Strong East Asian Summer Monsoon Research Articles

Multicentennial-scale coupling of the East Asian monsoon to North Atlantic climates during the Last Glacial Maximum

The Last Glacial Maximum (LGM) is the period when global ice volume reached its maximum, the radioactive forcing well-defined and the climate in the quasi-equilibrium state. However, few proxy records have a temporal resolution high enough to capture detailed climate variabilities at this timescale. Here we reconstruct absolutely-dated and high-resolution δ18O and δ13C records from Shima Cave, central China, covering from 22.4 to 20.2 ka BP, with a temporal resolution of ∼14 years. Both δ18O and δ13C records show clear multicentennial-scale variations. Comparison with highly-resolved geological archives from the mid-to-low latitudes shows that multicentennial-scale changes are evident in the East Asian summer monsoon (EASM) and South American summer monsoon regions, but in antiphased relationship. Altogether six multicentennial-scale strong EASM periods are consistent with warmings in Greenland and northward movement of the jet stream over the Euro-Asia continent, and monsoon weakenings are linked with the ice-rafted debris peaks and Greenland cooling, indicating persistent influence of the North Atlantic climates on the EASM through shifts of the atmospheric circulations during the LGM.

East Asian summer monsoon and early anthropogenic impacts on the lacustrine carbon cycle in the Otindag Sandy Land since the middle Holocene

Lake systems play a pivotal role in the global carbon cycle, yet the biogeochemical processes in alkaline and saline lakes have received little attention. In this study, we present a comprehensive analysis of δ13Ccarb and δ18Ocarb records from Lake Chagan in the Otindag Sandy Land, located in North China, spanning approximately 7000 years. Our aim is to explore how the lacustrine inorganic carbon cycle responded to both climate change and human activity. The findings reveal a notable highstand in Lake Chagan around 6.9–6.0 cal kyr BP, followed by a gradual regression leading to an unstable state over the past 1.6 cal kyr BP. The hydroclimate variations inferred from Lake Chagan align with other regional records, suggesting that long-term East Asian summer monsoon (EASM) precipitation trends were influenced by decreasing insolation and variations in solar irradiance on a centennial timescale. The sources of dissolved inorganic carbon (DIC) in lake water generally mirrored regional hydroclimate changes since the middle Holocene. Our evidence indicates that during periods of strong EASM activity, more allochthonous organic matter was converted to lake water DIC, coinciding with high vegetation cover and intense soil erosion. While hydroclimatic changes significantly impacted the lacustrine carbon cycle, the isotopic evidence also suggests substantial anthropogenic influences post-1.6 cal kyr BP, particularly in terms of the input of allochthonous organic matter into the lakes of the Otindag Sandy Land. These findings underscore the potential for anthropogenic-driven terrestrial carbon cycle feedback to global climate change over millennia.

How the enhanced East Asian summer monsoon regulates total gross primary production in eastern China

Recognizing the relationship between gross primary production (GPP) and precipitation in eastern China, the East Asian Summer Monsoon (EASM) plays a crucial role in shaping GPP. Despite confirmation of the strong link between EASM and GPP, there remains a notable research gap in understanding the specific impact of the EASM on GPP in different regions of eastern China. Here we used simulations from Trends in Net Land–Atmosphere Carbon Exchanges (TRENDY) models from 1951 to 2010 and divided eastern China into five subregions for the study. We also used the New East Asian Summer Monsoon Index (NEWI) as a quantitative metric to distinguish between periods of strong and weak EASM. Building on this, this study aims to investigate the response of GPP in different subregions of eastern China. Regionally, under strengthened EASM years (1954, 1957, 1965, 1969, 1977, 1980, 1983, 1987, 1993 and 1998), East China experienced the most pronounced increase in GPP at 12 ± 21 (mean ± 1 sigma) gC m−2 mon−1 compared to the weak EASM years (1958, 1961, 1972, 1973,1978, 1981, 1985, 1994, 1997 and 2004). In contrast, Southwest China showed a decline in GPP at −4 ± 10 gC m−2 mon−1. Moreover, GPP also increased in Northeast and North China when EASM strengthened, while South China showed a decline in GPP. This indicated that GPP changed with monsoon intensity. According to the mechanism analysis, during strong EASM, there was intense moisture convergence through alterations in the atmospheric circulation field over East China and abundant precipitation, which further contributed to the increase in GPP. Downward solar radiation in Southwest China decreased with EASM enhancement, which suppressed GPP and hindered vegetation growth. Overall, the results highlight the importance of accurately predicting the impact of different EASM intensities of regional carbon fluxes.

