scholarly journals Observaciones del manto de nieve durante una circunnavegación del casquete de hielo de Groenlandia (primavera de 2014)

2016 ◽  
Vol 42 (2) ◽  
pp. 369 ◽  
Author(s):  
J. I. López Moreno ◽  
M. Olivera-Marañón ◽  
J. Zabalza ◽  
R. H. De Larramendi
Keyword(s):  
Bulk Density ◽  
Snow Depth ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Atmospheric Temperature ◽  
Snow Accumulation ◽  
Dense Layer ◽  
Density Profiles ◽  
Highly Correlated ◽  
Snow Temperature

We report the characteristics of the Greenland ice sheet snowpack, based on data collected during the first wind-propelled circumnavigation of the ice sheet, undertaken in spring 2014. The dataset included snow depth measurements made in 100 m2 plots, and data on the snow bulk density and snowpack temperature at 1 m depth at 25 sites distributed along the 4301 km route traveled during the 49 days of the circumnavigation. In addition, eight snow pits of 1 m depth were dug to measure the snow temperature and density at 10 cm intervals in the upper layer of the snowpack. All this information may help to better understand snow characteristics on this remote area, and provide data to validate and calibrate atmospheric and cryospheric models.Snow depths exceeding 4 m were measured in the snow accumulation area, but in many cases the presence of an ice layer prevented penetration of the snow probe below 70 cm depth. This ice layer may be associated with the melting event that occurred in July 2012, and affected 98% of the ice sheet. Beyond the main snow accumulation zone, very constant snow depth values of approximately 1.5 m were measured. The snow temperature at 1 m depth generally ranged from –20°C to –10°C, and was highly correlated with the average atmospheric temperature during the 15 days prior to the snow temperature measurements. The snow bulk density was relatively homogeneous at the majority of sampling sites, ranging from 320 to 390 kg m–3. The snow temperature and density profiles measured in the snow pits indicated that the snowpack became progressively colder from the surface to 1 m depth. The temperature gradient measured in the snow pits was particularly steep (shallow) at the warmest (coldest) sampling sites. The snow density was characterized by denser snow at 60–80 cm depth, coinciding with the depth of the ice layer identified when depth was measured. A dense layer was also found close to the surface at the warmest snow pit sites, and it is likely that this corresponds to a more recent snow melt event.

scholarly journals Large surface meltwater discharge from the Kangerlussuaq sector of the Greenland ice sheet during the record-warm year 2010 explained by detailed energy balance observations

2012 ◽  
Vol 6 (1) ◽  
pp. 199-209 ◽  
Author(s):  
D. van As ◽  
A. L. Hubbard ◽  
B. Hasholt ◽  
A. B. Mikkelsen ◽  
M. R. van den Broeke ◽  
...  
Keyword(s):  
Energy Balance ◽  
High Temperatures ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Atmospheric Temperature ◽  
Snow Accumulation ◽  
Balance Model ◽  
Positive Anomaly ◽  
Positive Temperature ◽  
Ablation Zone

Abstract. This study uses data from six on-ice weather stations, calibrated MODIS-derived albedo and proglacial river gauging measurements to drive and validate an energy balance model. We aim to quantify the record-setting positive temperature anomaly in 2010 and its effect on mass balance and runoff from the Kangerlussuaq sector of the Greenland ice sheet. In 2010, the average temperature was 4.9 °C (2.7 standard deviations) above the 1974–2010 average in Kangerlussuaq. High temperatures were also observed over the ice sheet, with the magnitude of the positive anomaly increasing with altitude, particularly in August. Simultaneously, surface albedo was anomalously low in 2010, predominantly in the upper ablation zone. The low albedo was caused by high ablation, which in turn profited from high temperatures and low winter snowfall. Surface energy balance calculations show that the largest melt excess (∼170%) occurred in the upper ablation zone (above 1000 m), where higher temperatures and lower albedo contributed equally to the melt anomaly. At lower elevations the melt excess can be attributed to high atmospheric temperatures alone. In total, we calculate that 6.6 ± 1.0 km3 of surface meltwater ran off the ice sheet in the Kangerlussuaq catchment in 2010, exceeding the reference year 2009 (based on atmospheric temperature measurements) by ∼150%. During future warm episodes we can expect a melt response of at least the same magnitude, unless a larger wintertime snow accumulation delays and moderates the melt-albedo feedback. Due to the hypsometry of the ice sheet, yielding an increasing surface area with elevation, meltwater runoff will be further amplified by increases in melt forcings such as atmospheric heat.

