Arctic Snowpack Research Articles

Redox transformations of mercury in an Arctic snowpack at springtime

We investigated the springtime temporal dynamics of both total mercury (Hg) and gaseous Hg in snowpacks from the High Arctic. In situ incubation experiments of snow samples indicated that the production of volatile mercury in snow (VMS) was photo-mediated and occurred in the first 3 cm of snow. The newly produced VMS (consisting mainly of elemental Hg) was partly oxidized back to Hg(II) when light intensity declined or in the absence of UV radiation, probably through a chain of reactions involving photo-induced radicals and organic compounds in the surface snow. During a 2 week monitoring of total Hg in surface snow, we observed a sharp increase in total Hg concentrations, reaching levels 11 times higher than background concentrations, likely as a result of an atmospheric mercury depletion event. Stratigraphic depth profiles indicated that this increase was restricted to the first 2 cm of the snowpack. Total Hg levels subsequently decreased by 92%, reaching background concentrations within 2 days after this event. The photoproduction rate of VMS calculated on the basis of this episode could account for subsequent daily loss of total Hg from the surface of the snowpack.

Investigating the occurrence of persistent organic pollutants (POPs) in the arctic: their atmospheric behaviour and interaction with the seasonal snow pack

POPs in the Arctic are the focus of international concern due to their occurrence and accumulation in Arctic food webs. This paper presents an overview of the major pathways into the Arctic and details contemporary studies that have focused on the occurrence and transfer of POPs between the major Arctic compartments, highlighting areas where there is a lack of quantitative information. The behaviour of these chemicals in the Arctic atmosphere is scrutinised with respect to long-term trends and seasonal behaviour. Subtle differences between the PCBs and OC pesticides are demonstrated and related to sources outside of the Arctic as well as environmental processes within the Arctic. Unlike temperate regions, contaminant fate is strongly affected by the presence of snow and ice. A description of the high Arctic snow pack is given and the physical characteristics that determine chemical fate, namely the specific surface area of snow and wind driven ventilation, are discussed. Using a well-characterised fresh snow event observed at Alert (Canadian high Arctic) [Atmos. Environ. 36(2002) 2767] the flux of γ-HCH out of the snow is predicted following snow ageing. Under conditions of wind (10 m/s) it is estimated that ≈75% of the chemical may be re-emitted to the atmosphere within 24 h following snowfall, compared with just ≈5% under conditions of no wind. The implications of this are raised and areas of further research suggested.

Gaseous mercury distribution in interstitial air of snow pack in Station Nord, Greenland. Evidence of permanent mercury depletion event in the air of snow during polar sunrise

Gaseous Elemental Mercury (Hg°) concentrations have been measured in Station Nord, Greenland in the air of the snowpack from February 25 th to march 15 th , 2002, during twilight and low solar irradiation periods. The concentration of Hg° decreases rapidly with depth in the snow pack air from ∼1.5 ng/m 3 outside to 0.1 ng/m 3 at 120 cm depth. Adsorption of mercury on snow could not explain such profile since temperature increases with depth (∼ -13 °C at 120 cm below the surface and -35 °C at the surface). Additionally calculations indicate that a poor fraction of Hg° could be adsorbed onto snow. A possible argument to explain such a decrease of Hg° with depth is to investigate homogeneous and/or heterogeneous chemistry occurring at the air/snow interface initiated by sun light. The Arctic snowpack is known to produce active bromine and chlorine species in the frame of interactions between sea-salts, ozone and acid species in the snow. The lifetime of Hg° is calculated on the basis of reactions with various reactive species in the gaseous phase existing in the interstitial air during twilight and under low solar irradiation periods, such as Brcl, Br 2 , HOBr, Br - , BrO and OH + . We assume that the decrease of Hg° concentration with depth is the result of the reaction between Hg° and Br and/or BrO, which give a lifetime for Hg°<∼0.8-8 hours based on known kinetic constants found in the recent literature. This decrease of mercury in the air of the snowpack indicates that during polar sunrise in the Arctic, mercury is probably accumulated in the snowpack on its oxidised form Hg(II), probably HgO. Therefore, the snowpack could be a sink of mercury in the Arctic in spring where a permanent Mercury Depletion Event (M.D.E.) could exist at polar sunrise.

