Asian Summer Monsoon Variability Research Articles

Late Pleistocene island weathering and precipitation in the Western Pacific Warm Pool

Deciphering past climate variability in the Western Pacific Warm Pool (WPWP), the Earth’s largest heat and moisture centre, is vital for understanding the global climate system. Nevertheless, its long-term evolution remains controversial, largely due to ambiguities in existing proxy interpretations and discrepancies between records. Here, we present a weathering and erosion reconstruction from the WPWP spanning the last 140,000 years, based on the mineralogy and geochemistry of a sediment core from offshore of northern New Guinea. The paleo-weathering reconstruction is consistent with the simulated precipitation evolution on nearby islands, thereby suggesting a close coupling between climate variability and island weathering in a tropical setting. In addition, our combined data-model interpretation of WPWP climate history shows many similarities to the East Asian Summer Monsoon (EASM) variability over orbital timescales. Overall, our study highlights the critical role of precession-paced interhemispheric energy redistribution, via the West Pacific meridional sea-surface pressure gradient, in linking orbital-scale WPWP climate and EASM variability.

ENSO weakens the co-variability between the spring persistent rains and Asian summer monsoon: Evidences from tree-ring data in southeastern China

The Spring Persistent Rains (SPR) and the Asian Summer Monsoon (ASM) are the two dominant rainfall systems in East Asia, providing together a majority of annual rainfall in southeastern China (SEC). Since observational data in SEC were mostly unavailable until the 1950s, proxy records that are capable of capturing the SPR and ASM variations are required to examine the long-term co-variability patterns between them. Tree-ring earlywood and latewood δ18O records in SEC were found to respond to relative humidity (RH) during the SPR and ASM seasons, respectively, allowing us, for the first time, to reconstruct the RH changes of SPR and ASM back to 1801. The two reconstructions can explain 44.9 % and 42.3 % of the instrumental variance. We observed a long-lasting wet epoch in the 1920s–60s for both the SPR and ASM, caused by a peak in the land–ocean thermal contrast. The El Niño-Southern Oscillation (ENSO) and the Intertropical Convergence Zone (ITCZ) were found to be the two leading tropical systems that modulated the SPR and ASM co-variability. During a period with weakened ENSO variance, the RH of SPR and ASM showed in-phase changes driven by the ITCZ. However, when the ENSO variance became strengthened, the co-variability collapsed since the ENSO can offset the influence of the ITCZ via teleconnections.

PDO and AMO Modulation of the ENSO–Asian Summer Monsoon Teleconnection During the Last Millennium

AbstractObservations show that the teleconnection between the El Niño‐Southern Oscillation (ENSO) and the Asian summer monsoon (ASM) is non‐stationary. However, the underlying mechanisms are poorly understood due to inadequate availability of reliable, long‐term observations. This study uses two state‐of‐the‐art data assimilation‐based reconstructions of last millennium climate to examine changes in the ENSO–ASM teleconnection; we investigate how modes of (multi‐)decadal climate variability (namely, the Pacific Decadal Oscillation, PDO, and the Atlantic Multidecadal Oscillation, AMO) modulate the ENSO–ASM relationship. Our analyses reveal that the PDO exerts a more pronounced impact on ASM variability than the AMO. By comparing different linear regression models, we find that including the PDO in addition to ENSO cycles can improve prediction of the ASM, especially for the Indian summer monsoon. In particular, dry (wet) anomalies caused by El Niño (La Niña) over India become enhanced during the positive (negative) PDO phases due to a compounding effect. However, composite differences in the ENSO–ASM relationship between positive and negative phases of the PDO and AMO are not statistically significant. A significant influence of the PDO/AMO on the ENSO–ASM relationship occurred only over a limited period within the last millennium. By leveraging the long‐term paleoclimate reconstructions, we document and interrogate the non‐stationary nature of the PDO and AMO in modulating the ENSO–ASM relationship.

