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摘要
Under the complex influences including the monsoonal climates and tropical hydrological cycle, the features and forcing mechanisms of precipitation changes in the tropical monsoon regions remain controversial. The northern coast of the South China Sea (NCSCS), connecting the South China Sea (SCS) and the Pearl River Estuary (PRE), is a critical area providing reliable tropical precipitation records and probing the possible forcing mechanism of tropical precipitation, benefitted from its high deposition rate and hydro-climatic sensitivity. Here, delta O-18 variations of planktonic (delta(18)OG. ruber) and benthic foraminifera (delta(OC)-O-18. lobatulus) were investigated respectively to reconstruct a high-resolution low-latitude precipitation record from the core 17NH-NC3 in the NCSCS. The results show a distinct delta O-18 difference between delta(18)OG. ruber and delta(OC)-O-18. lobatulus, not only with respect to values, but also with respect to trends in some time intervals. The clear difference between the planktonic and benthic foraminifera (Delta delta(18)Ob-p) illustrates the significant vertical salinity strat-ification. And the temporal trend of Delta delta 18Ob-p indicates the degree of salinity stratification variated since the mid-Holocene. We assume that the degree of stratification in the NCSCS was mainly controlled by tropical precipitation changes. Thus, the trend of Delta delta(18)Ob-p values could indicate the temporal change of the tropical precipitation. The precipitation record of our research area is closely related to the tropical atmosphere-ocean dynamics stimulated by sea surface temperature (SST) changes of the tropical Pacific zone, analogous to the El Nin similar to o-Southern Oscillation (ENSO) events. During the mid-Holocene (from 8260 to 5180 cal yr B.P.), the sustainable higher Delta delta(18)Ob-p values (>1.23 parts per thousand) suggested a large amount of precipitation, pointing to a sustained state of La Nin similar to a-like, which is associated with lasted higher difference between Western SST and Eastern SST (W-E SST gradient) in the equatorial Pacific. Since 5180 cal yr B.P., the decreasing Delta delta 18Ob-p indicates less low-latitude precipitation, which can be ascribed to an El Nin similar to o-like mean state arising from decreased W-E SST gradient. Our study provides a new continuous high-resolution archive of low-latitude precipitation in the tropical monsoon region since 8260 cal yr B.P. And this record highlights that the thermal state of the tropical Pacific most likely adjusted the low-latitude precipitation since the mid-Holocene.
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