The mid-Cretaceous Oceanic Anoxic Event 2 (OAE2, similar to 94 Ma) stands as a prominent deep-time analogue for understanding global oceanic redox variations in response to major environmental perturbations. However, the mechanisms driving oceanic redox evolution in the eastern Tethys during OAE2, particularly the influence of water column stratification, remain poorly investigated. In this study, we analyze the connections between oceanic redox, stratification, and productivity changes in the eastern Tethys during OAE2 using biomarker records of glycerol dialkyl glycerol tetraethers (GDGTs) and n-alkanes from the Gongzha section, southern Tibet. Our results reveal pronounced increases in oceanic deoxygenation and stratification, alongside reduced productivity, through the carbon isotope stage C4, the main phase of OAE2 following the initial perturbation and prior to the recovery. Combining these findings with existing geological data from the Gongzha section, we infer that enhanced water column stratification may have driven the oceanic deoxygenation by diminishing oceanatmosphere exchange in the eastern Tethys during OAE2. This mechanism differs from that previously observed in the circum-proto-North Atlantic, where increased productivity and associated enhancement in the organic remineralization may have triggered the marine anoxia. By providing biological constraints, our study indicates the dominant role of water column structure in shaping redox evolution in the eastern Tethys, highlighting distinct regional controls on oceanic redox evolution during OAE2.

It is widely accepted that global cooling since the Late Miocene, particularly the Northern Hemisphere glaciation, has led to a progressive weakening of the East Asian summer monsoon and intensified aridification of Asian inland. Here we present a detailed record of monsoon precipitation over the past 7 Ma, retrieved from two carbonate carbon isotope profiles from the Chinese Loess Plateau (CLP). Our results show that the CLP at the northern edge of the East Asian summer monsoon has been getting wetter rather than drier since similar to 2.7 Ma. This climatic reversal coincided with the increased aridification in Central Asia. Combined with climate model simulations and existing Asia-Pacific hydroclimate records, we suggest that the Westerlies-monsoon interaction forced by the Northern Hemisphere glaciation, induced both a differential evolution of the East Asian summer monsoon at mid- and low-latitudes and an east-west antiphased precipitation change over the mid-latitude Asia since similar to 2.7 Ma. Specifically, the Northern Hemisphere glaciation, and the associated 'Arctic Amplification' intensified and shifted westerlies southward after similar to 2.7 Ma that blocked the northwestward invasion of monsoon moisture, thereby simultaneously drying Central Asia and placing more precipitation to North China. Our findings challenge the prevailing view of the evolution of Asian inland deserts and monsoon, and provide new insights into Asian climate change in the context of interactions between the Westerlies and the East Asian summer monsoon.

Dual carbon isotopes (delta C-13, Delta C-14) of biomarkers have been widely applied to constrain the sources of organic carbon (OC) in continental shelf sediments. The addition of biomarker hydrogen isotopes (delta H-2) can provide further constraints since biosynthetic processes and environmental responses impart hydrogen isotope signatures to lipids that are independent of carbon isotope signatures. In order to test the three-isotope system to constrain OC sources, we measured delta H-2, delta C-13, and Delta C-14 of C-28:0 and C-16:0 fatty acids; and delta H-2, delta C-13 of brassicasterol and dinosterol in suspended particles and surface sediments of the Pearl River estuary (PRE) and coastal sediments of the northern South China Sea (SCS). These four lipids have been widely used as biomarkers for terrestrial plants (C-28:0) and phytoplankton (brassicasterol, dinosterol), or, in the case of C-16:0, autocthonous organic matter in general. Higher delta H-2(brassicasterol) (-248 parts per thousand) and lower delta C-13(brassicasterol) (-34.6 parts per thousand) in the upper PRE than those in the lower PRE and offshore sites imply a substantial C-3 vascular plant source such as rapeseed crops, which are rich in brassicasterol and are common in southeastern China. High delta H-2(C28:0) (>-153 parts per thousand) values in the most offshore sediments are tentatively attributed to a relatively increased contribution of leaf wax fatty acids from wind-borne aerosols due to the reduced influence of river-borne suspended particles in distal settings. This supposition is supported by the higher Delta C-14(28:0) values at offshore sites compared to estuarine sites which suggests additional non-fluvial source contribution. High delta H-2(dinosterol) (-294 parts per thousand) values in suspended particles and sediment from the upper PRE, relative to the lower PRE, are attributed to dinoflagellates obtaining significant nutrition from grazed non-photoautotrophic biomass, at the expense of carbon fixation from photosynthesis. The commonly assumed phytoplankton origin for brassicasterol and river transportation for C-28:0 fatty acid may not be valid in certain estuarine, coastal and shelf sediments, such as those of the PRE and the northern SCS.

