SE ASIAN MONSOON VARIABILITY DURING DURING THE LAST 250,000 YRS IN THE LUOCHUAN LOESS SEQUENCE, CHINA

Loess deposits from the Chinese Central Plateau have been interpreted as representing a continuous record of the past 2.4 Myr climatic changes. Among the pioneer work, the measurement of the magnetic susceptibility was interpreted as providing a reliable record of past climatic changes, especially paleomonsoons. The chronology was independently determined by considering a constant deposition rate of magnetic mineral balanced by the value of the low field magnetic susceptibility. This time scale however does not match Pacific Ocean records based on d18O or eolian fluxes implying refinement of the dynamics of the deposition of dust, during glacial intervals, or of the soil formation, during interglacial times, in China. Here we present the study of terrestrial mollusks from the loess sequence in Luochuan which indicate alternating strengthened summer and winter paleomonsoons during the last two climatic cycles. These variations - based on the content of xerophilous, hygrophilous, and oriental species are in very good agreement with the variation inferred from pedology, sedimentology and climate modeling for the last 130,000 yrs. The comparison between mollusk records and pedological indices for the last 250,000 yrs indicate some discrepancies in the magnetic susceptibility chronology as suspected by marine records. We propose a new interpretation of the last 250,000 yrs record from the Chinese Loess Plateau in term of solar induced monsoon events which is supported by a comparison with the available data from the African and Indian monsoons.