Meteoric diagenesis influenced by East Asian Summer Monsoon: A case study from the Pleistocene carbonate succession, Xisha Islands, South China Sea

The East Asian Monsoon (EAM) has significantly influenced various depositional and diagenetic processes in carbonate sediments in much of East and South Asia during the Cenozoic. The relationship between the EAM and marine carbonate platforms, which are widely developed in this region, however, remains largely unknown. Based on petrographic, mineralogical, and geochemical analyses of the carbonate succession (∼237 m thick) on the Xisha Islands, South China Sea, meteoric diagenesis and its relationship with the East Asian Summer Monsoon (EASM) during the Pleistocene were studied. Various petrographic features, stable isotopes (δ13C, δ18O), and trace elements (Sr, Fe, Mn, Rare Earth Elements and Y) indicate that this succession was extensively altered by meteoric diagenesis, producing four exposed surfaces embedded in the shallow coral reef sediments. Given this data, we suggest that the meteoric diagenesis that affected this succession occurred during periods of low sea-level, and was potentially related to the relative intensity of the EASM. During strong EASM periods, particularly during the Mid-Pleistocene Transition ∼0.9 Ma, meteoric diagenesis was intense, as suggested by the complete alteration of unstable minerals, extreme dissolution, the presence of reddish-brown iron oxides, and a large negative excursion of δ13C (−6.2‰). The influence of the EASM on meteoric diagenesis of Pleistocene carbonate platforms can be identified throughout the South China Sea. This study sheds light on the relationship between meteoric diagenesis and paleo-climate conditions in carbonate platform regions that are influenced by monsoons.

Geochemical evidence of provenance diversity in Holocene sandy land of Qinghai Lake Basin in the north‐eastern margin of Qinghai–Tibet Plateau and its implications for climate change

ABSTRACTThe Qinghai Lake Basin, located in the north‐eastern Tibetan Plateau, is crucial for understanding the East Asian monsoon evolution and its interaction with westerlies. Palaeoclimatic studies in this region since the Holocene have primarily focused on interpreting proxy significance from sediments, resulting in being highly controversial. However, exploring palaeoclimate evolution through sediment provenance and proxy integration remains rare. This study analysed the elemental geochemical properties of two fluvial–lacustrine–aeolian profiles in Hudong Sandy Land, east of the Qinghai Lake Basin, and compared these with published modern basin sediments and extensively investigated Late Quaternary aeolian deposits. It was found that Hudong Sandy Land sediments exhibit similar geochemical compositions to other modern basin sediments, primarily consisting of SiO2, Al2O3 and CaO. Contrary to previous understanding, lacustrine sediments in the Hudong Sandy Land are closer to the upper continental crust average than aeolian deposits. Geochemical ratios and parameters suggested that Hudong Sandy Land sediments primarily derived from mixed source rocks of felsic igneous, quartzose sedimentary and intermediate igneous provenances. A comparison with published elemental geochemical data from the basin reveals distinct sediment sources during different periods in the Hudong Sandy Land. From 9.6 to 4.0 ka bp, Hudong Sandy Land hosted numerous lake environments, with sediments displaying a dominant role in sedimentary recycling and reworking, implying a continuously stronger East Asian summer monsoon. During 8.2 to 5.1 ka bp, the Hudong Sandy Land was a fluvial depositional sink for sediments from the Dabanshan Mountains. Bedrock clastic material generated by intense erosion and monsoonal runoff transport contributed to Hudong Sandy Land sedimentation, indicating the East Asian summer monsoon's peak since 9.6 ka bp. After 4.0 ka bp, thick aeolian sands accumulated in the Hudong Sandy Land, primarily derived from Lake Qinghai sediments due to declining water levels, indicating that westerlies and East Asian winter monsoon dominated the basin, with a weaker East Asia summer monsoon. This study facilitates a deeper understanding of the interaction between the East Asia summer monsoon and East Asia winter monsoon/westerlies.

