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Spring 2002

Science Bits

Earth’s longest and richest archive of climate to be drilled

Scientists from four U.S. universities next year will soon drill deep into arguably the longest and richest archive of Earth’s climate. Enabled by an economical new deep-lake drilling system, they will draw sediment cores roughly 400 meters (1,320 feet) in length from the bottom of Africa’s 7-million-year-old Lake Malawi. These previously untapped sediments may provide annual- to decadal-scale details on climate variations.

"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," says Andrew Cohen (University of Arizona). Geoscientists Cohen and David Dettman are principal investigators on the $2 million NSF project. Collaborating institutions include the University of Minnesota–Duluth, the University of Rhode Island, and Syracuse University.

Christopher Scholz (Syracuse) is lead investigator for logistics on the Malawi drilling, which will begin around the end of 2002. A team of about a dozen faculty and graduate students will acquire samples, perform preliminary analyses, and send cores to the

NSF-supported National Lacustrine Core Curation Facility at the University of Minnesota–Minneapolis.

Lake Malawi, Africa’s third largest, is home to more fish species than any other lake in the world. Each annual layer of lake sediment consists of a black zone—sediment deposited during the rainy season—alternating with a lighter-color seam of diatoms (single-celled algae) formed during the productivity bloom of each dry season.

"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," says Cohen. "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."

Of particular interest is whether changes in solar input due to precession (a long-term shift in Earth’s elliptical orbit) played a role in African climate between about 23,000 and 19,000 years ago, an influence suggested by previous data.

At about $3,000 a day, the Malawi drilling will be far less expensive than ocean drilling, which can run $75,000 a day. An NSF-funded university consortium built the Global Lake Drilling 800 rig, or GLAD800. The rig was installed on a floating platform and successfully field tested on 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.

Lake Tanganyika—twice as deep as Malawi—may yield an even longer climatic record. Scientists already strongly suspect that Lake Malawi dried up for awhile sometime during the Pleistocene, whereas Lake Tanganyika held water through the same periods of maximum aridity. 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. "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," says Cohen.

On the Web:
Lake Malawi Drilling Project

University of Arizona
University of Minnesota–Duluth
University of Rhode Island
Syracuse University

Auroras borealis and australis sampled together for first time

For the first time, the entire sequence of an auroral storm has been studied simultaneously over both hemispheres, yielding information that might help scientists issue warnings about potentially harmful storms. The results emerged from a teaming of data from the Polar NASA satellite and the agency’s Imager for Magnetopause-to-Aurora Global Exploration (IMAGE).

Patricia Reiff, director of the Rice Space Institute, has been studying the data collected during a geomagnetic storm on 17 August 2001. Collaborators include Harald Frey and Steve Mende (University of California, Berkeley), John Sigwarth and Louis Frank (University of Iowa), Terry Onsager (NOAA Space Environment Center), and Jerry Goldstein (Rice). "The question we’ve been wanting to answer is whether the southern and northern auroras are conjugate or anticonjugate," says Reiff.

Previous studies have shown a distinction based on latitude. Many lower-latitude auroras have been nearly conjugate, appearing at close to the same local time and latitude in both hemispheres. Auroras inside the polar caps are anticonjugate: a high-latitude aurora observed on the dawn side of the Northern Hemisphere would be accompanied by a complementary aurora on the dusk side of the Southern Hemisphere.

The high-latitude auroras from 17 August began as anticonjugates early in the storm, as the interplanetary magnetic field pulled the open field lines to the dusk in the southern hemisphere and toward the dawn in the northern hemisphere. But once the storm matured, the influence of Earth’s magnetic tail brought the two auroras in sync, making them conjugates. A few significant differences remained, says Reiff, possibly due to instabilities in the near-Earth environment.

"If we can trust that the aurora in the Northern Hemisphere is the same as in the Southern Hemisphere, we can use imagers over either pole as our monitors," Reiff said. "This will enable us to predict where the northern aurora will be located based on its appearance in the south, or vice versa."

Launched in March 2000, IMAGE has provided the most detailed picture to date of Earth’s inner magnetosphere, where the solar wind and the Earth’s magnetic field intersect. IMAGE follows a highly elliptical pole-to-pole orbit that varies in altitude from about 1,000 to 44,500 kilometers (600–27,600 miles). The satellite uses radio sounding techniques and measures neutral atoms and photons as a proxy for magnetospheric plasmas, which cannot be directly sensed through standard observing techniques.

On the Web:
IMAGE Science Center

Rice University
NOAA Space Environment Center
University of California, Berkeley
University of Iowa

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Edited by Bob Henson, bhenson@ucar.edu
Prepared for the Web by Jacque Marshall
Last revised: Thu Dec 20 16:42:17 MST 2001