The Indian Ocean Basin Mode (IOB), the dominant pattern of interannual sea surface temperature anomalies in the tropical Indian Ocean characterized by a basin-wide warming or cooling, is a recognized precursor that can trigger El Niño–Southern Oscillation (ENSO) with a lead time of about one year. How the IOB-ENSO inter-basin interaction will evolve under greenhouse warming is unknown and is of great interest for climate projection. Here, we show that greenhouse warming substantially enhances the influence of the IOB on Pacific ENSO. This is manifested by increased atmospheric response to IOB forcing, including amplified precipitation response over the tropical Indian Ocean and the consequent wind response over the western Pacific, which strengthen the teleconnection to the Pacific. Moreover, enhanced IOB variability further contributes to the strengthened IOB effect on ENSO. Our results identify the Indian Ocean as a key driver in the projected increase in extreme ENSO occurrences and a potential source of enhanced ENSO predictability under greenhouse warming, with an impact rivaling that of the Atlantic Ocean. Our findings call for a paradigm shift toward a fully-integrated pantropical framework for future climate projections.
Freshwater lakes serve as disproportionately large carbon sinks relative to their area extent, yet many shallow lakes are increasingly undergoing regime shifts toward algal dominance. How such ecological reorganizations affect long-term carbon sequestration remains poorly understood, creating a critical knowledge gap for inland water carbon budget assessment. Here, we reconstructed centennial-scale dynamics of aquatic primary producers (via sedimentary aquatic macrophyte pollen and algal pigments) and organic carbon (OC) burial in the littoral (open-water) zone and the pelagic zone (currently dominated by submerged macrophytes) of China's shallow Weishan Lake. A pronounced regime shift was identified in the littoral area during the 1980s, followed by a 15% decline in OC stocks, indicating diminished carbon sequestration with the switch of macrophyte-to-algae dominance. However, OC burial rates and stocks in the pelagic area both increased following elevated trophic levels and primary productivity. Although moderate nutrient loading initially promoted carbon burial in both pelagic and littoral areas, subsequent eutrophication and regime shifts decoupled carbon sequestration from nutrient-driven productivity, destabilizing carbon sequestration capacity through the reduced biomass preservation and increased mineralization of algal-derived OC. By revealing macrophytes as key regulators of the biological carbon pump, we highlight the maintenance of aquatic ecosystem stability as a core priority for enhancing freshwater carbon sequestration—a critical but previously neglected dimension of the carbon budget.
The nonglacial interval between the Guadalupian P3 and Lopingian P4 glacial periods represents a critical shift from icehouse to greenhouse conditions in the Late Paleozoic Ice Age, yet how low-latitude regions responded remains debated. Here we present a high-resolution environmental reconstruction across P3–P4 transition based on cyclostratigraphic and environmental magnetic analyses of the Fengshan section (Standard Auxiliary Boundary Stratotype for the Guadalupian–Lopingian boundary) in South China. An astronomical time scale was established using 405-kyr long-eccentricity cycles, and predominant hematite concentration was used to track continental weathering intensity. Integrating these analyses, the weathering evolution can be divided into three stages with boundary at ca. 262.2 Ma and ca. 260.1 Ma. Stage I (the waning of P3 glaciation) is marked by weakening chemical weathering and a slight decline in hematite. Stage II (nonglacial interval) begins with moderate weathering, followed by rapid fluctuations coinciding with marine regression and initial onset of volcanic activity. Stage III (the initial onset of P4 glaciation) records abrupt 3.5- to 4-fold increases in hematite concentration, indicating massive enhancement of weathering driven by erosion of the Emeishan large igneous province basalts. We infer that intensive chemical weathering of the Emeishan basalts, rather than direct volcanic CO₂ emissions, likely amplified CO₂ consumption, which may have contributed to the global cooling that facilitated the onset of the P4 glaciation. These findings favor the weathering fluctuations, ultimately linked to deep Earth processes, serve as an important contributing factor for the glacial−nonglacial transition during the late Paleozoic period.
The Middle Miocene Climatic Transition (MMCT) was a period of increased global aridity marked by reinforced evaporation and suppressed precipitation, respectively. While this aligns with general terrestrial paleoclimatic trends in Europe, the influence of land-vs-sea distribution and mountain building on regional climatic variability remains understudied. In particular, existing research suggests that southeastern Europe experienced pronounced aridity in the Miocene, linked to a rain shadow caused by the uplift of the Dinarides. However, poor age constraints hamper the establishment of clear causal relationships. In this work, we investigate how regional tectonic processes modulated global climatic trends in southeastern Europe. We conducted a sedimentologicl analysis of the basin fill and U-Pb zircon dating of intercalated volcaniclastic deposits in the Valjevo-Mionica Basin in western Serbia, allowing us to correlate the basin evolution with global and regional climatic forcing mechanisms. Our results reveal significant lake expansion between 14.1 and 13.5 Ma, which suggests a rise in precipitation coeval with the tectonically driven expansion of the Central Paratethys. A subsequent phase of progressive aridification occurred between 13.5 and 12.1 Ma. We correlate this with continued global cooling following the Middle Miocene Climatic Transition, consistent with an intensification of the rain-shadow effect in the Dinarides driven by changes in atmospheric circulation patterns.
