Variations in the timing of the rainy season in the northern South China Sea during the middle to late Holocene

The amount and timing of precipitation in East Asia are important aspects of the East Asian monsoon. Many paleoclimate records that act as proxies for wet or dry climatic conditions have been linked to changes in precipitation amounts and are thus used to indicate changes in the East Asian monsoon system. However, few studies have examined changes in the timing of the rainy season. Here, we consider the timing of the seasonal precipitation cycle during the middle to late Holocene, using records derived from coupled high-resolution Sr/Ca and O-18 records preserved in Porites corals from the northern South China Sea. These records indicate that the timing of the rainy season in this region changed during the middle to late Holocene. The present-day rainy season generally occurs over the summer and autumn (June-October), which has also been recorded in Porites coral, whereas the rainy season at around 1500 and 6800years B.P. occurred through the autumn and winter (August-December), and the rainy season at around 2540 and 5000years B.P. occurred in the winter and spring (January-April or December-March). During the period around 5900years B.P., the seasonal distribution of precipitation varied from year to year. These shifts in the timing of the rainy season require changes in temperature and humidity patterns and appear to agree with changes in the magnetic susceptibility of lake sediments in this region, which may reflect movements of the Intertropical Convergence Zone location and changes in atmospheric circulation during the middle to late Holocene.