Sedimental Journeys

Shimmering on a continent’s roof in the harsh sunlight of 11,400-feet altitude, Bolivia’s Lake Titicaca is both Earth’s highest big lake and South America’s largest. A jewel in many shades of blue nestled below a snow-capped crown of Andes Mountain peaks named for royalty, Titicaca stretches out in two parts on a lofty plateau—the Altiplano—that is as environmentally exotic as it is economically undernourished. Along the lake’s reedy shores, and on heights above it that can leave lowlanders gasping for oxygen, hardy and cash-poor Native Americans herd llamas and alpacas, weave spectacular fabrics, treat with herbal medicines, and grow sometimes-unfamiliar foods that can tolerate the chilly temperatures and seasonal dry spells.

Paul Baker, a geology professor at Duke’s Nicholas School of the Environment and Earth Sciences, has visited there often with his students and scientific colleagues. He has shipped and trucked increasingly large gear all the way from the United States up the steep Andean ramparts to probe the lake’s very heart. His goal is a record of the Altiplano’s climatic history dating back almost as long as Titicaca has been there.

Since Baker calls the lake a “rain gauge” for all of the humid tropical jungles east of the Andes, he says the facts they learn could help climatologists better understand one of the planet’s major water-vapor sources. Articles his team wrote this year in prestigious research journals are already challenging scientific dogma. He says his group’s data also may—Baker stresses “may”—help prognosticate the murky climatic future. The impact of global warming, a heat-trapping effect linked to human air pollution, is expected to alter where and when the rain will fall.

Well before recorded history, humans learned to live with the Altiplano climate’s fickleness. One crowning ancient achievement was the long-abandoned city of Tiwanaku, now located about nine miles from Lake Titicaca’s shallow southern edge, where archaeologists are slowly unearthing the monuments of a civilization that relied heavily on water management. These structures include a fifty-four-foot-tall step pyramid called Akapana. Its top was defiled in the sixteenth century by treasure-seeking Spanish invaders, who, in the process, destroyed a sacred reservoir fed by an underground network of stone plumbing. Nearby is a strange “semi-subterranean” temple, with sunken walls constructed of tightly fitting and mortarless blocks. Enigmatic stone faces are carved in three-dimensional relief on 322 of those building stones. Despite being below grade, the faces may have always remained dry due to an intricate drainage system.

Experts say Tiwanakuan agriculture depended on elaborate terraces that lined the steep hills above the valley. Terraces not only controlled erosion; they also collected rainwater and channeled it down the slopes for use in farming. Another innovation, called the “rich field systems” of causeways, canals, dikes, and mounds, grew crops on raised beds irrigated by water percolating up from underneath. Besides providing crucial moisture, the upwelling water is believed to have moderated ground temperatures. That created “microclimates” to help insulate crops from the extremes of both night and daytime temperatures—in essence outdoor greenhouses. “Two thousand years ago, the population there was probably three or four times today’s,” Baker says. “The people there really understood the environment and made it as productive as it could possibly be. Today I’d say the agriculture and form of living is probably a little more primitive than it was 2,000 years ago.”

Agriculturalists are now restoring some of the Altiplano’s ancient terraces and are recreating some of the rich fields. But the people who first built them left behind only silence and striking art and architecture. Tourists to Tiwanaku are struck by the scale, beauty, and oddness of the remnants. There is the “Gateway of the Sun,” carved with iconography some think is a precise calendar, and the Ponce monolith, an oversized statue with head band, earrings, face mask, bulging belt, and ankle tattoos. By about 1200 A.D., the culture had disappeared, well before the arrival of the Incas who were then conquered by the Spanish conquistadors. Some experts, but not all, believe the cause was a drought lasting as long as centuries. Others point to invasion by other pre-Incas, perhaps the Aymara, who populate the Altiplano now.

“Were there climatic reasons for the advent and the dying out of this group?” Baker asks. “I believe it’s certainly possible. Life could be very bad up there if you have a few summers without rain.” But with the scientific skepticism that sometimes maddens laymen in search of instant answers, Baker asserts that the experts haven’t proven their case.

That’s the reason Baker has been coming to the Altiplano for seven years. “The main motivation for this work is trying to understand the climate over the past,” says the geochemist, who otherwise works at sea and in the laboratory. “The tropics are really the heat engine for the whole climatic system globally, and the Amazon is one of three main convection centers that provide a large percentage of the energy to fuel atmospheric circulation.” He explains that, during the December-through-April southern hemispheric summer, atmospheric patterns called the “South American summer monsoon” draw Atlantic Ocean water vapor west over the Amazonian rain forests, then up high eastern Andes slopes. The result is rain on the jungles and frequent storms on Lake Titicaca and its surrounding watershed, the Altiplano’s wettest part. Then patterns shift in the wintertime to leave the lake’s watershed mostly dry.

