flora which survived one or several ice ages in the area. Comparing this evidence with recent information on the chronology of glaciations and post-glacial vegetation...

  13. Greenland ice sheet mass balance: a review

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Aschwanden, Andy; Bjørk, Anders A.

    2015-01-01

    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...

  14. Improved ice loss estimate of the northwestern Greenland ice sheet

    NARCIS (Netherlands)

    Kjeldsen, K.K.; Khan, S.A.; van den Broeke, M.R.; van Angelen, J.H.

    2013-01-01

    We estimate ice volume change rates in the northwest Greenland drainage basin during 2003–2009 using Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data. Elevation changes are often reported to be largest near the frontal portion of outlet glaciers. To improve the volume change

  15. High-resolution Greenland Ice Core data show abrupt climate change happens in few years

    DEFF Research Database (Denmark)

    Steffensen, Jørgen Peder; Andersen, Katrine Krogh; Bigler, Matthias

    2008-01-01

    The last two abrupt warmings at the onset of our present warm interglacial period, interrupted by the Younger Dryas cooling event, were investigated at high temporal resolution from the North Greenland Ice Core Project ice core. The deuterium excess, a proxy of Greenland precipitation moisture...... source, switched mode within 1 to 3 years over these transitions and initiated a more gradual change (over 50 years) of the Greenland air temperature, as recorded by stable water isotopes. The onsets of both abrupt Greenland warmings were slightly preceded by decreasing Greenland dust deposition...

  16. Hydrologic Outlets of the Greenland Ice Sheet, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — The Hydrologic Outlets of the Greenland Ice Sheet data set contains GIS point shapefiles that include 891 observed and potential hydrologic outlets of the Greenland...

  17. Seasonal ice dynamics of the Northeast Greenland Ice Stream

    DEFF Research Database (Denmark)

    Vijay, Saurabh; Khan, Shfaqat Abbas; Simonsen, Sebastian Bjerregaard

    2018-01-01

    and temporal details. This study focus on the Northeast Greenland Ice Stream (NEGIS), which consists of three main outlets, 79 North glacier (79N), Zachariae Isstrøm (ZI) and Storstrømmen Glacier (SG). While both 79 North and Storstrømmen have floating tongues, Zachariae Isstrøm is mostly grounded...

  18. Improved ice loss estimate of the northwestern Greenland ice sheet

    DEFF Research Database (Denmark)

    Kjeldsen, Kristian Kjellerup; Khan, Shfaqat Abbas; Wahr, J.

    2013-01-01

    We estimate ice volume change rates in the northwest Greenland drainage basin during 2003–2009 using Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data. Elevation changes are often reported to be largest near the frontal portion of outlet glaciers. To improve the volume change...... estimate, we supplement the ICESat data with altimeter surveys from NASA's Airborne Topographic Mapper from 2002 to 2010 and NASA's Land, Vegetation and Ice Sensor from 2010. The Airborne data are mainly concentrated along the ice margin and thus have a significant impact on the estimate of the volume...... change. Our results show that adding Airborne Topographic Mapper and Land, Vegetation and Ice Sensor data to the ICESat data increases the catchment-wide estimate of ice volume loss by 11%, mainly due to an improved volume loss estimate along the ice sheet margin. Furthermore, our results show...

  19. Clouds enhance Greenland ice sheet mass loss

    Science.gov (United States)

    Van Tricht, Kristof; Gorodetskaya, Irina V.; L'Ecuyer, Tristan; Lenaerts, Jan T. M.; Lhermitte, Stef; Noel, Brice; Turner, David D.; van den Broeke, Michiel R.; van Lipzig, Nicole P. M.

    2015-04-01

    Clouds have a profound influence on both the Arctic and global climate, while they still represent one of the key uncertainties in climate models, limiting the fidelity of future climate projections. The potentially important role of thin liquid-containing clouds over Greenland in enhancing ice sheet melt has recently gained interest, yet current research is spatially and temporally limited, focusing on particular events, and their large scale impact on the surface mass balance remains unknown. We used a combination of satellite remote sensing (CloudSat - CALIPSO), ground-based observations and climate model (RACMO) data to show that liquid-containing clouds warm the Greenland ice sheet 94% of the time. High surface reflectivity (albedo) for shortwave radiation reduces the cloud shortwave cooling effect on the absorbed fluxes, while not influencing the absorption of longwave radiation. Cloud warming over the ice sheet therefore dominates year-round. Only when albedo values drop below ~0.6 in the coastal areas during summer, the cooling effect starts to overcome the warming effect. The year-round excess of energy due to the presence of liquid-containing clouds has an extensive influence on the mass balance of the ice sheet. Simulations using the SNOWPACK snow model showed not only a strong influence of these liquid-containing clouds on melt increase, but also on the increased sublimation mass loss. Simulations with the Community Earth System Climate Model for the end of the 21st century (2080-2099) show that Greenland clouds contain more liquid water path and less ice water path. This implies that cloud radiative forcing will be further enhanced in the future. Our results therefore urge the need for improving cloud microphysics in climate models, to improve future projections of ice sheet mass balance and global sea level rise.

  20. Greenland Ice Shelves and Ice Tongues

    DEFF Research Database (Denmark)

    Reeh, Niels

    2017-01-01

    literature and physical properties are reviewed. There exists a difference between: (1) Floating glaciers in northern Greenland (>77°N) which experience bottom melting as their dominant ablation mechanism and calve relatively thin, but large (km-sized) tabular icebergs (‘ice islands’), and (2) Grounded...... glaciers further south (iceberg calving provides the dominant ablation mechanism. The relatively smaller iceberg discharge in northern Greenland is closely related to the occurrence of extended floating glacier sections, allowing bottom melting estimated at up to 10 m year−1 for locations...

  1. EBSD in Antarctic and Greenland Ice

    Science.gov (United States)

    Weikusat, Ilka; Kuiper, Ernst-Jan; Pennock, Gill; Sepp, Kipfstuhl; Drury, Martyn

    2017-04-01

    Ice, particularly the extensive amounts found in the polar ice sheets, impacts directly on the global climate by changing the albedo and indirectly by supplying an enormous water reservoir that affects sea level change. The discharge of material into the oceans is partly controlled by the melt excess over snow accumulation, partly by the dynamic flow of ice. In addition to sliding over bedrock, an ice body deforms gravitationally under its own weight. In order to improve our description of this flow, ice microstructure studies are needed that elucidate the dominant deformation and recrystallization mechanisms involved. Deformation of hexagonal ice is highly anisotropic: ice is easily sheared in the basal plane and is about two orders of magnitude harder parallel to the c-axis. As dislocation creep is the dominant deformation mechanism in polar ice this strong anisotropy needs to be understood in terms of dislocation activity. The high anisotropy of the ice crystal is usually ascribed to a particular behaviour of dislocations in ice, namely the extension of dislocations into partials on the basal plane. Analysis of EBSD data can help our understanding of dislocation activity by characterizing subgrain boundary types thus providing a tool for comprehensive dislocation characterization in polar ice. Cryo-EBSD microstructure in combination with light microscopy measurements from ice core material from Antarctica (EPICA-DML deep ice core) and Greenland (NEEM deep ice core) are presented and interpreted regarding substructure identification and characterization. We examined one depth for each ice core (EDML: 656 m, NEEM: 719 m) to obtain the first comparison of slip system activity from the two ice sheets. The subgrain boundary to grain boundary threshold misorientation was taken to be 3-5° (Weikusat et al. 2011). EBSD analyses suggest that a large portion of edge dislocations with slip systems basal gliding on the basal plane were indeed involved in forming subgrain

  2. Eemian interglacial reconstructed from a Greenland folded ice core

    DEFF Research Database (Denmark)

    Dahl-Jensen, Dorthe; Albert, M. R.; Aldahan, A.

    2013-01-01

    Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new No...

  3. Greenland ice sheet mass balance: a review.

    Science.gov (United States)

    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.

  4. A Synthesis of the Basal Thermal State of the Greenland Ice Sheet

    Science.gov (United States)

    Macgregor, J. A.; Fahnestock, M. A.; Catania, G. A.; Aschwanden, A.; Clow, G. D.; Colgan, W. T.; Gogineni, S. P.; Morlighem, M.; Nowicki, S. M. J.; Paden, J. D.; hide

    2016-01-01

    Greenland's thick ice sheet insulates the bedrock below from the cold temperatures at the surface, so the bottom of the ice is often tens of degrees warmer than at the top, because the ice bottom is slowly warmed by heat coming from the Earth's depths. Knowing whether Greenland's ice lies on wet, slippery ground or is anchored to dry, frozen bedrock is essential for predicting how this ice will flow in the future. But scientists have very few direct observations of the thermal conditions beneath the ice sheet, obtained through fewer than two dozen boreholes that have reached the bottom. Our study synthesizes several independent methods to infer the Greenland Ice Sheet's basal thermal state -whether the bottom of the ice is melted or not-leading to the first map that identifies frozen and thawed areas across the whole ice sheet. This map will guide targets for future investigations of the Greenland Ice Sheet toward the most vulnerable and poorly understood regions, ultimately improving our understanding of its dynamics and contribution to future sea-level rise. It is of particular relevance to ongoing Operation IceBridge activities and future large-scale airborne missions over Greenland.

  5. Greenland Ice sheet mass balance from satellite and airborne altimetry

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Bevis, M. G.; Wahr, J. M.

    Ice loss from the Greenland Ice Sheet (GrIS) is dominated by loss in the marginal areas. Dynamic induced ice loss and its associated ice surface lowering is often largest close to the glacier calving front and may vary from rates of tens of meters per years to a few meters per year over relatively...... short distances. Hence, high spatial resolution data are required to accurately estimate volume changes. Here, we estimate ice volume change rate of the Greenland ice sheet using data from Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter during 2003-2009 and CryoSat-2 data during 2010...

  6. Estimating the future ice sheet hydropower potential in Paakitsoq, Ilulissat, West Greenland

    DEFF Research Database (Denmark)

    Ahlstrøm, Andreas P.; Mottram, R.H.; Nielsen, C.

    2008-01-01

    sheet has emphasized the risk of sudden changes in catchment supply. In this study, we present a thorough investigation of hydropower feasibility at the Paakitsoq basin, near Ilulissat in West Greenland. The catchment is completely dominated by the Greenland ice sheet which provides large quantities...... of meltwater during the summer season. However, geometrical changes in the ice sheet, for example due to a retreat or an advance of the ice sheet margin, could change the hydrological catchment within the ice sheet. Such a change would have a devastating economical impact as a hydropower plant is a significant...... long-term investment for an Arctic community of modest population. Here we present a new bedrock and surface map of the Paakitsoq/Swiss Camp part of the Greenland ice sheet and a prediction of the future discharge up to 2080 AD using regional climate model output, dynamic ice sheet modelling...

  7. Oceans Melting Greenland: Early Results from NASA's Ocean-Ice Mission in Greenland

    DEFF Research Database (Denmark)

    Fenty, Ian; Willis, Josh K.; Khazendar, Ala

    2016-01-01

    the continental shelf, and about the extent to which the ocean interacts with glaciers. Early results from NASA's five-year Oceans Melting Greenland (OMG) mission, based on extensive hydrographic and bathymetric surveys, suggest that many glaciers terminate in deep water and are hence vulnerable to increased...... melting due to ocean-ice interaction. OMG will track ocean conditions and ice loss at glaciers around Greenland through the year 2020, providing critical information about ocean-driven Greenland ice mass loss in a warming climate....

  8. Net accumulation of the Greenland ice sheet

    DEFF Research Database (Denmark)

    Kiilsholm, Sissi; Christensen, Jens Hesselbjerg; Dethloff, Klaus

    2003-01-01

    High-resolution (50 km) climate change simulations for an area covering the entire Arctic have been conducted with the regional climate model (RCM) HIRHAM. The experiments were forced at the lateral boundary by large-scale atmospheric conditions from transient climate change scenario simulations...... with HIRHAM for periods representing present-day (1961-1990) and the future (2071-2100) in the two scenarios. We find that due to a much better representation of the surface topography in the RCM, the geographical distribution of present-day accumulation rates simulated by the RCM represents a substantial...... improvement compared to the driving OAGCM. Estimates of the regional net balance are also better represented by the RCM. In the future climate the net balance for the Greenland Ice Sheet is reduced in all the simulation, but discrepancies between the amounts when based on ECHAM4/OPYC3 and HIRHAM are found...

  9. Greenland Ice Sheet Melt Characteristics Derived from Passive Microwave Data

    Data.gov (United States)

    National Aeronautics and Space Administration — The Greenland ice sheet melt extent data, acquired as part of the NASA Program for Arctic Regional Climate Assessment (PARCA), is a daily (or every other day, prior...

  10. Greenland 5 km DEM, Ice Thickness, and Bedrock Elevation Grids

    Data.gov (United States)

    National Aeronautics and Space Administration — A Digital Elevation Model (DEM), ice thickness grid, and bedrock elevation grid of Greenland acquired as part of the PARCA program are available in ASCII text format...

  11. Dynamics of the Greenland Ice Sheet over multiple timescales

    DEFF Research Database (Denmark)

    Kjeldsen, Kristian Kjellerup

    to further constrain the individual components of the current budget, and in conjunction with longer records, it is important to provide a trustworthy basis for future projections. In this thesis, using airborne- and satellite derived data combined with terrestrial and marine observations, the dynamic...... become grounded and also assuming a similar warming pattern. This thesis implies that in order to investigate the response of the Greenland Ice Sheet to future climate change much is to be gained by merging and incorporating data from both marine and terrestrial geology, combined with air- and satellite...

  12. Self-inhibiting growth of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Langen, Peter Lang; Solgaard, Anne Munck; Hvidberg, Christine Schøtt

    2012-01-01

    The build-up of the Greenland Ice Sheet (GrIS) from ice-free conditions is studied in an ice sheet model (ISM) driven by fields from an atmospheric general circulation model (GCM) to demonstrate the importance of coupling between the two components. Experiments where the two are coupled off-line...... are augmented by one where an intermediate ice sheet configuration is coupled back to the GCM. Forcing the ISM with GCM fields corresponding to the ice-free state leads to extensive regrowth which, however, is halted when the intermediate recoupling step is included. This inhibition of further growth is due...... to a Föhn effect of moist air parcels being lifted over the intermediate ice sheet and arriving in the low-lying Greenland interior with high temperatures. This demonstrates that two-way coupling between the atmosphere and the ice sheet is essential for understanding the dynamics and that large scale...

  13. Advancing land-terminating ice margin in North Greenland - characteristics, evolution, and first field measurements

    Science.gov (United States)

    Steiner, J. F.; Prinz, R.; Abermann, J.

    2017-12-01

    More than 40% of the ice sheet in North Greenland terminate on land, however the characteristics of this ice margin and response to a changing climate have so far received little attention. While land-terminating ice cliffs are a feature commonly found and studied in other regions, detailed investigations in Greenland were only carried out more than six decades ago in the Thule area (Red Rock, Northwest Greenland). These studies showed a continuous advance at one location over multiple years, while the local mass balance was reported negative. The purpose of our study is to revisit the location previously studied and extend the analysis to the complete Northern ice margin employing newly available high-resolution digital terrain models (Arctic DEM). First results show that the advance at Red Rock is indeed long-term, continuing unabated today at rates of up to several meter per year. Similar magnitudes were found for large other stretches along the ice margin. With our study we aim to show (a) the main characteristics of the land-terminating ice margin in Northern Greenland, namely its slope and aspect distribution and comparison to spatial datasets of flow velocity and mass balance and (b) to provide further explanations of physical processes driving the advance. We have therefore mapped the complete ice margin and present the first results of this analysis. First field work provides new data on energy fluxes and ice temperatures at the Red Rock site as well as high resolution DEMs obtained with the use of UAVs.

  14. History of the Greenland Ice Sheet: paleoclimatic insights

    DEFF Research Database (Denmark)

    Alley, Richard B.; Andrews, John Thomas; Brigham-Grette, Julia

    2010-01-01

    Paleoclimatic records show that the Greenland Ice Sheet consistently has lost mass in response to warming, and grown in response to cooling. Such changes have occurred even at times of slow or zero sea-level change, so changing sea level cannot have been the cause of at least some of the ice-shee...

  15. Greenland Ice Sheet: High-Elevation Balance and Peripheral Thinning.

    Science.gov (United States)

    Krabill; Abdalati; Frederick; Manizade; Martin; Sonntag; Swift; Thomas; Wright; Yungel

    2000-07-21

    Aircraft laser-altimeter surveys over northern Greenland in 1994 and 1999 have been coupled with previously reported data from southern Greenland to analyze the recent mass-balance of the Greenland Ice Sheet. Above 2000 meters elevation, the ice sheet is in balance on average but has some regions of local thickening or thinning. Thinning predominates at lower elevations, with rates exceeding 1 meter per year close to the coast. Interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet, sufficient to raise sea level by 0.13 millimeter per year-approximately 7% of the observed rise.

  16. Hypsometric Amplification of Greenland Ice Sheet Meltwater Release

    Science.gov (United States)

    van As, D.; Hasholt, B.; Mikkelsen, A. B.; Holtegaard Nielsen, M.; Box, J.; Claesson Liljedahl, L.; Lindback, K.; Pitcher, L. H.

    2017-12-01

    Proglacial discharge monitoring provides valuable insights in Greenland ice sheet meltwater release. We use a 2006-2016 discharge time series from the Watson River draining 12000 km2 of the ice sheet in southwest Greenland to investigate the large variability in catchment-total meltwater production. An observationally-constrained reconstruction of past discharge shows that meltwater release has on average increased by a factor of 1.5 since 2003 compared to the 1949-2002 period, and that interannual variability has disproportionally increased by a factor of 2.1, suggesting that melt amplifiers are at play. We derive a hypsometric amplification factor of 1.6, which is the result of the exponential melt area increase with rising temperature. Peak meltwater discharge events such as during the July 2012 flooding are due to this and other melt amplifiers, but also require intense melting over a period exceeding the multi-day transit time for high-elevation meltwater to pass through the glacial drainage system.

  17. Limited Impact of Subglacial Supercooling Freeze-on for Greenland Ice Sheet Stratigraphy

    Science.gov (United States)

    Dow, Christine F.; Karlsson, Nanna B.; Werder, Mauro A.

    2018-02-01

    Large units of disrupted radiostratigraphy (UDR) are visible in many radio-echo sounding data sets from the Greenland Ice Sheet. This study investigates whether supercooling freeze-on rates at the bed can cause the observed UDR. We use a subglacial hydrology model to calculate both freezing and melting rates at the base of the ice sheet in a distributed sheet and within basal channels. We find that while supercooling freeze-on is a phenomenon that occurs in many areas of the ice sheet, there is no discernible correlation with the occurrence of UDR. The supercooling freeze-on rates are so low that it would require tens of thousands of years with minimal downstream ice motion to form the hundreds of meters of disrupted radiostratigraphy. Overall, the melt rates at the base of the ice sheet greatly overwhelm the freeze-on rates, which has implications for mass balance calculations of Greenland ice.

  18. Electrical conductivity measurements from the GISP2 and GRIP Greenland ice cores

    DEFF Research Database (Denmark)

    Dahl-Jensen, Dorthe; Clausen, Henrik Brink; Taylor, K. C.

    1993-01-01

    . Here we present electrical conductivity records for the Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice-core Project (GRIP) ice cores, drilled 28 km apart to enable direct comparison of the results. The upper parts of both records are consistent with previous evidence from other Greenland cores...

  19. North and northeast Greenland ice discharge from satellite radar interferometry

    DEFF Research Database (Denmark)

    Rignot, E.J.; Gogineni, S.P.; Krabill, W.B.

    1997-01-01

    Ice discharge from north and northeast Greenland calculated from satellite radar interferometry data of 14 outlet glaciers is 3.5 times that estimated from iceberg production. The satellite estimates, obtained at the grounding line of the outlet glaciers, differ from those obtained at the glacier...... front, because basal melting is extensive at the underside of the floating glacier sections. The results suggest that the north and northeast parts of the Greenland ice sheet may be thinning and contributing positively to sea-level rise....

  20. GREENLAND ICE SHEET CHANGES FROM SPACE USING LASER, RADAR AND

    DEFF Research Database (Denmark)

    Sørensen, Louise Sandberg; Stenseng, Lars; Simonsen, Sebastian Bjerregaard

    2010-01-01

    The Greenland cryosphere is undergoing rapid changes, and these are documented by remote sensing from space. In this paper, an inversion scheme is used to derive mass changes from gravity changes observed by GRACE, and to derive the mean annual mass loss for the Greenland Ice Sheet, which...... is estimated to be 204 Gt/yr for the period 2002-2010. NASA’s laser altimetry satellite ICESat has provided elevation estimates of the ice sheet since January 2003. In order to be able to compare GRACE and ICESat derived results, the ICESat volume change must be converted into a mass change estimate. Therefore...

  1. The extreme melt across the Greenland ice sheet in 2012

    Science.gov (United States)

    Nghiem, S. V.; Hall, D. K.; Mote, T. L.; Tedesco, M.; Albert, M. R.; Keegan, K.; Shuman, C. A.; DiGirolamo, N. E.; Neumann, G.

    2012-10-01

    The discovery of the 2012 extreme melt event across almost the entire surface of the Greenland ice sheet is presented. Data from three different satellite sensors - including the Oceansat-2 scatterometer, the Moderate-resolution Imaging Spectroradiometer, and the Special Sensor Microwave Imager/Sounder - are combined to obtain composite melt maps, representing the most complete melt conditions detectable across the ice sheet. Satellite observations reveal that melt occurred at or near the surface of the Greenland ice sheet across 98.6% of its entire extent on 12 July 2012, including the usually cold polar areas at high altitudes like Summit in the dry snow facies of the ice sheet. This melt event coincided with an anomalous ridge of warm air that became stagnant over Greenland. As seen in melt occurrences from multiple ice core records at Summit reported in the published literature, such a melt event is rare with the last significant one occurring in 1889 and the next previous one around seven centuries earlier in the Medieval Warm Period. Given its rarity, the 2012 extreme melt across Greenland provides an exceptional opportunity for new studies in broad interdisciplinary geophysical research.

  2. Airborne Geophysics and Remote Sensing Applied to Study Greenland Ice Dynamics

    Science.gov (United States)

    Csatho, Beata M.

    2003-01-01

    Overview of project: we combined and jointly analysed geophysical, remote sensing and glaciological data for investigating the temporal changes in ice flow and the role of geologic control on glacial drainage. The project included two different studies, the investigation of recent changes of the Kangerlussuaq glacier and the study of geologic control of ice flow in NW Greenland, around the Humboldt, Petermann and Ryder glaciers.

  3. Understanding Recent Mass Balance Changes of the Greenland Ice Sheet

    Science.gov (United States)

    vanderVeen, Cornelius

    2003-01-01

    The ultimate goal of this project is to better understand the current transfer of mass between the Greenland Ice Sheet, the world's oceans and the atmosphere, and to identify processes controlling the rate of this transfer, to be able to predict with greater confidence future contributions to global sea level rise. During the first year of this project, we focused on establishing longer-term records of change of selected outlet glaciers, reevaluation of mass input to the ice sheet and analysis of climate records derived from ice cores, and modeling meltwater production and runoff from the margins of the ice sheet.

  4. Sea ice and pollution-modulated changes in Greenland ice core methanesulfonate and bromine

    Science.gov (United States)

    Maselli, Olivia J.; Chellman, Nathan J.; Grieman, Mackenzie; Layman, Lawrence; McConnell, Joseph R.; Pasteris, Daniel; Rhodes, Rachael H.; Saltzman, Eric; Sigl, Michael

    2017-01-01

    Reconstruction of past changes in Arctic sea ice extent may be critical for understanding its future evolution. Methanesulfonate (MSA) and bromine concentrations preserved in ice cores have both been proposed as indicators of past sea ice conditions. In this study, two ice cores from central and north-eastern Greenland were analysed at sub-annual resolution for MSA (CH3SO3H) and bromine, covering the time period 1750-2010. We examine correlations between ice core MSA and the HadISST1 ICE sea ice dataset and consult back trajectories to infer the likely source regions. A strong correlation between the low-frequency MSA and bromine records during pre-industrial times indicates that both chemical species are likely linked to processes occurring on or near sea ice in the same source regions. The positive correlation between ice core MSA and bromine persists until the mid-20th century, when the acidity of Greenland ice begins to increase markedly due to increased fossil fuel emissions. After that time, MSA levels decrease as a result of declining sea ice extent but bromine levels increase. We consider several possible explanations and ultimately suggest that increased acidity, specifically nitric acid, of snow on sea ice stimulates the release of reactive Br from sea ice, resulting in increased transport and deposition on the Greenland ice sheet.

  5. Application of GRACE to the Evaluation of an Ice Flow Model of the Greenland Ice Sheet

    Science.gov (United States)

    Schlegel, N.; Wiese, D. N.; Watkins, M. M.; Larour, E. Y.; Box, J. E.; Fettweis, X.; van den Broeke, M. R.; Morlighem, M.; Boening, C.; Seroussi, H. L.

    2014-12-01

    Quantifying Greenland's future contribution to sea level rise is a challenging task and requires accurate estimates of ice flow sensitivity to climate change. Transient ice flow models are promising tools for estimating future ice sheet behavior. However, confidence in these types of future projections is low, especially because evaluation of model historical runs is so challenging due to the scarcity of continental-wide data for validation. For more than a decade, NASA's GRACE has continuously acquired time-variable measurements of the Earth's gravity field and has provided unprecedented surveillance of mass balance of the ice sheets, offering an opportunity for ice sheet model evaluation. Here, we take advantage of a new high-resolution (~300 km) monthly mascon solution for the purpose of mass balance comparison with an independent, historical ice flow model simulation using the Ice Sheet System Model (ISSM). The comparison highlights which regions of the ice sheet differ most from GRACE. Investigation of regional differences in trends and seasonal amplitudes between simulations forced with three different Regional Climate Model (RCM)-based estimates of surface mass balance (SMB) allows us to make conclusions about the relative contributions of various error sources in the model hindcast. This study constitutes the first regional comparison of GRACE data and an ice sheet model. Conclusions will aid in the improvement of RCM SMB estimates as well as ice sheet simulation estimates of present and future rates of sea level rise. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere Program and President's and Director's Fund Program.

  6. Greenland ice mass balance from GPS, GRACE and ICESat

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Kjær, Kurt H.; Korsgaard, Niels Jákup

    Greenland, using stereoscopic coverage by aerial photographs recorded in 1985, and subsequent comparative surface elevation data from ICESat (Ice, Cloud and land Elevation Satellite) and ATM (Airborne Topographic Mapper) supplemented with measurements from GPS and the Gravity Recovery and Climate Experiment...... (GRACE) satellite gravity mission, launched in March, 2002. The GRACE results provide a direct measure of mass loss, while the GPS data are used to monitor crustal uplift caused by ice mass loss close to the GPS sites....

  7. Polarimetric signatures of sea ice in the Greenland Sea

    DEFF Research Database (Denmark)

    Skriver, Henning; Pedersen, Leif Toudal

    1995-01-01

    Polarimetric SAR data of sea ice have been acquired by the Danish polarimetric SAR (EMISAR) during a mission at the Greenland Sea in August 1994. Video recordings from a low-altitude acquisition have been used for interpretation of the SAR data. Also, ERS-1 SAR data and NOAA AVHRR-data have been...

  8. Greenland Ice Sheet Mass Loss from GRACE Monthly Models

    DEFF Research Database (Denmark)

    Sørensen, Louise Sandberg; Forsberg, René

    2010-01-01

    The Greenland ice sheet is currently experiencing a net mass loss. There are however large discrepancies between the published qualitative mass loss estimates, based on different data sets and methods. There are even large differences between the results based on the same data sources, as is the ...

  9. An energy balance model for the Greenland ice sheet

    NARCIS (Netherlands)

    Wal, R.S.W. van de; Oerlemans, J.

    1994-01-01

    The sensitivity of the mass balance of the Greenland Ice Sheet is studied by means of an energy balance model. The model calculates the shortwave and longwave radiation and the turbulent fluxes on a grid with a grid point spacing of 20 km. Special attention is given to the parameterization of the

  10. The Greenland ice sheet in a warming climate

    NARCIS (Netherlands)

    van Angelen, J.H.|info:eu-repo/dai/nl/325922470

    2013-01-01

    In this thesis we assess multiple aspects of the Greenland climate, including the surface energy and mass balance of the ice sheet for the contemporary and near future climate. For these purposes we used output of the extensively and well-evaluated regional atmospheric climate model RACMO2. The

  11. Greenland ice core evidence for spatial and temporal variability of the Atlantic Multidecadal Oscillation

    NARCIS (Netherlands)

    Chylek, P.; Folland, C.K.; Frankcombe, L.M.; Dijkstra, H.A.; Lesins, G.; Dubey, M.

    2012-01-01

    [1] The Greenland δ18O ice core record is used as a proxy for Greenland surface air temperatures and to interpret Atlantic Multidecadal Oscillation (AMO) variability. An analysis of annual δ18O data from six Arctic ice cores (five from Greenland and one from Canada's Ellesmere Island) suggests a

  12. Timing of the Little Ice Age in southern Greenland

    DEFF Research Database (Denmark)

    Kjær, Kurt H.; Kjeldsen, Kristian K.; Bjørk, Anders A.

    2013-01-01

    as a signal for ice-free terrain being overridden by LIA glacier advances, and data from threshold lakes showing the onset of glacier-fed lakes, thus revealing the advance-maximum phase initiating the LIA. Finally, we have compiled lichenometry results indicating the onset of bedrock vegetation succeeding ice......Northern hemisphere temperatures reached their Holocene minimum and most glaciers reached their maximum during The Little Ice Age (LIA), but the timing of specific cold intervals is site-specific. In southern Greenland, we have compiled data from organic matter incorporated in LIA sediments, used...

  13. Algae Drive Enhanced Darkening of Bare Ice on the Greenland Ice Sheet

    Science.gov (United States)

    Stibal, Marek; Box, Jason E.; Cameron, Karen A.; Langen, Peter L.; Yallop, Marian L.; Mottram, Ruth H.; Khan, Alia L.; Molotch, Noah P.; Chrismas, Nathan A. M.; Calı Quaglia, Filippo; Remias, Daniel; Smeets, C. J. P. Paul; van den Broeke, Michiel R.; Ryan, Jonathan C.; Hubbard, Alun; Tranter, Martyn; van As, Dirk; Ahlstrøm, Andreas P.

    2017-11-01

    Surface ablation of the Greenland ice sheet is amplified by surface darkening caused by light-absorbing impurities such as mineral dust, black carbon, and pigmented microbial cells. We present the first quantitative assessment of the microbial contribution to the ice sheet surface darkening, based on field measurements of surface reflectance and concentrations of light-absorbing impurities, including pigmented algae, during the 2014 melt season in the southwestern part of the ice sheet. The impact of algae on bare ice darkening in the study area was greater than that of nonalgal impurities and yielded a net albedo reduction of 0.038 ± 0.0035 for each algal population doubling. We argue that algal growth is a crucial control of bare ice darkening, and incorporating the algal darkening effect will improve mass balance and sea level projections of the Greenland ice sheet and ice masses elsewhere.

  14. Probability based hydrologic catchments of the Greenland Ice Sheet

    Science.gov (United States)

    Hudson, B. D.

    2015-12-01

    Greenland Ice Sheet melt water impacts ice sheet flow dynamics, fjord and coastal circulation, and sediment and biogeochemical fluxes. Melt water exiting the ice sheet also is a key term in its mass balance. Because of this, knowledge of the area of the ice sheet that contributes melt water to a given outlet (its hydrologic catchment) is important to many ice sheet studies and is especially critical to methods using river runoff to assess ice sheet mass balance. Yet uncertainty in delineating ice sheet hydrologic catchments is a problem that is rarely acknowledged. Ice sheet catchments are delineated as a function of both basal and surface topography. While surface topography is well known, basal topography is less certain because it is dependent on radar surveys. Here, I a present a Monte Carlo based approach to delineating ice sheet catchments that quantifies the impact of uncertain basal topography. In this scheme, over many iterations I randomly vary the ice sheet bed elevation within published error bounds (using Morlighem et al., 2014 bed and bed error datasets). For each iteration of ice sheet bed elevation, I calculate the hydraulic potentiometric surface and route water over its path of 'steepest' descent to delineate the catchment. I then use all realizations of the catchment to arrive at a probability map of all major melt water outlets in Greenland. I often find that catchment size is uncertain, with small, random perturbations in basal topography leading to large variations in catchments size. While some catchments are well defined, others can double or halve in size within published basal topography error bars. While some uncertainty will likely always remain, this work points to locations where studies of ice sheet hydrology would be the most successful, allows reinterpretation of past results, and points to where future radar surveys would be most advantageous.

  15. Continuous methane measurements from a late Holocene Greenland ice core

    DEFF Research Database (Denmark)

    Rhodes, R.H.; Mitchell, L.E.; Brook, E.J.

    2013-01-01

    Ancient air trapped inside bubbles in ice cores can now be analysed for methane concentration utilising a laser spectrometer coupled to a continuous melter system. We present a new ultra-high resolution record of atmospheric methane variability over the last 1800yr obtained from continuous analysis...... of a shallow ice core from the North Greenland Eemian project (NEEM-2011-S1) during a 4-week laboratory-based measurement campaign. Our record faithfully replicates the form and amplitudes of multi-decadal oscillations previously observed in other ice cores and demonstrates the detailed depth resolution (5.3cm......), rapid acquisition time (30mday) and good long-term reproducibility (2.6%, 2s) of the continuous measurement technique.In addition, we report the detection of high frequency ice core methane signals of non-atmospheric origin. Firstly, measurements of air from the firn-ice transition region...

  16. Supraglacial bacterial community structures vary across the Greenland ice sheet

    DEFF Research Database (Denmark)

    Cameron, Karen A.; Stibal, Marek; Zarsky, Jakub D.

    2016-01-01

    The composition and spatial variability of microbial communities that reside within the extensive (>200 000 km(2)) biologically active area encompassing the Greenland ice sheet (GrIS) is hypothesized to be variable. We examined bacterial communities from cryoconite debris and surface ice across...... the GrIS, using sequence analysis and quantitative PCR of 16S rRNA genes from co-extracted DNA and RNA. Communities were found to differ across the ice sheet, with 82.8% of the total calculated variation attributed to spatial distribution on a scale of tens of kilometers separation. Amplicons related...... to Sphingobacteriaceae, Pseudanabaenaceae and WPS-2 accounted for the greatest portion of calculated dissimilarities. The bacterial communities of ice and cryoconite were moderately similar (global R = 0.360, P = 0.002) and the sampled surface type (ice versus cryoconite) did not contribute heavily towards community...

  17. Radiation Climatology of the Greenland Ice Sheet Derived from Greenland Climate Network Data

    Science.gov (United States)

    Steffen, Konrad; Box, Jason

    2003-01-01

    The magnitude of shortwave and longwave dative fluxes are critical to surface energy balance variations over the Greenland ice sheet, affecting many aspects of its climate, including melt rates, the nature of low-level temperature inversions, the katabatic wind regime and buoyant stability of the atmosphere. Nevertheless, reliable measurements of the radiative fluxes over the ice sheet are few in number, and have been of limited duration and areal distribution (e.g. Ambach, 1960; 1963, Konzelmann et al., 1994, Harding et al., 1995, Van den Broeke, 1996). Hourly GC-Net radiation flux measurements spanning 1995-2001 period have been used to produce a monthly dataset of surface radiation balance components. The measurements are distributed widely across Greenland and incorporate multiple sensors

  18. Mass balance and surface movement of the Greenland Ice Sheet at Summit, Central Greenland

    DEFF Research Database (Denmark)

    Hvidberg, C.S.; Keller, K.; Gundestrup, N.S.

    1997-01-01

    During the GRIP deep drilling in Central Greenland, the ice sheet topography and surface movement at Summit has been mapped with GPS. Measurements of the surface velocity are presented for a strain net consisting of 13 poles at distances of 25-60 km from the GRIP site. Some results are: The GRIP...... site is located approximately 2 km NW of the topographic summit; the surface velocity at the GISP 2 site is 1.7 m/yr in the W direction. The present mass balance at Summit is calculated to be -0.03+/-0.04 m/yr, i.e. close to steady state. This result is the best now available for Summit. A small...... thinning rate might be a transient response of the Greenland Ice Sheet due to the temperature increase at the Wisconsin-Holocene transition....

  19. Spatiotemporal variability in surface energy balance across tundra, snow and ice in Greenland

    DEFF Research Database (Denmark)

    Lund, Magnus; Stiegler, Christian; Abermann, Jakob

    2017-01-01

    The surface energy balance (SEB) is essential for understanding the coupled cryosphere–atmosphere system in the Arctic. In this study, we investigate the spatiotemporal variability in SEB across tundra, snow and ice. During the snow-free period, the main energy sink for ice sites is surface melt....... For tundra, energy is used for sensible and latent heat flux and soil heat flux leading to permafrost thaw. Longer snow-free period increases melting of the Greenland Ice Sheet and glaciers and may promote tundra permafrost thaw. During winter, clouds have a warming effect across surface types whereas during...

  20. Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

    Science.gov (United States)

    Padman, Laurie; Siegfried, Matthew R.; Fricker, Helen A.

    2018-03-01

    Ocean tides are the main source of high-frequency variability in the vertical and horizontal motion of ice sheets near their marine margins. Floating ice shelves, which occupy about three quarters of the perimeter of Antarctica and the termini of four outlet glaciers in northern Greenland, rise and fall in synchrony with the ocean tide. Lateral motion of floating and grounded portions of ice sheets near their marine margins can also include a tidal component. These tide-induced signals provide insight into the processes by which the oceans can affect ice sheet mass balance and dynamics. In this review, we summarize in situ and satellite-based measurements of the tidal response of ice shelves and grounded ice, and spatial variability of ocean tide heights and currents around the ice sheets. We review sensitivity of tide heights and currents as ocean geometry responds to variations in sea level, ice shelf thickness, and ice sheet mass and extent. We then describe coupled ice-ocean models and analytical glacier models that quantify the effect of ocean tides on lower-frequency ice sheet mass loss and motion. We suggest new observations and model developments to improve the representation of tides in coupled models that are used to predict future ice sheet mass loss and the associated contribution to sea level change. The most critical need is for new data to improve maps of bathymetry, ice shelf draft, spatial variability of the drag coefficient at the ice-ocean interface, and higher-resolution models with improved representation of tidal energy sinks.

  1. Spaceborne measurement of Greenland ice sheet changes: the ESA Greenland CCI project

    DEFF Research Database (Denmark)

    Forsberg, René; Sørensen, Louise Sandberg; Meister, Rakia

    The ESA “Greenland_ice_sheet_cci” project is currently making past and present space measurements of Greenland ice sheet changes available for use by scientists, stakeholders and the general public. The data are part of a large set of ECV’s (Essential Climate Variables) made available by the ESA...... Climate Initiative, as a contribution to the global Climate Observing System. The ECV data produced for the Greenlandice sheet include detailed grids of elevation changes and ice flow velocities, as well as line data of grounding lines and calving front locations for major outlet glaciers. The “ice_sheets......_cci” goal is to generate a consistent, validated, long-term and timely set of ECV’s, a.o. to improve the impact of satellite data on climate research and coupled ice sheet/climate models. Special focus is on use of data from ESA missions such as ERS, Envisat and the new Sentinel missions, but in the 2nd...

  2. Mass Balance of the Greenland Ice Sheet at High Elevations.

    Science.gov (United States)

    Thomas; Akins; Csatho; Fahnestock; Gogineni; Kim; Sonntag

    2000-07-21

    Comparison of ice discharge from higher elevation areas of the entire Greenland Ice Sheet with total snow accumulation gives estimates of ice thickening rates over the past few decades. On average, the region has been in balance, but with thickening of 21 centimeters per year in the southwest and thinning of 30 centimeters per year in the southeast. The north of the ice sheet shows less variability, with average thickening of 2 centimeters per year in the northeast and thinning of about 5 centimeters per year in the northwest. These results agree well with those from repeated altimeter surveys, except in the extreme south, where we find substantially higher rates of both thickening and thinning.

  3. Solitary Waves of Ice Loss Detected in Greenland Crustal Motion

    Science.gov (United States)

    Adhikari, S.; Ivins, E. R.; Larour, E. Y.

    2017-12-01

    The annual cycle and secular trend of Greenland mass loading are well recorded in measurements of solid Earth deformation. While bedrock vertical displacements are in phase with loading as inferred from space observations, horizontal motions have received almost no attention. The horizontal bedrock displacements can potentially track the spatiotemporal detail of mass changes with great fidelity. Our analysis of Greenland crustal motion data reveals that a significant excitation of horizontal amplitudes occurs during the intense Greenland melting. A suite of space geodetic observations and climate reanalysis data cannot explain these large horizontal displacements. We discover that solitary seasonal waves of substantial mass transport traveled through Rink Glacier in 2010 and 2012. We deduce that intense summer melting enhanced either basal lubrication or shear softening, or both, causing the glacier to thin dynamically. The newly routed upstream sublglacial water was likely to be both retarded and inefficient, thus providing a causal mechanism for the prolonged ice transport to continue well into the winter months. As the climate continues to produce increasingly warmer spring and summer, amplified seasonal waves of mass transport may become ever more present in years of future observations. Increased frequency of amplified seasonal mass transport may ultimately strengthen the Greenland's dynamic ice mass loss, a component of the balance that will have important ramifications for sea level rise. This animation shows a solitary wave passing through Rink Glacier, Greenland, in 2012, recorded by the motion of a GPS station (circle with arrow). Darker blue colors within the flow indicate mass loss, red colors show mass gain. The star marks the center of the wave. Credit: NASA/JPL-Caltech

  4. How Will Sea Ice Loss Affect the Greenland Ice Sheet? On the Puzzling Features of Greenland Ice-Core Isotopic Composition

    Science.gov (United States)

    Pausata, Francesco S. R.; Legrande, Allegra N.; Roberts, William H. G.

    2016-01-01

    The modern cryosphere, Earth's frozen water regime, is in fast transition. Greenland ice cores show how fast theses changes can be, presenting evidence of up to 15 C warming events over timescales of less than a decade. These events, called Dansgaard/Oeschger (D/O) events, are believed to be associated with rapid changes in Arctic sea ice, although the underlying mechanisms are still unclear. The modern demise of Arctic sea ice may, in turn, instigate abrupt changes on the Greenland Ice Sheet. The Arctic Sea Ice and Greenland Ice Sheet Sensitivity (Ice2Ice Chttps://ice2ice.b.uib.noD) initiative, sponsored by the European Research Council, seeks to quantify these past rapid changes to improve our understanding of what the future may hold for the Arctic. Twenty scientists gathered in Copenhagen as part of this initiative to discuss the most recent observational, technological, and model developments toward quantifying the mechanisms behind past climate changes in Greenland. Much of the discussion focused on the causes behind the changes in stable water isotopes recorded in ice cores. The participants discussed sources of variability for stable water isotopes and framed ways that new studies could improve understanding of modern climate. The participants also discussed how climate models could provide insights into the relative roles of local and nonlocal processes in affecting stable water isotopes within the Greenland Ice Sheet. Presentations of modeling results showed how a change in the source or seasonality of precipitation could occur not only between glacial and modern climates but also between abrupt events. Recent fieldwork campaigns illustrate an important role of stable isotopes in atmospheric vapor and diffusion in the final stable isotope signal in ice. Further, indications from recent fieldwork campaigns illustrate an important role of stable isotopes in atmospheric vapor and diffusion in the final stable isotope signal in ice. This feature complicates

  5. The state of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Simonsen, Sebastian Bjerregaard

    Firn is defined as snow that has survived a melt season and provides the link between the high-frequency variability of the atmosphere to the ”slower” reacting ice sheet.In this thesis, firn is described by a theoretical and statistical approach to accommodate the variability in observed firn...... compaction on ice sheet scales. The modeling objectives are multiple and aim at estimating the contribution from the firn to the observed volume change of the GrIS and to the diffusion of stable water isotopes. The firn modeling then provides crucial information on total mass balance of the Gr......IS and the paleo-temperature reconstructions retrieved from ice cores.The dynamical firn model developed in this thesis explains13 % of the observed volume change of the GrIS from 2003-2008, without contributing to the global sea-level rise. This emphasizes the need for well constraint firn-compaction models. Here...

  6. MASS BALANCE CHANGES AND ICE DYNAMICS OF GREENLAND AND ANTARCTIC ICE SHEETS FROM LASER ALTIMETRY

    Directory of Open Access Journals (Sweden)

    G. S. Babonis

    2016-06-01

    Full Text Available During the past few decades the Greenland and Antarctic ice sheets have lost ice at accelerating rates, caused by increasing surface temperature. The melting of the two big ice sheets has a big impact on global sea level rise. If the ice sheets would melt down entirely, the sea level would rise more than 60 m. Even a much smaller rise would cause dramatic damage along coastal regions. In this paper we report about a major upgrade of surface elevation changes derived from laser altimetry data, acquired by NASA’s Ice, Cloud and land Elevation Satellite mission (ICESat and airborne laser campaigns, such as Airborne Topographic Mapper (ATM and Land, Vegetation and Ice Sensor (LVIS. For detecting changes in ice sheet elevations we have developed the Surface Elevation Reconstruction And Change detection (SERAC method. It computes elevation changes of small surface patches by keeping the surface shape constant and considering the absolute values as surface elevations. We report about important upgrades of earlier results, for example the inclusion of local ice caps and the temporal extension from 1993 to 2014 for the Greenland Ice Sheet and for a comprehensive reconstruction of ice thickness and mass changes for the Antarctic Ice Sheets.

  7. Recent greenland accumulation estimated from regional climate model simulations and ice core analysis

    DEFF Research Database (Denmark)

    Dethloff, K.; Schwager, M.; Christensen, J. H.

    2002-01-01

    to precipitation. Maxima of precipitation and accumulation occur at the southwestern and southeastern coasts of Greenland and are connected with cyclonic activity and the main storm tracks around Greenland. The central region of the Greenland ice sheet acts as a blocking barrier on moving weather systems...... and prohibits cyclones moving from west to east across this region and, thus prevents moisture transports....

  8. High Arctic Holocene temperature record from the Agassiz ice cap and Greenland ice sheet evolution.

    Science.gov (United States)

    Lecavalier, Benoit S; Fisher, David A; Milne, Glenn A; Vinther, Bo M; Tarasov, Lev; Huybrechts, Philippe; Lacelle, Denis; Main, Brittany; Zheng, James; Bourgeois, Jocelyne; Dyke, Arthur S

    2017-06-06

    We present a revised and extended high Arctic air temperature reconstruction from a single proxy that spans the past ∼12,000 y (up to 2009 CE). Our reconstruction from the Agassiz ice cap (Ellesmere Island, Canada) indicates an earlier and warmer Holocene thermal maximum with early Holocene temperatures that are 4-5 °C warmer compared with a previous reconstruction, and regularly exceed contemporary values for a period of ∼3,000 y. Our results show that air temperatures in this region are now at their warmest in the past 6,800-7,800 y, and that the recent rate of temperature change is unprecedented over the entire Holocene. The warmer early Holocene inferred from the Agassiz ice core leads to an estimated ∼1 km of ice thinning in northwest Greenland during the early Holocene using the Camp Century ice core. Ice modeling results show that this large thinning is consistent with our air temperature reconstruction. The modeling results also demonstrate the broader significance of the enhanced warming, with a retreat of the northern ice margin behind its present position in the mid Holocene and a ∼25% increase in total Greenland ice sheet mass loss (∼1.4 m sea-level equivalent) during the last deglaciation, both of which have implications for interpreting geodetic measurements of land uplift and gravity changes in northern Greenland.

  9. Mountain glaciers vs Ice sheet in Greenland - learning from a new monitoring site in West Greenland

    Science.gov (United States)

    Abermann, Jakob; van As, Dirk; Wacker, Stefan; Langley, Kirsty

    2017-04-01

    Only 5 out of the 20.000 peripheral glaciers and ice caps surrounding Greenland are currently monitored due to logistical challenges and despite their significance for sea level rise. Large spatial coast-to-icesheet mass and energy balance gradients limit simple upscaling methods from ice-sheet observations, which builds the motivation for this study. We present results from a new mass and energy balance time series at Qasigiannguit glacier (64°09'N; 51°21'W) in Southwest Greenland. Inter-annual variability is discussed and the surface energy balance over two summers is quantified and a ranking of the main drivers performed. We find that short-wave net radiation is by far the most dominant energy source during summer, followed by similar amounts of net longwave radiation and sensible heat, respectively. We then relate these observations to synchronous measurements at similar latitude on an outlet glacier of the ice sheet a mere 100 km away. We find very pronounced horizontal surface mass balance gradients, with generally more positive values closer to the coast. We conclude that despite minor differences of atmospheric parameters (i.e. humidity, radiation, and temperature) the main reason for the strongly different signal is a pronounced winter precipitation gradient that translates in a different duration of ice exposure and through that an albedo gradient. Modelled energy balance gradients converted into mass changes show good agreement to measured surface mass balance gradients and we explore a latitudinal signal of these findings.

  10. Contrasting evidence of Holocene ice margin retreat, south-western Greenland

    DEFF Research Database (Denmark)

    Levy, L. B.; Larsen, N. K.; Davidson, T. A.

    2017-01-01

    Constraining the Greenland Ice Sheet's (GrIS) response to Holocene climate change provides calibrations for ice sheet models that hindcast past ice margin fluctuations. Ice sheet models predict enhanced ice retreat in south-western Greenland during the middle Holocene; however, few geological...... observations corroborating the extensive retreat are available. We present new data from lake sediment cores from the Isua region, south-western Greenland, which provide constraints on Holocene fluctuations of the GrIS margins. Our data indicate that the main GrIS margin was 30 km west of its present...

  11. Accelerated mass loss from Greenland ice sheet : Links to atmospheric circulation in the North Atlantic

    NARCIS (Netherlands)

    Seo, Ki-Weon; Waliser, Duane E.; Lee, Choon-Ki; Tian, Baijun; Scambos, Ted; Kim, Baek-Min; van Angelen, Jan H.; van den Broeke, Michiel R.

    Understanding the mechanisms that drive the mass imbalance of the Greenland ice sheet (GrIS) is critical to the accurate projection of its contribution to future sea level rise. Greenland's ice mass loss has been accelerating recently. Using satellite Earth-gravity and regional climate model data,

  12. An ice flow modeling perspective on bedrock adjustment patterns of the Greenland ice sheet

    Directory of Open Access Journals (Sweden)

    M. Olaizola

    2012-11-01

    Full Text Available Since the launch in 2002 of the Gravity Recovery and Climate Experiment (GRACE satellites, several estimates of the mass balance of the Greenland ice sheet (GrIS have been produced. To obtain ice mass changes, the GRACE data need to be corrected for the effect of deformation changes of the Earth's crust. Recently, a new method has been proposed where ice mass changes and bedrock changes are simultaneously solved. Results show bedrock subsidence over almost the entirety of Greenland in combination with ice mass loss which is only half of the currently standing estimates. This subsidence can be an elastic response, but it may however also be a delayed response to past changes. In this study we test whether these subsidence patterns are consistent with ice dynamical modeling results. We use a 3-D ice sheet–bedrock model with a surface mass balance forcing based on a mass balance gradient approach to study the pattern and magnitude of bedrock changes in Greenland. Different mass balance forcings are used. Simulations since the Last Glacial Maximum yield a bedrock delay with respect to the mass balance forcing of nearly 3000 yr and an average uplift at present of 0.3 mm yr−1. The spatial pattern of bedrock changes shows a small central subsidence as well as more intense uplift in the south. These results are not compatible with the gravity based reconstructions showing a subsidence with a maximum in central Greenland, thereby questioning whether the claim of halving of the ice mass change is justified.

  13. Interannual Variability of the Sea-Ice-Induced Salt Flux in the Greenland Sea

    DEFF Research Database (Denmark)

    Pedersen, Leif Toudal; Coon, M.D.

    2001-01-01

    The Greenland Sea is one of the few places in the World Ocean where deep convection takes place. The convection process is initiated by a density increase originating from rapid cooling and/or a salt flux to the upper layer of the ocean due to brine rejection from ice formation (Rudels, 1990......; Visbeck and others, 1995). The predominant ice types in the Greenland Sea arc frazil/grease ice and pancake ice. A numerical model has been developed relating ice formation and decay of these ice types as observed by the SMMR and SSM/I microwave radiometers and evaluating their contribution to salt...... redistribution in the Greenland Sea. The model has been used to calculate spatial distribution of the annual integrated net salt flux to the Greenland Sea from ice production and advection for the period 1979-97....

  14. Glaciers and ice caps outside Greenland

    Science.gov (United States)

    Sharp, Marin; Wolken, G.; Burgess, D.; Cogley, J.G.; Copland, L.; Thomson, L.; Arendt, A.; Wouters, B.; Kohler, J.; Andreassen, L.M.; O'Neel, Shad; Pelto, M.

    2015-01-01

    Mountain glaciers and ice caps cover an area of over 400 000 km2 in the Arctic, and are a major influence on global sea level (Gardner et al. 2011, 2013; Jacob et al. 2012). They gain mass by snow accumulation and lose mass by meltwater runoff. Where they terminate in water (ocean or lake), they also lose mass by iceberg calving. The climatic mass balance (Bclim, the difference between annual snow accumulation and annual meltwater runoff) is a widely used index of how glaciers respond to climate variability and change. The total mass balance (ΔM) is defined as the difference between annual snow accumulation and annual mass losses (by iceberg calving plus runoff).

  15. Early Holocene climate oscillations recorded in three Greenland ice cores

    DEFF Research Database (Denmark)

    Rasmussen, Sune Olander; Vinther, Bo Møllesøe; Clausen, Henrik Brink

    2007-01-01

    around 9.3 ka before present, and the Preboreal Oscillation during the first centuries of the Holocene. For each of these sections, we present a d18O anomaly curve and a common accumulation signal that represents regional changes in the accumulation rate over the Greenland ice cap....... and accumulation anomalies that are common to the three cores in the Early Holocene (7.9–11.7 ka before present). Three time periods with significant and synchronous anomalies in the d18O and accumulation signals stand out: the well-known 8.2 ka event, an event of shorter duration but of almost similar amplitude...

  16. A sea ice model for the marginal ice zone with an application to the Greenland Sea

    DEFF Research Database (Denmark)

    Pedersen, Leif Toudal; Coon, Max D.

    2004-01-01

    A model is presented that describes the formation, transport, and desalinization of frazil and pancake ice as it is formed in marginal seas. This model uses as input the total ice concentration evaluated from Special Sensor Microwave Imager and wind speed and direction. The model calculates...... the areal concentration, thickness, volume concentration, and salinity of frazil ice as well as the areal concentration, thickness, and salinity of pancakes. A simple parameterization for the Odden region of the Greenland Sea is presented. The model is run for the winter of 1996-1997. There are direct...... observations of the thickness and salinity of pancakes and the volume concentration of frazil ice to compare with the model. The model results compare very well with the measured data. This new ice model can be tuned to work in marginal seas elsewhere to calculate ice thickness, motion, and brine rejection...

  17. Reconstructing surface elevation changes for the Greenland Ice Sheet (1993-2013) and analysis of Zachariae Isstrom, northeast Greenland

    Science.gov (United States)

    Duncan, Kyle

    Previous studies investigating the velocity and elevation change records of the Greenland Ice Sheet (GrIS) revealed rapid and complex changes. It is therefore imperative to determine changes with both high spatial and temporal resolutions. By fusing multiple laser altimetry data sets, the Surface Elevation Reconstruction and Change (SERAC) program is capable of reconstructing surface elevation changes with high spatial and temporal resolution over the entire GrIS. The input data include observations from NASA's Ice, Cloud and land Elevation Satellite (ICESat) mission (2003-2009) as well as data collected by NASA's Airborne Topographic Mapper (ATM) (1993-2013) and Land, Vegetation and Ice Sensor (LVIS) (2007-2012) airborne laser altimetry systems. This study extends the record of surface elevation changes over the GrIS by adding 2012 and 2013 laser altimetry data to the previous 1993-2011 record. Extending the record leads to a new, more accurate and detailed altimetry record for 1993-2013. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Digital Elevation Models (DEMs) are fused with laser altimetry data over Zachariae Isstrom, northeast Greenland to analyze surface elevation changes and associated thinning rates during 1978-2014. Little to no elevation change occurred over Zachariae Isstrom from 1978-1999, however, from 1999-2014 elevation changes near the calving front became increasingly negative and accelerated. Calving front position showed steady retreat and grounding line position has been retreating towards the interior of the ice sheet at an increasing rate from 2010-2014 when compared to the 1996-2010 period. The measured elevation changes near the calving front have brought a large portion of the glacier close to the height of flotation. If the current thinning trend continues this portion of the glacier will reach flotation within the next 2-5 years allowing for further retreat and increased vulnerability to retreat for sections of

  18. Tracing Internal Radar Layers in the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Panton, Christian

    Internal layers in radio-echograms from the sounding of ice sheets have long been a valuable resource in glaciology, but their usefulness have been limited by availability of traced (digitized) layers. To speed up this process, we have developed an algorithm for semi-automatic tracing the internal...... layers and a fully automated algorithm for mapping the layer slope. The layer slope is inferred by the intensity response to a slanted Gaussian filter, whereafter layers can be traced using an active contour model. With these techniques we show that it possible to trace internal layers over distances...... of hundreds kilometers with minimal operator intervention, and the methods have been successfully validated between two Greenland deep ice cores with internal match points. In order to remove any operator assistance, we show how the layer slope can be used to detect disturbances in the deep radiostratigraphy...

  19. Extending remote sensing estimates of Greenland ice sheet melting

    Science.gov (United States)

    Heavner, M.; Loveland, R.

    2010-12-01

    The Melt Area Detection Index (MADI), a remote sensing algorithm to discriminate between dry and wet snow, has been previously developed and applied to the western portion of the Greenland ice sheet for the years 2000-2006, using Moderate Resolution Imaging Radiospectrometer (MODIS) data (Chylek et al, 2007). We extend that work both spatially and temporally by taking advantage of newly available data, and developing algorithms that facilitate the sensing of cloud cover and the automated inference of wet snow regions. The automated methods allow the development of a composite melt area data product with 0.25 km^2 spatial resolution and approximately two week temporal resolution. We discuss melt area dynamics that are inferred from this high resolution composite melt area. Chylek, P., M. McCabe, M. K. Dubey, and J. Dozier (2007), Remote sensing of Greenland ice sheet using multispectral near-infrared and visible radiances, J. Geophys. Res., 112, D24S20, doi:10.1029/2007JD008742.

  20. How much can Greenland melt? An upper bound on mass loss from the Greenland Ice Sheet through surface melting

    Science.gov (United States)

    Liu, X.; Bassis, J. N.

    2015-12-01

    With observations showing accelerated mass loss from the Greenland Ice Sheet due to surface melt, the Greenland Ice Sheet is becoming one of the most significant contributors to sea level rise. The contribution of the Greenland Ice Sheet o sea level rise is likely to accelerate in the coming decade and centuries as atmospheric temperatures continue to rise, potentially triggering ever larger surface melt rates. However, at present considerable uncertainty remains in projecting the contribution to sea level of the Greenland Ice Sheet both due to uncertainty in atmospheric forcing and the ice sheet response to climate forcing. Here we seek an upper bound on the contribution of surface melt from the Greenland to sea level rise in the coming century using a surface energy balance model coupled to an englacial model. We use IPCC Representative Concentration Pathways (RCP8.5, RCP6, RCP4.5, RCP2.6) climate scenarios from an ensemble of global climate models in our simulations to project the maximum rate of ice volume loss and related sea-level rise associated with surface melting. To estimate the upper bound, we assume the Greenland Ice Sheet is perpetually covered in thick clouds, which maximize longwave radiation to the ice sheet. We further assume that deposition of black carbon darkens the ice substantially turning it nearly black, substantially reducing its albedo. Although assuming that all melt water not stored in the snow/firn is instantaneously transported off the ice sheet increases mass loss in the short term, refreezing of retained water warms the ice and may lead to more melt in the long term. Hence we examine both assumptions and use the scenario that leads to the most surface melt by 2100. Preliminary models results suggest that under the most aggressive climate forcing, surface melt from the Greenland Ice Sheet contributes ~1 m to sea level by the year 2100. This is a significant contribution and ignores dynamic effects. We also examined a lower bound

  1. Late Quaternary glaciation history of northernmost Greenland - Evidence of shelf-based ice

    DEFF Research Database (Denmark)

    Larsen, Nicolaj K.; Kjær, Kurt H.; Funder, Svend Visby

    2010-01-01

    We present the mapping of glacial landforms and sediments from northernmost Greenland bordering 100 km of the Arctic Ocean coast. One of the most important discoveries is that glacial landforms, sediments, including till fabric measurements, striae and stoss-lee boulders suggest eastward ice......-flow along the coastal plain. Volcanic erratic boulders document ice-transport from 80 to 100 km west of the study area. We argue that these findings are best explained by local outlet glaciers from the Greenland Ice Sheet and local ice caps that merged to form a shelf-based ice in the Arctic Ocean...... and possibly confirming an extensive ice shelf in the Lincoln Sea between Greenland and Ellesmere Island. It is speculated that the shelf-based ice was largely affected by the presence of thick multiyear sea ice in the Arctic Ocean that prevented it from breaking up and forced the outlet glaciers to flow...

  2. Ice dynamic response to two modes of surface lake drainage on the Greenland ice sheet

    International Nuclear Information System (INIS)

    Tedesco, Marco; Alexander, Patrick; Willis, Ian C; Banwell, Alison F; Arnold, Neil S; Hoffman, Matthew J

    2013-01-01

    Supraglacial lake drainage on the Greenland ice sheet opens surface-to-bed connections, reduces basal friction, and temporarily increases ice flow velocities by up to an order of magnitude. Existing field-based observations of lake drainages and their impact on ice dynamics are limited, and focus on one specific draining mechanism. Here, we report and analyse global positioning system measurements of ice velocity and elevation made at five locations surrounding two lakes that drained by different mechanisms and produced different dynamic responses. For the lake that drained slowly (>24 h) by overtopping its basin, delivering water via a channel to a pre-existing moulin, speedup and uplift were less than half those associated with a lake that drained rapidly (∼2 h) through hydrofracturing and the creation of new moulins in the lake bottom. Our results suggest that the mode and associated rate of lake drainage govern the impact on ice dynamics. (letter)

  3. Recent Greenland Thinning from Operation IceBridge ATM and LVIS Data

    Science.gov (United States)

    Sutterley, T. C.; Velicogna, I.

    2015-12-01

    We investigate regional thinning rates in Greenland using two Operation IceBridge lidar instruments, the Airborne Topographic Mapper (ATM) and the Land, Vegetation and Ice Sensor (LVIS). IceBridge and Pre-IceBridge ATM data are available from 1993 to present and IceBridge and Pre-Icebridge LVIS data are available from 2007 to present. We compare different techniques for combining the two datasets: overlapping footprints, triangulated irregular network meshing and radial basis functions. We validate the combination for periods with near term overlap of the two instruments. By combining the two lidar datasets, we are able to investigate intra-annual, annual, interannual surface elevation change. We investigate both the high melt season of 2012 and the low melt season of 2013. In addition, the major 2015 IceBridge Arctic campaign provides new crucial data for determining seasonal ice sheet thinning rates. We compare our LVIS/ATM results with surface mass balance outputs from two regional climate models: the Regional Atmospheric Climate Model (RACMO) and the Modèle Atmosphérique Régional (MAR). We also investigate the thinning rates of major outlet glaciers.

  4. Changes in Greenland ice bed conditions inferred from seismology

    Science.gov (United States)

    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.

  5. Assessing the accuracy of Greenland ice sheet ice ablation measurements by pressure transducer

    Science.gov (United States)

    Fausto, R. S.; van As, D.; Ahlstrøm, A. P.

    2012-04-01

    In the glaciological community there is a need for reliable mass balance measurements of glaciers and ice sheets, ranging from daily to yearly time scales. Here we present a method to measure ice ablation using a pressure transducer. The pressure transducer is drilled into the ice, en-closed in a hose filled with a liquid that is non-freezable at common Greenlandic temperatures. The pressure signal registered by the transducer is that of the vertical column of liquid over the sensor, which can be translated in depth knowing the density of the liquid. As the free-standing AWS moves down with the ablating surface and the hose melts out of the ice, an increasingly large part of the hose will lay flat on the ice surface, and the hydrostatic pressure from the vertical column of liquid in the hose will get smaller. This reduction in pressure provides us with the ablation rate. By measuring at (sub-) daily timescales this assembly is well-suited to monitor ice ablation in remote regions, with clear advantages over other well-established methods of measuring ice ablation in the field. The pressure transducer system has the potential to monitor ice ablation for several years without re-drilling and the system is suitable for high ablation areas. A routine to transform raw measurements into ablation values will also be presented, including a physically based method to remove air pressure variability from the signal. The pressure transducer time-series is compared to that recorded by a sonic ranger for the climatically hostile setting on the Greenland ice sheet.

