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Articles 151 - 162 of 162
Full-Text Articles in Physical Sciences and Mathematics
The Contributions Of Snow, Fog, And Dry Deposition To The Summer Flux Of Anions And Cations At Summit, Greenland, M H. Bergin, J L. Jaffrezo, C Davidson, Jack E. Dibb, S N. Pandis, R Hillamo, W Maenhaut, H D. Kuhns, T Makela
The Contributions Of Snow, Fog, And Dry Deposition To The Summer Flux Of Anions And Cations At Summit, Greenland, M H. Bergin, J L. Jaffrezo, C Davidson, Jack E. Dibb, S N. Pandis, R Hillamo, W Maenhaut, H D. Kuhns, T Makela
Earth Sciences
Experiments were performed during the period May–July of 1993 at Summit, Greenland. Aerosol mass size distributions as well as daily average concentrations of several anionic and cationic species were measured. Dry deposition velocities for SO42− were estimated using surrogate surfaces (symmetric airfoils) as well as impactor data. Real-time concentrations of particles greater than 0.5 μm and greater than 0.01 μm were measured. Snow and fog samples from nearly all of the events occurring during the field season were collected. Filter sampler results indicate that SO42− is the dominant aerosol anion species, with Na+, NH …
Global Perspective Of Nitrate Flux In Ice Cores, Qinzhao Yang, Paul A. Mayewski, Sallie I. Whitlow, Mark S. Twickler, Michael Morrison, R. Talbot, Jack E. Dibb, Ernst Linder
Global Perspective Of Nitrate Flux In Ice Cores, Qinzhao Yang, Paul A. Mayewski, Sallie I. Whitlow, Mark S. Twickler, Michael Morrison, R. Talbot, Jack E. Dibb, Ernst Linder
Earth Sciences
The relationships between the concentration and the flux of chemical species (Cl-, NO3 - , SO42-, Na +, K + , NH4 + , Mg 2+ , Ca 2+) versus snow accumulation rate were examined at GISP2 and 20D in Greenland, Mount Logan from the St. Elias Range, Yukon Territory, Canada, and Sentik Glacier from the northwest end of the Zanskar Range in the Indian Himalayas. At all sites, only nitrate flux is significantly (a = 0.05) related to snow accumulation rate. Of all the chemical series, only nitrate concentration data are normally distributed. Therefore we suggest that nitrate concentration …
Soluble Acidic Species In Air And Snow At Summit, Greenland, Jack E. Dibb, R. Talbot, M H. Bergin
Soluble Acidic Species In Air And Snow At Summit, Greenland, Jack E. Dibb, R. Talbot, M H. Bergin
Earth Sciences
Simultaneous measurements of the concentrations of soluble acidic species in the gas, aerosol and snow phases at Summit, Greenland were made during summer 1993. Mean concentrations of gas phase HCOOH, CH3COOH, and HNO3 (49±28, 32±17 and 0.9±0.6 nmol m−3 STP, respectively) exceeded the concentrations of aerosol-associated HCOO−, CH3COO−, and NO3−by 1–3 orders of magnitude. On average, SO2 concentrations (0.9±0.6 nmol m−3 STP) were approximately 1/3 those of aerosol SO4=, but this ratio varied widely due largely to changes in the concentration of …
Estimation Of Stratospheric Input To The Arctic Troposphere: 7be And 10be In Aerosols At Alert, Canada, Jack E. Dibb, David Meeker, R C. Finkel, J Southon, Marc W. Caffee, Leonard A. Barrie
Estimation Of Stratospheric Input To The Arctic Troposphere: 7be And 10be In Aerosols At Alert, Canada, Jack E. Dibb, David Meeker, R C. Finkel, J Southon, Marc W. Caffee, Leonard A. Barrie
Earth Sciences
Concentrations of 7Be and 210Pb in 2 years of weekly high-volume aerosol samples collected at Alert, Northwest Territories, Canada, showed pronounced seasonal variations. We observed a broad winter peak in 210Pb concentration and a spring peak in 7Be. These peaks were similar in magnitude and duration to previously reported results for a number of stations in the Arctic Basin. Beryllium 10 concentrations (determined only during the first year of this study) were well correlated with those of 7Be; the atom ratio 10Be/7Be was nearly constant at 2.2 throughout the year. This relatively high value of 10Be/7Be indicates that the stratosphere …
Sulfate And Msa In The Air And Snow On The Greenland Ice Sheet, J L. Jaffrezo, C Davidson, M Legrand, Jack E. Dibb
Sulfate And Msa In The Air And Snow On The Greenland Ice Sheet, J L. Jaffrezo, C Davidson, M Legrand, Jack E. Dibb
Earth Sciences
Sulfate and methanesulfonic acid (MSA) concentrations in aerosol, surface snow, and snowpit samples have been measured at two sites on the Greenland Ice Sheet. Seasonal variations of the concentrations observed for these chemical species in the atmosphere are reproduced in the surface snow and preserved in the snowpit sequence. The amplitude of the variations over a year are smaller in the snow than in the air, but the ratios of the concentrations are comparable. The seasonal variations for sulfate are different at the altitude of the Ice Sheet compared to those observed at sea level, with low concentrations in winter …
137cs Gamma-Ray Detection At Summit, Greenland, P. P. Dunphy, Jack E. Dibb
137cs Gamma-Ray Detection At Summit, Greenland, P. P. Dunphy, Jack E. Dibb
Earth Sciences
Global fall-out from atmospheric testing of thermonuclear weapons produced horizon markers corresponding to the initiation of testing in 1953 and the maximum fall-out in 1963. The radioactive isotope 137Cs associated with these events has a half-life of 30.2 years. Therefore, with the appropriate radiation detectors, this fall-out can be used as a long-term temporal indicator in glaciers and snowpack. A prototype γ-ray detector system was successfully tested and was used to make in-situ measurements of the 137Cs marker in a borehole at Summit, Greenland. The system consisted of a 7.6 cm by 7.6 cm NaI (Tl) scintillation crystal/photomultiplier detector, commercial …
An Ice-Core-Based Record Of Biomass Burning In The Arctic And Subarctic, 1750-1980, Sallie I. Whitlow, Paul A. Mayewski, Jack E. Dibb, Mark S. Twickler, G Holdsworth
An Ice-Core-Based Record Of Biomass Burning In The Arctic And Subarctic, 1750-1980, Sallie I. Whitlow, Paul A. Mayewski, Jack E. Dibb, Mark S. Twickler, G Holdsworth
Earth Sciences
No abstract provided.
