A high-resolution millennial record of the south asian monsoon from himalayan ice cores

Deciphering dissolved organic matter characteristics and its fate in a glacier-fed desert river-the Tarim river, China

The bioavailable diverse dissolved organic matter (DOM) present in glacial meltwater significantly contributes to downstream carbon cycling in mountainous regions. However, the comprehension of molecular-level characteristics of riverine DOM, from tributary to downstream and their fate in glacier-fed desert rivers remains limited. Herein, we employed spectroscopic and high-resolution mass spectrometry techniques to study both optical and molecular-level characteristics of DOM in the Tarim River catchment, northwest China. The results revealed that the DOC values in the downstream were higher than those in the tributaries, yet they remained comparable to those found in other glacier-fed streams worldwide. Five distinct components were identified using EEM-PARAFAC analysis in both tributary and downstream samples. The dominance of three protein-like components in tributary samples, contrasting with a higher presence of humic-like components in downstream samples, which implied that the dilution and alterations of the glacier DOM signature and overprinting with terrestrial-derived DOM. Molecular composition revealed that thousands of compounds with higher molecular weight and increased aromaticity were transformed, generated and introduced from terrestrial inputs during downstream transportation. The twofold rise in polycyclic aromatic and polyphenolic compounds observed downstream compared to tributaries indicated a greater influx of terrestrial organic matter introduced into the downstream during water transportation. The study suggests that the glacier-sourced DOM experienced minimal photodegradations, with limited influence from human activities, while also being shaped by terrestrial inputs during its transit in the alpine-arid region. This unique scenario offers valuable insights into comprehending the fate of DOM originating from glacial meltwater in arid mountainous regions.

Interactive effects of climate-atmospheric cycling on aquatic communities and ecosystem shifts in mountain lakes of southeastern Tibetan Plateau

Recent climate warming and atmospheric reactive nitrogen (Nr) deposition are affecting a broad spectrum of physical, ecological and human systems that may be irreversible on a century time scale and have the potential to cause regime shifts in ecological systems. These changes may alter the limnological conditions with important but still unclear effects on lake ecosystems. We present changes in cladoceran with comparisons to diatom assemblages over the past ~200 years from high-resolution, well-dated sediment cores retrieved from six high mountain lakes in the southeastern (SE) margin of the Tibetan Plateau. Our findings suggest that warming and the exponential increase of atmospheric Nr deposition are the major drivers of ecological regime changes. Shifts in cladoceran and diatom communities in high alpine lakes began over a century ago and intensified since 1950 CE, indicating a regional-scale response to anthropogenic climate warming. Zooplankton in the forest lakes showed asynchronous trajectories, with increased Nr deposition as a significant explanatory factor. Forest lakes with higher dissolved organic carbon (DOC) concentrations partially buffered the impacts of Nr deposition with little structural change, while lakes with low DOC display symptoms of resilience loss related to Nr deposition. Biological community compositional turnover in subalpine lakes has shown marked shifts, equivalent to those of low-elevation lakes strongly affected by direct human impacts. This suggests that local effects override climatic forcing and that lake basin features modified by anthropogenic activity act as basin-specific filters of common forcing. Our results indicate that snow and glacial meltwaters along with nutrient enrichment related to climate warming and atmospheric Nr deposition, represent major threats for lake ecosystems, even in remote areas. We reveal that climate and atmospheric contaminants will further impact ecological conditions and alter aquatic food webs in higher altitude biomes if climate and anthropogenic forcing continue.

LncRNA and Protein Expression Profiles Reveal Heart Adaptation to High-Altitude Hypoxia in Tibetan Sheep

The Tibetan sheep has an intricate mechanism of adaptation to low oxygen levels, which is influenced by both genetic and environmental factors. The heart plays a crucial role in the adaptation of Tibetan sheep to hypoxia. In the present study, we utilized transcriptomic and proteomic technologies to comprehensively analyze and identify the long non-coding RNAs (lncRNAs), genes, proteins, pathways, and gene ontology (GO) terms associated with hypoxic adaptation in Tibetan sheep at three different altitudes (2500 m, 3500 m, and 4500 m). By integrating the differentially expressed (DE) lncRNA target genes, differentially expressed proteins (DEPs), and differentially expressed genes (DEGs), we were able to identify and characterize the mechanisms underlying hypoxic adaptation in Tibetan sheep. Through this integration, we identified 41 shared genes/proteins, and functional enrichment analyses revealed their close association with lipid metabolism, glycolysis/gluconeogenesis, and angiogenesis. Additionally, significant enrichment was observed in important pathways such as the PPAR signaling pathway, glycolysis/gluconeogenesis, the oxoacid metabolic process, and angiogenesis. Furthermore, the co-expression network of lncRNAs and mRNAs demonstrated that lncRNAs (MSTRG.4748.1, ENSOART00020025894, and ENSOART00020036371) may play a pivotal role in the adaptation of Tibetan sheep to the hypoxic conditions of the plateau. In conclusion, this study expands the existing database of lncRNAs and proteins in Tibetan sheep, and these findings may serve as a reference for the prevention of altitude sickness in humans.

