Snow chemistry of Agassiz Ice Cap, Ellesmere Island, Northwest Territories, Canada

AbstractPit-wall samples were collected from two sites about 2 km apart on Agassiz Ice Cap, Ellesmere Island, Northwest Territories, Canada, in 1992, 1993 and 1994, and from a site a further 1 km distant, in order to study spatial and seasonal variations in snow chemistry. Two of the pits were dug in wind-scoured zones and one in an unscoured zone. Although a large part of the winter snow is removed from the scoured zones (which do not show very negativeδ18O values) the winter/spring anion peaks are still evident; this may be due to the predominance of dry deposition in mid-winter. The Cl−and SO42–ions peak in late winter/early spring, while NO3−peaks both in late winter/early spring and in summer. Vertical concentration profiles of all anions did not significantly alter over a 2 year period, indicating that there are no serious post-depositional changes due to evaporation, snow melting or photochemical reactions. However, comparisons between stake/board snow-accumulation measurements and those derived from the least scoured pit indicate that a single pit will represent annual accumulation rates for a local area only

Use of Water Balance and Tracer-Based Approaches to Monitor Groundwater Recharge in the Hyper-Arid Gobi Desert of Northwestern China

The groundwater recharge mechanism in the hyper-arid Gobi Desert of Northwestern China was analyzed using water balance and tracer-based approaches. Investigations of evaporation, soil water content, and their relationships with individual rainfall events were conducted from April to August of 2004. Water sampling of rainwater, groundwater, and surface water was also conducted. During this period, 10 precipitation events with a total amount of 41.5 mm, including a maximum of 28.9 mm, were observed. Evaporation during the period was estimated to be 33.1 mm. Only the soil water, which was derived from the heaviest precipitation, remained in the vadose zone. This is because a dry surface layer, which was formed several days after the heaviest precipitation event, prevented evaporation. Prior to that, the heaviest precipitation rapidly infiltrated without being affected by evaporation. This is corroborated by the isotopic evidence that both the heaviest precipitation and the groundwater retained no trace of significant kinetic evaporation. Estimated δ-values of the remaining soil water based on isotopic fractionation and its mass balance theories also demonstrated no trace of kinetic fractionation in the infiltration process. Moreover, stable isotopic compositions of the heaviest precipitation and the groundwater were very similar. Therefore, we concluded that the high-intensity precipitation, which rapidly infiltrated without any trace of evaporation, was the main source of the groundwater

Including debris cover effects in a distributed model of glacier ablation

Distributed glacier melt models generally assume that the glacier surface consists of bare exposed ice and snow. In reality, many glaciers are wholly or partially covered in layers of debris that tend to suppress ablation rates. In this paper, an existing physically based point model for the ablation of debris-covered ice is incorporated in a distributed melt model and applied to Haut Glacier d’Arolla, Switzerland, which has three large patches of debris cover on its surface. The model is based on a 10 m resolution digital elevation model (DEM) of the area; each glacier pixel in the DEM is defined as either bare or debris-covered ice, and may be covered in snow that must be melted off before ice ablation is assumed to occur. Each debris-covered pixel is assigned a debris thickness value using probability distributions based on over 1000 manual thickness measurements. Locally observed meteorological data are used to run energy balance calculations in every pixel, using an approach suitable for snow, bare ice or debris-covered ice as appropriate. The use of the debris model significantly reduces the total ablation in the debris-covered areas, however the precise reduction is sensitive to the temperature extrapolation used in the model distribution because air near the debris surface tends to be slightly warmer than over bare ice. Overall results suggest that the debris patches, which cover 10% of the glacierized area, reduce total runoff from the glacierized part of the basin by up to 7%

Discharge of Ice across the Soya Coast

The flow velocity of about 2500m/year was obtained for the Shirase Glacier (70°S; 39°E), East Antarctica, by the analyses of aerophotographs taken in 1969 and 1975. Thicknesses of icebergs near the termini of the glaciers located along the Soya Coast were also obtained from the shadows on aerophotographs. These data made it possible to estimate the amount of discharge of ice more accurately than ever made. The total discharge from the Mizuho Plateau area across the Soya Coast is estimated at approximately 8.9×(10)^9t/year, which comprises 7.4×(10)^9t/year from the Shirase Glacier and 1.5×(10)^9t/year from other glaciers and the ice sheet

