Orbital forcing of terrestrial mollusks and climatic changes from the Loess Plateau of China during the past 350 ka

High-resolution analyses of terrestrial mollusks from two loess sequences i n the Chinese Loess Plateau provide continuous evidence of paleoecosystem a nd paleoclimate processes through the recent three glacial-interglacial cyc les. Systematic fluctuations in thermal-humidiphilous mollusk type (Punctum orphana) indicate that the strength of the SE Asian summer monsoon is sens itive to orbital forcing at the obliquity and precession periods (41 and 23 kyr, respectively). In contrast, the cold-aridiphilous mollusk (Vallonia t enera and Pupilla aeoli) variability displays a different pattern. The stro ngest powers are centered at about 100 kyr and 41 kyr periods, which drive the major period of winter monsoon variations in the Chinese loess. These d ifferent responses to winter and summer monsoon in the Loess Plateau of Chi na suggest that both of these monsoon systems are tightly coupled in the 41 kyr cycle, but are not coincident relative to the precession (19-23 kyr) a nd 100 kyr cycles. The relationship between the winter and summer monsoons is not a simple model reflecting a seesaw pattern.