Extreme precipitation stable isotopic compositions reveal unexpected summer monsoon incursions in the Qilian Mountains

Isotope composition and moisture sources of precipitation are important for understanding water cycles and reconstructing paleoclimate. Based on 15-years' precipitation stable Isotope composition (δ18O and δ2H) from four stations of the Qilian Mountains, we found unique δ18O and δ2H features associated with the incursion of the summer monsoon over the Qilian Mountains, northwestern China. In 12 of the 15 years, similar seasonal variations of δ18O and δ2H confirmed a dominant source of moisture from Westerly circulation, and higher intercepts of the local meteoric water line (LMWL) indicated strong recycling of continental moisture. However, in August 2016 and 2018, extremely low slopes and intercepts of the LMWL, and more negative δ18O and δ2H revealed substantial contributions of the Asian summer monsoon to precipitation of the Qilian Mountains, with extremely heavy precipitation in August 2016. The column moisture flux, land-sea thermal contrast, correlations of precipitation δ18O with East Asian Summer Monsoon Index and Westerlies Index, HYSPLIT modeling results and precipitation δ18O along backward trajectories confirmed incursions of the summer monsoon in August 2016 and 2018. Our redefining of the boundary of the summer monsoon region confirmed the summer monsoon incursion zone can extend to the west of longitude 96°E and north of latitude 40°N in strong monsoon years, corresponding to boundaries of monsoon incursions in the mid-Holocene. Temperature correlated with precipitation δ18O at monthly and shorter time scales, but not for whole seasons or at yearly scale, revealing that summer monsoon incursions are therefore more likely than changing temperature to explain the multi-year cycles in the Qilian Mountains ice archives. Continent-scale shifts in atmospheric circulation strongly influence water resources in the Qilian mountains, and may change in frequency as climate warms. This study therefore has important implications for understanding water resources in the Qilian mountains in the past and into the future.

Sediment geochemical records of water quality deterioration in lake Jiren, a remote alpine lake on the southeastern margin of the Tibetan Plateau

Limited human activities in catchments make remote alpine lakes valuable sites for studying the evolution of lake environments in response to climate change and atmospheric deposition; however, this issue remains rarely studied owing to the scarcity of monitoring data. In this study, water quality evolution in Lake Jiren, a remote alpine lake on the southeastern margin of the Tibetan Plateau, over the past two centuries was reconstructed through geochemical analyses of aliphatic hydrocarbons, major and trace elements, and organic matter (OM) pyrolysis products in a dated sediment core, and the associated drivers were identified by temporally comparing the geochemical results with document records. All geochemical data demonstrated that the lake water remained relatively pure until 1947, after which the n-alkane and αβ-hopane proxies indicated eutrophication and petroleum contamination. The OM pyrolysis proxy hydrocarbon index indicated more eutrophic conditions after 1957. Concurrently, hypolimnetic deoxygenation increased, as indicated by redox-sensitive proxies, such as the enrichment factors (EFs) of molybdenum (Mo). These proxies recorded further intensification of deoxygenation after 1976. The EFs for other trace elements indicated cadmium contamination after 1967. The greater anthropogenic emissions of reactive nitrogen, petroleum products, and heavy metals in East and South Asia since approximately 1950 and the subsequent atmospheric transport of these materials to the lake might be the basic driver of water quality deterioration. Eutrophication induced by nitrogen deposition was responsible for increased hypolimnetic deoxygenation by enhancing phytoplankton productivity and OM input. The further intensification of deoxygenation was attributed to climate warming since the 1970s, as prolonged water column stratification under this condition decreased oxygen input from the epilimnion to the lake bottom. These findings may be beneficial for understanding the natural and anthropogenic effects on the water quality of alpine lakes and help in the environmental management of Lake Jiren and other alpine lakes.