  6. Current and future darkening of the Greenland ice sheet

    Science.gov (United States)

    Tedesco, Marco; Stroeve, Julienne; Fettweis, Xavier; Warren, Stephen; Doherty, Sarah; Noble, Erik; Alexander, Patrick

    2015-04-01

    Surface melting over the Greenland ice sheet (GIS) promotes snow grains growth, reducing albedo and further enhancing melting through the increased amount of absorbed solar radiation. Using a combination of remote sensing data and outputs of a regional climate model, we show that albedo over the GIS decreased significantly from 1996 to 2012. Further, we show that most of this darkening can be accounted for by enhanced snow grain growth and the expansion of areas where bare ice is exposed, both of which are driven by increases in snow warming. An analysis of the impact of light-absorbing impurities on albedo trends detected from spaceborne measurements was inconclusive because the estimated impact for concentrations of impurities of order of magnitude found in Greenland is within the albedo uncertainty retrievable from space-based instruments. However, neither models nor observations show an increase in pollutants (black carbon and associated organics) in the atmosphere over the GIS in this time period. Additionally, we could not identify trends in the number of fires over North America and Russia, assumed to be among the sources of soot for Greenland. We did find that a 'dark band' of tilted ice plays a crucial role in decreasing albedo along the west margin, and there is some indication that dust deposition to the GIS may be decreasing albedo in this region but this is not conclusive. In addition to looking at the direct impact of impurities on albedo, we estimated the impact of impurities on albedo via their influence on grain growth and found it is relatively small (~ 1- 2 %), though more sophisticated analysis needs to be carried out. Projections obtained under different warming scenarios consistently point to a continued darkening, with anomalies in albedo driven solely by the effects of climate warming of as much as -0.12 along the west margin of the GIS by the end of this century (with respect to year 2000). Projected darkening is likely underestimated

  7. Movements of female polar bears (Usrus maritimus) in the East Greenland pack ice

    DEFF Research Database (Denmark)

    Wiig, Øystein; Born, Erik W.; Pedersen, Leif Toudal

    2003-01-01

    The movements of two adult female polar bears (Ursus maritimus) in East Greenland and the Greenland Sea area were studied by use of satellite telemetry between the fall of 1994 and the summer of 1998. One female was tracked for 621 days, the other for 1,415 days. During this time the females used...... for a closer monitoring of the effects of this change on the East Greenland polar bear population....... movement rates varied between 0.32 and 0.76km/h. Both bears had very large home ranges (242,000 and 468,000 km(2)) within the dynamic pack ice of the Greenland Sea. The facts that the bears made extensive use of the offshore sea ice and that there is a marked reduction of the Greenland Sea ice call...

  8. Mass loss of the Greenland Ice Sheet since the Little Ice Age, implications on sea level

    DEFF Research Database (Denmark)

    Kjeldsen, K. K.; Bjork, A. A.; Khan, Shfaqat Abbas

    The impact of mass loss from the Greenland Ice Sheet (GrIS) on 20th Century sea level rise (SLR) has long been subject to intense discussions. While globally distributed tide gauges suggest a global mean SLR of 15-20 cm, quantifying the separate components is of great concern - in particular...... for modeling sea level projections into the 21st Century. Estimates of the past GrIS contribution to SLR have been derived using a number of different approaches, e.g. surface mass balance (SMB) calculations combined with estimates of ice discharge found by in correlating SMB anomalies and calving rates. Here......-2010, NASA's Ice, Cloud, and land Elevation Satellite (ICESat) from 2003-2009, and NASA's Land, Vegetation, and Ice Sensor (LVIS) from 2010, to estimate mass loss throughout the 20th and early 21st Century. We present mass balance estimates of the GrIS since retreat commence from the maximum extent...

  9. Greenland ice sheet melt from MODIS and associated atmospheric variability.

    Science.gov (United States)

    Häkkinen, Sirpa; Hall, Dorothy K; Shuman, Christopher A; Worthen, Denise L; DiGirolamo, Nicolo E

    2014-03-16

    Daily June-July melt fraction variations over the Greenland ice sheet (GIS) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) (2000-2013) are associated with atmospheric blocking forming an omega-shape ridge over the GIS at 500 hPa height. Blocking activity with a range of time scales, from synoptic waves breaking poleward (days) to full-fledged blocks (≥5 days), brings warm subtropical air masses over the GIS controlling daily surface temperatures and melt. The temperature anomaly of these subtropical air mass intrusions is also important for melting. Based on the years with the greatest melt (2002 and 2012) during the MODIS era, the area-average temperature anomaly of 2 standard deviations above the 14 year June-July mean results in a melt fraction of 40% or more. Though the summer of 2007 had the most blocking days, atmospheric temperature anomalies were too small to instigate extreme melting. Short-term atmospheric blocking over Greenland contributes to melt episodesAssociated temperature anomalies are equally important for the meltDuration and strength of blocking events contribute to surface melt intensity.

  10. An ice sheet model validation framework for the Greenland ice sheet

    Science.gov (United States)

    Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; Howat, Ian M.; Neumann, Thomas; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey; Chambers, Don P.; Evans, Katherine J.; Kennedy, Joseph H.; Lenaerts, Jan; Lipscomb, William H.; Perego, Mauro; Salinger, Andrew G.; Tuminaro, Raymond S.; van den Broeke, Michiel R.; Nowicki, Sophie M. J.

    2017-01-01

    We propose a new ice sheet model validation framework - the Cryospheric Model Comparison Tool (CmCt) - that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013, using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin-scale and whole-ice-sheet-scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate a predictive skill with respect to observed dynamic changes that have occurred on Greenland over the past few decades. An extensible design will allow for continued use of the CmCt as future altimetry, gravimetry, and other remotely sensed data become available for use in ice sheet model validation.

  11. Higher surface mass balance of the Greenland ice sheet revealed by high - resolution climate modeling

    NARCIS (Netherlands)

    Ettema, Janneke; van den Broeke, Michiel R.; van Meijgaard, Erik; van de Berg, Willem Jan; Bamber, Jonathan L.; Box, Jason E.; Bales, Roger C.

    2009-01-01

    High‐resolution (∼11 km) regional climate modeling shows total annual precipitation on the Greenland ice sheet for 1958–2007 to be up to 24% and surface mass balance up to 63% higher than previously thought. The largest differences occur in coastal southeast Greenland, where the much higher

  12. Aerial photographs reveal late-20th-century dynamic ice loss in northwestern greenland

    DEFF Research Database (Denmark)

    Kjær, Kurt H.; Khan, Shfaqat Abbas; Korsgaard, Niels J

    2012-01-01

    Global warming is predicted to have a profound impact on the Greenland Ice Sheet and its contribution to global sea-level rise. Recent mass loss in the northwest of Greenland has been substantial. Using aerial photographs, we produced digital elevation models and extended the time record of recent...

  13. Greenland ice sheet surface mass balance: evaluating simulations and making projections with regional climate models

    NARCIS (Netherlands)

    Rae, J.G.L.; Aðalgeirsdóttir, G.; Edwards, T.L.; Fettweis, X.; Gregory, J.M.; Hewitt, H.T.; Lowe, J.A.; Lucas-Picher, P.; Mottram, R.H.; Payne, A.J.; Ridley, J.K.; Shannon, S.R.; van de Berg, W.J.; van de Wal, R.S.W.; van den Broeke, M.R.

    2012-01-01

    Four high-resolution regional climate models (RCMs) have been set up for the area of Greenland, with the aim of providing future projections of Greenland ice sheet surface mass balance (SMB), and its contribution to sea level rise, with greater accuracy than is possible from coarser-resolution

  14. Multi-decadal dynamic thinning on the northwest margin of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Korsgaard, Niels Jákup; Kjær, Kurt H.; Khan, Shfaqat Abbas

    records with a 25 m grid resolution and vertical uncertainty of 4.6m. Comparative DEMs were derived from laser altimetry data recorded in 2005 and 2010. Ice loss from the Greenland Ice Sheet (GrIS) can be partitioned into surface mass balance (SMB) processes (runoff and precipitation) and ice dynamics...

  15. Polarimetric C-Band SAR Observations of Sea Ice in the Greenland Sea

    DEFF Research Database (Denmark)

    Thomsen, Bjørn Bavnehøj; Nghiem, S.V.; Kwok, R.

    1998-01-01

    The fully polarimetric EMISAR acquired C-band radar signatures of sea ice in the Greenland Sea during a campaign in March 1995. The authors present maps of polarimetric signatures over an area containing various kinds of ice and discuss the use of polarimetric SAR for identification of ice types...

  16. Biogeochemical cycling in a subarctic fjord adjacent to the Greenland Ice Sheet

    NARCIS (Netherlands)

    Meire, L.

    2016-01-01

    Temperatures in the Arctic have increased rapidly in recent years resulting in the melting of sea ice and glaciers at unprecedented rates. In 2012, sea ice extent across the Arctic reached a record minimum and the melt extent of Greenland Ice Sheet reached a record maximum. The accelerated mass loss

  17. Vulnerability of Southeast Greenland Glaciers to Warm Atlantic Water From Operation IceBridge and Ocean Melting Greenland Data

    Science.gov (United States)

    Millan, R.; Rignot, E.; Mouginot, J.; Wood, M.; Bjørk, A. A.; Morlighem, M.

    2018-03-01

    We employ National Aeronautics and Space Administration (NASA)'s Operation IceBridge high-resolution airborne gravity from 2016, NASA's Ocean Melting Greenland bathymetry from 2015, ice thickness from Operation IceBridge from 2010 to 2015, and BedMachine v3 to analyze 20 major southeast Greenland glaciers. The results reveal glacial fjords several hundreds of meters deeper than previously thought; the full extent of the marine-based portions of the glaciers; deep troughs enabling warm, salty Atlantic Water (AW) to reach the glacier fronts and melt them from below; and few shallow sills that limit the access of AW. The new oceanographic and topographic data help to fully resolve the complex pattern of historical ice front positions from the 1930s to 2017: glaciers exposed to AW and resting on retrograde beds have retreated rapidly, while glaciers perched on shallow sills or standing in colder waters or with major sills in the fjords have remained stable.

  18. Annual accumulation over the Greenland ice sheet interpolated from historical and newly compiled observation data

    Science.gov (United States)

    Shen, Dayong; Liu, Yuling; Huang, Shengli

    2012-01-01

    The estimation of ice/snow accumulation is of great significance in quantifying the mass balance of ice sheets and variation in water resources. Improving the accuracy and reducing uncertainty has been a challenge for the estimation of annual accumulation over the Greenland ice sheet. In this study, we kriged and analyzed the spatial pattern of accumulation based on an observation data series including 315 points used in a recent research, plus 101 ice cores and snow pits and newly compiled 23 coastal weather station data. The estimated annual accumulation over the Greenland ice sheet is 31.2 g cm−2 yr−1, with a standard error of 0.9 g cm−2 yr−1. The main differences between the improved map developed in this study and the recently published accumulation maps are in the coastal areas, especially southeast and southwest regions. The analysis of accumulations versus elevation reveals the distribution patterns of accumulation over the Greenland ice sheet.

  19. Greenland coastal air temperatures linked to Baffin Bay and Greenland Sea ice conditions during autumn through regional blocking patterns

    Science.gov (United States)

    Ballinger, Thomas J.; Hanna, Edward; Hall, Richard J.; Miller, Jeffrey; Ribergaard, Mads H.; Høyer, Jacob L.

    2018-01-01

    Variations in sea ice freeze onset and regional sea surface temperatures (SSTs) in Baffin Bay and Greenland Sea are linked to autumn surface air temperatures (SATs) around coastal Greenland through 500 hPa blocking patterns, 1979-2014. We find strong, statistically significant correlations between Baffin Bay freeze onset and SSTs and SATs across the western and southernmost coastal areas, while weaker and fewer significant correlations are found between eastern SATs, SSTs, and freeze periods observed in the neighboring Greenland Sea. Autumn Greenland Blocking Index values and the incidence of meridional circulation patterns have increased over the modern sea ice monitoring era. Increased anticyclonic blocking patterns promote poleward transport of warm air from lower latitudes and local warm air advection onshore from ocean-atmosphere sensible heat exchange through ice-free or thin ice-covered seas bordering the coastal stations. Temperature composites by years of extreme late freeze conditions, occurring since 2006 in Baffin Bay, reveal positive monthly SAT departures that often exceed 1 standard deviation from the 1981-2010 climate normal over coastal areas that exhibit a similar spatial pattern as the peak correlations.

  20. The modelled liquid water balance of the Greenland Ice Sheet

    Science.gov (United States)

    Steger, Christian R.; Reijmer, Carleen H.; van den Broeke, Michiel R.

    2017-11-01

    Recent studies indicate that the surface mass balance will dominate the Greenland Ice Sheet's (GrIS) contribution to 21st century sea level rise. Consequently, it is crucial to understand the liquid water balance (LWB) of the ice sheet and its response to increasing surface melt. We therefore analyse a firn simulation conducted with the SNOWPACK model for the GrIS and over the period 1960-2014 with a special focus on the LWB and refreezing. Evaluations of the simulated refreezing climate with GRACE and firn temperature observations indicate a good model-observation agreement. Results of the LWB analysis reveal a spatially uniform increase in surface melt (0.16 m w.e. a-1) during 1990-2014. As a response, refreezing and run-off also indicate positive changes during this period (0.05 and 0.11 m w.e. a-1, respectively), where refreezing increases at only half the rate of run-off, implying that the majority of the additional liquid input runs off the ice sheet. This pattern of refreeze and run-off is spatially variable. For instance, in the south-eastern part of the GrIS, most of the additional liquid input is buffered in the firn layer due to relatively high snowfall rates. Modelled increase in refreezing leads to a decrease in firn air content and to a substantial increase in near-surface firn temperature. On the western side of the ice sheet, modelled firn temperature increases are highest in the lower accumulation zone and are primarily caused by the exceptional melt season of 2012. On the eastern side, simulated firn temperature increases are more gradual and are associated with the migration of firn aquifers to higher elevations.

  1. The significance of volcanic ash in Greenland ice cores during the Common Era

    Science.gov (United States)

    Plunkett, G.; Pilcher, J. R.; McConnell, J. R.; Sigl, M.; Chellman, N.

    2017-12-01

    Volcanic forcing is now widely regarded as a leading natural factor in short-term climate variability. Polar ice cores provide an unrivalled and continuous record of past volcanism through their chemical and particulate content. With an almost annual precision for the Common Era, the ice core volcanic record can be combined with historical data to investigate the climate and social impacts of the eruptions. The sulfate signature in ice cores is critical for determining the possible climate effectiveness of an eruption, but the presence and characterization of volcanic ash (tephra) in the ice is requisite for establishing the source eruption so that location and eruptive style can be better factored in to climate models. Here, we review the Greenland tephra record for the Common Era, and present the results of targeted sampling for tephra of volcanic events that are of interest either because of their suspected climate and societal impacts or because of their potential as isochrons in paleoenvironmental (including ice core) archives. The majority of identifiable tephras derive from Northern Hemisphere mid- to high latitude eruptions, demonstrating the significance of northern extra-tropical volcanic regions as a source of sulfates in Greenland. A number of targets are represented by sparse or no tephra, or shards that cannot be firmly correlated with a source. We consider the challenges faced in isolating and characterizing tephra from low latitude eruptions, and the implications for accurately modelling climate response to large, tropical events. Finally, we compare the ice core tephra record with terrestrial tephrostratigraphies in the circum-North Atlantic area to evaluate the potential for intercontinental tephra linkages and the refinement of volcanic histories.

  2. PIXE analysis as a tool for dating of ice cores from the Greenland ice sheet

    International Nuclear Information System (INIS)

    Hansson, H.C.; Swietlicki, E.; Larsson, N.P.O.; Johnsen, S.J.

    1993-01-01

    Sections from the 2037 m long Dye 3 ice core drilled in 1979-1981 in the ice sheet of Southern Greenland were analysed with PIXE. The seven selected sections were from depths between 1778 and 1813 m, which corresponds to a time interval between about 8 500 and 10 000 years B.C. at the end of the last Ice Age. During this time period, fast climatic changes of several degrees centrigrade per century are known to have taken place. The exact time scales of these changes need yet to be verified by renewed measurements using nonconventional stratigraphic dating techniques such as PIXE. The problem is highly relevant for the prediction of climatic changes in our present age. A new sample preparation technique was developed which enables the determination of annual thicknesses of the parts of the ice core representing 10 000-40 000 years before present, where the thickness of the annual ice layers are believed to be less than 2.5 cm. More commonly used techniques of dating, such as measurements of oxygen and hydrogen isotopes δ 18 O and δD, nitrate, acidity or conductivity all have difficulties in resolving annual cycles in thicknesses of less than about 2 cm. The new technique involves sublimation of 18 cm long ice sections, after which the material contained in the ice is deposited on the thin backing. In this way, the material to be analysed is preconcentrated through the removal of the H 2 O, while still retaining the spatial distribution pattern of the various water soluble and insoluble components along the ice core. The resulting spatial resolution of the sublimation technique is estimated to be ±1 mm. A PIXE analysis was performed in contiguous millimeter steps across the sublimated ice sections. Estimations of annual ice layer thicknesses were based on the patterns of seasonal variation along the ice sections for several major and minor elements quantified with PIXE. (orig./TW)

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

    Science.gov (United States)

    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

  4. Evolution of a Greenland Ice sheet Including Shelves and Regional Sea Level Variations

    Science.gov (United States)

    Bradley, Sarah; Reerink, Thomas; van de Wal, Roderik S. W.; Helsen, Michiel; Goelzer, Heiko

    2016-04-01

    Observational evidence, including offshore moraines and marine sediment cores infer that at the Last Glacial maximum (LGM) the Greenland ice sheet (GIS) grounded out across the Davis Strait into Baffin Bay, with fast flowing ice streams extending out to the continental shelf break along the NW margin. These observations lead to a number of questions as to weather the GIS and Laurentide ice sheet (LIS) coalesced during glacial maximums, and if so, did a significant ice shelf develop across Baffin Bay and how would such a configuration impact on the relative contribution of these ice sheets to eustatic sea level (ESL). Most previous paleo ice sheet modelling simulations of the GIS recreated an ice sheet that either did not extend out onto the continental shelf or utilised a simplified marine ice parameterisation to recreate an extended GIS, and therefore did not fully include ice shelf dynamics. In this study we simulate the evolution of the GIS from 220 kyr BP to present day using IMAU-ice; a 3D thermodynamical ice sheet model which fully accounts for grounded and floating ice, calculates grounding line migration and ice shelf dynamics. As there are few observational estimates of the long-term (yrs) sub marine basal melting rates (mbm) for the GIS, we developed a mbm parameterization within IMAU-ice controlled primarily by changes in paleo water depth. We also investigate the influence of the LIS on the GIS evolution by including relative sea level forcing's derived from a Glacial Isostatic Adjustment model. We will present results of how changes in the mbm directly impacts on the ice sheet dynamics, timing and spatial extent of the GIS at the glacial maximums, but also on the rate of retreat and spatial extent at the Last interglacial (LIG) minimum. Results indicate that with the inclusion of ice shelf dynamics, a larger GIS is generated which is grounded out into Davis strait, up to a water depth of -750 m, but significantly reduces the GIS contribution to Last

  5. Elastic uplift in southeast Greenland due to rapid ice mass loss

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Van dam, Tonie; Hamilton, Gordon S.

    2007-01-01

    The rapid unloading of ice from the southeastern sector of the Greenland ice sheet between 2001 and 2006 caused an elastic uplift of 35 mm at a GPS site in Kulusuk. Most of the uplift results from ice dynamic-induced volume losses on two nearby outlet glaciers. Volume loss from Helheim Glacier...... between 62N and 66N. Citation: Khan, S. A., J. Wahr, L. A. Stearns, G. S. Hamilton, T. van Dam, K. M. Larson, and O. Francis (2007), Elastic uplift in southeast Greenland due to rapid ice mass loss....

  6. Ice stratigraphy at the Pakitsoq ice margin, West Greenland, derived from gas records

    DEFF Research Database (Denmark)

    Schaefer, H.; Petrenko, V. V.; Brook, E. J.

    2009-01-01

    at Pakitsoq. Sections containing ice from every distinct climatic interval during Termination I, including Last Glacial Maximum, Bolling/Allerod, Younger Dryas and the early Holocene, are identified. In the early Holocene, we find evidence for climatic fluctuations similar to signals found in deep ice cores...... from Greenland. A second glacial-interglacial transition exposed at the extreme margin of the ice is identified as another outcrop of Termination I (rather than the onset of the Eemian interglacial as postulated in earlier work). Consequently, the main structural feature at Pakitsoq is a large......-scale anticline with accordion-type folding in both exposed sequences of the glacial-Holocene transition, leading to multiple layer duplications and age reversals....

  7. Revised estimates of Greenland ice sheet thinning histories based on ice-core records

    DEFF Research Database (Denmark)

    Lecavalier, B.S.; Milne, G.A.; Fisher, D.A.

    2013-01-01

    -based reconstructions and, to some extent, the estimated elevation histories. A key component of the ice core analysis involved removing the influence of vertical surface motion on the dO signal measured from the Agassiz and Renland ice caps. We re-visit the original analysis with the intent to determine if the use...... of more accurate land uplift curves can account for some of the above noted discrepancy. To improve on the original analysis, we apply a geophysical model of glacial isostatic adjustment calibrated to sea-level records from the Queen Elizabeth Islands and Greenland to calculate the influence of land...... in this selection is further complicated by the possible influence of Innuitian ice during the early Holocene (12-8 ka BP). Our results indicate that a more accurate treatment of the uplift correction leads to elevation histories that are, in general, shifted down relative to the original curves at GRIP, NGRIP, DYE...

  8. Ice_Sheets_CCI: Essential Climate Variables for the Greenland Ice Sheet

    Science.gov (United States)

    Forsberg, R.; Sørensen, L. S.; Khan, A.; Aas, C.; Evansberget, D.; Adalsteinsdottir, G.; Mottram, R.; Andersen, S. B.; Ahlstrøm, A.; Dall, J.; Kusk, A.; Merryman, J.; Hvidberg, C.; Khvorostovsky, K.; Nagler, T.; Rott, H.; Scharrer, M.; Shepard, A.; Ticconi, F.; Engdahl, M.

    2012-04-01

    As part of the ESA Climate Change Initiative (www.esa-cci.org) a long-term project "ice_sheets_cci" started January 1, 2012, in addition to the existing 11 projects already generating Essential Climate Variables (ECV) for the Global Climate Observing System (GCOS). The "ice_sheets_cci" goal is to generate a consistent, long-term and timely set of key climate parameters for the Greenland ice sheet, to maximize the impact of European satellite data on climate research, from missions such as ERS, Envisat and the future Sentinel satellites. The climate parameters to be provided, at first in a research context, and in the longer perspective by a routine production system, would be grids of Greenland ice sheet elevation changes from radar altimetry, ice velocity from repeat-pass SAR data, as well as time series of marine-terminating glacier calving front locations and grounding lines for floating-front glaciers. The ice_sheets_cci project will involve a broad interaction of the relevant cryosphere and climate communities, first through user consultations and specifications, and later in 2012 optional participation in "best" algorithm selection activities, where prototype climate parameter variables for selected regions and time frames will be produced and validated using an objective set of criteria ("Round-Robin intercomparison"). This comparative algorithm selection activity will be completely open, and we invite all interested scientific groups with relevant experience to participate. The results of the "Round Robin" exercise will form the algorithmic basis for the future ECV production system. First prototype results will be generated and validated by early 2014. The poster will show the planned outline of the project and some early prototype results.

  9. Preservation of a Preglacial Landscape Under the Center of the Greenland Ice Sheet

    Science.gov (United States)

    Bierman, Paul R.; Corbett, Lee B.; Graly, Joseph A.; Neumann, Thomas Allen; Lini, Andrea; Crosby, Benjamin T.; Rood, Dylan H.

    2014-01-01

    Continental ice sheets typically sculpt landscapes via erosion; under certain conditions, ancient landscapes can be preserved beneath ice and can survive extensive and repeated glaciation. We used concentrations of atmospherically produced cosmogenic beryllium-10, carbon, and nitrogen to show that ancient soil has been preserved in basal ice for millions of years at the center of the ice sheet at Summit, Greenland. This finding suggests ice sheet stability through the Pleistocene (i.e., the past 2.7 million years). The preservation of this soil implies that the ice has been non-erosive and frozen to the bed for much of that time, that there was no substantial exposure of central Greenland once the ice sheet became fully established, and that preglacial landscapes can remain preserved for long periods under continental ice sheets

  10. High-resolution ice thickness and bed topography of a land-terminating section of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Lindbäck, K.; Pettersson, R.; Doyle, S. H.

    2014-01-01

    We present ice thickness and bed topography maps with high spatial resolution (250 to 500 m) of a and-terminating section of the Greenland Ice Sheet derived from combined ground-based and airborne radar surveys. The data have a total area of ~12000 km2 and cover the whole ablation area of the out...

  11. Modelling the surface mass balance of the Greenland ice sheet and neighbouring ice caps : A dynamical and statistical downscaling approach

    NARCIS (Netherlands)

    Noël, B.P.Y.

    2018-01-01

    The Greenland ice sheet (GrIS) is the world’s second largest ice mass, storing about one tenth of the Earth’s freshwater. If totally melted, global sea level would rise by 7.4 m, affecting low-lying regions worldwide. Since the mid-1990s, increased atmospheric and oceanic temperatures have

  12. Observed runoff, jokulhlaups and suspended sediment load from the Greenland ice at Kangerlussuaq, West Greenland, 2007 and 2008

    Energy Technology Data Exchange (ETDEWEB)

    Mernild, Sebastian Haugard [Los Alamos National Laboratory; Hasholt, Bent [UNIV OF COPENHAGEN

    2009-01-01

    This study fills the gap in hydrologic measurements of runoff exiting a part of the Greenland Ice Sheet (GrIS), the Kangerlussuaq drainage area, West Greenland. The observations are of value for obtaining knowledge about the terrestrial freshwater and sediment output from part of the GrIS and the strip of land between the GrIS and the ocean, in the context of varying ice sheet surface melt and influx entering the ocean. High-resolution stage, discharge and suspended sediment load show a decrease in runoff of {approx} 25% and in sediment load of {approx} 40% from 2007 to 2008 in response to a decrease in the summer accumulated number of positive degree days. During the 2007 and 2008 runoff season, joekulhlaups are observed at Kangerlussuaq, drained from an ice-dammed lake at the margin of the GrIS.

  13. Towards an assessment of the balance state of the Greenland Ice Sheet

    Energy Technology Data Exchange (ETDEWEB)

    Boeggild, C.E.; Mayer, C.; Podlech, S.; Taurisano, A.; Nielsen, S.

    2004-07-01

    The climate of Europe is strongly influenced by heat transport by ocean currents flowing from equatorial regions towards the Arctic. During recent years, research has been increasingly focused on factors affecting this circulation, e.g. the freshwater budget of the Arctic that is influenced by glacial melt water from north and East Greenland outlet glaciers. Furthermore, the climate is affected by snow cover, which, apart from its contribution to the freshwater budget, provides feedback effects in that it reflects most of the solar radiation. Apart from Arctic sea-ice cover, the Greenland Ice Sheet is the largest permanent ice- and snow-covered area in the northern hemisphere, with an area of 1.67 x 10{sup 6} km{sup 2} and by far the largest storage of ice with a volume of 2.93 x 10{sup 6} km{sup 3}. Most of the mass loss from the Greenland Ice Sheet occurs in the marginal region of the ice sheet, which is also the area where the largest changes in albedo occur. The Geological Survey of Denmark and Greenland (GEUS) has for many years carried out research along the Greenland Ice Sheet margin to monitor changes of mass balance and melt conditions. (BA)

  14. Mass loss from the southern half of the Greenland Ice Sheet since the Little Ice Age

    DEFF Research Database (Denmark)

    Kjeldsen, Kristian K.; Kjær, Kurt H.; Bjørn, Anders A.

    2013-01-01

    Northern hemisphere temperatures reached their Holocene minimum and most glaciers reached their maximum during The Little Ice Age (LIA), but the timing of specific cold intervals is site-specific. In southern Greenland, we have compiled data from organic matter incorporated in LIA sediments, used...... retreat. Our results show that the advance of glaciers during the LIA occurs early after the Medieval Warm Period terminating soon after 1200 AD and culminates c. 1500-1600 AD. Historical maps also show that many glaciers on the western coast occupy a still-stand near the LIA maximum until 1900 AD before...

  15. Improving volume loss estimates of the northwestern Greenland Ice Sheet 2002-2010

    DEFF Research Database (Denmark)

    Korsgaard, Niels Jákup; Khan, Shfaqat Abbas; Kjeldsen, Kristian Kjellerup

    Studies have been carried out using various methods to estimate the Greenland ice sheet mass balance. Remote sensing techniques used to determine the ice sheet volume includes airborne and satellite radar and laser methods and measurements of ice flow of outlet glaciers use InSAR satellite radar......) does not work on sloping surfaces and is affected by radar penetration into the snow. InSAR estimates require knowledge of outlet glacier thickness. GRACE has limited spatial resolution and is affected by mass variations not just from ice changes, but also from hydrologic and ocean mass variability...... and mass redistribution within the solid Earth. The accuracy of ice mass and ice volume estimates can be assessed by comparing results from different techniques. Here, we focus on volume loss estimates from ICESat, ATM and LVIS data. We estimate catchment-wide ice volume change in northwest Greenland...

  16. Surface Energy and Mass Balance Model for Greenland Ice Sheet and Future Projections

    Science.gov (United States)

    Liu, Xiaojian

    The Greenland Ice Sheet contains nearly 3 million cubic kilometers of glacial ice. If the entire ice sheet completely melted, sea level would raise by nearly 7 meters. There is thus considerable interest in monitoring the mass balance of the Greenland Ice Sheet. Each year, the ice sheet gains ice from snowfall and loses ice through iceberg calving and surface melting. In this thesis, we develop, validate and apply a physics based numerical model to estimate current and future surface mass balance of the Greenland Ice Sheet. The numerical model consists of a coupled surface energy balance and englacial model that is simple enough that it can be used for long time scale model runs, but unlike previous empirical parameterizations, has a physical basis. The surface energy balance model predicts ice sheet surface temperature and melt production. The englacial model predicts the evolution of temperature and meltwater within the ice sheet. These two models can be combined with estimates of precipitation (snowfall) to estimate the mass balance over the Greenland Ice Sheet. We first compare model performance with in-situ observations to demonstrate that the model works well. We next evaluate how predictions are degraded when we statistically downscale global climate data. We find that a simple, nearest neighbor interpolation scheme with a lapse rate correction is able to adequately reproduce melt patterns on the Greenland Ice Sheet. These results are comparable to those obtained using empirical Positive Degree Day (PDD) methods. Having validated the model, we next drove the ice sheet model using the suite of atmospheric model runs available through the CMIP5 atmospheric model inter-comparison, which in turn built upon the RCP 8.5 (business as usual) scenarios. From this exercise we predict how much surface melt production will increase in the coming century. This results in 4-10 cm sea level equivalent, depending on the CMIP5 models. Finally, we try to bound melt water

  17. Photobiology of sea ice algae during initial spring growth in Kangerlussuaq, West Greenland

    DEFF Research Database (Denmark)

    Hawes, Ian; Lund-Hansen, Lars Chresten; Sorrell, Brian Keith

    2012-01-01

    We undertook a series of measurements of photophysiological parameters of sea ice algae over 12 days of early spring growth in a West Greenland Fjord, by variable chlorophyll fluorescence imaging. Imaging of the ice–water interface showed the development of ice algae in 0.3–0.4 mm wide brine...

  18. The response of the southern Greenland ice sheet to the Holocene thermal maximum

    DEFF Research Database (Denmark)

    Larsen, Nicolaj Krog; Kjaer, Kurt H.; Lecavalier, Benoit

    2015-01-01

    contribution of 0.16 m sea-level equivalent from the entire Greenland ice sheet, with a centennial ice loss rate of as much as 100 Gt/yr for several millennia during the Holocene thermal maximum. Our results provide an estimate of the long-term rates of volume loss that can be expected in the future...

  19. Using Airborne SAR Interferometry to Measure the Elevation of a Greenland Ice Cap

    DEFF Research Database (Denmark)

    Dall, Jørgen; Keller, K.; Madsen, S.N.

    2000-01-01

    A digital elevation model (DEM) of an ice cap in Greenland has been generated from airborne SAR interferometry data, calibrated with a new algorithm, and compared with airborne laser altimetry profiles and carrier-phase differential GPS measurements of radar reflectors deployed on the ice cap...... with GPS data and calibrated laser data....

  20. Drainage of the ice-dammed Lake Tinninilik, West Greenland; implication on bedrock uplift

    DEFF Research Database (Denmark)

    Kjeldsen, Kristian Kjellerup; Khan, Shfaqat Abbas; Bjørk, Anders Anker

    Drainage of ice-dammed lakes is regularly observed along the margin of the Greenland Ice Sheet. However, the speed of the drainage events and implications can vary depending on the size of the lakes and the local settings. Here, we assess the drainage pattern of Lake Tinninilik, dammed...

  1. Modelling the short-term response of the Greenland ice-sheet to global warming

    NARCIS (Netherlands)

    Wal, R.S.W. van de; Oerlemans, J.

    1997-01-01

    A two-dimensional vertically integrated ice flow model has been developed to test the importance of various processes and concepts used for the prediction of the contribution of the Greenland ice-sheet to sea-level rise over the next 350 y (short-term response). The mass balance is modelled by the

  2. Future climate warming increases Greenland ice sheet surface mass balance variability

    NARCIS (Netherlands)

    Fyke, J.G.; Vizcaino, M.; Lipscomb, W.; Price, S.

    2014-01-01

    The integrated surface mass balance (SMB) of the Greenland ice sheet (GrIS) has large interannual variability. Long-term future changes to this variability will affect GrIS dynamics, freshwater fluxes, regional oceanography, and detection of changes in ice volume trends. Here we analyze a simulated

  3. A Meteorological Experiment in the Melting Zone of the Greenland Ice Sheet

    NARCIS (Netherlands)

    Oerlemans, J.; Vugts, H.F.

    1993-01-01

    Preliminary results are described from a glaciometeorological experiment carried out in the margin (melting zone) of the Greenland ice sheet in the summers of 1990 and 1991. This work was initiated within the framework of a Dutch research program on land ice and sea level change. Seven

  4. Mass balance of the Greenland ice sheet (2003-2008) from ICESat data

    DEFF Research Database (Denmark)

    Sørensen, Louise Sandberg; Simonsen, Sebastian Bjerregaard; Nielsen, Karina

    2011-01-01

    ICESat has provided surface elevation measurements of the ice sheets since the launch in January 2003, resulting in a unique dataset for monitoring the changes of the cryosphere. Here, we present a novel method for determining the mass balance of the Greenland ice sheet, derived from ICESat...... studies of the Greenland ice sheet mass balance, based on different remote-sensing techniques....... altimetry data. Three different methods for deriving elevation changes from the ICESat altimetry dataset are used. This multi-method approach provides a method to assess the complexity of deriving elevation changes from this dataset. The altimetry alone can not provide an estimate of the mass balance...

  5. Retrieving a common accumulation record from Greenland ice cores for the past 1800 years

    DEFF Research Database (Denmark)

    Andersen, Katrine K.; Ditlevsen, Peter D.; Rasmussen, Sune Olander

    2006-01-01

    In the accumulation zone of the Greenland ice sheet the annual accumulation rate may be determined through identification of the annual cycle in the isotopic climate signal and other parameters that exhibit seasonal variations. On an annual basis the accumulation rate in different Greenland ice...... cores is highly variable, and the degree of correlation between accumulation series from different ice cores is low. However, when using multiyear averages of the different accumulation records, the correlation increases significantly. A statistical model has been developed to estimate the common...

  6. Surface elevation changes of the greenland ice sheet - results from ESA'S ice sheet CCI

    DEFF Research Database (Denmark)

    Fredenslund Levinsen, Joanna; Khvorostovky, Kirill; Meister, Rakia

    2013-01-01

    In order to ensure long-term climate data records for the Greenland Ice Sheet (GIS), ESA have launched the Climate Change Initiative (CCI). This work presents the preliminary steps towards the Ice Sheet CCI's surface elevation change (SEC) derivation using radar altimeter data. In order to find...... the most optimal method, a Round Robin exercise was conducted in which the scientific community was asked to provide their best SEC estimate over the Jakobshavn Isbr drainage basin. The participants used both repeat-track (RT), overlapping footprints, and the cross-over (XO) methods, and both ICESat laser...... and Envisat radar altimeter data were used. Based on this and feedback sheets describing their methods we found that a combination of the RT and XO techniques yielded the best results. In the following, the obtained results will be presented and discussed....

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

    Science.gov (United States)

    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.

  8. Development of ice floe tracker algorithm to measure Lagrangian statistics in the eastern Greenland coast

    Science.gov (United States)

    Lopez, Rosalinda; Wilhelmus, Monica M.; Schodlok, Michael; Klein, Patrice

    2017-11-01

    Sea ice export through Fram Strait is a key component of the Arctic climate system. The East Greenland Current (EGC) carries most of the sea ice southwards until it melts. Lagrangian methods using sea ice buoys have been used to map ice features in polar regions. However, their spatial and temporal coverage is limited. Satellite data can provide a better tool to map sea ice flow and its variability. Here, an automated sea ice floe detection algorithm uses ice floes as tracers for surface ocean currents. We process Moderate Resolution Imaging Spectroradiometer satellite images to track ice floes (length scale 5-10 km) in the north-eastern Greenland Sea region. Our matlab-based routines effectively filter out clouds and adaptively modify the images to segment and identify ice floes. Ice floes were tracked based on persistent surface features common in successive images throughout 2016. Their daily centroid locations were extracted and its resulting trajectories are used to describe surface circulation and its variability using differential kinematic parameters. We will discuss the application of this method to a longer time series and larger spatial coverage. This enables us to derive the inter-annual variability of mesoscale features along the eastern coast of Greenland. Supported by UCR Mechanical Engineering Departmental Fellowship.

  9. Multi-proxy Organic Geochemical Reconstruction of Holocene Hydroclimate Near the Western Greenland Ice Sheet Margin

    Science.gov (United States)

    Cluett, A.; Thomas, E. K.

    2017-12-01

    Anthropogenic warming is projected to drive profound change to the Arctic hydrological cycle within the century, most notably in the intensification of rainfall, with potential feedbacks to the climate system and cryosphere. However, the relationship between hydroclimate and cryosphere variability is poorly constrained in the long-term due to a scarcity of high-resolution hydroclimate records from the Arctic. We analyze the stable hydrogen isotopes (dD) of leaf wax biomarkers from lacustrine sediments spanning the Holocene to 9000 cal. year B.P. from Lake Gus (67.032ºN, 52.427ºW, 300 m a.s.l.; informal name), a small lake approximately 90 km from the modern western margin of the Greenland Ice Sheet. We interpret the signal of aquatic leaf wax isotopes in the context of a survey of 100 modern lake water samples from western Greenland across an aridity gradient to better understand the combined climatological and hydrological controls on lake water dD in the study area. We compare variability of aquatic and terrestrial leaf wax isotopes to infer changes in relative moisture throughout the Holocene, and complement our leaf wax record with analysis of glycerol dialkyl glycerol tetraethers (GDGTs) and alkenones, to produce records of summer temperature. Pairing temperature and leaf wax isotope records provides a means to constrain the changing dD-temperature relationship throughout the Holocene and infer moisture source variability. In combination, these proxies produce a comprehensive hydroclimate record at approximately centennial scale to evaluate shifts in relative moisture, temperature, and moisture source, and to investigate the interaction between hydroclimate and Greenland Ice Sheet margin fluctuations through the Holocene.

  10. MIS-11 duration key to disappearance of the Greenland ice sheet

    Science.gov (United States)

    Robinson, Alexander; Alvarez-Solas, Jorge; Calov, Reinhard; Ganopolski, Andrey; Montoya, Marisa

    2017-07-01

    Palaeo data suggest that Greenland must have been largely ice free during Marine Isotope Stage 11 (MIS-11). However, regional summer insolation anomalies were modest during this time compared to MIS-5e, when the Greenland ice sheet likely lost less volume. Thus it remains unclear how such conditions led to an almost complete disappearance of the ice sheet. Here we use transient climate-ice sheet simulations to simultaneously constrain estimates of regional temperature anomalies and Greenland's contribution to the MIS-11 sea-level highstand. We find that Greenland contributed 6.1 m (3.9-7.0 m, 95% credible interval) to sea level, ~7 kyr after the peak in regional summer temperature anomalies of 2.8 °C (2.1-3.4 °C). The moderate warming produced a mean rate of mass loss in sea-level equivalent of only around 0.4 m per kyr, which means the long duration of MIS-11 interglacial conditions around Greenland was a necessary condition for the ice sheet to disappear almost completely.

  11. Microalgal composition and primary production in Arctic sea ice: a seasonal study from Kobbeijord (Kangerluarsunnguaq), West Greenland

    DEFF Research Database (Denmark)

    Mikkelsen, Ditte Marie; Rysgaard, Søren; Glud, Ronnie N.

    2008-01-01

    We investigated the microalgal community in sea ice and in the water column of Kobbefjord, west Greenland, through an entire sea ice season, Temporal variation in physical (photosynthetically active radiation [PAR), temperature, brine volume) and chemical (salinity, nutrient concentration......) properties confirmed that sea ice is a very dynamic habitat. Nevertheless, a viable sea ice algal comuunity was present throughout the year, with a species succession from flagellate dominance (dinoflagellates and cryptophytes) in December to February, followed by Chaetoceros simplex (a centric diatom...... (maxima of 1.8 and 2.6 mu g chl](-1) in March and May, respectively). Primary production mirrored biomass dynamic, which had 2 seasonal peaks of ca. 21 and 15 mg Cm-2 d(-1). Integrated primary production over 7 mo was 0.8 g Cm-2 in sea ice and 94.4 g C m(-2) in the water column, with the vast majority...

  12. Microalgal composition and primary production in Arctic sea ice: a seasonal study from Kobbeijord (Kangerluarsunnguaq), West Greenland

    DEFF Research Database (Denmark)

    Mikkelsen, Ditte Marie; Rysgaard, Søren; Glud, Ronnie N.

    2008-01-01

    We investigated the microalgal community in sea ice and in the water column of Kobbefjord, west Greenland, through an entire sea ice season, Temporal variation in physical (photosynthetically active radiation [PAR), temperature, brine volume) and chemical (salinity, nutrient concentration...... (maxima of 1.8 and 2.6 mu g chl](-1) in March and May, respectively). Primary production mirrored biomass dynamic, which had 2 seasonal peaks of ca. 21 and 15 mg Cm-2 d(-1). Integrated primary production over 7 mo was 0.8 g Cm-2 in sea ice and 94.4 g C m(-2) in the water column, with the vast majority......) properties confirmed that sea ice is a very dynamic habitat. Nevertheless, a viable sea ice algal comuunity was present throughout the year, with a species succession from flagellate dominance (dinoflagellates and cryptophytes) in December to February, followed by Chaetoceros simplex (a centric diatom...

  13. Mass balance of Greenland and the Canadian Ice Caps from combined altimetry and GRACE inversion

    DEFF Research Database (Denmark)

    Forsberg, René; Simonsen, Sebastian Bjerregaard; Sørensen, Louise Sandberg

    The combination of GRACE and altimetry data may yield a high resolution mass balance time series of the Greenlandice sheet, highlighting the varying individual mass loss behaviour of major glaciers. By including the Canadian arctic ice caps in the estimation, a more reliable estimate of the mass...... loss of both Greenlandand the Canadian ice caps may be obtained, minimizing the leakage errors otherwise unavoidable by GRACE. Actually, the absolute value of the Greenlandice sheet mass loss is highly dependent on methods and how the effects of Arctic Canadian ice caps are separated in the GRACE...... loss of the ice caps and ice sheet basins for the period 2003-15. This period shows a marked increase of ice sheet melt, especially in NW and NE Greenland, but also show large variability, with the melt anomaly year of 2012 showing a record mass loss, followed by 2013 with essentially no Greenland mass...

  14. Mass loss of Greenland from GRACE, IceSat and CryoSat

    DEFF Research Database (Denmark)

    Forsberg, René; Sørensen, Louise Sandberg; Fredenslund Levinsen, Joanna

    2013-01-01

    CryoSat data over the Greenland Ice Sheet are used to continue elevation height change data over the Greenland ice sheet, following a decade of detailed monitoring of ice sheet changes with GRACE and IceSat. The combination and validation of the different data for measuring changes is quantified...... by using available airborne lidar data from IceBridge and CryoVEx. There is a special challenge of using CryoSat as fill-in between EnviSat and Sentinel-3 for the longterm measurements of surface elevation changes, a key essential climate variable in the ESA Climate Change Initiative. Another challenge...... is the joint utilization of both altimetry and gravity field change measurements for consistent estimates of regional change patterns. In the paper we analyze GRACE, IceSat and CryoSat data since 2003, and present consistent estimates of overall mass changes with average values around -220 GT/year, showing...

  15. Sea-ice thickness from airborne laser altimetry over the Arctic Ocean north of Greenland

    DEFF Research Database (Denmark)

    Hvidegaard, Sine Munk; Forsberg, René

    2002-01-01

    We present a new method to measure ice thickness of polar sea-ice freeboard heights, using airborne laser altimetry combined with a precise geoid model, giving estimates of thickness of ice through isostatic equilibrium assumptions. In the paper we analyze a number of flights from the Polar Sea off...... Northern Greenland, and estimate accuracies of the estimated freeboard values to be at a 13 cm level, corresponding to about 1 m in absolute thickness....

  16. Antarctic and Greenland ice sheet mass balance products from satellite gravimetry

    Science.gov (United States)

    Horwath, Martin; Groh, Andreas; Horvath, Alexander; Forsberg, René; Meister, Rakia; Barletta, Valentina R.; Shepherd, Andrew

    2017-04-01

    Because of their important role in the Earth's climate system, ESA's Climate Change Initiative (CCI) has identified both the Antarctic Ice Sheet (AIS) and the Greenland Ice Sheet (GIS) as Essential Climate Variables (ECV). Since respondents of a user survey indicated that the ice sheet mass balance is one of the most important ECV data products needed to better understand climate change, the AIS_cci and the GIS_cci project provide Gravimetric Mass Balance (GMB) products based on satellite gravimetry data. The GMB products are derived from GRACE (Gravity Recovery and Climate Experiment) monthly solutions of release ITSG-Grace2016 produced at TU Graz. GMB basin products (i.e. time series of monthly mass changes for the entire ice sheets and selected drainage basins) and GMB gridded products (e.g. mass balance estimates with a formal resolution of about 50km, covering the entire ice sheets) are generated for the period from 2002 until present. The first GMB product was released in mid 2016. Here we present an extended and updated version of the ESA CCI GMB products, which are freely available through data portals hosted by the projects (https://data1.geo.tu-dresden.de/ais_gmb, http://products.esa-icesheets-cci.org/products/downloadlist/GMB). Since the initial product release, the applied processing strategies have been improved in order to further reduce GRACE errors and to enhance the separation of signals super-imposed to the ice mass changes. While a regional integration approach is used by the AIS_cci project, the GMB products of the GIS_cci project are derived using a point mass inversion. The differences between both approaches are investigated through the example of the GIS, where an alternative GMB product was generated using the regional integration approach implemented by the AIS_cci. Finally, we present the latest mass balance estimates for both ice sheets as well as their corresponding contributions to global sea level rise.

  17. Insight into biogeochemical inputs and composition of Greenland Ice Sheet surface snow and glacial forefield river catchment environments.

    Science.gov (United States)

    Cameron, Karen; Hagedorn, Birgit; Dieser, Markus; Christner, Brent; Choquette, Kyla; Sletten, Ronald; Lui, Lu; Junge, Karen

    2014-05-01

    The volume of freshwater transported from Greenland to surrounding marine waters has tended to increase annually over the past four decades as a result of warmer surface air temperatures (Bamber et al 2012, Hanna et al 2008). Ice sheet run off is estimated to make up approximately of third of this volume (Bamber et al 2012). However, the biogeochemical composition and seeding sources of the Greenland Ice Sheet supraglacial landscape is largely unknown. In this study, the structure and diversity of surface snow microbial assemblages from two regions of the western Greenland Ice Sheet ice-margin was investigated through the sequencing of small subunit rRNA genes. Furthermore, the origins of microbiota were investigated by examining correlations to molecular data obtained from marine, soil, freshwater and atmospheric environments and to geochemical analytes measured in the snow. Snow was found to contain a diverse assemblage of bacteria (Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria) and eukarya (Alveolata, Fungi, Stramenopiles and Viridiplantae). Phylotypes related to archaeal Thaumarchaeota and Euryarchaeota phyla were also identified. The structure of microbial assemblages was found to have strong similarities to communities sampled from marine and air environments, and sequences obtained from the South-West region, near Kangerlussuaq, which is bordered by an extensive periglacial expanse, had additional resemblances to soil originating communities. Strong correlations were found between bacterial beta diversity and Na+ and Cl- concentrations. These data suggest that surface snow from western regions of Greenland contain microbiota that are most likely derived from exogenous, wind transported sources. Downstream of the supraglacial environment, Greenland's rivers likely influence the ecology of localized estuary and marine systems. Here we characterize the geochemical and biotic composition of a glacial and glacial forefield fed river catchment in

  18. Elevation change and remote-sensing mass-balance methods on the Greenland ice sheet

    DEFF Research Database (Denmark)

    Ahlstrøm, Andreas P.; Reeh, Niels; Christensen, Erik Lintz

    The mass balance of the Greenland Ice Sheet is virtually impossible to obtain with traditional ground-based methods alone due to its vast size. It is thus desirable to develop mass-balance methods depending on remote sensing instead and this field has experienced a dramatic development within...... of measured surface elevation change over a 50x50~km part of the western Greenland Ice-Sheet margin near Kangerlussuaq. In this region, the mean observed elevation change has been -0.5~m from 2000 to 2003. However, the change is unevenly distributed with the northern and central part generally in balance...... the last decade. Large amounts of data have been collected from satellite and airborne platforms, yielding surface elevation changes and surface velocity fields. Here we present data from the Greenland Ice-Sheet margin acquired with a new small-scale airborne system, designed for regional high...

  19. Greenland Ice Sheet Surface Temperature, Melt, and Mass Loss: 2000-2006

    Science.gov (United States)

    Hall, Dorothy K.; Williams, Richard S., Jr.; Luthcke, Scott B.; DiGirolamo, Nocolo

    2007-01-01

    Extensive melt on the Greenland Ice Sheet has been documented by a variety of ground and satellite measurements in recent years. If the well-documented warming continues in the Arctic, melting of the Greenland Ice Sheet will likely accelerate, contributing to sea-level rise. Modeling studies indicate that an annual or summer temperature rise of 1 C on the ice sheet will increase melt by 20-50% therefore, surface temperature is one of the most important ice-sheet parameters to study for analysis of changes in the mass balance of the ice-sheet. The Greenland Ice Sheet contains enough water to produce a rise in eustatic sea level of up to 7.0 m if the ice were to melt completely. However, even small changes (centimeters) in sea level would cause important economic and societal consequences in the world's major coastal cities thus it is extremely important to monitor changes in the ice-sheet surface temperature and to ultimately quantify these changes in terms of amount of sea-level rise. We have compiled a high-resolution, daily time series of surface temperature of the Greenland Ice Sheet, using the I-km resolution, clear-sky land-surface temperature (LST) standard product from the Moderate-Resolution Imaging Spectroradiometer (MODIS), from 2000 - 2006. We also use Gravity Recovery and Climate Experiment (GRACE) data, averaged over 10-day periods, to measure change in mass of the ice sheet as it melt and snow accumulates. Surface temperature can be used to determine frequency of surface melt, timing of the start and the end of the melt season, and duration of melt. In conjunction with GRACE data, it can also be used to analyze timing of ice-sheet mass loss and gain.

  20. Extreme Low Light Requirement for Algae Growth Underneath Sea Ice: A Case Study From Station Nord, NE Greenland

    Science.gov (United States)

    Hancke, Kasper; Lund-Hansen, Lars C.; Lamare, Maxim L.; Højlund Pedersen, Stine; King, Martin D.; Andersen, Per; Sorrell, Brian K.

    2018-02-01

    Microalgae colonizing the underside of sea ice in spring are a key component of the Arctic foodweb as they drive early primary production and transport of carbon from the atmosphere to the ocean interior. Onset of the spring bloom of ice algae is typically limited by the availability of light, and the current consensus is that a few tens-of-centimeters of snow is enough to prevent sufficient solar radiation to reach underneath the sea ice. We challenge this consensus, and investigated the onset and the light requirement of an ice algae spring bloom, and the importance of snow optical properties for light penetration. Colonization by ice algae began in May under >1 m of first-year sea ice with ˜1 m thick snow cover on top, in NE Greenland. The initial growth of ice algae began at extremely low irradiance (automated high-frequency temperature profiles. We propose that changes in snow optical properties, caused by temperature-driven snow metamorphosis, was the primary driver for allowing sufficient light to penetrate through the thick snow and initiate algae growth below the sea ice. This was supported by radiative-transfer modeling of light attenuation. Implications are an earlier productivity by ice algae in Arctic sea ice than recognized previously.

  1. Isotopes in Greenland Precipitation

    DEFF Research Database (Denmark)

    Faber, Anne-Katrine

    Greenland ice cores offer a unique opportunity to investigate the climate system behaviour. The objective of this PhD project is to investigate isotope modelling of present- day conditions and conduct model-data comparison using Greenland ice cores. Thus this thesis investigates how the integration...... of model and data can be used to improve the understanding of climate changes. This is done through analysis of isotope modelling, observations and ice core measurements. This dissertation comprises three projects: (1) Modelling the isotopic response to changes in Arctic sea surface conditions, (2......) Constructing a new Greenland database of observations and present-day ice core measurements, and (3) Performance test of isotope-enabled CAM5 for Greenland. The recent decades of rapid Arctic sea ice decline are used as a basis for an observational-based model experiment using the isotope-enabled CAM model 3...

  2. Spatiotemporal Variability of Meltwater Refreezing in Southwest Greenland Ice Sheet Firn

    Science.gov (United States)

    Rennermalm, A. K.; Hock, R.; Tedesco, M.; Corti, G.; Covi, F.; Miège, C.; Kingslake, J.; Leidman, S. Z.; Munsell, S.

    2017-12-01

    A substantial fraction of the summer meltwater formed on the surface of the Greenland ice sheet is retained in firn, while the remaining portion runs to the ocean through surface and subsurface channels. Refreezing of meltwater in firn can create impenetrable ice lenses, hence being a crucial process in the redistribution of surface runoff. To quantify the impact of refreezing on runoff and current and future Greenland surface mass balance, a three year National Science Foundation funded project titled "Refreezing in the firn of the Greenland ice sheet: Spatiotemporal variability and implications for ice sheet mass balance" started this past year. Here we present an overview of the project and some initial results from the first field season in May 2017 conducted in proximity of the DYE-2 site in the percolation zone of the Southwest Greenland ice sheet at elevations between 1963 and 2355 m a.s.l.. During this fieldwork two automatic weather stations were deployed, outfitted with surface energy balance sensors and 16 m long thermistor strings, over 300 km of ground penetrating radar data were collected, and five 20-26 m deep firn cores were extracted and analyzed for density and stratigraphy. Winter snow accumulation was measured along the radar tracks. Preliminary work on the firn-core data reveals increasing frequency and thickness of ice lenses at lower ice-sheet elevations, in agreement with other recent work in the area. Data collected within this project will facilitate advances in our understanding of the spatiotemporal variability of firn refreezing and its role in the hydrology and surface mass balance of the Greenland Ice Sheet.

  3. Ice-dynamic projections of the Greenland ice sheet in response to atmospheric and oceanic warming

    Directory of Open Access Journals (Sweden)

    J. J. Fürst

    2015-05-01

    Full Text Available Continuing global warming will have a strong impact on the Greenland ice sheet in the coming centuries. During the last decade (2000–2010, both increased melt-water runoff and enhanced ice discharge from calving glaciers have contributed 0.6 ± 0.1 mm yr−1 to global sea-level rise, with a relative contribution of 60 and 40% respectively. Here we use a higher-order ice flow model, spun up to present day, to simulate future ice volume changes driven by both atmospheric and oceanic temperature changes. For these projections, the flow model accounts for runoff-induced basal lubrication and ocean warming-induced discharge increase at the marine margins. For a suite of 10 atmosphere and ocean general circulation models and four representative concentration pathway scenarios, the projected sea-level rise between 2000 and 2100 lies in the range of +1.4 to +16.6 cm. For two low emission scenarios, the projections are conducted up to 2300. Ice loss rates are found to abate for the most favourable scenario where the warming peaks in this century, allowing the ice sheet to maintain a geometry close to the present-day state. For the other moderate scenario, loss rates remain at a constant level over 300 years. In any scenario, volume loss is predominantly caused by increased surface melting as the contribution from enhanced ice discharge decreases over time and is self-limited by thinning and retreat of the marine margin, reducing the ice–ocean contact area. As confirmed by other studies, we find that the effect of enhanced basal lubrication on the volume evolution is negligible on centennial timescales. Our projections show that the observed rates of volume change over the last decades cannot simply be extrapolated over the 21st century on account of a different balance of processes causing ice loss over time. Our results also indicate that the largest source of uncertainty arises from the surface mass balance and the underlying climate change

  4. Late Holocene spatio-temporal variability of the south Greenland Ice Sheet and adjacent mountain glaciers

    Science.gov (United States)

    Sinclair, G.; Carlson, A. E.; Rood, D. H.; Axford, Y.

    2017-12-01

    The late Holocene, with its spatially complex pattern of centennial-scale climate variation, is an ideal time period to test the response of the cryosphere to atmospheric and oceanic temperature changes. The south Greenland Ice Sheet (sGrIS), with its proximity to areas of North Atlantic Deep Water formation and a large spectrum of glaciological regimes over a relatively small area, provides an excellent location to examine the spatial heterogeneity of ice-sheet and glacier responses to climate change. Here, we will present 50 Be-10 surface exposure ages from eight moraines in six locations around the margin of the sGrIS. These moraines are located just outboard of historical moraines, and will therefore allow us to constrain the timing of the most extensive prehistoric late-Holocene advance and retreat of ice margins draining the sGrIS and independent valley glaciers. The dataset includes both marine- and land-terminating glaciers draining the sGrIS, the low-altitude Qassimiut lobe, the high-altitude alpine Julianhåb ice cap and isolated valley glaciers. This diverse dataset will allow us to determine to what extent late-Holocene centennial-scale behavior of the ice-sheet and glacier margins were synchronous, perhaps in response to an external climate forcing, or more stochastic, governed instead by local factors such as basal thermal regime, bedrock topography, or microclimates. This has implications for understanding the forcings and responses of cryospheric changes at timescales relevant to human society. In addition to providing context for paleoclimatic and glacial geologic investigations, this work will inform future sea-level projections by providing targets for validating high-resolution ice-sheet and glacier models.

  5. Glaciological and chemical studies on ice cores from Hans Tausen ice cap, Greenland

    DEFF Research Database (Denmark)

    Clausen, H.B.; Stampe, Mia; Hammer, C.U.

    2001-01-01

    The paper presents studies of various chemical and isotopical parameters from ice cores drilled in the northernmost located ice cap, Hans Tausen Iskappe, Pearyland, Greenland (HT). The 346 m main core (MC95) was drilled to bedrock in 1995 as well as a 35 m shallow core (SC95). A 60 m shallow core...... (SC75) and a 51 m shallow core (SC76) was drilled at two different positions in 1975 and 1976, respectively. A 6 m shallow core (SC94) was drilled in 1994. Continuous stable isotope records exist for all of these cores, total b-activity only from SC75 and SC76. Continuous ECM inferred acidity records...... exist along the 1995 cores (MC95 and SC95) and finally detailed records of dust and water soluble ion concentrations exist on selected parts of MC95. To determine a time scale for the ice core is an important prerequisite for the interpretation of other records. The age scale is based on acid layers...

  6. The Effect of Solar Forcing on the Greenland Ice Sheet during the Holocene - A Model Study

    Science.gov (United States)

    Bügelmayer, Marianne; Roche, Didier; Renssen, Hans

    2014-05-01

    Abrupt climate changes did not only happen during glacials but also during interglacials such as the Holocene. Marine sediments provide evidence for the periodic occurrence of centennial-scale events with enhanced iceberg discharge during the past 11.000 years (Bond et al., 2001). These events were chronologically linked to reduced solar activity as reconstructed using cosmogenic isotopes (Bond et al., 2001), indicating that even an external forcing that is considered to be small, has a potential impact on climate due to several feedback mechanisms (Renssen et al., 2006). The interactions between climate and solar irradiance have been investigated using numerical models (e.g. Haigh, 1996; Renssen et al, 2006), but so far without dynamically computing the Greenland ice sheet and iceberg calving. Thus, the impact of solar variations on iceberg discharge and the underlying mechanisms have not been analysed so far. To analyse the effect of variations in solar activity on the Greenland ice sheet (GIS) and the iceberg calving, as well as possible feedback mechanisms that enhance the impact of the total solar irradiance, we use the earth system model of intermediate complexity (iLOVECLIM, Roche et al., 2013), coupled to the ice sheet/ice shelf model GRISLI (Ritz et al., 2001) and to a dynamic-thermodynamic iceberg module (Jongma et al., 2009, Bügelmayer et al., 2014) to perform transient experiments of the last 6000 years. The experiments are conducted applying reconstructed atmospheric greenhouse gas concentrations, volcanic aerosol loads, orbital parameters and variations in the total solar irradiance. We present the response of the coupled model to different solar irradiance scenarios to evaluate modeled GIS sensitivity to relatively modest variations in radiative forcing. Moreover, we investigate the dependence of the model results on the chosen model sensitivity. References: Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M. N., Showers, W., … Bonani, G

  7. Possible contribution of ice-sheet/lithosphere interactions to past glaciological changes in Greenland

    Science.gov (United States)

    Alley, R. B.; Parizek, B. R.; Anandakrishnan, S.; Pollard, D.; Stevens, N. T.; Pourpoint, M.

    2017-12-01

    Ice-lithosphere interactions may have influenced the history of ice-sheet sensitivity to climate change. The Greenland ice sheet (GIS) is sensitive to warming, and is likely to be largely removed if subjected to relatively small additional temperature increases. The recent report (Schaefer et al., 2016, Nature) of near-complete GIS removal under modest Pleistocene forcing suggests that GIS sensitivity may be even greater than generally modeled, but lack of major Holocene retreat is more consistent with existing models. As shown by Stevens et al. (2016, JGR), peak lithospheric flexural stresses associated with ice-age GIS cycling are of the same order as dike-driving stresses in plutonic systems, and migrate over ice-age cycles. The full analysis by Stevens et al. suggests the possibility that the onset of cyclic ice-sheet loading allowed deep melt associated with the passage of the Icelandic hot spot beneath Greenland to work up though the crust to or near the base of the ice sheet, helping explain the anomalous geothermal heat fluxes observed at the head of the Northeast Greenland Ice Stream and elsewhere in the northern part of GIS. If ice-age cycling aided extraction of an existing reservoir of melted rock, then geothermal heat flux would have risen with the onset of extraction and migration, but with a subsequent fall associated with reservoir depletion. Simple parameterized flow-model simulations confirm intuition that a higher geothermal flux makes deglaciation easier, with the northern part of the ice sheet especially important. Large uncertainties remain in quantification, but we suggest the hypothesis that, following the onset of ice-age cycling, deglaciation of the GIS first became easier and then more difficult in response to feedbacks involving the ice sheet and the geological system beneath. In turn, this suggests that evidence of past deglaciation under moderate forcing is consistent with existing ice-sheet models.

  8. A SAR Ice-Motion Processing Chain in Support of PROMICE (Programme for the Monitoring of the Greenland Ice Sheet)

    DEFF Research Database (Denmark)

    Merryman Boncori, John Peter; Dall, Jørgen; Ahlstrøm, A. P.

    2010-01-01

    This paper reports on the development of a SAR icemotion processing chain developed for the PROMICE project – a long-term program funded by the Danish ministry of Climate and Energy to monitor the mass budget of the Greenland ice sheet. The end goal of the SAR data processing is to output map-pro...

  9. Meltwater storage in low-density near-surface bare ice in the Greenland ice sheet ablation zone

    Science.gov (United States)

    Cooper, Matthew G.; Smith, Laurence C.; Rennermalm, Asa K.; Miège, Clément; Pitcher, Lincoln H.; Ryan, Jonathan C.; Yang, Kang; Cooley, Sarah W.

