Southern Ocean sea-ice extent, productivity and iron flux over the past eight glacial cycles.

Sea ice and dust flux increased greatly in the Southern Ocean during the last glacial period. Palaeorecords provide contradictory evidence about marine productivity in this region, but beyond one glacial cycle, data were sparse. Here we present continuous chemical proxy data spanning the last eight glacial cycles (740,000 years) from the Dome C Antarctic ice core. These data constrain winter sea-ice extent in the Indian Ocean, Southern Ocean biogenic productivity and Patagonian climatic conditions. We found that maximum sea-ice extent is closely tied to Antarctic temperature on multi-millennial timescales, but less so on shorter timescales. Biological dimethylsulphide emissions south of the polar front seem to have changed little with climate, suggesting that sulphur compounds were not active in climate regulation. We observe large glacial-interglacial contrasts in iron deposition, which we infer reflects strongly changing Patagonian conditions. During glacial terminations, changes in Patagonia apparently preceded sea-ice reduction, indicating that multiple mechanisms may be responsible for different phases of CO2 increase during glacial terminations. We observe no changes in internal climatic feedbacks that could have caused the change in amplitude of Antarctic temperature variations observed 440,000 years ago.

Isotopic evidence for the source of lead in Greenland snows since the late 1960s.

IN 1969, Murozumi et al.1 demonstrated that the concentration of lead in Greenland snow had increased by a factor of 200 since ancient times, and concluded that most of this increase was a result of the use of alkyl-leaded petrol. Partly because of these findings, the United States and other western countries limited the use of lead additives in petrol from about 1970. Recently, Boutron et al.2 showed that the lead concentration in Greenland snow had decreased by a factor of ∼7.5 over the past 20 years, and suggested that this was a result of the decline in use of leaded petrol. We present here measurements of the 206Pb/207Pb ratio of the lead contained in the samples studied by Boutron et al. Because aerosols from the atmosphere above the United States are more radiogenic than those from Eurasia, we can trace the relative contributions of these two sources in the Greenland lead over the period analysed by Boutron et al.We find that the United States was a significant source of lead in the 1970s, but it has since declined considerably in relative importance. This decline mirrors the decrease in use of leaded petrol in the United States, confirming the earlier hypothesis.

Greenland ice evidence of hemispheric lead pollution two millennia ago by greek and roman civilizations.

Analysis of the Greenland ice core covering the period from 3000 to 500 years ago-the Greek, Roman, Medieval and Renaissance times-shows that lead is present at concentrations four times as great as natural values from about 2500 to 1700 years ago (500 B.C. to 300 A.D.). These results show that Greek and Roman lead and silver mining and smelting activities polluted the middle troposphere of the Northern Hemisphere on a hemispheric scale two millennia ago, long before the Industrial Revolution. Cumulative lead fallout to the Greenland Ice Sheet during these eight centuries was as high as 15 percent of that caused by the massive use of lead alkyl additives in gasoline since the 1930s. Pronounced lead pollution is also observed during Medieval and Renaissance times.

Clean conditions for the determination of ultra-low levels of mercury in ice and snow samples.

Laboratory facilities and methods are presented for the determination of ultra-low levels of mercury (Hg) in ice and snow samples originating from polar ice caps or temperate regions. Special emphasis will be given to the presentation of the clean laboratory and the cleaning procedures. The laboratory is pressurized with air filtered through high efficiency particle filters. This first filtration is not enough to get rid of contamination by Hg in air. Experiments are conducted in a clean bench, especially built for Hg analysis, equipped with both particle filter and activated charcoal filter. It allows to obtain very low levels of atmospheric Hg contamination. Ultrapure water is produced for cleaning all the plastic containers that will be used for ice and snow samples and also for the dilution of the standards. Hg content in laboratory water is about 0.08+/-0.02 pg/g. A Teflon system has been developed for the determination of Hg in ice and snow samples based on Hg(II) reduction to Hg(0) with a SnCl2/HNO3 solution followed by the measurement of gaseous Hg(0) with a Hg analyzer GARDIS 1A+ based on the Cold Vapor Atomic Absorption Spectroscopy method. Blank determination is discussed.

Heavy metals in antarctic ice from Law Dome: initial results.

