Asian monsoon is one of the most influential factors in global climate changes and affecting billions of people life. The past changes in the East Asian summer monsoon (EASM) are characterized by two distinct variabilities: one is the glacial-interglacial cycle (~100 kyr) related to global ice-sheet evolution, and the other is the precession cycle (~23 kyr) forced by solar insolation. The difference between the two dominated periodicities involves various forcing processes, and many efforts in the past two decades have been done to explain the mechanism behind this difference. However, reconciling the two dominated cycles has not been achieved yet, and one of the major problems is that no geological archive records both two cycles in dominance in a single profile. In this study, we present a mineralogical study of coastal sediments in the south Bohai Sea, East Asia by analyzing diffuse spectral reflectance and X-ray diffraction. The results show that the leading component of the reflectance derivative spectra accounts for 58.9% variance in total and its loading spectrum can be well correlated to that of mineral assemblages of illite and goethite. For this monsoonal record, orbital periodicities in precession and eccentricity bands are both highlighted, inferring an integrated forcing of solar insolation and ice-sheet evolution in the EASM during the late Quaternary. By comparing this mineral record to various monsoonal proxies, it is speculated that the precession variability in the EASM is mainly related to moisture changes, while the eccentricity variability is likely associated with temperature changes. Overall, the monsoonal record in the Bohai Sea offers an opportunity to harmonize the spectral difference between various monsoonal proxies, which is critical to extending our understanding of orbital variabilities of the EASM.
 

East Asian summer monsoon,mineral properties,solar insolation,global ice volume,Bohai Sea,Late Quaternary,orbital variability