Concentrations of CO, in glacier ice (ppm by volume) Concentrations of CO, in air bubbles from three Antarctic ice cores at the starting depth TABLE 2 Fig. 4. Errors of measurement of CO, in air bubbles of ice cores from Greenland and Ant- arctica (Oeschger et al., 1985) and claimed man-made increases of CO, level in recent Ant- arctic ice samples due to fossil fuel burning (A, Pearman et al., 1986; B, Raynaud and Barnola, 1985; C, Neftel et al., 1985). Solid lines indicate + 1 S.D.; broken lines indicate + 2 S.D. with the temporal differences in CO, concentrations in ice used in suppor’ of claims discussed above that the level of this gas has increased in the at mosphere due to man’s activity. This "CO, glacier signal’ was in the case o! Raynaud and Barnola (1985) 17 ppm, in the case of Neftel et al. (1985) 4¢ ppm, and in the case of Pearman et al. (1986) 13 ppm (Fig. 4). According tc Oeschger et al. (1985) the ‘errors’ (at assumed 68% probability) of singl measurements of CO, in air trapped in ice cores from Greenland and Ant arctica range between 11 and 24 ppm. At an assumed 95% probability, the ‘errors’ of measurements reach about 47 ppm (Fig. 4). Thus the claimec signals of man-made CO, increase are of the same magnitude as the range of uncertainty of measurements. In air hubbles from neishboring | 5-cm thick slices of an Antarctic ice Fig. 5. Two sets of CO, concentrations in gas recovered from the Byrd ice core (Antarctica); redrawn from Neftel et al. (1982) (dots and bars for median and range) and Neftel et al. (1988) (shadowed areas represent the reported lo errors). Because the data have very wide variations Neftel et al. (1982) have shown the median values. Note that wide variations high readings from both upper and lower parts of the core recorded in 1982 were not presented in 1988. samples were rich in cracks, the bubble pressure was much lower than the load pressure. This difference was due to gas release through the cracks. A similar pressure reduction was recorded in ice cores from various sites (Langway, 1958; Gow, 1968b; Gow and Wiliamson, 1975). In the Mizuho core the cracks were associated with up to an ~ 40% decrease in the gas con- tent of the ice (Nakawo and Narita, 1985). For the same Mizuho core, Narita and Nakawo (1985) reported pressure-cracked bubbles, with ’brims’ which might be caused by thermal shock and pressure release. Similar crack rings, and a fissure-like distortion of the ice structure, were observed in and around relaxed air bubbles by Shoji and Langway (1983). wT. .*4. «ff. Jl eT i kt! PE” io GY ch, Cee %y .— fi, ._4,% gf Bt gg le Concentrations of Pb and Zn in surface snow and contaminated ice cores from East Antarctica (pg/g) *Boutron et al. (1990). ’Boutron et al. (1987). Concentrations of SO,7", Al and Na in surface snow from Antarctica and in central parts o contaminated Vostok ice core (ng/g) Fig. 9. Schematic illustration of processes occurring in the top 1-2 m of snow and firn strata in cold polar ice sheets (not to scale). Absorption of solar radiation at low temperature partly volatilizes and melts the snow flakes. Snow is metamorphosed to firn. The thermal gradient and gravitational compression of snow cause upward movement of gas. Some air escapes from snow and firn back to the atmosphere, and H,O vapor condenses near the wind-cooled sur- face. Depth hoar forms due to loss of material by sublimation. Meltwater seeps down and col- lects over impermeable layers. Fig. 10. Concentrations of CO, in the Siple (Antarctica) ice core: (a) with, and (b) without assuming a 95-year younger age of air than the age of the enclosing ice. The crossed line represents the reported atmospheric CO, concentrations at Mauna Loa (Hawaii). The reported analytical uncertainty, = + 3 ppm, is larger than the size of the data points. The core was partially melted during transportation (Etheridge et al., 1988). Without assuming the age difference, the Siple and Mauna Loa curves cannot be made to overlay each other. (a) Adapted from Siegenthaler and Oeschger (1987) and Bolin et al. (1989); (b) from Fig. 3. Composition of air in the atmosphere and in glacier ice Fig. 11. Processes influencing the chemical and isotopic composition of air inclusions in ice. Depth is the dependent abscissa. Adapted after: Barnola et al. (1987) — CO, concentration in gas inclusions in the Vostok core and their assigned age; Gow (1971), Gow and Williamson (1975), Gow and Williamson (1976) — core volume expansion, air bubble disappearance, for- mation of secondary cavities, brittle ice, pressure in air inclusions 3 years after drilling, crystal size in the Byrd core; Vostretsov et al. (1984) — temperature in the Vostok borehole; the verti- cal arrow D indicates the total disappearance of air bubbles in the Vostok core, after Korotkevich et al. (1978); the vertical arrows C indicate the sites of highest contamination of the inner parts of the Vostok core with Pb, Zn, Al and Na from drilling fluid, after Boutron et al. (1987, 1990).
