Differences between East Asian and Indian monsoon climate records during MIS3 attributed to differences in their driving mechanisms: Evidence from the loess record in the Sichuan basin, southwestern China and other continental and marine climate records

摘要

Asian monsoons vary with global climatic change, as is well recorded by Chinese loess-paleosol sequences. A radiocarbon and OSL dated, grain size and magnetic susceptibility record of the loess-paleosol sequence from the Chengdu Basin, southwestern China, contains a greatly amplified MIS 3 Indian monsoon climate record. Comparison of this record with other continental and marine climate records in the temporal and frequency domains indicates that the "high-amplitude MIS3" feature dominates the Indian monsoon region and weakens northward but is not observed in East Asian monsoon climate records. These observed differences in the amplitude of MIS 3 climate variations between the two monsoonal regions may be caused by the different effects of the precession insolation forcing on the very different monsoonal driving mechanisms. The Indian monsoon, which originates from the subtropical Mascarene High in the Southern Hemisphere, carries large precession signals from the equatorial and tropic zones, leading to the overall intensification of MIS 3 climate signals. The northward decrease of the Indian monsoon strength reduces precessional climate signals carried by the monsoon. On the other hand, the East Asian monsoon is largely generated from the Western Pacific Subtropical High in the northern subtropical zone where the impact of precessional insolation forcing and heat-vapor transport are much weaker, thus exerting a more limited spatial and temporal influence on climate records.