Freshwater input variability in a west coastal area of Korea and its links to the global monsoon and ITCZ shifts during the period 8500–7800 cal yr BP

In East Asia, freshwater inputs in coastal areas are mainly controlled by rainfall occurring during the East Asian summer monsoon (EASM), which is linked to seasonal latitudinal shifts in the intertropical convergence zone (ITCZ). To investigate the centennial-time-scale relationship between those inputs and the seasonal shifts in the ITCZ, we examined the behaviors of terrestrial input proxies in coastal sediments of western Korea, including grain size, elemental ratios from XRF core scanning (e.g., Zr/Ti and Si/Al), and C/N ratios. Correlation tests linked these proxies to past freshwater input variability, suggesting that elemental ratios can serve as a proxy for past EASM changes. During the period 8500–7800 cal yr BP, the stronger EASMs described by high-resolution peaks of Zr/Ti ratios corresponded to periods of intensified Indian summer monsoons (ISMs) and weakened South American summer monsoon (SASMs), supporting the existence of synchronous global monsoon (GM) events induced by a northward ITCZ shift. This study also shows that the 8.2-ka cooling event recorded in Greenland ice cores synchronously influenced the GM through a southward shift in the ITCZ, resulting in a weakened EASM and ISM in the Northern Hemisphere and an intensified SASM in the Southern Hemisphere. Our study thus demonstrates that the elemental ratios in coastal sediments measured using an XRF core scanner can be utilized to trace high-resolution (at least centennial-time-scale) variability in the EASM in terms of GM-ITCZ coupling.

A Case Study on the Impact of East Asian Summer Monsoon on Surface O3 in China

The East Asian summer monsoon (EASM) was extremely strong in 2018, which substantially affected surface ozone (O3) in China. Taking 2018 and the average synthesis of 2003 and 2010 to represent the strong and weak EASM cases, respectively, GEOS-Chem with constant anthropogenic emission was employed to investigate the impact of the EASM on surface O3 in the east of China. Simulations show that surface O3 decreased in the northeast and the eastern coast of China and increased in most of the remaining regions during strong EASM. The difference in surface O3 between strong and weak EASM was around −15~7 ppbv. After analyzing relevant meteorological fields, it is found that the decrease in northeast China was mainly attributed to the large increase in vertical upward transport. The considerable decrease in the Huang-Huai-Hai region depended on the dilution and diffusion of eastward anomalous horizontal circulation. The increase in Hunan-Hubei-Guangdong Province was largely due to input from the north. In addition, the vast areas between the Yangtze River and the Yellow River were supported by higher temperatures and stronger shortwave solar radiation that promoted photochemical reactions. The reasons for changes in Shanxi-Sichuan-Yunnan Province were relatively more complex and thus require more in-depth exploration.

Chemical weathering evidence for East Asian Summer Monsoon rainfall variability in the upper reaches of the Yellow River since the Early Pleistocene

The East Asian Summer Monsoon (EASM) is critically important for determining the spatial variability of precipitation in the continental interior of East Asia. Hence, knowledge of past EASM variability may help predict the response of monsoon rainfall to ongoing global climate change, with important implications for the living environment of the large human population of East Asia. In this study, we obtained several geochemical records from the Hetao Basin in the upper reaches of the Yellow River (UYR), which we use to reconstruct variations in chemical weathering intensity since 1.68 Ma. Our results suggest that chemical weathering was significantly intensified during the interval of ∼0.47–0.18 Ma, evidenced by lower Rb/Sr and αAlSr values, and higher LEF Mg/Al values, within the lacustrine sediments during this period. This enhanced chemical weathering was closely linked to increased monsoon rainfall associated with a strong EASM. The long-term trends of EASM rainfall in the UYR were caused by variations in the atmospheric circulation over the Pacific Ocean, such as the ENSO cycle and the PDO phase transition, which may act as testable factors in the prediction of future EASM rainfall.