Variations in C4 plant abundance governs key aspects of the global carbon cycle and food security. However, the future dynamics of C4 vegetation are still poorly constrained. This study presents high-resolution late Miocene to Pliocene records of δ13C of black carbon, black carbon mass accumulation rates, and hematite-to-goethite ratio from the QZ6 core in the Qiongzhou Strait. Integrated with multiple statistical approaches, these records elucidate the dynamics and driving mechanisms of C4 plants in southern China. This study demonstrates the widespread occurrence of C4 plants in southern China during the warm Pliocene, revealing vegetation characterized by substantially higher C4 abundance than today and contrasting markedly with the modern forest-dominated landscape. Drought and associated fire disturbances were strongly associated with C4 plant expansion in southern China, while low atmospheric CO2 concentrations likely provided a favorable background condition. We further establish critical climatic thresholds for this expansion: C4 abundance increases markedly when annual precipitation falls below ~1350 mm. Frequent fire activity likely further facilitated this expansion, contributing to a shift from forest-dominated vegetation toward vegetation with greater C4 representation and increased openness in southern China. This study provides scientific references for predicting C4 plant evolutionary trajectories in southern China under global warming scenarios and offers a valuable reference for understanding C4 vegetation dynamics in other low-latitude regions.
Climate change has profoundly influenced human societies. In low-latitude regions, hydrometeorological events often drove the decline and even collapse of prehistoric societies by restricting settlement use and reducing crop yields. However, the extent to which agricultural systems, particularly crop structure, mediated prehistoric societal responses to climate shocks remains unclear. The Yunnan region, situated along the south-eastern margin of the Tibetan Plateau (TP), was a key corridor for prehistoric crop dispersal and north–south cultural interaction, and is highly sensitive to Indian Summer Monsoon (ISM) variability. This study focuses on the sediments of Jian Lake in northwestern Yunnan, adjacent to the Haimenkou archaeological site. Based on an AMS 14C age–depth model, we reconstructed the hydrological evolution of Jian Lake since ~13,300 cal yr BP by integrating sediment grain-size distributions, glycerol dialkyl glycerol tetraethers (GDGTs), and elemental geochemistry with lakeshore stratigraphic evidence. During the early Holocene, Jian Lake maintained a high lake-level state driven primarily by catchment precipitation. Since 5530 cal yr BP, multi-proxy records consistently indicate that Jian Lake entered a relatively low lake-level state, accompanied by weakened inflow and reduced terrigenous detrital input. Against this background, a pronounced decline in grain size end-member 2 (EM2) content identifies three centennial-scale extreme drought events: at 3490–3110, 3000–2880, and 2370–1980 cal yr BP. After 1370 cal yr BP, discrepancies between EM2-inferred lake levels and lakeshore stratigraphic constraints indicate increasing anthropogenic influence on Jian Lake sedimentation. Comparison of the hydrological reconstruction with archaeological evidence from Haimenkou indicates that mid- to late Holocene lake-level lowering initially favored settlement development by exposing habitable lakeshore areas. The subsequent introduction of wheat likely increased the settlement's dependence on water availability. Extreme droughts at 3000–2880 and 2370–1980 cal yr BP may therefore have intensified food stress, contributing to interruptions in occupation and eventual abandonment. Integration of regional archaeological evidence suggests that prehistoric settlements engaging in barley or wheat cultivation were more prone than those without these crops to decline or even collapse under the impact of extreme drought. These results demonstrate that crop structure transformation may have intensified extreme drought shocks on prehistoric settlements, shedding new light on the mechanisms linking late Holocene hydroclimatic variability and societal responses in southwestern China.
