Evergreen and deciduous broadleaved mixed forests (EDMF), which exhibit high sensitivity to climate fluctuations, are important transitional vegetation types in subtropical regions and possess the potential for palaeoenvironmental reconstruction. Nevertheless, at present, there is a dearth of relevant research, resulting in uncertainties regarding the internal succession characteristics and external driving patterns of mountain broadleaved forests. In this study, we reconstructed pollen-based biome changes since 5.8 ka with a resolution of 18 years from a mountain wetland in southwestern (SW) China. Based on the comparison between modern pollen and vegetation quadrats, it is inferred that since the mid-Holocene, the study area has been predominantly characterized by EDMF, and there have been significant changes in the internal taxa composition. From 5.8 to 3.4 ka, 2.3 to 1.6 ka, and 0.6 to 0 ka, the vegetation was classified as the deciduous (D)-type EDMF, mainly composed of deciduous taxa such as Quercus (D), Fagus, and Corylus. Conversely, from 3.4 to 2.3 ka and 1.6 to 0.6 ka, the proportion of evergreen taxa like Castanopsis, Cyclobalanopsis, and Ilex was relatively high, leading to a vegetational shift to the evergreen (E)-type EDMF. Through comparison with the TraCE simulations, it is demonstrated that the summer temperature and precipitation may jointly affect the internal transformation between D-type and E-type EDMF. On a larger spatial scale, it is inferred that this transformation may exhibit a teleconnection with ENSO frequency. Specifically, variations in ENSO frequency may exert selective effects on the internal taxa changes of subtropical EDMF.

Global winter temperatures show pronounced interdecadal variability compared to other seasons, yet the main modulators at a global scale remain unclear. We strengthened the signal of interdecadal winter temperature variability by eliminating the high-frequency signal driven by the El Niño-Southern Oscillation (ENSO). Our analysis, using observations and simulations, identifies Sea Surface Temperature (SST) variability in the East China Sea as a key driver of global interdecadal winter temperature anomalies. We introduce the East China Sea Mode (ECSM), a winter-specific mode that significantly influences global winter temperatures. The East China Sea, adjacent to the East Asian Winter Monsoon (EAWM) area, is a critical region impacted by this monsoon system. The ECSM induces global winter temperature anomalies by modulating the dominant interdecadal atmospheric teleconnections, positioned within a crucial area of the teleconnection wave train. Notably, the influence of the ECSM extends beyond the typical range of influence of the Pacific Decadal Oscillation (PDO), with the combined effects of ECSM and PDO shaping temperature patterns across Eurasia, North America, and parts of the Southern Hemisphere. This study highlights the critical role of SSTs in the East China Sea in affecting winter temperature variability, which complements the traditional focus on the eastern part as represented by the PDO.

Abstract East Asian Summer Monsoon (EASM) varied at orbital and millennial timescales during the Last Deglaciation (∼20–11 ka). The uniform δ 18 O response in East China is often linked to EASM circulation that drives a precipitation dipole in North and South China on orbital scale. Yet the relationship between stalagmite oxygen isotopes (δ 18 O c ) and regional rainfall remains ambiguous at millennial timescales. Combining proxy records with isotope‐enabled transient climate simulations (iTraCE), we demonstrate a decoupling between changes in δ 18 O c and regional precipitation in North China during millennial‐scale events. Although δ 18 O c responds uniformly across East China to AMOC changes and is correlated with South China rainfall, North China rainfall is instead largely driven by insolation, with negligible millennial‐scale variability. This reflects that East China δ 18 O c is driven by AMOC‐induced shifts in moisture source δ 18 O. Our findings emphasize that δ 18 O c records require forcing‐specific interpretation in East Asia across timescales.

Abstract East Asian Summer Monsoon (EASM) varied at orbital and millennial timescales during the Last Deglaciation (∼20–11 ka). The uniform δ18O response in East China is often linked to EASM circulation that drives a precipitation dipole in North and South China on orbital scale. Yet the relationship between stalagmite oxygen isotopes (δ18Oc) and regional rainfall remains ambiguous at millennial timescales. Combining proxy records with isotope‐enabled transient climate simulations (iTraCE), we demonstrate a decoupling between changes in δ18Oc and regional precipitation in North China during millennial‐scale events. Although δ18Oc responds uniformly across East China to AMOC changes and is correlated with South China rainfall, North China rainfall is instead largely driven by insolation, with negligible millennial‐scale variability. This reflects that East China δ18Oc is driven by AMOC‐induced shifts in moisture source δ18O. Our findings emphasize that δ18Oc records require forcing‐specific interpretation in East Asia across timescales.

