East Asian Summer Monsoon Intensity Research Articles

Impact of oceanic gateway and CO2 changes on the East Asian summer monsoon during the mid-pliocene in a coupled general circulation model

The Pliocene epoch from about 5.3 million to about 2.6 million years before present is the most recent period of sustained global warmth similar to the near future projections. The restriction of the Indonesian Passages, the closure of the Panama Seaway and declining atmospheric CO 2 -concentration are suggested to have caused the global climate evolution to the present-day condition. Here, we present the Pliocene sea surface temperature (SST) reconstructions along with sensitivity experimental results from a coupled General Circulation Model. We find that, in terms of SST, simulated model sensitivity to CO 2 is in good agreement with the Pliocene reconstructions in most regions except the North Atlantic and Arctic. This suggests the necessity for improved boundary conditions and a possible underestimation of internal climate feedback at the high-latitudes. The responses of East Asian Summer Monsoon (EASM) to the oceanic gateway and CO 2 are investigated. Influences of declining CO 2 on the EASM are more prominent. An intensification of the intensity of EASM by ∼50% is simulated in response to the declining CO 2 , which is largely attributed to the strengthened land-ocean thermal contrast, while the precipitation decreases by ∼4.8%. In contrast, the restriction of two seaway changes only drives relatively weak changes with respect to wind speed and precipitation. A water vapor budget analysis suggests that the reduced atmospheric moisture content due to decreasing CO 2 significantly contributes to precipitation response.

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.

Climate and ecology changes during the last deglaciation revealed by stalagmite from Shima Cave, central China

We reconstructed high-resolution paleoclimate records with 24 230Th/U dates, 706 sets of stable isotope values (δ18O and δ13C) from a stalagmite from Shima Cave, Hunan Province, central China. The stalagmite grew during the last deglaciation from 19.7 to 13.3 ka, with a 1500-year hiatus during Heinrich Stadial 1. We interpret stalagmite δ18O as the East Asian summer monsoon (EASM) intensity, while δ13C as terrestrial CO2 related with biomass production and local hydrogeochemical processes. Long-term trend and millennial-scale changes in δ18O record are absent in the δ13C record, possibly due to the low biomass production and small vegetation changes in central China across the studied period, which is contrast to an obvious recovery of the biomass in northern China during the Bølling-Allerød period. Besides, high frequency of δ13C record displays quasi periods of 30–50 years, which are consistent with typical periodicities of the Pacific Decadal Oscillation (PDO). Furthermore, comparison of our δ18O record with measures of solar variability shows clear evidence for solar forcing on the EASM on the centennial timescale, which could possibly be mediated by the Atlantic Meridional Overturning Circulation and El Niño/Southern Oscillation/PDO. Therefore, we suggest that monsoonal climate and ecological changes during the last deglaciation could have been modulated by solar activity and sea surface temperature variability in both the Atlantic and the Pacific Ocean.

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 >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.

Holocene Environmental Evolution Response to the Human Activities and East Asian Summer Monsoon Variation in the Liangzhu Ancient City Complex, Eastern China

The Liangzhu Ancient City Complex is located in a low-lying coastal delta area, and its environmental evolution would have had a significant impact on the human-environment interactions. In this study, element geochemistry and grain size of the sediment sequence from a dam section in Ganggongling (GGL) reveal crucial aspects of sedimentary dynamics, environmental evolution, human activities, and East Asian Summer Monsoon(EASM) variation in the Liangzhu area since 5500 a. Starting from the middle-to-late Holocene, the GGL section shows an overall transition from warm humidity to cold-dry, which is consistent with the climate record dimension in southern China. Through comprehensive analysis of the sedimentary environment before and after the dam’s completion, it can be found that the Ganggongling dam has played a positive role in regulating mountain torrents and met the needs of production and domestic water, such as rice planting through water storage. Further applications on the multi-decadal to centennial time scale demonstrate that variations in solar activity may control the EASM intensity mainly in southern China, which is subject to ENSO intensity changes.