scholarly journals Spatial and temporal variability of snow accumulation for the South-Western Greenland Ice Sheet

2019 ◽  
Author(s):  
Achim Heilig ◽  
Olaf Eisen ◽  
Martin Schneebeli ◽  
Michael MacFerrin ◽  
C. Max Stevens ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Snow Depth ◽  
Regional Scale ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Temporal Changes ◽  
Snow Accumulation ◽  
Small Scale ◽  
Spatial And Temporal Variability ◽  
Accumulation Pattern

Abstract. The Greenland ice sheet (GrIS) has experienced significant changes in recent decades. Data confirming those changes are derived from remote sensing, regional climate models (RCMs), firn cores and automatic weather stations (AWSs) on the ice sheet. Data sources comprise different extents in area coverage. While remote sensing and RCMs cover at least regional scales with an extent ranging from 1–10 km, AWS data and firn cores are point observations. To link such regional scales with point measurements, we investigate the spatial variability of snow accumulation within areas of approximately 1–4 km2 and its temporal changes. At three different sites of the southwestern GrIS (Swiss Camp, KAN-U, Dye-2), we performed extensive ground-penetrating radar (GPR) transects and numerous snow pits. In dry snow conditions, radar-measured two-way travel time can be converted to snow depth and snow accumulation if the density is known. Density variations per site for snow pits within distances of up to 1 km are found to be consistently within ±5 %. GPR transects were further filtered to remove small scale surface-related noise. The combined uncertainty of density variations and spatial filtering of radar transects is at 7–8 % per regional scale. To link point observations with regional scales, we analyze for spatial representativeness of snow pits. It occurs that with a probability of p = 0.8 (KAN-U) to p > 0.95 (Swiss Camp and Dye-2), randomly selected snow pits are representative in snow accumulation for entire regions with an offset of ±10 % from arithmetic means. However, to achieve such high representativeness of snow pits, it is required to average snow depth for an area of at least 20 m x 20 m. Interannual accumulation pattern at Dye-2 are very persistent for two subsequent accumulation seasons with similarity probabilities of p > 0.95, if again an error of ±10 % is included. Using target reflectors placed at respective end-of-summer-melt horizons, we additionally analyzed for occurrences of lateral redistribution within one melt season. In this study, we show that at Dye-2 lateral flow of meltwater cannot be evidenced in the current climate. Such studies of spatial representativeness and temporal changes in accumulation are inevitable to assess reliability of the linkage between point measurements and regional scale data and predictions, which are used for validation and calibration of remote sensing data and RCM outputs.

Changes in Greenland ice sheet elevation attributed primarily to snow accumulation variability

Nature ◽  
2000 ◽  
Vol 406 (6798) ◽  
pp. 877-879 ◽  
Author(s):  
J. R. McConnell ◽  
R. J. Arthern ◽  
E. Mosley-Thompson ◽  
C. H. Davis ◽  
R. C. Bales ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation

scholarly journals Snow Accumulation Studies on the Thule Peninsula, Greenland

1968 ◽  
Vol 7 (49) ◽  
pp. 59-76 ◽  
Author(s):  
Steven J. Mock
Keyword(s):  
Regional Scale ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Accumulation Rates ◽  
Surface Slope ◽  
Ice Flow ◽  
Accumulation Pattern ◽  
Flow Phenomena ◽  
Independent Parameters

AbstractData from stake measurements, marker boards and pits along a 136 km trail crossing the Thule peninsula sector of the Greenland ice sheet have been used to determine both the regional and local distribution of snow accumulation, On a regional scale trend surfaces of mean annual accumulation can be adequately predicted from a model using distance from moisture source and elevation as independent parameters. A series of step- or wave-like features break the smooth profile of the ice. sheet and cause profound changes in accumulation rates on a local scale. The accumulation pattern over these features can be predicted from surface slope and departure from regional elevation. Profiles of’ surface and subsurface topography indicate a direct relationship between subsurface hills and step-like features, but cannot be quantitatively accounted for by existing ice-flow theory. Detailed accumulation studies in conjunction with a program of spirit leveling in the vicinity of Camp Century has revealed the development a shallow valley-like feature. Within this feature accumulation rates have increased indicating that it is the result of flow phenomena.

scholarly journals Mass balance of the northeast sector of the Greenland ice sheet: a remote-sensing perspective

2000 ◽  
Vol 46 (153) ◽  
pp. 265-273 ◽  
Author(s):  
Eric Rignot ◽  
Guillaume Buscarlet ◽  
Beáta Csathó ◽  
Sivaprasad Gogineni ◽  
William Krabill ◽  
...  
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Ice Shelf ◽  
Synthetic Aperture Radar Interferometry ◽  
Model Predictions ◽  
Grounding Line ◽  
Ice Production ◽  
Inland Ice