Evolution of the Yangtze River and its biodiversity

Documenting the origins of megadiverse (sub)tropical aquatic ecosystems is an important goal for studies of evolution and ecology. Nonetheless, the geological and ecological establishment of the modern Yangtze River remains poorly understood. Here, we reconstruct the geographic and ecological history of an endemic clade of East Asian fishes based on the mitochondrial phylogenomics analysis of Cyprinidae using 15 fossil calibrations. We estimate an ancestral condition of benthic spawning with demersal or adhesive eggs in southern East Asia before ∼23 Ma and a derived condition of riverine spawning with semibuoyant eggs in the Yangtze by ∼18 Ma. These results imply the formation of Yangtze riverine ecosystems around the Oligocene-Miocene boundary in response to plateau uplift and monsoon strengthening. Some of these cyprinids reverted to benthic spawning with adhesive eggs by ∼15 Ma, a time of rising to peak net diversification rates,indicating the formation of potamo-lacustrine ecosystems by the mid-Miocene during a strong East Asian summer monsoon. Our study provides increased spatiotemporal resolution for the co-evolutionary histories of the Yangtze River and its biodiversity and highlights biological evidence concerning the geomorphological dynamics of the Yangtze River.

Classification and Causes of East Asian Marine Heatwaves during Boreal Summer

Abstract Marine heatwaves (MHWs) are among the most severe climatic events under global warming conditions; they damage marine ecosystems and result in socioeconomic losses. In East Asia, the sea surface temperature (SST) has increased significantly and is projected to increase further. Considering such increases in SST over East Asia, studies on MHWs are needed to minimize the damage caused. In this study, we classified the spatiotemporal characteristics of East Asian MHWs during boreal summer with a self-organizing map for 39 years (1982–2020) and determined their unexplored possible mechanisms. Four dominant modes of MHWs across East Asia were identified: the 1) Subtropical Gyre, 2) East China Sea, 3) East Sea/Japan Sea, and 4) Yellow Sea modes. The total annual number of MHW days has increased by about 1.23 days yr−1. The significant trend is mainly determined by the Subtropical Gyre mode, whereas other modes do not exhibit significant trends. We found that the East China Sea mode could be attributed to a strong East Asian summer monsoon via ocean stratification by the low-salinity water from the Yangtze (Changjiang) River. The East Sea/Japan Sea and Yellow Sea modes could be linked to remote forcings over the subtropics, leading to persistent anticyclonic circulation over East Asia. The anomalous anticyclone contributed to the MHW occurrences by enhancing downward shortwave radiation and reducing entrainment cooling caused by Ekman downwelling. These findings have important implications for distinguishing the characteristics of East Asian MHWs and reveal the possibility of predicting them by identifying their precursors. Significance Statement This study aimed to better understand East Asian marine heatwaves (MHWs) and their causes. We utilized a self-organizing map to classify four patterns of MHWs during boreal summer across East Asia—the Subtropical Gyre, East China Sea, East Sea/Japan Sea, and Yellow Sea modes. We found that enhanced shortwave radiation and latent heat flux play an important role in modulating MHWs in East Asia. A reduced vertical-mixing-amplified ocean warming, and the ocean dynamics drove different temporal evolutions of the MHWs among the four modes. We also identified the potential precursors, which would help in improving the future prediction of MHWs in East Asia.