Most geological materials record temperature changes at land/ocean surface rather than air temperatures. However, whether their long-term trends exhibit coherence during the Holocene remains debated. Here, we present brGDGT-derived land surface temperature (LST) variations over the past 25 kyr in the western Chinese Loess Plateau (CLP), revealing an overall Holocene cooling trend. Modern meteorological data indicate that surface conditions critically modulate regional LSTs, allowing the surface air temperatures (SATs) to be quantitatively estimated by incorporating vegetation cover and soil moisture. The reconstructed SATs show distinct early Holocene warming, mid-Holocene thermal maximum, and late Holocene cooling, aligning well with simulated SATs and global/regional temperature reconstructions. Our findings reconcile diverging LST and SAT trends through vegetation and moisture feedbacks, offering a new method to clarify land-air thermal interactions and improve proxy-model comparisons in paleoclimatology.

Lakes have great contributions to global CO2 emissions, yet reconstructions of historical CO2 sources/sinks in lakes remain limited, largely due to the lack of reliable indicators. This study addresses this gap by examining CO2 concentrations and aquatic plant delta 13C from 105 lakes in China. Our results demonstrate aquatic plant delta 13C faithfully record CO2 concentration variations, establishing it as a reliable indicator for paleolake CO2. Building on this finding, we analyzed delta 13C of aquatic plant remains in sediment cores from four Tibetan Plateau lakes. Integrating these data with published delta 13C records from ten additional lakes has enabled a 26,000-year reconstruction of lake CO2 concentrations. Our integrated record reveals that Tibetan lakes have functioned as persistent CO2 sources since the Last Glacial Maximum, with enhanced emissions during the last deglaciation and early Holocene. Thus, inland lakes played a substantial role in the global CO2 cycle during the deglaciation as compared to today.

Aquatic submerged plants represent a crucial component of lake ecosystems, yet their influence on lacustrine organic carbon burial remains poorly quantified, particularly regarding historical variations in submerged plant productivity-carbon burial relationships across different lake types. This study combines new total organic carbon (TOC) S13C data from Lake Sugan (a less-studied site on the northern Tibetan Plateau) and integrate these data with a comprehensive synthesis of published Holocene records, including: 22 lake cores (TOC S13C and content), 7 soil profiles (TOC S13C), 4 lake cores (C31 n-alkane S13C), and modern plant samples across the Tibetan Plateau. Our integrated analysis reveals: (1) TOC S13C of soil profiles (-27%o to-23%o) and C31 n-alkane S13C of sediments (-33%o to-29%o) consistently indicate C3 plants dominance throughout the Holocene; (2) significantly enriched TOC S13C in lake core sediments relative to C3 plants and soil profiles demonstrates substantial contributions from submerged plants, serving as a robust proxy for submerged plant productivity; and (3) distinct regional patterns emerge, with submerged plant productivity (controlled by water depth and terrestrial vegetation cover) driving organic carbon burial in northeastern and southwestern lakes, while terrestrial biomass dominates in southeastern lakes with minimal submerged plant input. These findings provide new insights into the complex interplay between aquatic and terrestrial carbon sources in high-altitude lake systems, highlighting the need for region-specific assessments of carbon burial mechanisms.