East Asian summer monsoon and human activity imprint on δ15Norg records at the northern coast of the South China Sea over the last 7500 years

In this study, we present high-resolution δ 15 N records of organic nitrogen (δ 15 N org ) from the northern inner shelf of the South China Sea (SCS) to reveal nitrogen processes in the coastal environment over the last 7500 years. To remove the bias effect from inorganic nitrogen (IN), mainly terrestrial clay lattice-fixed ammonia, on total/bulk nitrogen (TN) and its nitrogen isotopic composition (δ 15 N bulk ), a chemical method was used to separate organic nitrogen (ON) from TN. The results suggest that the IN accounts for a high proportion (35.79% on average) of TN in the coastal sediments from the northern SCS and has distinctive δ 15 N values that obscure δ 15 N bulk signal and may reflect a climatic control (e.g., precipitation) on lithogenic materials sourced from land. Before 2000 cal yr BP, δ 15 N org has a significant positive correlation with the sea surface temperature (SST) and a negative correlation with the (C/N) org . The variation of δ 15 N org during this period mainly reflect the East Asian summer monsoon (EASM) intensity, as high SST and fluvial discharge leads to higher nitrate utilization and elevated primary productivity from phytoplankton (low (C/N) org ), when the EASM prevails. However, over the past 2000 years, the EASM has been weaker and anthropogenic influences, particularly enhanced agricultural activity in the Pearl River Estuary (PRE), have replaced the EASM as the dominant driving force behind the increasing trend seen in δ 15 N org . The δ 15 N org signature preserved within the coastal sediments of the study area not only reflects the climate-controlled nitrogen processes but also the impacts of human activity. • From 7500 to 2000 cal yr BP, the δ 15 N org records mainly reflect the nitrate utilization, which is regulated by the EASM. • The IN and δ 15 N inorg reflect climatic control (e.g., precipitation) on lithogenic materials sourced from land. • Over the past 2000 years, human activity has replaced the EASM as the dominant driving force of the δ 15 N org tendency.

Strong coupling of the East Asian summer monsoon and hydroclimate footprints during 53–47 ka

A multi-proxy (δ18O, δ13C and trace elements) analysis of an absolutely-dated stalagmite in northern China is conducted to reconstruct the East Asian summer monsoon (EASM) intensity and local hydroclimate conditions during the period of 53.8–47.4 ka (BP, before 1950 CE). Our δ18O and δ13C records, with 24-yr resolution, clearly register the Dansgaard-Oeschger (DO) events 14 and 13. A clear double-peak structure for DO13, as previously detected in the NGRIP ice core, is identified in our δ18O and δ13C records, for the first time. This strong correspondence at the finer time-scale indicates a sensitive and rapid response of the EASM system to the North Atlantic climate changes through air-sea coupling. Our δ18O record shows that the EASM intensity deceased abruptly during latter stage of DO14 (51.1–50.3 ka). This abrupt change is different from other stalagmite δ18O records from central and southern China. On the other hand, both the δ13C and trace element records, representing local hydroclimatic changes, match well with the δ18O record, reflecting an integrated EASM system, on the timescale of the DO cycles. The covariance suggests that the hydrological variation in northern China could be modulated by the movement of the large-scale EASM circulation. Further comparison displays an anti-correlated relationship between the millennial precipitation changes in northern and southeastern China during the period of 51.5–47.4 ka. This anti-correlation is analogous to the “North-South” dipole mode in observed present-day precipitation. Overall, this study advances our understanding of the spatial and temporal evolution of the EASM precipitation on the millennial timescale.

Multicentennial to millennial–scale changes in the East Asian summer monsoon during Greenland interstadial 25

AbstractA multidecadal-resolved stalagmite δ18O record from two nearby caves, Lianhua and Dragon, in Shanxi Province, northern China, characterizes the detailed East Asian summer monsoon (EASM) intensity changes at 114.6–108.3 ka during Marine Oxygen Isotope Stage 5d. Our record shows an intensification of the EASM at 114.6–109.5 ka, followed by a rapid weakening at 109.5–108.4 ka. The millennial-scale strong monsoonal event appears to be correlated with the warm Greenland interstadial 25 (GI 25), whereas the weak monsoonal event is related to the cold Greenland stadial 25 within dating errors. The GI 25 monsoonal event registered in our record is also documented in various published time series from different regions of China. The lines of evidence indicate that this event occurred over the entirety of monsoonal China and was also broadly antiphase, similar to the corresponding event on a millennial time scale in the South American monsoon territory. In our record, one 700 yr weak monsoon event at 110.7+0.6−0.5 to 110.0+0.8−0.4 ka divides the GI 25 into three substages. These multicentennial to millennial–scale monsoon events correspond to two warm periods and an intervening cold interval for the intra-interstadial climate oscillations within GI 25, thus supporting a persistent coupling of the high- and low-latitude climate systems over the last glacial period.

