Northwestern Greenland Ice Sheet Research Articles

The Winds of Change: Foehn Drive Intense Melt

Atmospheric rivers on the northwestern Greenland Ice Sheet are driving dry winds across northeastern Greenland, forcing extreme short-term melt.

Inclusions in ice layers formed by melting and refreezing processes in a Greenland ice core

AbstractIn recent decades, surface melting on the inland Greenland ice sheet has increased, leading to significant meltwater-refreezing in the snow and firn. Increased knowledge of the physical and chemical characteristics of these melt features (i.e., ice layers) is needed to help estimate future global sea-level rise. Here, using a combination of microscopy and spectroscopy, we investigate the size, shape, location, and chemical compositions of inclusions in 12 ice layers of the SIGMA-A ice core in the northwestern Greenland ice sheet (78°03′06″N, 67°37′42″W, 1490 m a.s.l.). In the ice layers, we found inclusions exceeding 30 μm diameter that could only be formed by melting–refreezing, which we classify into columnar-, particle-, and rod-like inclusions. We propose that the smaller columnar- and particle-like inclusions of solid Na2SO4⋅10H2O and CaSO4⋅2H2O form first, within the ice grains, followed by the larger rod-like inclusions of brines with mainly Na+and Cl−in grain boundaries. Our results suggest a new proxy that may help identify past warm climates in deeper ice cores in Greenland and for studying future ice sheet melting behavior.

The Detection of Seismicity on Icy Ocean Worlds by Single‐Station and Small‐Aperture Seismometer Arrays

AbstractFuture missions carrying seismometer payloads to icy ocean worlds will measure global and local seismicity to determine where the ice shell is seismically active. We use two locations, a seismically active site on Gulkana Glacier, Alaska, and a more seismically quiet site on the northwestern Greenland Ice Sheet as geophysical analogs. We compare the performance of a single‐station seismometer against a small‐aperture seismic array to detect both high (>1 Hz) and low (<0.1 Hz) frequency events at each site. We created catalogs of high frequency (HF) and low frequency (LF) seismicity at each location using an automated short‐term average/long‐term average technique. We find that with a 1‐m small‐aperture seismic array, our detection rate increased (9% for Alaska and 46% for Greenland) over the single‐station approach. At Gulkana, we recorded an order of magnitude greater HF events than the Greenland site. We ascribe the HF events sources to a combination of icequakes, rockfalls, and ice‐water interactions, while very HF events are determined to result from bamboo poles that were used to secure gear. We further find that local environmental noise reduces the ability to detect LF global tectonic events. Based upon this study, we recommend that (a) future missions consider the value of the expanded capability of a small array compared to a single station, (b) design detection algorithms that can accommodate variable environmental noise, and (c) assess the potential landings sites for sources of local environmental noise that may limit detection of global events.

Effect of ice sheet thickness on formation of the Hiawatha impact crater

The discovery of a large putative impact crater buried beneath Hiawatha Glacier along the margin of the northwestern Greenland Ice Sheet has reinvigorated interest into the nature of large impacts into thick ice masses. This circular structure is relatively shallow and exhibits a small central uplift, whereas a peak-ring morphology is expected. This discrepancy may be due to long-term and ongoing subglacial erosion but may also be explained by a relatively recent impact through the Greenland Ice Sheet, which is expected to alter the final crater morphology. Here we model crater formation using hydrocode simulations, varying pre-impact ice thickness and impactor composition over crystalline target rock. We find that an ice-sheet thickness of 1.5 or 2 km results in a crater morphology that is consistent with the present morphology of this structure. Further, an ice sheet that thick substantially inhibits ejection of rocky material, which might explain the absence of rocky ejecta in most existing Greenland deep ice cores if the impact occurred during the late Pleistocene. From the present morphology of the putative Hiawatha impact crater alone, we cannot distinguish between an older crater formed by a pre-Pleistocene impact into ice-free bedrock or a younger, Pleistocene impact into locally thick ice, but based on our modeling we conclude that latter scenario is possible.

