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Title |
Highly deformed basal ice in the Vostok core, Antarctica |
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Journal Article |
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Year |
2002 |
Publication |
Geophysical research letters |
Abbreviated Journal |
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Volume |
29 |
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Keywords |
1040 Geochemistry: Isotopic composition/chemistry; 1827 Hydrology: Glaciology; 4540 Oceanography: Physical: Ice mechanics and air/sea/ice exchange processes; 9310 Information Related to Geographic Region: Antarctica |
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Abstract |
Our paper documents the build-up of a highly deformed basal ice layer in the basal part of the Vostok ice core. This is done mainly on the basis of an isotopic composition investigation of the ice. Complex deformation in the lower 228 m of the ice sheet has resulted in folding and intermixing of ice at a submetric scale and, for the upper part of this basal sequence, in interbedding of ice layers from distinct origins at a larger scale. This complex deformation occurred at a temperature largely below the pressure-melting point. The basal ice layer has built upwards and size-selective incorporation of bed material into the ice has taken place. The documentation of this complex basal deformation has implications for the maximum age of ice that will be useful in paleoclimate studies and for ice sheet dynamics. |
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902 |
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American Geophysical Union |
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0094-8276 |
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yes |
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Call Number  |
IPEV @ Thierry.Lemaire @ |
Serial |
5599 |
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Author |
Bhattacharya, S.K.; Chakraborty, S.; Savarino, J.; Thiemens, M.H. |
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Title |
Low-pressure dependency of the isotopic enrichment in ozone: Stratospheric implications |
Type |
Journal Article |
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Year |
2002 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
107 |
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Keywords |
1040 Geochemistry: Isotopic composition/chemistry; 4852 Oceanography: Biological and Chemical: Photochemistry |
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Abstract |
Stratospheric ozone is enriched in the heavy isotopes (17O and 18O) relative to the ambient oxygen from which it is formed. This enrichment varies with altitude, attaining very high values between 30 and 40 km. A recent theory of Y. Q. Gao and R. A. Marcus explores the reasons for isotopic enrichment in the process of ozone formation and is particularly useful to understand the laboratory results. The stratospheric variations are sought to be explained in terms of temperature dependence of isotopic enrichment, but the magnitude of variation does not match with predictions accurately. We demonstrate here that isotopic enrichment in ozone generated by oxygen photolysis depends on the pressure of the oxygen reservoir and can have very high values (at about 15 torr), comparable to the highest observed stratospheric values. Analysis of the data shows that secondary enrichment through ozone dissociation can add to the primary enrichment associated with ozone formation. The effect of dissociation is found to be more pronounced in the pressure range of 15 to 50 torr, resulting in high enrichment. It is shown that the relative kinetics, pressure and temperature conditions of ozone formation and dissociation play an important role in determining the ultimate value of the enrichment. The results are particularly useful to understand the stratospheric data and resolve the observed discrepancy. |
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399 |
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American Geophysical Union |
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0148-0227 |
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yes |
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IPEV @ Thierry.Lemaire @ |
Serial |
5611 |
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Title |
Metabolic adjustments in breeding female kittiwakes ( Rissa tridactyla ) include changes in kidney metabolic intensity |
Type |
Journal Article |
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Year |
2008 |
Publication |
Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology |
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Volume |
178 |
Issue |
6 |
Pages |
779-784 |
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330 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5613 |
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Author |
Trampert, J.; Snieder, R. |
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Title |
Model Estimations Biased by Truncated Expansions: Possible Artifacts in Seismic Tomography |
Type |
Journal Article |
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Year |
1996 |
Publication |
Science |
Abbreviated Journal |
Science |
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Volume |
271 |
Issue |
5253 |
Pages |
1257-1260 |
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Keywords |
seismology ; tomography ; errors ; mathematical models ; methods ; inverse problem ; elastic waves ; Rayleigh waves ; algorithms |