Holocene temperature variations exhibit significant spatial heterogeneity, yet their impacts on regional hydrological systems remain poorly understood. Here, we quantitatively reconstruct Holocene land surface temperature (LST) changes from the Jiangxigou loess record in the Qinghai Lake region using brGDGTs biomarkers and compare them with past meltwater variations on the Tibetan Plateau. Notably, while most global and regional records document the Holocene Thermal Maximum (HTM) between 9 and 5 ka, Jiangxigou exhibits progressive warming through the early-mid Holocene, reaching peak temperatures during the Mid-Late Holocene transition (5-3 ka) followed by gradual cooling. We attribute this anomalous thermal regime to combined solar activity and residual ice sheet effects. Crucially, the delayed HTM shows strong temporal coupling with amplified meltwater contributions, underscoring temperature's pivotal role in governing plateau meltwater dynamics. Our findings decode the hydrothermal coupling mechanisms of the "Asian Water Tower" during this climatic transition, offering vital benchmarks for projecting its water resource responses to future warming.

Western China experienced progressive aridification during the Late Cenozoic, yet the development of large lakes in the Tarim Basin indicates intervals of enhanced hydrological conditions, creating an apparent paradox. Here, we analyze carbonate mineralogy and oxygen isotope compositions from the LS2 drill core in Lop Nur to constrain the origin of lacustrine dolomite and the hydrological evolution between similar to 7 and 4.9 Ma. Dolomite abundance covaries with bulk carbonate delta O-18 values, with higher dolomite contents corresponding to isotopic enrichment. This relationship, together with pronounced stratigraphic variability, indicates that dolomite formed predominantly during deposition or early diagenesis under the control of lake-water chemistry, rather than through late-stage burial diagenesis. Although this pattern is consistent with evaporative concentration, the absence of a clear delta C-13-delta O-18 correlation and the lack of quantitative constraints on detrital carbonate input introduce uncertainty in attributing evaporation as the dominant control. Our results reveal a shallow saline lake system characterized by strong hydrological fluctuations superimposed on a persistently arid background. The environmental evolution can be divided into two stages: (1) 7.0-5.7 Ma, characterized by a shallow, reducing saline lake under generally warm and arid conditions, with intermittent cooling and humid episodes; and (2) 5.7-4.9 Ma, marked by continued shallow lacustrine conditions with higher-frequency hydrological variability, showing alternations between relatively warm-dry and cool-wet conditions, superimposed on an overall arid background with intensified evaporation and increasing salinity. Comparison with regional records suggests that Late Miocene lake expansion in Central Asia does not necessarily indicate sustained humid conditions, but instead reflects complex interactions among evaporation, basin hydrology, and climate forcing.

The bacterial denitrification method (Pseudomonas aureofaciens) is a widely used pretreatment technique for nitrogen and oxygen isotope analysis of nitrate (NO3-) and nitrite (NO2-), but concurrent reduction of both species (NO3- and NO2-) to N2O obscures their individual isotopic signals. This study developed an integrated ion-exchange (AG1-X8 resin) and denitrification for the methods, achieving quantitative NO3-/NO2- separation (0.25 mol per L KCl for NO2- and 0.5 mol per L HCl for NO3- at 0.5-3 mL min-1) and high-precision isotopic analysis (delta 15N: SD <= 0.2 parts per thousand and delta 18O: SD <= 0.3 parts per thousand for both NO2- and NO3- at >= 0.054 mmol L-1). This method provides a safe, stable, and high-accuracy approach for separation of NO3-/NO2- in high-NO2- freshwater systems. In addition, to effectively address the instability of NO2- during storage, samples can be preserved immediately upon collection by adsorption onto resin. In conclusion, this study has established an efficient and accurate pretreatment method for separating NO2- and NO3- and determining their individual N and O isotopes in natural freshwater. This method provides a reliable analytical technique for in-depth investigation of nitrogen transformation mechanisms, especially in high NO2- environments, using NO2- isotopic signatures as an indicator.

Hydroclimatic variations in mid-latitude Asia during the early to mid-Holocene and associated mechanisms remain disputed, hampering our understanding of atmospheric circulation controls on regional climatic changes. We report Holocene alkenone records from two Siberian lakes, documenting lake temperature and hydrological changes, and synthesize records from mid-latitude Asia to address regional hydroclimatic variability. Relatively dry conditions occurred in westerlies-dominated regions and extended to marginal monsoon regions before similar to 6,000 a BP, followed by wetting transitions during similar to 6,000-5,000 a BP, despite contrasting temperature variations between two regions. We suggest that early to mid-Holocene drought in mid-latitude Asian interior appears to be associated with enhanced anticyclonic system over mid-high latitude Eurasian continent, induced by prevailing cold airmasses, which extended its hydrological control to marginal monsoon regions. Our findings explain the spatial heterogeneity of hydrological changes in mid-latitude Asia, and opposite temperature-moisture associations within westerlies-dominated and marginal monsoon regions during the early to mid-Holocene.