Precisely constrained 134-ka strong monsoon event in the penultimate deglaciation by an annually laminated speleothem from the Asian monsoon domain

AbstractThe penultimate deglaciation was characterized by a sub-millennial-scale warm event in the Heinrich Stadial 11(HS11), termed the 134-ka event. However, its precise timing and structure remain poorly constrained due to the lack of high-resolution and precisely dated records. We present an oxygen isotope record of a speleothem with well-developed annual lamina from Zhangjia Cave, located on the north margin of the Sichuan Basin, characterizing Asian summer monsoon (ASM) changes in the 134-ka event, which included an increase excursion of ca. 149 years and decrease excursion of ca. 200 years, inferred from 3.3‰ δ18O variations. This event also divided the weak ASM interval-II (WMI-II), corresponding to HS11, into two stages, the WMI-IIa 132.8–134.1 ka and WMI-IIb 134.4–136.4 ka. With a comparable climatic pattern globally, the 134-ka event is essentially similar to the millennial-scale events in last glacial–deglacial period. Particularly, the observed weak-strong-weak ASM sequence (138.8–132.8 ka) is largely controlled by changes in the Atlantic Meridional Overturning Circulation (AMOC) forced by the meltwater of northern high-latitude ice sheets. Moreover, our results underpin that AMOC, rather than the global ice volume, is more critical to ASM variations during the last two deglaciations.

East Asian summer monsoon variations across the Miocene−Pliocene boundary recorded by sediments from the Guide Basin, northeastern Tibetan Plateau

Records of atmospheric carbon dioxide concentration, sea-surface temperature, and global vegetation show that Earth’s climate and environment changed significantly during the late Miocene−early Pliocene. Understanding the environmental response to insolation forcing during this transitional period may provide insights into future environmental variations resulting from the perturbation of the global carbon cycle caused by fossil fuel combustion. However, terrestrial paleoclimate records capable of resolving orbital time-scale environmental variations are mostly from Europe, especially from the region around the Mediterranean Sea. Here, we present high-resolution records of grain size, black carbon, and geochemistry from a sedimentary sequence from the northeastern margin of the Tibetan Plateau, where precipitation is mainly via the East Asian summer monsoon. We observed increases in sediment accumulation rate and black carbon mass accumulation rate at ca. 5.3 Ma, which we interpret as the result of intensified seasonal precipitation associated with the strengthening of the East Asian summer monsoon; concurrently, precessional and obliquity cycles became more prominent during the early Pliocene. Our results suggest that, in response to current and future high atmospheric carbon dioxide concentrations, changes in the East Asian summer monsoon are likely to result in increased precipitation and seasonality within its region of influence.

Magnetoclimatological Record of Late Pleistocene Loess in the Southern Hunshandake Sandy Land, Inner Mongolia: A Threshold Response to the East Asian Summer Monsoon Variations

AbstractWe report the first complete loess–paleosol record spanning the last 130 kyr from the southern extremity of the Hunshandake Sandy Land (HSL) in central‐eastern Mongolia. Our combined mineral magnetic and geochemical results demonstrate that during the last interglacial, the front of the East Asian summer monsoon (EASM) extended to central‐eastern Inner Mongolia, consistent with modern observations of climate change. However, during the last glacial, typical magnetic parameters (e.g., magnetic susceptibility and anhysteretic remanent magnetization and their ratios), which have been successfully adopted to denote the EASM variations on the Chinese Loess Plateau (CLP), show only muted temporal variations and cannot be readily correlated with equivalent records from the main body of the CLP. Remarkably, the Zr/Rb ratio, a robust geochemical indictor of the winter monsoon, is positively correlated with saturation isothermal remanent magnetization and saturation magnetization during the last glacial, demonstrating the strong control of wind vigor on high‐field magnetization signals dominated by lithogenic ferrimagnetic minerals. In contrast to the variable response of magnetic parameters to regional paleoclimatic fluctuations, the Rb/Sr and Ba/Sr ratios (two summer monsoon indicators) faithfully track weak chemical weathering processes and fine‐scale monsoon oscillations, especially during the last glacial. Additionally, we found that higher proportions of pedogenic high‐coercivity magnetic minerals were formed during the last interglacial, which may reflect relatively low rainfall but higher evapotranspiration in the southern extremity of the HSL compared with the CLP. We therefore attribute this complex magnetic record to a threshold response to the EASM variations in eastern Inner Mongolia.

