scholarly journals Characteristics of the Initial Densification of Snow/Firn in Wilkes Land, East Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 209 ◽  
Author(s):  
Qin Dahe ◽  
N. W. Young
Keyword(s):  
Accumulation Rate ◽  
Viscosity Coefficient ◽  
East Antarctica ◽  
Shallow Depth ◽  
Mean Annual Temperature ◽  
List Type ◽  
Densification Rate ◽  
The Core ◽  
Wilkes Land ◽  
The Mean

Fourteen shallow snow/firn cores were drilled with the Polar Ice Coring Office light-weight hand-coring auger in Wilkes Land, along a line approximately long. 111°E between lat. 66° and 74°S. Five of these cores, all between 20 and 30 m deep, are studied in detail in this paper: LJ, BJ, GC30, GC40 and GC46. The physical geographical conditions differ at these five stations, but the general trend is for mean annual accumulation rate and mean annual temperature to decrease farther south, with increasing elevation. At the southernmost station, GC46, the mean annual temperature is –52.5°C, and accumulation rate is 52 kg m−2 a−1. The density measurements of the snow/firn were made in a cold-room at temperatures from –14− to –18−C, by taking consecutive samples from the core and measuring the mass of each sample of known volume. The characteristics of the initial densification (to a density of 550 kg m−3) – variation in snow/firn density with depth, the densification rate of snow/firn, and the compactive viscosity coefficient of snow/firn – are studied, and the factors affecting this initial densification process are discussed. The following observations were made and conclusions reached: 1. Plots of all the measurements, from each core, of density against depth showed three different patterns. The first type, typical of the coastal areas, shows a very great variability of density at shallow depth, reducing with an increase in depth. The second, typical of the high inland stations, shows a smaller scatter of densities at shallow depth, again reducing with an increase in depth. The third type is a pattern intermediate between these two. So, the range of density fluctuation with a depth range in any core is greater at the top of the core than at the bottom, and at the same depth in different cores the variation in density is greater where the mean annual temperature is higher. 2. The snow/firn density increases with an increase in depth at all stations, and the densification rate is higher at stations with higher mean annual temperature. 3. The mean density of snow/firn in the top 1 m decreases farther inland, and this decrease appears to be closely related to the decrease in temperature. 4. The mean densification rate is compared with the mean annual temperature and the mean annual accumulation rate over the past 40 years in the most southerly cores. The mean annual temperature is found to be the more important factor affecting the densification rate in the surface snow/firn on the cold ice sheet. 5. At each station, for ρ = 550 kg m−3, a linear relationship is found between log compactive-viscosity coefficient of snow/firn and mean annual temperature for a constant density. If only stations with a mean annual temperature below –25°C (i.e. no melt features are present in the stratigraphy) are considered, then these results from Wilkes Land are very similar to the results obtained by Nishimura and others (1983) from Mizuho Plateau, East Antarctica.

scholarly journals Characteristics of the Initial Densification of Snow/Firn in Wilkes Land, East Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 209-209
Author(s):  
Qin Dahe ◽  
N. W. Young
Keyword(s):  
Accumulation Rate ◽  
Viscosity Coefficient ◽  
East Antarctica ◽  
Shallow Depth ◽  
Mean Annual Temperature ◽  
List Type ◽  
Densification Rate ◽  
The Core ◽  
Wilkes Land ◽  
The Mean

