Contributions of terrestrial and oceanic moisture sources to orbital-scale precipitation variations over the northern East Asian monsoon region

Water vapor is the material basis of precipitation and an important component of the global hydrological cycle. Quantifying the contributions of terrestrial and oceanic moisture sources is crucial for comprehending regional precipitation and hydroclimate changes. Previous studies have extensively investigated the East Asian summer monsoon and its precipitation changes using geological climate records, but it remains unclear how water vapor from different source regions affects the orbital-scale precipitation change in East Asia. In this study, a long-term transient simulation using a climate model with a water-tagging scheme was conducted for the past 300 kyr to explore the contributions of terrestrial and oceanic moisture sources to precipitation changes in the northern East Asian monsoon region (NEA, 35-45 degrees N, 105-120 degrees E). The results showed that for the climatologically annual NEA precipitation, the global land source was the primary moisture source, accounting for approximately 57.6% of the total precipitation, followed by Pacific Ocean source contributing 20.9%, while other sources had a minor contribution. The orbital-scale changes of annual NEA precipitation, dominated by the precipitation of the rainy season from May to September, were mainly characterized by a significant 23-kyr cycle and a weak 100-kyr cycle. Analyses of water vapor sources found that the significant 23-kyr cycle in NEA precipitation was caused by the superposition of the synchronous 23-kyr cycles of precipitations from the land and Pacific Ocean sources, while the nonsynchronous 100-kyr cyclic changes of precipitations from the land and Pacific Ocean sources led to the weak 100-kyr cycle of NEA total precipitation. Further analysis of water vapor flux showed that the orbital-scale NEA precipitation changes were mainly controlled by the precession-induced Northern Hemisphere summer insolation variations, while changes in the global ice volume also had a certain modulation effect on NEA precipitation by regulating the contribution rates of land and Pacific moisture sources. This study highlights the importance of terrestrial and oceanic moisture sources associated with external forcings in understanding the orbital-scale East Asian monsoon precipitation changes.