Mean Annual Accumulation Research Articles

Densification of Snow on the Ice Sheet of Ellsworth Land and the Southern Antarctic Peninsula

AbstractDensity-depth curves constructed from seismic travel-time data observed at 25 locations, show a large variation over an essentially isothermal area (T = −22±2.6° C). This is correlated with the wide range of mean annual accumulation values. (A = 20 to 50g./cm.2yr). Quantitative estimates of mean annual accumulation can be obtained from seismic refraction data in this area by the expression A = 23.5+0.049(3500−V200) where V200 is the compressional wave velocity (m./sec.) observed at 200 m. from the shot point. The density-depth curves can be used to give estimates of accumulation by the expression:where ρ40 is the density (g./cm.3) at 40 m. depth. The internal consistency of these methods is indicated by the standard deviation of ±2.9./cm.2 yr. for comparisons of accumulation estimates. The theoretical basis for these results is discussed.

Densification of Snow on the Ice Sheet of Ellsworth Land and the Southern Antarctic Peninsula

Abstract Density-depth curves constructed from seismic travel-time data observed at 25 locations, show a large variation over an essentially isothermal area (T = −22±2.6° C). This is correlated with the wide range of mean annual accumulation values. (A = 20 to 50g./cm.2yr). Quantitative estimates of mean annual accumulation can be obtained from seismic refraction data in this area by the expression A = 23.5+0.049(3500−V 200) where V 200 is the compressional wave velocity (m./sec.) observed at 200 m. from the shot point. The density-depth curves can be used to give estimates of accumulation by the expression: where ρ 40 is the density (g./cm.3) at 40 m. depth. The internal consistency of these methods is indicated by the standard deviation of ±2.9./cm.2 yr. for comparisons of accumulation estimates. The theoretical basis for these results is discussed.

Studies of Englacial Profiles in the Lake Hazen Area of Northern Ellesmere Island

AbstractGlaciological research on the ice cap to the north of Lake Hazen in northern Ellesmere Island was one of the main objectives of the Canadian I.G.Y. expedition to this area in 1957–1958. The method of nourishment of this ice cap and of Gilman Glacier, one of its southward-flowing outlets, was studied in pit and bore hole profiles above and below the equilibrium line, which was found at an elevation of about 1,200 m. Between an elevation of about 1,450 and 2,000 m. accumulation is by firn formation, while between about 1,280 and 1,450 m. interfingering of firn and superimposed ice occurs. At 1,800 m. the mean annual accumulation over the past twenty years is estimated as 12.8 g. cm.–2. On Gilman Glacier below the equilibrium line variations in density and crystal structure in an ice core to a depth of 25 m. are seen to depend on the proportion of firn to superimposed ice formed during accumulation. These variations correspond to past changes in the position of the equilibrium line. Englacial temperature measurements indicate a mean annual temperature of about –18.5° C. at an elevation of 1 ,040 m. A budget deficit for Gilman Glacier during two years of observations may be related to the increased summer melting of the last 20 years, deduced from pit studies at 1,800 m.

Studies of Englacial Profiles in the Lake Hazen Area of Northern Ellesmere Island

AbstractGlaciological research on the ice cap to the north of Lake Hazen in northern Ellesmere Island was one of the main objectives of the Canadian I.G.Y. expedition to this area in 1957–1958. The method of nourishment of this ice cap and of Gilman Glacier, one of its southward-flowing outlets, was studied in pit and bore hole profiles above and below the equilibrium line, which was found at an elevation of about 1,200 m. Between an elevation of about 1,450 and 2,000 m. accumulation is by firn formation, while between about 1,280 and 1,450 m. interfingering of firn and superimposed ice occurs. At 1,800 m. the mean annual accumulation over the past twenty years is estimated as 12.8 g. cm.–2. On Gilman Glacier below the equilibrium line variations in density and crystal structure in an ice core to a depth of 25 m. are seen to depend on the proportion of firn to superimposed ice formed during accumulation. These variations correspond to past changes in the position of the equilibrium line. Englacial temperature measurements indicate a mean annual temperature of about –18.5° C. at an elevation of 1 ,040 m. A budget deficit for Gilman Glacier during two years of observations may be related to the increased summer melting of the last 20 years, deduced from pit studies at 1,800 m.

