A Tropical 'Rain Gauge'
Revealing Secrets in the Depths of South America's Largest
Lake p.4
Since most climate textbooks say the tropics were arid during
glacial times, their findings in Science are controversial,
Baker acknowledged. The scientists drew their conclusions
primarily from Tapia's analysis of diatom types. But other
evidence they pulled from the sediments also supported the
fossil record. There were calcium carbonate levels that vary
with lake depths and salinity just like diatoms do. There
were the magnetic values that change when upland erosion ceases.
And there were ratios of two forms (isotopes) of oxygen in
water that vary with temperature and precipitation source.
Their report in a February issue of Nature drew similar
conclusions. It used a 50,000-year record of cores extracted
south of Titicaca, from a salt flat that can flood during
high rainfall periods. The principal evidence there was natural
gamma radiation in those sediments that were deposited in
wet and muddy times. Baker's Nature coauthors included
his wife, Catherine Rigsby, an East Carolina University geologist.
That paper suggests that parts of the Altiplano that are today
drier than Titicaca also got wet when ocean temperatures to
the north were unusually cold. It cited corroborating oxygen
isotope evidence in glacier ice other researchers collected
on a volcanic peak located between Lake Titicaca and the salt
flat.
Last April, Baker and his principal collaborators returned
to the Inca Utama Hotel with more help and much more equipment.
Workers and supervisors began arriving from Utah and Idaho.
Other boats, plus the hydrofoil craft that speed tourists
around the lake, were relocated from their usual moorings.
A consortium serving universities and research labs was about
to assemble a 24-by-60 foot floating drilling and coring platform
there - the first, large-scale system ever designed to operate
in deep lakes. Baker remained principal investigator of the
NSF-funded project that would probe even deeper into Titicaca.
Within days, the rig's sections arrived aboard nine tractor
trailers. Each section was a standardized 20-foot shipping
container, the kind that can carry international cargo from
ocean to railroad car to flatbed truck. In this case, the
containers were carrying all the pumps, motors, cables, pipes
and hardware needed to assemble a working coring rig. After
workers removed those parts, cranes turned each container
over and dropped it into the water to be linked together to
form the platform's hull.
The Neecho was in the harbor, too. After its hull was scraped
of lake weeds and algae, it would take on a new assignment:
towing the drilling platform around the lake and helping anchor
it in place. While construction workers - including the drilling
team - hurried to keep on schedule, the researchers prepared
for action. They set up a core analysis laboratory in a second
floor hotel room, booted up laptop computers in the covered
walkway outside, and dangled a gamma ray device from a balcony
to test it out. The investigators included two of Baker's
graduate students. Kim Arnold, who specializes in salt flat
deposits, would work in the lab analyzing the magnetic properties
of tubes of samples by passing them through a detector, and
Ashley Ballentyne, who planned to study some of the core samples
later to evaluate lake water nitrogen content.
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