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As a gauge for ocean precipitation conditions, sea surface salinity (SSS) is suspected to be an excellent indicator for variations in the global hydrological cycle. The SSS conditions in the South China Sea (SCS) are closely related to precipitation changes of the East Asian monsoon. However, the characteristics and driving mechanisms of the meridional pattern of East Asian monsoon rainfall during the warm periods of the late Holocene are not well understood because of a lack of high-resolution proxies from the SCS. Here, we present three precise chronologies of monthly stable coral skeleton oxygen isotopes (δ18O) and pair them with established composite strontium/calcium (Sr/Ca) records from the Xisha Islands to obtain a continuous reconstruction of the residual δ18O (Δδ18O, regarded as seawater δ18O) during 1980–2007 CE (Common Era), 1149–1205 CE, and 2070–2011 a BP (years before 1950 CE). The results confirm that coral Δδ18O is a good tracer for reconstructing SSS and precipitation changes in the northern SCS on seasonal and interannual timescales, with higher Δδ18O values implying more saline conditions and less precipitation. The mean value of fossil coral Δδ18O for 1149–1205 CE was higher than that of modern coral, suggesting the existence of salty surface waters and notable dry climate episodes in the northern SCS during the late Medieval Climate Anomaly (MCA). In contrast, the average coral Δδ18O for 2070–2011 a BP was significantly lighter by about 0.404‰ compared to that of recent decades, indicating that less saline and more humid conditions occurred in the northern SCS during the early Roman Warm Period (RWP). Synthesizing our coral records with other published precipitation reconstructions from eastern China suggested a meridional dipole spatial pattern of moisture variation over East Asia during the historical warm periods of the Holocene. During the MCA, drier conditions generally prevailed in the region south of the Yangtze River, and more humid conditions in the north. This may be closely related to the contemporaneous strong El Niño activity occurring at this time, which probably enhanced the East Asian summer monsoon (EASM) and caused a northward shift of the intertropical convergence zone (ITCZ), possibly inducing increased water vapor transport from the SCS to North China. During the RWP, the relatively weak El Niño–Southern Oscillation (ENSO) variability may weaken the intensity of the EASM and shift the ITCZ southward, possibly resulting in a spatial pattern of "wet south and dry north" in East Asia. • 145-year monthly seawater δ18O derived from corals in the northern South China Sea. • Salty surface waters for 1149–1205 CE and less saline for 2070–2011 a BP. • Meridional pattern of moisture over East Asia for the warm periods of late Holocene. • El Niño-Southern Oscillation modulates the strength of East Asian monsoon. [ABSTRACT FROM AUTHOR]

Coral reefs are well known for playing an important role in the global carbon cycle, however little research has been done into their potential for documenting carbon cycles of the past. Here we report the δ13C of coral reef carbonate from a 928.75-m-long core (CK2) from the northern South China Sea (SCS). The chronological profile of CK2 has been well established based on Strontium isotopes and magnetostratigraphy. Our aim is to explore the potential for δ13C in coral reef carbonate to act as a proxy for the seawater δ13C in the northern SCS and related regional carbon cycle in the geological time scale. Our results demonstrate that variations in CK2 δ13C values were generally consistent with changes in seawater δ13C levels in the northern SCS (as inferred from planktonic foraminifer in the northern SCS) over the past 1.8 Ma. This indicates that the δ13C in our CK2 coral reef carbonate was influenced by seawater δ13C levels. The δ13C values of CK2 also presented obvious periodic variations corresponding to glacial-interglacial cycles, with values being higher during glacial periods and lower during interglacial periods. We speculate that the higher δ13C values during glacial periods indicate higher seawater productivity, i.e., increased photosynthesis intensity in coral reefs. In addition, we also found a coherent relationship between changes in CK2 δ13C values and changes in the East Asian terrestrial ecosystem, and we suppose that the CK2 δ13C values maybe partially influenced by the East Asian terrestrial ecosystem through its regulation of SCS seawater δ13C levels. Therefore, we suggest that δ13C values of coral reef carbonate from the northern SCS represent a potential proxy for the seawater δ13C in the northern SCS and related carbon cycle changes in the East Asia. • The δ13C of coral reef carbonate from northern South China Sea can well document changes in seawater δ13C and the regional carbon cycle in the geological time scale. • The evolution of East Asian terrestrial ecosystem could partially influenced CK2 δ13C values through regulate the seawater δ13C levels. • Higher CK2 δ13C values during glacial periods but lower during inter-glacial periods, indicating that seawater productivity, i.e. photosynthesis intensity in coral reefs was higher during glacial periods than during inter-glacial periods. [ABSTRACT FROM AUTHOR]