Ancient sediment samples may hold clues to global environmental change
Ancient sediment samples may hold cluesto global environmental changeApril 22, 2005Edward Byrnesedbyrnes@syr.edu
A team of scientists from Syracuse University, The University of Arizona, the University of Minnesota-Duluth, the University of Rhode Island and the University of Bergen (Norway), have extracted deep samples of mud from East Africa’s Lake Malawi that may be as much as 1.5 million years old. The lake, situated in the Great Rift Valley, is considered by many scientists to be one of the natural wonders of the world.
After battling monumental engineering and logistical challenges, and enduring harsh environmental conditions including waterspouts and massive lightning storms during sampling efforts, the Lake Malawi Scientific Drilling Project team and scientists from the Malawi Geological Survey will perform a variety of analyses of the ancient sediment samples. They hope to ultimately contribute to a better understanding of African and global climate history. Initial results will be available in approximately six months. More detailed work will take three to five years to complete and will involve several laboratories around the world.
“The lake’s unique location and geology should enable us to reconstruct a high-resolution climate history–for example, changes in precipitation, temperature or wind extremes–possibly resolvable on an annual basis and extending back through the time when massive ice sheets periodically covered North America and Eurasia,” says principal investigator Christopher A. Scholz, associate professor in the Department of Earth Sciences at SU.
The project is the most ambitious and logistically challenging scientific lake drilling initiative ever funded by the National Science Foundation (NSF) and the International Continental Scientific Drilling Program. Nearly a quarter of a total project cost of approximately $3.8 million dollars went toward a portable dynamic positioning system for vessel stabilization, specially designed to stabilize the drilling vessel in a fixed location in deep water for weeks at a time, even in winds as high as 35 knots and waves of up to two meters in height. The system will be used on future scientific drilling projects on large lakes and the world’s oceans.
“This core can give us a record of climate change in the tropics that is comparable to what we’ve learned from the ice cores. It’s a big deal because we haven’t had access to such long records from the tropics. Up to now, the longest record in East Africa is about 100,000 years,” says Andrew S. Cohen, professor of geosciences at The University of Arizona and a member of the drilling project team. Other research team members include Thomas Johnson of the University of Minnesota-Duluth, Kate Moran of the University of Rhode Island and Michael Richard Talbot of the University of Bergen in Norway.
At depths of more than 2,298 feet and dated at more than 5 million years old, Lake Malawi is one of world’s deepest and oldest lakes. “This background climate record will allow climate modelers to better place natural boundary conditions on their computer models that are used, for instance, for drought prediction in Africa,” explains Scholz. “Malawi gets most of its electrical power from a hydroelectric plant located on the Shire River, Lake Malawi’s sole outlet. When lake levels drop precipitously, as has happened on several occasions in recent decades, power output from that plant is dramatically reduced. The geological record of lake level change that will be determined from the new drill cores will help put the historical shifts into better context.”
Malawi contains a rich assemblage of biological species found nowhere else on Earth. The lake is more than 372 miles long and is situated in tropical latitudes that serve as the atmosphere’s heat engine and drive global climate dynamics. Because of this, the team chose to obtain and study samples from deep below the lakebed.
“Obtaining extensive historical records of climate change in the tropics is very important and will enable scientists to make detailed comparisons with climate changes in temperate and polar regions,” says Scholz. “This project has the added benefit of recovering an archive of environmental change that occurred in concert with human evolution in East Africa’s Great Rift Valley, one of the richest ecosystems on the planet.”
In total, 2,044 feet of core samples were recovered from below the lakebed’s surface. At one site in the far north of Lake Malawi, the project drilled three holes in water depths of 1,150 feet and collected sediment samples to a depth of 131 feet, representing about 100,000 years. At a deeper site in central Lake Malawi, where the water depth is 1,968 feet, the project drilled four holes, the deepest of which extended 1,240 feet below the lake bottom. At this site, the oldest sediment samples collected are likely to be approximately 1.5 million years in age.
The project overcame difficult engineering and logistical challenges, the first of which was the construction of a drilling vessel on land-locked Lake Malawi. The project recycled an antiquated 160-foot fuel barge for use as the drilling platform, and had to ship the drilling rig, custom-designed sampling tools, personnel accommodations and the portable dynamic positioning system deep into inland Africa.
An engineering team began the project mobilization in Malawi in August 2004 by preparing the barge for the drilling equipment?including installing a moonpool through the hull of the vessel?and hooking up power and plumbing to the imported accommodation vans, galley and canteen. The science, drilling and marine crews slept in eight-man accommodation vans converted from shipping containers. Almost all the equipment was shipped to Africa from Europe and North America in 20- or 40-foot shipping containers, or container-shaped packages, in order to simplify the logistical effort. The project ran into early difficulties when the drilling rig, packed in several 40-foot containers, was stalled in an Indian Ocean port in Mozambique on the East African coast. Due to problems-first with the port’s crane system, and then because of rainy season storms repeatedly washing out railroad tracks across eastern Africa-it took more than eight weeks to move the equipment overland to the project’s mobilization port on the southern shores of Lake Malawi.
The drilling operation, supported by three supply ships, involved 26 personnel aboard the barge working continuously in 12-hour shifts. To collect the samples, scientists, drillers, seamen and support staff endured six weeks of living and working in tight quarters, withstanding intense tropical heat and periodic electrical storms, as well as the discomforting noise and exhaust of seven diesel engines running at all times. In all, more than 80 individuals actively contributed to the operational phase of the program. Within hours of obtaining the final sediment samples from northern Lake Malawi, when the drill crew was still bringing drilling pipe aboard the vessel, an intense electrical storm spawned a massive waterspout that passed within two miles of the drilling vessel.
The bulk of the project’s funding comes from the NSF’s Earth System History and Paleoclimate programs, which supports basic research into the geological record and processes of global environmental change.
More information on the project, including photographs, is available on the web at http://malawidrilling.syr.edu.