Fossil fuel combustion not only emits large amounts of CO2 but also generates significant water vapor (H2Ov). Currently, research on the isotopic composition of combustion-derived water vapor (CDWV) predominantly relies on theoretical calculations. This has hindered the comprehensive understanding of the characteristic patterns in isotopic variations and associated isotopic fractionation mechanisms during CDWV formation. In this study, we systematically investigated the variation characteristics in the isotopic composition of water vapor emitted from the combustion of various fuels and initially established the characteristic isotopic signatures of CDWV. The δ18O-H2Ov produced by fossil fuel combustion inherits the isotopic signature of atmospheric O2, resulting in a significantly positive δ18Ov value (> +10‰) and markedly negative d-excessv (< -200‰) characteristic. Through this study, we demonstrated the reliability and universality of the theoretical values of CDWV isotopic composition. Through experiments, we observed the dynamic variations in isotopic compositions and water vapor mixing ratios during fossil fuel combustion processes. The distinct isotopic disparity between the CDWV and the natural water vapor enables us to use d-excessv as a quantitative tracer for estimating the contribution of anthropogenic fossil fuel combustion to atmospheric moisture.

Millennial-scale climate variability (MCV) in the Asian summer monsoon (ASM) plays a crucial role in elucidating short-term monsoon dynamics and in improving projections of future Asian hydroclimate change. However, significant divergences remain in our understanding of how high- and low-latitude climate systems couple to drive and modulate MCV in ASM precipitation. These discrepancies primarily arise from a limited understanding of the spatial heterogeneity in precipitation MCV in marginal ASM regions. We present a new high-resolution (similar to 280-year) loess leaf-wax hydrogen isotope (delta Dwax) record from the central Chinese Loess Plateau (CLP) spanning the last glacial period. The record reconstructs regional precipitation isotopic variability on precessional and millennial timescales. The strong correspondence between the CLP delta Dwax record and 65 degrees N summer insolation demonstrates that orbital-scale variations in precipitation delta D across ASM marginal regions primarily reflect high-latitude insolation forcing. On millennial timescales, although the MCV of Xifeng (XF) precipitation delta D exhibits characteristics modulated by the precession periodicity, its exceptionally low mean absolute amplitude indicates that this modulating effect was significantly attenuated in this region during the last glacial period. Synthesis of precipitation isotope records across the monsoon region reveals complex spatial heterogeneity in the amplitude of MCV during the last glacial period. The Indian monsoon-affected region exhibits greater MCV overall than the East Asian monsoon-dominated region. Although both monsoon systems exhibit a trend of strengthening amplitude along their respective moisture transport pathways, MCV amplitudes decrease in the transitional zone. This pattern suggests that these regions were situated beyond the ASM marginal zone during the glacial period. Our findings further underscore that the pathways and strengths of moisture transport critically govern the spatial heterogeneity of monsoon precipitation MCV, revealing a glacial-state hydroclimate pattern where a region's response amplitude is dictated by its relative position on the moisture pathway.

Ion exchange is a traditional method for treating nitrate nitrogen and oxygen isotopes in surface water, and experimental blanks in the ion exchange process have a strong impact on nitrate isotope determination. The blanks can come from the reagents, the environment, the resin. This paper discusses the blanks and how to reduce blanks in three aspects. The results showed that: (1) the nitrate nitrogen content of 120 ml of 0.25 mol/l (M) KCl and 0.25 M NaCl was about 1.21 and 1.14 µg, and the nitrogen content could be reduced to less than 0.64 µg after burnt in a muffle furnace; (2) Nitrate nitrogen was limited to less than 0.33 µg in the determination of the environmental background blank, which was controlled by airtight equipment. (3) In particular, we found that the nitrate nitrogen content in 1 ml of resin was about 30 µg, the nitrogen content of 1 ml of resin could be reduced to 9 µg by overnight HCl soaking, and the nitrate nitrogen content of resin could be reduced to less than 0.15 µg/ml after pre-cleaning the resin by 120 ml of 0.25 M KCl or 0.25 M NaCl. This paper provides a more accurate pretreatment method for nitrate samples by ion exchange.

