Greenland ice sheet

Data for daily ice ablation on two outlets from the Greenland ice sheet, Nordbogletscher (1979–83) and Qamanârssûp sermia (1980–86), are used to test a simple energy-balance model which calculates ablation from climate data. The mean errors of the model are only −1.1 and −1.3 mm water d−1 for Nordbogletscher (14 months) and Qamanârssûp sermia (21 months), respectively, with standard deviations of ±13.6 and ±18.9 mm water d−1 for calculating daily ablation. The larger error for Qamanârssûp sermia may be due to variations in ice albedo but the model also underestimates ablation during Föhn events. According to the model, radiation accounts for about two-thirds of mean ablation for June-August at the two sites, while turbulent fluxes account for about one-third. The average ablation rate is higher at Qamanârssûp sermia than at Nordbogletscher because both sensible-heat flux and short-wave radiation are higher.

To improve Greenland Ice Sheet surface mass balance (SMB) simulation, the subsurface scheme of the HIRHAM5 regional climate model was extended to include snow densification, varying hydraulic conductivity, irreducible water saturation and other effects on snow liquid water percolation and retention. Sensitivity experiments to investigate the effects of the additions and the impact of different parameterization choices are presented. Compared with 68 accumulation area ice cores, the simulated mean annual net accumulation bias is −5% (correlation coefficient of 0.90). Modeled SMB in the ablation area compares favorably with 1041 PROMICE observations with regression slope of 0.95–0.97 (depending on model configuration), correlation coefficient of 0.75–0.86 and mean bias −3%. Weighting ablation area SMB biases at low-and high-elevation with the amount of runoff from these areas, we estimate ice sheet-wide mass loss biases in the ablation area at −5 and −7% using observed (MODIS-derived) and internally calculated albedo, respectively. Comparison with observed melt day counts shows that patterns of spatial (correlation ∼0.9) and temporal (correlation coefficient of ∼0.9) variability are realistically represented in the simulations. However, the model tends to underestimate the magnitude of inter-annual variability (regression slope ∼0.7) and overestimate that of spatial variability (slope ∼1.2). In terms of subsurface temperature structure and occurrence of perennial firn aquifers and perched ice layers, the most important model choices are the albedo implementation and irreducible water saturation parameterization. At one percolation area location, for instance, the internally calculated albedo yields too high subsurface temperatures below 5 m, but when using an implementation of irreducible saturation allowing higher values, an ice layer forms in 2011, reducing the deep warm bias in subsequent years. On the other hand, prior to the formation of the ice layer, observed albedos combined with lower irreducible saturation give the smallest bias. Perennial firn aquifers and perched ice layers occur in varying thickness and area for

In this study, we analysed the organic and inorganic content of the cryoconite holes along the altitudinal gradient at the lower elevations of the Russell glacier ablation zone in Southwest Greenland. We specifically focus on less studied industrial microscopic spheroidal carbonaceous particles (SCP; part of black carbon) to get more insights about their accumulation patterns on the glacier surface. We found no clear SCP distribution pattern, including concentration values. This outcome underlines the complexity of the ice margin zone and draws attention for further research on this topic with the inclusion of multiyear evaluation of SCP concentration at the even wider area that could possibly give results that can be compared to the emission source and long-way air pollution validation. In addition, our results indicate that during the summer of 2016, algae composition was formed of both green algae (Chlamydomonadaceae, Mesotaeniaceae) and cyanobacteria (Oscillatoriaceae). Green algae had a larger relative proportion than cyanobacteria in the cryoconite holes throughout the studied gradient.

A meteorological and glaciological experiment was carried out in July 1993 at the margin of the Greenland ice sheet in Kronprins Christian Land, eastern north Greenland. Within a small area (about 100 m2) daily measurements were made on ten ablation stakes fixed in “light” and “dark” ice and were compared to each other. Simultaneously, the components of the energy balance, including net radiation, sensible-heat flux, latent-heat flux and conductive-heat flux in the ice were determined. Global radiation, longwave incoming radiation and albedo were measured, and longwave outgoing radiation was calculated by assuming that the glacier surface was melting. Sensible-and latent-heat fluxes were calculated from air temperature, humidity and wind speed. Conductive-heat flux in the ice was estimated by temperature-profile measurements in the uppermost ice layer. Net radiation is the major source of ablation energy, and turbulent fluxes are smaller energy sources by about three times, while he...

The annual mass budget of the Greenland ice sheet (1992) and the fresh-water flux from Greenland including the coasts is determined using high-resolution regional climate model (REMO) simulations. The climate model is modified to include processes such as lateral flow over Greenland using a newly developed routing scheme, the effect of sub-grid-scale surface heterogeneity (orography) on surface temperature and runoff and an improved snow and ice model for the Greenland ice sheet for surface processes on the ice sheet. The high-resolution (0.125˚ grid size) simulations of accumulation and runoff fields are also assessed compared to the lower-resolution (0.5˚ grid size) simulations.

NASA's Program for Arctic Regional Climate Assessment (PARCA) includes measurements of ice velocity and ice thickness along the 2000 m elevation contour line in the western part of the ice sheet. Here we use these measurements together with published estimates of snow-accumulation rates to infer die mass balance, or rate of thickening/thinning, of the ice-sheet catchment area inland from the velocity traverse. Within the accuracy to which we know snow-accumulation rates, the entire area is in balance, but localized regions inland from Upernavik Isstrom and Jakobshavn Isbra both appear to be thickening by about 10 cm a-1.