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.

Asian summer monsoon responses to the change of land‒sea thermodynamic contrast in a warming climate: CMIP6 projections

It is of practical significance to use the updated Coupled Model Intercomparison Project Phase 6 (CMIP6) models to study the impact of changes in land‒sea thermodynamic contrast (TC) on the Asian summer monsoon under different scenarios and to compare the similarities and differences of the impact mechanisms between different monsoon regions. In this study, we investigated future changes of the Asian summer monsoon under four Shared Socioeconomic Pathway (SSP) scenarios using 19 CMIP6 models. The intensity of the South Asian summer monsoon (SASM) is projected to decrease by 2.6%, 6.3%, 10.1%, and 11.1%, while the East Asian summer monsoon (EASM) intensity is projected to increase by 4.6%, 7.9%, 7.4%, and 9.8% until the end of the 21st century for SSP126, SSP245, SSP370, and SSP585 scenarios, respectively. Moreover, summer precipitation in Asia is projected to increase remarkably in 2015–2099 under all four scenarios. The inconsistent warming trends over the Tibetan Plateau (TP), Northwest Pacific, and tropical Indian Ocean would greatly impact the monsoon circulations. The upper-troposphere warming trend over the surrounding oceans is remarkably greater than that over the TP, while the near-surface warming trend over the surrounding oceans is smaller than that over the TP. The decrease of upper-troposphere TC between the TP and tropical Indian Ocean results in a weakening of the SASM circulation. The enhancement of the lower-troposphere TC between the TP and Northwest Pacific would strengthen the EASM circulation. Moisture budget analysis shows that the water-vapor would increase in the future, which would thermodynamically enhance summer precipitation through the anomalous vertical moisture transport associated with mean flow. The strengthening of the meridional circulation of the EASM would increase monsoon precipitation, while the weakening of zonal circulation of the SASM would dynamically reduce South Asian summer precipitation.

Rapid Northwestward Extension of the East Asian Summer Monsoon Since the Last Deglaciation: Evidence From the Mollusk Record

The magnitude and rate of the expansion of the East Asian summer monsoon (EASM) rain belt under future climatic warming are unclear. Appropriate ecological proxy data may provide an improved understanding of the spatial extension of the EASM during past warming intervals. We reconstructed the spatiotemporal pattern of the extension of the EASM since the Last Glacial Maximum (LGM), using six well-dated mollusk fossil sequences from Chinese loess sections located on the modern northern edge of the EASM. The abundance of typical dominant mollusk species indicative of EASM intensity shows a delayed response, from ∼17 ka in the southeastern sections to ∼9 ka in the northwestern sections, during the last deglacial warming. Isoline plots based on a mollusk data synthesis show that the mollusk EASM indicators have a northeast–southwest zonal distribution for both the present-day, the cold LGM, and the warm mid-Holocene, which is consistent with the spatial pattern of modern precipitation. The resulting estimated expansion rate of EASM intensity accelerated during ∼12–9 ka (∼50 km/ka), which corresponds to the early Holocene interval of rapid climatic warming, a northwestward shift of ∼150 km compared to today. This implies that the northern fringe of the EASM in northern China will become wetter in the coming century, under moderate warming scenarios.

Index‐ and model‐dependent projections of East Asian summer monsoon in Coupled Model Intercomparison Project Phase 6 simulations

AbstractIn terms of five categories of East Asian summer monsoon (EASM) indices and one classic meridional wind index, we project the EASM intensity change over the 21st century using 27 global climate models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) under the mid‐range combined scenarios of Shared Socioeconomic Pathways and Representative Concentration Pathways (SSP2‐4.5). Results show that future changes in the EASM intensity are index‐ and model‐dependent. Relative to the reference period 1985–2014, the EASM intensity strengthens slightly based on the east–west thermal contrast indices but varies little as a whole based on the southwest monsoon indices over the 21st century, with large discrepancies among the models. However, it tends to weaken over time based on the other three categories of indices, including the north–south thermal contrast indices, the shear vorticity indices, and the South China Sea monsoon indices. In terms of the meridional wind index that directly measures the EASM circulation in the lower troposphere and holds valid under future global warming, the EASM intensity strengthens significantly over the 21st century as a consequence of increases in zonal and meridional land–sea thermal contrasts between the East Asian continent and the adjacent oceans of western North Pacific and South China Sea. There are certain relationships between the trends of the meridional wind index and other EASM indices. The projections are overall consistent between the ensemble means of all available 27 models and the 14 good models as selected according to their abilities to simulate the present EASM climatology, but with different magnitudes.

