In the past 25,000 years, the South American Andes Plateau has undergone repeated climate shifts. Now, US researchers have ascertained that for several thousands of years, long periods of drought alternated with periods of heavy precipitation. The latter would occur especially when the weather was unusually cold at higher latitudes - such as during the last Ice Age. An especially interesting feature are the shells of various one-celled types of algae, of which some favor deep water, while others prefer shallow lakes. The presence of such algae allowed the researchers to draw conclusions about the depth of a body of water, and by extension, about the past precipitation in the area.
Researchers are as yet unable to explain the strong climatic fluctuations.
Possible causes include the gyration of Earth's axis or unusually warm or cold ocean currents.