Snow Column Research Articles

The weathering of aeolian dusts in alpine snows

The chemistry of precipitation (snow and rainfall), snow cover and meltwaters was studied at a French alpine site during the winter-spring seasons of 1986–1987 and 1987–1988. Both acid ( < pH 5.6) and alkaline ( > pH 5.6) deposition events occurred. The strong-acid anions, SO 4 and BO 3, contributed to the acidity of precipitation but NO 3 was the principal anion associated with acidic snowfall. Many alkaline snowfalls are associated with airborne calcareous dusts from regional sources. The most alkaline snowfall, however, was associated with dust from the Sahara Desert. The weathering of dusts in the snow cover during melt leads to the consumption of acidity and an increase in the pH of meltwaters. The results of both field and laboratory experiments show that inputs of calcareous dusts by local aeolian erosion and transport can contribute significantly to the neutralization process. The laboratory experiments also show that the size and distribution of dusts in the snow cover have an effect on the degree of neutralization. Dust in the lower strata of snow cover is more efficient in neutralizing the acidity of meltwaters than dust in the upper strata. The relationship between the distribution of dust and its efficiency to neutralize the acidity of meltwaters can be explained by the kinetics of calcite dissolution under conditions of progressive decreases in the acidity of leached snow and the partial pressures of CO 2 within the snow column during the melt process.

Characteristics and distribution patterns of snow and meteoric ice in the Weddell Sea and their contribution to the mass balance of sea ice

Abstract. Based on snow- and ice-thickness measurements at &gt;11 000 points augmented by snow- and icecore studies during 4 expeditions from 1986 - 92 in the Weddell Sea, we describe characteristics and distribution patterns of snow and meteoric ice and assess their importance for the mass balance of sea ice. For first-year ice (FY) in the central and eastern Weddell Sea, mean snow depth amounts to 0.16 m (mean ice thickness 0.75 m) compared to 0.53 m (mean ice thickness 1.70 m) for second-year ice (SY) in the northwestern Weddell Sea. Ridged ice retains a thicker snow cover than level ice, with ice thickness and snow depth negatively correlated for the latter, most likely due to aeolian redistribution. During the different expeditions, 8, 15, 17 and 40% of all drill holes exhibited negative freeboard. As a result of flooding and brine seepage into the snow pack, snow salinities averaged 4‰. Through 18O measurements the distribution of meteoric ice (i.e. precipitation) in the sea-ice cover was assessed. Roughly 4% of the total ice thickness consist of meteoric ice (FY 3%, SY 5%). With a mean density of 290 kg/m3, the snow cover itself contributes 8% to total ice mass (7% FY, 11% SY). Analysis of ∆18O in snow indicates a local maximum in accumulation in the 65 to 75°S latitude zone. Hydrogen peroxide in the snow has proven useful as a temporal tracer and for identification of second-year floes. Drawing on accumulation data from stations at the Weddell Sea coast, it becomes clear that the onset of ice growth is important for the evolution of ice thickness and the interaction between ice and snow. Loss of snow to leads due to wind drift may be considerable, yet is reduced owing to metamorphic processes in the snow column. This is confirmed by a comparison of accumulation data from coastal stations and from snow depths over sea ice. Temporal and spatial accumulation patterns of snow are shown to be important in controlling the sea-ice cover evolution.

Microwave brightness temperatures of laboratory‐grown undeformed first‐year ice with an evolving snow cover