Biofuels Reserve Controlled Wildfire Regimes Since the Last Deglaciation: A Record From Gonghai Lake, North China

AbstractWildfire activity is an important activity in evolution of vegetation and carbon cycling. Whether wet weather will suppress wildfire or promote them by increasing fuel reserves during the Holocene is not clear. We obtained a record of black carbon from a sediment core spanning the last 14.8 kyr from Gonghai Lake, in North China. There is a close relationship between the timing of wildfire activity and vegetation development driven by the East Asian summer monsoon intensity. On a millennial timescales, wet climatic conditions provide a sufficient biofuels reserve, in the same period wildfire increase; thus, the regional potential biofuels reserve is shown to be an important controlling of regional wildfire activity in the monsoon region of China, under natural conditions. We infer that with the strengthening of Asian summer monsoon caused by global warming, the wildfire carbon emission in Asian monsoon region may increase in the future.

Variation of summer precipitation δ18O on the Chinese Loess Plateau since the last interglacial

ABSTRACTOrbital‐scale East Asian Summer Monsoon (EASM) variations inferred from loess deposits in northern China and speleothems from southern China display different dominant periods, complicating our understanding of monsoon response to insolation and ice‐volume forcings. Here we integrate a new microcodium δ18O record from a high‐resolution last interglacial loess profile with previously published data and provide a composite microcodium δ18O record on the Chinese Loess Plateau (CLP) since the last interglacial. The composite microcodium δ18O record displays distinct precessional cycles, consistent with speleothem δ18O records, but with different amplitude contrast (particularly during the peak interglacials). We propose that both loess and speleothem δ18O records exhibit covariations at precessional timescale oscillations. The discrepancy between loess and speleothem from southern China can be attributed to the influences of other processes besides summer precipitation on the proxies. A slight difference in amplitude between microcodium and speleothem δ18O records implies that the EASM is also influenced by inland surface boundary conditions, which has important impacts on the occurrence of EASM precipitation. Therefore, microcodium δ18O from the Chinese loess–paleosol sequences can be regarded as a representative proxy of EASM precipitation in northern China and then a reliable proxy reflecting the variation of EASM intensity.

Optical Stimulation Luminescence Dating of Deltas Revealed the Early to Mid-Holocene Lake-level Fluctuations of Daihai, Inner Mongolia, Northern China

Lake-level reconstruction of inland enclosed lakes especially for monsoon-sensitive areas is of great significance to reveal regional climate changes. Daihai, a typical enclosed lake at the marginal of the East Asian summer monsoon (EASM) area in north China, is sensitive to climate changes due to its unique regional characteristics. There were a series of lakeshore terraces, highstand lacustrine sediments, and braided river deltas, providing sufficient geomorphologic and stratigraphic evidence for the reconstruction of lake-level fluctuations of Daihai. Reconstructed lake-level variations during the early and mid-Holocene were constructed based on 22 quartz optical stimulated luminescence (OSL) ages from six well-preserved profiles around Daihai Basin. Our results indicated Daihai showed a relatively low level at 10.2 ka, and a gradually increasing lake level following the enhanced monsoon precipitation during the mid-Holocene. Specifically, the high lake level began to develop at 8.1 ka and reached the maximum at 5.2 ka, with ∼40 m higher than present. At this time, the lake area expanded to ∼400 km2, approximately six times as large as that of present, corresponding to the maximum monsoon precipitation and intensity of EASM during the mid-Holocene. However, our stratigraphic records showed a part of the depositional records in the north and east of the Daihai was missed after 5.2 ka, probably indicating a sudden drop of the Daihai lake level. These rapid level fluctuations were likely to be interpreted by some local scenarios and need to be further investigated in the future. Overall, the lake-level fluctuation of Daihai during the early and mid-Holocene was slightly different from that observed in the previously published regional records. Possibly, the interaction of the EASM and regional feedback from topography, and hydrology factors might have contributed to the spatial complexity and distinction.