How isotopic fractionation of snowmelt affects hydrograph separation

AbstractWe present the isotopic composition of meltwater samples from four seasonal snowpacks: a warm, maritime snowpack in California; a temperate continental snowpack in Vermont; a cold continental snowpack in Colorado; and an Arctic snowpack in Alaska. Despite the very different climate conditions the δ18O of meltwater from all four snowpacks increased as melting progressed. This trend is consistent with theoretical results that model isotopic exchange between water and ice as meltwater percolates through a snowpack.We have estimated the systematic error in the hydrograph separation if the isotopic composition of a snow core were used in place of that of meltwater. Assuming no error in the old water or stream water values, the error in the new water fraction depends on: (1) the isotopic difference between the snow core and the old water; (2) the isotopic difference between the snow core and the meltwater; and (3) the new water fraction contributing to the stream flow during a spring melt event. The error is large when snowmelt contributes a dominant fraction of the stream flow, which may be expected where infiltration of snowmelt is limited (e.g. permafrost, urban areas). A particular challenge will be how to incorporate the changes in isotopic composition of meltwater measured at a point into hydrograph separation models conducted at the watershed scale. Published in 2002 by John Wiley &amp; Sons, Ltd.

Acetaldehyde and acetone in the Arctic snowpack during the ALERT2000 campaign. Snowpack composition, incorporation processes and atmospheric impact

Acetaldehyde and acetone were measured in the seasonal snowpack near Alert (Nunavut, Canadian Arctic) in February and April 2000. Acetaldehyde concentrations in fresh surface snow in February were about 2.5 ppbw, decreasing to 1 ppbw after several days, while gas-phase acetaldehyde was about 75 pptv. Values for aged layers were 1.3–2.6 ppbw. In April, values for fresh snow were 5–10 ppbw, decreasing to 1–4 ppbw after several days (gas-phase values were around 230 pptv). Values for aged layers were in the range 0.7–3 ppbw. Snow-phase acetaldehyde represented 67% of the (snow+atmospheric mixing layer) system in winter and 94% in spring. Preliminary acetone measurements yielded values 1.5–3 ppbw in surface snow several days after deposition. To understand the kinetics of exchange of acetaldehyde between the air and the snow, its mechanism of incorporation in snow was investigated. Surface incorporation by adsorption, and volume incorporation by dissolution were considered. Winter and spring measurements showed very different trends, and spring concentrations were higher than winter ones, which is contrary to thermodynamic expectations. The photolytical production of acetaldehyde in the snowpack is proposed as an explanation.

Processes and properties of snow–air transfer in the high Arctic with application to interstitial ozone at Alert, Canada

Recent measurements of reactive chemical species in snow and firn at polar sites have served to underscore the importance of air–snow transfer processes in understanding changes in atmospheric chemistry. In this paper we present the first quantitative assessment of the impact of physical processes in the snow on air–snow chemical exchange of ozone. Measurements of snow properties, interstitial ozone concentrations, and an ozone kinetic depletion experiment results are presented along with two-dimensional model results of the diffusion and ventilation processes affecting gas exchange at Alert, Nunavut, Canada. The Arctic snowpack at Alert will allow rapid exchange of gases with the atmosphere. Even under natural ventilation conditions with moderate winds, the entire pack is exposed to air movement and therefore available for chemical exchange processes. Both measurements and model results indicate that ozone undergoes rapid depletion in the top centimeters of the snow—approximately within the top 5 cm under diffusion alone, and in the top 10 cm or less during ventilation. Due to the higher permeability of the snowpack on the sea ice site as compared to the terrestrial site, it is possible that chemical exchange processes could be even more rapid over the sea ice in the greater Arctic than at the terrestrial site. A quantitative discussion of complications that arise from current firn air sampling techniques is presented and possible improvements for future measurements are suggested.