Despite clearly documented in instrumental temperature records, the warming amplitude over the current warm period (CWP) inferred from lacustrine archive is very limited. The potential role of meltwater pulses in lake hydrology and their influence on lake water temperature under anthropogenic warming remain poorly investigated. Here we present and summarize lake water temperature and hydrology records in northern China to address potential meltwater effects over the last millennium. Our results show abrupt freshening and muted warming of lake water over the CWP, which appears to have also occurred along with climatic warming previously. Hence, substantial meltwater pulses to lakes, a transient response to climatic warming, could partly account for the muted warming over the CWP as indicated by lake water temperature records.

The Holocene East Asian summer monsoon (EASM) evolution has been extensively investigated, yet proxy records show inconsistent variations during the Bronze Age, and spatial patterns of hydroclimatic conditions remain controversial, limiting our understanding of monsoonal behavior and its potential association with culture development. Here we present multiple biomarker records from the northern coast of the South China Sea, which document the strength of monsoon-induced upwelling/mixing effect, to infer Holocene EASM variability. Our multiple biomarker records consistently indicate enhanced EASM circulation during similar to 6000-9000 cal a BP and similar to 3300-4500 cal a BP, superimposed on the long-term weakening trend. The enhanced EASM circulation during the Early to Middle Bronze Age challenges the presumed cool/dry climate background and lends support to a tripole pattern of hydroclimatic variability over East China during this period.

Paleoaltimetry data are essential for deciphering the growth trajectory of orogenic plateaus and underlying forcing mechanisms. However, paleoaltitude reconstructions using conventional paleotemperature analysis often have low resolution or large calibration uncertainties. Here, we use Group III alkenones, a marine paleothermometer normally not present in terrestrial basins, to reconstruct paleolake temperatures and refine the paleoelevation history of the Qaidam Basin, northern Tibetan Plateau, during the Late Miocene. Our results reveal a geologically rapid lake-surface cooling of 6.6° ± 1.8°C at either ~11.3 to 10.8 or ~7.7 to 7.6 million years ago (depending on the chronology used). This cooling, benchmarked against coeval sea surface temperatures, indicates a topographic rise of either 1650 ± 450 or 1525 ± 450 meters. Coupled with glycerol dialkyl glycerol tetraether–based paleotemperatures and existing tectonic records, our findings refine the timing and pace of a rapid uplift event within the final major phase of Tibetan Plateau growth, linked to mantle lithosphere detachment.

Quantifying past temperature changes during the Common Era (the past 2000 years) is essential for assessing the rates, magnitudes, and consequences of different climate forcings on current warming and projecting future climate change. At present, however, the quantitative evaluation of temperature changes at multi-centennial-to-millennial timescales remains not well understood. In this study, we provide a high-quality mean annual temperature record for the past 2000 years based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) in a well-dated sediment core retrieved from Lake Poyang in the middle and lower reaches of the Yangtze River. Our results show an overall pre-industrial cooling trend in the Poyang Lake region, with clear temperature changes associated with the Medieval Warm Period (MWP) and Little Ice Age (LIA), consistent with local, regional, and global records. The centennial to millennial temperature fluctuations, particularly the pronounced cooling at approximately 1500 CE, generally agrees with changes in total solar irradiance, supporting the importance of solar activity in affecting pre-industrial temperature changes. Further comparisons with other biomarker-based quantitative temperature reconstructions revealed that the temperature offset between the MWP and LIA increased with latitude and elevation, suggesting that centennial-scale temperature fluctuations were amplified at higher elevations and latitudes during the past two millennia.