The thickness and scale of the gypsum–salt rocks are critical for oil and gas preservation and accumulation. The Mesozoic Qiangtang Basin exhibits the greatest petroleum resource potential in the Tibetan Plateau and contains vital records of salt formation. However, whether large-scale gypsum–salt rock series is extensively developed in the basin remains unclear. Here, we integrated sedimentological, geochemical, and zircon U-Pb age data of the Quemoco Formation gypsum–salt rock series to elucidate the tectonic–sedimentary evolution and its responses to salt formation in the Northern Qiangtang sub-basin. The Quemoco Formation may be assigned to the Hettangian–Toarcian of the Early Jurassic (200–176 Ma), and exhibiting a deepening-upward transgressive succession. The source area of the Quemoco Formation experienced weak and moderate chemical weathering, and the provenance consists of recycled felsic and andesitic rocks from the Central Uplift Belt and proximal Late Triassic syn-rift volcanic rocks. The gypsum–salt rock series was formed in the mixed settings of rifting and collision. Late Triassic volcanic activity, Early Jurassic multiple transgression–regression cycles, relatively hot and arid climate, and restricted to semirestricted paleogeographic settings favor the formation of the gypsum–salt rocks. The thickest gypsum–salt rocks were mainly related to the migration of depositional centers of rift troughs and formed under the hottest and driest climate and the most restricted environments. These findings provide a strong case for salt formation in rift basins and offer broader insights for evaluating the preservation conditions of petroleum in the Qiangtang Basin.
The southern permafrost margin of Eurasia forms a highly climate-sensitive transition belt where modest warming can rapidly reorganize snow–soil–vegetation coupling and trigger nonlinear retreat. However, long-term, spatially continuous indicators of cold-season thermal penetration remain scarce, limiting the attribution of freeze-depth changes to coupled hydrothermal and land-surface controls. In this study, an integrated framework was developed by combining a surface frost number model, multisource environmental predictors and machine-learning-based SFD (soil freezing depth) inversion, and piecewise structural equation modeling (SEM) to explore the spatiotemporal evolution of permafrost in northeastern China, which is located at the southernmost tip of the Eurasian continent. By coupling an ensemble-mean gradient-boosted tree mapping framework, a spatially continuous SFD for 1980–2020 was reconstructed with high accuracy (R2 = 0.70, RMSE = 34.24 cm) under the station-wise chronological split. The regional average SFD decreased from 171.20 cm in 1980 to 154.25 cm in 2020, corresponding to an overall trend of −0.25 cm/y. A quick northward retreat of the permafrost southern boundary was identified, with the median latitude shifting from 48.37°N to 49.92°N at a rate of 4.31 km/y, producing a degrading permafrost belt of 1.75 × 105 km2 over the past four decades. Three permafrost types, i.e., consistent permafrost, degradation belt and seasonally frozen ground, were identified with contrasting changing characteristics. SEM analysis revealed a contrasting dominant type and corresponding controlling mechanism on the SFD across the three regions. The land surface thermal state regulates the SFD in the consistent permafrost region, whereas vegetation strongly indirectly controls the SFD through modulation of thermal state and soil moisture in the degradation belt. In contrast, hydroclimatic and snow processes are increasingly influential in seasonally frozen ground. Our findings provide a transferable framework for diagnosing changes in SFD and its drivers in warming permafrost transition zones beyond the eastern Eurasian permafrost margin and may be helpful in guiding the modeling of its evolution against the background of climate change.
Assessments of the vulnerability of vascular plant alpha diversity to climate change are an important facet of protected area (PA) management. However, few studies have attempted to determine the localities and numbers of species vulnerable to climate change. Accordingly, we sought to address these issues by quantifying the alpha diversity of vascular plants in PAs vulnerable to climate change. We used the Getis-Ord Gi* statistic in conjunction with a two-dimensional climate space derived from principal component analysis, coupled with changes in current and future alpha diversity, to determine the areas within PAs that are vulnerable to climate change. We found that vegetation in 27.6% of the worldwide PA areas was vulnerable to climate change. Moreover, we established that the alpha diversity of vascular plants in vulnerable PAs (mean: 33.1; SD: 20.1) was significantly higher than that in non-vulnerable PAs (mean: 25.2; SD: 11.7), with the tundra and tropical and subtropical moist broadleaf forests showing the largest differences between vulnerable and non-vulnerable PAs and the strongest negative climate change effects. Under high-emission scenarios, alpha diversity was expected to decrease globally in both vulnerable and non-vulnerable PAs. Specifically, vascular plant alpha diversity was vulnerable to climate change within PAs distributed across 137 ecoregions, with vulnerable areas covering more than 50% and 90% of the PAs in 34 and seven ecoregions, respectively. Our findings highlight the need to focus on enhancing biodiversity conservation and ecosystem management in vulnerable and non-vulnerable areas within protected areas to maintain a high diversity of vascular plants.
