Two-stage evolution of glacial-period Asian monsoon circulation by shifts of westerly jet streams and changes of North American ice sheets

Compilation of North American loess, dune, lacustrine, and glacial moraine morphological records at places along the retreating Laurentide Ice Sheet shows intra D-O/Heinrich-scale climate oscillations between 28,000 and 10,000 calibrated years before present (calBP). Grayscale variations of the loess-paleosol record that represents the composite stratigraphy reflect the poleward-equatorward displacement of westerly jet stream, associated with advance-retreat of the Laurentide Ice Sheet, both of which superpose on a 2-stage trend of drastic changes. Compilation of paleo-Asian monsoon records from NE, East Central, and SW China also shows a 2-stage evolution of Asian monsoon rainbelt distribution with patterns on intra D-O/Heinrich scales between 28,000 and 10,000 calBP. In stage 1, Asian monsoon rainfall intensity decreases over NE/SW but increases over EC, then drastically fluctuates over NE/SW and keeps constant over EC China. In stage 2, Asian monsoon rainbelts distribute a modern-synoptic-style tripole and reversed tripole mode during boreal interstadials and stadials. Additional compilation of more paleo-Asian monsoon rainfall records and state-of-the-science model precipitation records confirms these patterns over large geographic region and Asian continent during this period. The comparison of global climate forcing factors excludes Atlantic Meridional Overturning Circulation but suggests poleward-equatorward displacements of North American westerly jet streams coupled with ice sheet margin fluctuations at middle to upper midlatitudes, which altered the structures of Eurasian jet streams, to modulate the 2-stage intra D-O/Heinrich-scale changes on Asian monsoon evolution. The drastic retreating of the Laurentide Ice sheet during the second stage made the modern-synoptic-style monsoon rainbelt distribution with seesaw patterns on intra D-O/Heinrich warm and cold phases prominent at 16,000 calBP.