    2018-03-01

    We document the density and hydrologic properties of bare, ablating ice in a mid-elevation (1215 m a.s.l.) supraglacial internally drained catchment in the Kangerlussuaq sector of the western Greenland ice sheet. We find low-density (0.43-0.91 g cm-3, μ = 0.69 g cm-3) ice to at least 1.1 m depth below the ice sheet surface. This near-surface, low-density ice consists of alternating layers of water-saturated, porous ice and clear solid ice lenses, overlain by a thin (sheet ablation zone surface. A conservative estimate for the ˜ 63 km2 supraglacial catchment yields 0.009-0.012 km3 of liquid meltwater storage in near-surface, porous ice. Further work is required to determine if these findings are representative of broader areas of the Greenland ice sheet ablation zone, and to assess the implications for sub-seasonal mass balance processes, surface lowering observations from airborne and satellite altimetry, and supraglacial runoff processes.

  10. Evidence for ephemeral middle Eocene to early Oligocene Greenland glacial ice and pan-Arctic sea ice.

    Science.gov (United States)

    Tripati, Aradhna; Darby, Dennis

    2018-03-12

    Earth's modern climate is defined by the presence of ice at both poles, but that ice is now disappearing. Therefore understanding the origin and causes of polar ice stability is more critical than ever. Here we provide novel geochemical data that constrain past dynamics of glacial ice on Greenland and Arctic sea ice. Based on accurate source determinations of individual ice-rafted Fe-oxide grains, we find evidence for episodic glaciation of distinct source regions on Greenland as far-ranging as ~68°N and ~80°N synchronous with ice-rafting from circum-Arctic sources, beginning in the middle Eocene. Glacial intervals broadly coincide with reduced CO 2 , with a potential threshold for glacial ice stability near ~500 p.p.m.v. The middle Eocene represents the Cenozoic onset of a dynamic cryosphere, with ice in both hemispheres during transient glacials and substantial regional climate heterogeneity. A more stable cryosphere developed at the Eocene-Oligocene transition, and is now threatened by anthropogenic emissions.

  11. Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Kjaer, Kurt H.; Bevis, Michael

    2014-01-01

    The Greenland ice sheet has been one of the largest contributors to global sea-level rise over the past 20 years, accounting for 0.5 mm yr(-1) of a total of 3.2 mm yr(-1). A significant portion of this contribution is associated with the speed-up of an increased number of glaciers in southeast...... and northwest Greenland. Here, we show that the northeast Greenland ice stream, which extends more than 600 km into the interior of the ice sheet, is now undergoing sustained dynamic thinning, linked to regional warming, after more than a quarter of a century of stability. This sector of the Greenland ice sheet...... is of particular interest, because the drainage basin area covers 16% of the ice sheet (twice that of Jakobshavn Isbrae) and numerical model predictions suggest no significant mass loss for this sector, leading to an under-estimation of future global sea-level rise. The geometry of the bedrock and monotonic trend...

  12. A synthesis of the basal thermal state of the Greenland Ice Sheet.

    Science.gov (United States)

    MacGregor, Joseph A; Fahnestock, Mark A; Catania, Ginny A; Aschwanden, Andy; Clow, Gary D; Colgan, William T; Gogineni, S Prasad; Morlighem, Mathieu; Nowicki, Sophie M J; Paden, John D; Price, Stephen F; Seroussi, Hélène

    2016-08-10

    The basal thermal state of an ice sheet (frozen or thawed) is an important control upon its evolution, dynamics and response to external forcings. However, this state can only be observed directly within sparse boreholes or inferred conclusively from the presence of subglacial lakes. Here we synthesize spatially extensive inferences of the basal thermal state of the Greenland Ice Sheet to better constrain this state. Existing inferences include outputs from the eight thermomechanical ice-flow models included in the SeaRISE effort. New remote-sensing inferences of the basal thermal state are derived from Holocene radiostratigraphy, modern surface velocity and MODIS imagery. Both thermomechanical modeling and remote inferences generally agree that the Northeast Greenland Ice Stream and large portions of the southwestern ice-drainage systems are thawed at the bed, whereas the bed beneath the central ice divides, particularly their west-facing slopes, is frozen. Elsewhere, there is poor agreement regarding the basal thermal state. Both models and remote inferences rarely represent the borehole-observed basal thermal state accurately near NorthGRIP and DYE-3. This synthesis identifies a large portion of the Greenland Ice Sheet (about one third by area) where additional observations would most improve knowledge of its overall basal thermal state.

  13. A synthesis of the basal thermal state of the Greenland Ice Sheet

    Science.gov (United States)

    MacGregor, Joseph A; Fahnestock, Mark A; Catania, Ginny A; Aschwanden, Andy; Clow, Gary D.; Colgan, William T.; Gogineni, Prasad S.; Morlighem, Mathieu; Nowicki, Sophie M .J.; Paden, John D; Price, Stephen F.; Seroussi, Helene

    2016-01-01

    The basal thermal state of an ice sheet (frozen or thawed) is an important control upon its evolution, dynamics and response to external forcings. However, this state can only be observed directly within sparse boreholes or inferred conclusively from the presence of subglacial lakes. Here we synthesize spatially extensive inferences of the basal thermal state of the Greenland Ice Sheet to better constrain this state. Existing inferences include outputs from the eight thermomechanical ice-flow models included in the SeaRISE effort. New remote-sensing inferences of the basal thermal state are derived from Holocene radiostratigraphy, modern surface velocity and MODIS imagery. Both thermomechanical modeling and remote inferences generally agree that the Northeast Greenland Ice Stream and large portions of the southwestern ice-drainage systems are thawed at the bed, whereas the bed beneath the central ice divides, particularly their west-facing slopes, is frozen. Elsewhere, there is poor agreement regarding the basal thermal state. Both models and remote inferences rarely represent the borehole-observed basal thermal state accurately near NorthGRIP and DYE-3. This synthesis identifies a large portion of the Greenland Ice Sheet (about one third by area) where additional observations would most improve knowledge of its overall basal thermal state.

  14. The Effect of Topographic Shadowing by Ice on Irradiance in the Greenland Ice Sheet Ablation Zone

    Science.gov (United States)

    Leidman, S. Z.; Rennermalm, A. K.; Ryan, J.; Cooper, M. G.; Smith, L. C.

    2017-12-01

    Accurately predicting runoff contributions to global sea level rise requires more refined surface mass balance (SMB) models of the Greenland Ice Sheet (GrIS). Topographic shadowing has shown to be important in the SMB of snow-covered regions, yet SMB models for the GrIS 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

  15. Greenland and Antarctica Ice Sheet Mass Changes and Effects on Global Sea Level

    DEFF Research Database (Denmark)

    Forsberg, René; Sørensen, Louise Sandberg; Simonsen, Sebastian Bjerregaard

    2017-01-01

    Thirteen years of GRACE data provide an excellent picture of the current mass changes of Greenland and Antarctica, with mass loss in the GRACE period 2002–2015 amounting to 265 ± 25 GT/year for Greenland (including peripheral ice caps), and 95 ± 50 GT/year for Antarctica, corresponding to 0.......72 and 0.26 mm/year average global sea level change. A significant acceleration in mass loss rate is found, especially for Antarctica, while Greenland mass loss, after a corresponding acceleration period, and a record mass loss in the summer of 2012, has seen a slight decrease in short-term mass loss trend....... The yearly mass balance estimates, based on point mass inversion methods, have relatively large errors, both due to uncertainties in the glacial isostatic adjustment processes, especially for Antarctica, leakage from unmodelled ocean mass changes, and (for Greenland) difficulties in separating mass signals...

  16. Amplified melt and flow of the Greenland ice sheet driven by late-summer cyclonic rainfall

    DEFF Research Database (Denmark)

    Doyle, Samuel H.; Hubbard, Alun; van de Wal, Roderik S.W.

    2015-01-01

    and meteorological variables from the western margin of the Greenland ice sheet during a week of warm, wet cyclonic weather in late August and early September 2011. We find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice-sheet interior....... We suggest that the late-season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less-efficient winter mode. Reanalysis data reveal that similar cyclonic weather conditions prevailed across southern...

  17. Understanding Greenland ice sheet hydrology using an integrated multi-scale approach

    International Nuclear Information System (INIS)

    Rennermalm, A K; Moustafa, S E; Mioduszewski, J; Robinson, D A; Chu, V W; Smith, L C; Forster, R R; Hagedorn, B; Harper, J T; Mote, T L; Shuman, C A; Tedesco, M

    2013-01-01

    Improved understanding of Greenland ice sheet hydrology is critically important for assessing its impact on current and future ice sheet dynamics and global sea level rise. This has motivated the collection and integration of in situ observations, model development, and remote sensing efforts to quantify meltwater production, as well as its phase changes, transport, and export. Particularly urgent is a better understanding of albedo feedbacks leading to enhanced surface melt, potential positive feedbacks between ice sheet hydrology and dynamics, and meltwater retention in firn. These processes are not isolated, but must be understood as part of a continuum of processes within an integrated system. This letter describes a systems approach to the study of Greenland ice sheet hydrology, emphasizing component interconnections and feedbacks, and highlighting research and observational needs. (letter)

  18. Comparison of northern and central Greenland ice cores records of methanesulfonate covering the last glacial period

    DEFF Research Database (Denmark)

    Jonsell, U.; Hansson, M. E.; Siggaard-Andersen, M-L-

    2007-01-01

    Methanesulfonate (MS-) is measured in ice cores with the objective to obtain a proxy record of marine phytoplankton production of dimethylsulfide (DMS). We present a continuous MS- record covering the last glacial period from the North Greenland Ice Core Project (NGRIP) ice core and compare...... this record with the corresponding records previously presented from Greenland and, in particular, with the GISP2 ice core located 320 km south of NGRIP. Despite that the records have similar mean concentrations, their responses to climatic changes during the last glacial period are slightly different. NGRIP...... MS- concentrations were higher during the cold marine isotopic stages (MIS) 2 and 4 and lower during the warm MIS 5. This long-term trend in MS-, which is similar to the inverse of the corresponding trend in d 18O, is not detected in the GISP2 MS- record. A systematic response in MS- concentrations...

  19. Spread of ice mass loss into northwest Greenland observed by GRACE and GPS

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Wahr, John; Bevis, Michael

    2010-01-01

    Global Positioning System (GPS) measurements from three long-term sites on bedrock adjacent to the ice sheet. The GRACE results provide a direct measure of mass loss averaged over scales of a few hundred km. The GPS data are used to monitor crustal uplift caused by ice mass loss close to the sites....... The GRACE results can be used to predict crustal uplift, which can be compared with the GPS data. In addition to showing that the northwest ice sheet margin is now losing mass, the uplift results from both the GPS measurements and the GRACE predictions show rapid acceleration in southeast Greenland in late...... 2003, followed by a moderate deceleration in 2006. Because that latter deceleration is weak, southeast Greenland still appears to be losing ice mass at a much higher rate than it was prior to fall 2003. In a more general sense, the analysis described here demonstrates that GPS uplift measurements can...

  20. Sea ice and primary production proxies in surface sediments from a High Arctic Greenland fjord

    DEFF Research Database (Denmark)

    Ribeiro, Sofia; Sejr, Mikael K; Limoges, Audrey

    2017-01-01

    Monitoring Programme. Clear spatial gradients in organic carbon and biogenic silica contents reflected marine influence, nutrient availability and river-induced turbidity, in good agreement with in situ measurements. The sea ice proxy IP25 was detected at all sites but at low concentrations, indicating...... that IP25 records from fjords need to be carefully considered and not directly compared to marine settings. The sea ice-associated biomarker HBI III revealed an open-water signature, with highest concentrations near the mid-July ice edge. This proxy evaluation is an important step towards reliable......In order to establish a baseline for proxy-based reconstructions for the Young Sound–Tyrolerfjord system (Northeast Greenland), we analysed the spatial distribution of primary production and sea ice proxies in surface sediments from the fjord, against monitoring data from the Greenland Ecosystem...

  1. Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland

    Science.gov (United States)

    Willerslev, Eske; Cappellini, Enrico; Boomsma, Wouter; Nielsen, Rasmus; Hebsgaard, Martin B.; Brand, Tina B.; Hofreiter, Michael; Bunce, Michael; Poinar, Hendrik N.; Dahl-Jensen, Dorthe; Johnsen, Sigfus; Steffensen, Jørgen Peder; Bennike, Ole; Schwenninger, Jean-Luc; Nathan, Roger; Armitage, Simon; de Hoog, Cees-Jan; Alfimov, Vasily; Christl, Marcus; Beer, Juerg; Muscheler, Raimund; Barker, Joel; Sharp, Martin; Penkman, Kirsty E.H.; Haile, James; Taberlet, Pierre; Gilbert, M. Thomas P.; Casoli, Antonella; Campani, Elisa; Collins, Matthew J.

    2009-01-01

    One of the major difficulties in paleontology is the acquisition of fossil data from the 10% of Earth’s terrestrial surface that is covered by thick glaciers and ice sheets. Here we reveal that DNA and amino acids from buried organisms can be recovered from the basal sections of deep ice cores and allow reconstructions of past flora and fauna. We show that high altitude southern Greenland, currently lying below more than two kilometers of ice, was once inhabited by a diverse array of conifer trees and insects that may date back more than 450 thousand years. The results provide the first direct evidence in support of a forested southern Greenland and suggest that many deep ice cores may contain genetic records of paleoenvironments in their basal sections. PMID:17615355

  2. The fate of the Greenland Ice Sheet in a geoengineered, high CO2 world

    International Nuclear Information System (INIS)

    Irvine, Peter J; Lunt, Daniel J; Stone, Emma J; Ridgwell, Andy

    2009-01-01

    Solar radiation management (SRM) geoengineering has been proposed as one means of helping avoid the occurrence of dangerous climate change and undesirable state transitions ('tipping points') in the Earth system. The irreversible melting of the Greenland Ice Sheet is a case in point-a state transition that could occur as a result of CO 2 -driven elevated global temperatures, and one leading to potentially catastrophic sea-level rise. SRM schemes such as the creation of a 'sunshade' or injection of sulfate aerosols into the stratosphere could reduce incoming solar radiation, and in theory balance, in a global mean, the greenhouse warming resulting from elevated concentrations of CO 2 in the atmosphere. Previous work has highlighted that a geoengineered world would have: warming towards the poles, cooling in the tropics, and a reduction in the global hydrological cycle, which may have important implications for the Greenland Ice Sheet. Using a fully coupled global climate model in conjunction with an ice sheet model, we assess the consequences for the mass balance of the Greenland Ice Sheet of the reorganization of climate patterns by the combination of high CO 2 and geoengineering. We find that Greenland surface temperature and precipitation anomalies, compared to the pre-industrial situation, decrease almost linearly with increasing levels of SRM geoengineering, but that these combine to create a highly non-linear response of the ice sheet. The substantial melting of the Greenland Ice Sheet predicted for four times pre-industrial CO 2 levels is prevented in our model with only a partial application of SRM, and hence without having to fully restore the global average temperature back to pre-industrial levels. This suggests that the degree of SRM geoengineering required to mitigate the worst impacts of greenhouse warming, such as sea-level rise, need not be as extensive as generally assumed.

  3. Investigating Margin and Grounding Line Dynamics with a Coupled Ice and Sea Level Model

    Science.gov (United States)

    Kuchar, J.; Milne, G. A.

    2017-12-01

    We present results from the coupling of an adaptive mesh glaciological model (BISICLES) with a model of glacial isostatic adjustment and sea level. We apply this coupled model to study the deglaciation of the Greenland Ice Sheet (GrIS) from the last glacial maximum. The proximity of the GrIS to the much larger Laurentide results in an east-west gradient in sea level rates across Greenland during the deglaciation. We investigate the impacts of this sea level gradient on ice and grounding line dynamics at the margins, as well as the influence of both local and non-local ice on sea level and ice dynamics.

  4. Bathymetry and retreat of Southeast Greenland glaciers from Operation IceBridge and Ocean Melting Greenland data

    Science.gov (United States)

    Millan, R.; Rignot, E. J.; Morlighem, M.; Bjork, A. A.; Mouginot, J.; Wood, M.

    2017-12-01

    Southeast Greenland has been one of the largest contributors to ice mass loss in Greenland in part because of significant changes in glacier dynamics. The leading hypothesis for the changes in glacier dynamics is that enhanced thermal forcing from the ocean has dislodged a number of glaciers from their anchoring positions and some of them retreated rapidly along a reverse bed. The glaciers response has been observed to vary significantly from one fjord to the next, but until now there was not enough data to understand or interpret these changes. In particular, there was no data on glacier bed topography and seafloor bathymetry in the fjords. Here we present the results of new fjord mapping by the NASA Ocean Melting Greenland mission combined with a recent high-resolution airborne gravity survey by NASA Operation IceBridge. We combine these data with a reconstruction of the bed using a mass conservation approach upstream extending into the glacial fjords for the first time. In the fjord and along the ice-ocean transition, we employ a 3D inversion of gravity data to infer the bed elevation along a set of 9 survey boxes spanning south of Helheim Glacier to the southern tip of Southeast Greenland. We combine the results with an analysis of the glacier front history since the 1930's and Conductivity Temperature Depth data obtained in the fjord by OMG in 2016. The data reveals bed elevations several 100-m deeper than previously thought, for almost all the glaciers, up to 500 m for some of them. For many glaciers, the bed profiles help to completely understand the history of retreat of the glaciers. For instance, glaciers stranded on sills have been stable; glaciers on a reverse slope have retreated rapidly; and glaciers with a normal slope have retreated slowly. The mapping also helps document the extent of the marine portion of the glacier basins. In many of the fjords, we document the presence of warm, salty Atlantic Water which fuels large melt rates. We employ

  5. Test of Newton's inverse-square law in the Greenland ice cap

    International Nuclear Information System (INIS)

    Ander, M.E.; Zumberge, M.A.; Lautzenhiser, T.

    1989-01-01

    An Airy-type geophysical experiment was conducted in a 2-km-deep hole in the Greenland ice cap at depths between 213 and 1673 m to test for possible violations of Newton's inverse-square law. An anomalous gravity gradient was observed. We cannot unambiguously attribute it to a breakdown of Newtonian gravity because we have shown that it might be due to unexpected geological features in the rock below the ice

  6. Properties of horizontally oriented ice crystals observed by polarization lidar over summit, Greenland

    Directory of Open Access Journals (Sweden)

    Neely Ryan R.

    2018-01-01

    Full Text Available A source of error in microphysical retrievals and model simulations is the assumption that clouds are composed of only randomly oriented ice crystals. This assumption is frequently not true, as evidenced by optical phenomena such as parhelia. Here, observations from the Cloud, Aerosol and Polarization Backscatter Lidar at Summit, Greenland are utilized along with other sensors and beam imaging to examine the properties of horizontally oriented ice crystals and the environment conditions in which they occur.

  7. Greenland surface mass-balance observations from the ice-sheet ablation area and local glaciers

    DEFF Research Database (Denmark)

    Machguth, Horst; Thomsen, Henrik H.; Weidick, Anker

    2016-01-01

    Glacier surface mass-balance measurements on Greenland started more than a century ago, but no compilation exists of the observations from the ablation area of the ice sheet and local glaciers. Such data could be used in the evaluation of modelled surface mass balance, or to document changes in g...

  8. The pattern of anthropogenic signal emergence in Greenland Ice Sheet surface mass balance

    NARCIS (Netherlands)

    Fyke, J.G.; Vizcaino, M.; Lipscomb, W.H.

    2014-01-01

    Surface mass balance (SMB) trends influence observed Greenland Ice Sheet (GrIS) mass loss, but the component of these trends related to anthropogenic forcing is unclear. Here we study the simulated spatial pattern of emergence of an anthropogenically derived GrIS SMB signal between 1850 and 2100

  9. A 600-year annual 10Be record from the NGRIP ice core, Greenland

    DEFF Research Database (Denmark)

    Berggren, A.M.; Johnsen, Sigfus Johann; Vinther, Bo Møllesøe

    2009-01-01

    in an ice core from the NGRIP site in Greenland. NGRIP and Dye-3 10Be exhibits similar long-term variability, although occasional short term differences between the two sites indicate that at least two high resolution 10Be records are needed to assess local variations and to confidently reconstruct past...

  10. Greenland surface mass-balance observations from the ice-sheet ablation area and local glaciers

    NARCIS (Netherlands)

    Machguth, Horst; Thomsen, Henrik H.; Weidick, Anker; Ahlstrøm, Andreas P.; Abermann, Jakob; Andersen, Morten L.; Andersen, Signe B.; Bjørk, Anders A.; Box, Jason E.; Braithwaite, Roger J.; Bøggild, Carl E.; Citterio, Michele; Clement, Poul; Colgan, William; Fausto, Robert S.; Gleie, Karin; Gubler, Stefanie; Hasholt, Bent; Hynek, Bernhard; Knudsen, Niels T.; Larsen, Signe H.; Mernild, Sebastian H.; Oerlemans, Johannes; Oerter, Hans; Olesen, Ole B.; Smeets, C. J P Paul; Steffen, Konrad; Stober, Manfred; Sugiyama, Shin; Van As, Dirk; Van Den Broeke, Michiel R.; Van De Wal, Roderik S W

    2016-01-01

    Glacier surface mass-balance measurements on Greenland started more than a century ago, but no compilation exists of the observations from the ablation area of the ice sheet and local glaciers. Such data could be used in the evaluation of modelled surface mass balance, or to document changes in

  11. The observed katabatic flow at the edge of the Greenland ice sheet during GIMEX-91

    NARCIS (Netherlands)

    Broeke, M.R. van den; Duynkerke, P.G.; Oerlemans, J.

    1994-01-01

    Observations performed in the melting zone of the Greenland ice sheet and over the adjacent tundra in the summer of 1991 are described. The experimental area is the region near St ndre Stromfjord (67°N, 54°W), which is relatively dry and sunny, resulting in the highest mean temperature in

  12. Tomographic SAR analysis of subsurface ice structure in Greenland: first results

    DEFF Research Database (Denmark)

    Banda, Francesco; Dall, Jørgen; Tebaldini, Stefano

    2013-01-01

    structure with P-band SAR tomography. First results from ESA IceSAR 2012 campaign carried out in south-west Greenland are presented. It is found that significant penetration in the upper layers of glacial subsurface can be achieved up to an extent of about 20–60 m, conditional on the different type...

  13. Socio-economic and cultural aspecrs of changes in the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Moshøj, Charlotte Margaret

    2009-01-01

    ! is chapter evaluates the possibility for projecting socio-economic and cultural impacts on Greenland’s society caused directly or indirectly by changes in the Greenland Ice Sheet. ! ere are, as yet, no well-documented direct causative links between the conditions for a society dictated by nature...

  14. Spatial and temporal melt variability at Helheim Glacier, East Greenland, and its effect on ice dynamics

    DEFF Research Database (Denmark)

    Andersen, M. L.; Larsen, T. B.; Nettles, M.

    2010-01-01

    Understanding the behavior of large outlet glaciers draining the Greenland Ice Sheet is critical for assessing the impact of climate change on sea level rise. The flow of marine-terminating outlet glaciers is partly governed by calving-related processes taking place at the terminus but is also in...

  15. Hypsometric amplification and routing moderation of Greenland ice sheet meltwater release

    Science.gov (United States)

    van As, Dirk; Mikkelsen, Andreas Bech; Holtegaard Nielsen, Morten; Box, Jason E.; Claesson Liljedahl, Lillemor; Lindbäck, Katrin; Pitcher, Lincoln; Hasholt, Bent

    2017-06-01

    Concurrent ice sheet surface runoff and proglacial discharge monitoring are essential for understanding Greenland ice sheet meltwater release. We use an updated, well-constrained river discharge time series from the Watson River in southwest Greenland, with an accurate, observation-based ice sheet surface mass balance model of the ˜ 12 000 km2 ice sheet area feeding the river. For the 2006-2015 decade, we find a large range of a factor of 3 in interannual variability in discharge. The amount of discharge is amplified ˜ 56 % by the ice sheet's hypsometry, i.e., area increase with elevation. A good match between river discharge and ice sheet surface meltwater production is found after introducing elevation-dependent transit delays that moderate diurnal variability in meltwater release by a factor of 10-20. The routing lag time increases with ice sheet elevation and attains values in excess of 1 week for the upper reaches of the runoff area at ˜ 1800 m above sea level. These multi-day routing delays ensure that the highest proglacial discharge levels and thus overbank flooding events are more likely to occur after multi-day melt episodes. Finally, for the Watson River ice sheet catchment, we find no evidence of meltwater storage in or release from the en- and subglacial environments in quantities exceeding our methodological uncertainty, based on the good match between ice sheet runoff and proglacial discharge.

  16. Greenland Regional and Ice Sheet-wide Geometry Sensitivity to Boundary and Initial conditions

    Science.gov (United States)

    Logan, L. C.; Narayanan, S. H. K.; Greve, R.; Heimbach, P.

    2017-12-01

    Ice sheet and glacier model outputs require inputs from uncertainly known initial and boundary conditions, and other parameters. Conservation and constitutive equations formalize the relationship between model inputs and outputs, and the sensitivity of model-derived quantities of interest (e.g., ice sheet volume above floatation) to model variables can be obtained via the adjoint model of an ice sheet. We show how one particular ice sheet model, SICOPOLIS (SImulation COde for POLythermal Ice Sheets), depends on these inputs through comprehensive adjoint-based sensitivity analyses. SICOPOLIS discretizes the shallow-ice and shallow-shelf approximations for ice flow, and is well-suited for paleo-studies of Greenland and Antarctica, among other computational domains. The adjoint model of SICOPOLIS was developed via algorithmic differentiation, facilitated by the source transformation tool OpenAD (developed at Argonne National Lab). While model sensitivity to various inputs can be computed by costly methods involving input perturbation simulations, the time-dependent adjoint model of SICOPOLIS delivers model sensitivities to initial and boundary conditions throughout time at lower cost. Here, we explore both the sensitivities of the Greenland Ice Sheet's entire and regional volumes to: initial ice thickness, precipitation, basal sliding, and geothermal flux over the Holocene epoch. Sensitivity studies such as described here are now accessible to the modeling community, based on the latest version of SICOPOLIS that has been adapted for OpenAD to generate correct and efficient adjoint code.

  17. Direct observations of evolving subglacial drainage beneath the Greenland Ice Sheet.

    Science.gov (United States)

    Andrews, Lauren C; Catania, Ginny A; Hoffman, Matthew J; Gulley, Jason D; Lüthi, Martin P; Ryser, Claudia; Hawley, Robert L; Neumann, Thomas A

    2014-10-02

    Seasonal acceleration of the Greenland Ice Sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed via crevasses and moulins (vertical conduits connecting supraglacial water to the bed of the ice sheet). As the melt season progresses, the subglacial hydrologic system drains supraglacial meltwater more efficiently, decreasing basal water pressure and moderating the ice velocity response to surface melting. However, limited direct observations of subglacial water pressure mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood. Here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby (0.3-2 kilometres away) boreholes, indicating that moulins connect to an efficient, channelized component of the subglacial hydrologic system, which exerts the primary control on diurnal and multi-day changes in ice velocity. Our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the Paakitsoq region of western Greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin-connected channels to convey supraglacial melt. Instead, these observations suggest that decreasing late-season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system. Understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt-season dynamics affect ice velocity beyond the conclusion of the melt season.

  18. Mass balance of the Greenland ice sheet - a study of ICESat data, surface density and firn compaction modelling

    DEFF Research Database (Denmark)

    Sørensen, L. S.; Simonsen, Sebastian Bjerregaard; Nielsen, K.

    2010-01-01

    ICESat has provided surface elevation measurements of the ice sheets since the launch in January 2003, resulting in a unique data set for monitoring the changes of the cryosphere. Here we present a novel method for determining the mass balance of the Greenland ice sheet derived from ICESat...... in estimating the mass balance of the Greenland ice sheet. We find firn dynamics and surface densities to be important factors in deriving the mass loss from remote sensing altimetry. The volume change derived from ICESat data is corrected for firn compaction, vertical bedrock movement and an intercampaign...... boundary conditions. We find an annual mass loss of the Greenland ice sheet of 210 ± 21 Gt yr-1 in the period from October 2003 to March 2008. This result is in good agreement with other studies of the Greenland ice sheet mass balance, based on different remote sensing techniques....

  19. Detection of Supra-Glacial Lakes on the Greenland Ice Sheet Using MODIS Images

    Science.gov (United States)

    Verin, Gauthier; Picard, Ghislain; Libois, Quentin; Gillet-Chaulet, Fabien; Roux, Antoine

    2015-04-01

    During melt season, supra-glacial lakes form on the margins of the Greenland ice sheet. Because of their size exceeding several kilometers, and their concentration, they affect surface albedo leading to an amplification of the regional melt. Furthermore, they foster hydro-fracturing that propagate liquid water to the bedrock and therefore enhance the basal lubrication which may affect the ice motion. It is known that Greenland ice sheet has strongly responded to recent global warming. As air temperature increases, melt duration and melt intensity increase and surface melt area extends further inland. These recent changes may play an important role in the mass balance of the Greenland ice sheet. In this context, it is essential to better monitor and understand supra-glacial spatio-temporal dynamics in order to better assess future sea level rise. In this study MODIS (Moderate Resolution Imaging Spectroradiometer) images have been used to detect supra-glacial lakes. The observation site is located on the West margin of the ice sheet, between 65°N and 70°N where the concentration of lake is maximum. The detection is performed by a fully automatic algorithm using images processing techniques introduced by Liang et al. (2012) which can be summarized in three steps: the selection of usable MODIS images, mainly we exclude images with too many clouds. The detection of lake and the automatic correction of false detections. This algorithm is capable to tag each individual lake allowing a survey of all lake geometrical properties over the entire melt season. We observed a large population of supra-glacial lakes over 14 melt seasons, from 2000 to 2013 on an extended area of 70.000 km2. In average, lakes are observed from June 9 ± 8.7 days to September 13 ± 13.9 days, and reach a maximum total area of 699 km2 ± 146 km2. As the melt season progresses, lakes form higher in altitude up to 1800 m above sea level. Results show a very strong inter-annual variability in term of

  20. Greenland

    DEFF Research Database (Denmark)

    Gad, Ulrik Pram

    2014-01-01

    in 1979 and made the 1985 withdrawal possible. On 25 November 2008, a majority of the people of Greenland voted in favour of enhanced home rule – ‘self-government’ – still within formal Danish sovereignty. Denmark and Greenland alike are preparing for a future envisioned as involving climate change...

  1. Airborne Laser Altimetry Mapping of the Greenland Ice Sheet: Application to Mass Balance Assessment

    Science.gov (United States)

    Abdalati, W.; Krabill, W.; Frederick, E.; Manizade, S.; Martin, C.; Sonntag, J.; Swift, R.; Thomas, R.; Wright, W.; Yungel, J.

    2000-01-01

    In 1998 and '99, the Arctic Ice Mapping (AIM) program completed resurveys of lines occupied 5 years earlier revealing elevation changes of the Greenland ice sheet and identifying areas of significant thinning, thickening and balance. In planning these surveys, consideration had to be given to the spatial constraints associated with aircraft operation, the spatial nature of ice sheet behavior, and limited resources, as well as temporal issues, such as seasonal and interannual variability in the context of measurement accuracy. This paper examines the extent to which the sampling and survey strategy is valid for drawing conclusions on the current state of balance of the Greenland ice sheet. The surveys covered the entire ice sheet with an average distance of 21.4 km between each location on the ice sheet and the nearest flight line. For most of the ice sheet, the elevation changes show relatively little spatial variability, and their magnitudes are significantly smaller than the observed elevation change signal. As a result, we conclude that the density of the sampling and the accuracy of the measurements are sufficient to draw meaningful conclusions on the state of balance of the entire ice sheet over the five-year survey period. Outlet glaciers, however, show far more spatial and temporal variability, and each of the major ones is likely to require individual surveys in order to determine its balance.

  2. Greenland deep boreholes inform on sliding and deformation of the basal ice

    Science.gov (United States)

    Dahl-Jensen, D.

    2017-12-01

    Repeated measurements of the deformation of the deep boreholes on the Greenland ice sheet informs on the basal sliding, near basal deformation and in general on the horizontal velocity through the ice. Results of the logging of the boreholes at Dye3, GRIP, NGRIP, NEEM and Camp Century through the last 40 years by the Danish Ice and Climate group will be presented and discussed. The results on the flow will be compared with the information on ice properties, impurity load and bedrock entrained material from the deep ice cores and the radio echo sounding images near the drill sites.The results show that the basal movement often happens in an impurity rich zone above the bedrock while pure basal sliding is limited even in the presence of basal water and significant basal melt.Most of the deep ice core sites are located close to ice divides where the surface velocity is limited so significant basal sliding is not expected. Exceptions are the surface velocities at Camp Century and Dye 3, both being 13 m/yr.Finally, the ongoing deep drilling at EGRIP will shortly be presented where we are drilling in the center of the North East Greenland Ice Stream (NEGIS).

  3. Quantifying Local Ablation Rates for the Greenland Ice Sheet Using Terrestrial LIDAR

    Science.gov (United States)

    Kershner, C. M.; Pitcher, L. H.; LeWinter, A.; Finnegan, D. C.; Overstreet, B. T.; Miège, C.; Cooper, M. G.; Smith, L. C.; Rennermalm, A. K.

    2016-12-01

    Quantifying accurate ice surface ablation or melt rates for the Greenland Ice Sheet is important for calibrating and validating surface mass balance models and constraining sea level rise estimates. Common practice is to monitor surface ablation at defined points by manually measuring ice surface lowering in relation to stakes inserted into the ice / snow. However, this method does not account for the effects of local topography, solar zenith angle, and local variations in ice surface albedo/impurities on ablation rates. To directly address these uncertainties, we use a commercially available terrestrial LIDAR scanner (TLS) to monitor daily melt rates in the ablation zone of the Greenland Ice Sheet for 7 consecutive days in July 2016. Each survey is registered to previous scans using retroreflective cylinders and is georeferenced using static GPS measurements. Bulk ablation will be calculated using multi-temporal differential LIDAR techniques, and difficulties in referencing scans and collecting high quality surveys in this dynamic environment will be discussed, as well as areas for future research. We conclude that this novel application of TLS technology provides a spatially accurate, higher fidelity measurements of ablation across a larger area with less interpolation and less time spent than using traditional manual point based methods alone. Furthermore, this sets the stage for direct calibration, validation and cross-comparison with existing airborne (e.g. NASA's Airborne Topographic Mapper - ATM - onboard Operation IceBridge and NASA's Land, Vegetation & Ice Sensor - LVIS) and forthcoming spaceborne sensors (e.g. NASA's ICESat-2).

  4. Towards a new common Greenland Ice Core Chronology for the last 5000 years

    Science.gov (United States)

    Winstrup, Mai; Olander Rasmussen, Sune; Møllesøe Vinther, Bo; Cook, Eliza; Svensson, Anders; McConnell, Joe; Steffensen, Jørgen Peder

    2017-04-01

    Since the development of the Greenland Ice Core Chronology 2005 (GICC05), it has been widely used as a reference chronology in paleoclimate research. However, recent research (Sigl et al, 2015) demonstrated that this timescale has small, but significant, issues over historical time. These discrepancies was found by counting annual layers in high-resolution chemistry records from the NEEM S1 shallow core, and confirmed by linking via 10Be marker horizons to the layer-counted WAIS Divide ice core, Antarctica, and accurately-dated tree-ring series. This work showed that a revision of GICC05 is required prior to 1250AD. We here refine and extend this work. Layer-counting in a single core will always involve some uncertainty, and we hence use data from multiple Greenland ice cores, for which high-resolution impurity records recently have been measured. These ice cores have been synchronized using volcanic marker horizons, and the layer-counting is performed automatically using the StratiCounter algorithm (Winstrup et al, 2012), while ensuring that the number of layers between volcanic horizons are the same in all cores. Based on this extended multiple-core data set, we are further able to extend the new Greenland timescale another few thousand years back in time. This will, among others, provide a new ice-core date for the catastrophic volcanic eruption ( 1600 BC) that destroyed the Greek Minoan culture, an important time marker in Greek history.

  5. Mass balance of the Amitsulôq ice cap, West Greenland

    DEFF Research Database (Denmark)

    Ahlstrøm, Andreas P.; Bøggild, Carl Egede; Olesen, Ole B.

    2007-01-01

    We present detailed mass balance measurements from the Amitsulôq ice cap in West Greenland spanning from 1982 to 1990. The data includes summer and winter balances from 26 stake locations distributed over five transects covering the whole ice cap. The mass balance measurements are combined...... with a recent satellite-derived digital elevation model to calculate the specific balance, which is in turn compared to discharge data from the adjacent Tasersiaq basin. The correlation between specific summer balance and discharge is R2 = 0.93 indicating that the basin discharge is dominated by glacial...... meltwater, linking the hydropower potential of the basin closely to the fate of the adjoining Greenland ice-sheet margin....

  6. Implications of changing scattering properties on Greenland ice sheet volume change from Cryosat-2 altimetry

    DEFF Research Database (Denmark)

    Simonsen, Sebastian Bjerregaard; Sørensen, Louise Sandberg

    2017-01-01

    ) in the elevation change algorithm, to correct for temporal changes in the ratio between surface- and volume-scatter in Cryosat-2 observations. We present elevation and volume changes for the Greenland ice sheet in the period from 2010 until 2014. The waveform parameters considered here are the backscatter...... waveform parameters to be applicable for correcting for changes in volume scattering. The best results in the Synthetic Aperture Radar Interferometric mode area of the GrIS are found when applying only the backscatter correction, whereas the best result in the Low Resolution Mode area is obtained by only......Long-term observations of surface elevation change of the Greenland ice sheet (GrIS) is of utmost importance when assessing the state of the ice sheet. Satellite radar altimetry offers a long time series of data over the GrIS, starting with ERS-1 in 1991. ESA's Cryosat-2 mission, launched in 2010...

  7. An explanation for the dark region in the western melt zone of the Greenland ice sheet

    Directory of Open Access Journals (Sweden)

    I. G. M. Wientjes

    2010-07-01

    Full Text Available The western part of the Greenland ice sheet contains a region that is darker than the surrounding ice. This feature has been analysed with the help of MODIS images. The dark region appears every year during the summer season and can always be found at the same location, which makes meltwater unlikely as the only source for the low albedos. Spectral information indicates that the ice in this region contains more debris than the ice closer to the margin. ASTER images reveal a wavy pattern in the darker ice. Based on these findings we conclude that ice, containing dust from older periods, is presently outcropping near the margin, leading to albedos lower than observed for the remaining ablation area. Therefore it can be concluded that the accumulation of meltwater is a result rather than a cause of the darkening.

  8. Future projections of the Greenland ice sheet energy balance driving the surface melt

    Directory of Open Access Journals (Sweden)

    B. Franco

    2013-01-01

    Full Text Available In this study, simulations at 25 km resolution are performed over the Greenland ice sheet (GrIS throughout the 20th and 21st centuries, using the regional climate model MAR forced by four RCP scenarios from three CMIP5 global circulation models (GCMs, in order to investigate the projected changes of the surface energy balance (SEB components driving the surface melt. Analysis of 2000–2100 melt anomalies compared to melt results over 1980–1999 reveals an exponential relationship of the GrIS surface melt rate simulated by MAR to the near-surface air temperature (TAS anomalies, mainly due to the surface albedo positive feedback associated with the extension of bare ice areas in summer. On the GrIS margins, the future melt anomalies are preferentially driven by stronger sensible heat fluxes, induced by enhanced warm air advection over the ice sheet. Over the central dry snow zone, the surface albedo positive feedback induced by the increase in summer melt exceeds the negative feedback of heavier snowfall for TAS anomalies higher than 4 °C. In addition to the incoming longwave flux increase associated with the atmosphere warming, GCM-forced MAR simulations project an increase of the cloud cover decreasing the ratio of the incoming shortwave versus longwave radiation and dampening the albedo feedback. However, it should be noted that this trend in the cloud cover is contrary to that simulated by ERA-Interim–forced MAR for recent climate conditions, where the observed melt increase since the 1990s seems mainly to be a consequence of more anticyclonic atmospheric conditions. Finally, no significant change is projected in the length of the melt season, which highlights the importance of solar radiation absorbed by the ice sheet surface in the melt SEB.

  9. An in situ measurement of the radio-frequency attenuation in ice at Summit Station, Greenland

    OpenAIRE

    Avva, J.; Kovac, J. M.; Miki, C.; Saltzberg, D.; Vieregg, A. G.

    2014-01-01

    We report an in situ measurement of the electric field attenuation length Lα at radio frequencies for the bulk ice at Summit Station, Greenland, made by broadcasting radio-frequency signals vertically through the ice and measuring the relative power in the return ground bounce signal. We find the depth-averaged field attenuation length to be hLαi = 947+92 −85 m at 75 MHz. While this measurement has clear radioglaciological applications, the radio clarity of the ice also has implications for t...

  10. 110 years of local glacier and ice cap changes in Central- and North East Greenland

    Science.gov (United States)

    Bjork, A. A.; Aagaard, S.; Kjaer, K. H.; Khan, S. A.; Box, J.

    2014-12-01

    The local glaciers and ice caps of Greenland are becoming more apparent players in global sea-level rise, and their contribution to future changes is significant. Very little information on their historical fluctuations exists as much of the focus has been on the Greenland Ice Sheet. Now, we can for the first time present historic data that spans 110 years for more than 200 of the local glaciers and ice caps covering this large and important region of the Arctic. The central- and north eastern part of Greenland is of particular interest as these areas are predicted to exhibit a more active behavior with higher mass loss in the future - simultaneously with an increase in precipitation. Our results show that the glaciers and ice caps in the region are responding very rapidly to changes in temperature and precipitation. The present retreat is the fastest observed within the last eight decades, only surpassed by the rapid post LIA retreat. The 1930s was the golden era for scientific exploration in Central- and North East Greenland as several large expeditions visited the area and photographed from land, sea and air. We use historic recordings from Danish and Norwegian aerial missions and terrestrial recordings from the renowned American Explorer Louise Boyd. These unique pictures from the early 1930s form the backbone of the study and are supplemented the more recent aerial photographs the 1940s and onwards and satellite imagery from the mid-1960s and up until present. From high resolution aerial photographs we are able to map the maximum extent of the glaciers during the LIA (Little Ice Age), from which retreat in this area is estimated to commence in 1900. Using a new SMB (Surface Mass Balance) model and its components covering the entire observational period along with high resolution DEMs and historic sea-ice records we are now able to extract valuable information on the past and present triggers of glacial change.

  11. Greenland Ice Sheet Monitoring Network (GLISN): Contributions to Science and Society

    Science.gov (United States)

    Anderson, K. R.; Bonaime, S.; Clinton, J. F.; Dahl-Jensen, T.; Debski, W. M.; Giardini, D.; Govoni, A.; Kanao, M.; Larsen, T. B.; Lasocki, S.; Lee, W. S.; McCormack, D. A.; Mykkeltveit, S.; Nettles, M.; Stutzmann, E.; Strollo, A.; Sweet, J. R.; Tsuboi, S.; Vallee, M.

    2017-12-01

    The Greenland Ice Sheet Monitoring Network (GLISN) is a broadband, multi-use seismological network, enhanced by selected geodetic observations, designed with the capability to allow researchers to understand the changes currently occurring in the Arctic, and with the operational characteristics necessary to enable response to those changes as understanding improves. GLISN was established through an international collaboration, with 10 nations coordinating their efforts to develop the current 34-station observing network during the last eight years. All of the data collected are freely and openly available in near-real time. The network was designed to transform the community capability for recording, analysis, and interpretation of seismic signals generated by discrete events in Greenland and the Arctic, as well as those traversing the region. Data from the network support a wide range of uses, including estimation of the properties of the solid Earth that control isostatic adjustment rates and set key boundary conditions for ice-sheet evolution; analysis of tectonic earthquakes throughout Greenland and the Arctic; study of the seismic signals associated with large calving events and changing glacier dynamics; and variations in ice and snow properties within the Greenland Ice Sheet. Recordings from the network have also provided invaluable data for rapid evaluation and understanding of the devastating landslide and tsunami that occurred near Nuugaatsiaq, Greenland, in June, 2017. The GLISN strategy of maximizing data quality from a network of approximately evenly distributed stations, delivering data in near-real time, and archiving a continuous data stream easily accessible to researchers, allows continuous discovery of new uses while also facilitating the generation of data products, such as catalogs of tectonic and glacial earthquakes and GPS-based estimates of snow height, that allow for assessment of change over time.

  12. Validation and operational measurements with SUSIE – A sar ice motion processing chain developed within promice (Programme for monitoring of Greenland ice-sheet)

    DEFF Research Database (Denmark)

    Merryman Boncori, John Peter; Dall, Jørgen; Ahlstrøm, A. P.

    2010-01-01

    This paper describes the validation of an ice-motion processing chain developed for the PROMICE project – a long-term program funded by the Danish ministry of Climate and Energy to monitor the mass budget of the Greenland ice-sheet. The processor, named SUSIE, (Scripts and Utilities for SAR Ice...

  13. Meltwater chemistry and solute export from a Greenland ice sheet catchment, Watson River, West Greenland

    DEFF Research Database (Denmark)

    Yde, Jacob C.; Knudsen, N. Tvis; Hasholt, Bent

    2014-01-01

    –2010 for the Watson River sector of the GrIS that drains into the fjord Kangerlussuaq. The hydrochemistry is dominated by Ca2+ and HCO3− with a relatively high molar K+/Na+ ratio of 0.6 ± 0.1, typical for meltwaters draining a gneissic lithology. Low molar Ca2+/Na+ and Mg2+/Na+ ratios indicate that weathering....... However, when normalized by discharge the denudation rates are comparable to other Arctic sites. When extrapolating the results from the Watson River catchment to the entire Greenland for 2007–2010, the solute export from Greenland meltwater varied between 7.1 × 106 and 7.8 × 106 tons, whilst the major...

  14. The Distribution of Basal Water Beneath the Greenland Ice Sheet from Radio-Echo Sounding

    Science.gov (United States)

    Jordan, T.; Williams, C.; Schroeder, D. M.; Martos, Y. M.; Cooper, M.; Siegert, M. J.; Paden, J. D.; Huybrechts, P.; Bamber, J. L.

    2017-12-01

    There is widespread, but often indirect, evidence that a significant fraction of the Greenland Ice Sheet is thawed at the bed. This includes major outlet glaciers and around the NorthGRIP ice-core in the interior. However, the ice-sheet-wide distribution of basal water is poorly constrained by existing observations, and the spatial relationship between basal water and other ice-sheet and subglacial properties is therefore largely unexplored. In principle, airborne radio-echo sounding (RES) surveys provide the necessary information and spatial coverage to infer the presence of basal water at the ice-sheet scale. However, due to uncertainty and spatial variation in radar signal attenuation, the commonly used water diagnostic, bed-echo reflectivity, is highly ambiguous and prone to spatial bias. Here we introduce a new RES diagnostic for the presence of basal water which incorporates both sharp step-transitions and rapid fluctuations in bed-echo reflectivity. This has the advantage of being (near) independent of attenuation model, and enables a decade of recent Operation Ice Bride RES survey data to be combined in a single map for basal water. The ice-sheet-wide water predictions are compared with: bed topography and drainage network structure, existing knowledge of the thermal state and geothermal heat flux, and ice velocity. In addition to the fast flowing ice-sheet margins, we also demonstrate widespread water routing and storage in parts of the slow-flowing northern interior. Notably, this includes a quasi-linear `corridor' of basal water, extending from NorthGRIP to Petermann glacier, which spatially correlates with a region of locally high (magnetic-derived) geothermal heat flux. The predicted water distribution places a new constraint upon the basal thermal state of the Greenland Ice Sheet, and could be used as an input for ice-sheet model simulations.

  15. Climate change and forest fires synergistically drive widespread melt events of the Greenland Ice Sheet.

    Science.gov (United States)

    Keegan, Kaitlin M; Albert, Mary R; McConnell, Joseph R; Baker, Ian

    2014-06-03

    In July 2012, over 97% of the Greenland Ice Sheet experienced surface melt, the first widespread melt during the era of satellite remote sensing. Analysis of six Greenland shallow firn cores from the dry snow region confirms that the most recent prior widespread melt occurred in 1889. A firn core from the center of the ice sheet demonstrated that exceptionally warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires reduced albedo below a critical threshold in the dry snow region, and caused the melting events in both 1889 and 2012. We use these data to project the frequency of widespread melt into the year 2100. Since Arctic temperatures and the frequency of forest fires are both expected to rise with climate change, our results suggest that widespread melt events on the Greenland Ice Sheet may begin to occur almost annually by the end of century. These events are likely to alter the surface mass balance of the ice sheet, leaving the surface susceptible to further melting.

  16. Using Airborne Lidar Data from IcePod to Measure Annual and Seasonal Ice Changes Over Greenland

    Science.gov (United States)

    Frearson, N.; Bertinato, C.; Das, I.

    2014-12-01

    The IcePod is a multi-sensor airborne science platform that supports a wide suite of instruments, including a Riegl VQ-580 infrared scanning laser, GPS-inertial positioning system, shallow and deep-ice radars, visible-wave and infrared cameras, and upward-looking pyrometer. These instruments allow us to image the ice from top to bottom, including the surface of melt-water plumes that originate at the ice-ocean boundary. In collaboration with the New York Air National Guard 109th Airlift Wing, the IcePod is flown on LC-130 aircraft, which presents the unique opportunity to routinely image the Greenland ice sheet several times within a season. This is particularly important for mass balance studies, as we can measure elevation changes during the melt season. During the 2014 summer, laser data was collected via IcePod over the Greenland ice sheet, including Russell Glacier, Jakobshavn Glacier, Eqip Glacier, and Summit Camp. The Icepod will also be routinely operated in Antarctica. We present the initial testing, calibration, and error estimates from the first set of laser data that were collected on IcePod. At a survey altitude of 1000 m, the laser swath covers ~ 1000 m. A Northrop-Grumman LN-200 tactical grade IMU is rigidly attached to the laser scanner to provide attitude data at a rate of 200 Hz. Several methods were used to determine the lever arm between the IMU center of navigation and GPS antenna phase center, terrestrial scanning laser, total station survey, and optimal estimation. Additionally, initial bore sight calibration flights yielded misalignment angles within an accuracy of ±4 cm. We also performed routine passes over the airport ramp in Kangerlussuaq, Greenland, comparing the airborne GPS and Lidar data to a reference GPS-based ground survey across the ramp, spot GPS points on the ramp and a nearby GPS base station. Positioning errors can severely impact the accuracy of a laser altimeter when flying over remote regions such as across the ice sheets

  17. Detection of Organic Matter in Greenland Ice Cores by Deep-UV Fluorescence

    Science.gov (United States)

    Willis, M.; Malaska, M.; Wanger, G.; Bhartia, R.; Eshelman, E.; Abbey, W.; Priscu, J. C.

    2017-12-01

    The Greenland Ice Sheet is an Earthly analog for icy ocean worlds in the outer Solar System. Future missions to such worlds including Europa, Enceladus, and Titan may potentially include spectroscopic instrumentation to examine the surface/subsurface. The primary goal of our research is to test deep UV/Raman systems for in the situ detection and localization of organics in ice. As part of this effort we used a deep-UV fluorescence instrument able to detect naturally fluorescent biological materials such as aromatic molecules found in proteins and whole cells. We correlated these data with more traditional downstream analyses of organic material in natural ices. Supraglacial ice cores (2-4 m) were collected from several sites on the southwest outlet of the Greenland Ice Sheet using a 14-cm fluid-free mechanical coring system. Repeat spectral mapping data were initially collected longitudinally on uncut core sections. Cores were then cut into 2 cm thick sections along the longitudinal axis, slowly melted and analyzed for total organic carbon (TOC), total dissolved nitrogen (TDN), and bacterial density. These data reveal a spatial correlation between organic matter concentration, cell density, and the deep UV fluorescence maps. Our results provide a profile of the organics embedded within the ice from the top surface into the glacial subsurface, and the TOC:TDN data from the clean interior of the cores are indicative of a biological origin. This work provides a background dataset for future work to characterize organic carbon in the Greenland Ice Sheet and validation of novel instrumentation for in situ data collection on icy bodies.

  18. Toward Monitoring Surface and Subsurface Lakes on the Greenland Ice Sheet Using Sentinel-1 SAR and Landsat-8 OLI Imagery

    Directory of Open Access Journals (Sweden)

    Katie E. Miles

    2017-07-01

    Full Text Available Supraglacial lakes are an important component of the Greenland 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 satellite to investigate supraglacial lakes in West Greenland. A semi-automated algorithm is developed to detect surface lakes from Sentinel-1 images during the 2015 summer. A combined Landsat-8 and Sentinel-1 dataset, which has a comparable temporal resolution to MODIS (3 days vs. daily but a higher spatial resolution (25–40 vs. 250–500 m, is then used together with a fully automated lake drainage detection algorithm. Rapid (<4 days and slow (>4 days drainages are investigated for both small (<0.125 km2, the minimum size detectable by MODIS and large (≥0.125 km2 lakes through the summer. Drainage events of small lakes occur at lower elevations (mean 159 m, and slightly earlier (mean 4.5 days in the melt season than those of large lakes. The analysis is 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; 1,270 m mean elevation. Finally, the Sentinel-1 imagery is used to detect subsurface lakes and, for the first time, their dates of appearance and freeze-through (mean 9 August and 7 October, respectively. These subsurface lakes occur at higher elevations than the surface lakes detected in this study (mean 1,593 and 1,185 m, respectively. Sentinel-1 imagery therefore provides great potential for tracking melting, water movement and freezing within both the firn zone and ablation area of the Greenland Ice Sheet.

  19. Towards monitoring surface and subsurface lakes on the Greenland Ice Sheet using Sentinel-1 SAR and Landsat-8 OLI imagery

    Science.gov (United States)

    Miles, Katie E.; Willis, Ian C.; Benedek, Corinne L.; Williamson, Andrew G.; Tedesco, Marco

    2017-07-01

    Supraglacial lakes are an important component of the Greenland 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) satellite to investigate supraglacial lakes in West Greenland. A semi-automated algorithm is developed to detect surface lakes from Sentinel-1 images during the 2015 summer. A combined Landsat-8 and Sentinel-1 dataset, which has a comparable temporal resolution to MODIS (3 days versus daily) but a higher spatial resolution (25-40 m versus 250-500 m), is then used together with a fully-automated lake drainage detection algorithm. Rapid (days) and slow (> 4 days) drainages are investigated for both small (summer. Drainage events of small lakes occur at lower elevations (mean 159 m), and slightly earlier (mean 4.5 days) in the melt season than those of large lakes. The analysis is 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-1 imagery is used to detect subsurface lakes and, for the first time, their dates of appearance and freeze-through (mean 9 August and 7 October, respectively). These subsurface lakes occur at higher elevations than the surface lakes detected in this study (mean 1593 m and 1185 m, respectively). Sentinel-1 imagery therefore provides great potential for tracking melting, water movement and freezing within both the firn zone and ablation area of the Greenland Ice Sheet.

  20. A new regional high-resolution map of basal and surface topography for the Greenland ice-sheet margin at Paakitsoq, West Greenland

    DEFF Research Database (Denmark)

    Mottram, R.; Nielsen, C.; Ahlstrøm, A. P.

    2009-01-01

    In 2005 an airborne survey was carried out from a Twin Otter aircraft at Pâkitsup Akuliarusersua (Paakitsoq) near Ilulissat in West Greenland. The survey aimed to measure ice thickness with a 60 MHz cohrent radar and surface elevation with a scanning laser altimeter.......In 2005 an airborne survey was carried out from a Twin Otter aircraft at Pâkitsup Akuliarusersua (Paakitsoq) near Ilulissat in West Greenland. The survey aimed to measure ice thickness with a 60 MHz cohrent radar and surface elevation with a scanning laser altimeter....

  1. Levels of ammonium, sulfate, chloride, calcium, and sodium in snow and ice from southern Greenland

    International Nuclear Information System (INIS)

    Busenberg, E.; Langway, C.C. Jr.

    1979-01-01

    Chemical analysis of surface snows and dated ice core samples from Dye 3, Greenland, suggests that the ammonium cation is a major constituent in all samples and that the annual ammonium levels present in the south Greenland samples have varied from 3.3 to 26.3 μg/kg between the seventeenth century and the present time. The annual range of 1974--1975 surface samples was between 3.8 and 8.8 μg/kg, while the mean was 5.7 +- 1.8 μ/kg. The recent large-scale uses of fixed nitrogen fertilizers and industrial pollution have apparently not affected the levels of ammonia reaching southern Greenland. The sodium and chloride present are predominantly derived from ocean spray, while more than 90% of the calcium is of continental origin. The levels of these three elements have not apparently been affected by human activity since the industrial revolution. Sulfate levels have increased dramatically since the industrial revolution, suggesting that sulfate of anthropogenic origin is the most important source of sulfate in modern snows from southern Greenland. The amount of the sulfuric acid neutralized by the ammonium cations was approximately 100% in the seventeenth and eighteenth centuries, dropping to approximately 20% in the 1974--1975 samples. These figures imply that there has been in increase in the acidity of precipitation in southern Greenland since the end of the eighteenth ce

  2. Generation of a new Greenland Ice Sheet Digital Elevation Model

    DEFF Research Database (Denmark)

    Nagarajan, Sudhagar; Csatho, Beata M; Schenk, Anton F

    conditions, by fusing a photoclinometry DEM, SPOT and ASTER DEMs as well as elevations from ICESat, ATM and LVIS laser altimetry. The new multi-resolution DEM has a resolution of 40 m x 40 m in the marginal ice sheet regions and 250 m elsewhere. The ice sheet margin is mapped from SPOT and Landsat imagery...

  3. Oceanic Transport of Surface Meltwater from the Southern Greenland Ice Sheet

    Science.gov (United States)

    Luo, Hao; Castelao, Renato M.; Rennermalm, Asa K.; Tedesco, Marco; Bracco, Annalisa; Yager, Patricia L.; Mote, Thomas L.

    2016-01-01

    The Greenland ice sheet has undergone accelerating mass losses during recent decades. Freshwater runoff from ice melt can influence fjord circulation and dynamic1 and the delivery of bioavailable micronutrients to the ocean. It can also have climate implications, because stratification in the adjacent Labrador Sea may influence deep convection and the strength of the Atlantic meridional overturning circulation. Yet, the fate of the meltwater in the ocean remains unclear. Here, we use a high-resolution ocean model to show that only 1-15% of the surface meltwater runoff originating from southwest Greenland is transported westwards. In contrast, up to 50-60% of the meltwater runoff originating from southeast Greenland is transported westwards into the northern Labrador Sea, leading to significant salinity and stratification anomalies far from the coast. Doubling meltwater runoff, as predicted in future climate scenarios, results in a more-than-double increase in anomalies offshore that persists further into the winter. Interannual variability in offshore export of meltwater is tightly related to variability in wind forcing. The new insight that meltwaters originating from the west and east coasts have different fates indicates that future changes in mass loss rates and surface runoff will probably impact the ocean differently, depending on their Greenland origins.

  4. Local processes and regional patterns - Interpreting a multi-decadal altimetry record of Greenland Ice Sheet changes

    Science.gov (United States)

    Csatho, B. M.; Schenk, A. F.; Babonis, G. S.; van den Broeke, M. R.; Kuipers Munneke, P.; van der Veen, C. J.; Khan, S. A.; Porter, D. F.

    2016-12-01

    This study presents a new, comprehensive reconstruction of Greenland Ice Sheet elevation changes, generated using the Surface Elevation And Change detection (SERAC) approach. 35-year long elevation-change time series (1980-2015) were obtained at more than 150,000 locations from observations acquired by NASA's airborne and spaceborne laser altimeters (ATM, LVIS, ICESat), PROMICE laser altimetry data (2007-2011) and a DEM covering the ice sheet margin derived from stereo aerial photographs (1970s-80s). After removing the effect of Glacial Isostatic Adjustment (GIA) and the elastic crustal response to changes in ice loading, the time series were partitioned into changes due to surface processes and ice dynamics and then converted into mass change histories. Using gridded products, we examined ice sheet elevation, and mass change patterns, and compared them with other estimates at different scales from individual outlet glaciers through large drainage basins, on to the entire ice sheet. Both the SERAC time series and the grids derived from these time series revealed significant spatial and temporal variations of dynamic mass loss and widespread intermittent thinning, indicating the complexity of ice sheet response to climate forcing. To investigate the regional and local controls of ice dynamics, we examined thickness change time series near outlet glacier grounding lines. Changes on most outlet glaciers were consistent with one or more episodes of dynamic thinning that propagates upstream from the glacier terminus. The spatial pattern of the onset, duration, and termination of these dynamic thinning events suggest a regional control, such as warming ocean and air temperatures. 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. We use statistical methods, such as principal

  5. Mapping of a Hydrological Ice Sheet Drainage Basin on the West Greenland Ice Sheet Margin from ERS-1/2 SAR Interferometry, Ice-Radar Measurement, and Modelling

    DEFF Research Database (Denmark)

    Ahlstrøm, Andreas P.; Bøggild, C.E.; Stenseng, L.

    2002-01-01

    importance of the potential of the ice overburden pressure compared to the bedrock topography. The meltwater run-off for the basin delineations was modelled with an energy-balance model calibrated with observed ice-sheet ablation and compared to a 25 year time series of measured basin run-off. The standard......The hydrological ice-sheet basin draining into the Tasersiaq lake, West Greenland (66°13'N, 50°30'W), was delineated, First using standard digital elevation models (DEMs) for ice-sheet surface and bedrock, and subsequently using a new high-resolution dataset, with a surface DEM derived from repeat......-track interferometric synthetic aperture radar (SAR) and a bedrock topography derived from an airborne 60 MHz ice-penetrating radar. The extent of the delineation was calculated from a water-pressure potential as a function of the ice-sheet surface and bedrock elevations and a hydraulic factor κ describing the relative...

  6. Classification of new-ice in the Greenland Sea using Satellite SSM/I radiometer and SeaWinds scatterometer data and comparison with ice model

    DEFF Research Database (Denmark)

    Tonboe, Rasmus; Pedersen, Leif Toudal

    2005-01-01

    In the ice covered waters of the Greenland Sea the polarisation ratio of QuikSCAT SeaWinds Ku-band (13.4 GHz) scatterometer measurements and the polarisation ratio of DMSP-SSM/I 19 GHz radiometer measurements are used in combination to classify new-ice and mature ice. In particular, the formation...... to the physical transition of the ice cover from pancake ice to a consolidated young-ice sheet. The classification of each pixel into ice or water is done using two scatterometer parameters, namely the polarisation ratio and the daily standard deviation of the backscatter. (C) 2005 Elsevier Inc. All rights...

  7. Modeling the Sulfate Deposition to the Greenland Ice Sheet From the Laki Eruption

    Science.gov (United States)

    Oman, L.; Robock, A.; Stenchikov, G.; Thordarson, T.; Gao, C.

    2005-12-01

    Using the state of the art Goddard Institute for Space Studies (GISS) modelE general circulation model, simulations were conducted of the chemistry and transport of aerosols resulting from the 1783-84 Laki (64°N) flood lava eruption. A set of 3 ensemble simulations from different initial conditions were conducted by injecting our estimate of the SO2 gas into the atmosphere by the 10 episodes of the eruption and allowing the sulfur chemistry model to convert this gas into sulfate aerosol. The SO2 gas and sulfate aerosol is transported by the model and wet and dry deposition is calculated over each grid box during the simulation. We compare the resulting sulfate deposition to the Greenland Ice Sheet in the model to 23 ice core measurements and find very good agreement. The model simulation deposits a range of 169 to over 300 kg/km2 over interior Greenland with much higher values along the coastal areas. This compares to a range of 62 to 324 kg/km2 for the 23 ice core measurements with an average value of 158 kg/km2. This comparison is one important model validation tool. Modeling and observations show fairly large spatial variations in the deposition of sulfate across the Greenland Ice Sheet for the Laki eruption, but the patterns are similar to those we modeled for the 1912 Katmai and 1991 Pinatubo eruptions. Estimates of sulfate loading based on single ice cores can show significant differences, so ideally several ice cores should be combined in reconstructing the sulfate loading of past volcanic eruptions, taking into account the characteristic spatial variations in the deposition pattern.

  8. Hypsometric amplification and routing moderation of Greenland ice sheet meltwater release

    Directory of Open Access Journals (Sweden)

    D. van As

    2017-06-01

    Full Text Available Concurrent ice sheet surface runoff and proglacial discharge monitoring are essential for understanding Greenland ice sheet meltwater release. We use an updated, well-constrained river discharge time series from the Watson River in southwest Greenland, with an accurate, observation-based ice sheet surface mass balance model of the  ∼  12 000 km2 ice sheet area feeding the river. For the 2006–2015 decade, we find a large range of a factor of 3 in interannual variability in discharge. The amount of discharge is amplified  ∼  56 % by the ice sheet's hypsometry, i.e., area increase with elevation. A good match between river discharge and ice sheet surface meltwater production is found after introducing elevation-dependent transit delays that moderate diurnal variability in meltwater release by a factor of 10–20. The routing lag time increases with ice sheet elevation and attains values in excess of 1 week for the upper reaches of the runoff area at  ∼  1800 m above sea level. These multi-day routing delays ensure that the highest proglacial discharge levels and thus overbank flooding events are more likely to occur after multi-day melt episodes. Finally, for the Watson River ice sheet catchment, we find no evidence of meltwater storage in or release from the en- and subglacial environments in quantities exceeding our methodological uncertainty, based on the good match between ice sheet runoff and proglacial discharge.

