Ice Cores Hold Earth's Climate

As ice forms, gasses and other materials are trapped in the layers that build up over time. This makes the polar regions time machines. With more than 500,000 years of snow and ice accumulation, the ice sheets are ideal places for paleoclimatologists to set up their tubular drills and extract cores—long cylinders of sediment and rock—in order to read the history captured therein.

Working in the center of Antarctica's ice sheet, near the Russian research base of Vostok, a group of researchers from the United States, Russia, and France have extracted the world's deepest core. As a result, the scientists have differentiated more than four ice ages, or about 400,000 years of history.

What researchers are discovering is that Earth's climate is not stable, and never has been. Ice ages are punctuated by interglacial periods of relative warmth, such as the one marking the close of the twentieth century. The interglacial periods have been marked by sudden shifts in temperature, wind patterns, and sea levels.

"Some of these rapid changes occur in two decades," says Paul Mayewski, a glaciologist from the University of New Hampshire and a thirty-year veteran of NSF-funded research in Antarctica. "Some [of the pattern changes] actually start in less than two years." While he finds these dramatic shifts surprising, he also notes that Antarctic cores are in sync with the climate data found in the ice cores from Greenland.

Mayewski and his colleagues learn about these changes by examining the chemical indicators, such as sea salt, within the extracted ice cores. High sea salt levels signal increased storminess and stronger winds. In addition, measurements of oxygen isotopes in the ice reveal cooling during periods of increased sea salt. Other tests probe for indicators of wind patterns, volcanic activity, and sea level.

However, the researchers still don't know what caused the rapid climate pattern changes evidenced in the ice cores.

"We need to understand how these changes work in order to make a better assessment of natural climatic change," Mayewski says, "and a better assessment of the human impact on the future climate."