Fourteen shallow snow/firn cores were drilled with the Polar Ice Coring Office light-weight hand-coring auger in Wilkes Land, along a line approximately long. 111°E between lat. 66° and 74°S. Five of these cores, all between 20 and 30 m deep, are studied in detail in this paper: LJ, BJ, GC30, GC40 and GC46. The physical geographical conditions differ at these five stations, but the general trend is for mean annual accumulation rate and mean annual temperature to decrease farther south, with increasing elevation. At the southernmost station, GC46, the mean annual temperature is –52.5°C, and accumulation rate is 52 kg m−2 a−1.The density measurements of the snow/firn were made in a cold-room at temperatures from –14− to –18−C, by taking consecutive samples from the core and measuring the mass of each sample of known volume. The characteristics of the initial densification (to a density of 550 kg m−3) – variation in snow/firn density with depth, the densification rate of snow/firn, and the compactive viscosity coefficient of snow/firn – are studied, and the factors affecting this initial densification process are discussed.The following observations were made and conclusions reached:1.Plots of all the measurements, from each core, of density against depth showed three different patterns. The first type, typical of the coastal areas, shows a very great variability of density at shallow depth, reducing with an increase in depth. The second, typical of the high inland stations, shows a smaller scatter of densities at shallow depth, again reducing with an increase in depth. The third type is a pattern intermediate between these two. So, the range of density fluctuation with a depth range in any core is greater at the top of the core than at the bottom, and at the same depth in different cores the variation in density is greater where the mean annual temperature is higher.2.The snow/firn density increases with an increase in depth at all stations, and the densification rate is higher at stations with higher mean annual temperature.3.The mean density of snow/firn in the top 1 m decreases farther inland, and this decrease appears to be closely related to the decrease in temperature.4.The mean densification rate is compared with the mean annual temperature and the mean annual accumulation rate over the past 40 years in the most southerly cores. The mean annual temperature is found to be the more important factor affecting the densification rate in the surface snow/firn on the cold ice sheet.5.At each station, for ρ = 550 kg m−3, a linear relationship is found between log compactive-viscosity coefficient of snow/firn and mean annual temperature for a constant density. If only stations with a mean annual temperature below –25°C (i.e. no melt features are present in the stratigraphy) are considered, then these results from Wilkes Land are very similar to the results obtained by Nishimura and others (1983) from Mizuho Plateau, East Antarctica.

scholarly journals Glaciological Reconnaissance of an Ice Core Drilling Site, Penny Ice Cap, Baffin Island

1984 ◽  
Vol 30 (104) ◽  
pp. 3-15 ◽  
Author(s):  
G. Holdsworth
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Surface Air Temperature ◽  
Tritium Concentration ◽  
Mean Annual Temperature ◽  
Climatic Data ◽  
Baffin Island ◽  
The Core ◽  
Ice Cap ◽  
The Mean

AbstractA site situated close to the main divide of the Penny Ice Cap, Baffin Island was occupied in 1979 for the purpose of determining the suitability of this ice cap for providing proxy climatic data and other environmental time series for a span of 104a. A 20 m core was extracted and analysed for stable oxygen isotopes, tritium concentration, pH, electrolytic conductivity, major ion concentrations, and particulate concentration. An adjacent dedicated shallow core was analysed for pollen content to determine if a significant seasonal variation in the pollen rain existed. From these measurements, and from the observations made on the stratigraphic character of the core, the mean net accumulation rate over the approximately 30 year period covered by the core is found to be about 0.43 m water equivalent per year. This is in agreement with a single value determined 26 years earlier at a nearby site (Ward and Baird, 1954). The mean annual temperature in the bore hole was found to be close to −14.4° C, possibly some 2–5 deg warmer than the expected mean annual surface air temperature at the site. This difference is due to the expulsion of latent heat upon freezing of melt water at depth in the snow-pack which gives rise to the many ice layers observed in the core. The percentage thickness of ice layers per year may be correlated with summer temperatures.Total ice depths were measured using a 620 MHz radar echo-sounder. In the vicinity of the divide, over an area of 1 km2, the ice depths vary from about 460 to 515 m. These values compare favourably with values determined from an airborne radar depth-sounding flight carried out over the ice cap by a joint U.S.–Danish mission operating out of Søndre Strømfjord, Greenland. The data suggest that the ice-cap divide would be a worthwhile location to deep core drill with an expected useful coverage of at least the Holocene period.

scholarly journals Glaciological Reconnaissance of an Ice Core Drilling Site, Penny Ice Cap, Baffin Island

1984 ◽  
Vol 30 (104) ◽  
pp. 3-15 ◽  
Author(s):  
G. Holdsworth
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Surface Air Temperature ◽  
Tritium Concentration ◽  
Mean Annual Temperature ◽  
Climatic Data ◽  
Baffin Island ◽  
The Core ◽  
Ice Cap ◽  
The Mean