  9. New marine geophysical and sediment record of the Northeast Greenland Ice Stream.

    Science.gov (United States)

    Callard, L.; Roberts, D. H.; O'Cofaigh, C.; Lloyd, J. M.; Smith, J. A.; Dorschel, B.

    2017-12-01

    The NE Greenland Ice Stream (NEGIS) drains 16% of the Greenland Ice Sheet (GrIS) 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 GrIS 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

  10. Observations of runoff and sediment and dissolved loads from the Greenland Ice Sheet at Kangerlussuaq, West Greenland, 2007 to 2010

    DEFF Research Database (Denmark)

    Hasholt, Bent; Mikkelsen, Andreas Peter Bech; Nielsen, Morten Holtegaard

    2012-01-01

    Observations from 2007 to 2010 of runoff, sediment and solute delivery from a segment of the Greenland Ice Sheet (GrIS) and the proglacial landscape draining into the fjord at Kangerlussuaq are presented. The observations include at least three jökulhlaups and extreme recordings from 2010...... previously published for 2007 and 2008. The average effective erosion from the catchment was 0.28 mm (min. 0.18 and max. 0.45 mm). The erosion is larger than indicated from most other locations along the GrIS, but in the same order of magnitude as erosion in other glaciated areas at the same latitude, e.......g. Norway. The sandur in the proglacial area acts as a sediment sink for a lot of the sediments from the GrIS....

  11. Holocene landscape history and ground ice distribution in Svalbard and NE-Greenland

    DEFF Research Database (Denmark)

    Cable, Stefanie

    This PhD study contributes to the scarce knowledge of permafrost dynamics in mountainous terrain. In High-Arctic valleys, on Svalbard and in NE-Greenland, linkages between geomorphology and ground ice- and carbon distribution have been described, quantified and compared between landscape types...... and locations. To achieve this, detailed geomorphological mapping was combined with cryostratigraphic and laboratory analyses (grain size, solutes, radiocarbon- and optically stimulated luminescence-age) of 31 permafrost cores (up to 16 m) from seven different landforms. Ground ice in permafrost has been...

  12. Direct observation of salts as micro-inclusions in the Greenland GRIP ice core

    DEFF Research Database (Denmark)

    Dahl-Jensen, Dorthe; Sakurai, Toshimitsu; Iizuka, Yoshinori

    2009-01-01

    We provide the first direct evidence that a number of water-soluble compounds, in particular calcium sulfate (CaSO4·2H2O) and calcium carbonate (CaCO3), are present as solid, micron-sized inclusions within the Greenland GRIP ice core. The compounds are detected by two independent methods: micro...... distributions of the micro-inclusions. These results suggest that water-soluble aerosols in the GRIP ice core are dependable proxies for past atmospheric conditions. Udgivelsesdato: December...

  13. Design and results of the ice sheet model initialisation initMIP-Greenland: an ISMIP6 intercomparison

    Directory of Open Access Journals (Sweden)

    H. Goelzer

    2018-04-01

    Full Text Available Earlier large-scale Greenland ice sheet sea-level projections (e.g. those run during the ice2sea and SeaRISE initiatives have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. The goal of this initMIP-Greenland intercomparison exercise is to compare, evaluate, and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6, which is the primary activity within the Coupled Model Intercomparison Project Phase 6 (CMIP6 focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of (1 the initial present-day state of the ice sheet and (2 the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing and in response to a large perturbation (prescribed surface mass balance anomaly; they should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions, and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises.

  14. Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison

    Science.gov (United States)

    Goelzer, Heiko; Nowicki, Sophie; Edwards, Tamsin; Beckley, Matthew; Abe-Ouchi, Ayako; Aschwanden, Andy; Calov, Reinhard; Gagliardini, Olivier; Gillet-Chaulet, Fabien; Golledge, Nicholas R.; Gregory, Jonathan; Greve, Ralf; Humbert, Angelika; Huybrechts, Philippe; Kennedy, Joseph H.; Larour, Eric; Lipscomb, William H.; Le clec'h, Sébastien; Lee, Victoria; Morlighem, Mathieu; Pattyn, Frank; Payne, Antony J.; Rodehacke, Christian; Rückamp, Martin; Saito, Fuyuki; Schlegel, Nicole; Seroussi, Helene; Shepherd, Andrew; Sun, Sainan; van de Wal, Roderik; Ziemen, Florian A.

    2018-04-01

    Earlier large-scale Greenland ice sheet sea-level projections (e.g. those run during the ice2sea and SeaRISE initiatives) have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. The goal of this initMIP-Greenland intercomparison exercise is to compare, evaluate, and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6), which is the primary activity within the Coupled Model Intercomparison Project Phase 6 (CMIP6) focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of (1) the initial present-day state of the ice sheet and (2) the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing) and in response to a large perturbation (prescribed surface mass balance anomaly); they should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions, and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises.

  15. Land motion due to 20th century mass balance of the Greenland Ice Sheet

    Science.gov (United States)

    Kjeldsen, K. K.; Khan, S. A.

    2017-12-01

    Quantifying the contribution from ice sheets and glaciers to past sea level change is of great value for understanding sea level projections into the 21st century. However, quantifying and understanding past changes are equally important, in particular understanding the impact in the near-field where the signal is highest. We assess the impact of 20th century mass balance of the Greenland Ice Sheet on land motion using results from Kjeldsen et al, 2015. These results suggest that the ice sheet on average lost a minimum of 75 Gt/yr, but also show that the mass balance was highly spatial- and temporal variable, and moreover that on a centennial time scale changes were driven by a decreasing surface mass balance. Based on preliminary results we discuss land motion during the 20th century due to mass balance changes and the driving components surface mass balance and ice dynamics.

  16. A Bayesian Retrieval of Greenland Ice Sheet Internal Temperature from Ultra-wideband Software-defined Microwave Radiometer (UWBRAD) Measurements

    Science.gov (United States)

    Duan, Y.; Durand, M. T.; Jezek, K. C.; Yardim, C.; Bringer, A.; Aksoy, M.; Johnson, J. T.

    2017-12-01

    The ultra-wideband software-defined microwave radiometer (UWBRAD) is designed to provide ice sheet internal temperature product via measuring low frequency microwave emission. Twelve channels ranging from 0.5 to 2.0 GHz are covered by the instrument. A Greenland air-borne demonstration was demonstrated in September 2016, provided first demonstration of Ultra-wideband radiometer observations of geophysical scenes, including ice sheets. Another flight is planned for September 2017 for acquiring measurements in central ice sheet. A Bayesian framework is designed to retrieve the ice sheet internal temperature from simulated UWBRAD brightness temperature (Tb) measurements over Greenland flight path with limited prior information of the ground. A 1-D heat-flow model, the Robin Model, was used to model the ice sheet internal temperature profile with ground information. Synthetic UWBRAD Tb observations was generated via the partially coherent radiation transfer model, which utilizes the Robin model temperature profile and an exponential fit of ice density from Borehole measurement as input, and corrupted with noise. The effective surface temperature, geothermal heat flux, the variance of upper layer ice density, and the variance of fine scale density variation at deeper ice sheet were treated as unknown variables within the retrieval framework. Each parameter is defined with its possible range and set to be uniformly distributed. The Markov Chain Monte Carlo (MCMC) approach is applied to make the unknown parameters randomly walk in the parameter space. We investigate whether the variables can be improved over priors using the MCMC approach and contribute to the temperature retrieval theoretically. UWBRAD measurements near camp century from 2016 was also treated with the MCMC to examine the framework with scattering effect. The fine scale density fluctuation is an important parameter. It is the most sensitive yet highly unknown parameter in the estimation framework

  17. New geoid of Greenland: A case study of terrain and ice effects, GOCE and use of local sea level data

    DEFF Research Database (Denmark)

    Forsberg, René; Jensen, Tim Enzlberger

    2015-01-01

    Making an accurate geoid model of Greenland has always been a challenge due to the ice sheet and glaciers, and the rough topography and deep fjords in the ice free parts. Terrestrial gravity coverage has for the same reasons been relatively sparse, with an older airborne survey of the interior be...

  18. Holocene glacial history of the west Greenland Ice Sheet inferred from cosmogenic exposure ages and threshold lakes

    DEFF Research Database (Denmark)

    Larsen, Nicolaj Krog; Kjaer, K. H.; Colding, Sune Oluf

    2011-01-01

    In this study, we use a combination of 10Be exposure ages and threshold lakes to constrain the ice sheet history in Godthåbs- and Buksefjorden, west Greenland (63-64°N) during the Holocene. The 10Be cosmogenic exposure ages have been used to quantify both the ice retreat and thinning of the west...

  19. Elevation change of the Greenland Ice Sheet due to surface mass balance and firn processes, 1960-2014

    NARCIS (Netherlands)

    Kuipers Munneke, P.; Ligtenberg, S. R M; Noël, B. P Y; Howat, I. M.; Box, J. E.; Mosley-Thompson, E.; McConnell, J. R.; Steffen, K.; Harper, J. T.; Das, S. B.; Van Den Broeke, M. R.

    2015-01-01

    Observed changes in the surface elevation of the Greenland Ice Sheet are caused by ice dynamics, basal elevation change, basal melt, surface mass balance (SMB) variability, and by compaction of the overlying firn. The last two contributions are quantified here using a firn model that includes

  20. Estimating the rates of mass change, ice volume change and snow volume change in Greenland from ICESat and GRACE data

    NARCIS (Netherlands)

    Slobbe, D.C.; Ditmar, P.G.; Lindenbergh, R.C.

    2008-01-01

    The focus of this paper is on the quantification of ongoing mass and volume changes over the Greenland ice sheet. For that purpose, we used elevation changes derived from the Ice, Cloud, and land Elevation Satellite (ICESat) laser altimetry mission and monthly variations of the Earth’s gravity field

  1. Envisat-derived elevation changes of the Greenland ice sheet, and a comparison with ICESat results in the accumulation area

    DEFF Research Database (Denmark)

    Sørensen, Louise Sandberg; Simonsen, Sebastian Bjerregaard; Meister, Rakia

    2015-01-01

    We show, for the first time over the Greenland ice sheet, that an along track method for deriving rates of elevationchange can successfully be applied to Envisat radar altimetry data (2002–2010). The results provide improved resolution and coverage compared to previous results obtained from cross......-over methods. Also, we find that temporal changes in the elevation change rate can be derived from Envisat data, and show clearexamples of this by generating five-year running means for selected areas of the Greenland ice sheet. For a period between 2003 and 2009, the elevation of the ice sheetswas measured...

  2. Measurement of spectral sea ice albedo at Qaanaaq fjord in northwest Greenland

    Science.gov (United States)

    Tanikawa, T.

    2017-12-01

    The spectral albedos of sea ice were measured at Qaanaaq fjord in northwest Greenland. Spectral measurements were conducted for sea ice covered with snow and sea ice without snow where snow was artificially removed around measurement point. Thickness of the sea ice was approximately 1.3 m with 5 cm of snow over the sea ice. The measurements show that the spectral albedos of the sea ice with snow were lower than those of natural pure snow especially in the visible regions though the spectral shapes were similar to each other. This is because the spectral albedos in the visible region have information of not only the snow but also the sea ice under the snow. The spectral albedos of the sea ice without the snow were approximately 0.4 - 0.5 in the visible region, 0.05-0.25 in the near-infrared region and almost constant of approximately 0.05 in the region of 1500 - 2500 nm. In the visible region, it would be due to multiple scattering by an air bubble within the sea ice. In contrast, in the near-infrared and shortwave infrared wavelengths, surface reflection at the sea ice surface would be dominant. Since a light absorption by the ice in these regions is relatively strong comparing to the visible region, the light could not be penetrated deeply within the sea ice, resulting that surface reflection based on Fresnel reflection would be dominant. In this presentation we also show the results of comparison between the radiative transfer calculation and spectral measurement data.

  3. Improved retrieval of land ice topography from CryoSat-2 data and its impact for volume-change estimation of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Nilsson, Johan; Gardner, Alex; Sørensen, Louise Sandberg

    2016-01-01

    of the snow/ice surface with lower sensitivity to changes in near-surface dielectric properties. To demonstrate the utility of the new processing methodology we produce elevations, elevation changes, and total volume changes from CryoSat-2 data for the Greenland Ice Sheet during the period January 2011...... to January 2015. We find that the Greenland Ice Sheet decreased in volume at a rate of 289 ± 20km3 a-1, with high interannual variability and spatial heterogeneity in rates of loss. This rate is 65km3 a-1 more negative than rates determined from ESA's L2 product, highlighting the importance of CryoSat-2...

  4. A new field experiment in the Greenland ice cap to test Newton's inverse square law

    International Nuclear Information System (INIS)

    Ander, M.E.; Nieto, M.M.; Zumberge, M.A.; Parker, R.L.; Lautzenhiser, T.; Aiken, C.L.V.; Ferguson, J.F.; McMechan, G.A.

    1989-01-01

    Recent experimental evidence suggests that Newton's law of gravity may not be precise. There are modern theories of quantum gravity that, in their attempts to unify gravity with other forces of nature, predict non-Newtonian gravitational forces that could have ranges on the order of 10 2 --10 5 m. If they exist, these forces would be apparent as violations of Newton's inverse square law. A geophysical experiment was carried out to search for possible finite-range, non-Newtonian gravity over depths of 213--1673 m in the glacial ice of the Greenland ice cap. The principal reason for this choice of experimental site is that a hole drilled through the ice cap already existed and the uniformity of the ice eliminates one of the major sources of uncertainty arising in the first of earlier studies, namely, the heterogeneity of the rocks through which a mine shaft or drill hole passes. This paper presents observations made in the summer of 1987 at Dye 3, Greenland, in the 2033-m-deep borehole, which reached the basement rock

  5. Coupling of climate models and ice sheet models by surface mass balance gradients: application to the Greenland Ice Sheet

    Directory of Open Access Journals (Sweden)

    M. M. Helsen

    2012-03-01

    Full Text Available It is notoriously difficult to couple surface mass balance (SMB results from climate models to the changing geometry of an ice sheet model. This problem is traditionally avoided by using only accumulation from a climate model, and parameterizing the meltwater run-off as a function of temperature, which is often related to surface elevation (Hs. In this study, we propose a new strategy to calculate SMB, to allow a direct adjustment of SMB to a change in ice sheet topography and/or a change in climate forcing. This method is based on elevational gradients in the SMB field as computed by a regional climate model. Separate linear relations are derived for ablation and accumulation, using pairs of Hs and SMB within a minimum search radius. The continuously adjusting SMB forcing is consistent with climate model forcing fields, also for initially non-glaciated areas in the peripheral areas of an ice sheet. When applied to an asynchronous coupled ice sheet – climate model setup, this method circumvents traditional temperature lapse rate assumptions. Here we apply it to the Greenland Ice Sheet (GrIS. Experiments using both steady-state forcing and glacial-interglacial forcing result in realistic ice sheet reconstructions.

  6. Ice-Ocean Interactions to the North-West of Greenland: Glaciers, Straits, Ice Bridges, and the Rossby Radius (Invited)

    Science.gov (United States)

    Muenchow, A.; Falkner, K. K.; Melling, H.; Johnson, H. L.; Huntley, H. S.; Ryan, P.; Friends Of Petermann

    2010-12-01

    Petermann Glacier at 81 N latitude is a major outlet glacier adjacent to Nares Strait. It terminates in a long (70 km), narrow (16 km) and thin (50 m) floating tongue and has a grounding line more than 500 m below sea level. A calving event in 2010 reduced the floating area by 25% and produced a single 240 km2 ice island currently moving south in Nares Strait where it will likely interact with island to potentially create a temporary polynya in Nares Strait. The 2010 calving from Petermann Glacier contributes bridge formed regularly at the southern end of Nares Strait creating the North-Water polynya near 79 N latitude. Since 2006 this ice bridge has largely failed to form, leading, perhaps, to the occasional formation of a secondary ice bridge 300 km to the north where Nares Strait connects to the Arctic Ocean. However, this ice bridge appears to form for shorter periods only. Consequently Arctic sea ice can now exit the Arctic in winter via pathways to the west of Greenland all year. We speculate that this changed ocean and sea ice regime in Nares Strait and the Arctic Ocean may contribute to the recently observed calving events in Petermann Fjord.

  7. Mass loss from the southern half of the Greenland Ice Sheet since the Little Ice Age Maximum

    DEFF Research Database (Denmark)

    Kjeldsen, Kristian Kjellerup; Kjær, Kurt H.; Bjørk, Anders Anker

    Northern hemisphere temperatures reached their Holocene minimum and most glaciers reached their maximum during The Little Ice Age (LIA), but the timing of specific cold intervals is site-specific. In southern Greenland, we have compiled data from organic matter incorporated in LIA sediments, used...... retreat. Our results show that the advance of glaciers during the LIA occurs early after the Medieval Warm Period terminating soon after 1200 AD and culminates c. 1500-1600 AD. Historical maps also show that many glaciers on the western coast occupy a still-stand near the LIA maximum until 1900 AD before...

  8. Spatial pattern of mass loss processes across the Greenland Ice Sheet from the Little Ice Age to 2010

    DEFF Research Database (Denmark)

    Kjaer, K. H.; Korsgaard, N. J.; Kjeldsen, K. K.

    The Greenland Ice Sheet loses mass through surface meltwater runoff and discharge from marine terminating outlet glaciers. The spatial variability and magnitude of these processes have been studied and described in detail for the past decades. Here, we combine the mass loss between the LIA to 2010...... these components are variable between the different sectors of the GrIS, e.g. in the southeast sector of the GrIS we find substantial mass loss, possibly driven by high precipitation rates but also the presence of a large number of marine terminating glaciers. Furthermore many areas currently undergoing changes...

  9. Firn thickness variations across the Northeast Greenland Ice Stream margins indicating nonlinear densification rates

    Science.gov (United States)

    Riverman, K. L.; Anandakrishnan, S.; Alley, R. B.; Peters, L. E.; Christianson, K. A.; Muto, A.

    2013-12-01

    Northeast Greenland Ice Stream (NEGIS) is the largest ice stream in Greenland, draining approximately 8.4% of the ice sheet's area. The flow pattern and stability mechanism of this ice stream are unique to others in Greenland and Antarctica, and merit further study to ascertain the sensitivity of this ice stream to future climate change. Geophysical methods are valuable tools for this application, but their results are sensitive to the structure of the firn and any spatial variations in firn properties across a given study region. Here we present firn data from a 40-km-long seismic profile across the upper reaches of NEGIS, collected in the summer of 2012 as part of an integrated ground-based geophysical survey. We find considerable variations in firn thickness that are coincident with the ice stream shear margins, where a thinner firn layer is present within the margins, and a thicker, more uniform firn layer is present elsewhere in our study region. Higher accumulation rates in the marginal surface troughs due to drift-snow trapping can account for some of this increased densification; however, our seismic results also highlight enhanced anisotropy within the firn and upper ice column that is confined to narrow bands within the shear margins. We thus interpret these large firn thickness variations and abrupt changes in anisotropy as indicators of firn densification dependent on the effective stress state as well as the overburden pressure, suggesting that the strain rate increases nonlinearly with stress across the shear margins. A GPS strain grid maintained for three weeks across both margins observed strong side shearing, with rapid stretching and then compression along particle paths, indicating large deviatoric stresses in the margins. This work demonstrates the importance of developing a high-resolution firn densification model when conducting geophysical field work in regions possessing a complex ice flow history; it also motivates the need for a more

  10. Snapshots of the Greenland ice sheet configuration in the Pliocene to early Pleistocene

    DEFF Research Database (Denmark)

    Solgaard, Anne M.; Reeh, Niels; Japsen, Peter

    2011-01-01

    The geometry of the ice sheets during the Pliocene to early Pleistocene is not well constrained. Here we apply an ice-flow model in the study of the Greenland ice sheet (GIS) during three extreme intervals of this period constrained by geological observations and climate reconstructions. We study...... the extent of the GIS during the Mid-Pliocene Warmth (3.3-3.0 Ma), its advance across the continental shelf during the late Pliocene to early Pleistocene glaciations (3.0-2.4 Ma) as implied by offshore geological studies, and the transition from glacial to interglacial conditions around 2.4 Ma as deduced...... the variability of the GIS during the Pliocene to early Pleistocene and underline the importance of including independent estimates of the GIS in studies of climate during this period. We conclude that the GIS did not exist throughout the Pliocene to early Pleistocene, and that it melted during interglacials even...

  11. Nitrate addition has minimal short-term impacts on greenland ice sheet supraglacial prokaryotes

    DEFF Research Database (Denmark)

    Cameron, Karen A.; Stibal, Marek; Chrismas, Nathan

    2017-01-01

    Tropospheric nitrate levels are predicted to increase throughout the 21st century, with potential effects on terrestrial ecosystems, including the Greenland ice sheet (GrIS). This study considers the impacts of elevated nitrate concentrations on the abundance and composition of dominant bulk...... and active prokaryotic communities sampled from in situ nitrate fertilization plots on the GrIS surface. Nitrate concentrations were successfully elevated within sediment-filled meltwater pools, known as cryoconite holes; however, nitrate additions applied to surface ice did not persist. Estimated bulk...... cryoconite communities were not nitrate limited at the time of sampling. Instead, temporal changes in biomass and community composition were more pronounced. As these in situ incubations were short (6 weeks), and the community composition across GrIS surface ice is highly variable, we suggest that further...

  12. Sensitivity of Greenland Ice Sheet surface mass balance to surface albedo parameterization: a study with a regional climate model

    OpenAIRE

    Angelen, J. H.; Lenaerts, J. T. M.; Lhermitte, S.; Fettweis, X.; Kuipers Munneke, P.; Broeke, M. R.; Meijgaard, E.; Smeets, C. J. P. P.

    2012-01-01

    We present a sensitivity study of the surface mass balance (SMB) of the Greenland Ice Sheet, as modeled using a regional atmospheric climate model, to various parameter settings in the albedo scheme. The snow albedo scheme uses grain size as a prognostic variable and further depends on cloud cover, solar zenith angle and black carbon concentration. For the control experiment the overestimation of absorbed shortwave radiation (+6%) at the K-transect (west Greenland) for the period 2004–2009 is...

  13. Greenland ice sheet surface mass balance: evaluating simulations and making projections with regional climate models

    Directory of Open Access Journals (Sweden)

    J. G. L. Rae

    2012-11-01

    Full Text Available Four high-resolution regional climate models (RCMs have been set up for the area of Greenland, with the aim of providing future projections of Greenland ice sheet surface mass balance (SMB, and its contribution to sea level rise, with greater accuracy than is possible from coarser-resolution general circulation models (GCMs. This is the first time an intercomparison has been carried out of RCM results for Greenland climate and SMB. Output from RCM simulations for the recent past with the four RCMs is evaluated against available observations. The evaluation highlights the importance of using a detailed snow physics scheme, especially regarding the representations of albedo and meltwater refreezing. Simulations with three of the RCMs for the 21st century using SRES scenario A1B from two GCMs produce trends of between −5.5 and −1.1 Gt yr−2 in SMB (equivalent to +0.015 and +0.003 mm sea level equivalent yr−2, with trends of smaller magnitude for scenario E1, in which emissions are mitigated. Results from one of the RCMs whose present-day simulation is most realistic indicate that an annual mean near-surface air temperature increase over Greenland of ~ 2°C would be required for the mass loss to increase such that it exceeds accumulation, thereby causing the SMB to become negative, which has been suggested as a threshold beyond which the ice sheet would eventually be eliminated.

  14. Direct measurements of meltwater runoff on the Greenland ice sheet surface.

    Science.gov (United States)

    Smith, Laurence C; Yang, Kang; Pitcher, Lincoln H; Overstreet, Brandon T; Chu, Vena W; Rennermalm, Åsa K; Ryan, Jonathan C; Cooper, Matthew G; Gleason, Colin J; Tedesco, Marco; Jeyaratnam, Jeyavinoth; van As, Dirk; van den Broeke, Michiel R; van de Berg, Willem Jan; Noël, Brice; Langen, Peter L; Cullather, Richard I; Zhao, Bin; Willis, Michael J; Hubbard, Alun; Box, Jason E; Jenner, Brittany A; Behar, Alberto E

    2017-12-12

    Meltwater runoff from the Greenland ice sheet surface influences surface mass balance (SMB), ice dynamics, and global sea level rise, but is estimated with climate models and thus difficult to validate. We present a way to measure ice surface runoff directly, from hourly in situ supraglacial river discharge measurements and simultaneous high-resolution satellite/drone remote sensing of upstream fluvial catchment area. A first 72-h trial for a 63.1-km 2 moulin-terminating internally drained catchment (IDC) on Greenland's midelevation (1,207-1,381 m above sea level) ablation zone is compared with melt and runoff simulations from HIRHAM5, MAR3.6, RACMO2.3, MERRA-2, and SEB climate/SMB models. Current models cannot reproduce peak discharges or timing of runoff entering moulins but are improved using synthetic unit hydrograph (SUH) theory. Retroactive SUH applications to two older field studies reproduce their findings, signifying that remotely sensed IDC area, shape, and supraglacial river length are useful for predicting delays in peak runoff delivery to moulins. Applying SUH to HIRHAM5, MAR3.6, and RACMO2.3 gridded melt products for 799 surrounding IDCs suggests their terminal moulins receive lower peak discharges, less diurnal variability, and asynchronous runoff timing relative to climate/SMB model output alone. Conversely, large IDCs produce high moulin discharges, even at high elevations where melt rates are low. During this particular field experiment, models overestimated runoff by +21 to +58%, linked to overestimated surface ablation and possible meltwater retention in bare, porous, low-density ice. Direct measurements of ice surface runoff will improve climate/SMB models, and incorporating remotely sensed IDCs will aid coupling of SMB with ice dynamics and subglacial systems. Copyright © 2017 the Author(s). Published by PNAS.

  15. Efficient meltwater drainage through supraglacial streams and rivers on the southwest Greenland ice sheet.

    Science.gov (United States)

    Smith, Laurence C; Chu, Vena W; Yang, Kang; Gleason, Colin J; Pitcher, Lincoln H; Rennermalm, Asa K; Legleiter, Carl J; Behar, Alberto E; Overstreet, Brandon T; Moustafa, Samiah E; Tedesco, Marco; Forster, Richard R; LeWinter, Adam L; Finnegan, David C; Sheng, Yongwei; Balog, James

    2015-01-27

    Thermally incised meltwater channels that flow each summer across melt-prone surfaces of the Greenland ice sheet have received little direct study. We use high-resolution WorldView-1/2 satellite mapping and in situ measurements to characterize supraglacial water storage, drainage pattern, and discharge across 6,812 km(2) of southwest Greenland in July 2012, after a record melt event. Efficient surface drainage was routed through 523 high-order stream/river channel networks, all of which terminated in moulins before reaching the ice edge. Low surface water storage (3.6 ± 0.9 cm), negligible impoundment by supraglacial lakes or topographic depressions, and high discharge to moulins (2.54-2.81 cm⋅d(-1)) indicate that the surface drainage system conveyed its own storage volume every drainage to true outflow from the ice edge. However, Isortoq discharges tended lower than runoff simulations from the Modèle Atmosphérique Régional (MAR) regional climate model (0.056-0.112 km(3)⋅d(-1) vs. ∼0.103 km(3)⋅d(-1)), and when integrated over the melt season, totaled just 37-75% of MAR, suggesting nontrivial subglacial water storage even in this melt-prone region of the ice sheet. We conclude that (i) the interior surface of the ice sheet can be efficiently drained under optimal conditions, (ii) that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and (iii) that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater export from the ice sheet to the ocean.

  16. Direct measurements of meltwater runoff on the Greenland ice sheet surface

    Science.gov (United States)

    Smith, Laurence C.; Yang, Kang; Pitcher, Lincoln H.; Overstreet, Brandon T.; Chu, Vena W.; Rennermalm, Åsa K.; Ryan, Jonathan C.; Cooper, Matthew G.; Gleason, Colin J.; Tedesco, Marco; Jeyaratnam, Jeyavinoth; van As, Dirk; van den Broeke, Michiel R.; van de Berg, Willem Jan; Noël, Brice; Langen, Peter L.; Cullather, Richard I.; Zhao, Bin; Willis, Michael J.; Hubbard, Alun; Box, Jason E.; Jenner, Brittany A.; Behar, Alberto E.

    2017-12-01

    Meltwater runoff from the Greenland ice sheet surface influences surface mass balance (SMB), ice dynamics, and global sea level rise, but is estimated with climate models and thus difficult to validate. We present a way to measure ice surface runoff directly, from hourly in situ supraglacial river discharge measurements and simultaneous high-resolution satellite/drone remote sensing of upstream fluvial catchment area. A first 72-h trial for a 63.1-km2 moulin-terminating internally drained catchment (IDC) on Greenland's midelevation (1,207–1,381 m above sea level) ablation zone is compared with melt and runoff simulations from HIRHAM5, MAR3.6, RACMO2.3, MERRA-2, and SEB climate/SMB models. Current models cannot reproduce peak discharges or timing of runoff entering moulins but are improved using synthetic unit hydrograph (SUH) theory. Retroactive SUH applications to two older field studies reproduce their findings, signifying that remotely sensed IDC area, shape, and supraglacial river length are useful for predicting delays in peak runoff delivery to moulins. Applying SUH to HIRHAM5, MAR3.6, and RACMO2.3 gridded melt products for 799 surrounding IDCs suggests their terminal moulins receive lower peak discharges, less diurnal variability, and asynchronous runoff timing relative to climate/SMB model output alone. Conversely, large IDCs produce high moulin discharges, even at high elevations where melt rates are low. During this particular field experiment, models overestimated runoff by +21 to +58%, linked to overestimated surface ablation and possible meltwater retention in bare, porous, low-density ice. Direct measurements of ice surface runoff will improve climate/SMB models, and incorporating remotely sensed IDCs will aid coupling of SMB with ice dynamics and subglacial systems.

  17. Geophysical Investigations of Saline Permafrost at Ilulissat, Greenland

    DEFF Research Database (Denmark)

    Ingeman-Nielsen, Thomas; Foged, Niels Nielsen; Butzbach, Rune

    2008-01-01

    The technical properties and general state of permafrost in Greenland is not well documented. A new coordinated investigation has been initiated, for ground temperature measurements and permafrost mapping in Greenlandic towns in sporadic, discontinuous and continuous permafrost zones. We present...... investigation results from one of the sites, located at Ilulissat, in an area of discontinuous saline permafrost. We have established ground temperature measurement stations and conducted a shallow geoelectrical study. Our results show that the sediments in the studied area mainly consist of very frost...... susceptible silty clays. The area has permafrost with a maximum active layer thickness between 0.9 and 1 m. In spite of low permafrost temperatures a considerable part of the pore water is unfrozen, due to high residual salt concentrations. Consequently, the unfrozen water content dominates the technical...

  18. A Snow Density Dataset for Improving Surface Boundary Conditions in Greenland Ice Sheet Firn Modeling

    Directory of Open Access Journals (Sweden)

    Robert S. Fausto

    2018-05-01

    Full Text Available The surface snow density of glaciers and ice sheets is of fundamental importance in converting volume to mass in both altimetry and surface mass balance studies, yet it is often poorly constrained. Site-specific surface snow densities are typically derived from empirical relations based on temperature and wind speed. These parameterizations commonly calculate the average density of the top meter of snow, thereby systematically overestimating snow density at the actual surface. Therefore, constraining surface snow density to the top 0.1 m can improve boundary conditions in high-resolution firn-evolution modeling. We have compiled an extensive dataset of 200 point measurements of surface snow density from firn cores and snow pits on the Greenland ice sheet. We find that surface snow density within 0.1 m of the surface has an average value of 315 kg m−3 with a standard deviation of 44 kg m−3, and has an insignificant annual air temperature dependency. We demonstrate that two widely-used surface snow density parameterizations dependent on temperature systematically overestimate surface snow density over the Greenland ice sheet by 17–19%, and that using a constant density of 315 kg m−3 may give superior results when applied in surface mass budget modeling.

  19. Differences in plankton community structure and carbon cycling along a climate gradient from the Greenland Ice Sheet to offshore waters

    DEFF Research Database (Denmark)

    Arendt, K.E.; Nielsen, Torkel Gissel; Rysgaard, S.

    Huge differences in plankton community structures and biomasses are observed along a climate gradient from the Greenland Ice Sheet to offshore waters at the West Greenland coast. The offshore region has a high biomass of copepods dominated by Calanus spp., which are capable of consuming 55....... Protozooplankton accounts for 20-38% of the carbon turnover in the offshore and inland areas. However, protozooplankton like copepods has low ability to turn over the primary production close to the Ice Sheet. Increased run of from the Greenland Ice Sheet due to global warming could displace the existing climate...... gradient. This would have a profound influence on the future plankton community structure as well as the energy transfer to higher trophic levels in Arctic coastal ecosystems....

  20. Basin-scale partitioning of Greenland ice sheet mass balance components (2007-2011)

    DEFF Research Database (Denmark)

    Andersen, M.L.; Stenseng, Lars; Skourup, Henriette

    2015-01-01

    The current deficit in Greenland ice sheet mass balance is due to both a decrease in surface mass balance (SMB) input and an increase in ice discharge (D) output. While SMB processes are beginning to be well captured by observationally-constrained climate modeling, insight into D is relatively...... of the gate. Using a 1961-1990 reference climatology SMB field from the MAR regional climate model, we quantify ice sheet mass balance within eighteen basins. We find a 2007-2011 mean D of 515±57 Gtyr-1. We find a 2007-2011 mean total mass balance of -262±21 Gtyr-1, which is equal to a 0.73 mm yr-1 global sea...... limited. We use InSAR-derived velocities, in combination with ice thickness observations, to quantify the mass flux (F) across a flux perimeter around the ice sheet at ~1700 m elevation. To quantify D, we correct F for SMB, as well as changes in volume due to ice dynamics, in the area downstream...

  1. SEMIC: an efficient surface energy and mass balance model applied to the Greenland ice sheet

    Directory of Open Access Journals (Sweden)

    M. Krapp

    2017-07-01

    Full Text Available We present SEMIC, a Surface Energy and Mass balance model of Intermediate Complexity for snow- and ice-covered surfaces such as the Greenland ice sheet. SEMIC is fast enough for glacial cycle applications, making it a suitable replacement for simpler methods such as the positive degree day (PDD method often used in ice sheet modelling. Our model explicitly calculates the main processes involved in the surface energy and mass balance, while maintaining a simple interface and requiring minimal data input to drive it. In this novel approach, we parameterise diurnal temperature variations in order to more realistically capture the daily thaw–freeze cycles that characterise the ice sheet mass balance. We show how to derive optimal model parameters for SEMIC specifically to reproduce surface characteristics and day-to-day variations similar to the regional climate model MAR (Modèle Atmosphérique Régional, version 2 and its incorporated multilayer snowpack model SISVAT (Soil Ice Snow Vegetation Atmosphere Transfer. A validation test shows that SEMIC simulates future changes in surface temperature and surface mass balance in good agreement with the more sophisticated multilayer snowpack model SISVAT included in MAR. With this paper, we present a physically based surface model to the ice sheet modelling community that is general enough to be used with in situ observations, climate model, or reanalysis data, and that is at the same time computationally fast enough for long-term integrations, such as glacial cycles or future climate change scenarios.

  2. Impact of Greenland and Antarctic ice sheet interactions on climate sensitivity

    Energy Technology Data Exchange (ETDEWEB)

    Goelzer, H.; Huybrechts, P. [Vrije Universiteit Brussel, Earth System Sciences and Departement Geografie, Brussels (Belgium); Loutre, M.F.; Goosse, H.; Fichefet, T. [Universite Catholique de Louvain, Georges Lemaitre Centre for Earth and Climate Research (TECLIM), Earth and Life Institute, Louvain-la-Neuve (Belgium); Mouchet, A. [Universite de Liege, Laboratoire de Physique Atmospherique et Planetaire, Liege (Belgium)

    2011-09-15

    We use the Earth system model of intermediate complexity LOVECLIM to show the effect of coupling interactive ice sheets on the climate sensitivity of the model on a millennial time scale. We compare the response to a 2 x CO{sub 2} warming scenario between fully coupled model versions including interactive Greenland and Antarctic ice sheet models and model versions with fixed ice sheets. For this purpose an ensemble of different parameter sets have been defined for LOVECLIM, covering a wide range of the model's sensitivity to greenhouse warming, while still simulating the present-day climate and the climate evolution over the last millennium within observational uncertainties. Additional freshwater fluxes from the melting ice sheets have a mitigating effect on the model's temperature response, leading to generally lower climate sensitivities of the fully coupled model versions. The mitigation is effectuated by changes in heat exchange within the ocean and at the sea-air interface, driven by freshening of the surface ocean and amplified by sea-ice-related feedbacks. The strength of the effect depends on the response of the ice sheets to the warming and on the model's climate sensitivity itself. The effect is relatively strong in model versions with higher climate sensitivity due to the relatively large polar amplification of LOVECLIM. With the ensemble approach in this study we cover a wide range of possible model responses. (orig.)

  3. Crustal displacements in Greenland caused by ice mass variability

    DEFF Research Database (Denmark)

    Nielsen, Karina

    rates indicates, that the modeled elastic displacements are well captured. Based on this analysis, the GIA rates are estimated to -1 ± 0.6 mm/yr at KELY, 2 ± 0.7 mm/yr at SCOR, and 0.5 ± 0.5 mm/yr at QAQ1. At the sites KULU and THU2 the elastic displacement rates could not be accurately estimated...... modeled and removed. Over a period of a few decades, the GIA rate is assumed to be constant. Hence, changes in the observed rate results from the present-day changes. Here, mass change grids, derived from Ice, Cloud,and land Elevation Satellite (ICESat) data from three overlapping time spans are used...

  4. Meltwater retention in a transect across the Greenland ice sheet

    DEFF Research Database (Denmark)

    Bøggild, Carl Egede; Forsberg, René; Reeh, Niels

    2005-01-01

    by different physical mechanisms, their potential magnitude can be estimated, which has been done in a transect at 66 degrees N. Results show that SI declines from west to east and inversely correlates with accumulation. From the total retention capacity, theoretical lowest-runoff lines were determined......Meltwater retention by freezing is a highly climate-sensitive term in the mass budget since the cold content is directly controlled by winter climate, which is expected to change most in an anthropogenic-driven climate change. Meltwater released at the surface percolates into dry snow in a pattern...... with alternating horizontal and vertical water-flow directions, where the processes of pore refreezing (RF) (vertical flow) and superimposed ice (SI) formation (horizontal flow) occur. The flow cannot be forecasted and quantified when water first enters cold, dry snow. However, because the two processes are driven...

  5. Inverse stochastic-dynamic models for high-resolution Greenland ice core records

    DEFF Research Database (Denmark)

    Boers, Niklas; Chekroun, Mickael D.; Liu, Honghu

    2017-01-01

    as statistical properties such as probability density functions, waiting times and power spectra, with no need for any external forcing. The crucial ingredients for capturing these properties are (i) high-resolution training data, (ii) cubic drift terms, (iii) nonlinear coupling terms between the 18O and dust......Proxy records from Greenland ice cores have been studied for several decades, yet many open questions remain regarding the climate variability encoded therein. Here, we use a Bayesian framework for inferring inverse, stochastic-dynamic models from 18O and dust records of unprecedented, subdecadal...

  6. Chronology and alteration of cyclic drainage events for ice-dammed Lake Tiningnilik, Greenland, in 2010

    DEFF Research Database (Denmark)

    Haase, Eric Juergen; Furuya, Masato; Korsgaard, Niels Jákup

    pattern in nature lasting through the 19th and 20th centuries until now. In summer 2010 the lake drained after just 7 years and at a lower water stand than the 2003 pre-drainage levels. This represents an adjustment to new equilibrium conditions with the ice dam and might be an index of recent local...... climate change in Greenland. We take a close look at Lake Tiningnilik and previous studies to constrain the timing of the drainage events using historical air photos and satellite imagery starting in the 1940s and 1970s, respectively. Tiningnilik has been occasionally surveyed on the ground since the 1980...

  7. Greenland inland ice melt-off: Analysis of global gravity data from the GRACE satellites

    DEFF Research Database (Denmark)

    Nielsen, Allan Aasbjerg; Andersen, Ole Baltazar; Svendsen, Peter L.

    2011-01-01

    This paper gives an introductory analysis of gravity data from the GRACE (Gravity Recovery And Climate Experiment) twin satellites. The data consist of gravity data in the form of 10-day maximum values of 1◦ by 1◦ equivalent water height (EWH) in meters starting at 29 July 2002 and ending at 25...... August 2010. Results focussing on Greenland show statistically significant mass loss interpreted as inland ice melt-off to the SE and NW with an acceleration in the melt-off occurring to the NW and a possible deceleration to the SE. Also, there are strong indications of a transition taking place...

  8. Multi-decadal record of ice dynamics on Daugaard Jensen Gletscher, East Greenland, from satellite imagery and terrestrial measurements

    DEFF Research Database (Denmark)

    Stearns, L.A.; Hamilton, G.S.; Reeh, Niels

    2005-01-01

    The history of ice velocity and calving front position of Daugaard Jensen Gletscher, a large outlet glacier in East Greenland, is reconstructed from field measurements, aerial photography and satellite imagery for the period 1950-2001. The calving terminus of the glacier has remained in approxima......The history of ice velocity and calving front position of Daugaard Jensen Gletscher, a large outlet glacier in East Greenland, is reconstructed from field measurements, aerial photography and satellite imagery for the period 1950-2001. The calving terminus of the glacier has remained...

  9. Balance Mass Flux and Velocity Across the Equilibrium Line in Ice Drainage Systems of Greenland

    Science.gov (United States)

    Zwally, H. Jay; Giovinetto, Mario B.; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    Estimates of balance mass flux and the depth-averaged ice velocity through the cross-section aligned with the equilibrium line are produced for each of six drainage systems in Greenland. (The equilibrium line, which lies at approximately 1200 m elevation on the ice sheet, is the boundary between the area of net snow accumulation at higher elevations and the areas of net melting at lower elevations around the ice sheet.) Ice drainage divides and six major drainage systems are delineated using surface topography from ERS (European Remote Sensing) radar altimeter data. The net accumulation rate in the accumulation zone bounded by the equilibrium line is 399 Gt/yr and net ablation rate in the remaining area is 231 Gt/yr. (1 GigaTon of ice is 1090 kM(exp 3). The mean balance mass flux and depth-averaged ice velocity at the cross-section aligned with the modeled equilibrium line are 0.1011 Gt kM(exp -2)/yr and 0.111 km/yr, respectively, with little variation in these values from system to system. The ratio of the ice mass above the equilibrium line to the rate of mass output implies an effective exchange time of approximately 6000 years for total mass exchange. The range of exchange times, from a low of 3 ka in the SE drainage system to 14 ka in the NE, suggests a rank as to which regions of the ice sheet may respond more rapidly to climate fluctuations.

  10. Growth of plants on the Late Weichselian ice-sheet during Greenland interstadial-1?

    Science.gov (United States)

    Zale, R.; Huang, Y.-T.; Bigler, C.; Wood, J. R.; Dalén, L.; Wang, X.-R.; Segerström, U.; Klaminder, J.

    2018-04-01

    Unglaciated forelands and summits protruding from ice-sheets are commonly portrayed as areas where plants first establish at the end of glacial cycles. But is this prevailing view of ice-free refugia too simplistic? Here, we present findings suggesting that surface debris supported plant communities far beyond the rim of the Late Weichselian Ice-sheet during Greenland interstadial 1 (GI-1 or Bølling-Allerød interstadial). We base our interpretations upon findings from terrigenous sediments largely resembling 'plant-trash' deposits in North America (known to form as vegetation established on stagnant ice became buried along with glacial debris during the deglaciation). In our studied deposit, we found macrofossils (N = 10) overlapping with the deglaciation period of the area (9.5-10 cal kyr BP) as well as samples (N = 2) with ages ranging between 12.9 and 13.3 cal kyr BP. The latter ages indicate growth of at least graminoids during the GI-1 interstadial when the site was near the geographic center of the degrading ice-sheet. We suggest that exposure of englacial material during GI-1 created patches of supraglacial debris capable of supporting vascular plants three millennia before deglaciation. The composition and resilience of this early plant community remain uncertain. Yet, the younger group of macrofossils, in combination with pollen and ancient DNA analyses of inclusions, imply that shrubs (Salix sp., Betula sp. and Ericaceae sp) and even tree species (Larix) were present in the debris during the final deglaciation stage.

  11. Ice-dammed lake drainage evolution at Russell Glacier, west Greenland

    Science.gov (United States)

    Carrivick, Jonathan L.; Tweed, Fiona S.; Ng, Felix; Quincey, Duncan J.; Mallalieu, Joseph; Ingeman-Nielsen, Thomas; Mikkelsen, Andreas B.; Palmer, Steven J.; Yde, Jacob C.; Homer, Rachel; Russell, Andrew J.; Hubbard, Alun

    2017-11-01

    Glaciological and hydraulic factors that control the timing and mechanisms of glacier lake outburst floods (GLOFs) remain poorly understood. This study used measurements of lake level at fifteen minute intervals and known lake bathymetry to calculate lake outflow during two GLOF events from the northern margin of Russell Glacier, west Greenland. We used measured ice surface elevation, interpolated subglacial topography and likely conduit geometry to inform a melt enlargement model of the outburst evolution. The model was tuned to best-fit the hydrograph’s rising limb and timing of peak discharge in both events; it achieved Mean Absolute Errors of Lake water temperature, which strongly governed the enlargement rate, preconditioned the high peak discharge and short duration of these floods. We hypothesize that both GLOFs were triggered by ice dam flotation, and localised hydraulic jacking sustained most of their early-stage outflow, explaining the particularly rapid water egress in comparison to that recorded at other ice-marginal lakes. As ice overburden pressure relative to lake water hydraulic head diminished, flow became confined to a subglacial conduit. This study has emphasised the inter-play between ice dam thickness and lake level, drainage timing, lake water temperature and consequently rising stage lake outflow and flood evolution.

  12. Possible evidence for non-Newtonian gravity in the Greenland ice gap

    International Nuclear Information System (INIS)

    Ander, M.E.

    1988-01-01

    An Airy-type geophysical experiment was conducted down a 2 km deep hole in the Greenland ice cap in order to test for possible violations of Newton's inverse square law by making gravity measurements over a range of 213 m to 1460 m. A significant departure from Newtonian gravity was observed. This result can be explained by the existence of an attractive non-Newtonian component of gravity with a strength of about 3.4% that of Newtonian gravity at a scale of 1460 m. Unfortunately, we cannot completely, unambiguously attribute it to a breakdown of Newtonian gravity because we have shown that lateral density variations in the bedrock beneath the ice can cause such apparent departures. If such variations existed, they would have to be rather unusual but certainly no impossible. 8 refs

  13. A Snow Density Dataset for Improving Surface Boundary Conditions in Greenland Ice Sheet Firn Modeling

    DEFF Research Database (Denmark)

    S. Fausto, Robert; E. Box, Jason; Vandecrux, Baptiste Robert Marcel

    2018-01-01

    The surface snow density of glaciers and ice sheets is of fundamental importance in converting volume to mass in both altimetry and surface mass balance studies, yet it is often poorly constrained. Site-specific surface snow densities are typically derived from empirical relations based...... on temperature and wind speed. These parameterizations commonly calculate the average density of the top meter of snow, thereby systematically overestimating snow density at the actual surface. Therefore, constraining surface snow density to the top 0.1 m can improve boundary conditions in high-resolution firn......-evolution modeling. We have compiled an extensive dataset of 200 point measurements of surface snow density from firn cores and snow pits on the Greenland ice sheet. We find that surface snow density within 0.1 m of the surface has an average value of 315 kg m−3 with a standard deviation of 44 kg m−3, and has...

  14. Atmospheric summer teleconnections and Greenland Ice Sheet surface mass variations: insights from MERRA-2

    International Nuclear Information System (INIS)

    Lim, Young-Kwon; Schubert, Siegfried D; Molod, Andrea M; Cullather, Richard I; Zhao, Bin; Nowicki, Sophie M J; Lee, Jae N; Velicogna, Isabella

    2016-01-01

    The relationship between leading atmospheric teleconnection patterns and Greenland Ice Sheet (GrIS) temperature, precipitation, and surface mass balance (SMB) are investigated for the last 36 summers (1979–2014) based on Modern-Era Retrospective analysis for Research and Applications version 2 reanalyses. The results indicate that the negative phase of both the North Atlantic Oscillation (NAO) and Arctic Oscillation, associated with warm and dry conditions for the GrIS, lead to SMB decreases within 0–1 months. Furthermore, the positive phase of the East Atlantic (EA) pattern often lags the negative NAO, reflecting a dynamical linkage between these modes that acts to further enhance the warm and dry conditions over the GrIS, leading to a favorable environment for enhanced surface mass loss. The development of a strong negative NAO in combination with a strong positive EA in recent years leads to significantly larger GrIS warming compared to when the negative NAO occurs in combination with a negative or weak positive EA (0.69 K versus 0.13 K anomaly). During 2009 and 2011, weakened (as compared to conditions during the severe surface melt cases of 2010 and 2012) local high pressure blocking produced colder northerly flow over the GrIS inhibiting warming despite the occurrence of a strong negative NAO, reflecting an important role for the EA during those years. In particular, the EA acts with the NAO to enhance warming in 2010 and 2012, and weaken high pressure blocking in 2009 and 2011. In general, high pressure blocking primarily impacts the western areas of the GrIS via advective temperature increases, while changes in net surface radiative fluxes account for both western and eastern GrIS temperature changes. (letter)

  15. Molecular characterization of dissolved organic matter associated with the Greenland ice sheet

    Science.gov (United States)

    Bhatia, Maya P.; Das, Sarah B.; Longnecker, Krista; Charette, Matthew A.; Kujawinski, Elizabeth B.

    2010-07-01

    Subsurface microbial oxidation of overridden soils and vegetation beneath glaciers and ice sheets may affect global carbon budgets on glacial-interglacial timescales. The likelihood and magnitude of this process depends on the chemical nature and reactivity of the subglacial organic carbon stores. We examined the composition of carbon pools associated with different regions of the Greenland ice sheet (subglacial, supraglacial, proglacial) in order to elucidate the type of dissolved organic matter (DOM) present in the subglacial discharge over a melt season. Electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry coupled to multivariate statistics permitted unprecedented molecular level characterization of this material and revealed that carbon pools associated with discrete glacial regions are comprised of different compound classes. Specifically, a larger proportion of protein-like compounds were observed in the supraglacial samples and in the early melt season (spring) subglacial discharge. In contrast, the late melt season (summer) subglacial discharge contained a greater fraction of lignin-like and other material presumably derived from underlying vegetation and soil. These results suggest (1) that the majority of supraglacial DOM originates from autochthonous microbial processes on the ice sheet surface, (2) that the subglacial DOM contains allochthonous carbon derived from overridden soils and vegetation as well as autochthonous carbon derived from in situ microbial metabolism, and (3) that the relative contribution of allochthonous and autochthonous material in subglacial discharge varies during the melt season. These conclusions are consistent with the hypothesis that, given sufficient time (e.g., overwinter storage), resident subglacial microbial communities may oxidize terrestrial material beneath the Greenland ice sheet.

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

    Science.gov (United States)

    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.

  17. EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice

    Science.gov (United States)

    Weikusat, Ilka; Kuiper, Ernst-Jan N.; Pennock, Gill M.; Kipfstuhl, Sepp; Drury, Martyn R.

    2017-09-01

    Ice has a very high plastic anisotropy with easy dislocation glide on basal planes, while glide on non-basal planes is much harder. Basal glide involves dislocations with the Burgers vector b = 〈a〉, while glide on non-basal planes can involve dislocations with b = 〈a〉, b = [c], and b = 〈c + a〉. During the natural ductile flow of polar ice sheets, most of the deformation is expected to occur by basal slip accommodated by other processes, including non-basal slip and grain boundary processes. However, the importance of different accommodating processes is controversial. The recent application of micro-diffraction analysis methods to ice, such as X-ray Laue diffraction and electron backscattered diffraction (EBSD), has demonstrated that subgrain boundaries indicative of non-basal slip are present in naturally deformed ice, although so far the available data sets are limited. In this study we present an analysis of a large number of subgrain boundaries in ice core samples from one depth level from two deep ice cores from Antarctica (EPICA-DML deep ice core at 656 m of depth) and Greenland (NEEM deep ice core at 719 m of depth). EBSD provides information for the characterization of subgrain boundary types and on the dislocations that are likely to be present along the boundary. EBSD analyses, in combination with light microscopy measurements, are presented and interpreted in terms of the dislocation slip systems. The most common subgrain boundaries are indicative of basal 〈a〉 slip with an almost equal occurrence of subgrain boundaries indicative of prism [c] or 〈c + a〉 slip on prism and/or pyramidal planes. A few subgrain boundaries are indicative of prism 〈a〉 slip or slip of 〈a〉 screw dislocations on the basal plane. In addition to these classical polygonization processes that involve the recovery of dislocations into boundaries, alternative mechanisms are discussed for the formation of subgrain boundaries that are not related to the

  18. EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice

    Directory of Open Access Journals (Sweden)

    I. Weikusat

    2017-09-01

    Full Text Available Ice has a very high plastic anisotropy with easy dislocation glide on basal planes, while glide on non-basal planes is much harder. Basal glide involves dislocations with the Burgers vector b = 〈a〉, while glide on non-basal planes can involve dislocations with b = 〈a〉, b = [c], and b = 〈c + a〉. During the natural ductile flow of polar ice sheets, most of the deformation is expected to occur by basal slip accommodated by other processes, including non-basal slip and grain boundary processes. However, the importance of different accommodating processes is controversial. The recent application of micro-diffraction analysis methods to ice, such as X-ray Laue diffraction and electron backscattered diffraction (EBSD, has demonstrated that subgrain boundaries indicative of non-basal slip are present in naturally deformed ice, although so far the available data sets are limited. In this study we present an analysis of a large number of subgrain boundaries in ice core samples from one depth level from two deep ice cores from Antarctica (EPICA-DML deep ice core at 656 m of depth and Greenland (NEEM deep ice core at 719 m of depth. EBSD provides information for the characterization of subgrain boundary types and on the dislocations that are likely to be present along the boundary. EBSD analyses, in combination with light microscopy measurements, are presented and interpreted in terms of the dislocation slip systems. The most common subgrain boundaries are indicative of basal 〈a〉 slip with an almost equal occurrence of subgrain boundaries indicative of prism [c] or 〈c + a〉 slip on prism and/or pyramidal planes. A few subgrain boundaries are indicative of prism 〈a〉 slip or slip of 〈a〉 screw dislocations on the basal plane. In addition to these classical polygonization processes that involve the recovery of dislocations into boundaries, alternative mechanisms are discussed for the formation of subgrain

  19. Inverse stochastic–dynamic models for high-resolution Greenland ice core records

    Directory of Open Access Journals (Sweden)

    N. Boers

    2017-12-01

    Full Text Available Proxy records from Greenland ice cores have been studied for several decades, yet many open questions remain regarding the climate variability encoded therein. Here, we use a Bayesian framework for inferring inverse, stochastic–dynamic models from δ18O and dust records of unprecedented, subdecadal temporal resolution. The records stem from the North Greenland Ice Core Project (NGRIP, and we focus on the time interval 59–22 ka b2k. Our model reproduces the dynamical characteristics of both the δ18O and dust proxy records, including the millennial-scale Dansgaard–Oeschger variability, as well as statistical properties such as probability density functions, waiting times and power spectra, with no need for any external forcing. The crucial ingredients for capturing these properties are (i high-resolution training data, (ii cubic drift terms, (iii nonlinear coupling terms between the δ18O and dust time series, and (iv non-Markovian contributions that represent short-term memory effects.

  20. Inverse stochastic-dynamic models for high-resolution Greenland ice core records

    Science.gov (United States)

    Boers, Niklas; Chekroun, Mickael D.; Liu, Honghu; Kondrashov, Dmitri; Rousseau, Denis-Didier; Svensson, Anders; Bigler, Matthias; Ghil, Michael

    2017-12-01

    Proxy records from Greenland ice cores have been studied for several decades, yet many open questions remain regarding the climate variability encoded therein. Here, we use a Bayesian framework for inferring inverse, stochastic-dynamic models from δ18O and dust records of unprecedented, subdecadal temporal resolution. The records stem from the North Greenland Ice Core Project (NGRIP), and we focus on the time interval 59-22 ka b2k. Our model reproduces the dynamical characteristics of both the δ18O and dust proxy records, including the millennial-scale Dansgaard-Oeschger variability, as well as statistical properties such as probability density functions, waiting times and power spectra, with no need for any external forcing. The crucial ingredients for capturing these properties are (i) high-resolution training data, (ii) cubic drift terms, (iii) nonlinear coupling terms between the δ18O and dust time series, and (iv) non-Markovian contributions that represent short-term memory effects.

  1. The Greenland Ice Sheet at the peak of warming during the previous Interglacial

    Directory of Open Access Journals (Sweden)

    O. O. Rybak

    2014-01-01

    Full Text Available The Last Interglacial (LIG or the Eemian between ca. 130 and 115 kyr BP is probably the best analogue for future climate warming for which increasingly better proxy data are becoming available. The volume of the Greenland Ice Sheet (GrIS during this period is of particular interest to better assess how much and how fast sea-level can rise in a future Earth undergoing gradual climatic warming. Sea-level during the LIG is inferred to have been up to 9 meter higher than today, but contribution of the GrIS into this rise remains unclear. Various ice-sheet modeling studies have come up with a very broad range of the LIG volume loss by the GrIS to between 60 cm and 6 m of equivalent sea-level rise. This wide range is explained by the sensitivity of GrIS models to the imposed climatic conditions and to poor knowledge of the LIG climate itself in terms of the magnitude and precise timing of the maximum warming, as well as in terms of spatial and annual patterns. To partially circumvent these uncertainties we made use of the newest temperature record over the Central Greenland reconstructed from the isotopic composition of the recently obtained NEEM ice core containing undisturbed LIG segment to build the climatic forcing of the model. The NEEM record unequivocally indicates times of the start and of the end of the LIG warming in Greenland as well as the duration of the warmest time period within the Eemian. Using a three-dimensional thermomechanical ice-sheet model, we produced an ensemble of possible LIG configurations by varying only four key parameters for temperature, precipitation rate, surface melting magnitude and melting pattern within realistic bounds. The outcome of a series of the numerical experiments is a variety of glaciologically consistent GrIS geometries corresponding to a wide range of possible «climates». To constrain the ensemble of GrIS geometries, we used data inferred from 5 Greenland ice cores such as the presence or absence of

  2. Greenland ice sheet model parameters constrained using simulations of the Eemian Interglacial

    Directory of Open Access Journals (Sweden)

    A. Robinson

    2011-04-01

    Full Text Available Using a new approach to force an ice sheet model, we performed an ensemble of simulations of the Greenland Ice Sheet evolution during the last two glacial cycles, with emphasis on the Eemian Interglacial. This ensemble was generated by perturbing four key parameters in the coupled regional climate-ice sheet model and by introducing additional uncertainty in the prescribed "background" climate change. The sensitivity of the surface melt model to climate change was determined to be the dominant driver of ice sheet instability, as reflected by simulated ice sheet loss during the Eemian Interglacial period. To eliminate unrealistic parameter combinations, constraints from present-day and paleo information were applied. The constraints include (i the diagnosed present-day surface mass balance partition between surface melting and ice discharge at the margin, (ii the modeled present-day elevation at GRIP; and (iii the modeled elevation reduction at GRIP during the Eemian. Using these three constraints, a total of 360 simulations with 90 different model realizations were filtered down to 46 simulations and 20 model realizations considered valid. The paleo constraint eliminated more sensitive melt parameter values, in agreement with the surface mass balance partition assumption. The constrained simulations resulted in a range of Eemian ice loss of 0.4–4.4 m sea level equivalent, with a more likely range of about 3.7–4.4 m sea level if the GRIP δ18O isotope record can be considered an accurate proxy for the precipitation-weighted annual mean temperatures.

  3. Ice-Dammed Lake Drainage Evolution at Russell Glacier, West Greenland

    Directory of Open Access Journals (Sweden)

    Jonathan L. Carrivick

    2017-11-01

    Full Text Available KEY POINTS/HIGHLIGHTSTwo rapid ice-dammed lake drainage events gauged and ice dam geometry measured.A melt enlargement model is developed to examine the evolution of drainage mechanism(s.Lake temperature dominated conduit melt enlargement and we hypothesize a flotation trigger.Glaciological and hydraulic factors that control the timing and mechanisms of glacier lake outburst floods (GLOFs remain poorly understood. This study used measurements of lake level at 15 min intervals and known lake bathymetry to calculate lake outflow during two GLOF events from the northern margin of Russell Glacier, west Greenland. We used measured ice surface elevation, interpolated subglacial topography and likely conduit geometry to inform a melt enlargement model of the outburst evolution. The model was tuned to best-fit the hydrograph rising limb and timing of peak discharge in both events; it achieved Mean Absolute Errors of <5%. About one third of the way through the rising limb, conduit melt enlargement became the dominant drainage mechanism. Lake water temperature, which strongly governed the enlargement rate, preconditioned the high peak discharge and short duration of these floods. We hypothesize that both GLOFs were triggered by ice dam flotation, and localized hydraulic jacking sustained most of their early-stage outflow, explaining the particularly rapid water egress in comparison to that recorded at other ice-marginal lakes. As ice overburden pressure relative to lake water hydraulic head diminished, flow became confined to a subglacial conduit. This study has emphasized the inter-play between ice dam thickness and lake level, drainage timing, lake water temperature and consequently rising stage lake outflow and flood evolution.

  4. QUANTIFYING REGIONAL SEA LEVEL RISE CONTRIBUTIONS FROM THE GREENLAND ICE SHEET

    Directory of Open Access Journals (Sweden)

    Diandong Ren

    2013-01-01

    Full Text Available This study projects the sea level contribution from the Greenland ice sheet (GrIS through to 2100, using a recently developed ice dynamics model forced by atmospheric parameters derived from three different climate models (CGCMs. The geographical pattern of the near-surface ice warming imposes a divergent flow field favoring mass loss through enhanced ice flow. The calculated average mass loss rate during the latter half of the 21st century is ~0.64±0.06 mm/year eustatic sea level rise, which is significantly larger than the IPCC AR4 estimate from surface mass balance. The difference is due largely to the positive feedbacks from reduced ice viscosity and the basal sliding mechanism present in the ice dynamics model. This inter-model, inter-scenario spread adds approximately a 20% uncertainty to the IPCC ice model estimates. The sea level rise is geographically non-uniform and reaches 1.69±0.24 mm/year by 2100 for the northeast coastal region of the United States, amplified by the expected weakening of the Atlantic meridional overturning circulation (AMOC. In contrast to previous estimates, which neglected the GrIS fresh water input, both sides of the North Atlantic Gyre are projected to experience sea level rises. The impacts on a selection of major cities on both sides of the Atlantic and in the Pacific and southern oceans also are assessed. The other ocean basins are found to be less affected than the Atlantic Ocean.

  5. Reconstruction of the Greenland ice sheet dynamics in a fully coupled Earth System Model

    Science.gov (United States)

    Rybak, Oleg; Volodin, Evgeny; Huybrechts, Philippe

    2016-04-01

    Earth system models (ESMs) are undoubtedly effective tools for studying climate dynamics. Incorporation of evolving ice sheets to ESMs is a challenging task because response times of the climate system and of ice sheets differ by several orders of magnitude. Besides, AO GCMs operate on spatial and temporal resolutions substantially differing from those of ice sheet models (ICMs). Therefore elaboration of an effective coupling methodology of an AO GCM and an ICM is the key problem of an ESM construction and utilization. Several downscaling strategies of varying complexity exist now of data exchange between modeled climate system and ice sheets. Application of a particular strategy depends on the research objectives. In our view, the optimum approach for model studying of significant environmental changes (e.g. glacial/interglacial transitions) when ice sheets undergo substantial evolution of geometry and volume would be an asynchronous coupling. The latter allows simulation in the interactive way of growth and decay of ice sheets in the changing climatic conditions. In the focus of the presentation, is the overview of coupling aspects of an AO GCM INMCM32 elaborated in the Institute of Numerical Mathematics (Moscow, Russia) to the Greenland ice sheet model (GrISM, Vrije Uninersiteit Brussel, Belgium). To provide interactive coupling of INMCM32 (spatial resolution 5°×4°, 21 vertical layers and temporal resolution 6 min. in the atmospheric block) and GrISM (spatial resolution 20×20 km, 51 vertical layers and 1 yr temporal resolution), we employ a special energy- and water balance model (EWBM-G), which serves as a buffer providing effective data exchange between INMCM32 and GrISM. EWBM-G operates in a rectangle domain including Greenland. Transfer of daily meanings of simulated climatic variables (air surface temperature and specific humidity) is provided on the lateral boundarias of the domain and inside the domain (sea level air pressure, wind speed and total

  6. Climate Variability, Melt-Flow Acceleration, and Ice Quakes at the Western Slope of the Greenland Ice Sheet

    Science.gov (United States)

    Steffen, K.; Zwally, J. H.; Rial, J. A.; Behar, A.; Huff, R.

