Little Ice Age Wetting of Interior Asian Deserts and the Rise of the Mongol Empire

Thursday, 17 December 2015: 15:10
2003 (Moscone West)
Aaron E Putnam1,2, David Putnam3, Laia Andreu-Hayles1, Edward R Cook4, Jonathan Gray Palmer5, Elizabeth H Clark4, Chunzeng WANG3, Feng Chen6, George Denton2, Douglas P Boyle7, Scott Bassett8, Sean D Birkel9, Javier Martin Fernandez4, Irka Hajdas10, John Richard Southon11, Christopher Garner8 and Wallace S Broecker4, (1)Columbia University of New York, Palisades, NY, United States, (2)University of Maine, School of Earth and Climate Sciences and Climate Change Institute, Orono, ME, United States, (3)University of Maine at Presque Isle, Presque Isle, ME, United States, (4)Lamont -Doherty Earth Observatory, Palisades, NY, United States, (5)University of New South Wales, Sydney, Australia, (6)China Meteorological Administration, Institute of Desert Meteorology, Ürümqi, China, (7)University of Nevada Reno, Reno, NV, United States, (8)University of Nevada, Reno, Reno, NV, United States, (9)University of Maine, Orono, ME, United States, (10)ETH Zurich, Zurich, Switzerland, (11)University of California Irvine, Irvine, CA, United States
Documenting hydrological responses to past climate changes may provide insights into how ongoing warming will alter the distribution of Earth’s water resources. Here we report evidence suggesting that wetter-than-present conditions persisted during the past millennium in the deserts of the Tarim Basin, western China, located at the heart of Asia - Earth’s largest and most populous continent. Our assessment is based on observations of landforms composed of waterlain sediments occurring throughout the Taklamakan and Lop Deserts of the Tarim Basin. These landforms are associated with subfossil phreatophyte trees, reeds, and mollusk shells. We applied 14C and dendrochronological dating techniques to construct a chronology for when the Tarim Basin was wetter than today. We also employed hydrological modeling to estimate plausible climatic conditions under which the observed wet environment could have been sustained. Our results indicate that the core of the Asian desert belt was dominantly wetter than today during the last major cold spell of the Holocene: The Little Ice Age. Wetter conditions in the Tarim Basin deserts accompanied northern cooling, snowline lowering, a strengthened boreal jet, and coeval weakening of south Asian monsoons. Southward migration of grasslands in response to wetter conditions may have aided the spread of the Mongol Empire across Asian drylands. On the other hand, net drying over the 20th century has led to drought that is unprecedented for at least the past ~830 years, and which could intensify with further warming.