Palynological data confirm the occurrence of forest on the Loess Plateau of central China during the Middle Quaternary (MIS13)

The Loess paleosol sequence S5SS1 (top layer of S5 paleosol layers; marine isotope stage (MIS) 13) has been extensively studied because it is the most developed paleosol layer among all Quaternary soils in the China loess and represents the greatest humidity since the past 2.5 Ma. The question of whether forests occurred on the Loess Plateau tablelands when these paleosols were deposited is still a controversial scientific issue. This research provides a quantitative reconstruction of the past climate and forest cover between 544 and 480 ka based on a high-resolution pollen record together with magnetic susceptibility (χfd) and L*a*b* color parameters. Results suggest that the Luochuan area (central Loess Plateau) was sparsely covered by temperate deciduous forest under warm and humid conditions with a strong East Asian summer monsoon. The precipitation and woody cover during 544 and 531 ka were similar to those today and much greater than modern from 531 to 480 ka. Our findings are supported by paleosol profile research and modern vegetation studies. This study confirms that MIS 13 was a warm and humid period and that sparse forest developed on the tablelands of the central Loess Plateau, which provides new thinking on the ecosystem restoration program of the Loess Plateau.

Hydroclimate seasonality from paired coral Sr/Ca and δ18O records of Kikai Island, Southern Japan: Evidence of East Asian monsoon during mid-to late Holocene

The East Asian Monsoon (EAM) modulates the seasonal variability of sea surface temperature (SST), sea surface salinity (SSS), and rainfall in the region. However, seasonal-scale reconstructions showing the hydroclimate response to monsoon intensity shifts in Holocene are limited. We used paired coral Sr/Ca and oxygen isotope (δ18Ocoral) records from modern (1989–2015), 5.7 ka, 4.9 ka, and 3.2 ka corals from Kikai Island, Southern Japan to reconstruct past seasonal variability of hydroclimatic variables. The monthly δ18Ocoral-SSS relationship revealed a statistically significant positive linear correlation (r = 0.63; p < 0.000; n = 310) while the δ18Osw and rainfall showed a statistically significant negative linear correlation (r = 0.55; p < 0.000; n = 93).The large SST and SSS seasonality in 5.7 ka (ΔSSTmax-min = 9.5 °C; Δδ18Omax-min = 1.86‰) and 4.9 ka (ΔSSTmax-min = 10.2 °C; Δδ18Omax-min = 1.45‰) indicate an enhanced seasonal ocean warming which amplified the Western Pacific Subtropical High (WPSH) and the southwesterlies. In contrast, the small SST amplitude in 3.2 ka (ΔSSTmax-min = 7.8 °C; Δδ18Omax-min = 0.98‰) indicates a weakened WPSH and southwesterlies which led to reduced summer rainfall and positive SSS signal. The lower salinity records due to higher rainfall in 7.0 ka, 6.1 ka, 5.7 ka, and 4.9 ka coincide with the strong East Asian summer monsoon (EASM) from 8.2 to 4.7 ka in stacked sediment records. The δ18Ocoral record shows positive SSS driven by weakened summer monsoon rainfall in 4.4 ka, 4.2 ka, 3.8 ka, 3.4 ka, and 3.2 ka.The higher winter SSS (positive δ18Ocoral) and lower winter SST derived from 5.7 ka coral in Kikai Island agree with the strong East Asian winter monsoon (EAWM) intensity from 8.2 to 5.6 ka based on the stacked sediment record. The weak EAWM phase from 5.6 ka to 4.5 ka is consistent with the winter records of warm SST and lower SSS in 4.9 ka. The lower winter SSS and warmer winter SST in 3.2 ka support the evidence of a weak phase around 3.0 ka. The extratropical systems such as the intensified or weakened Siberian High and Aleutian Low have affected the northeasterly EAWM and consequently influenced the variability of winter SST and SSS in subtropical southern Japan in mid- and late Holocene.