The spatio-temporal pattern of Asian summer monsoon during glacial Termination II recorded by Chinese stalagmite δ18O

The difficulty in constraining the large-scale Asian summer monsoon (ASM) variability in the Chinese monsoon region (CMR) during glacial Termination II lies in our limited knowledge of the western part, primarily due to sparse paleoclimate records. To get a better picture of the ASM during Termination II, we examined a precisely dated stalagmite δ18O record between 133.1 and 127.0 kyr B.P. from Wanxiang Cave located at the ASM's northern edge in western China. In combination with published δ18O data from this cave, we have identified the ‘Weak Monsoon Interval’ (WMI) in the Wanxiang δ18O record and confirmed that the Heinrich 11 cold event in the North Atlantic caused the weakened ASM over the CMR via reorganization of the large-scale ocean-atmospheric circulation. However, the post-WMI change in δ18O is gradual, in contrast with the abrupt shift shown in the other cave records from southern and northeastern China. The rapid northward migration of the westerly jet relative to the Qinghai-Tibet Plateau is probably responsible for this discrepancy. This northward-positioned westerly jet prevented the more 18O-depleted moisture from the Indian Ocean from reaching the study site. Simultaneously, it facilitated the earlier northward movement of the East Asian summer monsoon (EASM) rainband that carries positive precipitation δ18O to obscure the abrupt decrease in our δ18O record. After the onset of the last interglacial, no obvious Younger Dryas (YD)-like event was recorded in Wanxiang Cave. This result is consistent with most stalagmite δ18O records in the CMR and further suggests a minimal impact of the YD-like event on ASM variabilities. The relatively large amplitude of δ18O variations observed in Wanxiang Cave between the late penultimate glacial and the last interglacial corresponds to a dominant control of the Indian summer monsoon (ISM), whereas smaller δ18O amplitudes were recorded in cave sites mainly under the influence of both ISM and EASM. Therefore, we posit that the heterogeneity of the hydroclimate in the CMR during Termination II resulted from a combination of multiple processes, that is, the westerly jet, ISM and EASM, rather than a single one.

Influence of a Rapidly Uplifting Orogen on the Preservation of Climate Oscillations

AbstractClimate oscillations preserved in sedimentary archives tend to decrease in resolution further back in Earth's history. High‐frequency climate cycles (e.g., ∼20‐Kyr precession cycles) are especially prone to poor preservation due to sediment reworking. Recent studies have shown, however, that given sufficient basin accommodation space and sedimentation rate, shallow‐marine paleoclimate archives record precession‐driven hydroclimate change in mid‐low latitude regions. Our study evaluates how the evolution of a rapidly uplifting orogen influences the recording of astronomical climate forcing in shallow‐marine sedimentary strata in the Taiwan Western Foreland Basin (WFB). Time‐series analysis of gamma‐ray records through the late Miocene–Pliocene Kueichulin Formation shows that during early stages of Taiwan orogenesis (before 5.4 Ma), preservation of precession‐driven East Asian Summer Monsoon variability is low despite increasing monsoon intensities between 8 and 3 Ma. The Taiwan Strait had not formed, and the southeast margin of Eurasia was open to the Pacific Ocean. Consequently, depositional environments in the WFB were susceptible to reworking by large waves, resulting in the obscuration of higher‐frequency precession cycles. From 5.4 to 4.92 Ma, during early stages of emergence of Taiwan, basin subsidence increased while sedimentation rates remained low, resulting in poor preservation of orbital oscillations. After 4.92 Ma and up to 3.15 Ma, Taiwan became a major sediment source to the WFB, and sheltered the WFB from erosive waves with the development of Taiwan Strait. The elevated sediment influx, increased basin accommodation as the WFB developed, and formation of a semi‐sheltered strait, resulted in enhanced preservation of precession‐driven East Asian Summer Monsoon variability.

