Deciphering orbital-scale precipitation changes in the northern East Asian monsoon region: insights into the roles of terrestrial and oceanic moisture sources

Water vapor is the essential substance for precipitation and a crucial 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 water vapor tracking climate model was conducted for the past 300 kyr to investigate the contributions of terrestrial and oceanic moisture sources to precipitation changes in the northern East Asian monsoon region (NEA, 35-45°N, 105-120°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. The dominant 23-kyr cycle of NEA precipitation reflects the effect of precession forcing, while the weak 100-kyr cycle implies the impact of the high-latitude ice sheet forcing, which triggers the antiphase change in the moisture contribution rates of the land and Pacific sources in the glacial-interglacial cycle. 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. As a preliminary attempt to track the orbital-scale variations of the terrestrial and oceanic moisture sources of East Asian monsoon precipitation by conducting a water vapor tracking transient simulation, this study provides new insights into the temporal-frequency characteristics and physical mechanisms of orbital-scale East Asian monsoon precipitation variations from the perspective of water vapor sources.