River avulsions shape vast floodplains that support populations and pose significant hazards. While previous studies emphasize climate change's role in small-to-medium avulsions, the general relationship between sediment flux, water discharge, erodibility, and large-scale avulsion occurrence in large river systems is poorly understood. Here, we use a fluvial erosion-deposition landscape evolution model to identify key controls on large-scale avulsions (i.e., displacing the river mouth >400 km) in the Lower Yellow River (LYR) over the past 100 kyr. Our model reproduces observed sediment flux magnitudes and spatiotemporal patterns of large-scale LYR avulsions. We show that erodibility and sediment deposition efficiency, through their control on magnitudes of sediment flux and deposition, primarily control large-scale LYR avulsion occurrence, while climate factors such as annual precipitation and sea-level change exert secondary influences. Large-scale LYR avulsion follows a preparatory stage, during which sediment accumulates upstream of the potential avulsion site, raising the riverbed, while headward erosion downstream lowers it, ultimately promoting the occurrence of large-scale LYR avulsion. We also evaluate the levels of fluvial erosion and sediment deposition necessary to trigger such large-scale LYR avulsions. Crossing a sediment flux threshold within the observed range is required to trigger large-scale LYR avulsions, but no significant relationship is found between sediment flux magnitude and avulsion frequency. Our findings clarify how integrated effects of erosion and sedimentation, together with changes in climate and sea level, drive large-scale LYR avulsions. More broadly, our work provides insights into the relationship between sediment flux and large-scale avulsion in river systems.

Evergreen and deciduous broadleaved mixed forests (EDMF), which exhibit high sensitivity to climate fluctuations, are important transitional vegetation types in subtropical regions and possess the potential for palaeoenvironmental reconstruction. Nevertheless, at present, there is a dearth of relevant research, resulting in uncertainties regarding the internal succession characteristics and external driving patterns of mountain broadleaved forests. In this study, we reconstructed the local biome changes over the past 5.8 ka based on a pollen record with an approximately 18–year resolution from a mountain wetland in southwestern (SW) China. The results suggest that since the mid–Holocene, the study area has been predominantly characterized by EDMF, and there have been distinct changes in the internal plant species composition. From 5.8 to 3.4 ka, 2.3 to 1.6 ka, and 0.6 to 0 ka, the vegetation was classified as the deciduous (D)–type EDMF, mainly composed of deciduous taxa such as Quercus (D), Fagus, and Corylus. Conversely, from 3.4 to 2.3 ka and 1.6 to 0.6 ka, the proportion of evergreen taxa like Castanopsis, Cyclobalanopsis, and Ilex was relatively high, leading to a vegetational shift to the evergreen (E)–type EDMF. Therefore, it is postulated that the expansion range of low–altitude evergreen broadleaved forests (EBLF) during this period might have been overestimated previously. Moreover, by comparing the results of pollen analysis with the TraCE simulations, it is shown that the thresholds of annual/summer temperature and precipitation may jointly influence the internal transformation between D–type and E–type EDMF. On a larger spatial scale, it is inferred that this transformation may exhibit a teleconnection with El Niño-Southern Oscillation (ENSO) variability. Specifically, different ENSO states may exert selective effects on the internal dynamic changes of subtropical transitional EDMF.

Holocene precipitation inferred by paleoclimate records in Northeast China (NEC), the northern margin of the East Asian monsoon region, exhibits different and sometimes opposite trends over a long-term period, especially from the mid-to late Holocene. The underlying mechanisms driving these precipitation changes remain poorly understood. Here we collect extensive paleoclimate records and compare them with the Transient Climate Evolution of the last 21,000 years (TraCE-21ka) simulation to better understand the variations in mean annual precipitation in NEC during the Holocene. The findings demonstrate strong alignment between the paleoclimate records and the simulation, highlighting consistent spatiotemporal patterns of mean annual precipitation. Both show an increase in mean annual precipitation from the early to mid-Holocene across the northern margin of the East Asian monsoon region. However, during the mid-to late Holocene, meridional out-of-phase patterns emerged, characterized by reduced mean annual precipitation in southern NEC but minimal changed or slightly increased mean annual precipitation in northern NEC. We attribute this meridional out-of-phase patterns of mean annual precipitation in NEC to the combined effects of diminished East Asian summer monsoon, strengthened westerlies, and the movement of the westerlies indicated by the simulated wind field.

