The interpretation and understanding of the relationship between Middle to Late Holocene climate change in monsoon margins of northwest China with the westerlies and Asian monsoon (AM) remain controversial. Here we present a new multi-proxy sedimentary dataset from the Heihe River basin in the middle part of the Hexi Corridor on the northern margin of the Qinghai-Tibet Plateau (QTP), which is a sensitive zone for the interaction between the westerlies and AM. Fluctuations in grain size, δ13Corg, δ18O, magnetic susceptibility, total organic carbon, total nitrogen, and C/N ratio document regional lake and climate evolution since 5334 cal yr BP. Results show that climate conditions on the millennial timescale are humid in the late Middle Holocene (MH) and dry to wet in the Late Holocene (LH). Combined with the multi-model ensemble simulation from PMIP3-CMIP5, high lake levels and wetter climate in the late MH are closely linked to the strengthening Asian summer monsoon. Simultaneously, the slight wetting trend since the late LH may be the superimposing effect of enhanced westerlies and the weakening Asian winter monsoon. These findings can provide insights into the interpretation of the interaction between the westerlies and AM during the Holocene in East Asia.

We investigated climate niches of grasses at regional scales and quantitatively reconstruct Asian monsoon precipitation at the sand-loess transitional zone in northern China. Our results provide direct evidence that certain grass lineages have been specialized in specific habitats: Pooideae grasses stand out and occupy a much cooler environment than all other subfamilies; Pooideae, Aristidoideae, and Chloridoieae occupy dry environments. Pooideae grasses occupy the coldest and driest environments compared to all other subfamilies, with a mean annual temperature (MAT) and precipitation (MAP) of ~13.6 to ~15.3°C and 224 to ~1674 mm, respectively, at a regional scale. We built a database for grasses and their corresponding climate parameters. Based on this database, past climate parameters at the margin of the Asian summer monsoon since ~70 ka were quantitatively reconstructed by phytolith assemblages. They show that this area was dominated by cold- and dry-adapted grasses since ~70 ka with a MAT and MAP of ~3.3 to ~11.0 °C and ~442 to ~900 mm, respectively, generally consistent with the results of phytolith-based transfer function reconstructions and with the results of previous nearby pollen-based quantitative reconstructions. With the improvement of the species-climate and ecosystem dataset, our database-based method is a promising quantitative reconstruction approach to past climatic change in the monsoon region.

A precisely 230Th-dated stalagmite δ13C profile from Hulu Cave, China, is presented to characterize the frequency and pattern of millennial-scale Asian monsoon (AM) variability from 160.6 to 132.5 ka. Evidence for an antiphased relationship of the δ13C and δ18O on the millennial scale suggests that the δ13C is indicative of the local hydrological cycle associated with changes in AM strength. Owing to the δ13C responding to AM changes more sensitively than the δ18O, we could identify 15 strong AM events that correlate to cold intervals recorded in Antarctic ice cores within 230Th dating uncertainty. This result supports a dynamic link of AM strength and southern hemispheric climates via the cross-equatorial airflows. Power spectrum analysis shows a predominant periodicity of 1.5–2.5 ka for the δ13C profile, similar to the Dansgaard-Oeschger frequency during the last glacial period. Moreover, the AM events are characterized by rapid transitions at the onset, suggesting that the observed millennial-scale AM variability is likely forced by northern high-latitude climates via north–south shifts of the Intertropical Convergence Zone associated with the bipolar seesaw mechanism. As evidence for a common mechanism for ice age terminations, a strong AM event (~134 ka) surrounding Termination II is analogous to the Bølling-Allerød warming interval.

The ‘Mystery Interval’ (MI, 17.5−14.5 ka) was the first stage of the last deglaciation, a key interval for understanding mechanisms of glacial–interglacial cycles. To elucidate possible causes of the MI, here we present three high-resolution, precisely dated oxygen-isotope records of stalagmites from Qingtian and Hulu Caves in China, reflecting changes in the East Asian summer monsoon (EASM) then. Based on well-established chronologies using precise 230Th dates and annual-band counting results, the two-cave δ18O profiles of ~7-yr resolution match well at decadal timescales. Both of the two-cave records document an abrupt weakening (2‰ of δ18O rise within 20 yr) in the EASM at ~16.1 ka, coinciding with the transition of the two-phased MI reconstructed from New Mexico's Lake Estancia. Our results indicate that the maximum southward displacement of the Intertropical Convergence Zone and associated southward shift of polar jet stream may generate this two-phase feature of the MI during that time. We also discover a linear relationship among decreasing EASM intensity, rising atmospheric CO2 and weakening Atlantic Meridional Overturning Circulation between the MI and Younger Dryas episodes, suggesting a strong coupling of atmospheric/oceanic circulations in response to the millennial-scale forcing, which in turn regulates global climate changes and carbon cycles.

Expansion or shrinkage of closed lakes is a natural response to fluctuations in precipitation and evaporation, linked closely to changes in strength or position of atmospheric circulation. In Tibet, there are many such lakes with paleo-shorelines that can be used for reconstructions of climate history. Despite the fact that many paleo-shorelines are well preserved in Tibet, dating them has been seriously hindered by various difficulties. Here we present the first optical dating chronology for a series of paleo-shorelines in Zhari Namco, the third-largest inland lake in central Tibet. Our results indicate that the lake level has dropped 128 m over the past 8.2 ka. Younger shorelines are found at lower altitudes, indicating that the shorelines follow a geomorphic-chronological order and a broadly continuous trend of stepwise shrinkage. The surface area of Zhari Namco has shrunk in size from 4605 km2 at 8.2 ka ago to 996 km2 at present; 300 km2 of water has been lost from this lake. Such a loss in water implies a significant reduction in precipitation over the past 8.2 ka, a likely result of a weakening Asian monsoon. Following the decreasing precipitation since the early Holocene, this area has become increasingly arid.