    2006-12-01

    The Greenland ice sheet experienced surface melt increase over the past 15 years with record melt years in 1987, 1991, 1998, 2002 and 2005. For the western part of the ice sheet the melt area increased by 30 percent (1979-2005). Monthly mean air temperatures increased in spring and fall by 0.23 deg. C per year since 1990, extending the length of melt and total ablation. Winter air temperatures increased by as much as 0.5 deg. C per year during the past 15 years. The equilibrium line altitude ranged between 400 and 1530 m above sea level at 70 deg. north along the western slope of the ice sheet for the past 15 years, equaling a horizontal distance of 100 km. The ELA has been below the Swiss Camp (1100 m elevation) in the nineties, and since 1997 moved above the Swiss Camp height. An increase in ELA leads to an increase in melt water run-off which has been verified by regional model studies (high-resolution re-analysis). Interannual variability of snow accumulation varies from 0.3 to 2.0 m, whereas snow and ice ablation ranges from 0 to 1.5 m water equivalent at Swiss Camp during 1990-2005. A GPS network (10 stations) monitors ice velocity, acceleration, and surface height change at high temporal resolution throughout the year. The network covers a range of 500 and 1500 m above sea level, close to the Ilulissat Icefjord World Heritage region. The ice sheet continued to accelerate during the height of the melt season with short-term velocity increases up to 100 percent, and vertical uplift rates of 0.5 m. There seems to be a good correlation between the change in ice velocity and total surface melt, suggesting that melt water penetrates to great depth through moulins and cracks, lubricating the bottom of the ice sheet. A new bore-hole video movie will be shown from a 110 m deep moulin close to Swiss Camp. A PASSCAL array of 10 portable, 3-component seismic stations deployed around Swiss Camp from May to August 2006 detected numerous microearthquakes within the ice

  7. The accuracy of satellite radar altimeter data over the Greenland ice sheet determined from airborne laser data

    DEFF Research Database (Denmark)

    Bamber, J.L.; Ekholm, Simon; Krabill, W.

    1998-01-01

    with airborne laser altimeter data an absolute accuracy typically in the range 2-10 cm +/- 10 cm. Comparison of differences between the radar and laser derived elevations, showed a correlation with surface slope. The difference between the two data sets ranged from 84 cm +/- 79 cm for slopes below 0.1 degrees......The 336 days of the geodetic phase of ERS-1 provides dense coverage, by satellite radar altimetry, of the whole of the Greenland ice sheet. These data have been used to produce a digital elevation model of the ice sheet. The errors present in the altimeter data were investigated via a comparison......, to 10.3 m +/- 8.4 m for a slope of 0.7 degrees ( the half power beam-width of the ERS-1 radar altimeter). An explanation for the behaviour of the difference as a function of surface slope is given in terms of the pattern of surface roughness on the ice sheet....

  8. Supraglacial Lakes in the Percolation Zone of the Western Greenland Ice Sheet: Formation and Development using Operation IceBridge Snow Radar and ATM (2009-2014)

    Science.gov (United States)

    Chen, C.; Howat, I. M.; de la Peña, S.

    2015-12-01

    Surface meltwater lakes on the Greenland Ice Sheet have appeared at higher elevations, extending well into the percolation zone, under recent warming, with the largest expansion occurring in the western Greenland Ice Sheet. The conditions that allow lakes to form atop firn are poorly constrained, but the formation of new lakes imply changes in the permeability of the firn at high elevations, promoting meltwater runoff. We explore the formation and evolution of new surface lakes in this region above 1500 meters, using a combination of satellite imagery and repeat Snow (2-6.5 GHz) radar echograms and LIDAR measurements from NASA's Operation IceBridge of 2009-2014. We identify conditions for surface lake formation at their farthest inland extent and suggest behaviors of persistence and lake drainage are due to differences in regional ice dynamics.

  9. The Abandoned Ice Sheet Base at Camp Century, Greenland, in a Warming Climate

    Science.gov (United States)

    Colgan, William; Machguth, Horst; Macferrin, Mike; Colgan, Jeff D.; Van As, Dirk; Macgregor, Joseph A.

    2016-01-01

    In 1959 the U.S. Army Corps of Engineers built Camp Century beneath the surface of the northwestern Greenland Ice Sheet. There they studied the feasibility of deploying ballistic missiles within the ice sheet. The base and its wastes were abandoned with minimal decommissioning in 1967, under the assumption they would be preserved for eternity by perpetually accumulating snowfall. Here we show that a transition in ice sheet surface mass balance at Camp Century from net accumulation to net ablation is plausible within the next 75years, under a business-as-usual anthropogenic emissions scenario (Representative Concentration Pathway 8.5). Net ablation would guarantee the eventual remobilization of physical, chemical, biological, and radiological wastes abandoned at the site. While Camp Century and four other contemporaneous ice sheet bases were legally established under a Danish-U.S. treaty, the potential remobilization of their abandoned wastes, previously regarded as sequestered, represents an entirely new pathway of political dispute resulting from climate change.

  10. Three recent ice entrapments of Arctic cetaceans in West Greenland and the eastern Canadian High Arctic

    Directory of Open Access Journals (Sweden)

    MP Heide-Jørgensen

    2002-07-01

    Full Text Available Three ice entrapments of Monodontids have been reported in the western North Atlantic since 1993. Hunters in Disko Bay, West Greenland, discovered one in March 1994 that included about 150 narwhals (Monodon monoceros. The entrapment occurred during a sudden cold period which caused ice to form rapidly. The trapped whales were subject to hunting, but about 50 of the killed whales could not be retrieved in the ice. The whales were trapped in a small opening in the ice and because of that they would probably have succumbed even if not discovered by hunters. Two entrapments involving white whales or belugas (Delphinapterus leucas occurred in the eastern Canadian Arctic in May 1999; one in Lancaster Sound discovered by polar bear (Ursus maritimus researchers and one in Jones Sound discovered by hunters. The first included one bowhead whale (Balaena mysticetus and about 40 belugas that were being preyed upon by polar bears. The second involved at least 170 belugas, of which about 100 were killed by polar bears and 17 were taken by hunters. The entrapments in Disko Bay and Jones Sound both occurred in areas where entrapments have previously been reported, whereas the one in Lancaster Sound was in a new area.

  11. Snowmelt on the Greenland Ice Sheet as Derived From Passive Microwave Satellite Data

    Science.gov (United States)

    Abdalati, Waleed; Steffen, Konrad

    1997-01-01

    The melt extent of the snow on the Greenland ice sheet is of considerable importance to the ice sheet's mass and energy balance, as well as Arctic and global climates. By comparing passive microwave satellite data to field observations, variations in melt extent have been detected by establishing melt thresholds in the cross-polarized gradient ratio (XPGR). The XPGR, defined as the normalized difference between the 19-GHz horizontal channel and the 37-GHz vertical channel of the Special Sensor Microwave/Imager (SSM/I), exploits the different effects of snow wetness on different frequencies and polarizations and establishes a distinct melt signal. Using this XPGR melt signal, seasonal and interannual variations in snowmelt extent of the ice sheet are studied. The melt is found to be most extensive on the western side of the ice sheet and peaks in late July. Moreover, there is a notable increasing trend in melt area between the years 1979 and 1991 of 4.4% per year, which came to an abrupt halt in 1992 after the eruption of Mt. Pinatubo. A similar trend is observed in the temperatures at six coastal stations. The relationship between the warming trend and increasing melt trend between 1979 and 1991 suggests that a 1 C temperature rise corresponds to an increase in melt area of 73000 sq km, which in general exceeds one standard deviation of the natural melt area variability.

  12. Bergy Bit and Melt Water Trajectories in Godthåbsfjord (SW Greenland) Observed by the Expendable Ice Tracker

    NARCIS (Netherlands)

    Carlson, D.F.; Boone, W.; Meire, L.; Abermann, J.; Rysgaard, S.

    2017-01-01

    Icebergs and bergy bits makes up a significant component of the total freshwater flux from the Greenland Ice Sheet to the ocean. Observations of iceberg trajectories are biased toward larger icebergs and, as a result, the drift characteristics of smaller icebergs and bergy bits are poorly

  13. Response of the Atlantic Ocean circulation to Greenland Ice Sheet melting in a strongly-eddying ocean model

    NARCIS (Netherlands)

    Weijer, W.; Maltrud, M.E.; Hecht, M.W.; Dijkstra, H.A.; Kliphuis, M.

    2012-01-01

    The sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to high-latitude freshwater input is one of the key uncertainties in the climate system. Considering the importance of the AMOC for global heat transports, and the vulnerability of the Greenland Ice Sheet (GrIS) to global

  14. Improved GRACE regional mass balance estimates of the Greenland ice sheet cross-validated with the input-output method

    NARCIS (Netherlands)

    Xu, Zheng; Schrama, Ernst J. O.; van der Wal, Wouter; van den Broeke, Michiel; Enderlin, Ellyn M.

    2016-01-01

    In this study, we use satellite gravimetry data from the Gravity Recovery and Climate Experiment (GRACE) to estimate regional mass change of the Greenland ice sheet (GrIS) and neighboring glaciated regions using a least squares inversion approach. We also consider results from the input–output

  15. Improved GRACE regional mass balance estimates of the Greenland ice sheet cross-validated with the input–output method

    NARCIS (Netherlands)

    Xu, Z.; Schrama, E.J.O.; van der Wal, W.; van den Broeke, MR; Enderlin, EM

    2016-01-01

    In this study, we use satellite gravimetry data from the Gravity Recovery and Climate Experiment (GRACE) to estimate regional mass change of the Greenland ice sheet (GrIS) and neighboring glaciated regions using a least squares inversion approach. We also consider results from the input–output

  16. Different bulk and active bacterial communities in cryoconite from the margin and interior of the Greenland ice sheet

    DEFF Research Database (Denmark)

    Stibal, Marek; Schostag, Morten; Cameron, Karen A.

    2015-01-01

    composition of cryoconite over a melt season at two contrasting sites at the margin and in the interior of the Greenland ice sheet, using sequence analysis and quantitative polymerase chain reaction of coextracted 16S rDNA and rRNA. Significant differences were found between bulk (rDNA) and potentially active...

  17. Estimating Greenland ice sheet surface mass balance contribution to future sea level rise using the regional atmospheric climate model MAR

    NARCIS (Netherlands)

    Fettweis, X.; Franco, B.; Tedesco, M.; van Angelen, J.H.; Lenaerts, J.T.M.; van den Broeke, M.R.; Gallee, H

    2012-01-01

    We report future projections of Surface Mass Balance (SMB) over the Greenland ice sheet (GrIS) obtained with the regional climate model MAR, forced by the outputs of three CMIP5 General Circulation Models (GCMs) when considering two different warming scenarios (RCP 4.5 and RCP 8.5). The GCMs

  18. CryoSat-2 Processing and Model Interpretation of Greenland Ice Sheet Volume Changes

    Science.gov (United States)

    Nilsson, J.; Gardner, A. S.; Sandberg Sorensen, L.

    2015-12-01

    CryoSat-2 was launched in late 2010 tasked with monitoring the changes of the Earth's land and sea ice. It carries a novel radar altimeter allowing the satellite to monitor changes in highly complex terrain, such as smaller ice caps, glaciers and the marginal areas of the ice sheets. Here we present on the development and validation of an independent elevation retrieval processing chain and respective elevation changes based on ESA's L1B data. Overall we find large improvement in both accuracy and precision over Greenland relative to ESA's L2 product when comparing against both airborne data and crossover analysis. The seasonal component and spatial sampling of the surface elevation changes where also compared against ICESat derived changes from 2003-2009. The comparison showed good agreement between the to product on a local scale. However, a global sampling bias was detected in the seasonal signal due to the clustering of CryoSat-2 data in higher elevation areas. The retrieval processing chain presented here does not correct for changes in surface scattering conditions and appears to be insensitive to the 2012 melt event (Nilsson et al., 2015). This in contrast to the elevation changes derived from ESA's L2 elevation product, which where found to be sensitive to the effects of the melt event. The positive elevation bias created by the event introduced a discrepancy between the two products with a magnitude of roughly 90 km3/year. This difference can directly be attributed to the differences in retracking procedure pointing to the importance of the retracking of the radar waveforms for altimetric volume change studies. Greenland 2012 melt event effects on CryoSat-2 radar altimetry./ Nilsson, Johan; Vallelonga, Paul Travis; Simonsen, Sebastian Bjerregaard; Sørensen, Louise Sandberg; Forsberg, René; Dahl-Jensen, Dorthe; Hirabayashi, Motohiro; Goto-Azuma, Kumiko; Hvidberg, Christine S.; Kjær, Helle A.; Satow, Kazuhide.

  19. Greenland ice-sheet contribution to sea-level rise buffered by meltwater storage in firn.

    Science.gov (United States)

    Harper, J; Humphrey, N; Pfeffer, W T; Brown, J; Fettweis, X

    2012-11-08

    Surface melt on the Greenland ice sheet has shown increasing trends in areal extent and duration since the beginning of the satellite era. Records for melt were broken in 2005, 2007, 2010 and 2012. Much of the increased surface melt is occurring in the percolation zone, a region of the accumulation area that is perennially covered by snow and firn (partly compacted snow). The fate of melt water in the percolation zone is poorly constrained: some may travel away from its point of origin and eventually influence the ice sheet's flow dynamics and mass balance and the global sea level, whereas some may simply infiltrate into cold snow or firn and refreeze with none of these effects. Here we quantify the existing water storage capacity of the percolation zone of the Greenland ice sheet and show the potential for hundreds of gigatonnes of meltwater storage. We collected in situ observations of firn structure and meltwater retention along a roughly 85-kilometre-long transect of the melting accumulation area. Our data show that repeated infiltration events in which melt water penetrates deeply (more than 10 metres) eventually fill all pore space with water. As future surface melt intensifies under Arctic warming, a fraction of melt water that would otherwise contribute to sea-level rise will fill existing pore space of the percolation zone. We estimate the lower and upper bounds of this storage sink to be 322 ± 44 gigatonnes and  1,289(+388)(-252) gigatonnes, respectively. Furthermore, we find that decades are required to fill this pore space under a range of plausible future climate conditions. Hence, routing of surface melt water into filling the pore space of the firn column will delay expansion of the area contributing to sea-level rise, although once the pore space is filled it cannot quickly be regenerated.

  20. Life on thin ice: Insights from Uummannaq, Greenland for connecting climate science with Arctic communities

    Science.gov (United States)

    Baztan, Juan; Cordier, Mateo; Huctin, Jean-Michel; Zhu, Zhiwei; Vanderlinden, Jean-Paul

    2017-09-01

    What are the links between mainstream climate science and local community knowledge? This study takes the example of Greenland, considered one of the regions most impacted by climate change, and Inuit people, characterized as being highly adaptive to environmental change, to explore this question. The study is based on 10 years of anthropological participatory research in Uummannaq, Northwest Greenland, along with two fieldwork periods in October 2014 and April 2015, and a quantitative bibliometric analysis of the international literature on sea ice - a central subject of concern identified by Uummannaq community members during the fieldwork periods. Community members' perceptions of currently available scientific climate knowledge were also collected during the fieldwork. This was done to determine if community members consider available scientific knowledge salient and if it covers issues they consider relevant. The bibliometric analysis of the sea ice literature provided additional insight into the degree to which scientific knowledge about climate change provides information relevant for the community. Our results contribute to the ongoing debate on the missing connections between community worldviews, cultural values, livelihood needs, interests and climate science. Our results show that more scientific research efforts should consider local-level needs in order to produce local-scale knowledge that is more salient, credible and legitimate for communities experiencing climate change. In Uummannaq, as in many Inuit communities with similar conditions, more research should be done on sea ice thickness in winter and in areas through which local populations travel. This paper supports the growing evidence that whenever possible, climate change research should focus on environmental features that matter to communities, at temporal and spatial scales relevant to them, in order to foster community adaptations to change. We recommend such research be connected to and

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

    Science.gov (United States)

    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.

  2. Characterization of icebergs and floating sea ice in the Yung Sund fjord in Greenland from satellite radar and optical images.

    Science.gov (United States)

    Guillaso, Stephane; Gay, Michel; Gervaise, Cedric

    2017-04-01

    At the Zackenberg site, sea ice starts to move between June and September resulting in icebergs flowing freely on the sea. Splitting into smaller parts, they reduce in size. Icebergs represent a risk for maritime transport and needs to be studied. In order to determine iceberg density per surface unit, size distribution, and movement of icebergs, we need to observe, detect, range and track them. The use of SAR images is particularly well adapted in regions where cloud cover is very present. We focused our study on the Yung Sund fjord in Greenland, where lots of icebergs and sea ice are generated during the summer. In the beginning of July, sea ice breaks up first, followed by icebergs created by the different glaciers based in the ocean. During our investigation, we noticed that the iceberg and sea ice were drifting very fast and thus, we needed to adapt our methodology. To achieve our goal, we collected all remote sensing data available in the region, principally Sentinel 1/2 and LandSAT 8 during one ice free season (from July 1st 2016 to September 30th, 2016). We developed an original approach in order to detect, characterize and track icebergs and sea ice independently from data. The iceberg detection was made using a watershed technique. The advantage of this technique is that it can be applied to both optical and radar images. For the latter, calibrated intensity is transformed into an image using a scaling function, in order to make ice brighter. Land data is masked using a topographic map. When data is segmented, a statistical test derived from the CFAR approach is performed to isolate an iceberg and floating sea ice from the ocean. Finally, a method, such SIFT or BRISK is used to identify and track the different segmented object. These approaches give a representation of the object and make the tracking easier and independent of the scale and rotation, which can occur because icebergs are dependent on ocean currents and wind. Finally, to fill in the gap

  3. Comparison of modelled runoff with observed proglacial discharge across the western margin of the Greenland ice sheet

    Science.gov (United States)

    Moustafa, S.; Rennermalm, A.; van As, D.; Overeem, I.; Tedesco, M.; Mote, T. L.; Koenig, L.; Smith, L. C.; Hagedorn, B.; Sletten, R. S.; Mikkelsen, A. B.; Hasholt, B.; Hall, D. K.; Fettweis, X.; Pitcher, L. H.; Hubbard, A.

    2017-12-01

    Greenland ice sheet surface ablation now dominates its total mass loss contributions to sea-level rise. Despite the increasing importance of Greenland's sea-level contribution, a quantitative inter-comparison between modeled and measured melt, runoff and discharge across multiple drainage basins is conspicuously lacking. Here we investigate the accuracy of model discharge estimates from the Modèle Atmosphérique Régionale (MAR v3.5.2) regional climate model by comparison with in situ proglacial river discharge measurements at three West Greenland drainage basins - North River (Thule), Watson River (Kangerlussuaq), and Naujat Kuat River (Nuuk). At each target catchment, we: 1) determine optimal drainage basin delineations; 2) assess primary drivers of melt; 3) evaluate MAR at daily, 5-, 10- and 20-day time scales; and 4) identify potential sources for model-observation discrepancies. Our results reveal that MAR resolves daily discharge variability poorly in the Nuuk and Thule basins (r2 = 0.4-0.5), but does capture variability over 5-, 10-, and 20-day means (r2 > 0.7). Model agreement with river flow data, though, is reduced during periods of peak discharge, particularly for the exceptional melt and discharge events of July 2012. Daily discharge is best captured by MAR across the Watson River basin, whilst there is lower correspondence between modeled and observed discharge at the Thule and Naujat Kuat River basins. We link the main source of model error to an underestimation of cloud cover, overestimation of surface albedo, and apparent warm bias in near-surface air temperatures. For future inter-comparison, we recommend using observations from catchments that have a self-contained and well-defined drainage area and an accurate discharge record over variable years coincident with a reliable automatic weather station record. Our study highlights the importance of improving MAR modeled surface albedo, cloud cover representation, and delay functions to reduce model

  4. Calculation of mass discharge of the Greenland ice sheet in the Earth System Model

    Directory of Open Access Journals (Sweden)

    O. O. Rybak

    2016-01-01

    Full Text Available Mass discharge calculation is a challenging task for the ice sheet modeling aimed at evaluation of their contribution to the global sea level rise during past interglacials, as well as one of the consequences of future climate change. In Greenland, ablation is the major source of fresh water runoff. It is approximately equal to the dynamical discharge (iceberg calving. Its share might have still larger during the past interglacials when the margins of the GrIS retreated inland. Refreezing of the melted water and its retention are two poorly known processes playing as a counterpart of melting and, thus, exerting influence on the run off. Interaction of ice sheets and climate is driven by energy and mass exchange processes and is complicated by numerous feed-backs. To study the complex of these processes, coupling of an ice sheet model and a climate model (i.e. models of the atmosphere and the ocean in one model is required, which is often called the Earth System Model (ESM. Formalization of processes of interaction between the ice sheets and climate within the ESM requires elaboration of special techniques to deal with dramatic differences in spatial and temporal variability scales within each of three ESM’s blocks. In this paper, we focus on the method of coupling of a Greenland ice sheet model (GrISM with the climate model INMCM having been developed in the Institute of Numerical Mathematics of Russian Academy of Sciences. Our coupling approach consists in applying of a special buffer model, which serves as an interface between GrISM and INMCM. A simple energy and water exchange model (EWBM-G allows realistic description of surface air temperature and precipitation fields adjusted to a relief of elevation of the GrIS surface. In a series of diagnostic numerical experiments with the present-day GrIS geometry and the modeled climate we studied sensitivity of the modeled surface mass balance and run off to the key EWBM-G parameters and compared

  5. Quantifying Black Carbon Deposition Over the Greenland Ice Sheet from Forest Fires in Canada

    Science.gov (United States)

    Thomas, J. L.; Polashenski, C. M.; Soja, Amber J.; Marelle, L.; Casey, K. A.; Choi, H. D.; Raut, J.-C.; Wiedinmyer, C.; Emmons, L. K.; Fast, J. D.; hide

    2017-01-01

    Black carbon (BC) concentrations observed in 22 snowpits sampled in the northwest sector of the Greenland ice sheet in April 2014 have allowed us to identify a strong and widespread BC aerosol deposition event, which was dated to have accumulated in the pits from two snow storms between 27 July and 2 August 2013. This event comprises a significant portion (57 on average across all pits) of total BC deposition over 10 months (July 2013 to April 2014). Here we link this deposition event to forest fires burning in Canada during summer 2013 using modeling and remote sensing tools. Aerosols were detected by both the Cloud-Aerosol Lidar with Orthogonal Polarization (on board CALIPSO) and Moderate Resolution Imaging Spectroradiometer (Aqua) instruments during transport between Canada and Greenland. We use high-resolution regional chemical transport modeling (WRF-Chem) combined with high-resolution fire emissions (FINNv1.5) to study aerosol emissions, transport, and deposition during this event. The model captures the timing of the BC deposition event and shows that fires in Canada were the main source of deposited BC. However, the model underpredicts BC deposition compared to measurements at all sites by a factor of 2100. Underprediction of modeled BC deposition originates from uncertainties in fire emissions and model treatment of wet removal of aerosols. Improvements in model descriptions of precipitation scavenging and emissions from wildfires are needed to correctly predict deposition, which is critical for determining the climate impacts of aerosols that originate from fires.

  6. Regions of open water and melting sea ice drive new particle formation in North East Greenland.

    Science.gov (United States)

    Dall Osto, M; Geels, C; Beddows, D C S; Boertmann, D; Lange, R; Nøjgaard, J K; Harrison, Roy M; Simo, R; Skov, H; Massling, A

    2018-04-17

    Atmospheric new particle formation (NPF) and growth significantly influences the indirect aerosol-cloud effect within the polar climate system. In this work, the aerosol population is categorised via cluster analysis of aerosol number size distributions (9-915 nm, 65 bins) taken at Villum Research Station, Station Nord (VRS) in North Greenland during a 7 year record (2010-2016). Data are clustered at daily averaged resolution; in total, we classified six categories, five of which clearly describe the ultrafine aerosol population, one of which is linked to nucleation events (up to 39% during summer). Air mass trajectory analyses tie these frequent nucleation events to biogenic precursors released by open water and melting sea ice regions. NPF events in the studied regions seem not to be related to bird colonies from coastal zones. Our results show a negative correlation (r = -0.89) between NPF events and sea ice extent, suggesting the impact of ultrafine Arctic aerosols is likely to increase in the future, given the likely increased sea ice melting. Understanding the composition and the sources of Arctic aerosols requires further integrated studies with joint multi-component ocean-atmosphere observation and modelling.

  7. How effective is albedo modification (solar radiation management geoengineering) in preventing sea-level rise from the Greenland Ice Sheet?

    International Nuclear Information System (INIS)

    Applegate, Patrick J; Keller, Klaus

    2015-01-01

    Albedo modification (AM) is sometimes characterized as a potential means of avoiding climate threshold responses, including large-scale ice sheet mass loss. Previous work has investigated the effects of AM on total sea-level rise over the present century, as well as AM’s ability to reduce long-term (≫10 3 yr) contributions to sea-level rise from the Greenland Ice Sheet (GIS). These studies have broken new ground, but neglect important feedbacks in the GIS system, or are silent on AM’s effectiveness over the short time scales that may be most relevant for decision-making (<10 3 yr). Here, we assess AM’s ability to reduce GIS sea-level contributions over decades to centuries, using a simplified ice sheet model. We drive this model using a business-as-usual base temperature forcing scenario, as well as scenarios that reflect AM-induced temperature stabilization or temperature drawdown. Our model results suggest that (i) AM produces substantial near-term reductions in the rate of GIS-driven sea-level rise. However, (ii) sea-level rise contributions from the GIS continue after AM begins. These continued sea level rise contributions persist for decades to centuries after temperature stabilization and temperature drawdown begin, unless AM begins in the next few decades. Moreover, (iii) any regrowth of the GIS is delayed by decades or centuries after temperature drawdown begins, and is slow compared to pre-AM rates of mass loss. Combined with recent work that suggests AM would not prevent mass loss from the West Antarctic Ice Sheet, our results provide a nuanced picture of AM’s possible effects on future sea-level rise. (letter)

  8. Investigations of the form and flow of ice sheets and glaciers using radio-echo sounding

    Energy Technology Data Exchange (ETDEWEB)

    Dowdeswell, J A; Evans, S [Scott Polar Research Institute, University of Cambridge, Cambridge CB2 1ER (United Kingdom)

    2004-10-01

    Radio-echo sounding (RES), utilizing a variety of radio frequencies, was developed to allow glaciologists to measure the thickness of ice sheets and glaciers. We review the nature of electromagnetic wave propagation in ice and snow, including the permittivity of ice, signal attenuation and volume scattering, along with reflection from rough and specular surfaces. The variety of instruments used in RES of polar ice sheets and temperate glaciers is discussed. The applications and insights that a knowledge of ice thickness, and the wider nature of the form and flow of ice sheets, provides are also considered. The thickest ice measured is 4.7 km in East Antarctica. The morphology of the Antarctic and Greenland ice sheets, and many of the smaller ice caps and glaciers of the polar regions, has been investigated using RES. These findings are being used in three-dimensional numerical models of the response of the cryosphere to environmental change. In addition, the distribution and character of internal and basal reflectors within ice sheets contains information on, for example, ice-sheet layering and its chrono-stratigraphic significance, and has enabled the discovery and investigation of large lakes beneath the Antarctic Ice Sheet. Today, RES from ground-based and airborne platforms remains the most effective tool for measuring ice thickness and internal character.

  9. Heat sources for glacial ice melt in a West Greenland tidewater outlet glacier fjord: The role of subglacial freshwater discharge

    DEFF Research Database (Denmark)

    Bendtsen, Jørgen; Mortensen, John; Lennert, Kunuk

    2015-01-01

    The melting of tidewater outlet glaciers from the Greenland Ice Sheet contributes significantly to global sea level rise. Accelerated mass loss is related to melt-processes in front of calving glaciers, yet the role of ocean heat transports is poorly understood. Here we present the first direct...... of the area near the glacier showed that ice melt was mainly due to ocean heat transport and that direct plume-associated melt was only important in periods with high meltwater discharge rates of ~100 m3 s−1. Ocean mixing outside of the plume area was thus the primary heat source for melting glacier ice....

  10. Mapping ice-bonded permafrost with electrical methods in Sisimiut, West Greenland

    DEFF Research Database (Denmark)

    Ingeman-Nielsen, Thomas

    2006-01-01

    Permafrost delineation and thickness determination is of great importance in engineering related projects in arctic areas. In this paper, 2D geoelectrical measurements are applied and evaluated for permafrost mapping in an area in West Greenland. Multi-electrode resistivity profiles (MEP) have been...... collected and are compared with borehole information. It is shown that the permafrost thickness in this case is grossly overestimated by a factor of two to three. The difference between the inverted 2D resistivity sections and the borehole information is explained by macro-anisotropy due to the presence...... of horizontal ice-lenses in the frozen clay deposits. It is concluded that where the resistivity method perform well for lateral permafrost mapping, great care should be taken in evaluating permafrost thickness based on 2D resistivity profiles alone. Additional information from boreholes or other geophysical...

  11. Observations of Pronounced Greenland Ice Sheet Firn Warming and Implications for Runoff Production

    Science.gov (United States)

    Polashenski, Chris; Courville, Zoe; Benson, Carl; Wagner, Anna; Chen, Justin; Wong, Gifford; Hawley, Robert; Hall, Dorothy

    2014-01-01

    Field measurements of shallow borehole temperatures in firn across the northern Greenland ice sheet are collected during May 2013. Sites first measured in 19521955 are revisited, showing long-term trends in firn temperature. Results indicate a pattern of substantial firn warming (up to +5.7C) at midlevel elevations (1400-2500 m) and little temperature change at high elevations (2500 m). We find that latent heat transport into the firn due to meltwater percolation drives the observed warming. Modeling shows that heat is stored at depth for several years, and energy delivered from consecutive melt events accumulates in the firn. The observed warming is likely not yet in equilibrium with recent melt production rates but captures the progression of sites in the percolation facies toward net runoff production.

  12. Periodic outburst floods from an ice-dammed lake in East Greenland.

    Science.gov (United States)

    Grinsted, Aslak; Hvidberg, Christine S; Campos, Néstor; Dahl-Jensen, Dorthe

    2017-08-30

    We report evidence of four cycles of outburst floods from Catalina Lake, an ice-dammed lake in East Greenland, identified in satellite imagery between 1966-2016. The lake measures 20-25 km 2 , and lake level drops 130-150 m in each event, corresponding to a water volume of 2.6-3.4 Gt, and a release of potential energy of 10 16  J, among the largest outburst floods reported in historical times. The drainage cycle has shortened systematically, and the lake filling rate has increased over each cycle, suggesting that the drainage pattern is changing due to climate warming with possible implications for environmental conditions in Scoresbysund fjord.

  13. Thermal tracing of retained meltwater in the lower accumulation area of the Southwestern Greenland ice sheet

    DEFF Research Database (Denmark)

    Charalampidis, Charalampos; Van As, Dirk; Colgan, William T.

    2016-01-01

    We present in situ firn temperatures from the extreme 2012 melt season in the southwestern lower accumulation area of the Greenland ice sheet. The upper 2.5 m of snow and firn was temperate during the melt season, when vertical meltwater percolation was inefficient due to a similar to 5.5 m thick...... no indication of meltwater percolation below 9 m depth or complete filling of pore volume above, firn at 10 and 15 m depth was respectively 4.2-4.5 ºC and 1.7 ºC higher than in a conductivity-only simulation. Even though meltwater percolation in 2012 was inefficient, firn between 2 and 15 m depth the following...

  14. Disentangling the Roles of Atmospheric and Oceanic Forcing on the Last Deglaciation of the Greenland Ice Sheet

    Science.gov (United States)

    Keisling, B. A.; Deconto, R. M.

    2017-12-01

    Today the Greenland Ice Sheet loses mass via both oceanic and atmospheric processes. However, the relative importance of these mass balance components is debated, especially their potential impact on ongoing and future mass imbalance. Discerning the impact of oceanic versus atmospheric forcing during past periods of mass loss provides potential insight into the future behavior of the ice sheet. Here we present an ensemble of Greenland Ice Sheet simulations of the last deglaciation, designed to assess separately the roles of the ocean and the atmosphere in driving mass loss over the last twenty thousand years. We use twenty-eight different ocean forcing scenarios along with a cutting-edge reconstruction of time-evolving atmospheric conditions based on climate model output and δ15N-based temperature reconstructions to generate a range of ice-sheet responses during the deglaciation. We then compare the simulated timing of ice-retreat in individual catchments with estimates based on both 10Be (exposure) and 14C (minimum-limiting) dates. These experiments allow us to identify the ocean forcing scenario that best match the data on a local-to-regional (i.e., 100-1000 km) scales, providing an assessment of the relative importance of ocean and atmospheric forcing components around the periphery of Greenland. We use these simulations to quantify the importance of the three major mass balance terms (calving, oceanic melting, and surface melting) and assess the uncertainty of the relative influence of these factors during the most recent periods of major ice loss. Our results show that mass balance components around different sectors of the ice sheet respond differently to forcing, with oceanic components driving the majority of retreat in south and east Greenland and atmospheric forcing dominating in west and north Greenland In addition, we target three areas at high spatial resolution ( 1 km) around Greenland currently undergoing substantial change (Jakobshavn, Petermann

  15. Resolving climate change in the period 15-23 ka in Greenland ice cores: A new application of spectral trend analysis

    NARCIS (Netherlands)

    de Jong, M.G.G.; Nio, D.S.; Böhm, A.R.; Seijmonsbergen, H.C.; de Graaff, L.W.S.

    2009-01-01

    Northern Hemisphere climate history through and following the Last Glacial Maximum is recorded in detail in ice cores from Greenland. However, the period between Greenland Interstadials 1 and 2 (15-23 ka), i.e. the period of deglaciation following the last major glaciation, has been difficult to

  16. Spatial gradients of temperature, accumulation and δ18O-ice in Greenland over a series of Dansgaard–Oeschger events

    Directory of Open Access Journals (Sweden)

    M. Guillevic

    2013-05-01

    Full Text Available Air and water stable isotope measurements from four Greenland deep ice cores (GRIP, GISP2, NGRIP and NEEM are investigated over a series of Dansgaard–Oeschger events (DO 8, 9 and 10, which are representative of glacial millennial scale variability. Combined with firn modeling, air isotope data allow us to quantify abrupt temperature increases for each drill site (1σ = 0.6 °C for NEEM, GRIP and GISP2, 1.5 °C for NGRIP. Our data show that the magnitude of stadial–interstadial temperature increase is up to 2 °C larger in central and North Greenland than in northwest Greenland: i.e., for DO 8, a magnitude of +8.8 °C is inferred, which is significantly smaller than the +11.1 °C inferred at GISP2. The same spatial pattern is seen for accumulation increases. This pattern is coherent with climate simulations in response to reduced sea-ice extent in the Nordic seas. The temporal water isotope (δ18O–temperature relationship varies between 0.3 and 0.6 (±0.08 ‰ °C−1 and is systematically larger at NEEM, possibly due to limited changes in precipitation seasonality compared to GISP2, GRIP or NGRIP. The gas age−ice age difference of warming events represented in water and air isotopes can only be modeled when assuming a 26% (NGRIP to 40% (GRIP lower accumulation than that derived from a Dansgaard–Johnsen ice flow model.

  17. MEaSUREs Greenland Ice Mapping Project (GIMP) Digital Elevation Model from GeoEye and WorldView Imagery, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set consists of an enhanced resolution digital elevation model (DEM) for the Greenland Ice Sheet. The DEM is derived from sub-meter resolution,...

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

    Science.gov (United States)

    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

  19. IceCube systematic errors investigation: Simulation of the ice

    Energy Technology Data Exchange (ETDEWEB)

    Resconi, Elisa; Wolf, Martin [Max-Planck-Institute for Nuclear Physics, Heidelberg (Germany); Schukraft, Anne [RWTH, Aachen University (Germany)

    2010-07-01

    IceCube is a neutrino observatory for astroparticle and astronomy research at the South Pole. It uses one cubic kilometer of Antartica's deepest ice (1500 m-2500 m in depth) to detect Cherenkov light, generated by charged particles traveling through the ice, with an array of phototubes encapsulated in glass pressure spheres. The arrival time as well as the charge deposited of the detected photons represent the base measurements that are used for track and energy reconstruction of those charged particles. The optical properties of the deep antarctic ice vary from layer to layer. Measurements of the ice properties and their correct modeling in Monte Carlo simulation is then of primary importance for the correct understanding of the IceCube telescope behavior. After a short summary about the different methods to investigate the ice properties and to calibrate the detector, we show how the simulation obtained by using this information compares to the measured data and how systematic errors due to uncertain ice properties are determined in IceCube.

  20. Satellite-derived submarine melt rates and mass balance (2011-2015) for Greenland's largest remaining ice tongues

    Science.gov (United States)

    Wilson, Nat; Straneo, Fiammetta; Heimbach, Patrick

    2017-12-01

    Ice-shelf-like floating extensions at the termini of Greenland glaciers are undergoing rapid changes with potential implications for the stability of upstream glaciers and the ice sheet as a whole. While submarine melting is recognized as a major contributor to mass loss, the spatial distribution of submarine melting and its contribution to the total mass balance of these floating extensions is incompletely known and understood. Here, we use high-resolution WorldView satellite imagery collected between 2011 and 2015 to infer the magnitude and spatial variability of melt rates under Greenland's largest remaining ice tongues - Nioghalvfjerdsbræ (79 North Glacier, 79N), Ryder Glacier (RG), and Petermann Glacier (PG). Submarine melt rates under the ice tongues vary considerably, exceeding 50 m a-1 near the grounding zone and decaying rapidly downstream. Channels, likely originating from upstream subglacial channels, give rise to large melt variations across the ice tongues. We compare the total melt rates to the influx of ice to the ice tongue to assess their contribution to the current mass balance. At Petermann Glacier and Ryder Glacier, we find that the combined submarine and aerial melt approximately balances the ice flux from the grounded ice sheet. At Nioghalvfjerdsbræ the total melt flux (14.2 ± 0.96 km3 a-1 w.e., water equivalent) exceeds the inflow of ice (10.2 ± 0.59 km3 a-1 w.e.), indicating present thinning of the ice tongue.

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

    Science.gov (United States)

    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

  2. Phylogenetic and physiological diversity of microorganisms isolated from a deep greenland glacier ice core

    Science.gov (United States)

    Miteva, V. I.; Sheridan, P. P.; Brenchley, J. E.

    2004-01-01

    We studied a sample from the GISP 2 (Greenland Ice Sheet Project) ice core to determine the diversity and survival of microorganisms trapped in the ice at least 120,000 years ago. Previously, we examined the phylogenetic relationships among 16S ribosomal DNA (rDNA) sequences in a clone library obtained by PCR amplification from genomic DNA extracted from anaerobic enrichments. Here we report the isolation of nearly 800 aerobic organisms that were grouped by morphology and amplified rDNA restriction analysis patterns to select isolates for further study. The phylogenetic analyses of 56 representative rDNA sequences showed that the isolates belonged to four major phylogenetic groups: the high-G+C gram-positives, low-G+C gram-positives, Proteobacteria, and the Cytophaga-Flavobacterium-Bacteroides group. The most abundant and diverse isolates were within the high-G+C gram-positive cluster that had not been represented in the clone library. The Jukes-Cantor evolutionary distance matrix results suggested that at least 7 isolates represent new species within characterized genera and that 49 are different strains of known species. The isolates were further categorized based on the isolation conditions, temperature range for growth, enzyme activity, antibiotic resistance, presence of plasmids, and strain-specific genomic variations. A significant observation with implications for the development of novel and more effective cultivation methods was that preliminary incubation in anaerobic and aerobic liquid prior to plating on agar media greatly increased the recovery of CFU from the ice core sample.

  3. An efficient regional energy-moisture balance model for simulation of the Greenland Ice Sheet response to climate change

    Directory of Open Access Journals (Sweden)

    A. Robinson

    2010-04-01

    Full Text Available In order to explore the response of the Greenland ice sheet (GIS to climate change on long (centennial to multi-millennial time scales, a regional energy-moisture balance model has been developed. This model simulates seasonal variations of temperature and precipitation over Greenland and explicitly accounts for elevation and albedo feedbacks. From these fields, the annual mean surface temperature and surface mass balance can be determined and used to force an ice sheet model. The melt component of the surface mass balance is computed here using both a positive degree day approach and a more physically-based alternative that includes insolation and albedo explicitly. As a validation of the climate model, we first simulated temperature and precipitation over Greenland for the prescribed, present-day topography. Our simulated climatology compares well to observations and does not differ significantly from that of a simple parameterization used in many previous simulations. Furthermore, the calculated surface mass balance using both melt schemes falls within the range of recent regional climate model results. For a prescribed, ice-free state, the differences in simulated climatology between the regional energy-moisture balance model and the simple parameterization become significant, with our model showing much stronger summer warming. When coupled to a three-dimensional ice sheet model and initialized with present-day conditions, the two melt schemes both allow realistic simulations of the present-day GIS.

  4. TRACEing Last Glacial Period (25-80 ka b2k) tephra horizons within North Atlantic marine cores and exploring links to the Greenland ice-cores

    Science.gov (United States)

    Abbott, P. M.; Davies, S. M.; Griggs, A. J.; Bourne, A. J.; Cook, E.; Pearce, N. J. G.; Austin, W. E. N.; Chapman, M.; Hall, I. R.; Purcell, C. S.; Scourse, J. D.; Rasmussen, T. L.

    2015-12-01

    Tephrochronology is a powerful technique for the correlation and synchronisation of disparate palaeoclimatic records from different depositional environments and has considerable potential for testing climatic phasing. For example, the relative timing of atmospheric and marine changes caused by the abrupt climatic events that punctuated the last glacial period within the North Atlantic region. Here we report on efforts to establish a framework of tephra horizons within North Atlantic marine sequences that can correlate these records and if traced in the Greenland ice-cores can act as isochronous tie-lines. Investigations have been conducted on a network of marine cores from a number of sites across the North Atlantic. Tephra horizons have been identified using cryptotephra extraction techniques more commonly applied to the study of terrestrial sequences. There are two main challenges with assessing cryptotephras in the glacial North Atlantic; i) determining the transportation processes and ii) assessing the influence of secondary reworking processes and the stratigraphic integrity of the isochrons. These processes and their influence are investigated for each cryptotephra using shard size variations, major element heterogeneity and co-variance of IRD input for some cores. Numerous Icelandic cryptophras have been successfully identified in the marine records and we will discuss the integration of a number of these with an isochronous nature into a marine tephra framework and how potential correlations to the Greenland ice-core tephra framework are determined. Spatial patterns in the nature of tephra records that are emerging from the core network will be highlighted to outline some of the key areas that could be explored in the future. In addition, the synchronisation of multiple North Atlantic records to the Greenland ice-cores using the North Atlantic Ash Zone II to test the synchroneity of an abrupt cooling in the North Atlantic will be discussed.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  7. Modelling seasonal meltwater forcing of the velocity of land-terminating margins of the Greenland Ice Sheet

    Science.gov (United States)

    Koziol, Conrad P.; Arnold, Neil

    2018-03-01

    Surface runoff at the margin of the Greenland Ice Sheet (GrIS) 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 GrIS. 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.

  8. Translating hydrologically-relevant variables from the ice sheet model SICOPOLIS to the Greenland Analog Project hydrologic modeling domain

    Science.gov (United States)

    Vallot, Dorothée; Applegate, Patrick; Pettersson, Rickard

    2013-04-01

    Projecting future climate and ice sheet development requires sophisticated models and extensive field observations. Given the present state of our knowledge, it is very difficult to say what will happen with certainty. Despite the ongoing increase in atmospheric greenhouse gas concentrations, the possibility that a new ice sheet might form over Scandinavia in the far distant future cannot be excluded. The growth of a new Scandinavian Ice Sheet would have important consequences for buried nuclear waste repositories. The Greenland Analogue Project, initiated by the Swedish Nuclear Fuel and Waste Management Company (SKB), is working to assess the effects of a possible future ice sheet on groundwater flow by studying a constrained domain in Western Greenland by field measurements (including deep bedrock drilling in front of the ice sheet) combined with numerical modeling. To address the needs of the GAP project, we interpolated results from an ensemble of ice sheet model runs to the smaller and more finely resolved modeling domain used in the GAP project's hydrologic modeling. Three runs have been chosen with three fairly different positive degree-day factors among those that reproduced the modern ice margin at the borehole position. The interpolated results describe changes in hydrologically-relevant variables over two time periods, 115 ka to 80 ka, and 20 ka to 1 ka. In the first of these time periods, the ice margin advances over the model domain; in the second time period, the ice margin retreats over the model domain. The spatially-and temporally dependent variables that we treated include the ice thickness, basal melting rate, surface mass balance, basal temperature, basal thermal regime (frozen or thawed), surface temperature, and basal water pressure. The melt flux is also calculated.

  9. Tracking millennial-scale Holocene glacial advance and retreat using osmium isotopes: Insights from the Greenland ice sheet

    Science.gov (United States)

    Rooney, Alan D.; Selby, David; Llyod, Jeremy M.; Roberts, David H.; Luckge, Andreas; Sageman, Bradley B.; Prouty, Nancy G.

    2016-01-01

    High-resolution Os isotope stratigraphy can aid in reconstructing Pleistocene ice sheet fluctuation and elucidating the role of local and regional weathering fluxes on the marine Os residence time. This paper presents new Os isotope data from ocean cores adjacent to the West Greenland ice sheet that have excellent chronological controls. Cores MSM-520 and DA00-06 represent distal to proximal sites adjacent to two West Greenland ice streams. Core MSM-520 has a steadily decreasing Os signal over the last 10 kyr (187Os/188Os = 1.35–0.81). In contrast, Os isotopes from core DA00-06 (proximal to the calving front of Jakobshavn Isbræ) highlight four stages of ice stream retreat and advance over the past 10 kyr (187Os/188Os = 2.31; 1.68; 2.09; 1.47). Our high-resolution chemostratigraphic records provide vital benchmarks for ice-sheet modelers as we attempt to better constrain the future response of major ice sheets to climate change. Variations in Os isotope composition from sediment and macro-algae (seaweed) sourced from regional and global settings serve to emphasize the overwhelming effect weathering sources have on seawater Os isotope composition. Further, these findings demonstrate that the residence time of Os is shorter than previous estimates of ∼104 yr.

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

    Science.gov (United States)

    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.

  11. Large-scale Modeling of the Greenland Ice Sheet on Long Timescales

    DEFF Research Database (Denmark)

    Solgaard, Anne Munck

    is investigated as well as its early history. The studies are performed using an ice-sheet model in combination with relevant forcing from observed and modeled climate. Changes in ice-sheet geometry influences atmospheric flow (and vice versa) hereby changing the forcing patterns. Changes in the overall climate...... and climate model is included shows, however, that a Föhn effect is activated and hereby increasing temperatures inland and inhibiting further ice-sheet expansion into the interior. This indicates that colder than present temperatures are needed in order for the ice sheet to regrow to the current geometry....... Accordingto this hypothesis, two stages of uplift since the Late Miocene lead to the present-day topography. The results of the ice-sheet simulations show geometries in line with geologicobservations through the period, and it is found that the uplift events enhance the effect of the climatic deterioration...

  12. Ice-ocean interaction and calving front morphology at two west Greenland tidewater outlet glaciers

    Science.gov (United States)

    Chauché, N.; Hubbard, A.; Gascard, J.-C.; Box, J. E.; Bates, R.; Koppes, M.; Sole, A.; Christoffersen, P.; Patton, H.

    2014-08-01

    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 (GrIS), 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 GrIS 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.

  13. Use and Limitations of a Climate-Quality Data Record to Study Temperature Trends on the Greenland Ice Sheet

    Science.gov (United States)

    Hall, Dorothy K.; Comiso, Josefino C.; Shuman, Christopher A.; Koenig, Lora S.; DiGirolamo, Nicolo E.

    2011-01-01

    Enhanced melting of the Greenland Ice Sheet has been documented in recent literature along with surface-temperature increases measured using infrared satellite data since 1981. Using a recently-developed climate-quality data record, 11- and 12-year trends in the clear-sky ice-surface temperature (IST) of the Greenland Ice Sheet have been studied using the Moderate-Resolution Imaging Spectroradiometer (MODIS) IST product. Daily and monthly MODIS ISTs of the Greenland Ice Sheet beginning on 1 March 2000 and continuing through 31 December 2010 are now available at 6.25-km spatial resolution on a polar stereographic grid as described in Hall et al. (submitted). This record will be elevated in status to a climate-data record (CDR) when more years of data become available either from the MODIS on the Terra or Aqua satellites, or from the Visible Infrared Imager Radiometer Suite (VIIRS) to be launched in October 2011. Maps showing the maximum extent of melt for the entire ice sheet and for the six major drainage basins have been developed from the MODIS IST dataset. Twelve-year trends of the duration of the melt season on the ice sheet vary in different drainage basins with some basins melting progressively earlier over the course of the study period. Some (but not all) of the basins also show a progressively-longer duration of melt. IST 12-year trends are compared with in-situ data, and climate data from the Modern Era Retrospective-Analysis for Research and Applications (MERRA) Reanalysis.

  14. The Greenland ice sheet - a model for its culmination and decay during and after the last glacial maximum

    DEFF Research Database (Denmark)

    Funder, Svend Visby; Hansen, Louise

    1996-01-01

    there was little change at all. The driving factor during this step was calving caused by rising sea level. This lasted until c. 10 ka, but may have been consumated before the Younger Dryas. The second step began with a glacier-readvance between 10 and 9.5 ka, and after this the fjord glaciers began to retreat....... Maximum Holocene uplift was attained in areas of the 10 ka ice margin, indicating that the uplift is essentially a response to the melting and unloading of ice that began at this time. In suppport of this, recent results in West, North and East Greenland indicate that the...

  15. Increasing meltwater discharge from the Nuuk region of the Greenland ice sheet and implications for mass balance (1960-2012)

    DEFF Research Database (Denmark)

    van As, Dirk; Langer Andersen, Morten; Petersen, Dorthe

    2014-01-01

    We assess the runoff and surface mass balance (SMB) of the Greenland ice sheet in the Nuuk region (southwest) using output of two regional climate models (RCMs) evaluated by observations. The region encompasses six glaciers that drain into Godthåbsfjord. RCM data (1960-2012) are resampled to a high...... spatial resolution to include the narrow (relative to the native grid spacing) glacier trunks in the ice mask. Comparing RCM gridded results with automaticweather station (AWS) point measurements reveals that locally models can underestimate ablation andoverestimate accumulation by up to tens of per cent...

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

    Science.gov (United States)

    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

  17. Validation of a Climate-Data Record of the "Clear-Kky" Surface Temperature of the Greenland Ice Sheet

    Science.gov (United States)

    Hall, Dorothy K.; Box, Jason E.; Koenig, Lora S.; DiGirolamo, Nicolo E.; Comiso, Josefino C.; Shuman, Christopher A.

    2011-01-01

    Surface temperatures on the Greenland Ice Sheet have been studied on the ground, using automatic weather station (AWS) data from the Greenland-Climate Network (GC-Net), and from analysis of satellite sensor data. Using Advanced Very High Frequency Radiometer (AVHRR) weekly surface temperature maps, warming of the surface of the Greenland Ice Sheet has been documented since 1981. We extended and refined this record using higher-resolution Moderate-Resolution Imaging Spectroradiometer (MODIS) data from March 2000 to the present. We developed a daily and monthly climate-data record (CDR) of the "clear-sky" surface temperature of the Greenland Ice Sheet using an ice-surface temperature (1ST) algorithm developed for use with MODIS data. Validation of this CDR is ongoing. MODIS Terra swath data are projected onto a polar stereographic grid at 6.25-km resolution to develop binary, gridded daily and mean-monthly 1ST maps. Each monthly map also has a color-coded image map that is available to download. Also included with the monthly maps is an accompanying map showing number of days in the month that were used to calculate the mean-monthly 1ST. This is important because no 1ST decision is made by the algorithm for cells that are considered cloudy by the internal cloud mask, so a sufficient number of days must be available to produce a mean 1ST for each grid cell. Validation of the CDR consists of several facets: 1) comparisons between ISTs and in-situ measurements; 2) comparisons between ISTs and AWS data; and 3) comparisons of ISTs with surface temperatures derived from other satellite instruments such as the Thermal Emission and Reflection Radiometer (ASTER) and Enhanced Thematic Mapper Plus (ETM+). Previous work shows that Terra MODIS ISTs are about 3 C lower than in-situ temperatures measured at Summit Camp, during the winter of 2008-09 under clear skies. In this work we begin to compare surface temperatures derived from AWS data with ISTs from the MODIS CDR. The

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

    DEFF Research Database (Denmark)

    Khan, Shfaqat A.; Sasgen, Ingo; Bevis, Michael

    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...

  19. Combined diurnal variations of discharge and hydrochemistry of the Isunnguata Sermia outlet, Greenland Ice Sheet

    Science.gov (United States)

    Graly, Joseph; Harrington, Joel; Humphrey, Neil

    2017-05-01

    In order to examine daily cycles in meltwater routing and storage in the Isunnguata Sermia outlet of the Greenland Ice Sheet, variations in outlet stream discharge and in major element hydrochemistry were assessed over a 6-day period in July 2013. Over 4 days, discharge was assessed from hourly photography of the outlet from multiple vantages, including where midstream naled ice provided a natural gauge. pH, electrical conductivity, suspended sediment, and major element and anion chemistry were measured in samples of stream water collected every 3 h.Photography and stream observations reveal that although river width and stage have only slight diurnal variation, there are large diurnal changes in discharge shown by the doubling in width of what we term the active channel, which is characterized by large standing waves and fast flow. The concentration of dissolved solutes follows a sinusoidal diurnal cycle, except for large and variable increases in dissolved solutes during the stream's waning flow. Solute concentrations vary by ˜ 30 % between diurnal minima and maxima. Discharge maxima and minima lag temperature and surface melt by 3-7 h; diurnal solute concentration minima and maxima lag discharge by 3-6 h.This phase shift between discharge and solute concentration suggests that during high flow, water is either encountering more rock material or is stored in longer contact with rock material. We suggest that expansion of a distributed subglacial hydrologic network into seldom accessed regions during high flow could account for these phenomena, and for a spike of partial silicate reaction products during waning flow, which itself suggests a pressure threshold-triggered release of stored water.

  20. Synchronizing Greenland ice-core records and the Meerfelder maar sediment record via the global cosmogenic radionuclide signature and insights on climate around 11,230 years BP

    Science.gov (United States)

    Mekhaldi, F.; Czymzik, M.; Brauer, A.; Martin-Puertas, C.; Aldahan, A.; Possnert, G.; Muscheler, R.

    2017-12-01

    The causal investigation of multiple paleoclimate records relies on the accuracy of their respective chronostratigraphy. To achieve relative synchronization, cosmogenic radionuclides are an excellent tool because their common signature is global and can be retrieved and measured in different paleoclimate archives. For instance, 10Be can be measured in both ice cores and lake sediments (Berggren et al., 2013; Czymzik et al., 2016) which allows for both archives to be anchored onto radiocarbon timescales by synchronizing 10Be with 14C. We investigate the period 11,500-11,000 years BP when a short cold climate spell is known, from ice-core proxy records, to have occurred in Greenland shortly after the onset of the Holocene - the Preboreal Oscillation (PBO). This period also coincides with one of the largest and longest-lived increase in 14C production rate during the Holocene, which most likely corresponds to a grand solar minimum (around 11,230-11,000 years BP). In consequence, this period ideally illustrates the potential of using a known and clear signal in the production rate of cosmogenic radionuclides as a synchronizing tool, such as caused by large variations in solar activity. Here we measure 10Be in Meerfelder Maar (a well-dated and widely used sediment record from Germany) around 11,230 years BP which allows us to align the 10Be signal in both the Meerfelder Maar (MFM) sediment record and the GRIP ice core to IntCal13. Doing so, we report that i) the structure of the grand solar minimum is well-preserved in the 10Be signal of MFM sediments, ii) the PBO in Greenland occurs during high levels of solar activity and is not clearly observed in MFM, and iii) the PBO in Greenland ends precisely at the onset of the grand solar minimum at 11,230 years BP which also corresponds to a depositional change in MFM sediments (Martin-Puertas et al., 2017). These results thus suggest that changes in solar activity could have been a forcing at play eventually resulting in the

  1. Derivation of High Spatial Resolution Albedo from UAV Digital Imagery: Application over the Greenland Ice Sheet

    Directory of Open Access Journals (Sweden)

    Jonathan C. Ryan

    2017-05-01

    Full Text Available Measurements of albedo are a prerequisite for modeling surface melt across the Earth's cryosphere, yet available satellite products are limited in spatial and/or temporal resolution. Here, we present a practical methodology to obtain centimeter resolution albedo products with accuracies of ±5% using consumer-grade digital camera and unmanned aerial vehicle (UAV technologies. Our method comprises a workflow for processing, correcting and calibrating raw digital images using a white reference target, and upward and downward shortwave radiation measurements from broadband silicon pyranometers. We demonstrate the method with a set of UAV sorties over the western, K-sector of the Greenland Ice Sheet. The resulting albedo product, UAV10A1, covers 280 km2, at a resolution of 20 cm per pixel and has a root-mean-square difference of 3.7% compared to MOD10A1 and 4.9% compared to ground-based broadband pyranometer measurements. By continuously measuring downward solar irradiance, the technique overcomes previous limitations due to variable illumination conditions during and between surveys over glaciated terrain. The current miniaturization of multispectral sensors and incorporation of upward facing radiation sensors on UAV packages means that this technique could become increasingly common in field studies and used for a wide range of applications. These include the mapping of debris, dust, cryoconite and bioalbedo, and directly constraining surface energy balance models.

  2. Derivation of high spatial resolution albedo from UAV digital imagery: application over the Greenland Ice Sheet

    Science.gov (United States)

    Ryan, Jonathan C.; Hubbard, Alun; Box, Jason E.; Brough, Stephen; Cameron, Karen; Cook, Joseph M.; Cooper, Matthew; Doyle, Samuel H.; Edwards, Arwyn; Holt, Tom; Irvine-Fynn, Tristram; Jones, Christine; Pitcher, Lincoln H.; Rennermalm, Asa K.; Smith, Laurence C.; Stibal, Marek; Snooke, Neal

    2017-05-01

    Measurements of albedo are a prerequisite for modelling surface melt across the Earth's cryosphere, yet available satellite products are limited in spatial and/or temporal resolution. Here, we present a practical methodology to obtain centimetre resolution albedo products with accuracies of 5% using consumer-grade digital camera and unmanned aerial vehicle (UAV) technologies. Our method comprises a workflow for processing, correcting and calibrating raw digital images using a white reference target, and upward and downward shortwave radiation measurements from broadband silicon pyranometers. We demonstrate the method with a set of UAV sorties over the western, K-sector of the Greenland Ice Sheet. The resulting albedo product, UAV10A1, covers 280 km2, at a resolution of 20 cm per pixel and has a root-mean-square difference of 3.7% compared to MOD10A1 and 4.9% compared to ground-based broadband pyranometer measurements. By continuously measuring downward solar irradiance, the technique overcomes previous limitations due to variable illumination conditions during and between surveys over glaciated terrain. The current miniaturization of multispectral sensors and incorporation of upward facing radiation sensors on UAV packages means that this technique will likely become increasingly attractive in field studies and used in a wide range of applications for high temporal and spatial resolution surface mapping of debris, dust, cryoconite and bioalbedo and for directly constraining surface energy balance models.

  3. A Climate-Data Record (CDR) of the "Clear-Sky" Surface Temperature of the Greenland Ice Sheet

    Science.gov (United States)

    Hall, Dorothy K.; Comiso, Josefino C.; DiGirolamo, Nocolo E.; Shuman, Christopher A.

    2011-01-01

    We have developed a climate-data record (CDR) of "clear-sky" ice-surface temperature (IST) of the Greenland Ice Sheet using Moderate-Resolution Imaging Spectroradiometer (MODIS) data. The CDR provides daily and monthly-mean IST from March 2000 through December 2010 on a polar stereographic projection at a resolution of 6.25 km. The CDR is amenable to extension into the future using Visible/Infrared Imager Radiometer Suite (VIIRS) data. Regional "clear-sky" surface temperature increases since the early 1980s in the Arctic, measured using Advanced Very High Resolution Radiometer (AVHRR) infrared data, range from 0.57 +/- 0.02 to 0.72 +/- 0.1 c per decade. Arctic warming has important implications for ice-sheet mass balance because much of the periphery of the Greenland Ice Sheet is already near O C during the melt season, and is thus vulnerable to rapid melting if temperatures continue to increase. An increase in melting of the ice sheet would accelerate sea-level rise, an issue affecting potentially billions of people worldwide. The IST CDR will provide a convenient data set for modelers and for climatologists to track changes of the surface temperature of the ice sheet as a whole and of the individual drainage basins on the ice sheet. The daily and monthly maps will provide information on surface melt as well as "clear-sky" temperature. The CDR will be further validated by comparing results with automatic-weather station data and with satellite-derived surface-temperature products.

  4. Sea Ice Retreat and its Impact on the Intensity of Open-Ocean Convection in the Greenland and Iceland Seas

    Science.gov (United States)

    Moore, K.; Våge, K.; Pickart, R. S.; Renfrew, I.

    2016-12-01

    The air-sea transfer of heat and freshwater plays a critical role in the global climate system. This is particularly true for the Greenland and Iceland Seas, where these fluxes drive ocean convection that contributes to Denmark Strait Overflow Water, the densest component of the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). This buoyancy transfer is most pronounced during the winter downstream of the ice edge, where the cold and dry Arctic air first comes in contact with the relatively warm ocean surface. Here we show that the wintertime retreat of sea ice in the region, combined with different rates of warming for the atmosphere and sea surface of the Greenland and Iceland Seas, has resulted in statistically significant reductions of approximately 20% in the magnitude of the winter air-sea heat fluxes since 1979. Furthermore, it is demonstrated that modes of climate variability other than the North Atlantic Oscillation (NAO) are required to fully characterize the regional air-sea interaction in this region. Mixed-layer model simulations imply that a continued decrease in atmospheric forcing will exceed a threshold for the Greenland Sea whereby convection will become depth limited, reducing the ventilation of mid-depth waters in the Nordic Seas. In the Iceland Sea, further reductions have the potential to decrease the supply of the densest overflow waters to the AMOC.

  5. On the importance of the albedo parameterization for the mass balance of the Greenland ice sheet in EC-Earth

    Directory of Open Access Journals (Sweden)

    M. M. Helsen

    2017-08-01

    Full Text Available The albedo of the surface of ice sheets changes as a function of time due to the effects of deposition of new snow, ageing of dry snow, bare ice exposure, melting and run-off. Currently, the calculation of the albedo of ice sheets is highly parameterized within the earth system model EC-Earth by taking a constant value for areas with thick perennial snow cover. This is an important reason why the surface mass balance (SMB of the Greenland ice sheet (GrIS is poorly resolved in the model. The purpose of this study is to improve the SMB forcing of the GrIS by evaluating different parameter settings within a snow albedo scheme. By allowing ice-sheet albedo to vary as a function of wet and dry conditions, the spatial distribution of albedo and melt rate improves. Nevertheless, the spatial distribution of SMB in EC-Earth is not significantly improved. As a reason for this, we identify omissions in the current snow albedo scheme, such as separate treatment of snow and ice and the effect of refreezing. The resulting SMB is downscaled from the lower-resolution global climate model topography to the higher-resolution ice-sheet topography of the GrIS, such that the influence of these different SMB climatologies on the long-term evolution of the GrIS is tested by ice-sheet model simulations. From these ice-sheet simulations we conclude that an albedo scheme with a short response time of decaying albedo during wet conditions performs best with respect to long-term simulated ice-sheet volume. This results in an optimized albedo parameterization that can be used in future EC-Earth simulations with an interactive ice-sheet component.

  6. Geochemical cycling and depositional patterns across the northeast region of the Greenland Ice Sheet as determined from trace element chemistry

    Science.gov (United States)

    Wong, G. J.; Osterberg, E. C.; Courville, Z.; Hawley, R. L.; Lutz, E.; Overly, T. B.