The mid-latitude ecological environment is highly vulnerable, and increasing hydroclimate variability poses a significant threat to it. However, the mechanisms driving this variability remain unclear due to short observational records and climate model biases. Here, we present a sub-millennial resolution precipitation record spanning the past ~5.7 million years (Myr), derived from a 300.8-meter fluvio-lacustrine sediment core in mid-latitude East Asia (northern China). Our results reveal a persistent influence of the westerly jet on mid-latitude precipitation since the Pliocene, as well as a marked reduction in mid-latitude precipitation variability alongside amplified low-latitude variability after ~3 million years ago (Ma). Based on idealized sensitivity simulations, we attribute the amplified mid-latitude precipitation variability before ~3 Ma to enhanced westerly jet waviness driven by Arctic warming. Given projected increases in jet waviness under future global warming, we predict more frequent hydroclimate extremes in mid-latitude regions.

Previous studies have advanced our understanding of paleoclimate features and dynamics in East Asia, particularly within the East Asian monsoon domain (EAMD) since the last glacial period. However, a lack of quantitative reconstructions in the boundary area between tropical and subtropical zones has largely hindered our spatial comprehension of the relationship between precipitation and temperature throughout the EAMD. In this study, we present a continuous pollen record from the Pearl River delta over the past 13.2 ka and a quantitative climate reconstruction using an updated modern pollen dataset. The findings indicate that from 13.2 ka to 9.9 ka, the study area was encompassed by mid-montane moist evergreen broadleaved forest (EBLF), transitioning to semi-humid EBLF or lowland monsoon EBLF during the late Holocene. Anthropochory plants have emerged as dominant taxa by about 1.9 ka, indicating a large-scale impact of human activities. The results of quantitative climate reconstruction indicate that the range of annual precipitation varies by ca. 80–120 mm, and the changing pattern is consistent with the traditional ‘Holocene thermal maximum’ mode, with summer solar radiation potentially being the primary controlling factor. The range of annual temperature variability fall between 19.5 °C and 22.5 °C, exhibiting a warming trend likely influenced by changes in Northern Hemisphere ice volume. There is a phase difference of about 2–4 ka between the peak values of precipitation and temperature. The variation patterns of change across eastern Asia exhibit distinct differences when compared to the proxy records in the EAMD. It appears that such asynchrony between precipitation and temperature is more pronounced in southern China. In comparison with model simulations, it is believed that spatiotemporal variation in winter cloud cover may play a crucial role in explaining this phenomenon of regional heterogeneity.

The changing climate has clearly influenced the vegetation in southwestern China since the last deglaciation. However, the varying vegetation succession patterns and responses to large-scale climate events during this period have sparked debate. Here, we present a well-dated, continuous pollen record from Erhai (EH) lake on the southeastern margin of the Tibetan Plateau, to discuss biome variation and its relative forcings over the past 17.2 kyr. Our results indicate that evergreen sclerophyll Quercus forests (ESQF) were predominant surrounding the EH site during the early deglaciation (17.2-12.5 cal ka BP), and that the ESQF transitioned to deciduous broadleaved forest (DBLF) and Tsuga forest (TSUF) around 12.5 cal ka BP during the YD event. During the early to midHolocene, the mountain vegetation belts surrounding EH lake were likely similar to the original vegetation present in modern times. Since approximately 2 cal ka BP, a significant increase in anthropochorous taxa proportions has been recorded, largely attributed to early human activities and fire disturbances. Although the warming and wetting trends did not exceed the optimal growth range for Quercus (ES) during the last deglaciation, allowing ESQF to continue growing extensively on sunny mountain slopes, our findings clearly disclosed the regional disparities in vegetation responses to climate change across SW China. Moreover, millennial-scale glacier fluctuations on the southeastern margin of the Tibetan Plateau, influenced by monsoon precipitation, likely played a role in driving vegetation succession in the mountains surrounding the EH lake and other areas of the Hengduan region since the deglaciation.

