中国科学院南京地质古生物研究所机构知识库

A 40-year delta O-18 record of the similar to 5.4 ka BP Porites lutea from the east coast of Hainan Island in the northern South China Sea (SCS) was analyzed to investigate evolution of Asian monsoon variability during the middle Holocene. The mean, maximum and minimum of the coral skeletal delta O-18 were 0.49 parts per thousand-0.69 parts per thousand and 0.14 parts per thousand higher than those of modern corals respectively. Thus, the sea surface temperature (SST) for mean annual, winter and summer at similar to 5.4 ka BP was 2.2 degrees C, 3.1 degrees C and 0.6 degrees C lower, and accordingly the surface salinity (SSS) was 1.5 parts per thousand, 2 parts per thousand and 1 parts per thousand higher than today. The delta O-18 amplitude of the similar to 5.4 ka coral for winter-summer (similar to 26% higher than modern values), winter (similar to 23% higher) and summer (similar to 18% lower than that of the modern corals) implied enhanced seasonality in winter, but decreased seasonality in summer for SST SSS and Asian monsoon conditions at similar to 5.4 ka BP relative to today. Thus, seasonal increment of coral delta O-18 mainly resulted from decrease of winter SST and increase of winter seawater delta O-18 during the middle Holocene, which possibly correlated with seasonal changes of insolation. The similar to 5.4 ka coral delta O-18 values indicate that interannual variability of the Asian monsoon was much stronger in winter-summer and winter, although much weaker in summer during the middle Holocene relative to today. Spectral analysis revealed a significant variance with a period of 18.7 years and sub-significant variances at interannual periods of 2.3-2.6 years, which implies that ENSO variance and a teleconnection between the atmospheric ENSO and monsoonal rainfall during the middle Holocene existed, although they were much weaker than today. The long-term decrease trends of the coral delta O-18 minima, mean and maxima are controlled by the long-term trends of SST increase, and SSS and local insolation decreases from the middle Holocene to the present. (C) 2009 Elsevier Ltd and INQUA. All rights reserved.