Heat exchange at surface of built-up ice platform during construction

Heat budget observations show that sensible heat loss accounts for most of the latent heat released during freezing of an exposed, shallow-water layer in the high Arctic in January. Combined evaporation and sensible heat losses were about four times larger for this flooding situation than expected in neutral conditions. Empirical and semi-empirical equations are derived for estimating the components of the heat flux from meteorological parameters.Des observations du bilan thermique montrent que des pertes de chaleur sensible constituent la majeure partie de la chaleur latente lib\ue9r\ue9e durant la cong\ue9lation d'une couche d'eau peu profonde expos\ue9e, en janvier dans le Haut-Arctique. L'\ue9vaporation et les pertes de chaleur sensible \ue9taient, ensemble, environ quatre fois sup\ue9rieures par arrosage \ue0 ce qu'elles seraient en situation neutre. On a d\ue9riv\ue9 des \ue9quations empiriques et semi-empiriques pour estimer les composants du flux thermique \ue0 partir des param\ue8tres m\ue9t\ue9orologiques. Les \ue9quations peuvent servir \ue0 estimer le taux d'accumulation de glace optimal \ue0 partir des donn\ue9es m\ue9t\ue9orologiques.Peer reviewed: YesNRC publication: Ye

Measurements on air porosity of sea ice

The air content of sea ice can be measured directly by melting a sample and collecting the released air, provided the air saturation ratio in the meltwater is known. The saturation ratio was found experimentally to be a function of three parameters: the time after an ice sample was melted, the average bubble size, and the air porosity of the sample. Since the last parameter is the term to be determined, an iteration method was employed in calculations of porosity. The bubble pressure was assumed to be at one atmospheric pressure. The vertical profile of air porosity was thus obtained for first-year sea ice in the Arctic. The results were in good agreement with estimations of porosity made from density values measured for the same samples. This indicates that the bubble pressure is near one atmospheric pressure.La teneur en air de la glace marine peut \ueatre mesur\ue9e directement en faisant fondre un \ue9chantillon et en r\ue9cup\ue9 rant l'air lib\ue9r\ue9, \ue0 condition que l'on connaisse le rapport de saturation de l'air dans l'eau de fonte. Les exp\ue9riences ont montr\ue9 que le rapport de saturation d\ue9pend de trois param\ue8tres: le temps \ue9coul\ue9 apr\ue8s que l'\ue9chantillon de glace a fondu, la taille moyenne des bulles, et la porosit\ue9 \ue0 l'air de l'\ue9chantillon. Comme le dernier param\ue8tre doit \ueatre d\ue9termin\ue9, une m\ue9thode it\ue9rative a \ue9t\ue9 employ\ue9e pour calculer la porosit\ue9. On a suppos\ue9 que la pression dans les bulles \ue9tait d'une atmosph\ue8re. Un profil vertical de la porosit\ue9 a ainsi \ue9t\ue9 obtenu pour les glaces de premi\ue8re ann\ue9e de l'Arctique. Les r\ue9sultats sont en accord avec les \ue9valuations de la porosit\ue9 faites \ue0 partir des valeurs de la densit\ue9 mesur\ue9e sur les m\ueames \ue9chantillons, ce qui indique que la pression dans les bulles est voisine d'une atmosph\ue8re.Peer reviewed: YesNRC publication: Ye

Field experiments to determine the effect of a debris layer on ablation of glacier ice