Structure, microphysics, and surface area of the Arctic snowpack near Alert during the ALERT 2000 campaign

The seasonal snowpack at Alert (North coast of Ellesmere Island, 82°29.94′N, 62°20.55′W) was studied in February and April 2000, on land and on sea ice. The stratigraphy was studied, and the density and specific surface area (SSA) of each snow layer were measured. SSA was measured by CH 4 adsorption at 77 K using a volumetric method. On land, the snowpack was 10–50 cm thick and consisted of a depth hoar layer covered by one or more hard wind-packed layers with densities between 0.35 and 0.52. These were sometimes separated by soft layers of more or less faceted crystals. The surface was covered by recent precipitation and surface hoar. The stratigraphy on sea ice was more variable, with numerous hard wind-packed layers alternating with soft layers of depth hoar or faceted crystals. SSA values ranged from 125 cm 2/g for depth hoar to 1500 cm 2/g for diamond dust and dendritic snow. The total surface area of the snowpack was calculated from the thickness, density, and SSA of each layer, and ranged from 1160 to 3710 m 2 of snow surface area per m 2 of ground. These values were used to estimate the potential impact of the snowpack on atmospheric chemistry, by adsorption/desorption of trace gases. Using the example of acetone, whose adsorption behavior on ice is estimated, it is found that the snowpack may sequester most of the acetone of the (snow+boundary layer) system most of the year. The release during metamorphism of trace gases dissolved in snow is also discussed. We propose that the frequency and intensity of wind storms will strongly affect the release of trace gases, as this will determine whether intense metamorphism leading to depositional depth hoar can happen.

Modelling the fate of non-polar organic chemicals during the melting of an Arctic snowpack

Recent advances in the understanding of the interactions between non-polar organic chemicals and frozen water have revealed the immense importance of the ice-air interface and the possibility of quantitatively treating the adsorption process on the ice surface in terms of chemical-specific interfacial partition coefficients and the snow specific surface area. A simple fugacity-based chemical fate model is used to describe quantitatively the behaviour of selected non-polar organic contaminants during snowpack melting, namely atmosphere-snow exchange, redistribution within the snowpack and draining with meltwater. The simulations are evaluated using field data on snowpack and meltwater concentrations of these chemicals measured in a small watershed in the Canadian Arctic during the melting period of 1993. The model reproduced the observed preferential elution of hexachlorocyclohexanes in the first meltwater fractions, and the relative retention of polychlorinated biphenyls within the snowpack. The model calculations indicate that the specific surface area of the ice crystals and the air-ice and air-water partition coefficients of the chemical are key parameters controlling the extent and timing of chemical loss with the meltwater. For particle-sorptive substances, the fate of particlcs during snowmelt must also be considered. Uncertainty in describing interfacial partitioning and the behaviour of particles during melting presently limits the capabilities of models to simulate and ultimately predict meltwater concentrations of non-polar organic contaminants.

C2-C7 Hydrocarbon Concentrations in Arctic Snowpack Interstitial Air: Potential Presence of Active Br within the Snowpack

Samples of interstitial air from within the snow pack on an ice floe on the Arctic Ocean were collected during the April 1994 Polar Sunrise Experiment. The concentrations of C2-C7 hydrocarbons are reported for the first time in the snow pack interstitial air. Alkane concentrations tended to be higher than concentrations in free air samples above the snow but very similar to winter measurements at various locations in the Arctic archipelago. However, ethyne concentrations in both interstitial and free air were highly correlated with ozone mixing ratios, consistent with previous demonstrations of the effects of Br atom chemistry. The analysis of total bromine within the snow pack indicate an enrichment in total Br at the interface layer between snow and free troposphere. The mixing ratios of some brominated compounds, such as CHBr3 and CHBr2Cl, are found to be higher in this top layer of snow relative to the boundary layer. Results were inconclusive due to the limited number of samples, but suggest the possible presence of active bromine in the snow pack and also that some differences exist between chemical reactions occurring in interstitial air compared to air in the boundary layer.

