Chuck Bednar for redOrbit.com – @BednarChuck
By studying mineral cave deposits known as speleothems, experts from Vanderbilt University, the Berkeley Geochronology Center in California, and elsewhere are learning more about what prehistoric climate was like and how it changed over the years.
The research team, led by Vanderbilt assistant professor of earth and environmental sciences Jessica Oster, is analyzing the past five decades of growth of a stalagmite located in the Mawmluh Cave in the northeastern Indian state of Meghalaya, a region often referred to as the rainiest place on Earth.
Water from rainfall collected calcium carbonate and other types of minerals, and it leaves behind mineral deposits as it drips into caves. Mineral layers grow during wet periods, and form dusty skins during dry periods. The researchers used this knowledge to collect data about precipitation cycles in the region.
Comparing cave data to historical records
In a paper published in the May 19 edition of the journal Geophysical Research Letters, Oster and her co-authors compared their findings to historical records in India, which suggested that reduced monsoon rainfall in the central part of the country occurred when sea-surface temperatures in parts of the Pacific Ocean were warmer than usual.
Naturally-recurring sea-surface temperature “anomalies” such as the El Niño Modoki and the Pacific Decadal Oscillation, cause huge differences in precipitation amount and temperature. When the team analyzed the Mawmluh stalagmites, they found that their predicted results matched up consistently with the historical records.
For example, during a year where El Niño caused localized storm activity, the researchers found mineral chemistry signals in the cave to support these events. During non-El Niño periods, the data revealed that the water traveled much farther before it fell and seeped into the cave, typical of monsoon activity.
“Now that we have shown that the Mawmluh cave record agrees with the instrumental record for the last 50 years, we hope to use it to investigate relationships between the Indian monsoon and El Niño during prehistoric times such as the Holocene,” Oster said in a statement.
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