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Abstract |
In most linear imaging problems, where the model to be sought is expanded in a set of basis functions, it is common practice to truncate the set at a certain (arbitrary) level. The solution then depends on the chosen parameterization, and neglected basis functions may leak into the solution to produce artifacts in the retrieved model. An unbiased estimate of the coefficients of the true model may be obtained in the chosen finite basis set ; here, a method to suppress leakage is illustrated on an example of global seismic tomography. |
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133 |
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0036-8075 |
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Notes |
10.1126/science.271.5253.1257 |
Approved |
yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5615 |
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Title |
New modeling of the Vostok ice flow line and implication for the glaciological chronology of the Vostok ice core |
Type |
Journal Article |
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Year |
2004 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
109 |
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Pages |
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Keywords |
glaciology; paleoclimatology; Antarctica; inverse theory; 1827 Hydrology: Glaciology; 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology; 3260 Mathematical Geophysics: Inverse theory; 9310 Information Related to Geographic Region: Antarctica |
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Abstract |
We have used new spaceborne (elevation) and airborne (ice thickness) data to constrain a 2D1/2 model of snow accumulation and ice flow along the Ridge B-Vostok station ice flow line (East Antarctica). We show that new evaluations of the ice flow line geometry (from the surface elevation), ice thickness (from low-frequency radar data), and basal melting and sliding change significantly the chronology of the Vostok ice core. This new Vostok dating model reconciles orbital and glaciological timescales and is in good agreement with the Dome Fuji glaciological timescale. At the same time, the new model shows significantly older ages than the previous GT4 timescale for the last glacial part, being thus in better agreement with the GRIP and GISP2 chronologies. |
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355 |
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American Geophysical Union |
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ISSN |
0148-0227 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5618 |
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Title |
Revised spherical cap harmonic analysis (R-SCHA): Validation and properties |
Type |
Journal Article |
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Year |
2006 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
111 |
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Pages |
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Keywords |
magnetism; regional modeling; Spherical Cap Harmonic Analysis; 1214 Geodesy and Gravity: Geopotential theory and determination; 1517 Geomagnetism and Paleomagnetism: Magnetic anomalies: modeling and interpretation; 1532 Geomagnetism and Paleomagnetism: Reference fields: regional, global; 1541 Geomagnetism and Paleomagnetism: Satellite magnetics: main field, crustal field, external field; 1545 Geomagnetism and Paleomagnetism: Spatial variations: all harmonics and anomalies |
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Abstract |
We recently proposed a technique able to represent the spatial variations of the magnetic field at regional scales. However, we pointed out that these preliminary developments were not suited for the complete representation of the geomagnetic field. In this paper, we propose a complete revision, the revised spherical cap harmonic analysis (R-SCHA), which introduces slight changes in order to rectify the previous shortcomings. In addition, some discussions shed a new light on the former spherical cap harmonic analysis (SCHA) and help us to demonstrate its deficiencies and approximations. We finally show that R-SCHA now fully satisfies the natural properties of potential fields. R-SCHA also yields analytical relationships with the spherical harmonics. Taking advantage of the mathematical equivalence of both representations, we explore the relevance of fundamental concepts like spectrum, minimum wavelength, or internal/external field separation. We conclude that these concepts are misleading and must be handled with care in regional modeling. A prime goal being the ability of R-SCHA to represent real data sets, we also investigate and illustrate the effect of finite series expansions. A norm for the regularization of the inverse problem is proposed as well. The conclusions drawn in this paper allow us to validate the method and to assert that the present proposal is suited for modeling and studying the lithospheric magnetic field from ground to satellite altitudes at regional scales. |
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139;905 |
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American Geophysical Union |
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ISSN |
0148-0227 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5626 |
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Author |
Sciare, J.; Baboukas, E.; Kanakidou, M.; Krischke, U.; Belviso, S.; Bardouki, H.; Mihalopoulos, N. |
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Title |