Autocatalytic release of bromine from Arctic snow pack during polar sunrise

Measurements and modeling studies strongly suggest that spring time depletion of ozone in the Arctic planetary boundary layer (PBL) is due to catalytic destruction by bromine atoms. However, the source of the bromine is uncertain. In this note, we propose that the source of the bromine at polar sunrise is the snow pack on the ice covering Arctic ocean and that it is released auto‐catalytically, stimulated by a bromine seed from one of the brominated organic compounds, such as CHBr3, by photolysis. In this manner ∼100 pptv of bromine can be transferred to the atmosphere where it can reside in the gas phase or, by scavenging, be partitioned in the aerosol or ice crystal phase. Moreover, it appears that heterogeneous recycling of bromine may be a process that self‐terminates as ozone depletes to low levels. We also have included chlorine chemistry in the model in order to simulate inferred levels of chlorine atoms. This is important as it results in the production of HCHO which acts to convert post ozone depletion active bromine into HBr which is then returned to the snow pack or scavenged by aerosols or ice crystals.

Water soluble organic constituents in Arctic aerosols and snow pack

Eight water‐soluble organic anions were measured in 70 aerosol samples and 10 snow samples at Barrow, Alaska in March–April, 1989. The ranking of the ions in aerosols according to total (coarse+fine aerosol) median concentrations was acetate (44 ng m−3), oxalate (27), benzoate (23), formate (22), propionate (6), methanesulfonate (5), lactate (4), and pyruvate (4). When added up, the median organic anion mass was 156 ng m−3. The organic anions/nssSO4= mass ratio had a median of 0.18 and 0.07 in the coarse (&gt;1 μm) and fine (&lt;1 μm) size fractions, respectively, but can be very high on occasions. On average, the organic anions made up more than 10% of the water‐soluble aerosol mass. A similar ranking in concentration was also found for the organic ions in the snow pack samples. The organic anion/nssSO4= mass ratio in these samples was &gt;0.5, substantially higher than in aerosols.

Sulfur in particles in Arctic hazes derived from airborne in situ and lidar measurements

Quantitative information is needed on arctic hazes in order to determine their effects on the radiation budget, clouds, the albedo and chemical properties of the arctic snowpack, and on ecosystems in the Arctic. Using airborne observations from lidar, and in situ measurements of particle light‐scattering coefficients, aerosol size distributions and meteorological parameters, we have related backscattering measured by the lidar to the mass concentrations of particles in two mesoscale haze layers encountered in the North American Arctic. Assuming that the haze particles were composed of H2SO4 in thermodynamic equilibrium with the ambient air, good agreement is obtained between sulfur concentrations measured on filters and those derived from the particle size distributions and lidar measurements. Time‐height cross sections are shown of the airborne concentrations of sulfur in particles derived from lidar backscatter measurements in a haze layer. The average concentrations of sulfur in accumulation mode particles in the two haze layers were 0.3 and 0.4 μg m−3, and the maximum concentration was ∼3 μg m−3, with substantial horizontal and vertical variability. We estimate lower limits for the total sulfur in particles in the two haze layers to be ∼3x;104 and ∼1x105 kg, respectively.

The buffering effect of snow cover to the impact of vehicles on the soil and vegetation cover in the north

Abstract The main properties of the arctic snowpack are analyzed, together with its role in protecting the soil and vegetation cover from mechanical impacts of vehicles, especially tracked all‐terrain vehicles. It was shown that at the start of snowmelt, snow is compacted in the tracks, thus forming a unique protective buffer where the snow is relatively dry. The characteristics of the process of snow compaction in the track, protecting the vegetation cover from the direct impact of metal grouser plates of Soviet all‐terrain vehicles are presented. The prospects of reducing the negative impact of vehicles on the soil and vegetation cover where a snow cover exists are discussed.