A laboratory experiment was performed to study a case in which a snow cover introduced on an established saline ice sheet resulted in physical processes that significantly affected the microwave brightness temperature over a period of a few weeks. Saline ice was grown to a thickness of 240 mm in an outdoor pool at ambient air temperatures. Precipitation, was allowed by use of a movable roof. Brightness temperatures were measured at 10 and 85 GHz before and for several weeks after one snowfall. During the same period, the vertical temperature profile and crystallography of the snow column, as well as ice structure and salinity at the original ice surface, were monitored. The 10‐GHz brightness temperature dropped by as much as 100 K from bare ice values during the first few days after the snow fell, because of a saline slush layer which formed at the bottom of the snow. The saline water in the slush layer apparently was forced up through the unbroken ice by the added snow load. The slush layer eventually froze into an added highly emissive frazil ice layer which raised the 10‐GHz brightness temperature to above its bare ice values. The frazil ice layer was similar to superimposed frazil ice observed on freezing leads in high‐latitude ice packs. The 85‐GHz brightness temperature did not change from bare ice values soon after the snowfall but dropped by about 40 K over the following 20 days. We use a simple dielectric model to qualitatively test the dependence of 10‐GHz brightness temperature on relevant physical conditions at the bottom of the snow. At 85 GHz the snow layer was optically thick, and the brightness temperature drop was probably the result of increased volume scatter from the growing snow grains.

A laboratory investigation of the leaching of solute from snowpack by rainfall

AbstractUnder controlled laboratory conditions, artificial rain leaches solute from snow columns, and gives rise to leachate with a composition similar to snowmelt, in addition to the solute initially present in the artificial rain. the initial concentration of ions in the leachate, normalized to the concentration of ions found in the original snow and corrected for the solute present in the artificial rain, is similar to those reported in other laboratory and field studies of snowmelt composition, but there is some evidence that the concentration of leached ions declines more rapidly than during snowmelt. Similarly, as in snowmelt studies, not all ions are leached with the same efficiency. Bearing in mind the confounding influences of snow crystal morphology and snow column hydrology, it seems likely that rain will leach solute from snowpack during rain‐on‐snow events, in a manner similar to leaching by snowmelt, and that the precise composition of the leachate will depend on the hydrological routing of rain‐meltwater mixtures through the snowpack.

A Theoretical Determination of the Characteristic Equation of Snow in the Pendular Regime

AbstractRecent mathematical models treat a natural snow-pack as a mixture body consisting of solid ice grains, liquid water, and a gas made up of air and water vapour. Such a model requires two independent constitutive equations for the two independent volume fractions. However, so far only one equation, a power law relating the liquid-water content to capillary pressure, has been suggested, by analogy with the so-called “characteristic” equation for liquid water in soils. Experimental data from drainage tests on snow columns may be used to determine the characteristic equation for snow for relatively high water contents. However, the experimental method is not valid when water exists in isolated inclusions in the snow, i.e. in the pendular regime. In this paper a theoretical method is used to derive two independent volume-fraction laws for snow in the pendular regime.

A Theoretical Determination of the Characteristic Equation of Snow in the Pendular Regime

AbstractRecent mathematical models treat a natural snow-pack as a mixture body consisting of solid ice grains, liquid water, and a gas made up of air and water vapour. Such a model requires two independent constitutive equations for the two independent volume fractions. However, so far only one equation, a power law relating the liquid-water content to capillary pressure, has been suggested, by analogy with the so-called “characteristic” equation for liquid water in soils. Experimental data from drainage tests on snow columns may be used to determine the characteristic equation for snow for relatively high water contents. However, the experimental method is not valid when water exists in isolated inclusions in the snow, i.e. in the pendular regime. In this paper a theoretical method is used to derive two independent volume-fraction laws for snow in the pendular regime.

Transport and Chemodynamics of Organic Micropollutants and Ions during Snowmelt

By means of laboratory experiments and field measurements we investigated the chemodynamics and transport behaviour of organic micropollutants and inorganic ions in melting snowpacks. Dissolved substances (e.g. ions) were released from the snowpack by convection and diffusion within the melt water. Substances which were adsorbed onto particles (e.g. PAH) were not desorbed to a significant degree. Moving particles were generally filtered out within the snowpack and, therefore, adsorbed substances were hardly leached by this way of transport. Frequent melt-freeze cycles and a deep snowpack lead to an enrichment of dissolved substances in the first melt water fractions and of substances adsorbed onto particles in the final fractions. A different macroscopic and microscopic spatial variation of ions within the snowpack results in different elution patterns during the snow melt. Since the PAH are predominantly adsorbed onto particles, approximately 90% of all PAH of a snow column were eluted with the last 20% of water during the snow melt. PAH with a high partition coefficient kow (e.g. benzo(a) pyrene, benzo(ghi)perylene) exhibited a stronger enrichment than fluoranthene with comparatively lower kow. Since the HCH isomers occur in dissolved as well as in adsorbed phase because of their low kow in melting snow, we observe an enrichment of the dissolved phase within the first fractions of melt water and of the adsorbed phase within the final fractions of melt water.