Climatic shifts, geomorphic change, ancient routes of migration and adaption in southwestern China: Site formation processes at Luojiaba, Sichuan Province

AbstractArchaeologists frequently invoke climate change as a driving cause for ancient expansions of human populations, but geomorphic changes can also play an important role in opening or closing routes of migration. In China, archaeological evidence demonstrates that valleys in the Jialing River's watershed were important routes for the movement of Neolithic populations from the catchments of the Yellow River to the Yangtze River. Here, we examine how fluvial geomorphological regime shifts may have also influenced the migration pathways and adaptive strategies of Neolithic people into the Sichuan Basin by using a combination of sedimentological and palynological analysis at Luojiaba, an archaeological site located on one of the eastern tributaries of the Jialing River. The results show that people settled on seasonally stable landforms, including the Zhonghe River floodplain at Luojiaba (5300–4800 cal. B.P.). They carried out fishing and hunting activities on the front edge of the floodplain close to the river channel and built dwelling features on the higher ground at the back edge of the floodplain, which was not affected by seasonal floods. We hypothesize that during the Holocene Climatic Optimum before 5500 cal. B.P., high water levels as well as severe surface erosion caused by a strong East Asian Summer Monsoon (EASM) blocked pathways into the upper reaches of the Jialing River watershed. Only after a series of cold, dry climate events driven by a decrease in EASM intensity ca. 5500–5000 cal. B.P. did water levels recede significantly. This allowed alluvial aggradation to occur, which created floodplains and terraces along the valley that may have opened a new route for the migration into the Sichuan Basin. Our results reveal the human–environment dynamics surrounding Luojiaba in the uplands of southwestern China and highlight the impact of coupled climatic‐geomorphic regime shifts on human settlement and subsistence strategies, across both space and time.

Composite Effects of ENSO and EASM on Summer Ozone Pollution in Two Regions of China

AbstractCombining the 3‐D reanalysis with the surface observational O3 data, this study investigated the composite effects of the El Niño‐Southern Oscillation (ENSO) and East Asian summer monsoon (EASM) on summer O3 pollution in two regions of China, that is, the Beijing‐Tianjin‐Hebei (BTH) and the Yangtze River Delta (YRD). The results show that the El Niño has significantly enhanced the near surface O3 pollution in the BTH, but has little effect on surface O3 in the YRD. On the contrary, the La Niña has mainly reduced the surface O3 pollution in the YRD with little effect in the BTH. When the El Niño and a strong EASM occurred at the same time, the effect on O3 was more significant than that by the El Niño event alone due to the extra intensification of the vertical transport of O3 with about 10–30 μg/m3 from stratosphere and the worsening of the horizontal diffusion conditions (easterly wind anomalies) in the BTH. The La Niña with a weak EASM played a dominant role in the reduction of O3 pollution in the YRD by improving the meteorological conditions (especially in total cloud cover) and horizontal diffusion conditions (westerly wind anomalies). These composite effects were reflected in the trends of summer surface O3 in the BTH and the YRD, and became the crucial contributors to the abnormal changes of summer surface O3 in some years when the ENSO/EASM happened.

Millennial‐ to centennial‐scale anti‐phase relationship between the Westerlies and the East Asian summer monsoon and its cultural response along the Silk Roads after a great earthquake in southern Altay ~ 3500 cal a BP

