Researchers connect end of Green Sahara with megadrush of Southeast Asia.
Physical evidence found in caves in Laos helps tell a story about a connection between the end of the Green Sahara – when once vegetated North Africa became a hyper-arid landscape – and a previously unknown mega-drought that flows southeast -Asia 4000 to 5000 years ago.
In a paper published today in Nature Communications, scientists at the University of California, Irvine, the University of Pennsylvania, William Paterson University of New Jersey and other international institutions explain how this major climate change has led to a shift in human settlement patterns in the Southeast. Asia, which is now inhabited by more than 600 million people.
“In this study, we provide the first evidence of a strong link between the end of the Green Sahara and Southeast Asian monsoon falls in the mid to late Holozene period,” said co-author Kathleen Johnson, UCI associate professor of Earth system science. “Our high resolution and well-dated record suggests a strong connection between North Africa and mainland Southeast Asia at this time.”
To set a paleoclimatic record for the study, co-author Kathleen Johnson, UCI associate professor of earth systems science, and other researchers collected stalagmite samples from caves in northern Laos. The specimens have geochemical evidence of past climate change in the highly populated Asian monsoon region. Credit: Amy Ellsworth
To set a paleoclimate record for the study, Johnson and other researchers collected stalagmite samples from caves in northern Laos. In their UCI laboratory, they measured the geochemical properties of the oxygen and carbon isotopes, carbon-14, and trace metals found in the specimens. This helped them to control the occurrence of drought and extrapolate its effects on the region.
Johnson said they combine data from the analysis of these stalagmite-derived proxies with a series of idealized simulations of climate models – conducted by co-author Francesco Pausata of the University of Quebec in Montreal – in which the Sahara vegetation and dust concentrations in a way were changed which allowed them to investigate the feedback of ocean atmosphere and teleconnections associated with such abrupt shift in precipitation.
The model experiments suggested that declining vegetation in the Sahara led to increased air dust that led to cooling of the Indian Ocean and shifting the Walker circulation pattern to the east, causing the behavior to be similar in current El Niño events. This eventually led to a large reduction in monsoon meal in Southeast Asia that lasted more than 1,000 years, according to Johnson.
Anthropologists and archaeologists have previously studied the effects of the fall of the Green Sahara, also known as the African Humid Period, on population centers closer to West Asia and North Africa, noting the collapse of the Akkadian Empire of Mesopotamia, the de-urbanization of Indus civilization (near present-day Pakistan and India) and the spread of pastoralism along the Nile River.
But the link to the origins of the mega-drought shifts in Southeast Asia and lifestyle patterns in the region had not been previously investigated, according to lead author Michael Griffiths, professor of environmental sciences at William Paterson University in New Jersey.
“Archaeologists and anthropologists have been studying this event for decades, in terms of social adaptations and circumstances, but the exact cause has distracted the scientific community,” said Griffiths, who was a National Oceanic and Atmospheric Administration-supported postdoctoral scientist in Johnson’s lab. and has worked with her on this research topic for more than 10 years.
“Results of this work provide a new and convincing explanation for the origins of Southeast Asia megadroch and could better help us to better understand the divergent social shifts in different parts of the tropics and extra-tropics,” he said.
The researchers suggest that the centuries-long mega-drought coincides with the ‘missing millennia’ in Southeast Asia between 4,000 and 6,000 years ago, a time characterized by a marked lack of archaeological evidence in the interior of Southeast Asia compared to earlier and later parts of the Holocene. .
They suggest that the mid-Holocene may have been a major impetus for mass population movements and the adoption of new, more resilient survival strategies – and that it should now be considered as a possible driver for the beginning of the Neolithic era on the mainland of the Southeast. -Asia.
“This is excellent evidence of the type of climate change that society must have influenced, what plants were available, what animals were available,” said co-author Joyce White, assistant professor of anthropology at the University of Pennsylvania. ‘All life had to adapt to this very different climate. From an archaeological point of view, this is really a game changer in how we try to understand or reconstruct the Middle Holozene period. “
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Reference: August 21, 2020, Nature communication.
DOI: 10.1038 / s41467-020-17927-6
The collection of speleothem samples from Laotian caves was made possible by Johnson’s collaboration since 2010 with the Middle Mekong Archaeological Project, managed by White, a senior scientist at the University of Pennsylvania Museum of Archeology and Anthropology. This project, which also involved researchers from the University of Oxford and the University of Northumbria in the United Kingdom, Los Alamos National Laboratory, and the University of New Mexico, was funded by the National Science Foundation, NOAA, the Swedish Research Council and a grant from the Henry Luce Foundation to the Penn Museum.