    2012-12-01

    The Greenland Ice Sheet is both a repository of climate history and a major driver in Arctic and global climate. Between 1952 and 1955, Carl Benson led a series of traverses of the Greenland Ice Sheet (GIS), and characterized the GIS via mapping of the spatial distribution of annual net accumulation and classifying the diagenetic glacier facies (Benson, 1962). While polar ice sheets represent a unique archive of past atmospheric and climatic conditions, little information exists on large-scale geographical trends in trace element snow chemistry across GIS because of the remote, challenging location. In the spring of 2011, we undertook a 1120 km traverse of the GIS from Thule Air Base to Summit Station. Samples from 11 snow pits and 3 firn cores, dated by stable water isotopes, were analyzed and evaluated in seasonal resolution for their trace element content (23Na, 24Mg, 27Al, 32S, 39K, 44Ca, 47Ti, 51V, 52Cr, 55Mn, 56Fe, 59Co, 63Cu, 66Zn, 75As, 88Sr, 111Cd, 133Cs, 138Ba, 139La, 140Ce, 141Pr, 208Pb, 209Bi, 238U). Here, we present an initial analysis of the spatial gradients of these trace elements and an interpretation of how their depositional patterns characterize the GIS. The seasonal trends coupled with spatial variability of certain trace elements establish the behavior of specific aerosols (e.g. dust, sea salt, pollution), which will be useful in quantifying geochemical cycling across the GIS and comparing characterizations with results from Benson's traverses. Benson, CS. 1962. Stratigraphic studies in the snow and firn of the Greenland Ice Sheet. SIPRE Research Report, 70, 89 pp.

  7. Contributions to the building and upgrading of the Greenland Ice Sheet Monitoring Network (GLISN)

    Science.gov (United States)

    Reusch, A. M.; Childs, D.; Anderson, K. R.

    2011-12-01

    The GLISN project began in 2009 and is now a 10-nation collaborative project (Canada, Denmark, France, Germany, Italy, Japan, Norway, Poland, Switzerland and the USA) with a long-term goal of establishing a real-time broadband seismic network of 25 stations within and around Greenland. The GLISN project provides publicly available data distributed by the IRIS Data Management Center that researchers can use in the characterization of tectonic and glacial earthquakes as well as other cryo-seismic phenomena (e.g. iceberg calving events, seiches, tidal patterns, and the draining of supra-glacial lakes). Cooperation among the 10 nations has provided a wealth of material and knowledge resources, contributing to the success of the project as a whole. At the same time, involving multiple intra-national and international organizations has also required increased efforts in coordination and shared decision-making. As of August 2011, the IRIS PASSCAL Instrument Center has contributed to the effort by building, installing and maintaining 6 new and upgrading 5 existing broadband seismic stations at both coastal and interior sites. Three of the 11 GLISN stations were installed along the main ice divide. Two of these ridge sites are equipped with borehole sensors in addition to the standard surface sensor, and all 3 stations have real-time geodetic-quality GPS receivers. The GLISN stations take advantage of the latest methods and technologies field-tested in Antarctica and other high-latitude regions by the PASSCAL Instrument Center. All stations are designed to operate year-round with cold-rated instrumentation, autonomous power generation (solar and wind) or protected AC power delivery systems when grid power is available. Data and state of health communication is through the Internet, when available, or via Iridium modem. The latter currently provides daily station state of health information along with a 10s data segment on an hourly basis. Development of an Iridium link is

  8. Extracting the annual signal from Greenland ice-core chemistry and isotopic records

    DEFF Research Database (Denmark)

    Rasmussen, Sune Olander; Andersen, Katrine K.; Andersen, Marie Louise Siggaard

    2002-01-01

    Stratigraphic dating of ice cores by identification and counting of annual cycles in, for example, chemical measurements requires skill and experience. The work presented here investigates a method of data enhancement which is a first step towards an automated and more objective method of annual...

  9. The 1988-2003 Greenland ice sheet melt extent using passive microwave satellite data and a regional climate model

    Energy Technology Data Exchange (ETDEWEB)

    Fettweis, Xavier; Ypersele, Jean-Pascal van [Universite Catholique de Louvain, Institut d' Astronomie et de Geophysique de G. Lemaitre, Louvain-La-Neuve (Belgium); Gallee, Hubert [CNRS, Laboratoire de Glaciologie et Geophysique de l' Environnement, Grenoble (France); Lefebre, Filip [Vito-IMS (Flemish Institute for Technological Research-Integral Environmental Studies), Mol (Belgium)

    2006-10-15

    Measurements from ETH-Camp and JAR1 AWS (West Greenland) as well as coupled atmosphere-snow regional climate simulations have highlighted flaws in the cross-polarized gradient ratio (XPGR) technique used to identify melt from passive microwave satellite data. It was found that dense clouds (causing notably rainfall) on the ice sheet severely perturb the XPGR melt signal. Therefore, the original XPGR melt detection algorithm has been adapted to better incorporate atmospheric variability over the ice sheet and an updated melt trend for the 1988-2003 period has been calculated. Compared to the original algorithm, the melt zone area increase is eight times higher (from 0.2 to 1.7% year{sup -1}). The increase is higher with the improved XPGR technique because rainfall also increased during this period. It is correlated to higher atmospheric temperatures. Finally, the model shows that the total ice sheet runoff is directly proportional to the melt extent surface detected by satellites. These results are important for the understanding of the effect of Greenland melting on the stability of the thermohaline circulation. (orig.)

  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

    Science.gov (United States)

    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. SAGE: Attribution of Biomass Burning Tracers sampled on the Greenland Ice Sheet in 2013

    Science.gov (United States)

    Soja, A. J.; Choi, H. D.; Polashenski, C.; Thomas, J. L.; Dibb, J. E.; Fairlie, T. D.; Winker, D. M.; Flanner, M.; Bergin, M.; Casey, K.; Ward, J. L.; Chen, J.; Courville, Z.; Trepte, C. R.; Lai, A.; Schauer, J. J.; Shafer, M. M.

    2016-12-01

    The SAGE team traversed and sampled the snow stratigraphy representing 2012-2014 snow accumulation in the northwest sector of the Greenland Ice Sheet (GrIS) and found evidence of aerosol deposition that originated from biomass burning (BB). Black carbon (BC) concentrations (range 2.8-43 ng/g) were closely correlated with ammonium (NH4), both of which are tracers that are indicative of BB events. Data indicated the strongest deposition events occurred in July and August of 2013. Using a combination of these in-situ samples, modeling and satellite data, the transport and attribution of deposited smoke is back-traced from the GrIS to particular fires. The Langley Research Center Trajectory Model (LaTM) is used to track deposition events from pit locations on the GrIS to particular source fires from June through August 2013, which includes 2 months when smoke is known to have strongly impacted the GrIS (July August 2013) and 1 month (June 2013) of relatively low smoke impact. Simulated smoke is injected every 100 vertical meters to 2km ( boundary layer) in the LaTM and run backwards in time and space from sample sites until coincident with fire (MODIS data). Ground-based and satellite data are used to verify transport. As an example, we focus on one case study that traces smoke from fires that started burning on July 22nd and continued to burn through July 26-29. A river of smoke crosses Canada and is transported to the GrIS, arriving August 1st-2nd. Overall, we find the largest BB events do not equate to the largest deposition events, rather this process requires a combination of: intense fires; conducive transport paths; and deposition and preservation opportunities (snowfall). Intensely burning fires produce thick smoke, which is less likely to be dispersed or diluted in transport, and the smoke is injected to higher altitudes, which ensure a faster transport. Because fire severity, extreme fire seasons, general circulation patterns and precipitating snowfall are

  12. Implications for carbon processing beneath the Greenland Ice Sheet from dissolved CO2 and CH4 concentrations of subglacial discharge

    Science.gov (United States)

    Pain, A.; Martin, J.; Martin, E. E.

    2017-12-01

    Subglacial carbon processes are of increasing interest as warming induces ice melting and increases fluxes of glacial meltwater into proglacial rivers and the coastal ocean. Meltwater may serve as an atmospheric source or sink of carbon dioxide (CO2) or methane (CH4), depending on the magnitudes of subglacial organic carbon (OC) remineralization, which produces CO2 and CH4, and mineral weathering reactions, which consume CO2 but not CH4. We report wide variability in dissolved CO2 and CH4 concentrations at the beginning of the melt season (May-June 2017) between three sites draining land-terminating glaciers of the Greenland Ice Sheet. Two sites, located along the Watson River in western Greenland, drain the Isunnguata and Russell Glaciers and contained 1060 and 400 ppm CO2, respectively. In-situ CO2 flux measurements indicated that the Isunnguata was a source of atmospheric CO2, while the Russell was a sink. Both sites had elevated CH4 concentrations, at 325 and 25 ppm CH4, respectively, suggesting active anaerobic OC remineralization beneath the ice sheet. Dissolved CO2 and CH4 reached atmospheric equilibrium within 2.6 and 8.6 km downstream of Isunnguata and Russell discharge sites, respectively. These changes reflect rapid gas exchange with the atmosphere and/or CO2 consumption via instream mineral weathering. The third site, draining the Kiagtut Sermiat in southern Greenland, had about half atmospheric CO2 concentrations (250 ppm), but approximately atmospheric CH4 concentrations (2.1 ppm). Downstream CO2 flux measurements indicated ingassing of CO2 over the entire 10-km length of the proglacial river. CO2 undersaturation may be due to more readily weathered lithologies underlying the Kiagtut Sermiat compared to Watson River sites, but low CH4 concentrations also suggest limited contributions of CO2 and CH4 from OC remineralization. These results suggest that carbon processing beneath the Greenland Ice Sheet may be more variable than previously recognized

  13. Climatology of increased temperatures and melt at Swiss Camp, western slope of Greenland ice sheet, 1991-2012

    Science.gov (United States)

    Steffen, K.; McGrath, D.

    2013-12-01

    Climate observations (1991-2012) will be discussed from the Swiss Camp (69deg 33‧53″N, 49deg 19‧51″W, 1176 m), located at the western slope of the Greenland ice sheet, 60 km inland from Ilulissat. The mean annual temperature of -12 C increased 3.6 C between 1991 and 2012 (1.7 C per decade) with large interannual variability in all seasons. The mean spring temperature increased from -16.0 C to -13.8 C, and the fall temperature increased from -12.4 C to -11.3 C in the same time. The winter temperature showed the largest increase of 6.5 C, whereas summer temperatures increased 3.0 C during the 21 years (1991 - 2012). Radiation has been monitored continuously at Swiss Camp since 1993. Net radiation of 50 W/ m2 was recorded in 2012, the warmest summer month on record. The entire annual snow cover melted at Swiss Camp, reducing the monthly albedo value to 0.4 with bare ice exposed. Interannual variability of snow accumulation ranged between 0.07 and 0.70 m water equivalent, whereas annual snow and ice ablation varied between +0.35 (net gain) and -1.8 m (net loss) for the time period 1991-2012. The equilibrium line altitude (ELA) is no longer located at Swiss Camp (1176 m elevation) with a net surface lowering of 9.5 m since 1991. Increasing summer air temperatures have resulted in an upward migration of both the percolation facies and ablation area of the Greenland ice sheet. The 0°C isothermal migrated upward at a rate of 35 m/a over the 1995-2012 period in West Greenland. There is a 50% probability of the mean annual dry snow line migrating above Summit by 2025, at which time Summit will experience routine melt on an annual basis. The surface mass balance observations similarly indicate that the ELA has migrated upwards at a rate of 44 m/a over the 1997-2011 period in West Greenland, resulting in a more than doubling of the ablation zone width during this period. Inter-annual variability of monthly mean albedo at the Swiss Camp (1993 - 2012). Albedo at 0.5 is

  14. Validation of a Climate-Data Record of the "Clear-Sky" Surface Temperature of the Greenland Ice Sheet

    Science.gov (United States)

    Hall, Dorothy K.; Box, Jason E.; Koenig, Lora S.; DiGirolamo, Nicolo E.; Comiso, Josefino C.; Shuman, Christopher A.

    2011-01-01

    Surface temperatures on the Greenland Ice Sheet have been studied on the ground, using automatic weather station (AWS) data from the Greenland-Climate Network (GC-Net), and from analysis of satellite sensor data. Using Advanced Very High Frequency Radiometer (AVHRR) weekly surface temperature maps, warming of the surface of the Greenland Ice Sheet has been documented since 1981. We extended and refined this record using higher-resolution Moderate-Resolution Imaging Spectroradiometer (MODIS) data from March 2000 to the present. We developed a daily and monthly climate-data record (CDR) of the "clear-sky" surface temperature of the Greenland Ice Sheet using an ice-surface temperature (1ST) algorithm developed for use with MODIS data. Validation of this CDR is ongoing. MODIS Terra swath data are projected onto a polar stereographic grid at 6.25-km resolution to develop binary, gridded daily and mean-monthly 1ST maps. Each monthly map also has a color-coded image map that is available to download. Also included with the monthly maps is an accompanying map showing number of days in the month that were used to calculate the mean-monthly 1ST. This is important because no 1ST decision is made by the algorithm for cells that are considered cloudy by the internal cloud mask, so a sufficient number of days must be available to produce a mean 1ST for each grid cell. Validation of the CDR consists of several facets: 1) comparisons between ISTs and in-situ measurements; 2) comparisons between ISTs and AWS data; and 3) comparisons of ISTs with surface temperatures derived from other satellite instruments such as the Thermal Emission and Reflection Radiometer (ASTER) and Enhanced Thematic Mapper Plus (ETM+). Previous work shows that Terra MODIS ISTs are about 3 C lower than in-situ temperatures measured at Summit Camp, during the winter of 2008-09 under clear skies. In this work we begin to compare surface temperatures derived from AWS data with ISTs from the MODIS CDR.

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

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Sasgen, Ingo; Bevis, Michael

    2016-01-01

    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 basinwide mass changes since the LGM. Unpredicted......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...

  16. The Cryosphere Model Comparison Tool (CmCt): Ice Sheet Model Validation and Comparison Tool for Greenland and Antarctica

    Science.gov (United States)

    Simon, E.; Nowicki, S.; Neumann, T.; Tyahla, L.; Saba, J. L.; Guerber, J. R.; Bonin, J. A.; DiMarzio, J. P.

    2017-12-01

    The Cryosphere model Comparison tool (CmCt) is a web based ice sheet model validation tool that is being developed by NASA to facilitate direct comparison between observational data and various ice sheet models. The CmCt allows the user to take advantage of several decades worth of observations from Greenland and Antarctica. Currently, the CmCt can be used to compare ice sheet models provided by the user with remotely sensed satellite data from ICESat (Ice, Cloud, and land Elevation Satellite) laser altimetry, GRACE (Gravity Recovery and Climate Experiment) satellite, and radar altimetry (ERS-1, ERS-2, and Envisat). One or more models can be uploaded through the CmCt website and compared with observational data, or compared to each other or other models. The CmCt calculates statistics on the differences between the model and observations, and other quantitative and qualitative metrics, which can be used to evaluate the different model simulations against the observations. The qualitative metrics consist of a range of visual outputs and the quantitative metrics consist of several whole-ice-sheet scalar values that can be used to assign an overall score to a particular simulation. The comparison results from CmCt are useful in quantifying improvements within a specific model (or within a class of models) as a result of differences in model dynamics (e.g., shallow vs. higher-order dynamics approximations), model physics (e.g., representations of ice sheet rheological or basal processes), or model resolution (mesh resolution and/or changes in the spatial resolution of input datasets). The framework and metrics could also be used for use as a model-to-model intercomparison tool, simply by swapping outputs from another model as the observational datasets. Future versions of the tool will include comparisons with other datasets that are of interest to the modeling community, such as ice velocity, ice thickness, and surface mass balance.

  17. A Climate-Data Record (CDR) of the "Clear Sky" Surface Temperature of the Greenland Ice Sheet

    Science.gov (United States)

    Hall, Dorothy K.; Comiso, J. C.; DiGirolamo, N. E.; Shuman, C. A.

    2011-01-01

    To quantify the ice-surface temperature (IST) we are developing a climate-data record (CDR) of monthly IST of the Greenland ice sheet, from 1982 to the present using Advanced Very High Resolution Radiometer (AVHRR) and Moderate-Resolution Imaging Spectroradiometer (MODIS) data at 5-km resolution. "Clear-sky" surface temperature increases have been measured from the early 1980s to the early 2000s in the Arctic using AVHRR data, showing increases ranging from 0.57-0.02 (Wang and Key, 2005) to 0.72 0.10 deg C per decade (Comiso, 2006). Arctic warming has implications for ice-sheet mass balance because much of the periphery of the ice sheet is near 0 deg C in the melt season and is thus vulnerable to more extensive melting (Hanna et al., 2008). The algorithm used for this work has a long history of measuring IST in the Arctic with AVHRR (Key and Haefliger, 1992). The data are currently available from 1981 to 2004 in the AVHRR Polar Pathfinder (APP) dataset (Fowler et al., 2000). J. Key1NOAA modified the AVHRR algorithm for use with MODIS (Hall et al., 2004). The MODIS algorithm is now being processed over Greenland. Issues being addressed in the production of the CDR are: time-series bias caused by cloud cover, and cross-calibration between AVHRR and MODIS instruments. Because of uncertainties, time series of satellite ISTs do not necessarily correspond with actual surface temperatures. The CDR will be validated by comparing results with in-situ (see Koenig and Hall, in press) and automatic-weather station data (e.g., Shuman et al., 2001).

  18. Bergy Bit and Melt Water Trajectories in Godthåbsfjord (SW Greenland Observed by the Expendable Ice Tracker

    Directory of Open Access Journals (Sweden)

    Daniel F. Carlson

    2017-08-01

    Full Text Available Icebergs and bergy bits makes up a significant component of the total freshwater flux from the Greenland Ice Sheet to the ocean. Observations of iceberg trajectories are biased toward larger icebergs and, as a result, the drift characteristics of smaller icebergs and bergy bits are poorly understood. In an attempt to fill this critical knowledge gap, we developed the open-source EXpendable Ice TrackEr (EXITE. EXITE is a low-cost, satellite-tracked GPS beacon capable of high-resolution temporal measurements over extended deployment periods (30 days or more. Furthermore, EXITE can transform to a surface drifter when its host iceberg capsizes or fragments. Here we describe basic construction of an EXITE beacon and present results from a deployment in Godthåbsfjord (SW Greenland in August 2016. Overall, EXITE trajectories show out-fjord surface transport, in agreement with a simple estuarine circulation paradigm. However, eddies and abrupt wind-driven reversals reveal complex surface transport pathways at time scales of hours to days.

  19. Spatial variations in snowpack chemistry, isotopic composition of NO3− and nitrogen deposition from the ice sheet margin to the coast of western Greenland

    Directory of Open Access Journals (Sweden)

    C. J. Curtis

    2018-01-01

    Full Text Available The relative roles of anthropogenic nitrogen (N deposition and climate change in causing ecological change in remote Arctic ecosystems, especially lakes, have been the subject of debate over the last decade. Some palaeoecological studies have cited isotopic signals (δ(15N preserved in lake sediments as evidence linking N deposition with ecological change, but a key limitation has been the lack of co-located data on both deposition input fluxes and isotopic composition of deposited nitrate (NO3−. In Arctic lakes, including those in western Greenland, previous palaeolimnological studies have indicated a spatial variation in δ(15N trends in lake sediments but data are lacking for deposition chemistry, input fluxes and stable isotope composition of NO3−. In the present study, snowpack chemistry, NO3− stable isotopes and net deposition fluxes for the largest ice-free region in Greenland were investigated to determine whether there are spatial gradients from the ice sheet margin to the coast linked to a gradient in precipitation. Late-season snowpack was sampled in March 2011 at eight locations within three lake catchments in each of three regions (ice sheet margin in the east, the central area near Kelly Ville and the coastal zone to the west. At the coast, snowpack accumulation averaged 181 mm snow water equivalent (SWE compared with 36 mm SWE by the ice sheet. Coastal snowpack showed significantly greater concentrations of marine salts (Na+, Cl−, other major cations, ammonium (NH4+; regional means 1.4–2.7 µmol L−1, total and non-sea-salt sulfate (SO42−; total 1.8–7.7, non-sea-salt 1.0–1.8 µmol L−1 than the two inland regions. Nitrate (1.5–2.4 µmol L−1 showed significantly lower concentrations at the coast. Despite lower concentrations, higher precipitation at the coast results in greater net deposition for NO3− as well as NH4+ and non-sea-salt sulfate (nss-SO42− relative to the inland regions

  20. Spatial variations in snowpack chemistry, isotopic composition of NO3- and nitrogen deposition from the ice sheet margin to the coast of western Greenland

    Science.gov (United States)

    Curtis, Chris J.; Kaiser, Jan; Marca, Alina; Anderson, N. John; Simpson, Gavin; Jones, Vivienne; Whiteford, Erika

    2018-01-01

    The relative roles of anthropogenic nitrogen (N) deposition and climate change in causing ecological change in remote Arctic ecosystems, especially lakes, have been the subject of debate over the last decade. Some palaeoecological studies have cited isotopic signals (δ(15N)) preserved in lake sediments as evidence linking N deposition with ecological change, but a key limitation has been the lack of co-located data on both deposition input fluxes and isotopic composition of deposited nitrate (NO3-). In Arctic lakes, including those in western Greenland, previous palaeolimnological studies have indicated a spatial variation in δ(15N) trends in lake sediments but data are lacking for deposition chemistry, input fluxes and stable isotope composition of NO3-. In the present study, snowpack chemistry, NO3- stable isotopes and net deposition fluxes for the largest ice-free region in Greenland were investigated to determine whether there are spatial gradients from the ice sheet margin to the coast linked to a gradient in precipitation. Late-season snowpack was sampled in March 2011 at eight locations within three lake catchments in each of three regions (ice sheet margin in the east, the central area near Kelly Ville and the coastal zone to the west). At the coast, snowpack accumulation averaged 181 mm snow water equivalent (SWE) compared with 36 mm SWE by the ice sheet. Coastal snowpack showed significantly greater concentrations of marine salts (Na+, Cl-, other major cations), ammonium (NH4+; regional means 1.4-2.7 µmol L-1), total and non-sea-salt sulfate (SO42-; total 1.8-7.7, non-sea-salt 1.0-1.8 µmol L-1) than the two inland regions. Nitrate (1.5-2.4 µmol L-1) showed significantly lower concentrations at the coast. Despite lower concentrations, higher precipitation at the coast results in greater net deposition for NO3- as well as NH4+ and non-sea-salt sulfate (nss-SO42-) relative to the inland regions (lowest at Kelly Ville 6, 4 and 3; highest at coast 9, 17

  1. Satellite-derived, melt-season surface temperature of the Greenland Ice Sheet (2000-2005) and its relationship to mass balance

    Science.gov (United States)

    Hall, D.K.; Williams, R.S.; Casey, K.A.; DiGirolamo, N.E.; Wan, Z.

    2006-01-01

    Mean, clear-sky surface temperature of the Greenland Ice Sheet was measured for each melt season from 2000 to 2005 using Moderate-Resolution Imaging Spectroradiometer (MODIS)–derived land-surface temperature (LST) data-product maps. During the period of most-active melt, the mean, clear-sky surface temperature of the ice sheet was highest in 2002 (−8.29 ± 5.29°C) and 2005 (−8.29 ± 5.43°C), compared to a 6-year mean of −9.04 ± 5.59°C, in agreement with recent work by other investigators showing unusually extensive melt in 2002 and 2005. Surface-temperature variability shows a correspondence with the dry-snow facies of the ice sheet; a reduction in area of the dry-snow facies would indicate a more-negative mass balance. Surface-temperature variability generally increased during the study period and is most pronounced in the 2005 melt season; this is consistent with surface instability caused by air-temperature fluctuations.

  2. Ice-dammed lake drainage in west Greenland: Drainage pattern and implications on ice flow and bedrock motion

    DEFF Research Database (Denmark)

    Kjeldsen, Kristian Kjellerup; Khan, Shfaqat Abbas; Bjørk, Anders

    2017-01-01

    of surface loading in addition to ice mass change, when assessing glacial isostatic adjustment or elastic rebound using geodetic data. Moreover, the results illustrates a linkage between subglacial discharge and ice surface velocity, important for assessing ice flux, and thus mass balance, in a future...

  3. 21st century projections of surface mass balance changes for major drainage systems of the Greenland ice sheet

    International Nuclear Information System (INIS)

    Tedesco, M; Fettweis, X

    2012-01-01

    Outputs from the regional climate model Modèle Atmosphérique Régionale at a spatial resolution of 25 km are used to study 21st century projected surface mass balance (SMB) over six major drainage basins of the Greenland ice sheet (GrIS). The regional model is forced with the outputs of three different Earth System Models (CanESM2, NorESM1 and MIROC5) obtained when considering two greenhouse gas future scenarios with levels of CO 2 equivalent of, respectively, 850 and >1370 ppm by 2100. Results indicate that the increase in runoff due to warming will exceed the increased precipitation deriving from the increase in evaporation for all basins, with the amount of net loss of mass at the surface varying spatially. Basins along the southwest and north coast are projected to have the highest sensitivity of SMB to increasing temperatures. For these basins, the global temperature anomaly corresponding to a decrease of the SMB below the 1980–99 average (when the ice sheet was near the equilibrium) ranges between +0.60 and +2.16 °C. For the basins along the northwest and northeast, these values range between +1.50 and +3.40 °C. Our results are conservative as they do not account for ice dynamics and changes in the ice sheet topography. (letter)

  4. Improved GRACE regional mass balance estimates of the Greenland Ice Sheet cross-validated with the input-output method (discussion paper)

    NARCIS (Netherlands)

    Xu, Z.; Schrama, E.J.O.; Van der Wal, W.; Van den Broeke, M.; Enderlin, E.M.

    2015-01-01

    In this study, we use satellite gravimetry data from the Gravity Recovery and Climate Experiment (GRACE) to estimate regional mass changes of the Greenland ice sheet (GrIS) and neighbouring glaciated regions using a least-squares inversion approach. We also consider results from the input-output

  5. Seasonal velocities of eight major marine-terminating outlet glaciers of the Greenland ice sheet from continuous in situ GPS instruments

    DEFF Research Database (Denmark)

    Ahlstrøm, A. P.; Andersen, S. B.; Andersen, M. L.

    2013-01-01

    We present 17 velocity records derived from in situ stand-alone single-frequency Global Positioning System (GPS) receivers placed on eight marine-terminating ice sheet outlet glaciers in South, West and North Greenland, covering varying parts of the period summer 2009 to summer 2012. Common to all...

  6. Correlation of Greenland ice-core isotope profiles and the terrestrial record of the Alpine Rhine glacier for the period 32-15 ka

    NARCIS (Netherlands)

    de Jong, M.G.G.; de Graaff, L.W.S.; Seijmonsbergen, A.C.; Böhm, A.R.

    2011-01-01

    We present a newly extended stratigraphic subdivision of the Greenland NGRIP, GRIP and GISP2 ice cores for the period 32-15 ka. Our classification emphasizes the multiscale nature of the climatic oscillations. Spectral trend analysis of isotopic data supports this interpretation. We compare this

  7. Description of Pyramimonas diskoicola sp. nov. and the importance of the flagellate Pyramimonas (Prasinophyceae) in Greenland sea ice during the winter–spring transition

    DEFF Research Database (Denmark)

    Harðardóttir, Sara; Lundholm, Nina; Moestrup, Øjvind

    2014-01-01

    Pyramimonas Schmarda is a genus of unicellular green flagellates, recorded in marine water and sea ice samples. Pyramimonas is within the prey size range of the most important protozoan grazers in Disko Bay, West Greenland, where this study took place. Despite the potential ecological importance...

  8. Estimating the Greenland ice sheet surface mass balance contribution to future sea level rise using the regional atmospheric climate model MAR

    NARCIS (Netherlands)

    Fettweis, X.; Franco, B.; Tedesco, M.; van Angelen, J.H.; Lenaerts, J.T.M.; van den Broeke, M.R.; Gallée, H.

    2013-01-01

    To estimate the sea level rise (SLR) originating from changes in surface mass balance (SMB) of the Greenland ice sheet (GrIS), we present 21st century climate projections obtained with the regional climate model MAR (Mod`ele Atmosph´erique R´egional), forced by output of three CMIP5 (Coupled Model

  9. The seasonal cycle and interannual variability of surface energy balance and melt in the ablation zone of the west Greenland ice sheet

    NARCIS (Netherlands)

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

    2011-01-01

    We present the seasonal cycle and interannual variability of the surface energy balance (SEB) in the ablation zone of the west Greenland ice sheet, using seven years (September 2003–August 2010) of hourly observations from three automatic weather stations (AWS). The AWS are situated along the 67◦ N

  10. Greenland, my greenland

    DEFF Research Database (Denmark)

    Andersen, Astrid

    2016-01-01

    In 2012, Visit Greenland, the Greenlandic national tourist organisation, conducted a survey on Danish prejudices towards Greenland and Greenlanders. The survey, linked to an ambivalent nation-building strategy that pitched Greenland as ‘the pioneering nation’, was aimed both at challenging...... tourist audience more concerned with preserving whales than with accepting the sustainable visions of indigenous modernity that are currently being articulated by Greenlanders. Contemporary Greenlandic nation branding is a response to these internal and external dichotomies....

  11. 21st century changes in the surface mass balance of the Greenland ice sheet simulated with the global model CESM

    Science.gov (United States)

    Vizcaíno, M.; Lipscomb, W. H.; Van den Broeke, M.

    2012-04-01

    We present here the first projections of 21st century surface mass balance change of the Greenland ice sheet simulated with the Community Earth System Model (CESM). CESM is a fully-coupled, global climate model developed at many research centers and universities, primarily in the U.S. The model calculates the surface mass balance in the land component (the Community Land Model, CLM), at the same resolution as the atmosphere (1 degree), with an energy-balance scheme. The snow physics included in CLM for non-glaciated surfaces (SNiCAR model, Flanner and Zender, 2005) are used over the ice sheet. The surface mass balance is calculated for 10 elevation classes, and then downscaled to the grid of the ice sheet model (5 km in this case) via vertical linear interpolation between elevation classes combined with horizontal bilinear interpolation. The ice sheet topography is fixed at present-day values for the simulations presented here. The use of elevation classes reduces computational costs while giving results that reproduce well the mass balance gradients at the steep margins of the ice sheet. The simulated present-day surface mass balance agrees well with results from regional models. We focus on the regional model RACMO (Ettema et al. 2009) to compare the results on 20th-century surface mass balance evolution and two-dimensional patterns. The surface mass balance of the ice sheet under RCP8.5. forcing becomes negative in the last decades of the 21st century. The equilibrium line becomes ~500 m higher on average. Accumulation changes are positive in the accumulation zone. We examine changes in refreezing, accumulation, albedo, surface fluxes, and the timing of the melt season.

  12. Significance of Thermal Fluvial Incision and Bedrock Transfer due to Ice Advection on Greenland Ice Sheet Topography

    Science.gov (United States)

    Crozier, J. A.; Karlstrom, L.; Yang, K.

    2017-12-01

    Ice sheet surface topography reflects a complicated combination of processes that act directly upon the surface and that are products of ice advection. Using recently-available high resolution ice velocity, imagery, ice surface elevation, and bedrock elevation data sets, we seek to determine the domain of significance of two important processes - thermal fluvial incision and transfer of bedrock topography through the ice sheet - on controlling surface topography in the ablation zone. Evaluating such controls is important for understanding how melting of the GIS surface during the melt season may be directly imprinted in topography through supraglacial drainage networks, and indirectly imprinted through its contribution to basal sliding that affects bedrock transfer. We use methods developed by (Karlstrom and Yang, 2016) to identify supraglacial stream networks on the GIS, and use high resolution surface digital elevation models as well as gridded ice velocity and melt rate models to quantify surface processes. We implement a numerically efficient Fourier domain bedrock transfer function (Gudmundsson, 2003) to predict surface topography due to ice advection over bedrock topography obtained from radar. Despite a number of simplifying assumptions, the bedrock transfer function predicts the observed ice sheet surface in most regions of the GIS with ˜90% accuracy, regardless of the presence or absence of supraglacial drainage networks. This supports the hypothesis that bedrock is the most significant driver of ice surface topography on wavelengths similar to ice thickness. Ice surface topographic asymmetry on the GIS is common, with slopes in the direction of ice flow steeper than those faced opposite to ice flow, consistent with bedrock transfer theory. At smaller wavelengths, topography consistent with fluvial erosion by surface hydrologic features is evident. We quantify the effect of ice advection versus fluvial thermal erosion on supraglacial longitudinal stream

  13. Engineering geological and geophysical investigations for road construction in the municipality of Sisimiut, West Greenland

    DEFF Research Database (Denmark)

    Ingeman-Nielsen, Thomas; Clausen, Helle; Foged, Niels Nielsen

    2007-01-01

    In connection with a road construction project between the towns of Sisimiut and Kangerlussuaq in Central West Greenland, the Arctic Technology Centre has been involved in prospecting and site investigations. This paper presents a selection of results concerning the climatic conditions...... and construction work in order to counter the effects of permafrost degradation and increased active layer thickness....

  14. Investigation and Retrofitting Proposal for a Panbo Type House in Sisimiut, Greenland

    DEFF Research Database (Denmark)

    Qu, Jing; Vladyková, Petra; Villumsen, Arne

    The ‘Blue House’ is a standard family detached house built by Panbo Huse A/S in 1985 in Sisimiut, Greenland. As an old building, it has many problems such as poor thermal comfort and high energy consumption, and therefore, the house has a potential to be retrofitted. The investigation of the ‘Blu...

  15. Quaternary redox transitions in deep crystalline rock fractures at the western margin of the Greenland ice sheet

    International Nuclear Information System (INIS)

    Drake, Henrik; Suksi, Juhani; Tullborg, Eva-Lena; Lahaye, Yann

    2017-01-01

    When planning for long term deep geological repositories for spent nuclear fuel knowledge of processes that will influence and change the sub-surface environment is crucial. For repositories in northern Europe and similar areas, influence from advancing and retreating continental ice sheets must be planned for. Rapid transport of meltwater into the bedrock may introduce oxic conditions at great depth, which may affect the copper canisters planned to encapsulate the spent fuel. The lack of direct observations has led to simplified modelling assumptions not reflecting the complexity of natural systems. As part of a unique field and modelling study, The Greenland Analogue Project, of a continental ice sheet and related sub-surface conditions, we here present mineralogical and U-series data unravelling the Quaternary redox history in the deep bedrock fracture system close to the margin of the Greenland ice sheet. The aim was to increase the understanding of circulation of potentially oxygenated glacial meltwater from the surface down to 650 m depth. Secondary mineral coatings were sampled from open fractures in cored boreholes down to 650 m, within and below the current permafrost. Despite continental ice sheet coverage and/or prevailing permafrost during large parts of the last 1 Ma, measured disequilibrium in the 238 U- 234 U- 230 Th system shows that water has circulated in the bedrock fracture system at various occasions during this time span. In fractures of the upper 60 m, infiltration of oxygenated surface water has resulted in a prominent near-surface ”oxidised zone” with abundant FeOOH precipitation. However, this zone must be relict because it is currently within permafrost and the U-series disequilibrium signatures of most fracture coatings show evidence of deposition of U prior to the Holocene and even prior to the last glaciation maximum which occurred less than 100 ka ago. This U deposition is found both within and below the near surface

  16. Automated Ground-based Time-lapse Camera Monitoring of West Greenland ice sheet outlet Glaciers: Challenges and Solutions

    Science.gov (United States)

    Ahn, Y.; Box, J. E.; Balog, J.; Lewinter, A.

    2008-12-01

    Monitoring Greenland outlet glaciers using remotely sensed data has drawn a great attention in earth science communities for decades and time series analysis of sensory data has provided important variability information of glacier flow by detecting speed and thickness changes, tracking features and acquiring model input. Thanks to advancements of commercial digital camera technology and increased solid state storage, we activated automatic ground-based time-lapse camera stations with high spatial/temporal resolution in west Greenland outlet and collected one-hour interval data continuous for more than one year at some but not all sites. We believe that important information of ice dynamics are contained in these data and that terrestrial mono-/stereo-photogrammetry can provide theoretical/practical fundamentals in data processing along with digital image processing techniques. Time-lapse images over periods in west Greenland indicate various phenomenon. Problematic is rain, snow, fog, shadows, freezing of water on camera enclosure window, image over-exposure, camera motion, sensor platform drift, and fox chewing of instrument cables, and the pecking of plastic window by ravens. Other problems include: feature identification, camera orientation, image registration, feature matching in image pairs, and feature tracking. Another obstacle is that non-metric digital camera contains large distortion to be compensated for precise photogrammetric use. Further, a massive number of images need to be processed in a way that is sufficiently computationally efficient. We meet these challenges by 1) identifying problems in possible photogrammetric processes, 2) categorizing them based on feasibility, and 3) clarifying limitation and alternatives, while emphasizing displacement computation and analyzing regional/temporal variability. We experiment with mono and stereo photogrammetric techniques in the aide of automatic correlation matching for efficiently handling the enormous

  17. Evaluation of a 12-km Satellite-Era Reanalysis of Surface Mass Balance for the Greenland Ice Sheet

    Science.gov (United States)

    Cullather, R. I.; Nowicki, S.; Zhao, B.; Max, S.

    2016-12-01

    The recent contribution to sea level change from the Greenland Ice Sheet is thought to be strongly driven by surface processes including melt and runoff. Global reanalyses are potential means of reconstructing the historical time series of ice sheet surface mass balance (SMB), but lack spatial resolution needed to resolve ablation areas along the periphery of the ice sheet. In this work, the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) is used to examine the spatial and temporal variability of surface melt over the Greenland Ice Sheet. MERRA-2 is produced for the period 1980 to the present at a grid spacing of ½° latitude by ⅝° longitude, and includes snow hydrology processes including compaction, meltwater percolation and refreezing, runoff, and a prognostic surface albedo. The configuration of the MERRA-2 system allows for the background model - the Goddard Earth Observing System model, version 5 (GEOS-5) - to be carried in phase space through analyzed states via the computation of analysis increments, a capability referred to as "replay". Here, a MERRA-2 replay integration is conducted in which atmospheric forcing fields are interpolated and adjusted to sub- atmospheric grid-scale resolution. These adjustments include lapse-rate effects on temperature, humidity, precipitation, and other atmospheric variables that are known to have a strong elevation dependency over ice sheets. The surface coupling is performed such that mass and energy are conserved. The atmospheric forcing influences the surface representation, which operates on land surface tiles with an approximate 12-km spacing. This produces a high-resolution, downscaled SMB which is interactively coupled to the reanalysis model. We compare the downscaled SMB product with other reanalyses, regional climate model values, and a second MERRA-2 replay in which the background model has been replaced with a 12-km, non-hydrostatic version of GEOS-5. The assessment

  18. The effect of sea-ice loss on beluga whales (Delphinapterus leucas) in West Greenland

    DEFF Research Database (Denmark)

    Heide-Jørgensen, M.P.; Laidre, K.L.; Simon, Malene Juul

    2009-01-01

    An aerial survey was conducted to estimate the abundance of belugas (Delphinapterus leucas) on their wintering ground in West Greenland in March-April 2006 and 2008. The survey was conducted as a double platform aerial line transect survey, and sampled approximately 17% of the total survey area o...

  19. Evidence of Influence of Human Activities and Volcanic Eruptions on Environmental Perchlorate from a 300-Year Greenland Ice Core Record.

    Science.gov (United States)

    Cole-Dai, Jihong; Peterson, Kari Marie; Kennedy, Joshua Andrew; Cox, Thomas S; Ferris, David G

    2018-06-26

    A 300-year (1700-2007) chronological record of environmental perchlorate, reconstructed from high-resolution analysis of a central Greenland ice core, shows that perchlorate levels in the post-1980 atmosphere were two-to-three times those of the pre-1980 environment. While this confirms recent reports of increased perchlorate in Arctic snow since 1980 compared with the levels for the prior decades (1930-1980), the longer Greenland record demonstrates that the Industrial Revolution and other human activities, which emitted large quantities of pollutants and contaminants, did not significantly impact environmental perchlorate, as perchlorate levels remained stable throughout the eighteenth, nineteenth, and much of the twentieth centuries. The increased levels since 1980 likely result from enhanced atmospheric perchlorate production, rather than from direct release from perchlorate manufacturing and applications. The enhancement is probably influenced by the emission of organic chlorine compounds in the last several decades. Prior to 1980, no significant long-term temporal trends in perchlorate concentration are observed. Brief (a few years) high concentration episodes appear frequently over an apparently stable and low background (~1 ng kg‒1). Several such episodes coincide in time with large explosive volcanic eruptions including the 1912 Novarupta/Katmai eruption in Alaska. It appears that atmospheric perchlorate production is impacted by large eruptions in both high and low latitudes, but not by small eruptions and non-explosive degassing.

  20. Statistically optimal estimation of Greenland Ice Sheet mass variations from GRACE monthly solutions using an improved mascon approach

    Science.gov (United States)

    Ran, J.; Ditmar, P.; Klees, R.; Farahani, H. H.

    2018-03-01

    We present an improved mascon approach to transform monthly spherical harmonic solutions based on GRACE satellite data into mass anomaly estimates in Greenland. The GRACE-based spherical harmonic coefficients are used to synthesize gravity anomalies at satellite altitude, which are then inverted into mass anomalies per mascon. The limited spectral content of the gravity anomalies is properly accounted for by applying a low-pass filter as part of the inversion procedure to make the functional model spectrally consistent with the data. The full error covariance matrices of the monthly GRACE solutions are properly propagated using the law of covariance propagation. Using numerical experiments, we demonstrate the importance of a proper data weighting and of the spectral consistency between functional model and data. The developed methodology is applied to process real GRACE level-2 data (CSR RL05). The obtained mass anomaly estimates are integrated over five drainage systems, as well as over entire Greenland. We find that the statistically optimal data weighting reduces random noise by 35-69%, depending on the drainage system. The obtained mass anomaly time-series are de-trended to eliminate the contribution of ice discharge and are compared with de-trended surface mass balance (SMB) time-series computed with the Regional Atmospheric Climate Model (RACMO 2.3). We show that when using a statistically optimal data weighting in GRACE data processing, the discrepancies between GRACE-based estimates of SMB and modelled SMB are reduced by 24-47%.

  1. Using ATM laser altimetry to constrain surface mass balance estimates and supraglacial hydrology of the Greenland Ice Sheet

    Science.gov (United States)

    Studinger, M.; Medley, B.; Manizade, S.; Linkswiler, M. A.

    2016-12-01

    Repeat airborne laser altimetry measurements can provide large-scale field observations to better quantify spatial and temporal variability of surface processes contributing to seasonal elevation change and therefore surface mass balance. As part of NASA's Operation IceBridge the Airborne Topographic Mapper (ATM) laser altimeter measured the surface elevation of the Greenland Ice Sheet during spring (March - May) and fall (September - October) of 2015. Comparison of the two surveys reveals a general trend of thinning for outlet glaciers and for the ice sheet in a manner related to elevation and latitude. In contrast, some thickening is observed on the west (but not on the east) side of the ice divide above 2200 m elevation in the southern half, below latitude 69°N.The observed magnitude and spatial patterns of the summer melt signal can be utilized as input into ice sheet models and for validating reanalysis of regional climate models such as RACMO and MAR. We use seasonal anomalies in MERRA-2 climate fields (temperature, precipitation) to understand the observed spatial signal in seasonal change. Aside from surface elevation change, runoff from meltwater pooling in supraglacial lakes and meltwater channels accounts for at least half of the total mass loss. The ability of the ATM laser altimeters to image glacial hydrological features in 3-D and determine the depth of supraglacial lakes could be used for process studies and for quantifying melt processes over large scales. The 1-meter footprint diameter of ATM laser on the surface, together with a high shot density, allows for the production of large-scale, high-resolution, geodetic quality DEMs (50 x 50 cm) suitable for fine-scale glacial hydrology research and as input to hydrological models quantifying runoff.

  2. Antarctica, Greenland and Gulf of Alaska Land-Ice Evolution from an Iterated GRACE Global Mascon Solution

    Science.gov (United States)

    Luthcke, Scott B.; Sabaka, T. J.; Loomis, B. D.; Arendt, A. A.; McCarthy, J. J.; Camp, J.

    2013-01-01

    We have determined the ice mass evolution of the Antarctica and Greenland ice sheets (AIS and GIS) and Gulf of Alaska (GOA) glaciers from a new GRACE global solution of equal-area surface mass concentration parcels (mascons) in equivalent height of water. The mascons were estimated directly from the reduction of the inter-satellite K-band range-rate (KBRR) observations, taking into account the full noise covariance, and formally iterating the solution. The new solution increases signal recovery while reducing the GRACE KBRR observation residuals. The mascons were estimated with 10 day and 1 arc degree equal-area sampling, applying anisotropic constraints. An ensemble empirical mode decomposition adaptive filter was applied to the mascon time series to compute annual mass balances. The details and causes of the spatial and temporal variability of the land-ice regions studied are discussed. The estimated mass trend over the total GIS, AIS and GOA glaciers for the time period 1 December 2003 to 1 December 2010 is -380 plus or minus 31 Gt a(exp -1), equivalent to -1.05 plus or minus 0.09 mma(exp -1) sea-level rise. Over the same time period we estimate the mass acceleration to be -41 plus or minus 27 Gt a(exp -2), equivalent to a 0.11 plus or minus 0.08 mm a(exp -2) rate of change in sea level. The trends and accelerations are dependent on significant seasonal and annual balance anomalies.

  3. GPS based surface displacements – a proxy for discharge and sediment transport from the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Hasholt, Bent; Khan, Shfaqat Abbas; Mikkelsen, Andreas Bech

    2014-01-01

    winter precipitation correlated fairly well with surface depression (R2=0.69). The relationships are based on seven years of runoff and sediment transport observations from the Watson River (2007–2013), winter precipitation from Kangerlussuaq Airport and GPS observations at Kellyville. GPS recordings...... of surface subsidence and uplift from 1996–2013 are used to calculate 18 years time series of annual runoff, sediment and solute transport and 10 winter precipitation. Runoff and related transport of sediment and solutes increase over the period, while winter precipitation (land depression) tends to decrease......The elastic respond of the Earth’s surface to mass changes has been measured with Global Positioning System (GPS). Mass loss as accumulated runoff and sediment transport from a 10000 km2 segment of the Greenland Ice Sheet (GrIS) correlated very well (R2=0.83) with GPS measured uplift. Accumulated...

  4. Seasonal variations in active microwave signatures of sea ice in the Greenland Sea during 1992 and 1993

    DEFF Research Database (Denmark)

    Thomsen, Bjørn Bavnehøj; Skriver, Henning; Pedersen, Leif Toudal

    1995-01-01

    into the research of other statistical features of the sea ice than the mean value and also their seasonal variations. This paper investigates the backscatter coefficient and texture of different sea ice types and water by using calibrated precision images (PRI) acquired by the synthetic aperture radar (SAR...

  5. Greenland Ice Sheet Mass Balance: Distribution of Increased Mass Loss with Climate Warming; 2003-07 Versus 1992-2002

    Science.gov (United States)

    Zwally, H. Jay; Li, Jun; Benner, Anita C.; Beckley, Matthew; Cornejo, Helen G.; DiMarzio, John; Giovinetto, Mario B.; Neumann, Thomas A.; Robbins, John; Saba, Jack L.; hide

    2011-01-01

    We derive mass changes of the Greenland ice sheet (GIS) for 2003-07 from ICESat laser altimetry and compare them with results for 1992-2002 from ERS radar and airborne laser altimetry. The GIS continued to grow inland and thin at the margins during 2003 07, but surface melting and accelerated flow significantly increased the marginal thinning compared with the 1990s. The net balance changed from a small loss of 7 plus or minus 3 Gt a 1(sup -1) in the 1990s to 171 plus or minus 4 Gt a (sup -1) for 2003-07, contributing 0.5 mm a(sup -1) to recent global sea-level rise. We divide the derived mass changes into two components: (1) from changes in melting and ice dynamics and (2) from changes in precipitation and accumulation rate. We use our firn compaction model to calculate the elevation changes driven by changes in both temperature and accumulation rate and to calculate the appropriate density to convert the accumulation-driven changes to mass changes. Increased losses from melting and ice dynamics (17-206 Gt a(sup-1) are over seven times larger than increased gains from precipitation (10 35 Gt a(sup-1) during a warming period of approximately 2 K (10 a)(sup -1) over the GIS. Above 2000m elevation, the rate of gain decreased from 44 to 28 Gt a(sup-1), while below 2000m the rate of loss increased from 51 to 198 Gt a(sup-1). Enhanced thinning below the equilibrium line on outlet glaciers indicates that increased melting has a significant impact on outlet glaciers, as well as accelerating ice flow. Increased thinning at higher elevations appears to be induced by dynamic coupling to thinning at the margins on decadal timescales.

  6. Frost flowers and sea-salt aerosols over seasonal sea-ice areas in northwestern Greenland during winter–spring

    Directory of Open Access Journals (Sweden)

    K. Hara

    2017-07-01

    Full Text Available Sea salts and halogens in aerosols, frost flowers, and brine play an important role in atmospheric chemistry in polar regions. Simultaneous sampling and observations of frost flowers, brine, and aerosol particles were conducted around Siorapaluk in northwestern Greenland during December 2013 to March 2014. Results show that water-soluble frost flower and brine components are sea-salt components (e.g., Na+, Cl−, Mg2+, K+, Ca2+, Br−, and iodine. Concentration factors of sea-salt components of frost flowers and brine relative to seawater were 1.14–3.67. Sea-salt enrichment of Mg2+, K+, Ca2+, and halogens (Cl−, Br−, and iodine in frost flowers is associated with sea-salt fractionation by precipitation of mirabilite and hydrohalite. High aerosol number concentrations correspond to the occurrence of higher abundance of sea-salt particles in both coarse and fine modes, and blowing snow and strong winds. Aerosol number concentrations, particularly in coarse mode, are increased considerably by release from the sea-ice surface under strong wind conditions. Sulfate depletion by sea-salt fractionation was found to be limited in sea-salt aerosols because of the presence of non-sea-salt (NSS SO42−. However, coarse and fine sea-salt particles were found to be rich in Mg. Strong Mg enrichment might be more likely to proceed in fine sea-salt particles. Magnesium-rich sea-salt particles might be released from the surface of snow and slush layer (brine on sea ice and frost flowers. Mirabilite-like and ikaite-like particles were identified only in aerosol samples collected near new sea-ice areas. From the field evidence and results from earlier studies, we propose and describe sea-salt cycles in seasonal sea-ice areas.

  7. Frost flowers and sea-salt aerosols over seasonal sea-ice areas in northwestern Greenland during winter-spring

    Science.gov (United States)

    Hara, Keiichiro; Matoba, Sumito; Hirabayashi, Motohiro; Yamasaki, Tetsuhide

    2017-07-01

    Sea salts and halogens in aerosols, frost flowers, and brine play an important role in atmospheric chemistry in polar regions. Simultaneous sampling and observations of frost flowers, brine, and aerosol particles were conducted around Siorapaluk in northwestern Greenland during December 2013 to March 2014. Results show that water-soluble frost flower and brine components are sea-salt components (e.g., Na+, Cl-, Mg2+, K+, Ca2+, Br-, and iodine). Concentration factors of sea-salt components of frost flowers and brine relative to seawater were 1.14-3.67. Sea-salt enrichment of Mg2+, K+, Ca2+, and halogens (Cl-, Br-, and iodine) in frost flowers is associated with sea-salt fractionation by precipitation of mirabilite and hydrohalite. High aerosol number concentrations correspond to the occurrence of higher abundance of sea-salt particles in both coarse and fine modes, and blowing snow and strong winds. Aerosol number concentrations, particularly in coarse mode, are increased considerably by release from the sea-ice surface under strong wind conditions. Sulfate depletion by sea-salt fractionation was found to be limited in sea-salt aerosols because of the presence of non-sea-salt (NSS) SO42-. However, coarse and fine sea-salt particles were found to be rich in Mg. Strong Mg enrichment might be more likely to proceed in fine sea-salt particles. Magnesium-rich sea-salt particles might be released from the surface of snow and slush layer (brine) on sea ice and frost flowers. Mirabilite-like and ikaite-like particles were identified only in aerosol samples collected near new sea-ice areas. From the field evidence and results from earlier studies, we propose and describe sea-salt cycles in seasonal sea-ice areas.

  8. High-resolution 129I bomb peak profile in an ice core from SE-Dome site, Greenland.

    Science.gov (United States)

    Bautista, Angel T; Miyake, Yasuto; Matsuzaki, Hiroyuki; Iizuka, Yoshinori; Horiuchi, Kazuho

    2018-04-01

    129 I in natural archives, such as ice cores, can be used as a proxy for human nuclear activities, age marker, and environmental tracer. Currently, there is only one published record of 129 I in ice core (i.e., from Fiescherhorn Glacier, Swiss Alps) and its limited time resolution (1-2 years) prevents the full use of 129 I for the mentioned applications. Here we show 129 I concentrations in an ice core from SE-Dome, Greenland, covering years 1956-1976 at a time resolution of ∼6 months, the most detailed record to date. Results revealed 129 I bomb peaks in years 1959, 1962, and 1963, associated to tests performed by the former Soviet Union, one year prior, in its Novaya Zemlya test site. All 129 I bomb peaks were observed in winter (1958.9, 1962.1, and 1963.0), while tritium bomb peaks, another prominent radionuclide associated with nuclear bomb testing, were observed in spring or summer (1959.3, and 1963.6; Iizuka et al., 2017). These results indicate that 129 I bomb peaks can be used as annual and seasonal age markers for these years. Furthermore, we found that 129 I recorded nuclear fuel reprocessing signals and that these can be potentially used to correct timing of estimated 129 I releases during years 1964-1976. Comparisons with other published records of 129 I in natural archives showed that 129 I can be used as common age marker and tracer for different types of records. Most notably, the 1963 129 I bomb peak can be used as common age marker for ice and coral cores, providing the means to reconcile age models and associated trends from the polar and tropical regions, respectively. Copyright © 2017 Elsevier Ltd. All rights reserved.

  9. Sustained high basal motion of the Greenland ice sheet revealed by borehole deformation

    DEFF Research Database (Denmark)

    Ryser, Claudia; Luethi, Martin P.; Andrews, Lauren C.

    2014-01-01

    amount of basal motion contribution to surface velocity of 44-73% in winter, and up to 90% 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...

  10. Lead pollution recorded in Greenland ice indicates European emissions tracked plagues, wars, and imperial expansion during antiquity.

    Science.gov (United States)

    McConnell, Joseph R; Wilson, Andrew I; Stohl, Andreas; Arienzo, Monica M; Chellman, Nathan J; Eckhardt, Sabine; Thompson, Elisabeth M; Pollard, A Mark; Steffensen, Jørgen Peder

    2018-05-29

    Lead pollution in Arctic ice reflects midlatitude emissions from ancient lead-silver mining and smelting. The few reported measurements have been extrapolated to infer the performance of ancient economies, including comparisons of economic productivity and growth during the Roman Republican and Imperial periods. These studies were based on sparse sampling and inaccurate dating, limiting understanding of trends and specific linkages. Here we show, using a precisely dated record of estimated lead emissions between 1100 BCE and 800 CE derived from subannually resolved measurements in Greenland ice and detailed atmospheric transport modeling, that annual European lead emissions closely varied with historical events, including imperial expansion, wars, and major plagues. Emissions rose coeval with Phoenician expansion, accelerated during expanded Carthaginian and Roman mining primarily in the Iberian Peninsula, and reached a maximum under the Roman Empire. Emissions fluctuated synchronously with wars and political instability particularly during the Roman Republic, and plunged coincident with two major plagues in the second and third centuries, remaining low for >500 years. Bullion in silver coinage declined in parallel, reflecting the importance of lead-silver mining in ancient economies. Our results indicate sustained economic growth during the first two centuries of the Roman Empire, terminated by the second-century Antonine plague.

  11. The Annual Glaciohydrology Cycle in the Ablation Zone of the Greenland Ice Sheet: Part 1. Hydrology Model

    Science.gov (United States)

    Colgan, William; Rajaram, Harihar; Anderson, Robert; Steffen. Konrad; Phillips, Thomas; Zwally, H. Jay; Abdalati, Waleed

    2012-01-01

    We apply a novel one-dimensional glacier hydrology model that calculates hydraulic head to the tidewater-terminating Sermeq Avannarleq flowline of the Greenland ice sheet. Within a plausible parameter space, the model achieves a quasi-steady-state annual cycle in which hydraulic head oscillates close to flotation throughout the ablation zone. Flotation is briefly achieved during the summer melt season along a approx.17 km stretch of the approx.50 km of flowline within the ablation zone. Beneath the majority of the flowline, subglacial conduit storage closes (i.e. obtains minimum radius) during the winter and opens (i.e. obtains maximum radius) during the summer. Along certain stretches of the flowline, the model predicts that subglacial conduit storage remains open throughout the year. A calculated mean glacier water residence time of approx.2.2 years implies that significant amounts of water are stored in the glacier throughout the year. We interpret this residence time as being indicative of the timescale over which the glacier hydrologic system is capable of adjusting to external surface meltwater forcings. Based on in situ ice velocity observations, we suggest that the summer speed-up event generally corresponds to conditions of increasing hydraulic head during inefficient subglacial drainage. Conversely, the slowdown during fall generally corresponds to conditions of decreasing hydraulic head during efficient subglacial drainage.

  12. Automatization of an inverse surface temperature modelling procedure for Greenland ice cores, developed and evaluated using nitrogen and argon isotope data measured on the Gisp2 ice core

    Science.gov (United States)

    Döring, Michael; Kobashi, Takuro; Leuenberger, Markus

    2017-04-01

    In order to study Northern Hemisphere climate interactions and variability during the Holocene, access to high resolution surface temperature records of the Greenland ice sheet is an integral condition. Surface temperature reconstruction relies on firn densification combined with gas and heat diffusion [Severinghaus et al. (1998)]. In this study we use the model developed by Schwander et al. (1997). A theoretical δ15N record is generated for different temperature scenarios and compared with measurements by minimizing the mean squared error (MSE). The goal of the presented study is an automatization of this inverse modelling procedure. To solve the inverse problem, the Holocene temperature reconstruction is implemented in three steps. First a rough first guess temperature input (prior) is constructed which serves as the starting point for the optimization. Second, a smooth solution which transects the δ15N measurement data is generated following a Monte Carlo approach. It is assumed that the smooth solution contains all long term temperature trends and (together with the accumulation rate input) drives changes in firn column height, which generate the gravitational background signal in δ15N. Finally, the smooth solution is superimposed with high frequency information directly extracted from the δ15N measurement data. Following the approach, a high resolution Holocene temperature history for the Gisp2 site was extracted (posteriori), which leads to modelled δ15N data that fits the measurements in the low permeg level (MSE) and shows excellent agreement in timing and strength of the measurement variability. To evaluate the reconstruction procedure different synthetic data experiments were conducted underlining the quality of the method. Additionally, a second firn model [Goujon et al. (2003)] was used, which leads to very similar results, that shows the robustness of the presented approach. References: Goujon, C., Barnola, J.-M., Ritz, C. (2003). Modeling the

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

    Science.gov (United States)

    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.

  14. The isotope X-ray fluorescence analysis and its application in geochemical investigations in Greenland

    International Nuclear Information System (INIS)

    Kunzendorf, H.

    1973-01-01

    The applicability of the isotope X-ray fluorescence analysis (IRFA) in the geochemical exploration was investigated. Detection limits of about 0.1% for the elements Ti, Zr, Nb, Mo and La+Ce were achieved in terrain measurements. Detection limits of 0.05% were found in the analysis of Cr, Ni, Cu, Zn, Zr, Nb, Mo, La+Ce and Pb in finely grinded rock samples. Geochemical investigations were carried out in the Ilimaussag-Intrusion in south Greenland as well as on the Mo deposits Malmbjerg and the heavy mineral occurence 'kote 800' in East Greenland. The use of portable IRFA equipment proved to be particularly suitable in the analysis of bed rocks, loose rock samples such as moraine material, in the semi-quantitative analysis of heavy mineral concentrates, the analysis of bored cores during the boring programme, as well as the analysis of finely grinded rock samples. (ORU) [de

  15. First identification and characterization of Borrobol-type tephra in the Greenland ice cores

    DEFF Research Database (Denmark)

    Cook, Eliza; Davies, Siwan M.; Guðmundsdóttir, Esther R.

    2018-01-01

    in the ice-cores or that it relates to just one of the ice-core events. A firm correlation cannot be established at present due to their strong geochemical similarities. The older tephra horizon, found within all three ice-cores and dated to 17326 ± 319 a b2k, can be correlated to a known layer within marine....... The older deposit is consistent with BT age estimates derived from Scottish sites, while the younger deposit overlaps with both BT and PT age estimates. We suggest that either the BT in Northern European terrestrial sequences represents an amalgamation of tephra from both of the GI-1e events identified...

  16. Circulation and fjord-shelf exchange during the ice-covered period in Young Sound-Tyrolerfjord, Northeast Greenland (74°N)

    Science.gov (United States)

    Boone, W.; Rysgaard, S.; Kirillov, S.; Dmitrenko, I.; Bendtsen, J.; Mortensen, J.; Meire, L.; Petrusevich, V.; Barber, D. G.

    2017-07-01

    Fjords around Greenland connect the Greenland Ice Sheet to the ocean and their hydrography and circulation are determined by the interplay between atmospheric forcing, runoff, topography, fjord-shelf exchange, tides, waves, and seasonal growth and melt of sea ice. Limited knowledge exists on circulation in high-Arctic fjords, particularly those not impacted by tidewater glaciers, and especially during winter, when they are covered with sea-ice and freshwater input is low. Here, we present and analyze seasonal observations of circulation, hydrography and cross-sill exchange of the Young Sound-Tyrolerfjord system (74°N) in Northeast Greenland. Distinct seasonal circulation phases are identified and related to polynya activity, meltwater and inflow of coastal water masses. Renewal of basin water in the fjord is a relatively slow process that modifies the fjord water masses on a seasonal timescale. By the end of winter, there is two-layer circulation, with outflow in the upper 45 m and inflow extending down to approximately 150 m. Tidal analysis showed that tidal currents above the sill were almost barotropic and dominated by the M2 tidal constituent (0.26 m s-1), and that residual currents (∼0.02 m s-1) were relatively small during the ice-covered period. Tidal pumping, a tidally driven fjord-shelf exchange mechanism, drives a salt flux that is estimated to range between 145 kg s-1 and 603 kg s-1. Extrapolation of these values over the ice-covered period indicates that tidal pumping is likely a major source of dense water and driver of fjord circulation during the ice-covered period.

  17. A tentative record of the last 1,000 years of Greenland temperature from occluded air in the GISP2 ice core

    Science.gov (United States)

    Kobashi, T.; Severinghaus, J. P.; Barnola, J.; Kawamura, K.; Beaudette, R.

    2005-12-01

    Ice borehole temperature inversion has been used to reconstruct Greenland surface temperature during the last millennium (Dahl-Jensen et al, Science, 1998). However, this technique does not preserve high frequencies because of diffusion of heat in the ice. Here, we present a tentative reconstruction of the past 1,000 years of central Greenland temperature using nitrogen and argon isotopes from occluded air in the GISP2 ice core. This technique preserves decadal-to-centennial-scale temperature variations and complements the borehole technique. Nitrogen and argon isotopes in the porous snow layer (~80m) experience two isotopic fractionations by gravitation and temperature gradients (ΔT) between the top and bottom of the snow layer. The simultaneous analysis of argon and nitrogen isotopes allows us to separate these two effects, and obtain a history of ΔT in the layer. To a first approximation, ΔT change on decadal to centennial time scales is a surface temperature history because the heat conductivity of snow is much smaller than that of ice, and the heat capacity of the ice sheet is quite large. The preliminary ΔT history (20-year interval) shows a Medieval Warm Period in the 11th to 12th centuries and the Little Ice Age in the 15th to 19th centuries. Furthermore, the record shows a clear similarity with the Be-10 record (a proxy for solar activity) with Wolf, Sporer, Maunder, and Dalton minima clearly seen in the cold periods. This finding is consistent with the hypothesis that solar activity influenced Greenland temperature during the past 1000 years.

  18. Using satellite laser ranging to measure ice mass change in Greenland and Antarctica

    Directory of Open Access Journals (Sweden)

    J. A. Bonin

    2018-01-01

    Full Text Available A least squares inversion of satellite laser ranging (SLR data over Greenland and Antarctica could extend gravimetry-based estimates of mass loss back to the early 1990s and fill any future gap between the current Gravity Recovery and Climate Experiment (GRACE and the future GRACE Follow-On mission. The results of a simulation suggest that, while separating the mass change between Greenland and Antarctica is not possible at the limited spatial resolution of the SLR data, estimating the total combined mass change of the two areas is feasible. When the method is applied to real SLR and GRACE gravity series, we find significantly different estimates of inverted mass loss. There are large, unpredictable, interannual differences between the two inverted data types, making us conclude that the current 5×5 spherical harmonic SLR series cannot be used to stand in for GRACE. However, a comparison with the longer IMBIE time series suggests that on a 20-year time frame, the inverted SLR series' interannual excursions may average out, and the long-term mass loss estimate may be reasonable.

