Records of the Mid-Brunhes Event in Chinese loess-paleosol sequences

Abstract

The Mid-Brunhes Event (MBE) was a climatic transition characterized by warmer temperatures, smaller ice volume and higher sea levels during interglacials since marine oxygen isotope stage (MIS) 11. Data from numerous long-term sedimentary sequences indicate that the MBE was expressed throughout the whole earth surface; however, conflicting evidence in terrestrial sequences from middle/high latitudes of the Northern Hemisphere mean that the event's existence and global synchronicity are a matter of debate. To address this problem, we investigated the MBE signal in paleoclimate records from the Chinese Loess Plateau (CLP). Higher magnetic susceptibility (χ) since S5 in the Luochuan, Yimaguan, and Lingtai sections, and since S4 in the Jingyuan and Xijin sections indicate that East Asian Summer Monsoon (EASM) precipitation strongly affected the central CLP since MIS 13, but exerts a relatively weak influence on the northwestern CLP until MIS 11 during the past 800 kyr. From MIS 13 to MIS 11, shrinkage of the Northern Hemisphere ice sheet resulted in northward movement of the Intertropical Convergence Zone and elevated sea-level. An ~25 m sea-level rise could have caused the coastline of the Asian continent to shift northwestward by ~50–100 km. These changes induced extension of EASM-domain areas into the northwestern CLP from the central CLP. The response to the MBE in loess-paleosol sequence of the CLP was expressed by variations in the geographic extent of EASM-domain areas, rather than changes in the EASM intensity. The MBE emerged at MIS 11 in the CLP, and was globally synchronous.