Magazine article Oceanus

Telltale 'Bathtub Rings' Reveal Ancient Rainfall

Magazine article Oceanus

Telltale 'Bathtub Rings' Reveal Ancient Rainfall

Article excerpt

In a landscape that could almost have been imaged by Mars rovers, Christine Chen examines stony deposits called tufas along the now dried-up shoreline of an ancient lake high atop the Andes Mountains of northern Chile. These tufas hold clues that reveal the history of the region's rainfall and climate stretching 10,000 to 150,000 years into the past.

Tufas are the fossilized remnants of fresh-water algal reefs that lived under water in the lakes. When rainfall diminished and/or evaporation increased, the lakes dried up, leaving concentric "bathtub rings" of tufas around the lakebeds, said Chen, a graduate student in the MIT-WHOI Joint Program.

"These bathtub-like rings are essentially ancient abandoned shorelines," she said. "For the modern climate, we have rain gauges, and we can calculate rates of evaporation. But no one was around thousands of years ago to set up a rain gauge."

In the field, Chen collects tufas and maps the extent of the ancient shorelines to determine the size of these once large lakes. …

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