A detailed understanding of long-term climatic and environmental change in southwestern China is hampered by a lack of long-term regional palaeorecords. Organic analysis (%TOC, %TN, C/N ratios and δ13C values) of a sediment sequence from Lake Shudu, Yunnan Province (ca. 22.6–10.5 cal ka BP) indicates generally low aquatic palaeoproductivity rates over millennial timescales in response to cold, dry climatic conditions. However, the record is punctuated by two marked phases of increased aquatic productivity from ca. 17.7 to 17.1 cal ka BP and from ca. 11.9 to 10.5 cal ka BP. We hypothesise that these shifts reflect a marked, stepwise lacustrine response to Asian summer monsoon strengthening during the last deglaciation.

Lake high-stand sediments are found in three onshore terraces at Lake Donggi Cona, northeastern Tibetan Plateau, and reveal characteristics of hydrological changes on lake shorelines triggered by climate change, geomorphological processes, and neo-tectonic movements. The terraces consist of fluvial–alluvial to littoral-lacustrine facies. End-member modeling of grain-size distributions allowed quantification of sediment transport processes and relative lake levels during times of deposition. Radiocarbon dating revealed higher than modern lake levels during the early and mid Holocene. Lake levels follow the trend of Asian monsoon dynamics, and are modified by local non-climatic drivers. Site-specific impacts explain fluctuations during the initial lake-level rise ~ 11 cal ka BP. Maximum lake extension reached ~ 9.2 cal ka BP, at ~ 16.5 m above present lake level (a.p.l.l.). Littoral and lacustrine sediment deposition paused during a phase of fluvial activity and post-depositional cryoturbations at ~ 8.5 cal ka BP, when the lake level fell to ~ 8 m a.p.l.l. After a second maximum at ~ 7.5 cal ka BP, lake level declined slightly at ~ 6.8 cal ka BP, probably due to a non-climatic pulse that caused lake opening. The level remained high until a transition towards drier conditions ~ 4.7 cal ka BP. Though discontinuous, high-stand sediments provide a unique, high-resolution archive.

The Asian monsoon is an important component of the global climate system. Seasonal variations in wind, rainfall, and temperature associated with the Asian monsoon systems affect a vast expanse of tropical and subtropical Asia. Speleothem-derived summer monsoon variation in East Asia was previously found to be closely associated with millennial-scale change in temperature in the North Atlantic region between 75 and 10 ka. New evidence recovered from East Asia, however, suggests that the teleconnection between summer monsoon in East Asia and temperature change in the North Atlantic region may have significantly reduced during 120 to ~ 110 ka, a period directly after the full last interglaciation and corresponding roughly to marine oxygen isotope stage 5d. This reduction may be due to the low ice volume in the North Hemisphere at that time, which makes the millennial-scale change in temperature in the North Atlantic region less effective in influencing the Asian summer monsoon. This is important for investigating the mechanisms controlling the Asian summer monsoon and the paleoclimatic teleconnection between East Asia and the North Atlantic region, and for predicting monsoon-associated precipitation in East Asia under a global-warming trend.

Annual radiocarbon from a massive Porites lutea coral collected from Hon Tre Island, Vietnam, South China Sea (SCS) was analyzed over a ~100-yr-long period from AD 1900 to 1986. The pre-bomb results from 1900–1953 show a steady Δ14C value of –54.4±1.8‰ (n=60). These values are similar to coral records located in the central and southern SCS and from Indonesian waters, but are lower than those from Japan. Following the input of anthropogenic bomb 14C, our results show a sharp increase in Δ14C from 1960, reaching a peak value of 155.3‰ in 1973. The Hon Tre Island post-bomb Δ14C values are lower than those of other corals located in the SCS and Japan, but higher compared to those in the Indonesian Seas. This study infers a seasonal input of upwelled water depleted in 14C from the deeper SCS basin that originates from the tropical Pacific via the Luzon Strait. The bifurcation of the North Equatorial Current feeds the surface and intermediate currents in the SCS and Makassar Strait region. However, unlike the Makassar site, this study’s coral Δ14C does not receive lower 14C water from the South Pacific Equatorial Current. The Vietnam record therefore represents a unique oceanographic position, reflecting the seasonal influence of older, deeper SCS waters that upwell periodically in this area and have modified the surface waters locally in this region over the last 100 yr.

The expedition of Zheng He's fleet to the Western Ocean1 in the first half of the 15th century is an important event in the history of navigation, which has attracted the broad attention of domestic and foreign scholars from different fields2. This paper reveals the relation between Zheng He's voyages and the Asian Monsoon from a geographical perspective. Historical records show that Zheng He's seven voyages to the Western Ocean were precisely organized and successfully carried out due to careful consideration of the conditions and periodical patterns of the Asian tropical and subtropical monsoon. Details such as fleet routes, sailing schedules, wind-waiting points, divergent and rendezvous points were painstakingly planned and arranged in advance by the organizers of the expedition, who all paid close attention to the changing patterns of the Asian Monsoon.