Isotope Input into Runoff Systems from Melting Snow Covers

Stable environmental isotope techniques contribute to reasonable separations of the direct runoff component in snowmelt hydrographs. For the separation procedure, the actual isotope input from snow cover outflows is required. In order to study the effects of isotope fractionation and exchange processes in the snow cover on the isotopic outflow concentrations several cold room experiments have been carried out with isotopically homogeneous and stratified snow columns. To simulate natural conditions the columns were treated with different heat supply and rainwater at the surface, and the outflows analysed for 2H and 18O contents. Some fundamental results are discussed with respect to the more complex natural situation. Finally, the hydrological application of such experience is demonstrated for a natural environment.

Measurements of Acoustic Properties of Hard-Pack Snow

AbstractThree experiments were conducted to assess acoustic properties of hard-pack snow. One test involved transmission of acoustic signals in the frequency range 100-20 000 Hz through natural snow-pack in order to measure signal loss of a point acoustic source. At all frequencies the relatively high-energy input signal decays rapidly by energy dissipation, with nominal diffusion occurring at large distances from the source. Signal persistence is greatest in the frequency range 100-200 Hz, In a second test, acoustic bursts in snow columns under deformation were recorded. Spectrum analysis in the frequency range 500-14000 Hz reveals dominance of signal amplitudes at frequencies between 1 000 and 10 000 Hz. This dominance is attributed to the strong attenuation properties of snow and suggests the use of waveguide or collector techniques to monitor natural acoustic emissions in snow-pack. In a third test several waveguide geometries and materials were evaluated for their acoustic signal interception and transmission characteristics. In general, metallic waveguides show the least attenuation of the configurations tested.

Measurements of Acoustic Properties of Hard-Pack Snow

Abstract Three experiments were conducted to assess acoustic properties of hard-pack snow. One test involved transmission of acoustic signals in the frequency range 100-20 000 Hz through natural snow-pack in order to measure signal loss of a point acoustic source. At all frequencies the relatively high-energy input signal decays rapidly by energy dissipation, with nominal diffusion occurring at large distances from the source. Signal persistence is greatest in the frequency range 100-200 Hz, In a second test, acoustic bursts in snow columns under deformation were recorded. Spectrum analysis in the frequency range 500-14000 Hz reveals dominance of signal amplitudes at frequencies between 1 000 and 10 000 Hz. This dominance is attributed to the strong attenuation properties of snow and suggests the use of waveguide or collector techniques to monitor natural acoustic emissions in snow-pack. In a third test several waveguide geometries and materials were evaluated for their acoustic signal interception and transmission characteristics. In general, metallic waveguides show the least attenuation of the configurations tested.

Equation of Isotope Fractionation Between Ice and Water in A Melting Snow Column with Continuous Rain and Percolation

AbstractPartial differential equations are derived to describe isotope fractionation between ice and water phases in temperate snow caps and glaciers. Numerical solutions are obtained and shown to be consistent with laboratory experiments and measurements of deuterium concentrations in temperate glaciers. The process of isotope fractionation as described is manifested by application of the model to tritium fractionation in temperate snow caps.

Equation of Isotope Fractionation Between Ice and Water in A Melting Snow Column with Continuous Rain and Percolation

Abstract Partial differential equations are derived to describe isotope fractionation between ice and water phases in temperate snow caps and glaciers. Numerical solutions are obtained and shown to be consistent with laboratory experiments and measurements of deuterium concentrations in temperate glaciers. The process of isotope fractionation as described is manifested by application of the model to tritium fractionation in temperate snow caps.