Temperature is the key variable in the study of climate changes in the past and future. Most previous studies on past temperature reconstructions, however, have focused on the mean annual temperature (MAT). Here, focusing on the seasonal temperature reconstructions in the Northern Hemisphere extratropics during the Holocene period, we show that the change in seasonal cycle of temperature reconstructions is severely underestimated in comparison with the expectation from present observations. Our study highlights the current uncertainty in seasonal temperature reconstructions in the Holocene, with an implication that the MAT simulation in current climate models may not be much biased.

Modelling studies and recent observations suggest that the westerlies-monsoon interactions (WMI) have led to a spatial imbalance in lake expansions across the Tibetan Plateau (TP) during the past decades under anthropogenic warming. However, whether such imbalance reflects a short-term phenomenon or a long-term climatic trend remains unclear. Here, we present a 240,000-year lake level reconstruction from the inner TP to examine the extent to which WMI also operated for previous interglacials, natural warm regimes with large-scale climatic boundary changes. Results suggest pronounced lake expansions accompanied by enhanced rainfall during the recent three interglacials, marine isotope stage (MIS) 7, 5, and 1, notably with varying amplitudes of "V" shape (MIS 5 < MIS 7 or MIS 1). This lake expansion pattern is coherent with North Hemisphere ice volume (NHIV) variations among these interglacials. Model simulation further suggests more NHIV may impact WMI by modulating westerlies' position, causing rainfall increase and lake expansion over the inner TP relative to its marginal areas. Our findings confirm that the projected importance of WMI to drive the spatial heterogeneity of hydroclimate changes has been maintained during the past natural warm periods. We thus predict that the climate warming and NHIV decreasing will further amplify the spatial imbalance of lake expansions across the TP, with more pronounced lake expansions in the north relative to the south.

Hydroclimatic variations on the Tibetan Plateau since the Last Glacial Maximum (LGM) are still debated. Here, we reconstructed climatic and hydrological variability in the southwestern Tibetan Plateau since the LGM using climate proxies based on molecular distributions of n-alkanes, hydrogen (SD) and carbon (S13C) isotopic compositions of terrestrial n-alkanes from sediments, and oxygen isotopic composition (S18O) of authigenic carbonate at Lake Zabuye. The impact of climatic and environmental factors on these multiple proxies was discussed, and the TraCE-21 ka simulation was employed to facilitate a comprehensive model-data comparison. Our findings indicate that the SD of nC31 alkane in this lake was primarily influenced by temperature from the LGM to early deglaciation period, shifting to a predominance of precipitation influence from the Heinrich event 1 (H1) to the Holocene period. In contrast, the carbonate S18O was found to be primarily governed by evaporative processes. Through comprehensive analysis of all proxies, we suggest that Lake Zabuye was dominated by the mid-latitude westerlies with cold and moist conditions from the LGM to early deglaciation. The H1 and Younger Dryas events were characterized by low temperatures and reduced precipitation due to the influence of the moderately intensified westerlies. The Indian summer monsoon (ISM) intensified during the B & oslash;lling/Aller & oslash;d period, and its strength was comparable to that of the westerlies, resulting in plentiful rainfall and high evaporation. The ISM was dominant during the Holocene, characterized by abundant rainfall and high evaporation.

Extensive research has explored how sweet spot conditions influence climate variability in the nonlinear Earth system. However, their effects throughout deglaciations remain unclear. Based on an annual‐laminated speleothem δ 18 O record with unprecedented chronology precision, we first identified a two‐step termination of the Asian Heinrich Period‐1 at 15.11 and 14.69 ky BP (thousand years before present, where the present is 1950 CE), each marked by a centennial‐scale strengthening of the Asian summer monsoon (ASM), in contrast to centennial‐scale ASM weakening events observed at 17.8 and 16.09 ky BP. These transitions occurred under intermediate CO 2 and ice volume conditions, which dynamically paced the Atlantic Meridional Overturning Circulation (AMOC) fluctuations and the subsequent reoccurrence of ASM events. It highlights the role of stochastic resonance in nonlinear climate system. Additionally, these AMOC/ASM events also resonated with abrupt CO 2 risings across various pervasive modes of variability, which account for half of total CO 2 rise during last deglaciation. This substantial contribution to CO 2 increases played a key role in ice termination.

