Summer Monsoon Changes Research Articles

Sensitive response of erosion and weathering to the Indian Summer Monsoon changes in South Asia during Dansgaard-Oeschger oscillations

Continental weathering plays a key role in regulating the long-term climate stability via negative feedback. However, whether and how erosion and weathering respond to rapid climate change (e.g millennial scale) in large river basins remains unclear, partly due to the lack of archives with robust age models and high sampling resolution. As one of the largest sediment source-to-sink systems, the Himalaya-Ganga/Brahmaputra River-Bay of Bengal system is considered as an ideal laboratory for examining the weathering-climate relationships over the past. Here we present the elemental and mineralogical data from well age-constrained core sediments in the Bay of Bengal, which document the erosion and weathering conditions in South Asia during the last glacial period. All proxies generally show larger values during glacial interstadials than the stadials, consistent with the millennial variabilities of regional sea surface temperature (SST) and the Indian Summer Monsoon (ISM) strength. We confirm that the erosion and chemical weathering signals in Ganga/Brahmaputra River basins, which sensitively respond to the ISM strength and/or temperature change, could be propagated through the large river systems and faithfully preserved in the South Asian marginal seas, without noticeable time lag on a millennial scale. Our findings provide valuable data for response of erosion and weathering dynamics in a large river basin to rapid climate changes, and highlight the immense potential of monsoon-driven continental silicate weathering in floodplains as a substantial short-term carbon sink, thus underscoring a pivotal natural carbon sequestration mechanism amidst the escalating threat of global warming.

Vertical biome shifts and climate changes since the last glacial maximum in the southeastern margin of the Tibetan plateau, Southwest China

Since the last glacial maximum (LGM), global warming has significantly influenced the intricate dynamics of vegetation on the southeastern margin of the Tibetan Plateau in southwest (SW) China. However, the responses of montane vegetation to glacial-interglacial climate changes have received less attention than those of modern alpine vegetation belts. Here, we present a continuous pollen record from the lake Caohai area of Guizhou Province and a quantitative reconstruction of the region's biome and climate changes over the past 21 ka. Our findings demonstrate that the study area was encompassed by evergreen sclerophyll Quercus forest during the LGM, which subsequently transitioned to deciduous broadleaved forest around 15.8 ka, shortly after the termination of the last glacial period. During the early Holocene, the deciduous forest underwent a transformation and gave way to evergreen broadleaved forest around 10.3 ka. The abundance of evergreen subtropical elements peaked between 9 and 5 ka, coinciding with the Holocene thermal maximum (HTM). This was followed by the return of deciduous taxa after the 4 ka in the late Holocene. However, anthropogenic impacts on local vegetation became apparent only from about 2 ka. The pollen-based biome reconstruction features clear vertical shifts that correspond to the modern vegetation belts at different elevations, with a maximum vertical movement of about 1000 m between the last glacial and the Holocene. Statistical analysis of pollen data reveals that principal components can serve as reliable climate indicators, consistent with climate simulations using the TraCE model. Both proxy and model results demonstrate that forest ecosystems undergo transformation when thermal and moisture conditions exceed bioclimatic thresholds, emphasizing the crucial role of climate boundaries in driving biome succession. Our findings unveil an extended cold and dry period during the LGM, with the lowest precipitation observed during the last glacial termination due to intense North Atlantic cooling and weak overturning circulation. The strong agreement between the transition from sclerophyll to deciduous forests and increasing temperatures suggests that deglacial warming primarily drove vertical biome shifts after the LGM in the southeastern margin of the Tibetan Plateau. Conversely, forest succession during the Holocene, which align with variations in fire intensity, were predominantly triggered by summer monsoon changes. The quantitative reconstructions of both biomes and climates presented in this study provide novel insights into temporal relationships between climate dynamics and ecosystem changes in SW China.

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.