AbstractA site situated close to the main divide of the Penny Ice Cap, Baffin Island was occupied in 1979 for the purpose of determining the suitability of this ice cap for providing proxy climatic data and other environmental time series for a span of 104 a. A 20 m core was extracted and analysed for stable oxygen isotopes, tritium concentration, pH, electrolytic conductivity, major ion concentrations, and particulate concentration. An adjacent dedicated shallow core was analysed for pollen content to determine if a significant seasonal variation in the pollen rain existed. From these measurements, and from the observations made on the stratigraphic character of the core, the mean net accumulation rate over the approximately 30 year period covered by the core is found to be about 0.43 m water equivalent per year. This is in agreement with a single value determined 26 years earlier at a nearby site (Ward and Baird, 1954). The mean annual temperature in the bore hole was found to be close to −14.4° C, possibly some 2–5 deg warmer than the expected mean annual surface air temperature at the site. This difference is due to the expulsion of latent heat upon freezing of melt water at depth in the snow-pack which gives rise to the many ice layers observed in the core. The percentage thickness of ice layers per year may be correlated with summer temperatures.Total ice depths were measured using a 620 MHz radar echo-sounder. In the vicinity of the divide, over an area of 1 km2, the ice depths vary from about 460 to 515 m. These values compare favourably with values determined from an airborne radar depth-sounding flight carried out over the ice cap by a joint U.S.–Danish mission operating out of Søndre Strømfjord, Greenland. The data suggest that the ice-cap divide would be a worthwhile location to deep core drill with an expected useful coverage of at least the Holocene period.

scholarly journals Growth Rate of Crystals Within the Surface-Snow/Firn Layer in Wilkes Land, East Antarctica

1988 ◽  
Vol 11 ◽  
pp. 121-125 ◽  
Author(s):  
Qin Dahe ◽  
Neal W. Young ◽  
Richard J. Thwaites
Keyword(s):  
Growth Rate ◽  
Crystal Size ◽  
Accumulation Rate ◽  
Mean Annual Temperature ◽  
Surface Layers ◽  
Vertical Temperature ◽  
Near Surface ◽  
Constant Rate ◽  
Wilkes Land ◽  
Type Relation

Measurements of crystal size have been made on seven firn cores drilled at sites covering a range of mean annual temperature from –12.6° to –52.5°C and a range of accumulation rate from 52 to 315 kg m−2 a−1. The sorting coefficient, which gives a measure of the dispersion of crystal sizes within a sample, shows an overall pattern when data from all cores are grouped together as a function of depth. The values are generally small near the surface, increasing to a maximum around 8 m depth, then decreasing but becoming more diffuse at greater depths. Below about 5 m depth, the crystal size increases at an essentially constant rate, which depends on temperature, but in the upper 5 or 7 m the size increases at 1.5 to 2 times this rate. The seasonal variation in temperature enhances the effective mean growth rate of crystals in the near-surface layers compared to conditions with a constant mean temperature and accounts for a part of that increase. But it is likely that vapour diffusion along strong vertical temperature gradients causes the greater part of the observed increase in growth rate. The dependence of crystal-growth rate on temperature is consistent with the Arrhenius-type relation found by other studies.

scholarly journals Growth Rate of Crystals Within the Surface-Snow/Firn Layer in Wilkes Land, East Antarctica

1988 ◽  
Vol 11 ◽  
pp. 121-125 ◽  
Author(s):  
Qin Dahe ◽  
Neal W. Young ◽  
Richard J. Thwaites
Keyword(s):  
Growth Rate ◽  
Crystal Size ◽  
Accumulation Rate ◽  
Mean Annual Temperature ◽  
Surface Layers ◽  
Vertical Temperature ◽  
Near Surface ◽  
Constant Rate ◽  
Wilkes Land ◽  
Type Relation

