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| Marine corer: the Research
Vessel Kerry Kelts shoves off from the dock |
| photo: Monte Basgall |
himmering 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 |
| photo:monte basgall |
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.
• continues on page two.
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