Soot in the Arctic snowpack: a cause for perturbations in radiative transfer

Recent data collected in the Arctic have demonstrated the transport of atmospheric aerosol of anthropogenic origin into that region. Concern over the radiative effect of the highly-absorbing soot component of this aerosol has resulted in a variety of atmospheric sampling efforts aimed at assessing the climatic impact of this component. However, little attention has been given to the measurement of soot deposited on the Arctic snowpack and the resulting perturbation of snow albedo, snowmelt rates and radiative transfer. Here we report measurements of light-absorbing material in the Arctic snowpack for longitudes from 25 E to 160 W. The contributions to light absorption due to natural crustal and soot aerosol are identified by their wavelength dependence. Reductions in Arctic snow albedo of one to several percent appear probable for the soot/ice mass fractions obtained to date. Estimates of the impact of this reduced albedo on the Arctic radiation budget over a season are shown to approximately equal that of the Arctic haze itself. The absorption of shortwave radiation by the springtime snowpack is estimated to be 5–10 % higher than that of soot-free snow for this data.

Basal Ice in High Arctic Snowpacks

In late May or June, meltwater percolating through cold arctic snowpacks often refreezes as ice layers. In the presence of a cold substrate, such layers form at the base of the snowpack. This basal ice continues to grow so long as meltwater supply is sustained and the substrate remains below 0?C. Upon exposure, the ice is destroyed by sublimation and surface melting or by thermal and mechanical erosion by water which runs on, in or under the ice. Multiyear ice is preserved when the incompletely melted basal ice is buried by subsequent snowfall or by a layer of earth materials. Multiple freezing and melting of water in basal ice layers complicate the snowmelt-runoff relationship in three principal ways. Where basal ice is abundant, the melt is prolonged and contributes to streamflow during the drier summer months. During breakup, the basal ice in stream beds tends to increase flow velocity and, consequently, the capacity for sediment transport. However, a basal ice layer in the channel will reduce opportunities for erosion.

Basal Ice in High Arctic Snowpacks

Basal Ice in High Arctic Snowpacks

Occurrence of Ice Layers at the Base of High Arctic Snowpacks

The formation of an ice layer at the base of to dissipate the latent heat released by the reHigh Arctic snowpacks is due to a refreezing freezing process, but through such latent heat of the meltwater percolating to the snow- transfer the warming of the active layer is acground interface. A cold substrate is required celerated.

Occurrence of Ice Layers at the Base of High Arctic Snowpacks

Occurrence of Ice Layers at the Base of High Arctic Snowpacks

Analysis of Error in the Determination of Snow Storage for Small High Arctic Basins

Abstract Water balance studies in tundra regions require accurate snowfall data but weather station records often underestimate basin snow storage. However, snow storage can be determined by snow surveys conducted prior to the melt period because Arctic snowpacks do not melt during winter. Topography strongly controls snow distribution. A basin can be subdivided into various terrain types and the snow survey then establishes the snow characteristics of each terrain type so that basin snow storage is obtained as their areally weighted mean. Such a survey was carried out in small basins near Resolute, Northwest Territories, traversing different types of terrain. The results confirmed that weather station snowfall grossly underestimated basin snow storage. Since it is also desirable to simplify future snow surveys by reducing the number of transects, an error analysis was performed to determine the error resulting from a grouping of terrain types. It was found that both maximum and mean error increased as th...

Hydrology of a small Canadian High Arctic basin during the snowmelt period

Investigations were carried out in a small Canadian High Arctic basin to determine the influence of snowmelt on the hydrologic behaviour of the active layer and on basin discharge. The snowpack was characteristically thin but rapid melting in late June released a substantial amount of water to a thinly-thawed active layer, resulting in overland flow or standing water conditions. Owing to an uneven distribution of basin snow cover, the meltwater source area was highly variable both in time and in space, thus giving rise to different active layer hydrologic regimes in different parts of the basin. Slopes with a snowbank often had a high water table while the water table in the slopes bared of snow showed a gradual decline. Since streamflow represents a basinwide integration of these two active layer hydrologic regimes, there was a progressive reduction in daily peak flow accompanied by a prolonged lag time between daily discharge and snowmelt as the basin snow storage decreased. Spatially, inhomogeneity of snow cover also affected the downstream changes in discharge so that the ratio of discharge between two gauging stations depends on the relative magnitudes of snowmelt, evaporation and storage requirements of the two sub-basins. Rapid melting of an unevenly distributed Arctic snowpack therefore strongly influences the hydrologic behaviour of the active layer which in turn affects the streamflow regime.