End of GreenSahara Responsible for Monsoon Failure and Societal Shifts in Mainland Southeast Asia
Abstract
The mid-to-late Holocene in eastern Africa and Eurasia was characterized by one of the largest climate anomalies of the past 10,000 years (the so-called '4.2 ka event'), yet the nature and geographical extent of this event, especially in mainland southeast Asia, remains elusive. This is somewhat surprising given that this period also coincides with major shifts in human settlement patterns and population movements across East Asia. Here we have compiled three new speleothem oxygen (δ18O) and carbon (δ13C) isotope records from Tham Doun Mai cave in northern Laos for the Holocene. The δ18O profiles show a general increasing trend through much of the Holocene, which is interpreted to reflect an overall weakening of the Southeast Asian monsoon. This general trend is punctuated by a marked positive δ18O shift at 4-5 ka, signifying an overall reduction in monsoon strength. Interestingly, it is also coeval with a cessation in speleothem growth for two speleothems and a 5 per mil δ13C increase for the speleothem that continued to grow, interpreted to reflect a marked reduction in cave recharge.
The onset of this abrupt 'megadrought' in northern Laos is coincident with abrupt cooling in the Indo-Pacific Warm Pool and matches the timing of African monsoon failure during the termination of the 'Green Sahara'. Using fully coupled ocean-atmosphere model simulations, we show that reduced vegetation and increased dust emissions (such as the case during the end of the Green Sahara) cool the Indian Ocean and shift eastward the Walker circulation, causing a weakening of the Indian and southeast Asian summer monsoon systems. Modern climate dynamics also suggest that the Indian monsoon onset is delayed during El Niño events due to a southward shift of the ITCZ, a result that is also reinforced by the model experiments.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP22C..05G
- Keywords:
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- 9340 Indian Ocean;
- GEOGRAPHIC LOCATIONDE: 1615 Biogeochemical cycles;
- processes;
- and modeling;
- GLOBAL CHANGEDE: 1807 Climate impacts;
- HYDROLOGYDE: 4904 Atmospheric transport and circulation;
- PALEOCEANOGRAPHY