AbstractIt is strongly debated whether the Westerlies and the East Asian summer monsoon (EASM) are in‐phase, anti‐phase or out‐of‐phase, and how hydroclimatic changes in the above two climate systems affected trans‐Eurasian cultural exchanges during the late Holocene. In this study, we establish a 3500‐a‐long paleoclimatic sequence based on high‐resolution analyses of sedimentological and geochemical data of a well‐dated sediment core from Yileimu Lake in southern Altay. High percentages of the &gt;63‐µm fraction and high values of Zr/Rb and Rb/Sr ratios indicate strong transport of weakly weathered, coarse sediments into the depocenter of the lake caused by enhanced surface runoff and catchment erosion associated with a wet climate, and vice versa. High values of Ca and total inorganic carbon (TIC) contents imply increased precipitation of endogenic carbonates in the lake water under intense evaporation associated with a dry climate, and vice versa. This new record indicates two wet intervals at 3500–2300 and 600–100 cal a bp, interrupted by a severe and prolonged dry interval from 2300 to 1000 cal a bp, and a mild dry interval with occasionally wet conditions from 1000 to 600 cal a bp. These results are broadly consistent with other paleoclimatic records in Westerlies‐dominated Asia and are generally anti‐phase with those in the EASM region. We suggest that a strengthening/weakening and southward/northward migration of the Westerlies during a negative/positive phase of the North Atlantic Oscillation (NAO) transported more/less water vapor into arid Asia. Meanwhile, a decreasing/increasing El Niño‐Southern Oscillation (ENSO) superimposed on a southward/northward shift of the Intertropical Convergence Zone (ITCZ) triggered a weakening/strengthening and southward/northward movement of the West‐Pacific subtropical high (WPSH), resulting in decreasing/increasing EASM intensity. In addition, the wet climate from 3500 to 2300 cal a bp may have contributed to the development of nomadic herding in the eastern Eurasian Steppe and Altay region, and to the opening of the proto‐Silk Roads. Potentially, intense seismic activities in the Altay Mountains ~3500 cal a bp may have also promoted the opening of the proto‐Silk Roads by forcing the herdsmen to move to the inter‐mountainous basins. The strong EASM intensity from 2300 to 1000 cal a bp in eastern China may have contributed to the creation of the ancient Silk Roads by the Han Dynasty.

Summer ozone pollution in China affected by the intensity of Asian monsoon systems

Ozone in the troposphere is harmful to human health and ecosystems. It has become the most severe air pollutant in China. Here, based on global atmospheric chemistry model simulations during 1981–2019 and nation-wide surface observations, the impacts of interannual variations in Asian summer monsoon (ASM), including East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM), on surface O3 concentrations during June-July-August (JJA) in China are investigated. EASM intensity has a significant positive correlation with the surface O3 concentration in south-central China (97.5°–117.5°E, 20°–35°N) with a correlation coefficient of 0.6. Relative to the weak EASM years, O3 concentrations in strong EASM years increased by up to 5 ppb (10 % relative to the average) due to the weakened transboundary transport of O3 resulting from the decrease in prevailing southwesterlies. SASM can be divided into two components. The one near East Asia has a similar relation with O3 in southern China (100°–117.5°E, 22°–32°N) as that of EASM. The other component of SASM is negatively correlated with surface O3 concentration in eastern China (110°–117.5°E, 22°–34°N) and the maximum difference in O3 concentrations exceeded 5 ppb (10 %) between the strong and weak monsoon years, which can be explained by the O3 divergence caused by the anomalous southerlies blowing pollutants away from the northern boundary of eastern China. This study shows that the ASM has an important impact on the O3 concentrations in China, primarily through changing transboundary transport related to the variability of large-scale circulations, which has great implications for air pollution prevention and mitigation in China. Future projections of ASM suggests that the sustainable and medium development scenarios are the perfect pathways that can help to mitigate O3 pollution, while high social vulnerability and radiative forcing scenarios could enhance future O3 pollution in China.

Holocene East Asian Summer Monsoon Variation Recorded by Sensitive Grain Size Component from the Pearl River-Derived Mud in the Northern South China Sea

Abstract To better understand the environmental significance of sediment grain size in continental shelf of the South China Sea (SCS), we carried out a detailed grain size study of sediments from the YJ Core, derived from the mud deposits of the northern SCS. Based on the grain size-standard deviation method, two sensitive grain size components were identified, namely, component 1 (8.2 ~ 9.3 μm) and component 2 (106.8 ~ 120.7 μm), respectively. The results indicate that the sensitive component 1 is likely to derive from fine-grained materials of the Pearl River. These fine-grained materials could be transported by the southwestward coastal current during the wet season, with the domination of the East Asian summer monsoon (EASM). Accordingly, the sensitive component 1 could be sensitive to climate change and has a great potential to reconstruct details of EASM variations. During the period of 7500-6800 cal yr BP, the sensitive component 1 may be controlled by both sea level change and EASM intensity. Besides, the curve of the sensitive component 1 in the YJ Core presents a strong EASM during the interval 6800-3500 cal yr BP and a weak EASM during the period of 3500-2000 cal yr BP, which is synchronous with other paleoclimate records in southern China. In the past 2000 years, the sensitive component 1 may reflect the increasing of human activities. It is essential to carry out more studies with higher resolution in mud areas to clarify a detailed historical evolution of EASM intensity over the whole Holocene.

