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.

Abstract: A study of atmospheric dimethylsulfide (DMS) and dimethylsulfoxide (DMSO) was conducted on a subdaily basis during austral summer months (450 samples from mid-December 1998 to late-February 1999) at Dumont d'Urville, a coastal Antarctic site (66° 40'S, 140° 01'E). In addition, subdaily aerosol samplings were analyzed for particulate methanesulfonate (MSA) and non-sea-salt sulfate (nssSO4 2?). During these summer months, DMS and DMSO levels fluctuated from 34 to 2923 pptv (mean of 290 ± 305 pptv) and from 0.4 to 57 pptv (mean of 3.4 ± 4.4 pptv), respectively. Mean MSA and non-sea-salt sulfate (nssSO4 2?) mixing ratios were close to 12.5 ± 8.2 pptv and 68.1 ± 35.0 pptv, respectively. In two occasions characterized by stable wind conditions and intense insolation, it was possible to examine the local photochemistry of DMS. During these events, DMSO levels tracked quite closely the solar flux and particulate MSA levels were enhanced during the afternoons. Photochemical calculations reproduce quite well observed diurnal variations of DMSO when we assume an 0.8 yield of DMSO from the DMS/OH addition channel and an heterogeneous loss rate of DMSO proportional to the OH radical concentration: 0.5×10?10 [OH] + 5.5x10?5 (in s?1). If correct, on a 24 hour average the heterogeneous loss of DMSO is estimated to be 2 times faster than the DMSO/OH gas phase oxidation in these regions. Very low levels of DMSO were found in the aerosol phase (less than 0.01 pptv), suggesting that an efficient oxidation of DMSO subsequently takes place onto the aerosol surface. The observed increase of MSA levels which takes place quasi-immediately after the noon DMSO maximum suggests that an heterogeneous oxidation of DMSO onto aerosols represents a more efficient pathway producing MSA compared to the gas phase DMSO/OH pathway. Since only a third of the total amount of DMSO lost can be explained by the observed enhancement of MSA levels, further studies investigating other species including methanesulfinic acid and dimethylsulfone (DMSO2) formed during the oxidation of DMS are here needed. When katabatic winds took place, bringing continental Antarctic air at the site, enrichments of DMSO relative to DMS and MSA relative to non-sea-salt sulfate levels were observed. That is in agreement with the hypothesis of an accumulation of DMSO and probably of gaseous MSA in the free Antarctic troposphere in relation to a less efficient heterogeneous loss rate of DMSO.

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.

Abstract: To investigate the oxidation chemistry of dimethylsulfide (DMS) in the marine atmosphere, atmospheric DMS, SO2, as well as several DMS oxidation products in aerosol phase such as non-sea-salt sulfate (nss-SO4), methanesulfonate (MSA), and dimethylsulfoxide (DMSOp) have been measured during the Albatross campaign in the Atlantic Ocean from October 9 to November 2, 1996. Long-range transport, local sea-to-air flux of DMS (F DMS), marine boundary layer (MBL) height variation, and photochemistry were found to be the major factors controlling atmospheric DMS concentration which ranged from 29 to 396 parts per trillion by volume (pptv) (mean of 120±68 pptv) over the cruise. The spatial variability of MSA and DMSOp follows the latitudinal variations of F DMS. A 2-day period of intensive photochemistry associated with quite stable atmospheric conditions south of the equator allowed the observation of anticorrelated diurnal variations between DMS and its main oxidation products. A chemical box model describing sulfur chemistry in the marine atmosphere was used to reproduce these variations and investigate coherence of experimentally calculated fluxes F DMS with observed DMS atmospheric concentrations. The model results reveal that the measured OH levels are not sufficient to explain the observed DMS daytime variation. Oxidizing species other than OH, probably BrO, must be involved in the oxidation of DMS to reproduce the observed data.

Abstract: A primary goal of developing the CO2 atmospheric measurement network is to better characterize the sources and sinks of atmospheric CO2. Atmospheric transport models can be used to interpret atmospheric measurements in terms of surface fluxes using inverse methodology. In this paper we present a three-dimensional (3-D) inversion of CO2 measurements in order to infer annual sources and sinks of CO2 at a continental scale (continents and ocean basins) for a climatological year representing the 1985–1995 period. Solving this inverse problem requires (1) a data space representing monthly CO2 measurements, here at 77 sites (surface, ships, planes), (2) a flux space describing a priori fluxes between carbon reservoirs, and (3) a 3-D transport model linking the flux space to the data space. Knowledge of these three elements, together with their associated errors, allows one to reduce the uncertainties of the CO2 sources and sinks. In the 1985–1995 period, for our control inversion, the global continental sink is found to be 2.7±1.5 Gt C yr1 for an optimized deforestation source of 1.4±0.6 Gt C yr1, yielding a net land uptake of 1.3±1.6 Gt C yr1 (fossil fuel removed). The continental partition of this budget is (in units of Gt C yr1): Arctic +0.2±0.3, North America ?0.5±0.6, Europe ?0.3±0.8, north Asia ?1.5±0.7, tropics (except Asia) +0.3±0.9, tropical Asia +0.8±0.4, and Southern Hemisphere ?0.1±0.3. The inferred partition for the controversial Northern Hemisphere CO2 sink reveals that a major sink is located over the north Asia continent. For oceans we find a net global sink of 1.5±0.5 Gt C yr1 with the following partition (in units of Gt C yr1): North Pacific ?0.3±0.2, North Atlantic ?0.8±0.3, equator +0.6±0.2, 20°S–50°S oceans ?0.9±0.3, and austral ocean ?0.1±0.1.