Impacts of the seesaw mode between the Indian and East Asian summer monsoons on interannual variations in surface solar radiation across the low‐latitude highlands of China

AbstractThe relationship between the seesaw mode that connects the Indian summer monsoon (ISM) and East Asian summer monsoon (EASM), and variations in summer surface solar radiation (SSR) across the low‐latitude highlands of China (CLLH), was investigated using atmospheric reanalysis and NOAA global gridded precipitation and outgoing longwave radiation datasets. Singular value decomposition, correlation analysis, and composite analysis were employed. The results indicate that the interannual variations in summer SSR in the CLLH are significantly modulated by the seesaw mode that connects the ISM with the EASM. During the boreal summer, the CLLH SSR variability is positively correlated with ISM intensity, but negatively correlated with EASM intensity. When a strong ISM and a weak EASM occur together, significant anomalous northeasterly winds appear over the CLLH, which reduces the moisture supply to the region from the Bay of Bengal. In addition, significant anomalous descending motion dominates the CLLH, leading to significant negative relative humidity anomalies over the CLLH. Consequently, water vapour, total liquid water form column clouds and high cloud cover decreased significantly over the CLLH, resulting in a higher CLLH SSR than average. Conversely, a lower‐than‐normal CLLH SSR seems to result from the approximately opposite physical process during the years where the ISM is weak and EASM is strong over the CLLH. Given the fact that the correlation between the aerosol optical depth (AOD) and the CLLH SSR is relatively weak, the AOD variability may not be the main control on interannual variations of summer CLLH SSR.

A Modeling Study of the Tripole Pattern of East China Precipitation Over the Past 425 ka

AbstractThe traditional paleoclimatological view suggests that monsoonal China was overall wetter when the East Asian summer monsoon (EASM) was strong. However, this view is at odds with the understanding of modern climate, which demonstrates an analogous “tripole precipitation pattern” in monsoonal China. Little is known about the spatial pattern of paleo‐precipitation in monsoonal China, particularly during the past glacial‐interglacial cycles. Here, we provide evidence for a potential tripole precipitation pattern in monsoonal China over the past 425 ka using climate modeling, and compare the results with paleoclimate records available from China. Our simulations illustrate that more (less) precipitation in North China and South China, and less (more) precipitation in the Central‐East China during strong (weak) EASM periods associated with high (low) boreal summer insolation. Our results agree with the present understanding of modern East Asian climate, and furthermore confirm that the boreal summer insolation is the dominant forcing for the intensity of EASM and the response of subtropical high pressures is fundamental in modulating the precipitation pattern in monsoonal China on orbital timescales. This temporal and spatial variability of precipitation, as revealed in our simulations, shows the potential high complexities in hydroclimatic conditions in monsoonal China throughout the past glacial‐interglacial cycles. Nevertheless, whether the tripole precipitation pattern in monsoonal China over the past 425 ka is robust enough still should be tested, preferable by taking advantage of existing and new well‐dated and explicit indicative precipitation archives in Central‐East China.

Lake-level variation of Dali Lake in mid-east of inner Mongolia since the Late Holocene

In recent years, the area of Dali Lake has shrunk significantly, resulting in extremely serious ecological and environmental problems. Combining records from lake sediments and ancient shorelines is effective for investigating paleolake evolution and predicating the lake life trend. This study explored the lake area evolution of Dali Lake using remote sensing images and optical stimulated luminescence (OSL) dating. The results suggest the following: 1) on the century time scale, there has been a significant linear relationship between age and elevation from ca. 1.8 cal ka BP to the present (R2 = 0.99) and a potential quadratic polynomial relationship since ca. 4.2 cal ka BP (R2 = 0.99). 2) According to the δ2H and δ18O composition, monthly changes in the lake area, and water balance analysis, the groundwater was the main water source to recharge Dali Lake which originated from an external source, whereby the water may be from the Xar Moron Fault or has been transported by a volcanic conduit. 3) Since ca. 1.3 cal ka BP, the clear differences between lake levels and local precipitation indicated that the changes of the lake level are predominantly determined by groundwater. We conclude that the East Asian summer monsoon intensity and groundwater table variations in this area have jointly controlled the lake level evolution since the late Holocene.