Spatial and temporal variability of atmospheric sulfur-containing gases and particles during the Albatross campaign |
Type |
Journal Article |
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Year |
2000 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
105 |
Issue |
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344 |
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American Geophysical Union |
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0148-0227 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5632 |
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Author |
Legrand, M.; Sciare, J.; Jourdain, B.; Genthon, C. |
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Title |
Subdaily variations of atmospheric dimethylsulfide, dimethylsulfoxide, methanesulfonate, and non-sea-salt sulfate aerosols in the atmospheric boundary layer at Dumont d'Urville (coastal Antarctica) during summer |
Type |
Journal Article |
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Year |
2001 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
106 |
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241;415 |
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Publisher |
American Geophysical Union |
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ISSN |
0148-0227 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5636 |
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Author |
Tackett, P.J.; Cavender, A.E.; Keil, A.D.; Shepson, P.B.; Bottenheim, J.W.; Morin, S.; Deary, J.; Steffen, A.; Doerge, C. |
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Title |
A study of the vertical scale of halogen chemistry in the Arctic troposphere during Polar Sunrise at Barrow, Alaska |
Type |
Journal Article |
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Year |
2007 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
112 |
Issue |
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Pages |
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Keywords |
Arctic; halogen chemistry; vertical profiles; 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0736 Cryosphere: Snow; 0738 Cryosphere: Ice; 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes; 0322 Atmospheric Composition and Structure: Constituent sources and sinks |
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Programme |
457 |
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Publisher |
American Geophysical Union |
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ISSN |
0148-0227 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5635 |
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Title |
Effect of density on electrical conductivity of chemically laden polar ice |
Type |
Journal Article |
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Year |
2002 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
107 |
Issue |
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Pages |
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Keywords |
0634 Electromagnetics: Measurement and standards; 1863 Hydrology: Snow and ice; 1894 Hydrology: Instruments and techniques; 9310 Information Related to Geographic Region: Antarctica |
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Abstract |
Electrical conductivity measurements made using the dielectric profiling technique (DEP) are compared to chemical data from the top 350 m of the Dome C ice core in Antarctica. The chemical data are used to calculate the concentration of the major acidic impurities in the core: sulphuric acid and hydrochloric acid. The conductivity coefficients in solid ice for sulphuric acid (?H2SO4) and hydrochloric acid (?HCl) are found to be 4.9 and 4.5 S m?1M?1. These are consistent with previously found values for the acid conductivity coefficient at different sites and suggest that the same conductivity mechanisms are important in all polar ice. A method of rolling regression analysis is used to find the variation of the pure ice conductivity (?? pure) and the conductivity coefficient of sulphuric acid, ?H2SO4, with depth. Then ?? pure and ?H2SO4are assessed against changes in core density and hence volume fraction of ice, v, due to the inclusion of air bubbles in the firn. Looyenga's model for dielectric mixtures applied to conduction in firn broadly predicts the variation observed in ?? purebut does not fit well for ice above 110 m. A previous application of the theory of percolation in random lattices is used to model the conductivity coefficient in firn. The coefficient ?H2SO4 is linked to vby the power law: ?H2SO4(v) ? ?H2SO4(1) (v ? vc)t; where vc is a threshold volume fraction below which no conduction can take place and is related to the geometry of the conducting lattice being modeled. The value of the exponent tis also dependent on the structure of the lattice and is here found to be t = 2.5, which is slightly lower than the previously obtained value of t = 2.7 for a structure where each grain has between 14 and 16 nearest neighbors. This model is consistent with the concept of conduction, via liquid H2SO4, taking place at two grain boundaries for firn. The model does not, however, preclude conduction taking place via acid situated at three grain boundaries or in an interconnected vein network at densities above 640 kg m?3. |
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Programme |
960 |
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Publisher |
American Geophysical Union |
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ISSN |
0148-0227 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5640 |
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