Preliminary Results of the Glaciological Work on the Trans-Antarctic Expedition, 1955–58

AbstractAt the inland station “Southice” (at approximately lat. 82° S., long. 29° W.) investigation in firn to 45m. included profiles of temperature, density, granularity and crystal size. Mean annual accumulation and temperature are interpolated and crystal fabric analyses briefly discussed. A study of drifting snow is outlined.Similar studies, but without crystal observations, were continued across the continent using snow cores to 11 m. depth and supplemented by Rammsonde soundings. These sub-surface observations with the sastrugi forms noted, permit the interpolation of the mean accumulation, temperature and wind direction at different heights across the continent. Radiation flux, wind speed and air and snow temperature profiles were recorded at various halts.

Preliminary Results of the Glaciological Work on the Trans-Antarctic Expedition, 1955–58

Abstract At the inland station “Southice” (at approximately lat. 82° S., long. 29° W.) investigation in firn to 45m. included profiles of temperature, density, granularity and crystal size. Mean annual accumulation and temperature are interpolated and crystal fabric analyses briefly discussed. A study of drifting snow is outlined. Similar studies, but without crystal observations, were continued across the continent using snow cores to 11 m. depth and supplemented by Rammsonde soundings. These sub-surface observations with the sastrugi forms noted, permit the interpolation of the mean accumulation, temperature and wind direction at different heights across the continent. Radiation flux, wind speed and air and snow temperature profiles were recorded at various halts.

Snow Accumulation in North Greenland

AbstractMeasurements of the annual snow accumulation have been made at many points on a traverse of north Greenland. In lat. 77–78° N. the annual accumulation above 1800 m. was about 13 gm. cm.−2in the years 1948–53 and, in contrast to results which have been obtained further south, did not vary with longitude. In 1953–54 the accumulation was greater. The annual accumulation in north and central Greenland has varied significantly over the last 50 years, but similar variations are not shown in the precipitation records at coastal stations. Using all the available information, the mean annual accumulation on the Greenland Ice Sheet has been calculated as 29±3 gm. cm.−2.

Snow Accumulation in North Greenland

AbstractMeasurements of the annual snow accumulation have been made at many points on a traverse of north Greenland. In lat. 77–78° N. the annual accumulation above 1800 m. was about 13 gm. cm.−2 in the years 1948–53 and, in contrast to results which have been obtained further south, did not vary with longitude. In 1953–54 the accumulation was greater. The annual accumulation in north and central Greenland has varied significantly over the last 50 years, but similar variations are not shown in the precipitation records at coastal stations. Using all the available information, the mean annual accumulation on the Greenland Ice Sheet has been calculated as 29±3 gm. cm.−2.

Contributions to the Glaciology of the Antarctic

AbstractDuring a winter in Terre Adélie in 1951 (Antarctica) certain glaciological studies were made. These were strongly hampered by the extraordinary strength and persistence of the blizzards from the ice cap. Near the coast the wind dominates the distribution of snow completely. The firn limit on the open ice cap is at a height of 450 m. (1500 ft.). The deposited snow is very tightly packed with a density of 0.4–0.5 gm./cm.3. On the ice cap the mean annual accumulation is 20–30 cm. water. At the coast and particularly on the ice cap measurements and calculations of the radiation balance show a strong loss for most of the time owing to the high albedo of the snow. The snow surface is almost continuously colder then the snow below and the air above. The radiation loss is mainly replaced by the influx of warmer air into the continent. The density of the drifting snow was measured. On a day with heavy blizzard the snow transport across each m. of the coast line is 2.5–3 kg. /m.sec. In a year at least 20 million tons pass each km. (30 million tons per mile). In Terre Adélie the drifting snow is an important item in the mass economy of the ice cap.

Ice Movement and Temperature Distribution in Glaciers and Ice Sheets

AbstractThe distribution of temperature throughout an ice sheet has been considered, taking into account the influence of ice movement as well as other items previously considered, such as conduction, the geothermal outflow of heat and heat generated by ice movement. By making certain simplifying assumptions, a quantitative method of estimating the temperature distribution near the centre of an ice sheet has been put forward.It is shown that even a small mean annual accumulation will have considerable effect on the temperature distribution in a large ice sheet. For a moderate rate of accumulation a substantial fraction of the total thickness of ice at the centre of a large ice sheet may be isothermal at the prevailing surface ice temperature. Under these conditions at some distance from the centre, the change in the surface ice temperature with elevation may produce a temperature gradient opposite to normal, that is the temperature falls with increasing depth below the surface, due to the outward movement of the ice. Observed temperature gradients on ice sheets fit the proposed hypotheses roughly, but it appears that climatic change should also be taken into account.It is suggested that a rise from temperatures below melting point at the base of ice sheets may provide an explanation of the occasional catastrophic advances of certain glaciers.