Organic carbon burial (OCB) in lakes, a critical component of the global carbon cycle, surpasses that in oceans, yet its response to global warming and associated feedbacks remains poorly understood. Using a well-dated biomarker sequence from the southern Tibetan Plateau and a comprehensive analysis of Holocene total organic carbon variations in lakes across the region, here we demonstrate that lake OCB significantly declined throughout the Holocene, closely linked to changes in temperature seasonality. Process-based land surface model simulations clarified the key impact of temperature seasonality on OCB in lakes: increased seasonality in the early Holocene saw warmer summers enhancing ecosystem productivity and organic matter deposition, while cooler winters improved organic matter preservation. The Tibetan Plateau's heightened sensitivity to climate and ecosystem dynamics amplifies these effects. With declining temperature seasonality, we predict a significant slowdown or reduction in OCB across these lake sediments, leading to carbon emissions and amplified global warming.

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 delta 18 O 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 Nino-Southern o-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.

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.

Water is critical for ecological systems in arid regions, making it imperative to understand how moisture in arid Central Asia (CA) responds to anthropogenic warming. The oscillation of warming and cooling events since the Last Glacial Maximum (LGM, similar to 24-19.5 ka) provides a window for exploring the relationship between moisture and temperature. Employing 109 luminescence ages derived from eight sand dune sediment cores in the Bayanbulak Basin in the CA, this study endeavors to reconstruct the evolution of sand accumulation, and by extension, moisture dynamics. We found that pre-Holocene sand accumulation was predominant during the LGM and Heinrich Stadial 1 (HS1, similar to 18-14.6 ka), indicative of a cold-dry climate prevailing during these two cold stages. During the Holocene, sand accumulation during Early Holocene is significantly stronger than that during Middle-late Holocene, supporting a long-term wetting trend. Additionally, this study reveals that the colder Little Ice Age (LIA, similar to 0.55-0.2 ka) exhibited a wetter condition compared to the warmer Medieval Warming Period (MWP, similar to 1-0.55 ka), indicating a cold-humid climate during the LIA. Corroborated by TraCE-21ka (Transient Climate of the Last 21,000 Years) simulation, we propose that diminished evaporation over North Atlantic during the LGM and HS1 potentially led to a reduction in water vapor transported by westerlies to the CA. During the Middle and Late Holocene, increased evaporation over North Atlantic, attributed to decreased ice sheet, westerlies intensity became the primary limiting factor. Notably, stronger westerlies during the LIA could have contributed to elevated moisture levels compared to the MWP. These findings not only resolve the debate surrounding the transition from cold-dry to cold-humid conditions but also enhance our comprehension of future moisture variations.

The existence and causes of the recently observed rainfall heterogeneity over monsoonal east Asia in historical periods remain unclear. Here we show that such rainfall heterogeneity has been present at least in the last millennium, with decadal to centennial precipitation variations over southeast Asia and north China being broadly synchronous, while central to southwest China’s variations are generally out-of-phase with those in southeast Asia and north China. We propose that the western Pacific subtropical high, which reduces decadal to centennial precipitation over central to southwest China due to its anticyclonic feature, could be responsible for the observed rainfall heterogeneity over subtropical East Asia. Further analyses suggest that intensified decadal to centennial solar activity can lead to enhanced and northward and westward extension of the western Pacific subtropical high, resulting in tripolar rainfall heterogenous patterns over monsoonal East Asia. Over the past millennium, subtropical east Asia has experienced rainfall heterogeneity, with synchronous variations in southeast Asia and north China but heterogeneous rainfall patterns in central to southwest China due to the influence of the western Pacific subtropical high, according to analysis of Asian precipitation records.

The Holocene temperature conundrum, the discrepancy between proxy-based Holocene global cooling and simulated global annual warming trends, remains controversial. Meanwhile, reconstructions and simulations show inconsistent spatial patterns of terrestrial temperature changes. Here we report Holocene alkenone records to address spatial patterns over mid-latitude Eurasia. In contrast with long-term cooling trends in warm season temperatures in northeastern China, records from southwestern Siberia are characterized by colder conditions before ~6,000 years ago, thus long-term warming trends. Together with existing records from surrounding regions, we infer that colder airmass might have prevailed in the interior of mid-latitude Eurasian continent during the early to mid-Holocene, perhaps associated with atmospheric response to remnant ice sheets. Our results challenge the proposed seasonality bias in proxies and modeled spatial patterns in study region, highlighting that spatial patterns of Holocene temperature changes should be re-considered in record integrations and model simulations, with important implications for terrestrial hydroclimate changes.