Synthesis of stalagmite climatic records in southern China during the last glacial-interglacial cycle

In this study, a 140 kyr stack (MT2022) of 95 stalagmite δ18O records from Southern China was synthesized using the error weighted mean method and the linear weighted mean method. This stack record was derived from approximately 1100 U/Th dating and 40000 δ18O data points. On orbital scale, MT2022 agrees with the variation of the summer (21 July) insolation at 65°N and restores as much detail as possible of the actual variability of Asian Summer Monsoon (ASM) from stalagmite records. The age model of MT2022 was established according to the dating results of each sample record, and the start and end periods of each weak monsoon event were constrained by at least five stalagmite sample records, with average errors of less than 0.2 kyr. By comparison, we find that MT2022 was generally consistent with the Speleothem Interstadial Onset Compilation data set (SIOC19) and had more sample records from the ASM domain, which is more suitable to represent the ASM evolution. Furthermore, comparing MT2022 to three Greenland ice core timescales, we discovered that MT2022 was quite consistent with NGRIP (GICC05) over the last 60 kyr and differed from GRIP (ss09sea) and GISP2 (Meese-Sowers). The main discrepancy between MT2022 and GRIP occurs around Dansgaard-Oeschger (DO) events 14 and 20–23, whereas MT2022 and GISP2 start to deviate prominently beyond 40 kyr BP. The high degree of consistency between GICC05 and MT2022 allows their accuracy to be validated against each other, thus, MT2022 may provide a new chronological reference for climatic events in the last glacial-interglacial cycle as well as an age calibration standard for other palaeoclimate archives.

Current status and progress in the seasonal prediction of the Asian summer monsoon

The Asian summer monsoon (ASM) has a considerable impact on human lives in the most populated region in the world. Thus, its seasonal prediction is a high-profile application in Earth Science. However, the prediction skill of the regional ASM variability has long been limited due to a formidable difficulty in accurately simulating the complex interactions of the atmosphere-ocean variability and its remote influence on regional climate in numerical models. This study updates the current status and assesses progress in the ASM seasonal prediction performance. This study evaluated the seasonal prediction skill of two generations of models in hindcast data archived by the WCRP Climate-system Historical Forecast Project (CHFP) and Copernicus Climate Change Service (C3S). A special focus was put on the representation of the predominant teleconnections associated with the ENSO and Indian Ocean variability. It was found that the latest seasonal prediction systems (C3S) generally outperform previous-generation systems (CHFP) in terms of the reproducibility of the observed precipitation climatology and the prediction skill of the interannual variability of seasonal precipitation over the ASM region. Furthermore, the results suggested that the improvement of the prediction skill of the ASM likely stems from the improved representation of the monsoon climatology and teleconnections in the models. These analyses highlight the steady progress of the atmosphere-ocean coupled modelling and promise future improvements in the seasonal ASM prediction.

Orbital Effect on North Atlantic Freshwater Forced Millennial‐Scale East Asian Summer Monsoon Variability During the Holocene

AbstractUnderstanding millennial‐scale East Asian summer monsoon (EASM) variability is critical for climate projection in East Asia in the context of slowing Atlantic Meridional Overturning Circulation (AMOC) caused by global warming. This study performs two groups of sensitivity experiments at 8.2 and 4.2 ka BP, both forced by the same North Atlantic freshwater hosing and corresponding orbital parameters using the Community Earth System Model, to explore the orbital effect on millennial‐scale EASM variability. Our simulations reveal that EASM variability differs significantly between these two cold events. During the 8.2 ka BP (4.2 ka BP) (0 BP = 1950 AD) cold event, North Atlantic freshwater forcing weakens the EASM, generating a meridional tripole (dipole) pattern of EASM precipitation anomalies. Furthermore, the same freshwater discharge causes a greater decline in the EASM, contrasting to a slight weaker AMOC slowdown, at 4.2 ka BP than at 8.2 ka BP. This suggests orbital parameters significantly influence the EASM response to North Atlantic cold events. The East Asian subtropical westerly jet, whose meridional position and intensity are controlled by summer insolation on an orbital timescale, plays a key role in this orbital effect. The westerly jet's meridional position determines the spatial pattern of EASM precipitation anomalies, while its intensity affects the amplitude of the EASM's response to freshwater forcing. Because of a larger EASM decline due to freshwater hosing with lower summer insolation, we anticipate a profound declining EASM precipitation in the future with low summer insolation if the AMOC continues to weaken.