  19. Using satellite laser ranging to measure ice mass change in Greenland and Antarctica

    Science.gov (United States)

    Bonin, Jennifer A.; Chambers, Don P.; Cheng, Minkang

    2018-01-01

    A least squares inversion of satellite laser ranging (SLR) data over Greenland and Antarctica could extend gravimetry-based estimates of mass loss back to the early 1990s and fill any future gap between the current Gravity Recovery and Climate Experiment (GRACE) and the future GRACE Follow-On mission. The results of a simulation suggest that, while separating the mass change between Greenland and Antarctica is not possible at the limited spatial resolution of the SLR data, estimating the total combined mass change of the two areas is feasible. When the method is applied to real SLR and GRACE gravity series, we find significantly different estimates of inverted mass loss. There are large, unpredictable, interannual differences between the two inverted data types, making us conclude that the current 5×5 spherical harmonic SLR series cannot be used to stand in for GRACE. However, a comparison with the longer IMBIE time series suggests that on a 20-year time frame, the inverted SLR series' interannual excursions may average out, and the long-term mass loss estimate may be reasonable.

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

    Science.gov (United States)

    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.

  1. Inverted Basal Shear Stress of Antarctic and Greenland Ice Streams and Glaciers, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set includes basal shear distributions inferred from surface observations - surface ice velocities (Joughin et al., 2010, Rignot et al., 2011), bed and...

  2. Changes in the Mass Balance of the Greenland Ice Sheet in a Warming Climate During 2003-2009

    Science.gov (United States)

    Zwally, H. Jay; Luthcke, Scott

    2010-01-01

    Mass changes of the Greenland ice sheet (GIS) derived from ICESat and GRACE data both show that the net mass loss from GIS during 2003-2009 is about 175 Gt/year, which contributes 0.5mm/yr global sea-level rise. The rate of mass loss has increased significantly since the 1990's when the GIS was close to mass balance. Even though the GIS was close to mass balance during the 1990's, it was already showing characteristics of responding to8 warmer climate, specifically thinning at the margins and thickening inland at higher elevations. During 2003-2009, increased ice thinning due to increases in melting and acceleration of outlet glaciers began to strongly exceed the inland thickening from increases in accumulation. Over the entire GIS, the mass loss between the two periods, from increased melting and ice dynamics, increased by about 190 Gt/year while the mass gain, from increased precipitation and accumulation, increased by only about 15Gt/year. These ice changes occurred during a time when the temperature on GIS changed at rate of about 2K/decade. The distribution of elevation and mass changes derived from ICESat have high spatial resolution showing details over outlet glaciers, by drainage systems, and by elevation. However, information on the seasonal cycle of changes from ICESat data is limited, because the ICESat lasers were only operated during two to three campaigns per year of about 35 days duration each. In contrast, the temporal resolution of GRACE data, provided by the continuous data collection, is much better showing details of the seasonal cycle and the inter-annual variability. The differing sensitivity of the ICESat altimetry and the GRACE gravity methods to motion of the underlying bedrock from glacial isostatic adjustment (GIA) is used to evaluate the GIA corrections provided by models. The two data types are also combined to make estimates of the partitioning of the mass gains and losses among accumulation, melting, and ice discharge from outlet

  3. Formal definition and dating of the GSSP (Global Stratotype Section and Point) for the base of the Holocene using the Greenland NGRIP ice core, and selected auxiliary records

    DEFF Research Database (Denmark)

    Walker, Mike; Johnsen, Sigfus Johann; Rasmussen, Sune Olander

    2009-01-01

    The Greenland ice core from NorthGRIP (NGRIP) contains a proxy climate record across the Pleistocene-Holocene boundary of unprecedented clarity and resolution. Analysis of an array of physical and chemical parameters within the ice enables the base of the Holocene, as reflected in the first signs...... the Global Stratotype Section and Point (GSSP) for the base of the Holocene Series/Epoch (Quaternary System/Period) has been ratified by the International Union of Geological Sciences. Five auxiliary stratotypes for the Pleistocene-Holocene boundary have also been recognised....

  4. Energy-efficient Building in Greenland: Investigation of the Energy Consumption and Indoor Climate

    DEFF Research Database (Denmark)

    Luc, Katarzyna Marta; Kotol, Martin; Lading, Tove

    2016-01-01

    Recently, a brand new single family home was built in Sisimiut, Greenland. The building was constructed as a wooden house typical for Greenland. However, some non-traditional measures were implemented in order to reduce the energy consumption and improve indoor air quality. Assessment...... was installed in the house. It enables the evaluation of the indoor air quality, as well as building's energy performance. The aim of this investigation was to evaluate the performance of the newly constructed house by and compare it with the performance of identical house built in a traditional way by using...... a computer model. The data obtained from the measurements in the new house were used to verify the model. Significant energy savings and improvements of indoor air quality were found in the new house when compared to the traditional one. Moreover, all the extra measures have a feasible payback time despite...

  5. Greenland in Warm (1.5 °C) and Warmer (RCP 8.5) Worlds: The Influence of the Paris Agreement on Ice Sheet Surface Melting

    Science.gov (United States)

    Reusch, D. B.

    2017-12-01

    Melting on the surface of the Greenland ice sheet has been changing dramatically as global air temperatures have increased in recent decades, including melt extent often exceeding the 1981-2010 median through much of the melt season and the onset of intermittent melt moving to earlier in the year. To evaluate potential future change, we investigate surface melting characteristics under both "low" (limited to 1.5 °C) and "high" (RCP 8.5) warming scenarios including analysis of differences in scenario outcomes. Climatologies of melt-relevant variables are developed from two publicly available ensembles of CESM1-CAM5-BGC GCM runs: the 30-member Large Ensemble (CESM LE; Kay et al. 2015) for historical calibration and the RCP 8.5 scenario and the 11-member Low Warming ensemble (CESM LW; Sanderson et al. 2017) for the 1.5 °C scenario. For higher spatial resolution (15 km) and improved polar-centric model physics, we also apply the regional forecast model Polar WRF to decadal subsets (1996-2005; 2071-80) using GCM data archived at sub-daily resolution for boundary conditions. Models were skill-tested against ERA-Interim Reanalysis (ERAI) and AWS observations. For example, CESM LE tends to overpredict both maximum (above-freezing) and minimum daily average surface temperatures compared to observations from the GC-Net Swiss Camp AWS. Ensembles of members differing only by initial conditions allow us to also estimate intramodel uncertainty. Historical (1981-2000) CESM LE spatially averaged July temperatures are 2 +/- 0.2 °C cooler than ERAI while local anomalies in individual members reach up to +/- 2 °C. As expected, Greenland does not escape future (2081-2100) warming (and expectations of more widespread surface melting) even in the LW scenario, but positive changes versus ERAI are mostly coastal (2-3 °C) with the interior showing only minor change (+/- 1 °C). In contrast, under RCP 8.5, the entire ice sheet has warmed by 2-6 °C, or a median increase of 5 °C versus

  6. High spatial variation in terrestrial arthropod species diversity and composition near the Greenland ice cap

    DEFF Research Database (Denmark)

    Hansen, Rikke Reisner; Hansen, Oskar Liset Pryds; Bowden, Joseph James

    2016-01-01

    Arthropods form a major part of the terrestrial species diversity in the Arctic, and are particularly sensitive to temporal changes in the abiotic environment. It is assumed that most Arctic arthropods are habitat generalists and that their diversity patterns exhibit low spatial variation....... The empirical basis for this assumption, however, is weak. We examine the degree of spatial variation in species diversity and assemblage structure among five habitat types at two sites of similar abiotic conditions and plant species composition in southwest Greenland, using standardized field collection...... methods for spiders, beetles and butterflies. We employed non-metric multidimensional scaling, species richness estimation, community dissimilarity and indicator species analysis to test for local (within site)- and regional (between site)-scale differences in arthropod communities. To identify specific...

  7. Towards Greenland Glaciation: cumulative or abrupt transition?

    Science.gov (United States)

    Ramstein, Gilles; Tan, Ning; Ladant, Jean-baptiste; Dumas, Christophe; Contoux, Camille

    2017-04-01

    During the mid-Pliocene warming period (3-3.3 Ma BP), the global annual mean temperatures inferred by data and model studies were 2-3° warmer than pre-industrial values. Accordingly, Greenland ice sheet volume is supposed to reach at the most, only half of that of present-day [Haywood et al. 2010]. Around 2.7-2.6 Ma BP, just ˜ 500 kyr after the warming peak of mid-Pliocene, the Greenland ice sheet has reached its full size [Lunt et al. 2008]. A crucial question concerns the evolution of the Greenland ice sheet from half to full size during the 3 - 2.5 Ma period. Data show a decreasing trend of atmospheric CO2 concentration from 3 Ma to 2.5 Ma [Seki et al.2010; Bartoli et al. 2011; Martinez et al. 2015]. However, a recent study [Contoux et al. 2015] suggests that a lowering of CO2 is not sufficient to initiate a perennial glaciation on Greenland and must be combined with low summer insolation to preserve the ice sheet during insolation maxima. This suggests rather a cumulative process than an abrupt event. In order to diagnose the evolution of the ice sheet build-up, we carry on, for the first time, a transient simulation of climate and ice sheet evolutions from 3 Ma to 2.5 Ma. This strategy enables us to investigate the waxing and waning of the ice sheet during several orbital cycles. We use a tri-dimensional interpolation method designed by Ladant et al. (2014), which allows the evolution of CO2 concentration and of orbital parameters, and the evolution of the Greenland ice sheet size to be taken into account. By interpolating climatic snapshot simulations ran with various possible combinations of CO2, orbits and ice sheet sizes, we can build a continuous climatic forcing that is then used to provide 500 kyrs-long ice sheet simulations. With such a tool, we may offer a physically based answer to different CO2 reconstructions scenarios and analyse which one is the most consistent with Greenland ice sheet buildup.

  8. Sediment plume response to surface melting and supraglacial lake drainages on the Greenland ice sheet

    DEFF Research Database (Denmark)

    Chu, Vena W.; Smith, Laurence C; Rennermalm, Asa K.

    2009-01-01

    ) supraglacial lake drainage events from MODIS. Results confirm that the origin of the sediment plume is meltwater release from the ice sheet. Interannual variations in plume area reflect interannual variations in surface melting. Plumes appear almost immediately with seasonal surface-melt onset, provided...... the estuary is free of landfast sea ice. A seasonal hysteresis between melt extent and plume area suggests late-season exhaustion in sediment supply. Analysis of plume sensitivity to supraglacial events is less conclusive, with 69% of melt pulses and 38% of lake drainage events triggering an increase in plume...... area. We conclude that remote sensing of sediment plume behavior offers a novel tool for detecting the presence, timing and interannual variability of meltwater release from the ice sheet....

  9. Timing and origin of recent regional ice-mass loss in Greenland

    DEFF Research Database (Denmark)

    Sasgen, Ingo; van den Broeke, Michiel; Bamber, J.L.Jonathan L.

    2012-01-01

    and Kanagaratnam, 2006) together with output of the regional atmospheric climate modelling (RACMO2/GR; Ettema et al., 2009), and surface-elevation changes from the Ice, cloud and land elevation satellite (ICESat; Sørensen et al., 2011). We show that changing ice discharge (D), surface melting and subsequent run-off...... (M/R) and precipitation (P) all contribute, in a complex and regionally variable interplay, to the increasingly negative mass balance of the GrIS observed within the last decade. Interannual variability in P along the northwest and west coasts of the GrIS largely explains the apparent regional mass...

  10. Bedrock displacements in Greenland manifest ice mass variations, climate cycles and climate change

    DEFF Research Database (Denmark)

    Bevis, Michael; Wahr, John; Khan, Shfaqat Abbas

    2012-01-01

    for by an annual oscillation superimposed on a sustained trend. The oscillation is driven by earth’s elastic response to seasonal variations in ice mass and air mass (i.e., atmospheric pressure). Observed vertical velocities are higher and often much higher than predicted rates of postglacial rebound (PGR......), implying that uplift is usually dominated by the solid earth’s instantaneous elastic response to contemporary losses in ice mass rather than PGR. Superimposed on longer-term trends, an anomalous ‘pulse’ of uplift accumulated at many GNET stations during an approximate six-month period in 2010...

  11. Reconstruction of the 1979–2006 Greenland ice sheet surface mass balance using the regional climate model MAR

    Directory of Open Access Journals (Sweden)

    X. Fettweis

    2007-10-01

    Full Text Available Results from a 28-year simulation (1979–2006 over the Greenland ice sheet (GrIS reveal an increase of solid precipitation (+0.4±2.5 km3 yr−2 and run-off (+7.9±3.3 km3 yr−2 of surface meltwater. The net effect of these competing factors is a significant Surface Mass Balance (SMB loss of −7.2±5.1 km3 yr−2. The contribution of changes in the net water vapour flux (+0.02±0.09 km3 yr−2 and rainfall (+0.2±0.2 km3 yr−2 to the SMB variability is negligible. The meltwater supply has increased because the GrIS surface has been warming up +2.4°C since 1979. Sensible heat flux, latent heat flux and net solar radiation have not varied significantly over the last three decades. However, the simulated downward infrared flux has increased by 9.3 W m−2 since 1979. The natural climate variability (e.g. the North Atlantic Oscillation does not explain these changes. The recent global warming, due to the greenhouse gas concentration increase induced by human activities, could be a cause of these changes. The doubling of surface meltwater flux into the ocean over the period 1979–2006 suggests that the overall ice sheet mass balance has been increasingly negative, given the likely meltwater-induced acceleration of outlet glaciers. This study suggests that increased melting overshadows over an increased accumulation in a warming scenario and that the GrIS is likely to keep losing mass in the future. An enduring GrIS melting will probably affect in the future an certain effect on the stability of the thermohaline circulation and the global sea level rise.

  12. A characterization of Greenland Ice Sheet surface melt and runoff in contemporary reanalyses and a regional climate model

    Directory of Open Access Journals (Sweden)

    Richard eCullather

    2016-02-01

    Full Text Available For the Greenland Ice Sheet (GrIS, large-scale melt area has increased in recent years and is detectable via remote sensing, but its relation to runoff is not known. Historical, modeled melt area and runoff from Modern-Era Retrospective Analysis for Research and Applications (MERRA-Replay, the Interim Re-Analysis of the European Centre for Medium Range Weather Forecasts (ERA-I, the Climate Forecast System Reanalysis (CFSR, the Modèle Atmosphérique Régional (MAR, and the Arctic System Reanalysis (ASR are examined. These sources compare favorably with satellite-derived estimates of surface melt area for the period 2000-2012. Spatially, the models markedly disagree on the number of melt days in the interior of the southern part of the ice sheet, and on the extent of persistent melt areas in the northeastern GrIS. Temporally, the models agree on the mean seasonality of daily surface melt and on the timing of large-scale melt events in 2012. In contrast, the models disagree on the amount, seasonality, spatial distribution, and temporal variability of runoff. As compared to global reanalyses, time series from MAR indicate a lower correlation between runoff and melt area (r2 = 0.805. Runoff in MAR is much larger in the second half of the melt season for all drainage basins, while the ASR indicates larger runoff in the first half of the year. This difference in seasonality for the MAR and to an extent for the ASR provide a hysteresis in the relation between runoff and melt area, which is not found in the other models. The comparison points to a need for reliable observations of surface runoff.

  13. Application of GRACE to the assessment of model-based estimates of monthly Greenland Ice Sheet mass balance (2003-2012)

    Science.gov (United States)

    Schlegel, Nicole-Jeanne; Wiese, David N.; Larour, Eric Y.; Watkins, Michael M.; Box, Jason E.; Fettweis, Xavier; van den Broeke, Michiel R.

    2016-09-01

    Quantifying the Greenland Ice Sheet's future contribution to sea level rise is a challenging task that requires accurate estimates of ice sheet sensitivity to climate change. Forward ice sheet models are promising tools for estimating future ice sheet behavior, yet confidence is low because evaluation of historical simulations is challenging due to the scarcity of continental-wide data for model evaluation. Recent advancements in processing of Gravity Recovery and Climate Experiment (GRACE) data using Bayesian-constrained mass concentration ("mascon") functions have led to improvements in spatial resolution and noise reduction of monthly global gravity fields. Specifically, the Jet Propulsion Laboratory's JPL RL05M GRACE mascon solution (GRACE_JPL) offers an opportunity for the assessment of model-based estimates of ice sheet mass balance (MB) at ˜ 300 km spatial scales. Here, we quantify the differences between Greenland monthly observed MB (GRACE_JPL) and that estimated by state-of-the-art, high-resolution models, with respect to GRACE_JPL and model uncertainties. To simulate the years 2003-2012, we force the Ice Sheet System Model (ISSM) with anomalies from three different surface mass balance (SMB) products derived from regional climate models. Resulting MB is compared against GRACE_JPL within individual mascons. Overall, we find agreement in the northeast and southwest where MB is assumed to be primarily controlled by SMB. In the interior, we find a discrepancy in trend, which we presume to be related to millennial-scale dynamic thickening not considered by our model. In the northwest, seasonal amplitudes agree, but modeled mass trends are muted relative to GRACE_JPL. Here, discrepancies are likely controlled by temporal variability in ice discharge and other related processes not represented by our model simulations, i.e., hydrological processes and ice-ocean interaction. In the southeast, GRACE_JPL exhibits larger seasonal amplitude than predicted by the

  14. Ancient biomolecules from deep ice cores reveal a forested southern Greenland

    DEFF Research Database (Denmark)

    Willerslev, Eske; Cappellini, Enrico; Boomsma, Wouter Krogh

    2007-01-01

    It is difficult to obtain fossil data from the 10% of Earth's terrestrial surface that is covered by thick glaciers and ice sheets, and hence, knowledge of the paleoenvironments of these regions has remained limited. We show that DNA and amino acids from buried organisms can be recovered from the...

  15. GNET detected an anomalous "spike" in ice loss in Greenland during the 2010 melting season

    DEFF Research Database (Denmark)

    Bevis, Michael G; Wahr, John M; Khan, Shfaqat Abbas

    ’s instantaneous elastic response to contemporary losses in ice mass. Superimposed on longer term trends, an anomalous ‘pulse’ of uplift accumulated at many GNET stations during a ~5 month period in 2010, and we will show that this anomalous uplift is spatially correlated with the 2010 melting day anomaly (Tedesco...

  16. Greenland meltwater storage in firn limited by near-surface ice formation

    DEFF Research Database (Denmark)

    Machguth, Horst; MacFerrin, Mike; van As, Dirk

    2016-01-01

    above sea level), firn has undergone substantial densification, while at lower elevations, where melt is most abundant, porous firn has lost most of its capability to retain meltwater. Here, the formation of near-surface ice layers renders deep pore space difficult to access, forcing meltwater to enter...

  17. How Greenland melts

    Directory of Open Access Journals (Sweden)

    van den Broeke M.R.

    2010-12-01

    Full Text Available Satellite altimetry and gravimetry show that the Greenland ice sheet has been losing volume and mass since the beginning of this century. However, from these short time series of direct measurements we cannot infer what the causes of the mass loss are, i.e. ice dynamics or surface processes, or that maybe the ice sheet returns to normal after a period of volume increase and mass gain. By modelling and observing the individual components of the ice sheet mass balance, i.e. snowfall, meltwater runoff and iceberg production, we are able to identify the processes that led to the recent mass loss. We conclude that the Greenland ice sheet is significantly out of balance. Acceleration of outlet glaciers and increased runoff have contributed equally to recent Greenland mass loss. The potential for mass loss by surface processes, however, was three times greater than actually observed, due to refreezing and enhanced snowfall.

  18. How robust are in situ observations for validating satellite-derived albedo over the dark zone of the Greenland Ice Sheet?

    Science.gov (United States)

    Ryan, J.; Hubbard, A., II; Irvine-Fynn, T. D.; Doyle, S. H.; Cook, J.; Stibal, M.; Smith, L. C.; Box, J. E.

    2017-12-01

    Calibration and validation of satellite-derived ice sheet albedo data require high-quality, in situ measurements commonly acquired by up and down facing pyranometers mounted on automated weather stations (AWS). However, direct comparison between ground and satellite-derived albedo can only be justified when the measured surface is homogeneous at the length-scale of both satellite pixel and in situ footprint. We used digital imagery acquired by an unmanned aerial vehicle to evaluate point-to-pixel albedo comparisons across the western, ablating margin of the Greenland Ice Sheet. Our results reveal that in situ measurements overestimate albedo by up to 0.10 at the end of the melt season because the ground footprints of AWS-mounted pyranometers are insufficient to capture the spatial heterogeneity of the ice surface as it progressively ablates and darkens. Statistical analysis of 21 AWS across the entire Greenland Ice Sheet reveals that almost half suffer from this bias, including some AWS located within the wet snow zone.

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

    Science.gov (United States)

    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).

  20. Greenland climate change

    DEFF Research Database (Denmark)

    Masson-Delmotte, Valérie; Swingedouw, Didier; Landais, Amaëlle

    2012-01-01

    Climate archives available from deep-sea and marine shelf sediments, glaciers, lakes and ice cores in and around Greenland allow us to place the current trends in regional climate, ice sheet dynamics, and land surface changes in a broader perspective. We show that during the last decade (2000s......), atmospheric and sea-surface temperatures are reaching levels last encountered millennia ago when northern high latitude summer insolation was higher due to a different orbital configuration. Concurrently, records from lake sediments in southern Greenland document major environmental and climatic conditions...... regional climate and ice sheet dynamics. The magnitude and rate of future changes in Greenland temperature, in response to increasing greenhouse gas emissions, may be faster than any past abrupt events occurring under interglacial conditions. Projections indicate that within one century Greenland may...

  1. Groundwater flow modelling under ice sheet conditions in Greenland (phase II)

    International Nuclear Information System (INIS)

    Jaquet, Olivier; Namar, Rabah; Siegel, Pascal; Jansson, Peter

    2012-11-01

    Within the framework of the GAP project, this second phase of geosphere modelling has enabled the development of an improved regional model that has led to a better representation of groundwater flow conditions likely to occur under ice sheet conditions. New data in relation to talik geometry and elevation, as well as to deformation zones were integrated in the geosphere model. In addition, more realistic hydraulic properties were considered for geosphere modelling; they were taken from the Laxemar site in Sweden. The geological medium with conductive deformation zones was modelled as a 3D continuum with stochastically hydraulic properties. Surface and basal glacial meltwater rates provided by a dynamic ice sheet model were assimilated into the groundwater flow model using mixed boundary conditions. The groundwater flow system is considered to be governed by infiltration of glacial meltwater in heterogeneous faulted crystalline rocks in the presence of permafrost and taliks. The characterisation of the permafrost-depth distribution was achieved using a coupled description of flow and heat transfer under steady state conditions. Using glaciological concepts and satellite data, an improved stochastic model was developed for the description at regional scale for the subglacial permafrost distribution in correlation with ice velocity and bed elevation data. Finally, the production of glacial meltwater by the ice sheet was traced for the determination of its depth and lateral extent. The major improvements are related to the type and handling of the subglacial boundary conditions. The use of meltwater rates provided by an ice sheet model applied as input to a mixed boundary condition enables to produce a more plausible flow field in the Eastern part of the domain, in comparison to previous modelling results (Jaquet et al. 2010). In addition, the integration of all potential taliks within the modelled domain provides a better characterisation of the likely groundwater

  2. Groundwater flow modelling under ice sheet conditions in Greenland (phase II)

    Energy Technology Data Exchange (ETDEWEB)

    Jaquet, Olivier; Namar, Rabah; Siegel, Pascal [In2Earth Modelling Ltd, Lausanne (Switzerland); Jansson, Peter [Dept. of Physical Geography and Quaternary Geology, Stockholm Univ., Stockholm (Sweden)

    2012-11-15

    Within the framework of the GAP project, this second phase of geosphere modelling has enabled the development of an improved regional model that has led to a better representation of groundwater flow conditions likely to occur under ice sheet conditions. New data in relation to talik geometry and elevation, as well as to deformation zones were integrated in the geosphere model. In addition, more realistic hydraulic properties were considered for geosphere modelling; they were taken from the Laxemar site in Sweden. The geological medium with conductive deformation zones was modelled as a 3D continuum with stochastically hydraulic properties. Surface and basal glacial meltwater rates provided by a dynamic ice sheet model were assimilated into the groundwater flow model using mixed boundary conditions. The groundwater flow system is considered to be governed by infiltration of glacial meltwater in heterogeneous faulted crystalline rocks in the presence of permafrost and taliks. The characterisation of the permafrost-depth distribution was achieved using a coupled description of flow and heat transfer under steady state conditions. Using glaciological concepts and satellite data, an improved stochastic model was developed for the description at regional scale for the subglacial permafrost distribution in correlation with ice velocity and bed elevation data. Finally, the production of glacial meltwater by the ice sheet was traced for the determination of its depth and lateral extent. The major improvements are related to the type and handling of the subglacial boundary conditions. The use of meltwater rates provided by an ice sheet model applied as input to a mixed boundary condition enables to produce a more plausible flow field in the Eastern part of the domain, in comparison to previous modelling results (Jaquet et al. 2010). In addition, the integration of all potential taliks within the modelled domain provides a better characterisation of the likely groundwater

  3. /sup 36/Cl and /sup 10/Be profiles in Greenland ice: Dating and production rate variations

    Energy Technology Data Exchange (ETDEWEB)

    Elmore, D; Conard, N J; Kubik, P W; Gove, H E; Wahlen, M; Beer, J; Suter, M

    1987-11-01

    Concentrations of the cosmogenic radioistopes /sup 36/Cl and /sup 10/Be have been measured in the top portion of the 1966 Camp Century deep ice core using tandem accelerator mass spectrometry. The primary motivations were to look for correlations with solar activity and to test the possibility that the ratio of /sup 10/Be to /sup 36/Cl would provide a means for dating old ice. An increase in each radioisotope is seen during the Maunder sunspot minimum (1650 to 1715 A.D.), as expected, but there are fluctuations of a factor of 2 or more over short time periods and a possible correlation with solar activity is apparent only when the data is mathematically smoothed. Variations of the /sup 10/Be//sup 36/Cl ratio by about a factor of five are observed which means that dating of ice by single /sup 10/Be//sup 36/Cl measurements covering the precipitation of only a few years will not be possible.

  4. Gravity anomaly at a Pleistocene lake bed in NW Alaska interpreted by analogy with Greenland's Lake Taserssauq and its floating ice tongue

    Science.gov (United States)

    Barnes, D.F.

    1987-01-01

    A possible example of a very deep glacial excavation is provided by a distinctive gravity low located at the front of a valley glacier that once flowed into glacial Lake Aniuk (formerly Lake Noatak) in the western Brooks Range. Geologic and geophysical data suggest that sediments or ice filling a glacially excavated valley are the most probable cause of the 30-50 mGal anomaly. Reasonable choices of geometric models and density contrasts indicate that the former excavation is now filled with a buried-ice thickness of 700 m or sediment thicknesses greater than 1 km. No direct evidence of efficient excavation was observed in Greenland, but efficient glacial erosion behind a floating polar ice tongue could explain the excavation that caused the Alaskan gravity anomaly. -from Author

  5. Laboratory investigation of nitrile ices of Titan's stratospheric clouds

    Science.gov (United States)

    Nna Mvondo, D.; Anderson, C. M.; McLain, J. L.; Samuelson, R. E.

    2017-09-01

    Titan's mid to lower stratosphere contains complex cloud systems of numerous organic ice particles comprised of both hydrocarbon and nitrile compounds. Most of these stratospheric ice clouds form as a result of vapor condensation formation processes. However, there are additional ice emission features such as dicyanoacetylene (C4N2) and the 220 cm-1 ice emission feature (the "Haystack") that are difficult to explain since there are no observed vapor emission features associated with these ices. In our laboratory, using a high-vacuum chamber coupled to a FTIR spectrometer, we are engaged in a dedicated investigation of Titan's stratospheric ices to interpret and constrain Cassini Composite InfraRed Spectrometer (CIRS) far-IR data. We will present laboratory transmittance spectra obtained for propionitrile (CH3CH2CN), cyanogen (C2N2) and hydrogen cyanide (HCN) ices, as well as various combinations of their mixtures, to better understand the cloud chemistry occurring in Titan's stratosphere.

  6. Evaluation of aerosol composition changes in the last 60 years around southeastern Greenland by analyzing micro-inclusions in the SE-Dome ice core using Raman spectroscopy.

    Science.gov (United States)

    Ando, T.; Iizuka, Y.; Ohno, H.; Sugiyama, S.

    2017-12-01

    Emission regulation of anthropogenic NOX and SOX since late 90's rather caused excess atmospheric ammonium (NH3) in agricultural regions (Warner et al., 2017, Geophys. Res. Lett.). The Arctic is one of the most sensitive areas for future warming. Aerosols in the Arctic are transported from the Northern Hemisphere and mostly experience wet deposition (Breider et al., 2014, Jour. of Geophys. Res.: Atmos.). Ice cores preserve past water-soluble aerosols. From these viewpoints, ice cores from the Arctic is suitable to evaluate recent variation in aerosol composition due to human activity in the Northern Hemisphere and aerosol transportation. We analyzed ion concentrations in the ice core samples from a southeastern dome in Greenland (SE-Dome). The concentrations increased for NH4+ and decreased for SO42- after late 90's. The NH4+ increasing trend is due to excess NH3 emission in North America. Cloud nuclei formation depends on chemical form of aerosols. Thus, differences in chemical forms of these ammonium aerosols in SE-Dome samples are important to evaluate the effect on climate change in Greenland. In this study, we identified the chemical form of aerosols (water-soluble inclusions) in the SE-Dome ice core by using micro-Raman spectroscopy. SE-Dome ice core samples were collected in 2015 and enabled us to reconstruct seasonal variation owing to extremely higher accumulation rate ( 1m/yr.). The ice samples were sublimated and accumulated inclusions on the Ni sheets in a clean booth under -22 degrees Celsius. We identified CaSO4, Na2SO4, (NH4)2SO4, NaNO3, NH4NO3 by Raman spectra. This is the first report to identify ammonium salts ((NH4)2SO4 and NH4NO3) from ice core sample. In the summer samples, the relative abundances of CaSO4 and NaNO3 are lower but (NH4)2SO4 are higher than those in the spring samples. NH4+ rapidly react with SO24- under higher temperature. Higher concentration of NH3 in the warmest season possibly enhanced the formation of (NH4)2SO4 in North

  7. Arctic Ocean UNCLOS Article 76 Work for Greenland Starts on Land

    Science.gov (United States)

    Dahl-Jensen, T.; Marcussen, C.; Jackson, R.; Voss, P.

    2005-12-01

    One of the most lonely and desolate stretches of coastline on the planet has become the target for UNCLOS article 76 related research. The Danish Continental Shelf Project has launched a work program to investigate the possibilities for Greenland to claim an area outside the 200 nm limit in the Arctic Ocean. The role of the Lomonosov Ridge as a Natural Prolongation of Greenland/Canada is an important issue, and in order to better evaluate the connection between Greenland and the Lomonosov Ridge the nature of not only the ridge but also of Northern Greenland is the target of deep crustal investigations. The North Greenland Fold belt covers the ice-free part of North Greenland and continues west in the Canadian Arctic. The foldbelt was formed during the Ellesmerian orogeny, where sediments from the Franklinian Basin where compressed and deformed. The deep structure of basin and its subsequent closure are broadly unknown. Three broad band earthquake seismological stations where installed in North Greenland to supplement the existing stations at Alert (Canada) and Station Nord to the east, and the first data was available summer 2005. Crustal thickness data from these first results are presented. Plans for the spring 2006 consist of wide-angle acquisition on the sea ice from the Greenland-Canadian mainland out onto the Lomonosov Ridge, a joint Danish - Canadian project with a 400 km long profile over difficult ice conditions, 18 tons of explosives, three helicopters, a Twin Otter and about 30 participants.

  8. A Satellite-Derived Climate-Quality Data Record of the Clear-Sky Surface Temperature of the Greenland Ice Sheet

    Science.gov (United States)

    Hall, Dorothy K.; Comiso, Josefino C.; DiGirolamo, Nikolo E.; Shuman, Christopher A.; Key, Jeffrey R.; Koenig, Lora S.

    2012-01-01

    We have developed a climate-quality data record of the clear-sky surface temperature of the Greenland Ice Sheet using the Moderate-Resolution Imaging Spectroradiometer (MODIS) ice-surface temperature (1ST) algorithm. A climate-data record (CDR) is a time series of measurements of sufficient length, consistency, and continuity to determine climate variability and change. We present daily and monthly MODIS ISTs of the Greenland Ice Sheet beginning on 1 March 2000 and continuing through 31 December 2010 at 6.25-km spatial resolution on a polar stereographic grid. This record will be elevated in status to a CDR when at least nine more years of data become available either from MODIS Terra or Aqua, or from the Visible Infrared Imager Radiometer Suite (VIIRS) to be launched in October 2011. Our ultimate goal is to develop a CDR that starts in 1981 with the Advanced Very High Resolution (AVHRR) Polar Pathfinder (APP) dataset and continues with MODIS data from 2000 to the present, and into the VIIRS era. Differences in the APP and MODIS cloud masks have so far precluded the current 1ST records from spanning both the APP and MODIS time series in a seamless manner though this will be revisited when the APP dataset has been reprocessed. The complete MODIS 1ST daily and monthly data record is available online.

  9. Determining and Interpreting Detailed Ice Surface Elevation Changes of the Glaciers in Upernavik Isstrøm, Northwest Greenland, 1985-2016

    Science.gov (United States)

    Wendler, L.; Csatho, B. M.; Schenk, A. F.

    2017-12-01

    The several distinct glaciers of Upernavik Isstrøm in NW Greenland exhibit variable thinning, retreat, and velocity behaviors, despite being in close proximity, draining into the same fjord, and experiencing similar climatic conditions. This study reconstructed the 1985-2016 surface elevation change history for each Upernavik glacier. The data sets used included altimetry data collected by NASA's ATM, LVIS, and ICESat systems and digital elevation models (DEMs) derived from 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 fusing with the altimetry data. The spatiotemporal pattern of ice surface change was partitioned into changes related to surface processes and ice dynamics. The resulting ice thickness change time series were compared to 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 causing the variable behavior of the glaciers. Major findings include detection of rapid dynamic thinning of glacier 1 between 2005 and 2006, during a period of a stable calving front position. Continuing 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 reduction of lateral drag might have contributed to the thinning. While the study reinforces that bed topography is a major factor in controlling outlet glacier dynamic thinning, it also

  10. Empirical Retrieval of Surface Melt Magnitude from Coupled MODIS Optical and Thermal Measurements over the Greenland Ice Sheet during the 2001 Ablation Season.

    Science.gov (United States)

    Lampkin, Derrick; Peng, Rui

    2008-08-22

    Accelerated ice flow near the equilibrium line of west-central Greenland Ice Sheet (GIS) has been attributed to an increase in infiltrated surface melt water as a response to climate warming. The assessment of surface melting events must be more than the detection of melt onset or extent. Retrieval of surface melt magnitude is necessary to improve understanding of ice sheet flow and surface melt coupling. In this paper, we report on a new technique to quantify the magnitude of surface melt. Cloud-free dates of June 10, July 5, 7, 9, and 11, 2001 Moderate Resolution Imaging Spectroradiometer (MODIS) daily reflectance Band 5 (1.230-1.250μm) and surface temperature images rescaled to 1km over western Greenland were used in the retrieval algorithm. An optical-thermal feature space partitioned as a function of melt magnitude was derived using a one-dimensional thermal snowmelt model (SNTHERM89). SNTHERM89 was forced by hourly meteorological data from the Greenland Climate Network (GC-Net) at reference sites spanning dry snow, percolation, and wet snow zones in the Jakobshavn drainage basin in western GIS. Melt magnitude or effective melt (E-melt) was derived for satellite composite periods covering May, June, and July displaying low fractions (0-1%) at elevations greater than 2500m and fractions at or greater than 15% at elevations lower than 1000m assessed for only the upper 5 cm of the snow surface. Validation of E-melt involved comparison of intensity to dry and wet zones determined from QSCAT backscatter. Higher intensities (> 8%) were distributed in wet snow zones, while lower intensities were grouped in dry zones at a first order accuracy of ~ ±2%.

  11. The Greenland ice sheet during LGM – a model based on field observations

    DEFF Research Database (Denmark)

    Funder, Svend Visby; Kjeldsen, Kristian Kjellerup; Kjær, Kurt H.

    The issue is complicated by the circumstance that during LGM (Last glacial maximum) the ice sheet margins around the whole perimeter stood on the shelf and “classical” evidence, such as large moraine belts, extensive sandurs and major drainage diversions do not apply. The first estimates were therefore......, and not in between. Also, it was often assumed that if it could be demonstrated that the margin reached the shelf edge in one area, this should apply to the whole perimeter. Modelling, mainly on the basis of palaeoclimatic data, have presented a similar disparity between maximum and minimum estimates, assessing...... to the present was on the shelf beyond the coast, and only one third on land and in fjord basins. The evidence also indicates that the glacial regimes varied between regions....

  12. Ice shelf melt rates in Greenland and Antarctica using time-tagged digital imagery from World View and TanDEM-X

    Science.gov (United States)

    Charolais, A.; Rignot, E. J.; Milillo, P.; Scheuchl, B.; Mouginot, J.

    2017-12-01

    The floating extensions of glaciers, or ice shelves, melt vigorously in contact with ocean waters. Melt is non uniform, with the highest melt taking place in the deepest part of the cavity, where thermal forcing is the greatest because of 1) the pressure dependence of the freezing point of the seawater/ice mixture and 2) subglacial water injects fresh, buoyant, cold melt water to fuel stronger ice-ocean interactions. Melt also forms along preferential channels, which are not stationary, and create lines of weakness in the shelf. Ice shelf melt rates have been successfully measured from space over the entire Antarctic continent and on the ice shelves in Greenland using an Eulerian approach that combines ice thickness, ice velocity vectors, surface mass balance data, and measurements of ice thinning rates. The Eulerian approach is limited by the precision of the thickness gradients, typically of a few km, and requires significant spatial averaging to remove advection effects. A Lagrangian approach has been shown to be robust to advection effects and provides higher resolution details. We implemented a Lagrangian methodology for time-tagged World View DEMs by the Polar Geoscience Center (PGS) at the University of Minnesota and time-tagged TanDEM-X DEMs separated by one year. We derive melt rates on a 300-m grid with a precision of a few m/yr. Melt is strongest along grounding lines and along preferred channels. Channels are non-stationary because melt is not the same on opposite sides of the channels. Examining time series of data and comparing with the time-dependent grounding line positions inferred from satellite radar interferometry, we evaluate the magnitude of melt near the grounding line and even within the grounding zone. A non-zero melt rate in the grounding zone has vast implications for ice sheet modeling. This work is funded by a grant from NASA Cryosphere Program.

  13. Greenland plateau jets

    Directory of Open Access Journals (Sweden)

    George William Kent Moore

    2013-08-01

    Full Text Available The high ice-covered topography of Greenland represents a significant barrier to atmospheric flow and, as a direct and indirect result, it plays a crucial role in the coupled climate system. The wind field over Greenland is important in diagnosing regional weather and climate, thereby providing information on the mass balance of the ice sheet as well as assisting in the interpretation of ice core data. Here, we identify a number of hitherto unrecognised features of the three-dimensional wind field over Greenland; including a 2500-km-long jet along the central ice sheet's western margin that extends from the surface into the middle-troposphere, as well as a similar but smaller scale and less intense feature along its eastern margin. We refer to these features as Greenland Plateau Jets. The jets are coupled to the downslope katabatic flow and we argue that they are maintained by the zonal temperature gradients associated with the strong temperature inversion over the central ice sheet. Their importance for Greenland's regional climate is discussed.

  14. Ice sheet in peril

    DEFF Research Database (Denmark)

    Hvidberg, Christine Schøtt

    2016-01-01

    Earth's large ice sheets in Greenland and Antarctica are major contributors to sea level change. At present, the Greenland Ice Sheet (see the photo) is losing mass in response to climate warming in Greenland (1), but the present changes also include a long-term response to past climate transitions...

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  17. Estimating the Greenland ice sheet surface mass balance contribution to future sea level rise using the regional atmospheric climate model MAR

    Directory of Open Access Journals (Sweden)

    X. Fettweis

    2013-03-01

    Full Text Available To estimate the sea level rise (SLR originating from changes in surface mass balance (SMB of the Greenland ice sheet (GrIS, we present 21st century climate projections obtained with the regional climate model MAR (Modèle Atmosphérique Régional, forced by output of three CMIP5 (Coupled Model Intercomparison Project Phase 5 general circulation models (GCMs. Our results indicate that in a warmer climate, mass gain from increased winter snowfall over the GrIS does not compensate mass loss through increased meltwater run-off in summer. Despite the large spread in the projected near-surface warming, all the MAR projections show similar non-linear increase of GrIS surface melt volume because no change is projected in the general atmospheric circulation over Greenland. By coarsely estimating the GrIS SMB changes from GCM output, we show that the uncertainty from the GCM-based forcing represents about half of the projected SMB changes. In 2100, the CMIP5 ensemble mean projects a GrIS SMB decrease equivalent to a mean SLR of +4 ± 2 cm and +9 ± 4 cm for the RCP (Representative Concentration Pathways 4.5 and RCP 8.5 scenarios respectively. These estimates do not consider the positive melt–elevation feedback, although sensitivity experiments using perturbed ice sheet topographies consistent with the projected SMB changes demonstrate that this is a significant feedback, and highlight the importance of coupling regional climate models to an ice sheet model. Such a coupling will allow the assessment of future response of both surface processes and ice-dynamic changes to rising temperatures, as well as their mutual feedbacks.

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

    Science.gov (United States)

    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.

  19. Energy-efficient Building in Greenland: Investigation of the Energy Consumption and Indoor Climate

    DEFF Research Database (Denmark)

    Luc, Katarzyna Marta; Kotol, Martin; Lading, Tove

    2015-01-01

    Recently, a brand new single family home was built in Sisimiut, Greenland. The building was constructed as a wooden house typical for Greenland. However, some non-traditional measures were implemented in order to reduce the energy consumption and improve indoor air quality. Assessment of the infl...

  20. Evolution of ocean-induced ice melt beneath Zachariæ Isstrøm, Northeast Greenland combining observations and an ocean general circulation model from 1978 to present

    Science.gov (United States)

    Cai, C.; Rignot, E. J.; Menemenlis, D.; Millan, R.; Bjørk, A. A.; Khan, S. A.; Charolais, A.

    2017-12-01

    Zachariæ Isstrøm, a major ice stream in northeast Greenland, lost a large fraction of its ice shelf during the last decade. We study the evolution of subaqueous melting of its floating section from 1978 to present. The ice shelf melt rate depends on thermal forcing from warm, salty, subsurface ocean waters of Atlantic origin (AW), the mixing of AW with fresh, buoyant subglacial discharge at the calving margin, and the shape of the sub-ice-shelf cavity. Subglacial discharge doubled as a result of enhanced ice sheet runoff caused by warmer air temperatures. Ocean thermal forcing has increased due to enhanced advection of AW. Using an Eulerian method, MEaSUREs ice velocity, Operation IceBridge (OIB) ice thickness, and RACMO2.3 surface balance data, we evaluate the ice shelf melt rate in 1978, 1999 and 2010. The melt rate doubled from 1999 to 2010. Using a Lagrangian method with World View imagery, we map the melt rate in detail from 2011 to 2016. We compare the results with 2D simulations from the Massachusetts Institute of Technology general circulation model (MITgcm), at a high spatial resolution (20-m horizontal and 40-m vertical grid spacing), using OIB ice thickness and sub-ice-shelf cavity for years 1978, 1996, 2010 and 2011, combined with in-situ ocean temperature/salinity data from Ocean Melting Greenland (OMG) 2017. We find that winter melt rates are 2 3 times smaller than summer rates and melt rates increase by one order magnitude during the transition from ice shelf termination to near-vertical calving wall termination. As the last remaining bits of floating ice shelf disappear, ice-ocean interaction will therefore play an increasing role in driving the glacier retreat into its marine-based basin. This work was performed under a contract with NASA Cryosphere Program at UC Irvine and Caltech's Jet Propulsion Laboratory.

  1. First investigations of an ice core from Eisriesenwelt cave (Austria

    Directory of Open Access Journals (Sweden)

    B. May

    2011-02-01

    Full Text Available Investigations into the genesis and dynamical properties of cave ice are essential for assessing the climate significance of these underground glaciers. We drilled an ice core through a 7.1 m-thick ice body filling a large cavern of the dynamic ice cave Eisenriesenwelt (Austria. In addition to visual core inspections, quasi-continuous measurements at 2 cm resolution comprised particulate matter, stable water isotope (δ18O, δD and electrolytic conductivity profiles supplemented by specifically selected samples analyzed for tritium and radiocarbon. We found that recent ablation led to an almost complete loss of bomb-derived tritium removing any ice accumulated since, at least, the early fifties leaving the actual ice surface even below the natural tritium level. The small particulate organic masses rendered radiocarbon dating inconclusive, though a crude estimate gave a basal ice age in the order of several thousand years. The visual stratigraphy and all investigated parameters showed a clear dichotomy between the upper 2 m and the bottom 3 m of the core, which points to a substantial change in the ice formation process. Main features of the core comprise the changing appearance and composition of distinct cryocalcite layers, extremely low total ion content and a surprisingly high variability of the isotope signature. Co-isotope evaluation (δD versus δ18O of the core in comparison with data from precipitation and karst spring water clearly indicate that ice formation is governed by (slow freezing of dripping water.

  2. Marginal thinning in Northwest Greenland during 2002-2011

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Kjær, K. H.; Wahr, J. M.

    2012-01-01

    Many glaciers along the southeast and northwest coast of Greenland have accelerated, increasing the Greenland ice sheet's (GrIS) contribution to global sea-level rise. Here, we map elevation changes in northwest Greenland during 2003-2009 using high-resolution Ice, Cloud and land Elevation Satell...

  3. Enhanced melting of the Greenland ice sheet and its impact on the Subpolar North Atlantic and AMOC

    NARCIS (Netherlands)

    Bamber, J.L.; Behrens, E.; Boening, C.; van den Broeke, M.; Lenaerts, J.; Ettema, J.; Rignot, E.

    2012-01-01

    Freshwater (FW) fluxes from river runoff and precipitation minus evaporation for the pan Arctic seas are relatively well documented and prescribed in ocean GCMs. Fluxes from Greenland on the other hand are generally ignored altogether, despite their potential impacts on ocean circulation and marine

  4. Addendum to Site Assessment and Feasibility of a New Operations Base on the Greenland Ice Sheet: Addendum to Preliminary Report

    Science.gov (United States)

    2015-11-01

    advertising , publication, or promotional purposes. Ci- tation of trade names does not constitute an official endorsement or approval of the use of...and Development Center. McGrath, D., W. Colgan, N. Bayou, A. Muto, and K. Steffen. 2013. Recent warming at Summit, Greenland: Global context and

  5. Statistically optimal estimation of Greenland Ice Sheet mass variations from GRACE monthly solutions using an improved mascon approach

    NARCIS (Netherlands)

    Ran, J.; Ditmar, P.G.; Klees, R.; Farahani, H.

    2017-01-01

    We present an improved mascon approach to transform monthly spherical harmonic solutions based on GRACE satellite data into mass anomaly estimates in Greenland. The GRACE-based spherical harmonic coefficients are used to synthesize gravity anomalies at satellite altitude, which are then inverted

  6. On the importance of the albedo parameterization for the mass balance of the Greenland ice sheet in EC-Earth

    NARCIS (Netherlands)

    Helsen, Michiel M.; van de Wal, Roderik S. W.; Reerink, Thomas J.; Bintanja, Richard; Madsen, Marianne S.; Yang, Shuting; Li, Qiang; Zhang, Qiong

    2017-01-01

    The albedo of the surface of ice sheets changes as a function of time due to the effects of deposition of new snow, ageing of dry snow, bare ice exposure, melting and run-off. Currently, the calculation of the albedo of ice sheets is highly parameterized within the earth system model EC-Earth by

  7. On the importance of the albedo parameterization for the mass balance of the Greenland ice sheet in EC-Earth

    NARCIS (Netherlands)

    Helsen, Michiel M.; Van De Wal, Roderik S.W.; Reerink, Thomas J.; Bintanja, Richard; Madsen, Marianne S.; Yang, Shuting; Li, Qiang; Zhang, Qiong

    2017-01-01

    The albedo of the surface of ice sheets changes as a function of time due to the effects of deposition of new snow, ageing of dry snow, bare ice exposure, melting and run-off. Currently, the calculation of the albedo of ice sheets is highly parameterized within the earth system model ECEarth by

  8. Identification and synchronization of the common cosmic-ray signal in the IntCal13 14C calibration and the Greenland ice-core 10Be records

    Science.gov (United States)

    Muscheler, Raimund; Adolphi, Florian; Bronk Ramsey, Christopher; Rasmussen, Sune; Hughen, Konrad; Cooper, Alan; Turney, Chris

    2017-04-01

    The production rates of cosmogenic radionuclides (such as 10Be and 14C) are modulated by the solar and geomagnetic shielding of galactic cosmic rays. In addition, 14C and 10Be are influenced by the carbon cycle and the atmospheric transport and deposition, respectively. Isolating and identifying the common production signal allows us to synchronize ice core 10Be and tree ring 14C records during the Holocene (Adolphi and Muscheler, 2016), thereby connecting ice core climate records with 14C-dated records. Extending this comparison further back in time is challenging due to deteriorating quality of the 14C calibration record, IntCal13, (Reimer et al., 2013) and possible unidentified climate influences on the ice-core 10Be records. Nevertheless, by focusing on the most prominent production-rate features this comparison can be extended far back into the last glacial where, for example, the linkage of tree-ring based Kauri 14C data and the Greenland ice-core time scale (GICC05) suggested unresolved data and/or time scale differences around the period of the Laschamp geomagnetic field minimum at about 42000 yrs BP (Muscheler et al., 2014). Here we show that the data underlying the IntCal13 14C record and the ice-core 10Be records exhibit common variability that allows us to tentatively link the ice core GICC05 time scale to the radiocarbon time scale for almost the complete radiocarbon dating range. The observed time scale differences could be related to uncertainties in both the U/Th-based dating of the IntCal13 calibration data set and the GICC05 time scale, and we show that the two can be reconciled within the uncertainties of the ice-core layer counting. This direct comparison between IntCal13 and 10Be also suggests that the 14C differences shown in (Muscheler et al., 2014) around the Laschamp geomagnetic field minimum can be reduced by moderate adjustments to the GICC05 time scale. References: Adolphi, F., and Muscheler, R., 2016, Synchronizing the Greenland ice

  9. Experimental Investigation of Ice Phase Change Material Heat Exchangers

    Science.gov (United States)

    Leimkuehler, Thomas O.; Stephan, Ryan A.

    2012-01-01

    Phase change materials (PCM) may be useful for spacecraft thermal control systems that involve cyclical heat loads or cyclical thermal environments. Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. This can result in a decreased turndown ratio for the radiator and a reduced system mass. The use of water as a PCM rather than the more traditional paraffin wax has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. A number of ice PCM heat exchangers were fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion were investigated. This paper presents an overview of the results of this investigation from the past three years.

  10. The effect of signal leakage and glacial isostatic rebound on GRACE-derived ice mass changes in Iceland

    DEFF Research Database (Denmark)

    Sørensen, Louise Sandberg; Jarosch, Alexander H.; Adalgeirsdottir, Gudfinna

    2017-01-01

    Monthly gravity field models from the GRACE satellite mission are widely used to determine ice mass changes of large ice sheets as well as smaller glaciers and ice caps. Here, we investigate in detail the ice mass changes of the Icelandic ice caps as derived from GRACE data. The small size...... of the Icelandic ice caps, their location close to other rapidly changing ice covered areas and the low viscosity of the mantle below Iceland make this especially challenging. The mass balance of the ice caps is well constrained by field mass balance measurements, making this area ideal for such investigations. We...... the Little Ice Age (∼ 1890 AD). To minimize the signal that leaks towards Iceland from Greenland, we employ an independent mass change estimate of the Greenland Ice Sheet derived from satellite laser altimetry. We also estimate the effect of post Little Ice Age glacial isostatic adjustment, from knowledge...

  11. Seasonal monitoring of melt and accumulation within the deep percolation zone of the Greenland Ice Sheet and comparison with simulations of regional climate modeling

    Science.gov (United States)

    Heilig, Achim; Eisen, Olaf; MacFerrin, Michael; Tedesco, Marco; Fettweis, Xavier

    2018-06-01

    Increasing melt over the Greenland Ice Sheet (GrIS) 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

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

    Energy Technology Data Exchange (ETDEWEB)

    Mernild, Sebastian Haugard [Los Alamos National Laboratory; Liston, Glen [COLORADO STATE UNIV.; Hasholt, Bent [UNIV OF COPENGAGEN; Steffen, Konrad [UNIV OF COLORADO; Van Den Broeke, Michiel [UTRECHT UNIV; Mcgrath, Daniel [UNIV OF COLORADO; Yde, Jacob [UNIV OF AARHUS

    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 ice 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 simulation

  13. The Greenland Analogue Project, Yearly Report 2009

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2011-08-15

    To advance the understanding of processes associated with glaciation and their impact on the long-term performance of a deep geological repository, the Greenland Analogue Project (GAP), a four-year field and modelling study of the Greenland ice sheet and sub-surface conditions, has been initiated collaboratively by SKB, Posiva and NWMO. The study site encompasses a land terminus portion of the Greenland ice sheet east of Kangerlussuaq and is in many ways considered to be an appropriate analogue of the conditions that are expected to prevail in much of Canada and Fennoscandia during future glacial cycles. The project is planned to run from 2009 until 2012. The GAP will conduct the first in situ investigations of some of the parameters and processes needed to achieve a realistic understanding of how an ice sheet may impact a deep repository, and will provide measurements, observations and data that may significantly improve our safety assessments and risk analyses of glaciation scenarios. The project includes three sub-projects (A-C) with specific individual objectives, which collectively aim at contributing knowledge and input to the overall project aim. Three field campaigns were carried out in SPA during 2009. These campaigns focused on: (1) deployment and maintenance of AWS and GPS stations and to test the deep-look radar equipment; (2) investigating the hydrological processes and feedbacks and testing of passive seismic equipment; (3) downloading of weather station data and GPS data and winterizing the equipment. An extensive archive of real-time satellite remote sensing datasets has been obtained to be able to better constraint the surface elevation and dynamics of basal hydrological mechanisms. From this archive it has been possible to obtain Russell Glacier Cachment (RGC)-wide constraints on annual, seasonal and specific temporal snapshots of surface speed, initial lake and moulin distribution, drainage and network connections along with the temporal

  14. The Greenland Analogue Project, Yearly Report 2009

    International Nuclear Information System (INIS)

    2011-08-01

    To advance the understanding of processes associated with glaciation and their impact on the long-term performance of a deep geological repository, the Greenland Analogue Project (GAP), a four-year field and modelling study of the Greenland ice sheet and sub-surface conditions, has been initiated collaboratively by SKB, Posiva and NWMO. The study site encompasses a land terminus portion of the Greenland ice sheet east of Kangerlussuaq and is in many ways considered to be an appropriate analogue of the conditions that are expected to prevail in much of Canada and Fennoscandia during future glacial cycles. The project is planned to run from 2009 until 2012. The GAP will conduct the first in situ investigations of some of the parameters and processes needed to achieve a realistic understanding of how an ice sheet may impact a deep repository, and will provide measurements, observations and data that may significantly improve our safety assessments and risk analyses of glaciation scenarios. The project includes three sub-projects (A-C) with specific individual objectives, which collectively aim at contributing knowledge and input to the overall project aim. Three field campaigns were carried out in SPA during 2009. These campaigns focused on: (1) deployment and maintenance of AWS and GPS stations and to test the deep-look radar equipment; (2) investigating the hydrological processes and feedbacks and testing of passive seismic equipment; (3) downloading of weather station data and GPS data and winterizing the equipment. An extensive archive of real-time satellite remote sensing datasets has been obtained to be able to better constraint the surface elevation and dynamics of basal hydrological mechanisms. From this archive it has been possible to obtain Russell Glacier Cachment (RGC)-wide constraints on annual, seasonal and specific temporal snapshots of surface speed, initial lake and moulin distribution, drainage and network connections along with the temporal

  15. Numerical Investigation of Ice Slurry Flow in a Horizontal Pipe

    Science.gov (United States)

    Rawat, K. S.; Pratihar, A. K.

    2018-02-01

    In the last decade, phase changing material slurry (PCMS) gained much attention as a cooling medium due to its high energy storage capacity and transportability. However the flow of PCM slurry is a complex phenomenon as it affected by various parameters, i.e. fluid properties, velocity, particle size and concentration etc.. In the present work ice is used as a PCM and numerical investigation of heterogeneous slurry flow has been carried out using Eulerian KTGF model in a horizontal pipe. Firstly the present model is validated with existing experiment results available in the literature, and then model is applied to the present problem. Results show that, flow is almost homogeneous for ethanol based ice slurry with particle diameter of 0.1 mm at the velocity of 1 m/s. It is also found that ice particle distribution is more uniform at higher velocity, concentration of ice and ethanol in slurry. Results also show that ice concentration increases on the top of the pipe, and the effect of particle wall collision is more significant at higher particle diameter.

  16. Structural integrity investigations of feeder pipe ice plugging procedures

    International Nuclear Information System (INIS)

    Flaman, M.T.; Shah, N.N.

    1985-03-01

    A procedure involving the use of a liquid nitrogen cooled heat exchanger to form internal ice plugs in feeder pipes is routinely used in nuclear generating stations. The use of this procedure has caused concerns with regard to the safety of station maintenance personnel, and in regard to the integrity of the feeder pipes. This report describes the results of laboratory stress and pressure measurements which were performed on a feeder pipe section during ice plugging operations to investigate these concerns. From the results of this study, and from the results of previous studies of material behaviour at low temperatures, it has been determined that the ice plugging procedure can be performed on feeder pipes in a safe and effective manner

  17. Glaciation and geosphere evolution - Greenland Analogue Project

    International Nuclear Information System (INIS)

    Hirschorn, S.; Vorauer, A.; Belfadhel, M.B.; Jensen, M.

    2011-01-01

    The deep geological repository concept for the long-term management of used nuclear fuel involves the containment and isolation of used nuclear fuel in a suitable geological formation. A key objective of the Canadian Nuclear Waste Management Organization (NWMO) geoscience technical research program is to advance the understanding of geosphere stability and its resilience to perturbations over time frames of relevance to a deep geological repository. Glaciation has been identified as the most probable and intense perturbation relevant to a deep geological repository associated with long-term climate change in northern latitudes. Given that the North American continent has been re-glaciated nine times over the past million years, it is strongly expected that a deep geological repository within a suitable crystalline or sedimentary rock formation in Canada will be subject to glaciation events associated with long-term climate change. As such, NWMO's geoscience research program has placed particular emphasis on investigations of the response of the geosphere to glaciations. As surface conditions change from present day conditions to periglacial, followed by ice-sheet cover of variable thickness and rapid glacial retreat, transient geochemical, hydraulic, mechanical and temperature conditions will be simultaneously imposed on groundwater systems. NWMO research activities related to glaciation events and their impacts on groundwater system evolution are being undertaken using a multi-disciplinary approach aimed at collecting multiple lines of evidence. These investigations include assessment of the: Impact of an ice sheet on groundwater composition at repository depth using the Greenland Ice Sheet as an analogue to future glaciations in North America; Expected physical and temporal surface boundary conditions related to potential future glaciation events by estimating the magnitude and time rate of change of ice sheet thickness, ground surface temperature and

  18. The use of vertical and horizontal surface displacements at EPOS GNSS stations in Greenland to study ice sheet mass balance

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas

    2014-01-01

    The European Plate Observing System (EPOS) includes e.g. seismic and geodetic permanent national monitoring networks on a European scale. The main purpose is to create data platforms for monitoring and study geophysics processes like earthquakes, volcanoes, surface dynamics and tectonics. Here we...... present data from arctic GNSS stations included in the EPOS network. The arctic EPOS GNSS network consists of 16 continuous GPS stations spread across Greenland. This network is able to map the velocity fields associated with, plate motion, postglacial rebound and improve our understanding of tectonic...

  19. Geophysical investigations of the East Greenland Caledonides using receiver functions, gravity and topography data

    DEFF Research Database (Denmark)

    Schiffer, Christian; Balling, N.; Jacobsen, B. H.

    The present-day topography and crustal structure of the East Greenland Caledonides are a product of various events, including the Caledonian orogeny, lithospheric extensional collapse, continental breakup and erosional processes. The topographic elevation appears high in this region, still after ...

  20. Envisioning Greenland

    DEFF Research Database (Denmark)

    Ren, Carina Bregnholm

    2012-01-01

    Currently, the traditional ‘cool’ representation of Greenland as a frozen landscape devoid of people and human structures is being challenged by an emerging vision of Greenland as ‘hot’. This article presents and describes these two versions of Greenland, showing how demarcations of what is ‘nature...

  1. Investigation of land ice-ocean interaction with a fully coupled ice-ocean model: 1. Model description and behavior

    Science.gov (United States)

    Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.; Hallberg, R.; Oppenheimer, M.

    2012-06-01

    Antarctic ice shelves interact closely with the ocean cavities beneath them, with ice shelf geometry influencing ocean cavity circulation, and heat from the ocean driving changes in the ice shelves, as well as the grounded ice streams that feed them. We present a new coupled model of an ice stream-ice shelf-ocean system that is used to study this interaction. The model is capable of representing a moving grounding line and dynamically responding ocean circulation within the ice shelf cavity. Idealized experiments designed to investigate the response of the coupled system to instantaneous increases in ocean temperature show ice-ocean system responses on multiple timescales. Melt rates and ice shelf basal slopes near the grounding line adjust in 1-2 years, and downstream advection of the resulting ice shelf thinning takes place on decadal timescales. Retreat of the grounding line and adjustment of grounded ice takes place on a much longer timescale, and the system takes several centuries to reach a new steady state. During this slow retreat, and in the absence of either an upward-or downward-sloping bed or long-term trends in ocean heat content, the ice shelf and melt rates maintain a characteristic pattern relative to the grounding line.

  2. A relationship between ion balance and the chemical compounds of salt inclusions found in the Greenland Ice Core Project and Dome Fuji ice cores

    DEFF Research Database (Denmark)

    Johnsen, Sigfus Johann; Dahl-Jensen, Dorthe; Steffensen, Jørgen Peder

    2008-01-01

    We have proposed a method of deducing the chemical compounds found in deep polar ice cores by analyzing the balance between six major ions (Cl-, NO3 -, SO4 2-, Na+, Mg2+, and Ca2+). The method is demonstrated for the Holocene and last glacial maximum regions of the Dome Fuji and GRIP ice cores...... on individual salt inclusions. The abundances in the ice cores are shown to reflect differences in climatic periods (the acidic environment of the Holocene versus the reductive environment of the last glacial maximum) and regional conditions (the marine environment of Antarctica versus the continental...

  3. Ice Sheets & Ice Cores

    DEFF Research Database (Denmark)

    Mikkelsen, Troels Bøgeholm

    Since the discovery of the Ice Ages it has been evident that Earth’s climate is liable to undergo dramatic changes. The previous climatic period known as the Last Glacial saw large oscillations in the extent of ice sheets covering the Northern hemisphere. Understanding these oscillations known....... The first part concerns time series analysis of ice core data obtained from the Greenland Ice Sheet. We analyze parts of the time series where DO-events occur using the so-called transfer operator and compare the results with time series from a simple model capable of switching by either undergoing...

  4. Impact of improved Greenland ice sheet surface representation in the NASA GISS ModelE2 GCM on simulated surface mass balance and regional climate

    Science.gov (United States)

    Alexander, P. M.; LeGrande, A. N.; Fischer, E.; Tedesco, M.; Kelley, M.; Schmidt, G. A.; Fettweis, X.