East Asian summer monsoon enhanced by COVID-19.

Anthropogenic emissions decreased dramatically during the COVID-19 pandemic, but its possible effect on monsoon is unclear. Based on coupled models participating in the COVID Model Intercomparison Project (COVID-MIP), we show modeling evidence that the East Asian summer monsoon (EASM) is enhanced by 2.2% in terms of precipitation and by 5.4% in terms of the southerly wind at lower troposphere, and the amplitude of the forced response reaches about 1/3 of the standard deviation for interannual variability. The enhanced EASM during COVID-19 pandemic is a fast response to reduced aerosols, which is confirmed by the simulated response to the removal of all anthropogenic aerosols. The observational evidence, i.e., the anomalously strong EASM observed in 2020 and 2021, also supports the simulated enhancement of EASM. The essential mechanism for the enhanced EASM in response to COVID-19 is the enhanced zonal thermal contrast between Asian continent and the western North Pacific in the troposphere, due to the reduced aerosol concentration over Asian continent and the associated latent heating feedback. As the enhancement of EASM is a fast response to the reduction in aerosols, the effect of COVID-19 on EASM dampens soon after the rebound of emissions based on the models participating in COVID-MIP.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00382-022-06247-8.

A preliminary attempt on decadal prediction of the East Asian summer monsoon

The East Asian summer monsoon (EASM) is one of the major synoptic systems that affect the summer climate in China. Decadal prediction of the EASM is of great significance, yet few attempts have been made by far. This study represents a preliminary attempt that uses the decadal increment method to predict the decadal variability of the EASM. The 3-year increment of the decadal EASM (DI_EASMI) is firstly predicted by the leading 4 years tropical ocean and the leading 5 years sea ice over Barents Sea. These two leading predictors with quasi-10-year oscillation can explain most variance of the DI_EASMI, especially in recent decades. The predicted DI_EASMI is combined with the observed EASM at 3 years ago to get the final prediction result. The results of cross-validation and independent hindcast show that the decadal increment method can well predict decadal variability of the EASM during the recent century. The real-time prediction results show that the chance for the occurrence of strong decadal EASM would be rare in 2021. The method developed in the present study provides a new approach for decadal prediction of the EASM.

Magnesium isotopic evidence for staged enhancement of the East Asian Summer Monsoon precipitation since the Miocene

Knowledge of the evolution of the East Asian Summer Monsoon (EASM) provides a valuable opportunity to uncover the dynamic interactions of land-ocean-atmosphere system in the late Cenozoic. However, the evolutionary history of EASM remains debatable, mainly due to the difficulty in separating EASM precipitation and temperature signals. In this study, precipitation proxies of Sr/Ca ratio and δ26Mg value in loess secondary calcite (carbonate nodule (NC) and fine carbonate (FC) (grain size < 4 μm)) are further verified, with high precipitation corresponding to high δ26MgFC but low δ26MgNC and Sr/CaNC ratio, and vice versa. Then, these proxies are investigated in well-researched Chinese loess eolian deposits since ∼22.5 Ma. Results suggests that the EASM precipitation was staged enhancement in the mid-Miocene (∼16.5–14.0 Ma) and the Quaternary (∼2.6–0 Ma). The mid-Miocene enhancement can be compared with the strong EASM intensity and the warmest global temperature since the Miocene. Global warming thus is considered as the dominant force for this enhancement via an expansion in the latitudinal extent of the Indo-Pacific Intertropical Convergence Zone (ITCZ). In contrast, the Quaternary enhancement was accompanied by decreases in global temperature. We propose their linkage via the reinforcement of the Pacific Walker Circulation and a northward shift of the subtropical ridge in the western Pacific. Our study provides a new insight into EASM evolution and its dynamic linkage with global climate changes.