Fritz and her colleagues study lake mud and its contents to reconstruct the history of climate change and develop a long-term perspective on how humans impact their environment. "We know from the recent geologic record that 20th century environmental history is not representative of the full range of natural variability," Fritz said. "Developing our knowledge of what has happened in the past is critical to understanding how the environment works and thus for dealing with the unknown future."
Unearthing the tropics' past
A UNL geoscientists' team studied Lake Titicaca's history to learn how climates might change in the future
Toward the end of the 1969 movie Butch Cassidy and the Sundance Kid, Paul Newman (Butch) turns to Robert Redford (Sundance) and says, "The next time I say, 'Let's go some place like Bolivia,' let's go some place like Bolivia."
Although UNL geoscientist Sheri Fritz and her team in a $1.6 million National Science Foundation-funded expedition to Bolivia's Lake Titicaca in 2001 weren't being hunted by the law, they may have understood the frustration the two outlaws felt after spending time in South America's poorest country.
The scientists - Fritz, geochemist Paul Baker of Duke University and geologist Geoff Seltzer of Syracuse University - did know what they were getting into in Bolivia. They had spent enough time there over the previous six years that it became economical for them to rent an apartment in the capital, La Paz. The earlier trips had laid the groundwork for this "ultimate" project in which they hoped to pull enough sediment cores from Titicaca's lake bed to establish a 500,000-year record of the climate history of the South American tropics.
Their ultimate project, however, nearly proved to be the ultimate in frustration.
After years of preparation, the expedition began with a lost week because of a paperwork snafu that impounded their research vessel, the Kerry Kelts, in Bolivian Customs. Soon after they finally got out onto Titicaca to begin their round-the-clock drilling for sediment cores, they ran into an unexpectedly thick sand deposit that swallowed their drilling tools, resulting in another idle week while replacement parts were shipped from the United States. There were constant health worries about water- and food-borne parasites, and additional concerns when Fritz had to arrange for a rabies vaccine to be shipped in for a driller who had been bitten by a dog. There was unseasonably rotten nighttime weather on the large, deep lake located 12,500 above sea level. High winds, heavy waves, cold, drenching rains, snow and even an occasional funnel cloud prevented the night crew from doing anything more than keep the drill hole open during its 12-hour shift.
Finally, there was more thick sand at a second drill site that forced the drillers to stop well short of their goal. Instead of a half-million-year record, Fritz estimated their work would yield a record more like 150,000 years. But the scientists were cheered by the fact that they would still have a much longer record than anyone has compiled before, allowing them to present an unprecedented picture of the climate history of the South American tropics as their analysis of the cores proceeds over the next few years.
"Our total depths of recovery were less than what we proposed, but I think that scientifically, we're going to learn almost everything that we wanted to," Baker said. "Nobody has a clue what Lake Titicaca or the Amazon were like 100,000 years ago. Nobody has a clue. And that's pretty exciting."
The thick sand in itself was an important discovery, Baker said - an indication that Titicaca was 170 meters shallower when the sand was deposited. He estimated that for an extended period of time, precipitation in the lake's basin was as much as 60 percent lower than it is today.
Analysis of the cores (in storage at the University of Minnesota) will allow Fritz, Baker and Seltzer to build on a 25,000-year record of glacial cycles in the tropical Andes that they had established in their earlier trips. Their central finding in that record was that the South American tropics were extremely wet during the northern hemisphere's last Ice Age, which peaked about 21,000 years ago. The finding was controversial because it challenged the prevailing view that the Amazon basin was dry during glacial times.
The longer record from drilling will answer many of the questions raised by their earlier work, Fritz said. More importantly, their results will provide benchmarks in the study of how the Earth's climate has changed in the past, and therefore provide important clues as to how it might change in the future.
"The real question is not what did Lake Titicaca do, per se," Fritz said. "There's just all these questions about how the global climate system works and what are the triggers for large-scale climate changes. We can only start to address these questions about what are the relative roles of various parts of the climate system once we have a large network of sites globally and we can compare them.
"We have virtually an unparalleled record of the South American tropics that opens up all sorts of opportunities to try to figure out what the tropical Andes are doing on these longtime scales and relate them to other regions. We simply don't know because these records haven't existed before."