Measurements of crystal size have been made on seven firn cores drilled at sites covering a range of mean annual temperature from –12.6° to –52.5°C and a range of accumulation rate from 52 to 315 kg m−2 a−1. The sorting coefficient, which gives a measure of the dispersion of crystal sizes within a sample, shows an overall pattern when data from all cores are grouped together as a function of depth. The values are generally small near the surface, increasing to a maximum around 8 m depth, then decreasing but becoming more diffuse at greater depths. Below about 5 m depth, the crystal size increases at an essentially constant rate, which depends on temperature, but in the upper 5 or 7 m the size increases at 1.5 to 2 times this rate. The seasonal variation in temperature enhances the effective mean growth rate of crystals in the near-surface layers compared to conditions with a constant mean temperature and accounts for a part of that increase. But it is likely that vapour diffusion along strong vertical temperature gradients causes the greater part of the observed increase in growth rate. The dependence of crystal-growth rate on temperature is consistent with the Arrhenius-type relation found by other studies.

scholarly journals Microwave Emission From Snow and Glacier Ice

1976 ◽  
Vol 16 (74) ◽  
pp. 23-39 ◽  
Author(s):  
T.C. Chang ◽  
P. Gloersen ◽  
T. Schmugge ◽  
T.T. Wilheit ◽  
H.J. Zwally
Keyword(s):  
Accumulation Rate ◽  
Mie Scattering ◽  
Microwave Emission ◽  
Mean Annual Temperature ◽  
Particle Sizes ◽  
Grain Sizes ◽  
Glacier Ice ◽  
The Mean ◽  
The Individual ◽  
Two Parameters

AbstractThe microwave emission from a model snow field, consisting of randomly spaced ice spheres which scatter independently, is calculated. Mie scattering and radiative transfer theory are applied in a manner similar to that used in calculating microwave and optical properties of clouds. The extinction coefficient is computed as a function of both microwave wavelength and ice-particle radius. Volume scattering by the individual ice particles in the snow field significantly decreases the computed emission for particle radii greater than a few hundredths of the microwave wavelength. Since the mean annual temperature and the accumulation rate of dry polar firn mainly determine the grain sizes upon which the microwave emission depends, these two parameters account for the main features of the 1.55 cm emission observed from Greenland and Antarctica with the Nimbus-5 scanning radiometer. For snow particle sizes normally encountered, most of the calculated radiation emanates from a layer on the order of 10 m in thickness at a wavelength of 2.8 cm, and less at shorter wavelengths. A marked increase in emission from wet versus dry snow is predicted, a result which is consistent with observations. The model results indicate that the characteristic grain sizes in the radiating layers, dry-firn accumulation rales, areas of summer melting, and physical temperatures, can be determined from multispectral microwave observations.

A continuous 250-year record of volcanic activity from Princess Elizabeth Land, East Antarctica

2002 ◽  
Vol 14 (1) ◽  
pp. 55-60 ◽  
Author(s):  
M.J. Zhang ◽  
Z.Q. Li ◽  
C.D. Xiao ◽  
D.H. Qin ◽  
H.A. Yang ◽  
...  
Keyword(s):  
Volcanic Activity ◽  
Major Ions ◽  
Accumulation Rate ◽  
Ice Core ◽  
Volcanic Eruptions ◽  
East Antarctica ◽  
Mean Annual Temperature ◽  
High Definition ◽  
Concentration Data ◽  
High Accumulation

A 51.85 m ice core collected from site LGB65 (accumulation rate 127 kg m−2 a−1, mean annual temperature −33.1°C) in Princess Elizabeth Land, East Antarctica, during the 1996–97 Chinese First Antarctic Inland Expedition has been analysed for chemical composition and oxygen isotope ratio. Based on the high definition of seasonal variations of major ions, the ice core was dated with errors within ± 3 years. The continuous sulphate analysis of the ice core provides an annually resolved proxy history of southern hemisphere volcanism in the past 250 years. High nssSO42−, concentrations seem to be well correlated to some explosive volcanic eruptions, such as Tambora (AD 1815), Coseguina (AD 1835), Krakatoa (AD 1883) and Tarawera (AD 1886). In comparison with other volcanic records, it seems that nssSO42− concentration data provide a better proxy for detecting volcanic activity than nssSO42− fluxes in low and intermediate accumulation regions, however, in high accumulation regions, small and moderate events may be more identifiable using of nssSO42− flux data.