Simulated Cycles of East Asian Temperature and Precipitation Over the Past 425 ka

AbstractRecords from a wide range of geological archives covering the last few glacial‐interglacial cycles show large inconsistencies in the East Asian summer monsoon variability, which severely hampers our understanding of the evolution and potential mechanisms of the regional East Asian climate on orbital timescales. Here, we examine the simulated temperature and precipitation in East Asia based on a series of equilibrium simulations conducted for the past 425 ka, and we investigate the sensitivity of temperature and precipitation to potential forcings. Our simulations show that, in East Asia, the seasonal mean temperature is dominated by a ∼20‐kyr cycle, and the annual mean temperature (AMT) is dominated by a ∼100‐kyr cycle, which is consistent with previous modeling efforts and geological reconstructions. Additional sensitivity experiments indicate that the greenhouse gas concentration, in combination with the ice volume, is the dominant force for the variations of AMT in East Asia on orbital timescales. For the precipitation in East Asia, our equilibrium simulations and additional sensitivity experiments, together with comprehensive model‐data intercomparison analysis, suggest that the cycles of simulated annual mean precipitation over East Asia are highly model‐dependent, although the dominant ∼20‐kyr cycle in summer precipitation appears to be a robust feature. Overall, the results highlight the large model uncertainty with regard to the relative roles of forcings in hydroclimate variations in East Asia on orbital time scales. There is, therefore, an urgent need to implement more realistic precipitation schemes in models in order to decrease the model spread in simulated precipitation.

Strong link between Asian summer monsoon and westerlies for the past 4750 years

The hydroclimatic relationship between the Asian summer monsoon (ASM) and westerlies at different time scales remains controversial. Here, we reconstructed the ASM variability between 4750 and 80 years before the present (yr B.P., before 1950 AD) with sub-decadal resolution, based on 29 230Th ages and 954 δ18O data in a stalagmite (HD12) collected from the Dark Cave, northern Guizhou Province, Southwest China. The record reveals a long-term decrease in monsoon intensity, consistent with previous monsoonal Chinese stalagmites and precipitation modeling in Southwest China, as well as with changes in the summer insolation at 30°N, supporting the primary role of orbital solar forcing on monsoon precipitation. The detrended and standardized data revealed millennial-scale quasi-periodic weak monsoon intervals during the periods 4191–3650, 3491–3220, 2537–2135, 1543–1176, and 665–420 yr B.P. The results indicate a general anti-phase relationship with other paleoclimate records of westerlies-dominated Asia and southern Europe, while being broadly in phase with those of the Nordic and Greenlandic regions. We then conclude that the observed Monsoon-Westerlies antiphase hydroclimate pattern on the millennial-centennial time scale over the past 4750 years has been affected by the north-south migration of the mid-latitude westerlies and the Intertropical Convergence Zone (ITCZ), possibly related to North Atlantic variability and Latitudinal Temperature Gradient (LTG) changes in the Northern Hemisphere.