The process of riming significantly impacts the microphysical characteristics of clouds. This study uses aircraft and radar observation data in stratiform clouds with convection embedded that occurred in the central and southern regions of North China on 22 May 2017. The microphysical structural characteristics and processes near the embedded convection core and in the stratiform cloud are analyzed comparatively. Particular attention is given to the effect of riming on the microphysical properties near the upper boundary of the melting layer and to the factors influencing riming efficiency. The collaborative observations reveal that the particle size distributions observed near the convection core and in the stratiform region are close, while the particle properties like habit and riming degree are quite different. Above the melting layer, larger plate-like ice particles and supercooled water droplets (D > 50 μm) are more abundant near the convective core, leading to higher collision efficiencies between ice particles and supercooled water droplets. Larger fluctuation amplitudes of vertical airflow near the convective core also contribute to the increased riming activity and the formation of more heavily rimed particles, such as graupel. Furthermore, in situ measurements from airborne probes also revealed that above the melting layer, the riming process involves two stages: the mass of snow crystals grows as supercooled droplets merge internally without changing size, followed by external freezing that significantly enlarges the crystals.

Hydrogen isotope compositions (delta D) of lipids are widely used in hydrological research, yet there have been limited investigations into the relationships between salinity and delta D values of aquatic plants in natural lakes, which hinders the broader application of delta D compositions as indicators of paleosalinity reconstructions. In this study, we examined delta D compositions of n-alkanes in aquatic plants and lake water from 58 lakes (containing 18 brackish/saline lakes) across diverse regions of China (including the Tibetan Plateau, Inner Mongolia Plateau, Chinese Loess Plateau, Tarim Basin, and Yangtze Plain). Subsequently, we examined the correlations between salinity and n-alkane delta D values in aquatic plants. Our findings indicate that delta D values of n-alkanes from aquatic plants record variations in lake water delta D (R-2 = 0.53, p < 0.01). Furthermore, delta D values of lake water in brackish/saline lakes exhibit a positive correlation with salinity (R-2 = 0.74, p < 0.01). Thus, a positive correlation (R-2 = 0.68, p < 0.01) is observed between delta D values of n-alkanes from aquatic plants and lake salinity, whose changes both co-vary with lake water delta D variations. Therefore, n-alkane delta D values of aquatic plants can serve as indirect indicators of salinity for reconstructing paleosalinity in brackish/saline lakes. It is important to note that paleosalinity reconstruction in lakes using n-alkane delta D values is generally more effective when lake salinity experiences large variations, whereas caution should be exercised when lake salinity changes are more subtle.

Temperature regulates the metabolic rate of organisms and, together with salinity, determines seawater density, a key driver of ocean circulation and heat transport. The hydrogen isotope composition (H-2/H-1) of phytoplankton lipids has been shown to vary systematically with salinity and applied as a paleosalinity proxy in marine sediments. The influence of temperature on H-2/H-1 ratios of lipids from different phytoplankton groups remains poorly constrained, especially when other growth parameters known to influence H-2/H-1 fractionation are held constant, such as growth rate, irradiance, and salinity. We investigated H-2/H-1 ratios responses of lipid biomarkers (fatty acids (FAs), sterols and alkenones) to temperature (12 similar to 27 degrees C) in three marine phytoplankton taxa, the diatom Phaeodactylum tricornutum, the dinoflagellate Prorocentrum donghaiense, and the coccolithophorid Emiliania huxleyi using semi-continuous cultures. We show that H-2/H-1 fractionation of FAs in the dinoflagellate decreased by 2.2 +/- 0.3 parts per thousand degrees C-1 (p < 0.05), while that of sterols in the dinoflagellate and fatty acid C-14:0 in the diatom increased by 2.3 parts per thousand degrees C-1 and 1.9 parts per thousand degrees C-1 (p < 0.05), respectively, as temperature increased. H-2/H-1 fractionation of the three types of lipids in the coccolithophores did not vary systematically with temperature. The underlying mechanism by which temperature alters lipid H-2/H-1 fractionation likely involves its effect on the proportions of photosynthetic and metabolic NADPH incorporated into lipids, NADPH residence time in the chloroplast, the contribution of extra-plastidic pyruvate to FA synthesis, and the proportion of mevalonic acid- versus methylerythritol phosphate-derived precursors in sterols.