Weakening of the East Asian summer monsoon at 1000–1100 A.D. within the Medieval Climate Anomaly: Possible linkage to changes in the Indian Ocean-western Pacific

摘要

Monsoon droughts, especially on a decadal-to-centennial timescale, may have a profound impact on the populations of East Asia. Previous work has suggested that the East Asian summer monsoon (EASM) was synchronously strong across East Asia during the Medieval Climate Anomaly (MCA, 900–1300 A.D.); however, there is a dearth of studies addressing the issue ofwhether or not the EASM varied significantly during the entire duration of the MCA. Here we present results from a diverse range of proxy paleoclimatic records from the monsoonal and temperate Asian region in order to evaluate the occurrence of such short timescale variability within the MCA. Within the context of an overall strong EASM during the MCA, a weakening of the monsoon was detected in many of the records during the period 1000–1100 A.D. Comparison of the timing of this event with variations of sea surface temperature (SST) of the Indian Ocean-western Pacific and with proxy records of solar activity reveals a significant covariation, suggesting that the driver of the event may have resulted from changes in the Indian Ocean-western Pacific, related to changes in solar activity. To further address the issue of a terrestrial-oceanic linkage, we used the ECHAM and the global Hamburg Ocean Primitive Equation (ECHO-G) coupled climate model to simulate the variation of EASM precipitation over the last millennium. The model results suggest an interval of weak East Asian summer monsoon at 1000–1100 A.D., and they also reveal a significant positive correlation with the SST of the Indian Ocean-western Pacific.