If that’s the climatic picture today, how was it in the past? Vegetation-covered sand dunes discovered in the Amazon hint at far-different former weather there. But good scientific evidence of ancient climates is hard to gather in the fast-growing, ever-changing, usually wet, jungle lowlands, Baker says. That’s why he and other investigators are using the lake as a proxy field site. Geoffrey Seltzer, an associate professor of earth sciences at Syracuse University, has been bouncing shock waves off the underwater lake bed—a technique called seismic reflection profiling—to discern the presence of ancient, now submerged, former shorelines. Sherilyn Fritz, an associate geology professor at the University of Nebraska at Lincoln, has been studying remains of tiny fossilized plants called diatoms with her Peruvian graduate student, Pedro Tapia. Now embedded in lake-bottom sediments, these silica-crusted algae vary according to how deep or shallow, salty or fresh, Titicaca was in the past.

Recycled: shipping containers that held drilling hardware form floating platforms for coring operation.

Baker has been evaluating the telltale chemistries and magnetic properties of layer upon layer of those sediments, which collect when aquatic plants die and settle, or as soil and stones wash down from the land. He also studies the water entrapped within all that mud and debris. “I think of Lake Titicaca as a little ocean,” he says. “Scientifically, we have to figure out how it works. How much water comes in? How much of it evaporates off? How does the chemistry change with depth? How does the circulation change? Generations of people have figured out how the ocean works. We need to know that in Lake Titicaca if we want to interpret what the sediment tells about the climate.”

To collect sediment from the lake bed, Baker, Fritz, Seltzer, and others have been teaming up to do what is known as “coring.” Researchers remove cores by forcing hollow pipes into the mud. The pipes are then pulled up to extract layer-cake cylinders of sediment samples trapped in an inner plastic tube. “Old-time marine geologists did a lot of coring,” notes Baker, “but there’s not too much expertise for that left in the oceanographic community.” Up on the continents, scientists core in little lakes all the time, using relatively primitive equipment, but not in big lakes as deep as Titicaca, where depths average 443 feet in its largest part—Lago Grande or “Big Lake.” “It hasn’t been done before,” he says. “We’re doing things on the edge of our knowledge, both scientifically and logistically.”

In 1996, after delays caused by the Shining Path guerrilla insurgency in Peru—which shares Lake Titicaca with Bolivia—the researchers began doing seismic studies and limited coring on parts of Titicaca in both countries. They used a twenty-nine-foot-vessel, the Yakuza, as part of a Peruvian-Bolivian lake-research agreement with funding from the National Science Foundation. The quest for something better became an adventure that began in Massachusetts.

Another Baker colleague, geologist and coring expert James Broda of the Woods Hole Oceanographic Institution, located a mothballed vessel called the Neecho (“Clear Water” in Algonquin) at a nearby U.S. Geological Survey station. Broda had the thirty-eight-foot boat and its fifty-foot trailer towed to the institution to begin a cleanup from five years of disuse. Built for seismic studies in deep lakes, the Neecho had been stripped of much of its original equipment. Broda added lighter-weight versions of the kind of coring gear used in oceans. Key improvements included two power winches to lower and raise pipes, and an “A-frame” crane that pivots out over the water to better assemble and drop cores. There was more deck space, plenty of electric power, and two large diesel engines to propel the boat across wave-tossed Titicaca. Baker managed to get ownership transferred from the geological survey to Duke.

Leaving Woods Hole, the Neecho was stranded overnight on the Massachusetts Turnpike when the brake lines on the truck hauling it froze in late winter. Upon rescue, boat and trailer reached Newark, New Jersey, and were loaded on a container ship called the Inca. Their ocean voyage took them through the Panama Canal to Arica, Chile, a port for land-locked Bolivia. There began their rugged mountain-climbing trek aboard another truck equipped with a special axle to handle power losses caused by low oxygen. Truck and cargo had to struggle to ascend slowly to a 16,000-foot Andean pass before dropping a little to 13,000-foot El Alto, the location of a Bolivian customs warehouse. El Alto is where tourists deplane at the international airport serving La Paz, the world’s highest capital city. Its air is almost thin enough to drop oxygen masks, and jetliners must take off and land with reduced fuel loads to maintain enough lift.

