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Concentration measurements of nitric oxide (NO), nitrogen dioxide (NO 2), nitrous acid (HONO), nitric acid (HNO3), formaldehyde (HCHO), hydrogen peroxide (H2O2), formic acid (HCOOH) and acetic acid (CH3COOH) were performed in air filtered through the pore spaces of the surface snowpack (firn air) at Summit, Greenland, in summer 2000. In general, firn air concentrations of NO, NO2, HONO, HCHO, HCOOH, and CH3COOH were enhanced compared to concentrations in the atmospheric boundary layer above the snow. Only HNO3 and H 2O2 normally exhibited lower concentrations in the firn air. In most cases differences were highest during the day and lowest during nighttime hours. Shading experiments showed a good agreement with a photochemical NOx source in the surface snow. Patterns of H 2O2, CH3COOH, and HNO3 observed within the surface snow-firn air system imply that the number of molecules in the snow greatly exceeded that in the firn air. Deduced partitioning indicates that the largest fractions of the acids were present at the ice grain-air interface. In all cases, the number of molecules located at the interface was significantly higher than the amount in the firn air. Therefore, snow surface area and surface coverage are important parameters, which must be considered for the interpretation of firn air concentrations. © 2004 Elsevier Ltd. All rights reserved.

Measurements at Summit, Greenland, performed from June-August 1999, showed significant enhancement in concentrations of several trace gases in the snowpack (firn) pore air relative to the atmosphere. We report here measurements of alkenes, halocarbons, and alkyl nitrates that are typically a factor of 2-10 higher in concentration within the firn air than in the ambient air 1-10m above the snow. Profiles of concentration to a depth of 2m into the firn show that maximum values of these trace gases occur between the surface and 60cm depth. The alkenes show highest pore mixing ratios very close to the surface, with mixing ratios in the order ethene>propene>1-butene. Mixing ratios of the alkyl iodides and alkyl nitrates peak slightly deeper in the firn, with mixing ratios in order of methyl>ethyl>propyl. These variations are likely consistent with different near-surface photochemical production mechanisms. Diurnal mixing ratio variations within the firn correlate well with actinic flux for all these gases, with a temporal offset between the solar maximum and peak concentrations, lengthening with depth. Using a snow-filled chamber under constant flow conditions, we calculated production rates for the halocarbons and alkenes that ranged between 103-105 and 106molecules cm-3s-1, respectively. Taken together, these results suggest that photochemistry associated with the surface snowpack environment plays an important role in the oxidative capacity of the local atmospheric boundary layer, and influences post-depositional chemistry, which in turn may affect the interpretation of certain aspects of the ice core records collected previously at Summit. © 2002 Elsevier Science Ltd. All rights reserved.

WindSat has systematically collected the first global fully polarimetric passive microwave data over both land and ocean. As the first spaceborne polarimetric microwave radiometer, it was designed to measure ocean surface wind speed and direction by including the third and fourth Stokes parameters, which are mostly related to the asymmetric structures of the ocean surface roughness. Although designed for wind vector retrieval, WindSat data are also collected over land and ice, and this new data has revealed, for the first time, significant land signals in the third and fourth Stokes parameter channels, particularly over Greenland and the Antarctic ice sheets. The third and fourth Stokes parameters show well-defined large azimuth modulations that appear to be correlated with geophysical variations, particularly snow structure, melting, and metamorphism, and have distinct seasonal variation. The polarimetric signatures are relatively weak in the summer and are strongest around spring. This corresponds well with the formation and erosion of the sastrugi in the dry snow zone and snowmelt in the soaked zone. In this paper, we present the full polarimetric signatures obtained from WindSat over Greenland, and use a simple empirical observation model to quantify the azimuthal variations of the signatures in space and time. Index Terms--Greenland ice sheet, ice, polarimetric microwave radiometry, snow, WindSat.

Direct observations of the size of the Greenland Ice Sheet during Quaternary interglaciations are sparse yet valuable for testing numerical models of ice sheet history and sea level contribution. Recent measurements of cosmogenic nuclides in bedrock from beneath the Greenland Ice Sheet collected during past deep drilling campaigns reveal that the ice sheet was significantly smaller, and perhaps largely absent, sometime during the past 1.1 million years. These discoveries from decades-old basal samples motivate new, targeted sampling for cosmogenic nuclide analysis beneath the ice sheet. Current drills available for retrieving bed material from the US Ice Drilling Program require <700 m ice thickness and a frozen bed, while quartz-bearing bedrock lithologies are required for measuring a large suite of cosmogenic nuclides. We find that these and other requirements yield only ~3.4% of the Greenland Ice Sheet bed as a suitable drilling target using presently available technology. Additional factors related to scientific questions of interest are which areas of the present ice sheet are the most sensitive to warming, where a retreating ice sheet would expose bare ground rather than leave a remnant ice cap, and which areas are most likely to remain frozen bedded throughout glacial cycles and thus best preserve cosmogenic nuclides? Here we identify locations beneath the Greenland Ice Sheet that are best suited for potential future drilling and analysis. These include sites bordering Inglefield Land in northwestern Greenland, near Victoria Fjord and Mylius-Erichsen Land in northern Greenland, and inland from the alpine topography along the ice margin in eastern and northeastern Greenland. [ABSTRACT FROM AUTHOR]

Change is ubiquitous in Earth's history, and evidence is clear that Earth's climate is changing rapidly now. The harbingers of change can be seen vividly in the polar regions. The [...]

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. [ABSTRACT FROM AUTHOR]