Inter-annual and inter-decade variability of the oxygen isotopic composition of massive corals from the South China Sea and the ciimatic influencing factors

摘要

Coral colonies of Porites lutea and P. lobata were collected from the east offshore of Hainan Island, South China Sea. Oxygen isotope ratios, ~(18)O/~(16)O, were analyzed along the major axis of growth at a resolution of 25-28 samples within an annual band from three colonies in order to study the relation between coral oxygen isotopic composition and the monsoonal climate in seasonal, inter-annual and inter-decade time scales. The results indicate that the seasonal and inter-annual variations of coral delta ~(18)O are mainly controlled by temperature. While the coral delta ~(18)O is mainly controlled by SST, deviations of the delta ~(18)O from SST correlate statistically with sea surface salinity. Therefore, we suggest that the inter-annual variation of the annual coral delta ~(18)O minima is mainly controlled by seawater composition. Seawater composition analysis indicates that its delta ~(18)O and salinity are simultaneously affected by freshwater inputs primarily from precipitation, which is mainly supplied by the Asian summer monsoon. Thus seasonal alternations of the winter and summer monsoon mainly control the coral delta ~(18)O, thereby allowing reconstruction of these monsoonai variables. These inter-decadal trends are roughly consistent with salinity changes, but not with temperature and precipitation, suggesting that seawater composition controlled by freshwater inputs from distant source areas, rather than from local precipitation, is responsible for the trends in seawater composition and coral delta ~(18) O which is probably the consequence of monsoonal precipitation over the source areas of freshwater, evaporation and the water exchange between South China Sea and Pacific Ocean.