It took boat, trailer, and truck about eighteen hours to reach there from the coast, with long lines of cars backed up behind. The Neecho’s final passage was a relatively painless fifty miles across the high plateau to the vessel’s home away from home, the dock of the Inca Utama Hotel—a spa at the town of Huatajata located on Lago Huiñaimarca, Titicaca’s smaller and shallower arm. The Neecho was big by Lake Titicaca standards. Its roomier deck allowed the team to handle longer cores. It also provided a bit more reassurance in heavy weather. While Titicaca’s swarms of tiny lateen sail fishing boats may give an illusion of safety, the lake can be dangerous, with waterspouts and monster waves. “You don’t want to have a problem in this lake,” Baker says. “There’s nobody that can come out and help you. There’s a Bolivian Navy, but they have no boats that are large enough.”

Collecting and analyzing years of information back at their home campuses, the team began publishing some important reports in scientific journals. The first, a 1998 report in Geology principally written by Seltzer, used seismic reflection profile data collected aboard the Yakuza to document a 278-foot drop in lake levels between 4,000 and 6,000 years ago—before the Tiwanaku culture began to flower. The team’s report last January in Science used core-sediment analysis to deduce a precipitation record going back 25,000 years in both Lago Grande and Lago Huiñaimarca. Using the Neecho to collect cores as long as forty-six feet, below water as deep as 754 feet, their article asserted that the lake was especially fresh and deep during Earth’s last ice age and other especially cold intervals.

“We have a unique record of climate change in tropical South America that shows when global climate conditions cooled and the glaciers advanced, wetter climates prevailed in the Andes,” Baker says. He acknowledges that their conclusions, made principally from Tapia’s analysis of diatom fossils in the ancient sediments, are controversial. Most climate textbooks say the tropics were arid in glacial times. But other evidence they pulled from the mud supported the fossil record. The other evidence included calcium carbonate levels that vary with lake depth and salinity, just like diatoms do. There were also magnetic values that change when upland erosion ceases, and ratios of two forms (isotopes) of oxygen in water that vary with the temperature and the source of precipitation. 
  A third report in a February issue of Nature drew similar conclusions from a 50,000-year record of cores extracted from a salt flat south of Titicaca that can flood during high rainfall periods. The principal evidence was natural gamma radiation in sediments that had been deposited in wet and muddy times. Baker and his co-authors—including his wife, Catherine Rigsby, an East Carolina University geologist—suggested that parts of the Altiplano that are drier today got wet when ocean temperatures to the north were unusually cold. That report also cited corroborating evidence, oxygen isotope ratios in glacial ice collected by other researchers at nose-bleeding heights on a volcanic peak between Lake Titicaca and the salt flat.

Research trio: Syracuse's Geoffrey Seltzer, from left, Duke's Paul Baker, and Woods Hole's James Broda aboard the Neecho.

This set the stage for mid-April, when the Inca Utama was hit by a full-scale scientific invasion. There was air of a reunion as the original Neecho team reassembled. Hydrofoils and other craft were relocated from their moorings at the hotel dock. All this was necessary because a 24-by-60-foot floating drilling and coring platform would be assembled there. The venerable Neecho would then tow the heavy craft out into the lake so the experienced crews could begin dropping connected strings of pipes as deep as 2,600 feet below Titicaca’s surface. The technology is called “wireline coring,” a system that allows inner cylinders containing core samples to be pulled back to the surface with cables at the same time that the rotating outer pipes remain in the mud to ream and cut. It was a much higher-level operation than the Neecho’s, with a choice of different coring and cutting ends for use in different kinds of lake-bottom deposits.

Later, the rig’s sections arrived behind nine big trucks. Each was a standardized twenty-foot shipping container. Inside the containers were all the pumps, motors, cables, pipes, and hardware needed for a working drilling rig. After workers removed the parts, a crane turned over each rectangular shell and lowered it into the water. Workers, sometimes wearing scuba gear, linked the Chinese-made containers together to form the platform itself. As the rig’s maiden coring operations on stormy Great Salt Lake demonstrated, the big metal boxes can be made into a strong floating platform. 

