Goujon, C.; Barnola, J.-M.; Ritz, C. (2003). Modeling the densification of polar firn including heat diffusion: Application to close-off characteristics and gas isotopic fractionation for Antarctica and Greenland sites. J. Geophys. Res., 108.
Abstract: Modeling the densification of polar firn is essential to estimate variations of close-off characteristics (density, close-off depth, delta age) in relation with past climate parameters (temperature and accumulation rates). Furthermore, the air composition in the firn is modified by gravitational and thermal fractionation, and stable isotope measurements of permanent gases like nitrogen or argon can provide information on the amplitude of these fractionations. In this work, we propose a new model coupling firn densification and heat diffusion. In addition to the determination of the firn thickness and gas-ice age differences, the model allows a reconstruction of the time evolution of the temperature for different sites in Antarctica (Vostok) and Greenland (GISP2) and therefore the evolution of gravitational and thermal isotopic fractionations in firn. Under present-day conditions, the modeled profiles are in good agreement with the available temperature measurements in firn. For sites with low accumulation rates such as Vostok, the results show the existence of temperature gradients in the firn column even when no rapid climatic changes occur. The comparison of the modeled ?15N results to measurements allows to better constrain the ?18O-temperature relationship, used to infer the surface temperature history, and for GISP2, the model validates the long-term borehole-based temperature.
Keywords: 1827 Hydrology: Glaciology; 1863 Hydrology: Snow and ice; 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology
Programme: 902
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Jouzel J., Vimeux F., Caillon N., Delaygue G., Hoffmann G., Masson Delmotte V. & Parre. (2003). Magnitude of the isotope-temperature scaling for interpretation of central Antarctic ice cores. J. Geophys. Res., 108, 1029–1046.
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Barnes, P.R.F.; Wolff, E.W.; Mader, H.M.; Udisti, R.; Castellano, E.; Röthlisberger, R. (2003). Evolution of chemical peak shapes in the Dome C, Antarctica, ice core. J. Geophys. Res., 108.
Abstract: Interpretation of the chemical layers measured in ice cores requires knowledge of processes occurring after their deposition on the ice sheet. We present evidence for the diffusion of soluble ions in the top 350 m of the Dome C ice core, Antarctica, that helps in explaining the unexpectedly broad volcanic peaks observed at depth. A windowed-differencing operation applied to chemical time series indicates a damping of the signals over the past 11,000 years, independent of minor climatic variation, for sulfate and chloride, but not sodium. This implies a diffusive process is transporting both sulfate and chloride ions while the sodium ions remain fixed. We estimate the effective diffusivity in the core to be 4.7 × 10?8 m2 yr?1 for sulfate and 2.0 × 10?7 m2 yr?1 for chloride. These values are not high enough to significantly disrupt chemical interpretation in this section of core, but could be significant for older ice. The temperature of this section of ice (?53°C) implies that the predominantly acidic sulfate (and possibly chloride ions) will exist in the liquid phase while the sodium may be solid. We propose and develop two new mechanisms that could explain the observed solute movement. One involves the diffusion of solute through a connected vein network driven by liquid concentration imbalances instigated by the process of grain growth. The other considers a system of discontinuous veins where grain growth increases connectivity between isolated vein clusters allowing the spread of solute. In both mechanisms, the effective diffusivity is governed indirectly by grain growth rate; this may be a significant factor controlling effective diffusion in other cores.
Keywords: 1863 Hydrology: Snow and ice; 9310 Information Related to Geographic Region: Antarctica; 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology; 3999 Mineral Physics: General or miscellaneous; 0325 Atmospheric Composition and Structure: Evolution of the atmosphere
Programme: 960
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Schmidt, M., R. Graul, et al. (2003). The Schauinsland CO2 record: 30 years of continental observations and their implications for the variability of the European CO2 budget. J. Geophys. Res., 108(d19), 4619.
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Cosme, E.; Genthon, C.; Martinerie, P.; Boucher, O.; Pham, M. (2002). The sulfur cycle at high-southern latitudes in the LMD-ZT General Circulation Model. J. Geophys. Res., 107.
Abstract: This modeling study was motivated by the recent publication of year-round records of dimethylsulfide (DMS) and dimethylsulfoxide (DMSO) in Antarctica, completing the available series of sulfate and methanesulfonic acid (MSA). Sulfur chemistry has been incorporated in the Laboratoire de Météorologie Dynamique-Zoom Tracers (LMD-ZT) Atmospheric General Circulation Model (AGCM), with high-resolution and improved physics at high-southern latitudes. The model predicts the concentration of six major sulfur species through emissions, transport, wet and dry deposition, and chemistry in both gas and aqueous phases. Model results are broadly realistic when compared with measurements in air and snow or ice, as well as to results of other modeling studies, at high- and middle-southern latitudes. Atmospheric MSA concentrations are underestimated and DMSO concentrations are overestimated in summer, reflecting the lack of a DMSO heterogeneous sink leading to MSA. Experiments with various recently published estimates of the rate of this sink are reported. Although not corrected in this work, other defects are identified and discussed: DMS concentrations are underestimated in winter, MSA and non-sea-salt (nss) sulfate concentrations may be underestimated at the South Pole, the deposition scheme used in the model may not be adapted to polar regions, and the model does not adequately reproduces interannual variability. Oceanic DMS sources have a major contribution to the variability of sulfur in these regions. The model results suggest that in a large part of central Antarctica ground-level atmospheric DMS concentrations are larger in winter than in summer. At high-southern latitudes, high loads of DMS and DMSO are found and the main chemical sink of sulfur dioxide (SO2) is aqueous oxidation by ozone (O3), whereas oxidation by hydrogen peroxide (H2O2) dominates at the global scale. A comprehensive modeled sulfur budget of Antarctica is provided.
Keywords: 0305 Atmospheric Composition and Structure: Aerosols and particles; 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; 3319 Meteorology and Atmospheric Dynamics: General circulation; 9310 Information Related to Geographic Region: Antarctica
Programme: 414;903
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Beine H.J., Honrath R.E., Domine F., Simpson W.R. & Fuentes J.D. (2002). NOx during background and ozone depletion periods at Alert: Fluxes above the snow surface. J. Geophys. Res., 107(d21), 4584.
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Lengagne T., Aubin T., Jouventin P. & Lauga J. (2000). Perceptual salience of individually distinctive features in the calls of adult king penguins. J. Acoust. Soc. Am., 107(1), 508–516.
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Leyrit H. (1995). La menace volcanique dans les territoires français d'outre mer. Géologues, 107, 9–32.
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Delmas R. (1998). Ice-core records of global climate and environment changes. Journal of earth system science, 107(4), 307–319.
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Gabrielli P., Barbante C., Planchon F A.M., Ferrari C., Delmonte B. & Boutron C.F. (2003). Changes in the occurrence of heavy metals in polar ice during the last climatic cycles, with special emphasis on the possible link between cosmic dust accretion rate and the 100 kyr cycle. Journal de Physique, 107, 499–503.
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