Mollusk record of monsoon variability during the L2-S2 cycle in the Luochuan Loess sequence, China

Molluscan changes that occurred in China over the S2-L2 upper middle Pleist ocene series may be caused by monsoon variation. Study of terrestrial mollu sks from the loess sequence in Luochuan, gathered in ecological groups acco rding to the moisture and temperature requirements of the identified specie s, indicates alternating strengthened summer and winter paleomonsoons betwe en 130,000 and 244,000 yr. The four occurrences of species, currently distr ibuted in S.E. China in the sequence, indicate that the climate conditions were warmer and wetter than today between about 242,000 and 233,000 yr, at about 210,000, 164,000, and 140,000 yr. The main occurrence of xerophilous taxa at about 180,000, 154,000, and 138,000 yr is interpreted as indicating a drier environment than today. Such suggestions are in agreement with oth er proxy data such as grain size distribution. Higher numbers of individual s in the different ecological groups from the S2-L2 sequence indicate more favorable general environmental conditions than in the youngest S1-L1. This may agree with an increase in the regional aridity, since 500,000 yr, dedu ced from the study of the eolian flux in the northwestern Pacific downwind from China. (C) 1999 University of Washington.