Centennial-Scale Climatic Oscillations during the Dansgaard–Oeschger 14 Revealed by Stalagmite Isotopic Records from Shouyuangong Cave, Southern China

During the last glacial, Dansgaard–Oeschger (DO) events are mostly characterized by moderate and shorter fluctuations. Here, we present the three-year-resolution stalagmite isotopic record from Shouyuangong Cave (SYG), southern China, revealing a detailed history of Asian summer monsoon (ASM) and local environmental changes during the middle and late period of DO 14. During this period, the SYG1 δ18O is characterized by the persistence of centennial-scale oscillations. These centennial δ18O enrichment excursions are clearly mirrored in the δ13C signal. This correlation suggests that changes in soil CO2 production at this site are closely correlated with centennial-scale ASM variability. Furthermore, power spectrum analysis shows that δ18O and δ13C display the common periodicities consistent with solar activity cycles, implicating a control of solar activity on the ASM and soil humidity. Particularly, weak solar activity generally corresponds to weak ASM and a decline in soil CO2 production. One possible link between them is that external forcing controls the ASM intensity via the thermal contrast between the ocean and land. Subsequently, the balance of soil moisture co-varies with the hydrological responses. Finally, the soil CO2 production is further amplified by ecological effect.

Chinese Interstadials 14–17 recorded in a precisely U-Th dated stalagmite from the northern edge of the Asian summer monsoon during the MIS 4/3 boundary

The Marine Isotope Stage (MIS) 4/3 boundary, the so-called unfinished or failed termination, is a time period during which climate shifted from glacial to near-interglacial conditions that is akin to the Termination I. Paleoclimate records on this boundary can provide insights into the mechanisms of abrupt climate change under the circumstances when the global climate system has not reached a full threshold state. However, investigations on this specific climate period are sparse largely due to limited geological records with high temporal resolution. Here, we present a new highly resolved stalagmite record from Wanxiang Cave in western China that provides a detailed evolution of the Asian summer monsoon (ASM) from its northern fringe region. Established with 7 high-precision UTh dates and 647 pairs of isotope data (δ18O and δ13C), this record spans from 59.99 kyr B.P. to 52.94 kyr B.P., and contains the whole MIS 4/3 boundary. Its δ18O reveals three Chinese Interstadials (CISs) on millennial scales, i.e., CISs A.16–17 and 14. Sub-millennial events CIS A.17a and 16a correspond to the Greenland Interstadials 17 and 16 (GISs 16 and 17). The CIS A.17b is related to the ‘precursor events’ (PE 17), while the PEs 14 and 16 events are not evident in our δ18O record, probably due to the gradual change of the CIS A.14b and the lower amplitude of the CIS A.16b. Compared with other climate records, particularly those from the high latitudes, our δ18O record strengthens the notion of the close teleconnection between the ASM and high-latitude climates. Gradual change in δ18O from the CIS A.17b to 17a and the smaller amplitude of the CIS A.16b and 14b are likely coupled to the gradual Antarctic temperature variations, suggesting a dominant role of southern climate process to modulate ASM variability in western China via reorganization of atmospheric circulation. In addition, the westerly jet position relative to the Qinghai-Tibet Plateau may also have suppressed the abrupt 18O-depletion during these periods. At the onset of the MIS 4/3 boundary (at ∼59.82 kyr B.P.), an increase in the Northern Hemisphere summer insolation resulted in rapid ocean-atmospheric reorganizations between the high and low latitudes. This process led to an abrupt increase in precipitation associated with strengthening of ASM circulation, which promoted soil microbial activity and the transition of vegetation type from C4 to C3 as indicated by the δ13C decreasing in the record. After that, centennial-scale variations in δ13C are mainly related to soil humidity change throughout the MIS 4/3 boundary. Our δ18O record further confirms that the MIS 4/3 deglaciation is dominated by a northern-residing forcing, but also involves climate change process from the south. On a regional scale, the δ18O record from Wanxiang Cave may be largely influenced by the Indian summer monsoon, and thus inherits signatures from the south characterized by slightly more negative δ18O than other Chinese stalagmite records on millennial timescales.