Tree rings provide annually resolved and precisely dated climate information on past climate variability. However, in disturbance-prone areas, tree-ring width (TRW) can be strongly affected by stand dynamics and geomorphic disturbances, introducing non-climatic noise into chronologies and causing non-stationary climate–growth relationships. Here, we combined a newly developed ring-width index (RWI) with a tree-ring δ18O chronology from Pinus tabuliformis at Mt. Cuifeng, located along the western margin of the East Asian summer monsoon (EASM) on the eastern Tibetan Plateau margin, to evaluate the relative robustness of the two proxies in recording hydroclimate. Raw TRW measurements exhibit a prolonged juvenile effect and a pronounced growth release in the mid-20th century. In contrast, the tree-ring δ18O record is comparatively stable, showing neither a systematic juvenile trend nor a corresponding isotopic anomaly during the growth release period. Climate response analyses indicate that RWI responds negatively to temperature, primarily reflecting the limiting effect of temperature-induced growing-season moisture stress on radial growth. Tree-ring δ18O is more closely related to moisture-balance variables, including previous October precipitation, May–August vapor pressure deficit (VPD), and July–September scPDSI. This mid- to late-summer seasonality coincides with the period when the EASM rain belt prevails over the monsoon-margin region. Regional network comparisons further show weak inter-site coherence among RWI chronologies, likely reflecting site-specific disturbance histories, microenvironmental heterogeneity, and local growth limitations. Tree-ring δ18O chronologies maintain significant spatial synchrony across sites, even across different bioclimatic settings. Our study demonstrates that, compared with RWI, tree-ring δ18O provides a more physically interpretable and comparatively disturbance-resistant hydroclimate proxy, thereby improving hydroclimate reconstruction reliability in disturbance-affected landscapes.
The mountain-basin structures in Central Asia promote complex interactions between advected moisture and locally recycled moisture, leading to ongoing debates on the altitude or inverse altitude effects of water vapor isotopes in a westerlies-dominated arid environment. To quantify the altitude gradient of near-surface water vapor isotopes, we designed a vehicle-based observation campaign along four elevation transects in Central Asia during the summer of 2024, measuring the altitudinal variation in near-surface water vapor δ18O and examining the circulation mechanisms responsible for these gradients. The results show positive δ18O–altitude gradients along the Altai, Tianshan, and Kunlun transects. This pattern is most pronounced in the Altai and Tianshan transects, with overall gradients of approximately 1.7‰/km and 1.2‰/km, respectively, whereas the Kunlun transect shows a weaker positive gradient of about 0.4‰/km. In contrast, the Pamir transect exhibits a negative gradient, with substantial differences in the altitude gradients among geomorphic and catchment units. The relationships between near-surface meteorological variables and δ18O are strongly subregion-dependent and cannot, by themselves, explain the differences in altitude gradients among the transects. The back-trajectory analysis and the relationships between isotopes and specific humidity indicate that the Altai and Tianshan transects are more strongly influenced by stable and continuous westerly moisture transport, with weaker mixing from local or nearby moisture sources. These conditions favor the development of a pronounced inverse altitude effect in near-surface water vapor isotopes. By contrast, the Kunlun and Pamir transects are more strongly affected by topographic blocking, valley transitions, and local moisture inputs, which weaken or reorganize the westerly isotopic signal. Differences in underlying surface conditions may regulate δ18O through evapotranspiration and local moisture recycling, but their influence is largely confined to specific terrain units and is insufficient to alter the transect-scale circulation control. This study demonstrates that the inverse altitude effect of near-surface water vapor δ18O in Central Asia is primarily associated with stable westerly moisture transport, while also being modulated by local meteorology, topography, and land–atmosphere coupling processes. These findings provide modern process-based constraints for understanding anomalous altitudinal gradients in Central Asian precipitation, surface waters, and isotope-based proxies, and indicate that a stable depletion in water isotopes with increasing elevation should not be assumed in paleoaltimetric or paleohydrological interpretations within westerly-influenced regions.
Reconstructing Holocene winter temperatures remains challenging and debated, primarily due to the scarcity of reliable winter-specific proxies. In this study, we present a novel proxy for winter sea surface temperature (SST) derived from sediment trap data collected in the northern South China Sea (SCS). We found that over 93% of the planktonic foraminifera Globigerina bulloides occurred during the winter half-year in the Xisha Trough. Stable oxygen isotope (δ18O) analyses of Globigerina ruber and G. bulloides from the same sediment traps indicate that G. bulloides calcified within the upper mixed layer. We utilized δ18O and Mg/Ca ratios of G. bulloides from core GHE 27 L in the northern SCS to reconstruct variations in Holocene winter SST. Results show a gradual decline in winter SST from 11.5 ka, reaching a minimum between 8.5 and 5.8 ka, followed by a warming trend from 5.8 to 1.3 ka. This pattern aligns with East Asian Winter Monsoon (EAWM) records in this region, but it contrasts with the Holocene Thermal Maximum (HTM) observed during the mid-Holocene. The anomalously low winter SST and the intensified EAWM during the mid-Holocene imply a potential absence of HTM in winter temperatures in the low latitudes of East Asian. We attribute the enhanced EAWM and the unusually low winter SST primarily to persistent La Niña-like conditions in the tropical Pacific and a northward displacement of the Intertropical Convergence Zone.
