Researcher Mary Davis examines a thick layer of dust inside
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Researcher Mary Davis examines a thick layer of dust inside an ice core

June 1, 2010
Researcher Mary Davis examines a thick layer of dust inside an ice core taken from Mt. Kilimanjaro in Tanzania, Africa. The dust layer signifies a major drought event that struck the region in the past. Researchers have been analyzing ice cores taken from the ice sheets on Kilimanjaro in search of clues to past climate conditions at this tropical locale. [One of 5 related images. See Next Image.]

More about this Image Ice cores contain an abundance of information about the earth's climate in the past. They are the most effective natural recorder of climate change, more so than tree rings or sediment layers. Ice cores taken from certain undisturbed locations can contain an uninterrupted, detailed climate record extending back hundreds of thousands of years. This record can include temperature, precipitation, chemistry and gas composition of the lower atmosphere, volcanic eruptions, solar variability, sea-surface productivity and a variety of other climate indicators.

In 2000, National Science Foundation-grantee Lonnie Thompson, a geological science professor from Ohio State University (OSU), led an expedition to drill six ice cores from the ice fields on Mt. Kilimanjaro. While camping for a month at their drill site located above 19,300 feet, Thompson and his team collected 215 meters (705 feet) of frozen ice core, which they brought back to OSU's Byrd Polar Research Center.

Analysis of the core suggests dramatic changes in the climate and temperature on and around Mt. Kilimanjaro since the ice fields were formed approximately 11,700 years ago. For example, around 9,500 years ago, the landscape was far wetter and different. Today, Lake Chad is the fourth largest body of water on the African continent, measuring about 17,000 square kilometers. But 9,500 years ago, it covered some 350,000 square kilometers--an area larger than the Caspian Sea!

Analysis of the ice cores also indicates evidence of three catastrophic droughts that took place:

* A 500-year-period beginning around 8,300 years ago, when methane levels in the ice dropped dramatically. Thompson believes this represents a time when Africa's lakes were drying up.

* An abrupt depletion in oxygen-18 isotopes that researchers believe signals a second drought event occurring around 5,200 years ago.

* A visible dust layer in the ice cores dating back to about 4,000 years ago. Thompson believes this marks a severe 300-year drought that struck the region. Historical records show that a massive drought rocked the Egyptian empire at the time. According to Thompson, up until this time, people had been able to survive in areas that are now just barren Sahara Desert.

Thompson believes that whatever happened to cause these dramatic climate changes in the past, could certainly occur again. He has already predicted that Kilimanjaro's ice fields will vanish within 15 years. His team found that the summit of the ice fields has lowered by at least 17 meters (nearly 56 feet) since 1962, an average shrinkage of about a half-meter in height each year. In addition, the margin of the ice field has retreated as much as one meter since 2000--a meter's worth of ice lost from a wall 50 meters (164 feet) high! (Year of image: 2000)

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