Respective and Combined Impacts of North Indian Ocean and Tropical North Atlantic SST Anomalies on the Subseasonal Evolution of Anomalous Western North Pacific Anticyclones

Abstract The subseasonal variation of the anomalous western North Pacific anticyclone (WNPAC) has important implications for East Asian summer monsoon variability. How the WNPAC evolves on the subseasonal time scale under the different configurations of tropical North Atlantic (TNA) Ocean and north Indian Ocean (NIO) SST warming is elucidated in this study. The WNPAC forced by individual TNA SST warming shows an obvious subseasonal variation with a stepwise northward movement. In contrast, the WNPAC forced by individual NIO SST warming shows a weak subseasonal variation, being nearly stabilized at around 20°N from June to August and thereby causing long-lasting and intense positive mei-yu–baiu–changma rainfall anomalies. The physical mechanism for the different subseasonal variation of WNPAC is further investigated. The TNA SST warming generates a WNPAC via a Rossby wave–induced divergence/convergence chain response. In this process, the TNA SST warming-induced suppressed convection over the western Pacific moves northward with the northward movement of climatological intertropical convergence zone and summer monsoon region, which generates a northward shift of the WNPAC. However, the NIO SST warming produces a WNPAC via a Kelvin wave–induced suppressed convection over the western Pacific Ocean. This suppressed convection is stabilized at around 20°N because of the Kelvin wave activity scope being limited within 20°N, which finally produces a nearly stationary WNPAC from June to August. In addition, under the simultaneous occurrence of the TNA and NIO SST warming, the subseasonal variation of WNPAC bears a resemblance to that for the individual NIO SST warming condition, where the TNA SST warming fails to exert its impact.

Decadal modulation of East Asian summer monsoon variations by external forcing and internal variability

Both external forcing and internal climate variability are playing significant roles in driving the East Asian summer monsoon (EASM) changes. However, dynamic linkages between these natural forcings and EASM on decadal timescales remain uncertain, partly due to the limited instrumental climate data. Here, we present a high-resolution EASM record over the past 200 years based on 2315 δ18O measurements from two annually laminated stalagmites (YX92 and YX120) in Yongxing Cave over the middle Yangtze River Valley (mid-YRV). Our records match well with the δ18O records from the nearby Heshang Cave, showing that EASM intensity in the mid-YRV varies at a dominant periodicity of ∼80 years. The multidecadal-scale oscillations in the EASM intensity are closely related to the ENSO-like states, supporting a notion that the ENSO dominantly modulates the EASM variability. Furthermore, the decadal oscillations in EASM and ENSO are synchronous with tropical volcanic eruptions during the solar minima, probably leading to the enhanced El Niño-like response, intensified EASM and strengthened ENSO-EASM coupling. Our findings imply that external forcings potentially contribute to the anomalies in ENSO and EASM during the ongoing global warming.

Comparisons between CMIP5 and CMIP6 models in simulations of the climatology and interannual variability of the east asian summer Monsoon

Comparisons between CMIP5 and CMIP6 models in simulations of the climatology and interannual variability of the east asian summer Monsoon

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.

Role of the Tibetan plateau glaciers in the Asian summer monsoon

The Tibetan plateau (TP) plays an important role in the Asian summer monsoon (ASM) dynamics as a heat source during the pre-monsoon and monsoon seasons. A significant contribution to the pre-monsoon TP heating comes from the sensible heat flux (SHF), which depend on the surface properties. A glaciated surface would have a different SHF compared to a non-glaciated surface. Therefore, the TP glaciers potentially can also impact the hydrological cycle in the Asian continent by impacting the ASM rainfall via its contribution to the total plateau heating. However, there is no assessment of this putative link available. Here, we attempt to qualitatively study the role of TP glaciers on ASM by analyzing the sensitivity of an atmospheric model to the absence of TP glaciers. We find that the absence of the glaciers is most felt in climatologically less snowy regions (which are mostly located at the south-central boundary of the TP during the pre-monsoon season), which leads to positive SHF anomalies. The resulting positive diabatic heating leads to rising air in the eastern TP and sinking air in the western TP. This altered circulation in turn leads to a positive SHF memory in the western TP, which persists until the end of the monsoon season. The impact of SHF anomalies on diabatic heating results in a large-scale subsidence over the ASM domain. The net result is a reduced seasonal ASM rainfall. Given the relentless warming and the vulnerability of glaciers to warming, this is another flag in the ASM variability and change that needs further attention.