Sediment production at a terrestrial section of the ice-sheet margin in West Greenland is dominated by debris released through the basal ice layer. The debris flux through the basal ice at the margin is estimated to be 12–45 m3 m−1 a−1. This is three orders of magnitude higher than that previously reported for East Antarctica, an order of magnitude higher than sites reported from in Norway, Iceland and Switzerland, but an order of magnitude lower than values previously reported from tidewater glaciers in Alaska and other high-rate environments such as surging glaciers. At our site, only negligible amounts of debris are released through englacial, supraglacial or subglacial sediment transfer. Glaciofluvial sediment production is highly localized, and long sections of the ice-sheet margin receive no sediment from glaciofluvial sources. These findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a...

Two SeaWinds radar scatterometers operated in tandem for 9 months in 2003, enabling resolution of the diurnal cycle in Greenland. This dataset provides unprecedented temporal resolution for Ku-band scattering observations of snow and ice melt conditions. As a step towards improved radar-based melt intensity estimation, a simple Markov melt–thaw model is developed to estimate melt and refreeze indices. The melt indices model is evaluated with the aid of a simple geophysical–electromagnetic model and validated by comparing tandem SeaWinds observations against automated weather station data. The new approach is used to analyse the melt conditions over the Greenland ice-sheet in 2003. The strengths and limitations of the approach are considered. 1.

The Greenland ice sheet contains enough water to raise sea levels by 7 m. However, its present mass balance and future contribution to sea level rise is poorly understood 1. Accelerated mass loss has been observed near the ice sheet margin, partly as a result of faster ice motion 2, 3, 4. Surface melt waters can reach the base of the ice sheet and enhance basal ice motion 5, 6. However, the response of ice motion to seasonal variations in meltwater supply is poorly constrained both in space and time. Here we ...

Eolian landforms are widespread alongside proglacial valley-sandurs in West Greenland and comprise low-relief sand sheets, climbing dunes, and upland loess. Sedimentary facies mainly reflect distance to outwash-source zones and the influence of vegetation cover. The sediments show stratification types typical for poorly to moderately vegetated sand-sheets, alternately laminated silt/peat sequences, and unstratified loess. Twenty-five accelerator mass spectrometry 14C dates provide

In recent years, two alarming trends in North Atlantic climate have been noted: an increase in the intensity and frequency of Atlantic hurricanes and a rapid decrease in Greenland ice sheet volume. Both of these phenomena occurred while a significant warming took place in North Atlantic sea surface temperatures (SSTs), thus sparking a debate on whether the warming is a consequence of natural climate variations, anthropogenic forcing, or both; and if both, what their relative roles are. Here models and observations are used to detect and attribute long-term (multidecadal) twentieth-century North Atlantic (NA) SST changes to their anthropogenic and natural causes. A suite of Intergovernmental Panel on Climate Change (IPCC) twentieth-century (C20C) coupled model simulations with multiple ensemble members and a signal-to-noise maximizing empirical orthogonal function analysis are used to identify a model-based estimate of the forced, anthropogenic component in NA SST variability. Compar...

In this study, we analysed the organic and inorganic content of the cryoconite holes along the altitudinal gradient at the lower elevations of the Russell glacier ablation zone in Southwest Greenland. We specifically focus on less studied industrial microscopic spheroidal carbonaceous particles (SCP; part of black carbon) to get more insights about their accumulation patterns on the glacier surface. We found no clear SCP distribution pattern, including concentration values. This outcome underlines the complexity of the ice margin zone and draws attention for further research on this topic with the inclusion of multiyear evaluation of SCP concentration at the even wider area that could possibly give results that can be compared to the emission source and long-way air pollution validation. In addition, our results indicate that during the summer of 2016, algae composition was formed of both green algae (Chlamydomonadaceae, Mesotaeniaceae) and cyanobacteria (Oscillatoriaceae). Green al...

Annual ice ablation has been measured at three locations at the margin of the Greenland ice sheet: Nordbogletscher (for 6 years: 1977–78 to 1982– 83), Qamanârssûp sermia (8 years: 1979–80 to 1986–87) and at Paakitsup Akuliarusersua (7 years: 1982–83 to the present). As the data sets cover different periods, it is difficult to compare ablation directly between the three sites. However, measured series at each site can be extended over the last 30 years (1961–90) by simulations using climatic data, and the extended data series can be compared. The pattern of calculated ablation variations at the three locations is remarkably similar with no sign of any trend towards increased ablation in recent years. There was generally low ablation from the mid-1970s to the mid-1980s that may explain the recent thickening of the ablation area which has been detected by satellite radar altimetry. Ablation varies substantially from year to year, e.g. with a standard deviation of the order of ±0.5 m wa...

We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs) in very high abundances, implying most likely either an unprecedented influx of extraterrestrial (ET) material or a cosmic impact event that occurred after the last glacial episode. From that layer, we extracted n-diamonds and hexagonal diamonds (lonsdaleite), an accepted ET impact indicator, at abundances of up to about 5×106 times background levels in adjacent younger and older ice. The NDs in the concentrated layer are rounded, suggesting they most likely formed during a cosmic impact through some process similar to carbon-vapor deposition or high-explosive detonation. This morphology has not been reported previously in cosmic material, but has been observed in terrestrial impact material. This is the first highly enriched, discrete layer of NDs observed in glacial ice anywhere, and its presence indicates that ice caps are important archives of ET events of varying magnitudes. Using ...

Lacustrine deposits from Lake Igaliku, South Greenland (N61°00'22'', W45°26'28'') were studied to investigate subarctic Holocene climate history. Analyses of the well dated sediment sequence (22 radiocarbone dates) used high-resolution grain size analysis, high-resolution geophysical (MSCL) and geochemical core scanning (XRF core scanner), X-ray radiography, ICP-MS geochemistry, DRX mineralogy and organic geochemistry. The 4 meters long sequence recovered from Lake Igaliku