Ablation of glacier ice has been observed with artifical debris layers prepared with Ottawa sand (ASTM C-109) ranging from 0.01 to 0.1 m thick. Data on external variables observed during the experiments and determination of physical constants of the debris layers have allowed the testing of a proposed simple model. Theoretical predictions compare favourably with the observations. Discussion is extended to a proposal for a simple method by which ablation under a debris layer could be estimated even if the thermal conductivity or thermal resistance of the material were unknown.On a observ\ue9 l'ablation d'un glacier suite \ue0 l'application de couches de roches d\ue9tritiques artificielles, pr\ue9par\ue9es avec du sable d'Ottawa (ASTM C-109), dont l'\ue9paisseur variait de 0.01 \ue0 0.1 m. Les donn\ue9es recueillies sur les variables ext\ue9rieures observ\ue9es en cours d'exp\ue9rience, de m\ueame que l'identification positive des constantes physiques des couches d\ue9tritiques, ont permis de mettre \ue0 l'essai un mod\ue8le simple propos\ue9. Les observations ont permis de constater la justesse des pr\ue9dictions th\ue9oriques. Les auteurs de cette recherche ont voulu aller plus loin en proposant une m\ue9thode simple qui permettrait de pr\ue9dire l'ablation sous une couche d\ue9tritique, m\ueame si la conductivit\ue9 ou la r\ue9sistance thermique du mat\ue9riau utilis\ue9 n'\ue9taient pas connues.Peer reviewed: YesNRC publication: Ye

Ice action on Nanisivik Wharf, Winter 1979-1980

During the period December 1979 to June 1980, five visits were made to observe and measure ice behaviour around the wharf at Nanisivik, on Baffin Island. The measurements included ice thickness, temperature, salinity, and density, as well as horizontal movements of the ice cover. In March 1980, additional measurements and observations were made of tides, rotations of the ice sheet, and grain structure of the ice. A model for the formation of an active zone of ice between the wharf and the adjacent ice cover has been proposed, based on the observed evolution of ice conditions and internal structure of the active zone. Horizontal growth of the active zone displaces the adjacent ice cover away from the wharf, and in so doing, generates ice pressure estimated at 69 kPa on the wharf.Entre d\ue9cembre 1979 et juin 1980 on a effectu\ue9 cinq visites au quai de Nanisivik sur l'\ueele de Baffin afin d'y observer le comportement de la glace et d'en mesurer les d\ue9placements. On a mesur\ue9 l'\ue9paisseur, la temperature, la salinit\ue9 et la densit\ue9 de la glace ainsi que les d\ue9placements horizontaux de la couverture de glace. En mars 1980 on a effectu\ue9 de nouvelles mesures et observations des mar\ue9es, des rotations de la couche de glace et de la structure granulaire de la glace. On a propos\ue9 un mod\ue8le de la formation d'une zone active entre le quai et la glace adjacente bas\ue9 sur l'evolution observ\ue9e des conditions de glace et de la structure interne de la zone active. L'agrandissement dans le plan horizontal de la zone active \ue9 loigne du quai la couverture de glace adjacente et engendre ainsi des charges estim\ue9es \ue0 69 kPa sur le quai.Peer reviewed: YesNRC publication: Ye

Growth of first-year sea ice, eclipse sound, Baffin Island, Canada

A simple numerical integration method has been developed for predicting growth of ice under snow cover where solar radiation does not play a dominant role. The method is capable of incorporating variations in snow conditions and physical properties of ice and snow during the growth period. Theoretical predictions compare favourably with field observations in Eclipse Sound, Baffin Island, for the winter seasons of 1977-78 and 1978-79.Une m\ue9thode simple d'int\ue9gration num\ue9rique a \ue9t\ue9 mise au point pour la pr\ue9diction de la croissance de la glace sous un champ de neige, dans les situations o\uf9 le r\uf4le du rayonnement solaire n'est pas d\ue9terminant. Cette m\ue9thode permet de tenir compte des variations dans les conditions de la neige et des propri\ue9t\ue9s physiques de la glace et de la neige durant la p\ue9riode de croissance. Les observations qui ont \ue9t\ue9 effectu\ue9es au cours des hivers 1977-78 et 1978-79 \ue0 Eclipse Sound, terre de Baffin, ont confirm\ue9, dans une large mesure, les pr\ue9dictions th\ue9oriques.Peer reviewed: YesNRC publication: Ye