This is the same part of the world where humans first evolved.

Enabled by a newly developed and affordable deep-lake drilling system called GLAD800, they will for the first time core sediments from the bottom of one of the African Great Lakes, 7-million-year-old Lake Malawi.

"Our goal is to get something on the order of a half-million to million-year record on past climate and environment, taking advantage of the fact that these lake sediments are frequently annually layered," said University of Arizona Professor Andrew Cohen.

Cohen and David Dettman of the UA geosciences department are principal investigators on the award for the UA. They collaborate on the project with scientists from Syracuse University, the University of Minnesota-Duluth and the University of Rhode Island.

Christopher Scholz of Syracuse University is principal investigator for logistics on the Malawi Lake drilling project, which is funded by a new $2 million grant from the National Science Foundation.

Each annual layer of Lake Malawi sediment consists of a black zone -- the sediment runoff from land deposited during the rainy season -- and a light-color seam of diatoms, or single-celled algae, that formed during the productivity bloom of each dry season, Cohen said.

"The annual layers in the sediments are like tree rings, but they contain a heck of a lot more information than tree rings," Cohen added. "It's not exaggerating to say that there are probably a hundred different things we can analyze from the cores.

"But a big question for us has always been whether the global climate engine has been driven by advance and retreat of glaciers at high latitudes or by circulation patterns at the tropics.

"It has long been assumed that Earth's climate engine was driven by the ice sheets themselves. But based on theory, there's good reason to believe the tropics may be driving the global climate system. So one of the first things we want to address is the question of whether the climate history of the tropics leads or lags behind climate of the polar regions," Cohen said.

In addition to studying clues on past climate, the scientists will analyze sediment cores for insight on how aquatic organisms in the region evolved through time.

This is research that complements the Nyanza Project, a 6-year-old research training program in tropical lake studies funded with grants and contracts from the NSF and the World Wildlife Fund. Cohen directs the Nyanza Project and its international field station at Lake Tanganyika.

Preparation for Lake Malawi drilling will begin in October, with actual drilling to begin in December or January 2003, Scholz said. A team of a dozen faculty-level researchers and graduate students will work in the field for 70 days, acquiring samples and performing preliminary analyses.

The expedition will send the cores to the United States, where they will be stored at the NSF-supported National Lacustrine Core Curation Facility at the University of Minnesota in Minneapolis as a resource for further research.

An NSF-funded university consortium called DOSECC (Drilling,Observation and Sampling of the Earth's Continental Crust) built the Global Lake Drilling 800 rig, or GLAD800, with funds from the International Continental Scientific Drilling Program (ICDP). The rig was installed on a floating platform and successfully field tested on the Great Salt Lake and nearby Bear Lake, Utah, in August 2000.

"GLAD800 technology has made what we've planned and dreamed of for decades affordable," Cohen said. "It costs about $75,000 a day to operate the ship used in the Ocean Drilling Program. It costs about $3,000 a day to operate GLAD800, which brings it within the realm of what's realistic for people outside the ocean sciences. And, we can pick up and move from lake to lake."

Normally, GLAD800 would be set up on a barge anchored over the drill site, project members say. But it is impossible to anchor the system in the deep waters of Lake Malawi, so the drill rig and barge can only float free on the lake. Thrusters linked to a Global Positioning System (GPS) will continually adjust the barge's position above the drill hole.

"This is a risky scientific expedition, to be sure," said David Verardo of the NSF Earth System History program. "We are moving a new drilling system into a technologically challenging environment. Lake Malawi is deep and the weather window for drilling operations is short and unforgiving. What spurs us on, however, is the potential scientific payoff in recovering critical baseline data on Earth's climate system...Betting on future climates without such baseline data is like investing in a company's stock without assessing its past performance. It just isn't prudent."

Cohen said that drilling sediment cores at Lake Tanganyika is his ultimate goal.

"At Tanganyika, there is potential from getting much longer records than from Malawi. Lake Malawi is 750 meters deep. Tanganyika is around 1,500 meters deep." Scientists already strongly suspect that Lake Malawi dried up sometime during the Pleistocene, whereas Lake Tanganyika "held water through the same periods of maximum aridity," he added.

A bonus is that Lake Tanganyika is actually two deep basins connected by submerged ridges. Because of gravity, more sediment is carried into the deeper holes, while much thinner layers accumulate on the ridges.

"Which means that for a given length of drilling, you can get a much longer record -- back 5 or 10 million years, instead of a half million or a million years," Cohen said.

[Contact: Andrew S. Cohen, David Dettman]

05-Feb-2002