scholarly journals A middle Pleistocene paleosol sequence from Dawson Range, Central Yukon Territory

2002 ◽  
Vol 53 (3) ◽  
pp. 313-322 ◽  
Author(s):  
Lionel E. Jackson ◽  
Charles Tarnocai ◽  
Robert J. Mott
Keyword(s):  
Yukon Territory ◽  
Middle Pleistocene ◽  
Mean Annual Temperature ◽  
Sedimentary Sequence ◽  
The Core ◽  
The Mean

AbstractFour paleosols were intersected in a core drilled into the colluvial fill of a largely buried meltwater channel that was last active during the youngest of the pre-Reid glaciation (0.99-0.78 Ma) in the Dawson Range, Yukon Territory. The paleosols are classified as Podzols. The sedimentary sequence and paleosols indicate that at least two middle Pleistocene glacial and interglacial periods are represented in the core. The mean annual temperature exceeded 0° C for thousands of years in the upland environment of the Dawson Range at 61° N during these interglacial periods.

scholarly journals Firn Densification: An Empirical Model

1980 ◽  
Vol 25 (93) ◽  
pp. 373-385 ◽  
Author(s):  
Michael M. Herron ◽  
Chester C. Langway
Keyword(s):  
Empirical Model ◽  
Accumulation Rate ◽  
Rate Equations ◽  
Constant Density ◽  
Square Root ◽  
Accumulation Rates ◽  
Densification Rate ◽  
Second Stage ◽  
The Mean ◽  
Two Stages

AbstractAn empirical model of firn densification from the surface to the zone of pore close-off has been constructed. Fundamental rate equations have been derived for the first two stages of densification. In the first stage, for densities less than 0.55 Mg m−3, the densification rate is proportional to the mean annual accumulation times the term (ρi − ρ), where ρ is the density of the snow and ρi is the density of pure ice. The densification rate in the second stage, where 0.55 Mg m −3 < ρ < 0.8 Mg m−3, is proportional to the square root of the accumulation rate and to (ρi− ρ). Depth–density and depth–age calculations from this model are compared with observation. Model accumulation rates are within about 20% of values obtained by other techniques. It is suggested that depth intervals of constant density in some Antarctic cores may represent a synchronous event in the 1880 ’s when ten times the normal accumulation fell within a year or two.

scholarly journals Microwave Emission From Snow and Glacier Ice

1976 ◽  
Vol 16 (74) ◽  
pp. 23-39 ◽  
Author(s):  
T.C. Chang ◽  
P. Gloersen ◽  
T. Schmugge ◽  
T.T. Wilheit ◽  
H.J. Zwally
Keyword(s):  
Accumulation Rate ◽  
Mie Scattering ◽  
Microwave Emission ◽  
Mean Annual Temperature ◽  
Particle Sizes ◽  
Grain Sizes ◽  
Glacier Ice ◽  
The Mean ◽  
The Individual ◽  
Two Parameters

AbstractThe microwave emission from a model snow field, consisting of randomly spaced ice spheres which scatter independently, is calculated. Mie scattering and radiative transfer theory are applied in a manner similar to that used in calculating microwave and optical properties of clouds. The extinction coefficient is computed as a function of both microwave wavelength and ice-particle radius. Volume scattering by the individual ice particles in the snow field significantly decreases the computed emission for particle radii greater than a few hundredths of the microwave wavelength. Since the mean annual temperature and the accumulation rate of dry polar firn mainly determine the grain sizes upon which the microwave emission depends, these two parameters account for the main features of the 1.55 cm emission observed from Greenland and Antarctica with the Nimbus-5 scanning radiometer. For snow particle sizes normally encountered, most of the calculated radiation emanates from a layer on the order of 10 m in thickness at a wavelength of 2.8 cm, and less at shorter wavelengths. A marked increase in emission from wet versus dry snow is predicted, a result which is consistent with observations. The model results indicate that the characteristic grain sizes in the radiating layers, dry-firn accumulation rales, areas of summer melting, and physical temperatures, can be determined from multispectral microwave observations.

Sign in / Sign up

Export Citation Format

Share Document