After several days, the platform, with drilling crew aboard, was ready to move. It was now named the Kerry Kelts in tribute to a deceased University of Minnesota researcher who pushed for its development. Baker, Fritz, and Broda climbed on the Neecho’s deck, while Seltzer sat in the driver’s seat. As the slow tow began, the Neecho’s oxygen-deficient engines briefly belched black smoke. Soon boat, towing cable, and barge were linked in an arc gently swinging up Lago Huiñaimarca’s middle. As the ensemble moved out of Huatajata, the magnificent snow-capped mountains of the Andes’ eastern Cordillera Real (Royal Range) revealed themselves behind the lake’s steep terraced shoreline. The tow continued until the following afternoon, passing through the Straits of Tiquina, which buses, trucks, and cars must cross by barge, and into vast Lago Grande. The platform finally stopped near Isla del Sol (Island of the Sun), the Inca’s mythical birthplace, where flowing spring water courses beside 180 steep Inca Steps. The Neecho maneuvered from corner to corner to rig the Kerry Kelts’ anchors.

By evening Baker was aboard to help lead the first coring operations after a thirty-minute hydrofoil ride from Copacabana, where most of the team was temporarily rooming. While the day had been brisk but sunny, the night brought storms. “When we went out the first night, we had no idea how good the platform was going to be, and we got pounded,” Baker recalls. “We were putting ourselves on the line out there.”

The following morning dawned sunny, with the day shift reaching never-before-achieved coring depths. Later, connections bogged down and snapped in a sand deposit. That first carefully chosen site, in 465 feet of water, was supposed to be “our prime site,” he says. But what he suspects was the remains of an ancient beach, formed when lake levels were much lower, stymied progress. After eight frustrating days and more broken equipment, they penetrated the lake floor only 164 feet, before pulling out and moving to the second site, a full hour’s hydrofoil ride out into the Big Lake.

“We didn’t really want to go there,” Baker says of Site Two. An hour by hydrofoil from Copacabana, its location put them farther away from rescue. The lake floor is 754 feet below the surface, deeper than the platform’s anchor was designed to reach. Nevertheless, drilling began, and continued for five days and nights. When Baker would arrive about six p.m., the day crew would be basking in the late sun. But “usually the clouds were gathering,” he says. “By eight o’clock, we were getting hit hard, almost every night, with rain, sleet, snow, hail, and lightning. Usually we were there as caretakers, not core drillers. We couldn’t possibly drill.” Sometimes the waves would break over the separate cramped “shacks” set up on deck as shelters for drillers and scientists. 

Alarmed by reports of a large catamaran hotel ship that sank in a monster wave just the year before, Baker had arranged for everyone to have survival suits. “At first we were just standing by with our survival suits right next to us,” he recalls. “Then, after we weathered one really bad storm, I wasn’t worried about the platform anymore.” Somehow, the Kerry Kelts’ drillers managed to penetrate 446 feet into the sediment without breaking the rotating 1,200-foot connection with the floating drill tower. That took the scientists far back in time. “My guess is we have 100,000 years here, and five glacial cycles,” Baker says of the Run 2 core collection.

Finally the Neecho towed the Kerry Kelts to Site 3, back into the calmer waters of smaller Lago Huiñaimarca, which Baker calls a “piece of cake.” The platform teams slept once more at the Inca Utama Hotel, and could reach the rig in twenty minutes. “Again, we got terrible weather at nighttime,” says Baker. “It snowed every night on the platform, and there was lightning, but we could work. We were really kicking, We felt good about that.” Coring in only 134 feet of water, day and night crews managed to penetrate a total of 410 feet down before “we hit big chunks of gravel. We couldn’t possibly go any farther.”

Ashore in the hotel lab at Huatajata, Fritz’s graduate student Pedro Tapia spent most of the twenty-three-day coring period, which ended in late May, before a microscope. He looked at diatoms extracted from the cylinders of samples that arrived regularly from the platform via hydrofoil and pickup truck. Kim Arnold, one of Baker’s graduate students, who specializes in salt-flat deposits, prepared microscope slides when she wasn’t analyzing the samples’ magnetic properties. Baker’s second graduate student on this trip, Ashley Ballantyne, plans to study some of the core samples to evaluate lake-water nitrogen content.

In late July, Baker sat back in his Duke office near the model reed boat and reed couch that were made for him made by the same Aymara family that built the Ra for explorer Thor Heyerdahl. He pronounced the expedition successful, though analysis is still under way. “Depthwise, we didn’t get everything we wanted,” he acknowledges. “But I think scientifically we got everything we wanted. It would have been nice to get more meters. It was impossible to get more. There’s probably no way you can get more anywhere in Lake Titicaca.” 

Basgall is senior science writer in Duke’s Office of Research Communications.