Interhemispheric ice sheet controls the South Asian summer monsoon changes since 12 Ma

Interhemispheric ice sheet controls the South Asian summer monsoon changes since 12 Ma

Spatial-Temporal Seasonal Variability of Extreme Precipitation under Warming Climate in Pakistan

Climate science has confirmed the alteration of the hydrological cycle attributed to global warming. This warming tendency affects the monsoon precipitation in Pakistan with an unprecedented intensity, causing severe flooding. Therefore, it is inevitable to observe the recent spring and summer monsoon changes in extreme precipitation throughout Pakistan. The present study examined 8 precipitation indices in the past 50-year period (1971–2020) (stretched to two data periods; 1971–1998 and 1999–2020) using Mann–Kendall and Sen’s method to investigate the direction and magnitude of the observed trends. Spring and summer wet days significantly increased in the central eastern (Kakul, Kotli, Jhelum) and western (Cherat, Chitral, Peshawar) regions in the 1st data period but significantly decreased in areas including the southern region in the 2nd data period. We further observed the high-intensity precipitation days (R10, R20) in the same seasons. The intensity of summer R20 was much stronger throughout Pakistan in the 1st data period which reduced significantly during the 2nd data period in northern and southern regions. We extended the circle of investigation to very heavy and extreme precipitation (R30 and R50). The intensity of R30 and R50 in summer followed the same pattern as observed for R10 and R20. However, R30 and R50 in pre-monsoon significantly increased in the northern, east-western, and south-eastern regions during the 2nd data period. Summer monsoon and westerly humid regions experienced a decreasing tendency of very heavy and severe precipitation in the 1st data period. Our results concluded that the most significant changes in precipitation extremes occurred with higher intensity and recurring frequency for all indices in spring and summer monsoon during the 2nd data period.

Phytoplankton productivity and community structure changes in the middle Okinawa Trough since the last deglaciation

Marine phytoplankton plays an important role in the ocean biological pump, whereas our understandings of phytoplankton growth in response to global climate and enviromment changes are still debated. Due to the forcing from the strong land-ocean interaction between the East Asia and the Indo-Pacific Warm Pool, the Okinawa Trough is characterized by high phytoplankton productivity and fast sediment accumulation, therefore it provides ideal archives to study marine productivity changes on millennial-to-orbital timescales. In this study, lipid biomarkers of C37 alkenones, dinosterol and brassicasterol, were analyzed in a sediment core M063–05 retrieved from the middle Okinawa Trough to reconstruct phytoplankton productivity and community structure changes over the last 15.8 kyr. We find that temporal variations of these lipid biomarker contents are parallel with precipitation changes in the Changjiang drainage basin during the last deglaciation, with high values during increased precipitation interval (14.5–12.7 ka) and low values during decreased precipitation intervals (15.8–15.0 ka and 12.7–11.5 ka). We propose that precipitation-induced terrestrial nutrient supply controlled phytoplankton growth in the middle Okinawa Trough during the last deglaciation. Lipid biomarker ratios reveal high (low) contributions of diatoms and dinoflagellates to total phytoplankton productivity during increased (decreased) precipitation intervals. The phytoplankton community structure record is also consistent with precipitation-induced terrestrial nutrient forcing during the deglacial stage, with higher nutrient condition favored diatom and dinoflagellate growth. Precipitation in the Changjiang drainage basin was mainly controlled by the East Asian summer monsoon change and the Intertropical Convergence Zone migration, however the deglacial sea level rise also modulated the forcing of precipitation on phytoplankton growth by affecting the delivery distance of terrestrial nutrients to our site. From the last deglaciation to the Holocene, the biomarker content decreased and the contribution of coccolithophorids to total phytoplankton productivity increased at the expense of dinoflagellates and diatoms. The most likely explanation is the regime shift of major nutrient sources supporting phytoplankton growth, from terrestrial riverine nutrients during the deglaciation to the Kuroshio subsurface water nutrients during the Holocene. Our results provide new insight of past phytoplankton responses to climate and environment changes.

Inter‐Model Spread of the Simulated East Asian Summer Monsoon Rainfall and the Associated Atmospheric Circulations From the CMIP6 Models