Pb, Cd, Cu, and Zn have been measured using ultraclean procedures in eight sections taken from two well-dated ice cores from Law Dome, an independent small size ice cap with high accumulation rate situated in the coastal area of East Antarctica. Seven sections were dated from the 1830s to 1940s and one was dated from three millennia ago. The data show that there are strong seasonal variations in the concentrations of Pb and Cd, with values approximately tow-to fourfold higher in winter than in spring-summer. Evaluation of the contributions from the different sources suggests that contribution from sea salt spray is relatively important, especially for Cd. Contribution from marine biogenic emissions could also be very significant. The importance of marine contributions is consistent with strong intrusions of marine air masses at this coastal site, especially during wintertime.

Tracing the origin of pollution in French Alpine snow and aerosols using lead isotopic ratios.

Fresh snow samples collected at 15 remote locations and aerosols collected at one location in the French Alps between November 1998 and April 1999 have been analyzed for Pb concentration and isotopic composition by thermal ionization mass spectrometry. The snow samples contained 19-1300 pg/g of Pb with isotopic ratios 206Pb/207Pb (208Pb/207Pb) of 1.1279-1.1607 (2.3983-2.4302). Airborne Pb concentrations at one sampling site ranged from 0.42 to 6.0 ng/m3 with isotopic ratios of 1.1321-1.1427 (2.4029-2.4160). Air mass trajectory analysis combined with isotopic compositions of potential source regions did not show discernible evidence of the long-range atmospheric transport of pollutants. Isotopic ratios in the Alpine snow samples and thus the free troposphere were generally higher than airborne Pb isotopic ratios in urban France, which coupled with the relatively high Pb concentrations suggested a regional anthropogenic Pb source, probably Italy but possibly Eastern Europe.

Lead concentrations and isotopic signatures in vintages of French wine between 1950 and 1991.

Vintages of French wine from 1950 to 1991 were analyzed for lead isotopes and concentrations to investigate whether they might be used to archive the isotopic composition of the anthropogenic lead in aerosols to which the vineyard was exposed. Early vintages (1950-1980) contained 78-227 ng/g of lead with 206Pb/207Pb ratios between 1.152 and 1.173, while the later vintages displayed significantly lower concentrations and a smaller range of isotopic ratios. The concentration of trimethyl lead, which is associated with automobile emissions, was found to be poorly correlated with total lead in the wines, suggesting that automobile aerosols were not a significant source of the lead. This result was supported by lead isotope data which showed a poor correlation with the available petrol and aerosol data. To identify its origin lead isotopes were measured in vineyard aerosols, soil particles, bottle caps, corks, and brass components used to dispense the wine. Although a dominant source could not be identified there was some evidence to suggest that brass which had a high lead concentration was a significant contributor. Because the lead contribution from the processing of wine was probably relatively high in the past it is unlikely that old vintages of wine will be a suitable archive for lead isotopes in aerosols.

Determination of Rh, Pd, and Pt in Polar and Alpine Snow and Ice by Double-Focusing ICPMS with Microconcentric Nebulization.

The performance of a double-focusing inductively coupled plasma mass spectrometer equipped with a microconcentric nebulizer was investigated for the direct simultaneous determination of Rh, Pd, and Pt in less than 1 mL of melted snow and ice samples originating from remote sites. Ultraclean procedures were adopted in the laboratories and during the pretreatment steps, to avoid possible contamination problems. Spectroscopic and nonspectroscopic interferences affecting the determination of Rh, Pd, and Pt were carefully considered. Detection limits of 0.02, 0.08, and 0.008 pg g(-)(1) for Rh, Pd, and Pt, respectively, were obtained using the following isotopes: (103)Rh, (106)Pd, and (195)Pt. Repeatability of measurements, as RSD, was 27, 28, and 29%, for Rh, Pd, and Pt, respectively. The new method was applied to the analysis of samples coming from Greenland, Antarctica, and the Alps in order to assess the past natural background concentrations and to determine the present level of these polluting substances. The extremely low detection limits allowed the direct analysis of all samples except for two Greenland ice core sections dating from 7260 and 7760 years ago for which a preconcentration step was necessary. Concentration ranges for all snow samples were (in pg g(-)(1)) as follows: Rh (0.0005-0.39), Pd (0.01-16.9), and Pt (0.008-2.7). The lowest concentrations were measured in the enriched Greenland ancient ice samples.