New Data On Old Climates

ANALYSIS of ice retrieved from more than 3,000 meters below the frigid surface of Antarctica is providing a clearer picture of vacillating temperature cycles at the South Pole during the past 800,000 years, according to a report in the journal Science (DOI: 10.1126/science.1141038).

Data from the Dome C ice core reveal that average temperatures during eight glacial ice ages and the periods between them ranged from 10 ??C cooler than the present, reached about 20,000 years ago, to 4.5 ??C warmer than the present, reached about 130,000 years ago. The results are helping confirm the "tight linkage between climate and the greenhouse gas effect," notes Jean Jouzel of France's Laboratory of Climate & Environmental Sciences, who led the research team.

The Dome C ice core was drilled and is being analyzed by the European Project for Ice Coring in Antarctica (EPICA). Researchers finished drilling the 3,260-meter core in 2004 just before hitting rock, and they have been reporting their findings in a series of journal papers. The latest results provide the first look at data from the final 120 meters of the core, the deepest and oldest section.

Estimates of global temperatures come from analysis of the ice for the isotopic ratio of deuterium to hydrogen. The ratio is higher during warmer periods because more heavy water evaporates from Earth's surface, thereby enriching the deuterium content of snow that subsequently is compressed into ice. The data are corroborated by data from other ice cores and from ocean sediment cores.

"The correlation between temperature in Antarctica and variations in sea level as recorded in marine sediments is remarkable over the entire 800,000-year record," Jouzel notes.

Younger sections of the EPICA Dome C core previously were analyzed for the deuterium-hydrogen ratio and for the content of the greenhouse gases methane, carbon dioxide, and nitrous oxide trapped in air bubbles in the ice. The earlier data reveal that CO₂ and CH₄ concentrations are higher now than for any period covered by the ice core, suggesting the impact of human activities. Elemental analyses of dust particles in the ice core and greenhouse gas analysis of the oldest core section are under way.