AbstractSynthetic-aperture radar interferometry data and airborne ice-sounding radar (ISR) data are employed to obtain modern estimates of the inland ice production from Nioghalvfjerdsbræ (NB) and Zachariae Isstrøm (ZI), the two largest glaciers draining the northeast sector of the Greenland ice sheet. Ice fluxes are measured at the grounding line (14.2 ±1 km3 ice a−1 for NB and 10.8 ±1 km3 ice a−1 for ZI) with an ice thickness deduced from ice-shelf hydrostatic equilibrium, and along an ISR profile collected upstream of the grounding line (14.3 ± 0.7 km3 ice a−1 for NB and 11.6 ± 0.6 km3 ice a−1 for ZI). Balance fluxes calculated from a map of snow accumulation and model predictions of surface melt are 11.9 ± 2 km3 ice a−1 for NB and 10.0 ± 2 km3 ice a−1 for ZI at the grounding line, and 12.2 and 10.3 km3 ice a−1, respectively, at the ISR line. The two glaciers therefore exhibit a negative mass balance equivalent to 14% of their balance flux, with a ±12% uncertainty. Independently, we detect a retreat of the grounding line of NB between 1992 and 1996 which is larger at the glacier center (920 ± 250 m) than on the sides (240 ± 50 m). The corresponding ice-thinning rates (2 ± 1 m a−1 at the glacier center and 0.6 ± 0.3 m a−1 on the sides) are too large to be accommodated by temporal changes in ablation or accumulation, and must be due to dynamic thinning.

scholarly journals Snow Accumulation in North Greenland

1958 ◽  
Vol 3 (24) ◽  
pp. 237-248 ◽  
Author(s):  
C. Bull
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
The Mean ◽  
Precipitation Records ◽  
Available Information ◽  
North Greenland

AbstractMeasurements of the annual snow accumulation have been made at many points on a traverse of north Greenland. In lat. 77–78° N. the annual accumulation above 1800 m. was about 13 gm. cm.−2in the years 1948–53 and, in contrast to results which have been obtained further south, did not vary with longitude. In 1953–54 the accumulation was greater. The annual accumulation in north and central Greenland has varied significantly over the last 50 years, but similar variations are not shown in the precipitation records at coastal stations. Using all the available information, the mean annual accumulation on the Greenland Ice Sheet has been calculated as 29±3 gm. cm.−2.

scholarly journals Snow Accumulation Studies on the Thule Peninsula, Greenland

1968 ◽  
Vol 7 (49) ◽  
pp. 59-76 ◽  
Author(s):  
Steven J. Mock
Keyword(s):  
Regional Scale ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Accumulation Rates ◽  
Surface Slope ◽  
Ice Flow ◽  
Accumulation Pattern ◽  
Flow Phenomena ◽  
Independent Parameters

Abstract Data from stake measurements, marker boards and pits along a 136 km trail crossing the Thule peninsula sector of the Greenland ice sheet have been used to determine both the regional and local distribution of snow accumulation, On a regional scale trend surfaces of mean annual accumulation can be adequately predicted from a model using distance from moisture source and elevation as independent parameters. A series of step- or wave-like features break the smooth profile of the ice. sheet and cause profound changes in accumulation rates on a local scale. The accumulation pattern over these features can be predicted from surface slope and departure from regional elevation. Profiles of’ surface and subsurface topography indicate a direct relationship between subsurface hills and step-like features, but cannot be quantitatively accounted for by existing ice-flow theory. Detailed accumulation studies in conjunction with a program of spirit leveling in the vicinity of Camp Century has revealed the development a shallow valley-like feature. Within this feature accumulation rates have increased indicating that it is the result of flow phenomena.

scholarly journals Recent changes on Greenland outlet glaciers

2009 ◽  
Vol 55 (189) ◽  
pp. 147-162 ◽  
Author(s):  
R. Thomas ◽  
E. Frederick ◽  
W. Krabill ◽  
S. Manizade ◽  
C. Martin
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Dynamic Changes ◽  
Laser Altimeter ◽  
Outlet Glacier ◽  
Thickness Change ◽  
Grounding Line ◽  
Break Up ◽  
Glacier Velocity