Reconstruction of Sea Ice Concentration in Northern Baffin Bay Using Deuterium Excess in a Coastal Ice Core From the Northwestern Greenland Ice Sheet

AbstractVariations in the conditions of sea ice in the northern part of Baffin Bay and North Open Water polynya influence human activity in northwestern Greenland through oceanic circulation and heat balance between air and sea. To evaluate the impact of variations in sea ice conditions on the surrounding environment, it is important to understand the mechanism of sea ice variations over long periods. In this study, we estimated the age of the SIGMA‐A ice core collected northwestern Greenland Ice Sheet and researched the relationship between annual or seasonal deuterium excess (d‐excess) and seasonal sea ice concentration. We found that a temporal variation in the spring d‐excess in the ice core negatively correlated significantly with that of sea ice concentration in February–April in northern Baffin Bay from 1979–2005 (r = −0.61, p < 0.001). Using this relationship, we reconstructed the temporal variations in sea ice concentrations for 100 years from the ice core drilled in the northwestern Greenland Ice Sheet. The sea ice concentration in the early twentieth century was lower than that in the present. The decrease in sea ice concentration was consistent with analytical results for marine sediments obtained from Baffin Bay. We also suggested that the sea ice concentration was controlled by atmospheric conditions from the 1920s to 1940s based on examinations of correlations with the North Atlantic Oscillation index and air temperature in Ilulissat and by oceanographic conditions from 1945–1955, 1959–1969, and 1982–1992 based on the Atlantic Multidecadal Oscillation index and meridional heat transport to western Greenland.

The Northwestern Greenland Ice Sheet During The Early Pleistocene Was Similar To Today

AbstractThe multi‐million year history of the Greenland Ice Sheet remains poorly known. Ice‐proximal glacial marine diamict provides a direct but discontinuous record of ice sheet behavior; it is underutilized as a climate archive. Here, we present a novel multiproxy analysis of an Early Pleistocene marine diamict from northwestern Greenland. Low cosmogenic nuclide concentrations indicate minimal near‐surface exposure, similar to modern terrestrial sediment. Detrital apatite (U‐Th‐Sm)/He (AHe) ages all predate glaciation by >150 million years, suggesting the northwestern Greenland Ice Sheet had, by 1.9 Ma, not yet incised fjords of sufficient depth to excavate grains with young AHe ages. The diamict contains terrestrial plant leaf wax, likely from land surfaces surrounding the ice sheet. These data indicate that a persistent, dynamic ice sheet existed in northwestern Greenland by 1.9 Ma and that diamict is a useful archive of ice sheet history and process.

500–2000-MHz Brightness Temperature Spectra of the Northwestern Greenland Ice Sheet

An ultra-wideband radiometer has been developed to measure subsurface properties of the cryosphere including ice sheets and sea ice. The radiometer measures brightness temperature spectra from 0.5 to 2 GHz using 12 channels, each of which measures scene brightness temperatures over an ~88-MHz bandwidth resolved into 0.24-MHz intervals. The instrument was flown over northwestern Greenland in September 2016 and acquired the first, wideband, low-frequency brightness temperature spectra over the ice sheet and coastal region. The results reveal strong spatial and spectral variations that correlate well with the physical properties of the surface encountered along the flight path, which started over ocean, then passed the rock near the coast, and then up onto the ablation, wet, percolation, and dry snow zones of the interior ice sheet. In particular, strong spectral responses in percolation and dry snow zones are observed and plausibly explained by varying the distribution of horizontal density layers and isolated icy bodies in the upper portion of the firn. The success of the airborne deployment of the instrument and subsequent implementation of algorithms to limit radio frequency interference in unprotected bands is motivating continued airborne investigations as well as stimulating research into the feasibility of a spaceborne instrument.

Field activities at the SIGMA-A site, northwestern Greenland Ice Sheet, 2017（2017年グリーンランド氷床北西部SIGMA-Aサイトにおける観測報告）

Field activities at the SIGMA-A site, northwestern Greenland Ice Sheet, 2017（2017年グリーンランド氷床北西部SIGMA-Aサイトにおける観測報告）

The abandoned ice sheet base at Camp Century, Greenland, in a warming climate

AbstractIn 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 75 years, 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.

