Lake Titicaca, which is relatively close to the Amazon River, the world's largest source of fresh water, is also one of the best registers of global climate.

According to Paul Baker, professor of geology at Duke University's Nicolas School for the Environment and Earth Sciences in North Carolina, “Lake Titicaca is a beautiful rain gauge.”

The study of the lake's sediment core samples revealed that most books on paleoclimatology—the study of ancient climates—are wrong, because they claim South America was a dry region during the last Ice Age.

While climates cooled as glaciers advanced in the rest of the world, the Andean region was wet and temperate, asserted Baker, who has published the results of the study in Science magazine.

Researchers from five U.S. universities, and Bolivian and Peruvian doctoral students in the United States, were among those who contributed to the study of Lake Titicaca sediments.

The scientists used “Neecho,” a research ship from the U.S. Geological Service in Woods Hole, Massachusetts, to drill core samples measuring up to 15 meters long (some 49 feet) in three different areas of the lake, at depths of 50, 100 and 200 meters (some 164, 328, and 656 feet).

The researchers studied the magnetic values, fossilized diatoms—a type of tiny silica-encased aquatic algae - calcium carbonate concentrations and the oxygen isotope ratios of the core samples.

Based on this geological evidence, “the study's results suggest that the South American tropics were wet during cold eras and advancing ice in the Northern Hemisphere,” the article, published in Science magazine, noted.

The Lake Titicaca region was not only wet during the last Ice Age, which began some 25,000 years ago and lasted until some 15,000 years ago, but also during the last cold periods of the North Atlantic Ocean region.

Although the study of fossil sediments can explain some of the climate changes of the past, Baker cautioned against
forecasting future climate patterns because of the influence of human-caused climate change.

“Human influence is so dominant now that whatever is going to go on in the tropics has much less to do with sea surface temperatures and Earth's orbital parameters and much more to do with deforestation, increasing atmospheric carbon dioxide, and global warming,” the researcher explained.

Lake Titicaca, which measures 195 kilometers (121 miles) by 80 kilometers (some 50 miles), has undergone a series of drastic changes since the last Ice Age, some 250 centuries ago.

The Altiplano, a 12,000-foot plateau below the Andean Mountains in Bolivia and Peru, and the Amazon River basin were wetter than they are now, researchers found.

One of the most dramatic changes observed in Lake Titicaca was a notable decrease in the water table 6,000 years ago, but scientists have not been able to find its cause.

The researchers noted that the fact that alternate wet and dry periods occur in cycles of 1,000 years or more could be influenced by the Earth's movement around the Sun.