    2017-12-01

    Towards achieving coupled simulations between the NASA Goddard Institute for Space Studies (GISS) ModelE2 general circulation model (GCM) and ice sheet models (ISMs), improvements have been made to the representation of the ice sheet surface in ModelE2. These include a sub-grid-scale elevation class scheme, a multi-layer snow model, a time-variable surface albedo scheme, and adjustments to parameterization of sublimation/evaporation. These changes improve the spatial resolution and physical representation of the ice sheet surface such that the surface is represented at a level of detail closer to that of Regional Climate Models (RCMs). We assess the impact of these changes on simulated Greenland Ice Sheet (GrIS) surface mass balance (SMB). We also compare ModelE2 simulations in which winds have been nudged to match the European Center for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis with simulations from the Modèle Atmosphérique Régionale (MAR) RCM forced by the same reanalysis. Adding surface elevation classes results in a much higher spatial resolution representation of the surface necessary for coupling with ISMs, but has a negligible impact on overall SMB. Implementing a variable surface albedo scheme increases melt by 100%, bringing it closer to melt simulated by MAR. Adjustments made to the representation of topography-influenced surface roughness length in ModelE2 reduce a positive bias in evaporation relative to MAR. We also examine the impact of changes to the GrIS surface on regional atmospheric and oceanic climate in coupled ocean-atmosphere simulations with ModelE2, finding a general warming of the Arctic due to a warmer GrIS, and a cooler North Atlantic in scenarios with doubled atmospheric CO2 relative to pre-industrial levels. The substantial influence of changes to the GrIS surface on the oceans and atmosphere highlight the importance of including these processes in the GCM, in view of potential feedbacks between the ice sheet

  5. Validation and inter-comparison of surface elevation changes derived from altimetry over the Jakobshavn Isbræ drainage basin, Greenland – Round Robin results from ESA's Ice_Sheets_CCI (ID #EGU2013-6007)

    DEFF Research Database (Denmark)

    Fredenslund Levinsen, Joanna; Khvorostovsky, Kirill; Ticconi, Francesca

    elevation changes (SEC), surface velocities, calving front locations, and grounding line locations. This work focuses on SEC, and the goal is to develop the best routine for estimating this by means of radar altimetry. In order to find the most optimal approach we have completed a Round Robin experiment (RR......In order to ensure long-term climate records, ESA has launched the Climate Change Initiative (ESA CCI), which puts focus on 13 different Essential Climate Variables, one of them being Ice Sheets. In this program, four selected key parameters will be determined for the Greenland Ice Sheet: Surface...

  6. Tidal Modulation of Ice Flow on Kangerdlugssuaq and Helheim Glaciers, East Greenland, from High-Rate GPS Measurements

    DEFF Research Database (Denmark)

    Hamilton, G. S.; Stearns, L. A.; Elosegui, P.

    knowledge of ice thickness and fjord bathymetry. Here, we use high-rate GPS measurements collected at sites within a few km of the calving fronts of Kangerdlugssuaq and Helheim glaciers to examine the effect of ocean tide on ice flow. Data were collected at 5-15 s sampling rate during several campaign...... appears to have a short floating tongue, based on an analysis of GPS data collected in June-August 2006 at several stations located at increasing distances from the calving front. Glacier uplift was in phase with measured and modeled tidal height, but attenuated rapidly beyond ~~1 km from the terminus. We...

  7. Seismic Monitoring and Characterization of the 2012 Outburst Flood of the Ice-Dammed Lake A.P.Olsen (NE Greenland)

    Science.gov (United States)

    Behm, M.; Walter, J. I.; Binder, D.; Mertl, S.

    2017-12-01

    Since the Zackenberg Research Station (ZRS) in NE-Greenland was established in 1995, regular floods of the adjacent Zackenberg River have been observed. The floods result from the sudden discharge of a marginal, ice-dammed lake at the pre-dominantly cold-based A.P. Olsen Ice Cap about 35 km inland. The lake filling usually starts with the melting season in May/June and ends with the flood sometime after early July. The run-off water from the lake discharges through the subsurface of the adjacent Argo glacier. The actual migration paths and depth of the water within the glacier are unknown until it re-appears at the glacier terminus at a distance of 4 km to the ice-dam. In spring 2012 a surface seismic monitoring network was installed on Argo glacier in 2-3 m boreholes near the lake to acquire continuous data for the whole fill- and drain cycle from start of May to end of November. The network comprises 3 stations with three-component sensors and 2 stations designed as tripartite arrays with vertically oriented sensors. The maximum interstation distance is 1.2 km. Microseismic event detection and localization is facilitated by the homogenous seismic structure of the ice and the extremely high S/N ratio of the borehole installations. An initial detection based on an STA/LTA algorithm and event assocator results in order-of-magnitude 100,000 seismic events. These events are generally attributed to the opening of surface crevasses due to the presence of weak body waves and strong surface wave energy, interpreted to be Rayleigh waves with dominant frequencies around 1-4 Hz. Time-lapse cross-correlations of the ambient seismic noise field reconstruct the surface waves travelling between the stations. Weekly stacks of the cross-correlations are stable, and show a distinct change correlated with the outburst flood. Apparent surface wave velocities increase slightly several weeks prior to the outburst event, which itself is characterized by a decrease in the correlation

  8. Ice-margin and meltwater dynamics during the mid-Holocene in the Kangerlussuaq area of west Greenland

    DEFF Research Database (Denmark)

    Carrivick, Jonathan L.; Yde, Jacob; Russell, Andrew J.

    2017-01-01

    likely relate to mid-Holocene subglacial hydrology. In comparison to the geomorphological record at other Northern Hemisphere ice-sheet margins the depositional landforms in this study area are few in number and variety and small in scale, most likely due to a restricted sediment supply. They include...

  9. Simultaneous determination of picogram per gram concentrations of Ba, Pb and Pb isotopes in Greenland ice by thermal ionisation mass spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Jimi, Salah I.; Rosman, Kevin J.R.; Candelone, Jean-Pierre; Burn, Laurie J. [Curtin University of Technology, Department of Imaging and Applied Physics, Perth (Australia); Hong, Sungmin [Polar Research Centre, Korean Ocean Research and Development Institute, Ansan, P.O. Box 29, Seoul (Korea); Boutron, Claude F. [Domaine Universitaire, Laboratoire de Glaciologie et Geophysique du l' Environnement, 54 rue Moliere, Saint Martin d' Heres (France); UFR de Mecanique, Universite Joseph Fourier de Grenoble (Institut Universitaire de France), Domaine Universitaire, Grenoble (France)

    2008-01-15

    A technique has been developed to simultaneously measure picogram per gram concentrations of Ba and Pb by isotope dilution mass spectrometry, as well as Pb isotopic ratios in polar ice by thermal ionisation mass spectrometry. BaPO{sup +}{sub 2} and Pb{sup +} ions were employed for these determinations. A calibrated mixture of enriched {sup 205}Pb and {sup 137}Ba was added to the samples providing an accuracy of better than approximately 2% for Pb/Ba element ratio determinations. Interference by molecular ions in the Pb mass spectrum occurred only at {sup 204}Pb and {sup 205}Pb, but these contributions were negligible in terms of precisions expected on picogram-sized Pb samples. The technique is illustrated with measurements on Greenland firn, using a drill-core section that includes the Laki volcanic eruption of 1783-1784. The data show deviations from the element concentrations indicating volatile metal enrichments, but the Pb isotopic signature of the Laki lava could not be identified. (orig.)

  10. Measuring stable isotopes of hydrogen and oxygen in ice by means of laser spectrometry : The Bolling transition in the Dye-3 (south Greenland) ice core

    NARCIS (Netherlands)

    Trigt, R. van; Meijer, H.A.J.; Sveinbjornsdottir, A.E.; Johnsen, S.J.; Kerstel, E.R.Th.

    2002-01-01

    We report on the first application of a new technique in ice-core research, based on direct absorption infrared laser spectrometry (LS), for measuring H-2 O-17 and O-18 isotope ratios. The data are used to calculate the deuterium excess d (defined as delta(2)H - 8delta(18)O) for a section of the

  11. Quantifying black carbon deposition over the Greenland ice sheet from forest fires in Canada: BC DEPOSITION FROM FOREST FIRES

    Energy Technology Data Exchange (ETDEWEB)

    Thomas, J. L. [LATMOS/IPSL, UPMC University Paris 6 Sorbonne Universités, UVSQ, CNRS, Paris France; Polashenski, C. M. [USACE-CRREL, Fort Wainwright Alaska USA; Thayer School of Engineering, Dartmouth College, Hanover New Hampshire USA; Soja, A. J. [National Institute of Aerospace, NASA Langley Research Center, Hampton Virginia USA; Marelle, L. [Center for International Climate and Environmental Research-Oslo (CICERO), Oslo Norway; Casey, K. A. [Thayer School of Engineering, Dartmouth College, Hanover New Hampshire USA; Cryospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt Maryland USA; Choi, H. D. [National Institute of Aerospace, NASA Langley Research Center, Hampton Virginia USA; Raut, J. -C. [LATMOS/IPSL, UPMC University Paris 6 Sorbonne Universités, UVSQ, CNRS, Paris France; Wiedinmyer, C. [National Center for Atmospheric Research, Boulder Colorado USA; Emmons, L. K. [National Center for Atmospheric Research, Boulder Colorado USA; Fast, J. D. [Pacific Northwest National Laboratory, Richland Washington USA; Pelon, J. [LATMOS/IPSL, UPMC University Paris 6 Sorbonne Universités, UVSQ, CNRS, Paris France; Law, K. S. [LATMOS/IPSL, UPMC University Paris 6 Sorbonne Universités, UVSQ, CNRS, Paris France; Flanner, M. G. [Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor Michigan USA; Dibb, J. E. [Earth Systems Research Center, EOS, University of New Hampshire, Durham New Hampshire USA

    2017-08-05

    We identify an important Black Carbon (BC) aerosol deposition event that was observed in snow stratigraphy and dated to between 27 July 2013 – 2 August 2013. This event comprises a significant portion (~60%) of total deposition over a 10 month period (July 2013 – April 2014). Here we link this event to forest fires burning in Canada during summer 2013 using modeling and remote sensing tools. Aerosols were detected by both the CALIOP and MODIS instruments during transport between Canada and Greenland, confirming that this event involved emissions from forest fires in Canada. We use high-resolution regional chemical transport mod-eling (WRF-Chem) combined with high-resolution fire emissions (FINNv1.5) to study aerosol emissions, transport, and deposition during this event. The model accurately captures the timing of the BC deposition event and shows that the major contribution to deposition during this event is emissions originating from fires in Canada. However, the model under-predicts aerosol deposition compared to measurements at all sites by a factor of 2–100. Under-prediction of modeled BC deposition originates from uncertainties in fire emissions combined with uncertainties in aerosol scavenging by clouds. This study suggests that it is possible to describe the transport of an exceptional smoke event on regional and continental scales. Improvements in model descriptions of precipitation scavenging and emissions from wildfires are needed to correctly predict deposition, which is critical for determining the climate impacts of aerosols that originate from fires.

  12. Magnetotelluric investigation in West Greenland - considering the polar electrojet, ocean and fjords

    DEFF Research Database (Denmark)

    Lauritsen, Nynne Louise Berthou

    results, however the multiple station technique improves the data quality around 1 s compared to the single station technique. Different challenges are connected with the survey location, where ocean and fjord systems have a large impact on the transferfunctions. A 3D model study of the impact of fjords...... on induction arrows is presented, illustrating the importance of including these in magnetotelluric modelling. This informationis included in the 3D modelling of the magnetotelluric survey in Greenland, together with the bathymetry of the ocean. The modelling shows that the impact from the fjords and ocean...

  13. Holocene environmental changes and climate development in Greenland

    International Nuclear Information System (INIS)

    Engels, Stefan; Helmens, Karin

    2010-12-01

    readability of this chapter, we decided to divide Greenland in 4 geographical regions, which is also done in Chapter 3. Chapter 3 forms the major part of this report, and provides summaries of reconstructions of temperature, precipitation, vegetation and other climatic and environmental parameters. These climate reconstructions are most often based on different climate-indicators, both biological (i.e. organisms, e.g. diatoms) and geochemical (e.g. oxygen isotopes or Pb-pollution). Unfortunately, major parts of Greenland have not been investigated in detail with respect to Holocene environmental development, inevitably leading to gaps in our overview. Also, a lot of information was available from e.g. the Greenland ice-core records, but we only summarize the most relevant papers in this report. Chapter 4 continues with an introduction to the so-called 'transfer function approach', where the development of training sets and mathematical techniques are discussed, followed by an overview of the work that has been done in Greenland. Chapter 5 summarizes the period right after deglaciation as reconstructed from many lake-records, and discusses delayed responses of parts of the vegetation

  14. Holocene environmental changes and climate development in Greenland

    Energy Technology Data Exchange (ETDEWEB)

    Engels, Stefan; Helmens, Karin (Dept. of Physical Geography and Quaternary Geology, Stockholm Univ., Stockholm (Sweden))

    2010-12-15

    readability of this chapter, we decided to divide Greenland in 4 geographical regions, which is also done in Chapter 3. Chapter 3 forms the major part of this report, and provides summaries of reconstructions of temperature, precipitation, vegetation and other climatic and environmental parameters. These climate reconstructions are most often based on different climate-indicators, both biological (i.e. organisms, e.g. diatoms) and geochemical (e.g. oxygen isotopes or Pb-pollution). Unfortunately, major parts of Greenland have not been investigated in detail with respect to Holocene environmental development, inevitably leading to gaps in our overview. Also, a lot of information was available from e.g. the Greenland ice-core records, but we only summarize the most relevant papers in this report. Chapter 4 continues with an introduction to the so-called 'transfer function approach', where the development of training sets and mathematical techniques are discussed, followed by an overview of the work that has been done in Greenland. Chapter 5 summarizes the period right after deglaciation as reconstructed from many lake-records, and discusses delayed responses of parts of the vegetation

  15. Seismic explosion sources on an ice cap

    DEFF Research Database (Denmark)

    Shulgin, Alexey; Thybo, Hans

    2015-01-01

    crustal model can be modelled. A crucial challenge for applying the technique is to control the sources. Here, we present data that describe the efficiency of explosive sources in the ice cover. Analysis of the data shows, that the ice cap traps a significant amount of energy, which is observed......Controlled source seismic investigation of crustal structure below ice covers is an emerging technique. We have recently conducted an explosive refraction/wide-angle reflection seismic experiment on the ice cap in east-central Greenland. The data-quality is high for all shot points and a full...

  16. A Detailed Geophysical Investigation of the Grounding of Henry Ice Rise, with Implications for Holocene Ice-Sheet Extent.

    Science.gov (United States)

    Wearing, M.; Kingslake, J.

    2017-12-01

    It is generally assumed that since the Last Glacial Maximum the West Antarctic Ice Sheet (WAIS) has experienced monotonic retreat of the grounding line (GL). However, recent studies have cast doubt on this assumption, suggesting that the retreat of the WAIS grounding line may have been followed by a significant advance during the Holocene in the Weddell and Ross Sea sectors. Constraining this evolution is important as reconstructions of past ice-sheet extent are used to spin-up predictive ice-sheet models and correct mass-balance observations for glacial isostatic adjustment. Here we examine in detail the formation of the Henry Ice Rise (HIR), which ice-sheet model simulations suggest played a key role in Holocene ice-mass changes in the Weddell Sea sector. Observations from a high-resolution ground-based, ice-penetrating radar survey are best explained if the ice rise formed when the Ronne Ice Shelf grounded on a submarine high, underwent a period of ice-rumple flow, before the GL migrated outwards to form the present-day ice rise. We constrain the relative chronology of this evolution by comparing the alignment and intersection of isochronal internal layers, relic crevasses, surface features and investigating the dynamic processes leading to their complex structure. We also draw analogies between HIR and the neighbouring Doake Ice Rumples. The date of formation is estimated using vertical velocities derived with a phase-sensitive radio-echo sounder (pRES). Ice-sheet models suggest that the formation of the HIR and other ice rises may have halted and reversed large-scale GL retreat. Hence the small-scale dynamics of these crucial regions could have wide-reaching consequences for future ice-sheet mass changes and constraining their formation and evolution further would be beneficial. One stringent test of our geophysics-based conclusions would be to drill to the bed of HIR to sample the ice for isotopic analysis and the bed for radiocarbon analysis.

  17. Seasonal migration, vertical activity and winter temperature experience of Greenland halibut Reinhardtius hippoglossoides (Walbaum) in West Greenland waters

    DEFF Research Database (Denmark)

    Boje, Jesper; Neuenfeldt, Stefan; Sparrevohn, Claus Reedtz

    2014-01-01

    resident in Disko Bay (mean range 2.6°C) than when resident in the ice fjord (mean range 1.4°C). Using the tagged halibut as a 'live tool,' we show that parts of the ice fjord are hundreds of meters deeper than previously thought. We also document the first seawater temperature measurements made beneath......The deep-water flatfish Greenland halibut Reinhardtius hippoglossoides (Walbaum) is common along the West Greenland coast. In the northwestern fjords, Greenland halibut is an important socio-economic resource for the Greenland community, but due to the deep and partly ice-covered environment, very...

  18. Investigating Arctic Sea Ice Survivability in the Beaufort Sea

    Directory of Open Access Journals (Sweden)

    Matthew Tooth

    2018-02-01

    Full Text Available Arctic sea ice extent has continued to decline in recent years, and the fractional coverage of multi-year sea ice has decreased significantly during this period. The Beaufort Sea region has been the site of much of the loss of multi-year sea ice, and it continues to play a large role in the extinction of ice during the melt season. We present an analysis of the influence of satellite-derived ice surface temperature, ice thickness, albedo, and downwelling longwave/shortwave radiation as well as latitude and airborne snow depth estimates on the change in sea ice concentration in the Beaufort Sea from 2009 to 2016 using a Lagrangian tracking database. Results from this analysis indicate that parcels that melt during summer in the Beaufort Sea reside at lower latitudes and have lower ice thickness at the beginning of the melt season in most cases. The influence of sea ice thickness and snow depth observed by IceBridge offers less conclusive results, with some years exhibiting higher thicknesses/depths for melted parcels. Parcels that melted along IceBridge tracks do exhibit lower latitudes and ice thicknesses, however, which indicates that earlier melt and breakup of ice may contribute to a greater likelihood of extinction of parcels in the summer.

  19. The glacial inception as recorded in the NorthGRIP Greenland ice core: timing, structure and associated abrupt temperature changes

    Energy Technology Data Exchange (ETDEWEB)

    Landais, Amaelle [UMR CEA-CNRS, CEA Saclay, IPSL/Laboratoire des Sciences du Climat et de l' Environnement, Gif-sur -Yvette (France); Hebrew University, Institute of Earth Sciences, Givat Ram, Jerusalem (Israel); Masson-Delmotte, Valerie; Jouzel, Jean; Minster, Benedicte [UMR CEA-CNRS, CEA Saclay, IPSL/Laboratoire des Sciences du Climat et de l' Environnement, Gif-sur -Yvette (France); Raynaud, Dominique [LGGE, UMR CNRS-UJF, St Martin d' Heres (France); Johnsen, Sigfus [University of Copenhagen, Department of Geophysics, Copenhagen (Denmark); Huber, Christof; Leuenberger, Markus; Schwander, Jakob [University of Bern, Physics Institute, Bern (Switzerland)

    2006-02-01

    The mechanisms involved in the glacial inception are still poorly constrained due to a lack of high resolution and cross-dated climate records at various locations. Using air isotopic measurements in the recently drilled NorthGRIP ice core, we show that no evidence exists for stratigraphic disturbance of the climate record of the last glacial inception ({proportional_to}123-100 kyears BP) encompassing Dansgaard-Oeschger events (DO) 25, 24 and 23, even if we lack sufficient resolution to completely rule out disturbance over DO 25. We quantify the rapid surface temperature variability over DO 23 and 24 with associated warmings of 10{+-}2.5 and 16{+-}2.5 C, amplitudes which mimic those observed in full glacial conditions. We use records of {delta}{sup 18}O of O{sub 2} to propose a common timescale for the NorthGRIP and the Antarctic Vostok ice cores, with a maximum uncertainty of 2,500 years, and to examine the interhemispheric sequence of events over this period. After a synchronous North-South temperature decrease, the onset of rapid events is triggered in the North through DO 25. As for later events, DO 24 and 23 have a clear Antarctic counterpart which does not seem to be the case for the very first abrupt warming (DO 25). This information, when added to intermediate levels of CO{sub 2} and to the absence of clear ice rafting associated with DO 25, highlights the uniqueness of this first event, while DO 24 and 23 appear similar to typical full glacial DO events. (orig.)

  20. Dynamics of the Greenland Ice Sheet and Icelandic Glaciers in the 20th Century Using Geodetic Methods

    DEFF Research Database (Denmark)

    Korsgaard, Niels Jákup

    by bedrock geometry. It is revealed that dynamic ice loss recently seen in the southeast and northwest GrIS also occurred in the northwest between 1985 and 1993, highlighting the difficulty of capturing these events in mass balance models. Extending the record back to the LIA, the results show...... that for the past 110 years, the surface mass balance has been decreasing, while the dynamic term has been constant. The spatial pattern of thinning in the 20th century is identical to that of current change, suggesting this pattern will continue in the near future. The mass change of the GrIS in 20th century...

  1. Short-term impacts of enhanced Greenland freshwater fluxes in an eddy-permitting ocean model

    Directory of Open Access Journals (Sweden)

    R. Marsh

    2010-07-01

    Full Text Available In a sensitivity experiment, an eddy-permitting ocean general circulation model is forced with realistic freshwater fluxes from the Greenland Ice Sheet, averaged for the period 1991–2000. The fluxes are obtained with a mass balance model for the ice sheet, forced with the ERA-40 reanalysis dataset. The freshwater flux is distributed around Greenland as an additional term in prescribed runoff, representing seasonal melting of the ice sheet and a fixed year-round iceberg calving flux, for 8.5 model years. By adding Greenland freshwater fluxes with realistic geographical distribution and seasonality, the experiment is designed to investigate the oceanic response to a sudden and spatially/temporally uniform amplification of ice sheet melting and discharge, rather than localized or gradual changes in freshwater flux. The impacts on regional hydrography and circulation are investigated by comparing the sensitivity experiment to a control experiment, without additional fluxes. By the end of the sensitivity experiment, the majority of additional fresh water has accumulated in Baffin Bay, and only a small fraction has reached the interior of the Labrador Sea, where winter mixed layer depth is sensitive to small changes in salinity. As a consequence, the impact on large-scale circulation is very slight. An indirect impact of strong freshening off the west coast of Greenland is a small anti-cyclonic component to the circulation around Greenland, which opposes the wind-driven cyclonic circulation and reduces net southward flow through the Canadian Archipelago by ~10%. Implications for the post-2000 acceleration of Greenland mass loss are discussed.

  2. The Greenland analogue project. Yearly report 2010

    Energy Technology Data Exchange (ETDEWEB)

    Harper, J; Brinkerhoff, D; Johnson, J [University of Montana, Missoula (United States); Ruskeeniemi, T; Engstroem, J; Kukkonen, I [Geological Survey of Finland (Finland); and others

    2012-04-15

    A four-year field and modelling study of the Greenland ice sheet and subsurface conditions, Greenland Analogue Project (GAP), has been initiated collaboratively by SKB, Posiva and NWMO to advance the understanding of processes associated with glaciation and their impact on the long-term performance of a deep geological repository. The study site encompasses a land terminus portion of the Greenland ice sheet, east of Kangerlussuaq, and is in many ways considered to be an appropriate analogue of the conditions that are expected to prevail in much of Canada and Fennoscandia during future glacial cycles. The project begins in 2009 and is scheduled for completion in 2012. Our current understanding of the hydrological, hydrogeological and hydrogeochemical processes associated with cold climate conditions and glacial cycles, and their impact on the long-term performance of deep geological repositories for spent nuclear fuel, will be significantly improved by studying a modern analogue. The GAP will conduct the first in situ investigations of some of the parameters and processes needed to achieve a better understanding of how an ice sheet may impact a deep repository, and will provide measurements, observations and data that may significantly improve our safety assessments and risk analyses of glaciation scenarios. This report was produced by the GAP team members and presents an overview of the activities within the GAP during the interval January 1 to December 31, 2010, as well as research results obtained during this time frame. Research for the GAP is ongoing, and additional results related to the data presented here may become available in the future and will be presented in subsequent annual reports. (orig.)

  3. The Greenland analogue project. Yearly report 2010

    International Nuclear Information System (INIS)

    Harper, J.; Brinkerhoff, D.; Johnson, J.; Ruskeeniemi, T.; Engstroem, J.; Kukkonen, I.

    2012-04-01

    A four-year field and modelling study of the Greenland ice sheet and subsurface conditions, Greenland Analogue Project (GAP), has been initiated collaboratively by SKB, Posiva and NWMO to advance the understanding of processes associated with glaciation and their impact on the long-term performance of a deep geological repository. The study site encompasses a land terminus portion of the Greenland ice sheet, east of Kangerlussuaq, and is in many ways considered to be an appropriate analogue of the conditions that are expected to prevail in much of Canada and Fennoscandia during future glacial cycles. The project begins in 2009 and is scheduled for completion in 2012. Our current understanding of the hydrological, hydrogeological and hydrogeochemical processes associated with cold climate conditions and glacial cycles, and their impact on the long-term performance of deep geological repositories for spent nuclear fuel, will be significantly improved by studying a modern analogue. The GAP will conduct the first in situ investigations of some of the parameters and processes needed to achieve a better understanding of how an ice sheet may impact a deep repository, and will provide measurements, observations and data that may significantly improve our safety assessments and risk analyses of glaciation scenarios. This report was produced by the GAP team members and presents an overview of the activities within the GAP during the interval January 1 to December 31, 2010, as well as research results obtained during this time frame. Research for the GAP is ongoing, and additional results related to the data presented here may become available in the future and will be presented in subsequent annual reports. (orig.)

  4. Modelling Greenland icebergs

    Science.gov (United States)

    Marson, Juliana M.; Myers, Paul G.; Hu, Xianmin

    2017-04-01

    The Atlantic Meridional Overturning Circulation (AMOC) is well known for carrying heat from low to high latitudes, moderating local temperatures. Numerical studies have examined the AMOC's variability under the influence of freshwater input to subduction and deep convections sites. However, an important source of freshwater has often been overlooked or misrepresented: icebergs. While liquid runoff decreases the ocean salinity near the coast, icebergs are a gradual and remote source of freshwater - a difference that affects sea ice cover, temperature, and salinity distribution in ocean models. Icebergs originated from the Greenland ice sheet, in particular, can affect the subduction process in Labrador Sea by decreasing surface water density. Our study aims to evaluate the distribution of icebergs originated from Greenland and their contribution to freshwater input in the North Atlantic. To do that, we use an interactive iceberg module coupled with the Nucleus for European Modelling of the Ocean (NEMO v3.4), which will calve icebergs from Greenland according to rates established by Bamber et al. (2012). Details on the distribution and trajectory of icebergs within the model may also be of use for understanding potential navigation threats, as shipping increases in northern waters.

  5. Crustal structure beneath Eastern Greenland

    DEFF Research Database (Denmark)

    Reiche, Sönke; Thybo, H.; Kaip, G.

    2011-01-01

    is recorded by 350 Reftek Texan receivers for 10 equidistant shot points along the profile. We use forward ray tracing modelling to construct a two-dimensional velocity model from the observed travel times. These results show the first images of the subsurface velocity structure beneath the Greenland ice...

  6. Is there a see-saw over an ice-free Arctic Ocean?

    Science.gov (United States)

    Stendel, Martin; Yang, Shuting; Langen, Peter; Rodehacke, Christian; Mottram, Ruth; Hesselbjerg Christensen, Jens

    2017-04-01

    The "see-saw" in winter temperatures between western Greenland and the Canadian Arctic on one side and northern Europe on the other has been described by Loewe already in 1937, but actually this behaviour was at least known since the Danish colonization of Greenland in the early 18th century. The see-saw is associated with pressure anomalies not only near the region of interest, but as remote as the Mediterranean and the North Pacific. Recent research has pointed out the role of sea ice in maintaining the see-saw in either its warm or its cold phase over extended periods, which strongly affects European winter temperatures. What would happen to the seesaw if Arctic sea ice were to disappear suddenly? In the framework of the FP7-funded project ice2ice, we try to answer this and related questions. We have conducted a very long global simulation with a global climate model interactively coupled to a Greenland ice sheet component, covering the period 1850-3250 at a horizontal resolution of approximately 125 km. Up to 2005, the forcing is from observed greenhouse gas concentrations, and from 2006 onward it follows the extended RCP8.5 scenario, in which greenhouse gas concentrations continue to increase and eventually level out around 2250. With such a strong forcing, all Arctic sea ice has completely disappeared by roughly the same time, and the surface mass balance of the Greenland Ice Sheet becomes strongly negative. We investigate how the see-saw behaves in such an ice-free world and which implications circulation changes have in the Arctic and over Europe. To further elucidate the role of sea ice distribution on the atmospheric flow and the role of surface fluxes in maintaining the Greenland-European see-saw, we intend at a later time to expand our analysis to include a contrasting simulation with both western Greenland and northern Europe covered by ice during the Last Glacier Maximum.

  7. Glacial meltwater influences on plankton community structure and the importance of top-down control (of primary production) in a NE Greenland fjord

    DEFF Research Database (Denmark)

    Arendt, Kristine Engel; Agersted, Mette Dalgaard; Sejr, Mikael Kristian

    2016-01-01

    Freshwater runoff from the Greenland Ice Sheet (GIS) can be an important driver influencing plankton community structure in Greenland fjords. In the present study, we describe physical, taxonomic and functional differences in the plankton community in Young Sound, a NE Greenland fjord, from......, and their grazing impact was the highest among the copepod groups. Copepod grazing impact on the phytoplankton standing stock, however, was exceeded by microzooplankton grazing, investigated by dilution experiments, with the highest grazing impact on the phytoplankton standing stock of 63% d−1 in the inner part...

  8. Laboratory investigations of refractory uranium minerals from the Kvanefjeld uranium deposit, Greenland

    International Nuclear Information System (INIS)

    Rose-Hansen, J.; Soerensen, H.; Makovicky, M.; Konnerup-Madsen, J.; Holm, P.M.

    1982-01-01

    The project described in this report is a contribution to a large project on the beneficiation of the Kvanefjeld uranium deposit in the Ilimaussaq intrusion in South Greenland. The main object of our project has been to undertake laboratory experiments on steenstrupine in order to define the optimum extraction conditions. A pressurized carbonate leaching method was introduced. The Risoe experiments are carried out on bulk samples of the ore while we decided to study the minerals, first of all steenstrupine, and carbonate solutions as leaching media. Our experiments demonstrated that the leaching conditions arrived at by the Risoe group give the highest recovery and thus may be termed the optimum conditions using sodium carbonate leaching methods. Studies of the solid products left after the leaching experiments by means of the electron microprobe show that the grains of steenstrupine remain and that the leaching of uranium proceeds from the margins of the grains and towards their interior. We decided also to study the effect of applying ammonium sulphate solutions. These gave significantly higher recoveries. We consider the results of the experiments using ammonium sulphate solutions as an essential new information on the extractability of the Kvanefjeld ore and as a main result of our study. It is demonstrated that in the 13 types of rocks examined, including lujavrites, 25-75 % of the thorium and 2-58 % of the uranium contained in the rocks can be leached out and are thus not firmly bound in the minerals. (author)

  9. A tracer investigation of the atmospheric dispersion in the Dyrnaes Valley, Greenland

    International Nuclear Information System (INIS)

    Gryning, S.-E.; Lyck, E.

    1983-02-01

    Mining at Kvanefjeld, Greenland, will result in releases of air pollution gases. In order to measure the dilution of these gases tracer experiments were carried out in July-August 1981. Results from these experiments are described. The Kvanefjeld constitutes the northwestern side of a valley. The tracer was released at the Kvanefjeld during the night and sampled in the valley. The measured tracer concentrations were compared with those calculated by use of a conventional model of the dispersion of plumes. The dilution of the tracer was found to correspond to the dilution at ground level of a plume from a stack of 100-200 m height in atmospheric neutral conditions (wind speed 5 m/s). General aspects of the flow-field in the valley are discussed. It was observed that the flow direction in the valley shifts between downvalley and upvalley with a period of approximately 1 hour. It is suggested that this behaviour is caused by the interplay of a drainage flow and a sea-breeze. (author)

  10. Highly temporally resolved response to seasonal surface melt of the Zachariae and 79N outlet glaciers in Northeast Greenland

    DEFF Research Database (Denmark)

    Rathmann, N. M.; Hvidberg, C. S.; Solgaard, A. M.

    2017-01-01

    The seasonal response to surface melting of the Northeast Greenland Ice Stream outlets, Zachariae and 79N, is investigated using new highly temporally resolved surface velocity maps for 2016 combined with numerical modelling. The seasonal speed-up at 79N of 0.15km/yr is suggested to be driven by ...

  11. Geodetic measurements of postglacial adjustments in Greenland

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Wahr, J.; Leuliette, E.

    2008-01-01

    We analyze data from seven continuous Global Positioning System ( GPS) receivers and one tide gauge, all located along the edge of the Greenland ice sheet, to determine vertical uplift rates. We compare our results with predictions based on the ICE-5G deglaciation model of Peltier ( 2004). Results...

  12. An Inverse Modeling Approach to Investigate Past Lead Atmospheric Deposition in Southern Greenland

    Science.gov (United States)

    Massa, C.; Monna, F.; Bichet, V.; Gauthier, E.; Richard, H.

    2013-12-01

    The aim of this study is to model atmospheric pollution lead fluxes using two different paleoenvironmental records, covering the last 2000 years, located in southern Greenland. Fifty five sediment samples from the Lake Igaliku sequence (61°00.403'N, 45°26.494'W) were analyzed for their Pb and Al contents, and for lead isotopic compositions. The second archive consists in a previously published dataset (Shotyk et al., 2003), including Zr and Pb concentrations, and lead isotopic compositions, obtained from a minerogenic peat deposit located 16 km northwest of Lake Igaliku (61°08.314'N, 45°33.703'W). As natural background concentrations are high and obliterate most of the airborne anthropogenic lead, it is not possible to isolate this anthropogenic contribution through time with classical methods (i.e. Pb is normalized to a lithogenic and conservative element). Moreover, the background 206Pb/207Pb ratio is rather noisy because of the wide geological heterogeneity of sediment sources, which further complicated unambiguous detection of the lead pollution. To overcome these difficulties, an inverse modeling approach based on assumptions about past lead inputs was applied. This method consists of simulating a range of anthropogenic fluxes to determine the best match between measured and simulated data, both for Pb concentrations and isotopic compositions. The model is validated by the coherence of the results obtained from the two independent datasets that must reflect a similar pollution history. Although notable 206Pb/207Pb ratio shifts suggest that the first signs of anthropogenic inputs may have occurred in the 15th century, the signal-to-noise ratio was too low to significantly influence the sediment composition. Nevertheless we were able to estimate that anthropogenic lead fluxes did not exceed 2700 μg m-2 yr-1, a maximum value recorded during the 1960s. The comparison with other records from the North Atlantic Islands reveals a spatial gradient most likely due

  13. Laboratory, Computational and Theoretical Investigations of Ice Nucleation and its Implications for Mixed Phase Clouds

    Science.gov (United States)

    Yang, Fan

    Ice particles in atmospheric clouds play an important role in determining cloud lifetime, precipitation and radiation. It is therefore important to understand the whole life cycle of ice particles in the atmosphere, e.g., where they come from (nucleation), how they evolve (growth), and where they go (precipitation). Ice nucleation is the crucial step for ice formation, and in this study, we will mainly focus on ice nucleation in the lab and its effect on mixed-phase stratiform clouds. In the first half of this study, we investigate the relevance of moving contact lines (i.e., the region where three or more phases meet) on the phenomenon of contact nucleation. High speed video is used to investigate heterogeneous ice nucleation in supercooled droplets resting on cold substrates under two different dynamic conditions: droplet electrowetting and droplet vibration. The results show that contact-line motion is not a sufficient condition to trigger ice nucleation, while locally curved contact lines that can result from contact-line motion are strongly related to ice nucleation. We propose that pressure perturbations due to locally curved contact lines can strongly enhance the ice nucleation rate, which gives another interpretation for the mechanism for contact nucleation. Corresponding theoretical results provide a quantitative connection between pressure perturbations and temperature, providing a useful tool for ice nucleation calculations in atmospheric models. In this second half of the study, we build a minimalist model for long lifetime mixed-phase stratiform clouds based on stochastic ice nucleation. Our result shows that there is a non-linear relationship between ice water contact and ice number concentration in the mixed-phase cloud, as long as the volume ice nucleation rate is constant. This statistical property may help identify the source of ice nuclei in mixed-phase clouds. In addition, results from Lagrangian ice particle tracking in time dependent fields

  14. Challenges for Greenland-wide mass balance from Cryosat-2 radar-altimetry

    DEFF Research Database (Denmark)

    Simonsen, Sebastian Bjerregaard; Forsberg, René; Sørensen, Louise Sandberg

    As the Greenland ice sheet warms, a change in the structure of the upper snow/firn occurs. This change further induces changes in the reflective properties of the firn seen from satellite radar altimetry. If not identified as changes in the reflective properties of the firn, these may be interpre......As the Greenland ice sheet warms, a change in the structure of the upper snow/firn occurs. This change further induces changes in the reflective properties of the firn seen from satellite radar altimetry. If not identified as changes in the reflective properties of the firn, these may...... be interpreted as actual surface elevation changes seen from the satellite radar altimetry (Nilsson et al., 2015).Here, we investigate how to correct the elevation change observed from the ESA Cryosat-2 radar altimetry mission to derive elevation change of the air/snow interface of the Greenland ice sheet....... The elevation change of this “real” physical surface is crucial, if the goal is to derive Greenland mass balance as done for LiDAR missions.The investigations look into waveform parameters to correct for the observed bias between Radar and LiDAR observations when using Croysat-2 level-2 data. Based...

  15. Investigating cosmic rays and air shower physics with IceCube/IceTop

    Science.gov (United States)

    Dembinski, Hans

    2017-06-01

    IceCube is a cubic-kilometer detector in the deep ice at South Pole. Its square-kilometer surface array, IceTop, is located at 2800 m altitude. IceTop is large and dense enough to cover the cosmic-ray energy spectrum from PeV to EeV energies with a remarkably small systematic uncertainty, thanks to being close to the shower maximum. The experiment offers new insights into hadronic physics of air showers by observing three components: the electromagnetic signal at the surface, GeV muons in the periphery of the showers, and TeV muons in the deep ice. The cosmic-ray flux is measured with the surface signal. The mass composition is extracted from the energy loss of TeV muons observed in the deep ice in coincidence with signals at the surface. The muon lateral distribution is obtained from GeV muons identified in surface signals in the periphery of the shower. The energy spectrum of the most energetic TeV muons is also under study, as well as special events with laterally separated TeV muon tracks which originate from high-pT TeV muons. A combination of all these measurements opens the possibility to perform powerful new tests of hadronic interaction models used to simulate air showers. The latest results will be reviewed from this perspective.

  16. Investigating cosmic rays and air shower physics with IceCube/IceTop

    Directory of Open Access Journals (Sweden)

    Dembinski Hans

    2017-01-01

    Full Text Available IceCube is a cubic-kilometer detector in the deep ice at South Pole. Its square-kilometer surface array, IceTop, is located at 2800 m altitude. IceTop is large and dense enough to cover the cosmic-ray energy spectrum from PeV to EeV energies with a remarkably small systematic uncertainty, thanks to being close to the shower maximum. The experiment offers new insights into hadronic physics of air showers by observing three components: the electromagnetic signal at the surface, GeV muons in the periphery of the showers, and TeV muons in the deep ice. The cosmic-ray flux is measured with the surface signal. The mass composition is extracted from the energy loss of TeV muons observed in the deep ice in coincidence with signals at the surface. The muon lateral distribution is obtained from GeV muons identified in surface signals in the periphery of the shower. The energy spectrum of the most energetic TeV muons is also under study, as well as special events with laterally separated TeV muon tracks which originate from high-pT TeV muons. A combination of all these measurements opens the possibility to perform powerful new tests of hadronic interaction models used to simulate air showers. The latest results will be reviewed from this perspective.

  17. Continuous Chemistry in Ice Cores

    DEFF Research Database (Denmark)

    Kjær, Helle Astrid

    on parameters involved in the study of photolysis as a source of in situ CO2. The concentration of organic substances in Greenland ice is poorly known due to their low levels and the fact that only a few studies evaluate the concentrations of specific organic compounds. Light does not penetrate deep...... depth was found as a function of wavelength. Further, by computational chemistry hybrid density functional methods (DFT), the four most common conformers of pyruvic acid were investigated in both gas, water and ice using the DFT model CAM-B3LYP with dielectric medium methods. A de rease of the energy...

  18. Improved Upper Ocean/Sea Ice Modeling in the GISS GCM for Investigating Climate Change

    Science.gov (United States)

    1998-01-01

    This project built on our previous results in which we highlighted the importance of sea ice in overall climate sensitivity by determining that for both warming and cooling climates, when sea ice was not allowed to change, climate sensitivity was reduced by 35-40%. We also modified the GISS 8 deg x lO deg atmospheric GCM to include an upper-ocean/sea-ice model involving the Semtner three-layer ice/snow thermodynamic model, the Price et al. (1986) ocean mixed layer model and a general upper ocean vertical advection/diffusion scheme for maintaining and fluxing properties across the pycnocline. This effort, in addition to improving the sea ice representation in the AGCM, revealed a number of sensitive components of the sea ice/ocean system. For example, the ability to flux heat through the ice/snow properly is critical in order to resolve the surface temperature properly, since small errors in this lead to unrestrained climate drift. The present project, summarized in this report, had as its objectives: (1) introducing a series of sea ice and ocean improvements aimed at overcoming remaining weaknesses in the GCM sea ice/ocean representation, and (2) performing a series of sensitivity experiments designed to evaluate the climate sensitivity of the revised model to both Antarctic and Arctic sea ice, determine the sensitivity of the climate response to initial ice distribution, and investigate the transient response to doubling CO2.

  19. Improved Upper Ocean/Sea Ice Modeling in the GISS GCM for Investigating Climate Change

    Science.gov (United States)

    1997-01-01

    This project built on our previous results in which we highlighted the importance of sea ice in overall climate sensitivity by determining that for both warming and cooling climates, when sea ice was not allowed to change, climate sensitivity was reduced by 35-40%. We also modified the Goddard Institute for Space Studies (GISS) 8 deg x lO deg atmospheric General Circulation Model (GCM) to include an upper-ocean/sea-ice model involving the Semtner three-layer ice/snow thermodynamic model, the Price et al. (1986) ocean mixed layer model and a general upper ocean vertical advection/diffusion scheme for maintaining and fluxing properties across the pycnocline. This effort, in addition to improving the sea ice representation in the AGCM, revealed a number of sensitive components of the sea ice/ocean system. For example, the ability to flux heat through the ice/snow properly is critical in order to resolve the surface temperature properly, since small errors in this lead to unrestrained climate drift. The present project, summarized in this report, had as its objectives: (1) introducing a series of sea ice and ocean improvements aimed at overcoming remaining weaknesses in the GCM sea ice/ocean representation, and (2) performing a series of sensitivity experiments designed to evaluate the climate sensitivity of the revised model to both Antarctic and Arctic sea ice, determine the sensitivity of the climate response to initial ice distribution, and investigate the transient response to doubling CO2.

  20. Greenland shark (Somniosus microcephalus) feeding behavior on static fishing gear, effect of SMART (Selective Magnetic and Repellent-Treated) hook deterrent technology, and factors influencing entanglement in bottom longlines

    Science.gov (United States)

    Sullivan, Rennie; Hedges, Kevin J.

    2018-01-01

    The Greenland Shark (Somniosus microcephalus) is the most common bycatch in the Greenland halibut (Reinhardtius hippoglossoides) bottom longline fishery in Cumberland Sound, Canada. Historically, this inshore fishery has been prosecuted through the ice during winter but winter storms and unpredictable landfast ice conditions since the mid-1990s have led to interest in developing a summer fishery during the ice-free season. However, bycatch of Greenland shark was found to increase substantially with 570 sharks captured during an experimental Greenland halibut summer fishery (i.e., mean of 6.3 sharks per 1,000 hooks set) and mortality was reported to be about 50% due in part to fishers killing sharks that were severely entangled in longline gear. This study investigated whether the SMART (Selective Magnetic and Repellent-Treated) hook technology is a practical deterrent to Greenland shark predation and subsequent bycatch on bottom longlines. Greenland shark feeding behavior, feeding kinematics, and variables affecting entanglement/disentanglement and release are also described. The SMART hook failed to deter Greenland shark predation, i.e., all sharks were captured on SMART hooks, some with more than one SMART hook in their jaw. Moreover, recently captured Greenland sharks did not exhibit a behavioral response to SMART hooks. In situ observations of Greenland shark feeding show that this species uses a powerful inertial suction mode of feeding and was able to draw bait into the mouth from a distance of 25–35 cm. This method of feeding is suggested to negate the potential deterrent effects of electropositive metal and magnetic alloy substitutions to the SMART hook technology. The number of hooks entangled by a Greenland shark and time to disentangle and live-release a shark was found to increase with body length.

  1. Greenland shark (Somniosus microcephalus) feeding behavior on static fishing gear, effect of SMART (Selective Magnetic and Repellent-Treated) hook deterrent technology, and factors influencing entanglement in bottom longlines.

    Science.gov (United States)

    Grant, Scott M; Sullivan, Rennie; Hedges, Kevin J

    2018-01-01

    The Greenland Shark ( Somniosus microcephalus ) is the most common bycatch in the Greenland halibut ( Reinhardtius hippoglossoides ) bottom longline fishery in Cumberland Sound, Canada. Historically, this inshore fishery has been prosecuted through the ice during winter but winter storms and unpredictable landfast ice conditions since the mid-1990s have led to interest in developing a summer fishery during the ice-free season. However, bycatch of Greenland shark was found to increase substantially with 570 sharks captured during an experimental Greenland halibut summer fishery (i.e., mean of 6.3 sharks per 1,000 hooks set) and mortality was reported to be about 50% due in part to fishers killing sharks that were severely entangled in longline gear. This study investigated whether the SMART (Selective Magnetic and Repellent-Treated) hook technology is a practical deterrent to Greenland shark predation and subsequent bycatch on bottom longlines. Greenland shark feeding behavior, feeding kinematics, and variables affecting entanglement/disentanglement and release are also described. The SMART hook failed to deter Greenland shark predation, i.e., all sharks were captured on SMART hooks, some with more than one SMART hook in their jaw. Moreover, recently captured Greenland sharks did not exhibit a behavioral response to SMART hooks. In situ observations of Greenland shark feeding show that this species uses a powerful inertial suction mode of feeding and was able to draw bait into the mouth from a distance of 25-35 cm. This method of feeding is suggested to negate the potential deterrent effects of electropositive metal and magnetic alloy substitutions to the SMART hook technology. The number of hooks entangled by a Greenland shark and time to disentangle and live-release a shark was found to increase with body length.

  2. Climate variability in West Greenland during the past 1500 years

    DEFF Research Database (Denmark)

    dos Santos Ribeiro, Sofia Isabel; Moros, Matthias; Ellegaard, Marianne

    2012-01-01

    -surface temperatures in Disko Bay are out-of-phase with Greenland ice-core reconstructed temperatures and marine proxy data from South and East Greenland. This is probably governed by an NAO-type pattern, which results in warmer sea-surface conditions with less extensive sea ice in the area for the later part....... Sea ice cover and primary productivity were identified as the two main factors driving dinoflagellate cyst community changes through time. Our data provide evidence for an opposite climate trend in West Greenland relative to the NE Atlantic region from c. AD 500 to 1050. For the same period, sea...

  3. MIZEX. A Program for Mesoscale Air-Ice-Ocean Interaction Experiments in Arctic Marginal Ice Zones. II. A Science Plan for a Summer Marginal Ice Zone Experiment in the Fram Strait/Greenland Sea: 1984.

    Science.gov (United States)

    1983-05-01

    size and thickness characteris- tics. N’ore complete analysis will require combin- ing ice data with data obtained by the oceano - graphic... sol concentration and microwave brightness tem- perature. A long-range aircraft and a light aircraft Hying from Spitzbergen will study mesoscale

  4. Geophysical Investigations of Habitability in Ice-Covered Ocean Worlds

    Science.gov (United States)

    Vance, Steven D.; Panning, Mark P.; Stähler, Simon; Cammarano, Fabio; Bills, Bruce G.; Tobie, Gabriel; Kamata, Shunichi; Kedar, Sharon; Sotin, Christophe; Pike, William T.; Lorenz, Ralph; Huang, Hsin-Hua; Jackson, Jennifer M.; Banerdt, Bruce

    2018-01-01

    Geophysical measurements can reveal the structures and thermal states of icy ocean worlds. The interior density, temperature, sound speed, and electrical conductivity thus characterize their habitability. We explore the variability and correlation of these parameters using 1-D internal structure models. We invoke thermodynamic consistency using available thermodynamics of aqueous MgSO4, NaCl (as seawater), and NH3; pure water ice phases I, II, III, V, and VI; silicates; and any metallic core that may be present. Model results suggest, for Europa, that combinations of geophysical parameters might be used to distinguish an oxidized ocean dominated by MgSO4 from a more reduced ocean dominated by NaCl. In contrast with Jupiter's icy ocean moons, Titan and Enceladus have low-density rocky interiors, with minimal or no metallic core. The low-density rocky core of Enceladus may comprise hydrated minerals or anhydrous minerals with high porosity. Cassini gravity data for Titan indicate a high tidal potential Love number (k2>0.6), which requires a dense internal ocean (ρocean>1,200 kg m-3) and icy lithosphere thinner than 100 km. In that case, Titan may have little or no high-pressure ice, or a surprisingly deep water-rock interface more than 500 km below the surface, covered only by ice VI. Ganymede's water-rock interface is the deepest among known ocean worlds, at around 800 km. Its ocean may contain multiple phases of high-pressure ice, which will become buoyant if the ocean is sufficiently salty. Callisto's interior structure may be intermediate to those of Titan and Europa, with a water-rock interface 250 km below the surface covered by ice V but not ice VI.

  5. Surface science investigations of photoprocesses in model interstellar ices

    International Nuclear Information System (INIS)

    Thrower, J. D.; Collings, M. P.; McCoustra, M. R. S.; Burke, D. J.; Brown, W. A.; Dawes, A.; Holtom, P. D.; Kendall, P.; Mason, N. J.; Jamme, F.; Fraser, H. J.; Clark, I. P.; Parker, A. W.

    2008-01-01

    The kinetic energy of benzene and water molecules photodesorbed from astrophysically relevant ices on a sapphire substrate under irradiation by a UV laser tuned to the S 1 (leftarrow)S 0 π→π* transition of benzene has been measured using time-of-flight mass spectrometry. Three distinct photodesorption mechanisms have been identified--a direct adsorbate-mediated desorption of benzene, an indirect adsorbate-mediated desorption of water, and a substrate-mediated desorption of both benzene and water. The translational temperature of each desorbing population was well in excess of the ambient temperature of the ice matrix

  6. Experimental Investigation of Aerodynamic Instability of Iced Bridge Cable Sections

    DEFF Research Database (Denmark)

    Koss, Holger; Lund, Mia Schou Møller

    2013-01-01

    The accretion of ice on structural bridge cables changes the aerodynamic conditions of the surface and influences hence the acting wind load process. Full-scale monitoring indicates that light precipitation at moderate low temperatures between zero and -5°C may lead to large amplitude vibrations...... of bridge cables under wind action. This paper describes the experimental simulation of ice accretion on a real bridge cable sheet HDPE tube segment (diameter 160mm) and its effect on the aerodynamic load. Furthermore, aerodynamic instability will be estimated with quasi-steady theory using the determined...

  7. A Validation Dataset for CryoSat Sea Ice Investigators

    DEFF Research Database (Denmark)

    Julia, Gaudelli,; Baker, Steve; Haas, Christian

    Since its launch in April 2010 Cryosat has been collecting valuable sea ice data over the Arctic region. Over the same period ESA’s CryoVEx and NASA IceBridge validation campaigns have been collecting a unique set of coincident airborne measurements in the Arctic. The CryoVal-SI project has...... community. In this talk we will describe the composition of the validation dataset, summarising how it was processed and how to understand the content and format of the data. We will also explain how to access the data and the supporting documentation....

  8. Norse Greenland

    DEFF Research Database (Denmark)

    Arneborg, Jette

    2015-01-01

    human agency, landscape changes, climate changes, resilience, sustainability and adaptation are key words and research has moved from local to more global perspectives. New results from research projects in recent years have diversified the discussion claiming that the Norse Greenlanders created...

  9. Possible Greenland

    DEFF Research Database (Denmark)

    2012-01-01

    at Greenland's structure, and ask some threshold questions. Which aspects of society are rooted in our human hardware? And, if we had the rare opportunity to build a new nation, what would we choose for ourselves? We hope this will inspire an open, imaginative and thoroughly human discussion about how...

  10. Runoff and mass-balance simulations from the Greenland Ice Sheet at Kangerlussuaq (Søndre Strømfjord) in a 30-year perspective, 1979-2008

    NARCIS (Netherlands)

    Mernild, S. H.; Liston, G. E.; Steffen, K.; van den Broeke, M.R.; Hasholt, B.

    2010-01-01

    This study provides insights into surface mass-balance (SMB) and runoff exiting the Watson River drainage basin, Kangerlussuaq, West Greenland during a 30 year period (1978/1979–2007/2008) when the climate experienced increasing temperatures and precipitation. The 30-year simulations quantify the

  11. Chinese mineral dust and anthropogenic aerosol inter-continental transport: a Greenland perspective

    Science.gov (United States)

    Bory, A.; Abouchami, W.; Galer, S.; Svensson, A.; Biscaye, P.

    2012-04-01

    Impurities contained in snow and ice layers in Greenland provide a record of the history of atmospheric dustiness and pollution in the Northern Hemisphere. The source of the particles deposited onto the ice cap may be investigated using specific intrinsic tracers. Provenance discrimination may then provide valuable constraints for the validation of atmospheric transport models as well as for the monitoring of natural and anthropogenic aerosols emissions at a global scale. Clay mineralogy combined with the strontium and neodymium isotope composition of the insoluble particles extracted from recent snow deposits at NorthGRIP (75.1°N, 042.3°W), for instance, enabled us to demonstrate that the Taklimakan desert of North-western China was the main source of mineral dust reaching central Greenland at present [Bory et al., EPSL, 2002 ; GRL, 2003a]. Here we report the lead isotopic signature of these snow-pit samples, covering the 1989-1995 and 1998-2001 time periods. Unradiogenic lead isotopic composition of our Greenland samples, compared to Asian dust isotopic fingerprints, implies that most of the insoluble lead reaching the ice cap is of anthropogenic origin. Lead isotopes reveal likely contributions from European/Canadian and, to a lesser extent, US sources, as well as a marked overprinted signature typical of Chinese anthropogenic lead sources. The relative contribution of the latter appears to have been increasing steadily over the last decade of the 20th century. Quantitative estimates suggest that, in addition to providing most of the dust, China may have already become the most important supplier of anthropogenic lead deposited in Greenland by the turn of the 20th to the 21st century. The close timing between dust and anthropogenic particles deposition onto the ice cap provides new insights for our understanding of Chinese aerosols transport to Greenland.

  12. 100,000-year-long terrestrial record of millennial-scale linkage between eastern North American mid-latitude paleovegetation shifts and Greenland ice-core oxygen isotope trends

    Science.gov (United States)

    Litwin, Ronald J.; Smoot, Joseph P.; Pavich, Milan J.; Markewich, Helaine Walsh; Brook, George; Durika, Nancy J.

    2013-01-01

    We document frequent, rapid, strong, millennial-scale paleovegetation shifts throughout the late Pleistocene, within a 100,000+ yr interval (~ 115–15 ka) of terrestrial sediments from the mid-Atlantic Region (MAR) of North America. High-resolution analyses of fossil pollen from one core locality revealed a continuously shifting sequence of thermally dependent forest assemblages, ranging between two endmembers: subtropical oak-tupelo-bald cypress-gum forest and high boreal spruce-pine forest. Sedimentary textural evidence indicates fluvial, paludal, and loess deposition, and paleosol formation, representing sequential freshwater to subaerial environments in which this record was deposited. Its total age"depth model, based on radiocarbon and optically stimulated luminescence ages, ranges from terrestrial oxygen isotope stages (OIS) 6 to 1. The particular core sub-interval presented here is correlative in trend and timing to that portion of the oxygen isotope sequence common among several Greenland ice cores: interstades GI2 to GI24 (≈ OIS2–5 d). This site thus provides the first evidence for an essentially complete series of "Dansgaard"Oeschger" climate events in the MAR. These data reveal that the ~ 100,000 yr preceding the Late Glacial and Holocene in the MAR of North America were characterized by frequently and dynamically changing climate states, and by vegetation shifts that closely tracked the Greenland paleoclimate sequence.

  13. Investigating the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle

    Directory of Open Access Journals (Sweden)

    S. Bonelli

    2009-07-01

    Full Text Available A 2.5-dimensional climate model of intermediate complexity, CLIMBER-2, fully coupled with the GREMLINS 3-D thermo-mechanical ice sheet model is used to simulate the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle and to investigate the ice sheets responses to both insolation and atmospheric CO2 concentration. This model reproduces the main phases of advance and retreat of Northern Hemisphere ice sheets during the last glacial cycle, although the amplitude of these variations is less pronounced than those based on sea level reconstructions. At the last glacial maximum, the simulated ice volume is 52.5×1015 m3 and the spatial distribution of both the American and Eurasian ice complexes is in reasonable agreement with observations, with the exception of the marine parts of these former ice sheets.
    A set of sensitivity studies has also been performed to assess the sensitivity of the Northern Hemisphere ice sheets to both insolation and atmospheric CO2. Our results suggest that the decrease of summer insolation is the main factor responsible for the early build up of the North American ice sheet around 120 kyr BP, in agreement with benthic foraminifera δ18O signals. In contrast, low insolation and low atmospheric CO2 concentration are both necessary to trigger a long-lasting glaciation over Eurasia.

  14. The Greenland Analogue Project (GAP). Literature review of hydrogeology/ hydrogeochemistry

    International Nuclear Information System (INIS)

    Wallroth, Thomas; Lokrantz, Hanna; Rimsa, Andrius

    2010-09-01

    This report is produced as part of the Greenland Analogue Project (GAP), carried out as a collaboration project with the Canadian Nuclear Waste Management Organization (NWMO), Posiva Oy and the Swedish Nuclear Fuel and Waste Management Co (SKB). The overall aim of the project is to improve the current understanding of hydrogeological and hydrogeochemical processes associated with continental-scale glacial periods including with the presence of permafrost and the advance/retreat of ice sheets. The project will focus on studying how an ice sheet affects groundwater flow and water chemistry around a deep geological repository in crystalline bedrock. The Greenland Analogue Project consists of three active sub-projects (A-C) with individual objectives. Field studies are conducted in the Kangerlussuaq region, in central Western Greenland. Sub-projects A and B collectively aim at improving the understanding of ice sheet hydrology by combining investigations on surface water processes with ice sheet drilling and instrumentation. In sub-project C, the penetration of glacial melt water into the bedrock, groundwater flow and the chemical composition of water will be studied. Main planned activities in sub-project C include drilling of a deep borehole in front of the ice sheet, in which different downhole surveys, sampling and monitoring will be carried out. The primary aim of this report is to review available information about hydrogeology and hydrogeochemistry in central Western Greenland, with special emphasis on the area around Kangerlussuaq. The relevant information about this area is however very limited, and it was decided to extend the review to briefly include studies made in other regions with similar conditions in terms of geology, climate and glaciology. The number of published studies made in other areas with glaciers, ice sheets or permafrost is very large, and the review and list of references in this report is far from complete. It is also obvious that both

  15. The Greenland Analogue Project (GAP). Literature review of hydrogeology/ hydrogeochemistry

    Energy Technology Data Exchange (ETDEWEB)

    Wallroth, Thomas; Lokrantz, Hanna; Rimsa, Andrius (Bergab Consulting Geologists, Goeteborg (Sweden))

    2010-09-15

    This report is produced as part of the Greenland Analogue Project (GAP), carried out as a collaboration project with the Canadian Nuclear Waste Management Organization (NWMO), Posiva Oy and the Swedish Nuclear Fuel and Waste Management Co (SKB). The overall aim of the project is to improve the current understanding of hydrogeological and hydrogeochemical processes associated with continental-scale glacial periods including with the presence of permafrost and the advance/retreat of ice sheets. The project will focus on studying how an ice sheet affects groundwater flow and water chemistry around a deep geological repository in crystalline bedrock. The Greenland Analogue Project consists of three active sub-projects (A-C) with individual objectives. Field studies are conducted in the Kangerlussuaq region, in central Western Greenland. Sub-projects A and B collectively aim at improving the understanding of ice sheet hydrology by combining investigations on surface water processes with ice sheet drilling and instrumentation. In sub-project C, the penetration of glacial melt water into the bedrock, groundwater flow and the chemical composition of water will be studied. Main planned activities in sub-project C include drilling of a deep borehole in front of the ice sheet, in which different downhole surveys, sampling and monitoring will be carried out. The primary aim of this report is to review available information about hydrogeology and hydrogeochemistry in central Western Greenland, with special emphasis on the area around Kangerlussuaq. The relevant information about this area is however very limited, and it was decided to extend the review to briefly include studies made in other regions with similar conditions in terms of geology, climate and glaciology. The number of published studies made in other areas with glaciers, ice sheets or permafrost is very large, and the review and list of references in this report is far from complete. It is also obvious that both

  16. Measured and modelled absolute gravity changes in Greenland

    DEFF Research Database (Denmark)

    Nielsen, Jens Emil; Forsberg, René; Strykowski, Gabriel

    2014-01-01

    in Greenland. Theresult is compared with the initial measurements of absolute gravity (AG) change at selected GreenlandNetwork (GNET) sites.We find that observations are highly influenced by the direct attraction from the ice and ocean. Thisis especially evident in the measurements conducted at the GNET...

  17. Hunting and fishing settlements in Upernavik district of Northern Greenland

    DEFF Research Database (Denmark)

    Hendriksen, Kåre; Jørgensen, Ulrik

    2015-01-01

    Inuit in the Upernavik district of Northern Greenland has in generations used the winter sea ice as the basis for the essential hunting of seals, white- and narwhales. Since the late 1980’ies hunting has been combined with increasing fishery of Greenland halibut during summer from dinghies and in...

  18. Albedo decline on Greenland's Mittivakkat Gletscher in a warming climate

    DEFF Research Database (Denmark)

    Mernild, Sebastian H; Malmros, Jeppe K.; Yde, Jacob Clement

    2015-01-01

    Albedo is one of the parameters that govern energy availability for snow and ice surface ablation, and subsequently the surface mass balance conditions of temperate glaciers and ice caps (GIC). Here, we document snow and ice albedo changes for Mittivakkat Gletscher (MG) in Southeast Greenland (20...

  19. Investigating and Modeling Ecosystem Response to an Experimental and a Natural Ice Storm

    Science.gov (United States)

    Fakhraei, H.; Driscoll, C. T.; Rustad, L.; Campbell, J. L.; Groffman, P.; Fahey, T.; Likens, G.; Swaminathan, R.

    2017-12-01

    Our understanding of ecosystem response to the extreme events is generally limited to rare observations from the natural historical events. However, investigating extreme events under controlled conditions can improve our understanding of these natural phenomena. A novel field experiment was conducted in a northern hardwood forest at the Hubbard Brook Experimental Forest in New Hampshire in the northeastern United States to quantify the influence of ice storms on the ecological processes. During subfreezing conditions in the winters of 2016 and 2017, water from a nearby stream was pumped and sprayed on the canopy of eight experimental plots to accrete ice to a targeted thickness on the canopy. The experiment was conducted at three levels of icing thickness (0.25, 0.5, 0.75 in.) in 2016 comparable to the naturally occurring 1998 ice storm and a second 0.5 in. treatment 2017 which were compared with reference plots. The most notable response of the icing treatments was a marked increase in fine and course litter fall which increased exponentially with increases in the icing thickness. Post-treatment openings in the canopy caused short-term increases in soil temperature in the ice-treatment plots compared to the reference plots. No response from the ice storm treatments were detected for soil moisture, net N mineralization, net nitrification, or denitrification after both natural and experimental ice storm. In contrast to the marked increase in the stream water nitrate after the natural occurring 1998 ice storm, we have not observed any significant change in soil solution N concentrations in the experimental ice storm treatments. Inconsistency in the response between the natural and experimental ice storm is likely due to differences in geophysical characteristics of the study sites including slope and lateral uptake of nutrient by the trees outside the experimental plots. In order to evaluate the long-term impacts of ice storms on northern hardwood forests, we used

  20. Extreme Low Light Requirement for Algae Growth Underneath Sea Ice

    DEFF Research Database (Denmark)

    Hancke, Kasper; Lund-Hansen, Lars C.; Lamare, Maxim L.

    2018-01-01

    Microalgae colonizing the underside of sea ice in spring are a key component of the Arctic foodweb as they drive early primary production and transport of carbon from the atmosphere to the ocean interior. Onset of the spring bloom of ice algae is typically limited by the availability of light......, and the current consensus is that a few tens-of-centimeters of snow is enough to prevent sufficient solar radiation to reach underneath the sea ice. We challenge this consensus, and investigated the onset and the light requirement of an ice algae spring bloom, and the importance of snow optical properties...... for light penetration. Colonization by ice algae began in May under >1 m of first-year sea ice with approximate to 1 m thick snow cover on top, in NE Greenland. The initial growth of ice algae began at extremely low irradiance (...