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

Abstract. 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 method (IOM). The IOM quantifies the difference between the mass input and output of the GrIS by studying the surface mass balance (SMB) and the ice discharge (D). We use the Regional Atmospheric Climate Model version 2.3 (RACMO2.3) to model the SMB and derive the ice discharge from 12 years of high-precision ice velocity and thickness surveys. We use a simulation model to quantify and correct for GRACE approximation errors in mass change between different subregions of the GrIS, and investigate the reliability of pre-1990s ice discharge estimates, which are based on the modeled runoff. We find that the difference between the IOM and our improved GRACE mass change estimates is reduced in terms of the long-term mass change when using a reference discharge derived from runoff estimates in several subareas. In most regions our GRACE and IOM solutions are consistent with other studies, but differences remain in the northwestern GrIS. We validate the GRACE mass balance in that region by considering several different GIA models and mass change estimates derived from data obtained by the Ice, Cloud and land Elevation Satellite (ICESat). We conclude that the approximated mass balance between GRACE and IOM is consistent in most GrIS regions. The difference in the northwest is likely due to underestimated uncertainties in the IOM solutions.

グリーンランド北西氷床(SIGMA-D)アイスコアを用いた過去157年間の気候復元

グリーンランド北西氷床(SIGMA-D)アイスコアを用いた過去157年間の気候復元

Mineral dust and major ion concentrations in snowpit samples from the NEEM site, Greenland

Polar ice sheets conserve atmospheric aerosols at the time of snowfall, which can be used to reconstruct past climate and environmental conditions. We investigated mineral dust and major ion records in snowpit samples obtained from the northwestern Greenland ice sheet near the North Greenland Eemian Ice Drilling (NEEM) camp in June 2009. We analyzed the samples for mineral dust concentrations as well as stable water isotopes (δ18O, δD, and deuterium excess) and major ions (Cl−, SO42-, methanesulfonic acid (MSA), Na+, and Ca2+). Seasonal δ18O and δD cycles indicate that the snowpit samples covered a six-year period from spring 2003 to early summer 2009. Concentrations of mineral dust, nss-Ca2+, and nss-SO42- showed seasonal deposition events with maxima in the winter–spring layers. On the other hand, the Cl−/Na+ ratio and the concentrations of MSA exhibited maxima in the summer layers, making them useful indicators for the summer season. Moreover, an anomalous atmospheric mineral dust event was recorded at a depth of 165–170 cm corresponding to late winter 2005 to spring 2006. A back trajectory analysis suggests that a major contributor to the Greenland aerosol was an air mass passing over the Canadian Arctic and North America. Several trajectories point to Asian regions as a dust source. The mineral dust deposited at NEEM was strongly influenced by long-range atmospheric transport and dust input from arid source areas in northern China and Mongolia.

Glaciological and meteorological observations at the SIGMA-D site, northwestern Greenland Ice Sheet（グリーンランド氷床北西部SIGMA-Dサイトにおける雪氷・気象観測）

Glaciological and meteorological observations at the SIGMA-D site, northwestern Greenland Ice Sheet（グリーンランド氷床北西部SIGMA-Dサイトにおける雪氷・気象観測）

Spatial variations of δ18O and ion species in the snowpack of the northwestern Greenland ice sheet

To determine the transport processes of water vapor and aerosols over the northwestern Greenland ice sheet, we undertook a glaciological observation at a coastal site on the northwestern part of the ice sheet and revealed spatial variations in δ 18 O and in the concentrations of chemical substances in surface snow and the snowpack. On the outlet glacier (the Meehan glacier), water vapor and sea salt were transported from the coast. On the inland ice sheet in northwestern Greenland, water vapor, mineral dust, anthropogenic substances such as NO 3 - and SO4 2- , and CH3SO3 - from marine phytoplankton were transported from the west coast of Greenland via the central part of the Greenland ice sheet. 18 O, ion species

Improved ice loss estimate of the northwestern Greenland ice sheet

[1] 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 a significant acceleration in mass loss at elevations above 1200 m. Both the improved mass loss estimate along the ice sheet margin and the acceleration at higher elevations have implications for predictions of the elastic adjustment of the lithosphere caused by present-day ice mass changes. Our study shows that the use of ICESat data alone to predict elastic uplift rates biases the predicted rates by several millimeters per year at GPS locations along the northwestern coast.