AbstractThe model uncertainty, one of the major sources of projection uncertainty, is still a challenge in the climate change projection. In this study, the model uncertainty in simulating the East Asian summer monsoon rainfall and its physical link to the upper‐level jet streams and the western North Pacific subtropical high (WNPSH) are investigated from the Coupled Model Inter‐comparison Project Phase 6 (CMIP6) models. The results show that extracted by the inter‐model Empirical Orthogonal Function method, the leading inter‐model mode of the rainfall is characterized as a meridional pattern. The positive mode (a continent‐wet‐ocean‐dry pattern) is closely associated with a northward shift of the oceanic branch of the East Asian subtropical jet and a northward movement of the WNPSH, while the negative mode (a continent‐dry‐ocean‐wet pattern) is highly correlated with an enhanced East Asian polar‐front jet combined with a weakened land branch of the East Asian subtropical jet as well as a weakened and eastward recess of the WNPSH. This systematic link among the atmospheric circulations and the leading inter‐model mode is maintained by the negative phase of the Victoria Mode in the North Pacific and warming over the Atlantic Ocean in the positive mode, and the cooling over the Indian Ocean, Atlantic Ocean and the warming over the central Pacific in the negative mode. Our findings suggest that the physical linkage between the atmospheric circulations and monsoon rainfall is useful to understand the model uncertainty, which would be helpful in providing potential indicators of the East Asia summer monsoon change.

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.

Asian Summer Monsoon Changes Inferred From a Stalagmite δ18O Record in Central China During the Last Glacial Period

The reconstruction of Asian summer monsoon (ASM) changes during the last glacial period is of great significance for better understanding monsoon dynamics. The phase relationship between the Indian summer monsoon (ISM) and East Asian summer monsoon (EASM) subsystems on different timescales is still unclear. The comparative analysis of speleothem records in the ISM region, EASM region, and central China helps to clarify the relationship between the ISM and EASM. Based on the well-dated isotope records of stalagmite DDH-B15 from the Didonghe (DDH) Cave in Hanzhong, Shaanxi, we reconstructed ASM changes during the past 34–13 thousand years before the present (kyr BP). The small average error (61 years) of 18 uranium-series ages enables a precise comparison of the stalagmite δ18O record with other well-dated records from the orbital to the millennial timescales. The δ18O signal of the DDH-B15 stalagmite is controlled by changes of the low latitude northern hemisphere summer insolation (NHSI) on the orbital timescale. It records cold Heinrich Stadial (HS) and Dansgaard–Oeschger (DO) cycles which are originated from the northern high latitude on the millennial time scale. The δ18O changes of stalagmites from the three regions are similar on the millennial and centennial timescales. But on the orbital-suborbital timescale, stalagmite δ18O changes during the last glacial cycle have different characteristics. The stalagmite δ18O values in eastern China became gradually negative, and the stalagmite δ18O values in the Indian monsoon domain showed a increasing trend, but the stalagmite δ18O values in Central China adopted an intermediate state between the EASM and ISM. Then we argued that the δ18O value of stalagmites in Central China is a mixed signal of the ISM and EASM, which indicates a change of the water vapor source as an important influence on the Chinese stalagmite δ18O record.

East Asian summer monsoon changes in subtropical China since late Pleistocene: Evidence from the Ailuropoda-Stegodon fauna

East Asian summer monsoon changes in subtropical China since late Pleistocene: Evidence from the Ailuropoda-Stegodon fauna

Insolation control of millennial-scale Asian summer monsoon changes evidenced by Chinese stalagmites δ18O records

High-resolution stalagmite δ18O records, representing Asian summer monsoon (ASM) intensity, were reconstructed from Wulu and Xiao caves, southwestern China, over Chinese Interstadials (CIS) 25 and 22. A most prominent feature of these stalagmite records is a persistent ASM strengthening throughout the entire event, different from a gradual cooling in corresponding events at Greenland and Antarctica. It implicates that the cooling in the Southern Hemisphere may intensify the ASM circulation through increased cross-equatorial flow, which overwhelms the northern high-latitude impact. Combined with previous published records over the past two interglacial-glacial cycles, diverse trends of CIS events generally match with changes in North Hemisphere summer insolation (NHSI). Accordingly, three modes of CIS ASM variability can be observed, i.e., ASM strengthening when NHSI increases, weakening when NHSI decreases, and a relatively stable ASM during NHSI peak. We argue that NHSI variability or interhemispheric gradient could change the strength of cross-equatorial flow, and in turn, alter the landward transport of monsoonal moisture. The mean isotopic composition of moisture, inherited by stalagmite δ18O signal especially in southern China, is likely a reflection of energy balance between hemispheres.