AbstractAircraft laser-altimeter surveys during the 1990s showed near-coastal parts of the Greenland ice sheet to be thinning; despite slow thickening at higher elevations, the ice sheet lost mass to the ocean. Many outlet glaciers thinned more rapidly than could be explained by increased melting during the recent warmer summers, indicating dynamic imbalance between glacier velocity and upstream snow accumulation. Results from more recent surveys, presented here, show that thinning rates have increased in most coastal regions. For almost half of the surveys, these increases might have resulted from increases in summer melting, but rapid thinning on others is indicative of dynamic changes that increased with time. In particular, thinning rates on the three fastest glaciers increased to tens of m a−1 after 2000, and other observations show an approximate doubling in their velocities. The deep beds of these glaciers appear to have a strong influence on rates of grounding-line retreat and thickness change, with periods of glacier acceleration and rapid thinning initiated by flotation and break-up of lightly grounded glacier snouts or break-up of floating ice tongues. Near-simultaneous thinning of these widely separated glaciers suggests that warming of deeper ocean waters might be a common cause. Nearby glaciers without deep beds are thinning far more slowly, suggesting that basal lubrication as a result of increased surface melting has only a marginal impact on Greenland outlet-glacier acceleration

scholarly journals Surface mass balance of the Greenland ice sheet from climate-analysis data and accumulation/runoff models

2002 ◽  
Vol 35 ◽  
pp. 67-72 ◽  
Author(s):  
Edward Hanna ◽  
Philippe Huybrechts ◽  
Thomas L. Mote
Keyword(s):  
Mass Balance ◽  
Satellite Data ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Surface Elevation ◽  
Great Promise ◽  
Surface Mass Balance ◽  
Ice Dynamics ◽  
Surface Mass

AbstractWe used surface climate fields from high-resolution (~0.5660.56˚) European Centre for Medium-RangeWeather Forecasts (ECMWF) operational analyses (1992–98), together with meteorological and glaciological models of snow accumulation and surface meltwater runoff/retention, to produce novel maps of Greenland ice sheet (GIS) net accumulation, net runoff and surface mass balance (SMB). We compared our runoff maps with similar-scaled runoff (melt minus refreezing) maps based on passive-microwave satellite data. Our gross spatial/temporal patterns of runoff compared well with those from the satellite data, although amounts of modelled runoff are likely too low. Mean accumulation was 0.287 (0.307)ma–1, and mean runoff was 0.128 (0.151)ma–1, averaged across the W. Abdalati (T. L. Mote) GIS mask. Corresponding mean SMB was 0.159 (0.156)ma–1, with considerable interannual variability (standard deviation ~0.11ma–1) primarily due to variations in runoff. Considering best estimates of current iceberg calving, overall the GIS is probably currently losing mass. Our study shows great promise for meaningfully modelling SMB based on forthcoming ``second-generation’’ ECMWF re-analysis (ERA-40) data, and comparing the results with ongoing laser/radarmeasurements of surface elevation. This should help elucidate to what extent surface elevation changes are caused by short-term SMB variations or other factors (e.g. ice dynamics).

scholarly journals Partitioning of melt energy and meltwater fluxes in the ablation zone of the west Greenland ice sheet

2008 ◽  
Vol 2 (2) ◽  
pp. 179-189 ◽  
Author(s):  
M. van den Broeke ◽  
P. Smeets ◽  
J. Ettema ◽  
C. van der Veen ◽  
R. van de Wal ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Ablation Zone ◽  
The West ◽  
Near Surface ◽  
Surface Mass ◽  
West Greenland ◽  
Ice Melt ◽  
June July

Abstract. We present four years (August 2003–August 2007) of surface mass balance data from the ablation zone of the west Greenland ice sheet along the 67° N latitude circle. Sonic height rangers and automatic weather stations continuously measured accumulation/ablation and near-surface climate at distances of 6, 38 and 88 km from the ice sheet margin at elevations of 490, 1020 and 1520 m a.s.l. Using a melt model and reasonable assumptions about snow density and percolation characteristics, these data are used to quantify the partitioning of energy and mass fluxes during melt episodes. The lowest site receives very little winter accumulation, and ice melting is nearly continuous in June, July and August. Due to the lack of snow accumulation, little refreezing occurs and virtually all melt energy is invested in runoff. Higher up the ice sheet, the ice sheet surface freezes up during the night, making summer melting intermittent. At the intermediate site, refreezing in snow consumes about 10% of the melt energy, increasing to 40% at the highest site. The sum of these effects is that total melt and runoff increase exponentially towards the ice sheet margin, each time doubling between the stations. At the two lower sites, we estimate that radiation penetration causes 20–30% of the ice melt to occur below the surface.

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