Beryllium 7 And Lead 210 In The Western Hemisphere Arctic Atmosphere: Observations From Three Recent Aircraft-Based Sampling Programs, Jack E. Dibb, R. Talbot, G L. Gregory
Beryllium 7 And Lead 210 In The Western Hemisphere Arctic Atmosphere: Observations From Three Recent Aircraft-Based Sampling Programs, Jack E. Dibb, R. Talbot, G L. Gregory
Earth Sciences
Concentrations of the natural radionuclides 7Be and 210Pb were determined in aerosol samples collected in the western hemisphere Arctic during the recent NOAA Arctic Gas and Aerosol Sampling Program (AGASP 3) and NASA Global Tropospheric Experiment/Arctic Boundary Layer Expeditions (GTE/ABLE 3A and ABLE 3B) missions. Beryllium 7 showed a free tropospheric concentration maximum between 4 and 5 km in the summer of 1990. Previous 7Be data obtained in the late 1950s and early 1960s also indicated a similar vertical distribution of 7Be near 70°N. Injection of stratospheric air through tropopause folds associated with the Arctic jet …
The Accumulation Of 210pb At Summit, Greenland Since 1855, Jack E. Dibb
The Accumulation Of 210pb At Summit, Greenland Since 1855, Jack E. Dibb
Earth Sciences
The decay corrected activity of 210Pb at the time of deposition shows considerable short term variability, but no clear seasonal or annual periodicity. 210Pb activity in surface snow at this site has averaged 0.7 pCi kg-1 since 1927, but the period 1915-1927 is characterized by a steady decline from higher levels. The average annual accumulation of 210Pb has markedly declined since at least 1870. Similar observation at Dye 3 suggest that 210Pb accumulation has decreased throughout this century over much of the Greenland Ice Sheet. If the records of 210Pb in the firn of the Greenland Ice Sheet are mainly …
Beryllium-7 And Lead-210 In The Atmosphere And Surface Snow Over The Greenland Ice Sheet In The Summer Of 1989, Jack E. Dibb
Beryllium-7 And Lead-210 In The Atmosphere And Surface Snow Over The Greenland Ice Sheet In The Summer Of 1989, Jack E. Dibb
Earth Sciences
The concentrations of 7Be and 210Pb were measured in surface air and fresh and aging snow samples from Summit (72°20′N, 38°45′W) and Dye 3 (65°10′N, 44°45′W) Greenland, during June and July 1989. The aerosol concentrations of these radionuclides showed rapid variations at both sites, but were nearly twice as high, on average, at Summit. Concentrations in the 16 fresh snowfall events that were sampled also showed wide variability, but the averages were the same at the two sites. The apparent difference in air-snow fractionation and the lack of coherence in the concentration in air time series between the …
Recent Deposition Of 210pb On The Greenland Ice Sheet: Variations In Space And Time, Jack E. Dibb
Recent Deposition Of 210pb On The Greenland Ice Sheet: Variations In Space And Time, Jack E. Dibb
Earth Sciences
Detailed 210Pb profiles were determined for four "Chernobyl dated' snowpits sampled during a wide-ranging survey of the Greenland ice sheet during the 1988 season. The profiles from widely separated pits show little or no coherence; even for two pits only 40 km apart the profiles differ in detail. There does not appear to have been any seasonality in the deposition of 210Pb onto the ice sheet in the two years since the Chernobyl accident. The total deposition of 210Pb during this period (10-20 bq m-2) was about 20 times less than has been observed at mid-latitude sites in the eastern …
The Chernobyl Reference Horizon (?) In The Greenland Ice Sheet, Jack E. Dibb
The Chernobyl Reference Horizon (?) In The Greenland Ice Sheet, Jack E. Dibb
Earth Sciences
Published reports of the presence of radioactive debris from the Chernobyl reactor accident in snow on the Greenland ice sheet raised the strong prospect that such debris might constitute a valuable time stratigraphic marker all over the ice sheet. Large volume snow samples to test this possibility were collected from 7 snowpits as part of a wide ranging regional snow chemistry survey conducted during 1987 and 1988. Snow “labeled” with Chernobyl derived radioactivity was detected in all of the pits. However, the total amount of radioactive debris found at the different locations varied over a 20 fold range. The variability …