Geochemical characteristics of Holocene loess-paleosol sequences in central Chinese Loess Plateau and their implications for East Asian monsoon evolution

The geochemical composition and magnetic susceptibility (MS) of three sections (Weinan, Jingchuan and Jingbian) in the central Chinese Loess Plateau, located along a north-south climate gradient, were analyzed at high resolution in order to reconstruct changes in weathering intensity and hence Asian monsoon evolution during the Holocene. The results show distinct differences in element composition between the loess and paleosol layer, as well as spatial differences which reflect changes in mean annual temperature and annual precipitation along the climatic gradient. The measured major element compositions, combined with the results of previous research, indicate that the provenance of the Holocene loess-paleosol sequences in the central Chinese Loess Plateau was constant over time and space. The degree of chemical weathering in the study area is relatively weak and at an intermediate weathering stage. Based on a magnetic susceptibility age model, the East Asian summer monsoon changes recorded by the loess-paleosol sequences show a distinct two-stage pattern of evolution, with a gradual increase during 13.1–8.5 ka and a gradual decrease thereafter. Comparison of the results with climate records from elsewhere indicates that the East Asian monsoon evolution was mainly controlled by changes in Northern Hemisphere summer insolation and ice sheets.

Impact of Indian Summer Monsoon Change on Ancient Indian Civilizations During the Holocene

A large part of South Asia receives rainfall mainly during the Indian Summer Monsoon (ISM) season of the year (Jun–Sep). The socioeconomic conditions of most of the developing countries in this region largely depend on the ISM rains. It also played important roles in rise and collapse of ancient civilizations in this region. However, the influence of the ISM on Indian ancient civilizations has not yet been fully explored though there were some attempts to correlate monsoon variation with their rise and fall. For example, in the mid to late Holocene period, Indus Valley or Harappan Civilization flourished in the western part of India from its early development, through its urbanization and eventual transformation into a rural society. Probably a prolonged decrease in the ISM rainfall caused the decline in the urban phase of the Indus Civilization around the 4.2 kyr BP global climate event. Another well-recorded early Holocene global climate event is the 8.2 kyr BP cooling event which also reportedly influenced ISM significantly, but its impact on human settlement is not clear in this region. The present study is a comprehensive review of the archaeological and climatological researches carried out on the role of ISM variability on the rise and fall of ancient Indian civilizations for the most part of the ongoing interglacial period, the Holocene. The review covers the studies on the period of the last 10 kyr as evidence suggests that human settlement and cultural developments in this region started around the beginning of this period. We have noted that the existing studies are mostly restricted to vague qualitative analysis of the weakening/strengthening of the ISM, and researches related to quantitative estimations of changes of the monsoon strengths and durations of drought events that caused collapse of civilizations are limited. Therefore, in the present analysis, emphasis has also been given on the requirement of estimating the absolute changes that might have caused cultural shifts. Some possible ways to quantitatively estimate the changes of some climate parameters are discussed.

Centennial- to millennial-scale Asian summer monsoon changes during the MIS 5/4 transition revealed by high-resolution stalagmite records from southwestern China

During the Marine Isotope Stage (MIS) 5/4 transition, the global climate changed from an interglacial to a glacial state, and hence it was characterized by high-amplitude climate changes. High-resolution stalagmite records can potentially improve our understanding of climate change during this transition. Here we use a high-precision 230Th-dated, 50-yr-resolution stalagmite δ18O record from Yangkou Cave, in Chongqing, southwestern China, to reveal centennial- to millennial-scale changes in Asian summer monsoon (ASM) intensity during the interval of 98.8–59.3 kyr B.P. (thousands of years before 1950 CE). The record reveals five Chinese Interstadial events, namely CIS 18–22, and pronounced centennial-scale oscillations are evident and verified within these millennial-scale events. There are four centennial-scale events of monsoon strengthening in both CIS 21 and CIS 22, corresponding to Greenland Interstadial events GI 21 and GI 22. By contrast, CIS 18, CIS 19 and CIS 20 differ in both structure and onset time relative to the corresponding GI events during MIS 4. During MIS 5, reduced ice sheet and sea-ice cover and strong Atlantic Meridional Overturning Circulation (AMOC) forced the Intertropical Convergence Zone (ITCZ) towards its northern limit, which enhanced the teleconnection between the ASM and climate change in northern high latitudes. During MIS 5, the millennial-scale events (CIS 21 and 22) show a rapid atmospheric teleconnection between the ASM and the climate of northern high latitudes, but this coupling did not exist during MIS 4. The weakening of Northern Hemisphere summer insolation, the expansion of ice sheets and sea ice, combined with the increased influence of Antarctica, may have led to the decoupling of the Asian summer monsoon and climate change in high northern latitudes.

