A Tropical 'Rain Gauge'

Revealing Secrets in the Depths of South America's Largest Lake

by Monte Basgall

HUATAJATA, BOLIVIA - In mid-April, a Bolivian spa on the shore of Earth's highest large lake was hit by a full-scale invasion of scientists and mud drillers.

It was the latest and most dramatic phase of a Nicholas School geology professor's seven-year probe of the climatic history of South America's largest lake, Titicaca, which glitters in many shades of blue below a stretch of spectacular snow-capped Andes Mountains peaks called the Cordillera Real, or "Royal Range."

Paul Baker of the Nicholas School's Earth and Ocean Sciences Division and his students keep coming back to this exotic 11,400-foot setting, where native Aymara still make boats out of the lake's sturdy reeds as well as herd fleecy llama and alpaca and grow crops unfamiliar to North Americans, such as quinua.

A geochemist, who otherwise works at sea and in the lab, Baker has arranged to haul up impressively large equipment to study Lake Titicaca because he considers it a present and past "rain gauge" for the tropical jungles of the humid Amazon to the Andes' east.

"The main motivation for this work is trying to understand the climate over the past," the tall, slim researcher, his face wrapped in a thin beard, said in one of a series of interviews at Duke and in Bolivia.

"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 percent of the energy to fuel atmospheric circulation," he added.

Baker thinks the information that he and his colleagues learn by pulling sediment from Lake Titicaca's depths and probing it with sound waves could help climatologists better understand weather on the Amazon, one of Earth's major terrestrial sources of water vapor.

While public attention surrounding global warming is focused on heat trapping effects of the extra carbon dioxide released by human activities, water vapor also is a potent "greenhouse effect" gas as well as Nature's raw material for precipitation.

During the southern hemispheric summer, an atmospheric circulatory pattern - sometimes called the "South American summer monsoon" - draws Atlantic Ocean water vapor west over the Amazon, then forces it up over the high Andes eastern slopes. The result is rain both in the jungle and on the high plateau - the Altiplano - where Lake Titicaca is located.

The pattern shifts during the South American winter, the Altiplano's dry season. Then precipitation mostly stays down in the Amazon lowlands.

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