This summer, Penn Museum archaeologist Joyce White and her paleoclimatologist collaborators at the University of California, Irvine published a paper detailing a historic discovery—the existence of a 1,000-year-long drought approximately 5,000 years ago. Evidence from stalagmite samples was gathered from Laos’ Luang Prabang Province and has opened the door to a new body of material through which researchers can better understand life during that period.

“This kind of research, when you combine archaeology, paleoclimatology, and modeling, will more effectively bring out this type of finding.”

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Southeast Asia typically evokes rich and wet tropical forests. So, the discovery of a drought more than 1,000 years long beginning about 5,000 years ago was an unexpected outcome from research started by the Penn Museum’s Joyce White nearly two decades ago. She and colleagues from the University of California, Irvine; William Paterson University; the University of Quebec; and more published these findings in the journal Nature Communications.

Evidence for the megadrought came from Laos’ Luang Prabang Province, where White has worked since 2001. A Henry Luce Foundation grant enabled the research program to expand starting in 2008, and a paleoclimate team that included William Paterson’s Michael Griffiths and Kathleen Johnson of UCI, co-lead authors on the latest paper, joined in 2010. Some of their work included collecting stalagmite samples from the Tham Doun Mai cave along the Ou River.

Much like tree rings, stalagmites have rings that contain datable signs of changing climate. As rainwater drips through cracks in a cave’s roof, it interacts with a mineral called calcite to form stalactites on the cave’s ceiling. As that water-mineral mixture drips from the stalactite, stalagmites form on the floor below, building over time, layer by layer.

“From those rings, we can interpret the occurrence of various climate events,” says White, who directs the Penn Museum’s Middle Mekong Archaeological Project and is an adjunct professor in Penn’s Department of Anthropology. “In this case, two of the stalagmites stopped growing for several hundred years, then started to grow again.” Chemical analyses confirmed that a prolonged drought lasting more than 1,000 years caused the cessation.

When combined with climate modeling, the cave evidence seems connected to changes in vegetation and dust in northern Africa that happened around the same time—right around when the Sahara transitioned from forest to desert. The modeling also showed how such changes in northern Africa could affect rainfall across Southeast Asia. Penn Today talked with White about what the discovery means, plus the work that led to it.

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