The Contribution of Internal Variability to Asian Midlatitude Warming

AbstractThe tropospheric warming in the Northern Hemisphere (NH) midlatitudes has been an important factor in regulating weather and climate since the twentieth century. Apart from anthropogenic forcing leading to the midlatitude warming, this study investigates the possible contribution of internal variability to Asian midlatitude warming and its role in East Asian circulation changes in boreal summer, using four reanalysis datasets in the past century and a set of 1800-yr preindustrial control simulations of the Community Earth System Model version 1 large ensemble (CESM-LE). The surface and tropospheric warming in the Asian midlatitudes is associated with a strong upper-level geopotential height rise north of the Tibetan Plateau (TP). Linear trends of 200-hPa geopotential height (Z200) confirm a dipole of an anomalous high north of the TP and an anomalous low over the Iranian Plateau in 1958–2017. The leading internal circulation mode bears a striking resemblance to the Z200 trend in the past 60 and 111 years, indicating that the long-term trend may be partially of internal origin. The Asian midlatitude warming is also found in preindustrial simulations of CESM-LE, further suggesting that internal variability explains at least part of the temperature change in the Asian midlatitudes, which is in a chain of wave trains along the NH midlatitudes. The Asian warming decreases the meridional gradient of geopotential height, resulting in the weakening of westerly winds over the TP and the TP thermal forcing. Thus, it is essential to consider the role of internal variability in shaping East Asian surface temperature and East Asian summer monsoon changes in the past decades.

A Continuum Approach to Understanding Changes in the ENSO–Indian Monsoon Relationship

AbstractIt is well documented that the relationship between the El Niño–Southern Oscillation (ENSO) and the Indian summer monsoon changes on interdecadal time scales, yet an explanation for the variations is still a subject of debate. Here, using a continuum framework based on one-point partial correlation maps, we show that the ENSO–Indian rainfall relationship is influenced by the gradient of sea surface temperature anomalies (SSTA) across the Niño-3 region. Based on this identified SSTA pattern, a simple trans-Niño-3 (TN3) index is created that explains up to 50% of all-India rainfall variability during the mid- to late monsoon season after the 1960s. It is also shown that the influence of the TN3 pattern on the relationship between common ENSO metrics and all-India rainfall is strongest during the August–September (AS) monsoon subseason and weakest during the June–July subseason. The TN3 pattern accounts for up to 80% of the change and sign reversal in the AS Niño-1+2–all-India rainfall relationship in recent decades. The 1940s coincides with the intensification of the TN3 pattern and its influence. As the TN3 index is nearly orthogonal to the Niño-3 index, and both are strongly correlated with all-India rainfall, the strengthening TN3 influence must be systematically associated with the weakening Niño-3–all-India relationship in recent decades. This work supports arguments that recent changes in the ENSO–Indian rainfall relationship are not solely related to noise.

Lacustrine record from the eastern Tibetan Plateau associated with Asian summer monsoon changes over the past ~ 6 ka and its links with solar and ENSO activity

A multi-parameter, absolute-dated lacustrine record from the eastern Tibetan Plateau provides a continuous history of the Asian summer monsoon (ASM) over the past ~ 6000 years. The record broadly follows the trend in northern hemisphere summer insolation. However, it diverges during a period of increased moisture and thermal conditions during the past ~ 1300 years, broadly corresponding to the ASM “2-kyr shift”. This shift as referred by Cheng et al. (Nature 534:640–646, 10.1038/nature18591, 2016) may be related to Atlantic Meridional Overturning Circulation variations, and potentially to increased forcing by greenhouse gases coincident with reduced ENSO activity. The record is punctuated by several weak monsoon intervals. Cross-correlation of the sub-millennial-scale monsoon record with solar activity and ENSO records shows that most of the monsoon variability potentially results from changes in solar irradiation, and has a strong teleconnection with ENSO activity.

Millennial-scale summer monsoon oscillations over the last 260 ka revealed by high-resolution elemental results of the Mangshan loess-palaeosol sequence from the southeastern Chinese Loess Plateau

Loess-based proxies have been widely used to infer glacial-interglacial to millennial-scale changes of the East Asian monsoon. However, the characteristic of millennial-scale variability is still unclear during glacial-interglacial cycles in loess-palaeosol sequence. Here, we present high-resolution (5-cm) elemental results of a 96.7-m thick Mangshan loess-palaeosol sequence on the southeastern Chinese Loess Plateau to emphasize millennial monsoon changes. We explore time series of loess proxies (magnetic susceptibility, CaCO3 content, Ca/K, Fe/K, and Rb/Sr ratios) and speleothem δ18O records and decompose these proxies into intrinsic components using the ensemble empirical mode decomposition method. Synthesized signals of low- and high-frequency components can track the monsoon variability at glacial-interglcial and millennial timescales, respectively. The proportions of millennial components of the loess proxies vary from 9.4%~13.4%, less than that in Chinese speleothem δ18O record (~24.4%). Among five loess proxies, Fe/K ratio is the most sensitive indicator of millennial-scale summer monsoon oscillations, exhibiting abrupt changes similar to that of the Chinese speleothem δ18O record. The amplitude of abrupt monsoon changes recorded in Mangshan is larger during interglacials than glacials, which is in line with Gulang records, implying the lower sensitivity of loess proxies to weak weathering during glacilals and an interglacial amplification of abrupt summer monsoon changes.

Reexamining the Mechanisms of East Asian Summer Monsoon Changes in Response to Non–East Asian Anthropogenic Aerosol Forcing

AbstractThis study examines the mechanisms by which the East Asian summer monsoon (EASM) changes in response to non–East Asian (NEA) anthropogenic aerosol forcing by distinguishing the fast direct atmospheric response and slow ocean-mediated response to forcing using a global aerosol–climate coupled model. The results show that NEA aerosol forcing significantly exacerbates the weakening of the EASM due to local aerosol forcing. The fast response is dominant in the weakening of the EASM and an anomalous precipitation pattern over eastern China resembling the “southern flood and northern drought” pattern in the total response to NEA aerosol forcing. Changes in upper-tropospheric temperature caused by the fast response play a major role in the impact of NEA aerosol forcing on the EASM. Anomalous cooling occurs during summer in the upper troposphere (at ~40°N) over East Asia caused by the fast response. This is due to the combined effects of strong eastward cold advection in the Northern Hemisphere midlatitudes caused by increased aerosol loading in Europe and the resulting change in local meridional heat transport in East Asia. Subsequently, the zonal wind speed changes on either side of the anomalous cooling, and the East Asian subtropical jet shifts equatorward, thereby weakening the EASM. The changes in atmospheric temperature and the local Hadley cell caused by the slow response to NEA aerosol forcing are conducive to strengthening the southwesterly winds over eastern China. Our study suggests the importance of NEA aerosol forcing in driving changes in the EASM on a fast time scale.

Moisture variations in Lacustrine−eolian sequence from the Hunshandake sandy land associated with the East Asian Summer Monsoon changes since the late Pleistocene

Paleoclimate records currently lack sufficient geographic detail to understand the spatiotemporal evolution of East Asian Summer Monsoon (EASM) rain belt since the late Pleistocene. In particular, there is no consensus on whether the EASM rain belt reached its modern northern limit by the early Holocene. Here, we present inferred moisture variations from a multi-parameter, absolute-dated lacustrine−eolian sequence from northern China that date back to the late Pleistocene (∼14 ka BP or thousand years ago). We observed a sharp transition towards wet conditions at the onset of the Holocene Epoch. Maximum wet climate occurred here during ∼11.3–8.5 ka. The climate remained predominantly wet until ∼4.2 ka, then it became progressively drier. We observed alternating organic-rich, fine-grained lake deposits and organic-depleted, coarse-grained eolian sand layers during ∼14−7 ka. These layers correspond to sedimentation associated with the Allerød, Younger Dryas (YD), post YD warming, pre-Boreal oscillation (PBO), early Holocene and 8.2 ka event. We interpreted the orbital scale moisture variation at our study site to the changes in insolation, assigning these abrupt and short-lived changes during the late Pleistocene−Holocene transition to a persistent teleconnection between the North Atlantic and east Asian climate zones.