Dust dominates glacier darkening across majority of the Tibetan Plateau based on new measurements

Rapid retreat and darkening of most glaciers in the Tibetan Plateau (TP) are enhanced by the deposition of light-absorbing particles (LAPs). Here, we provided new knowledge on the estimation of albedo reduction caused by black carbon (BC), water-insoluble organic carbon (WIOC), and mineral dust (MD), based on a comprehensive study of snowpit samples from ten glaciers across the TP collected in the spring of 2020. According to the albedo reductions caused by the three LAPs, the TP was divided into three sub-regions: the eastern and northern margins, Himalayas and southeastern TP, and western to inner TP. Our findings indicated that MD had a dominant role in causing snow albedo reductions across the western to inner TP, with comparable effects to WIOC but stronger effects than BC in the Himalayas and southeastern TP. BC played a more important role in the eastern and northern margins of the TP. In conclusion, the findings of this study emphasize not only the important role of MD in glacier darkening across majority of the TP but also the influence of the WIOC in enhancing glacier melting which indicates the dominant contribution of non-BC components in the LAP-related glacier melting of the TP.

Autumn migration of black-necked crane (Grus nigricollis) on the Qinghai-Tibetan and Yunnan-Guizhou plateaus

Despite previous research efforts, the majority migration routes of the black-necked cranes (Grus nigricollis) have remained veiled. In this study, we utilized satellite telemetry data from 45 cranes between 2015 and 2021 to unveil critical insights. Our results revealed 11 distinct autumn migration routes and one sedentary flock, of which eight routes and the sedentary flock were previously undocumented. Our findings highlighted the remarkable diversity in the migration routes of black-necked cranes, especially in terms of migration orientations, spatial-temporal patterns, and altitudinal movement patterns. Cranes breeding on the eastern, northern, and central Qinghai-Tibetan Plateau migrated southward, while those on the northern slopes of the Himalayas migrated eastward, westward, northward, or opted to remain sedentary. Moreover, we expanded the known range of migration distances to 84-1520 km at both ends (excluding sedentary individuals) and identified two long-term (Da Qaidam and Chaka) and one short-term (Gyatong grassland) stopover sites. Furthermore, our study revealed that the breeding colonies in the Qilian Mountains on the northeastern Qinghai-Tibetan Plateau utilized long-term stopover sites before embarking on significant altitude ascent, while other flocks displayed more urgent migration patterns, preferring to roost only at night. By unveiling the near-complete autumn migration routes of black-necked cranes, our research has contributed to discovering the critical habitats and connectivity among various breeding colonies, which is instrumental in developing effective seasonal conservation plans.

Genomic evidence reveals intraspecific divergence of the hot-spring snake (Thermophis baileyi), an endangered reptile endemic to the Qinghai-Tibet plateau

Understanding how and why species evolve requires knowledge on intraspecific divergence. In this study, we examined intraspecific divergence in the endangered hot-spring snake (Thermophis baileyi), an endemic species on the Qinghai-Tibet Plateau (QTP). Whole-genome resequencing of 58 sampled individuals from 15 populations was performed to identify the drivers of intraspecific divergence and explore the potential roles of genes under selection. Our analyses resolved three groups, with major intergroup admixture occurring in regions of group contact. Divergence probably occurred during the Pleistocene as a result of glacial climatic oscillations, Yadong-Gulu rift, and geothermal fields differentiation, while complex gene flow between group pairs reflected a unique intraspecific divergence pattern on the QTP. Intergroup fixed loci involved selected genes functionally related to divergence and local adaptation, especially adaptation to hot spring microenvironments in different geothermal fields. Analysis of structural variants, genetic diversity, inbreeding, and genetic load indicated that the hot-spring snake population has declined to a low level with decreased diversity, which is important for the conservation management of this endangered species. Our study demonstrated that the integration of demographic history, gene flow, genomic divergence genes, and other information is necessary to distinguish the evolutionary processes involved in speciation.

Importance of precipitation and dust storms in regulating black carbon deposition on remote Himalayan glaciers

Black carbon (BC) can be transported over long distances and is an important trigger of climate warming and glacier melting at remote high mountains and polar regions. It is normally assumed that the variation of BC flux in remote regions is dominated by its emissions. However, after a comprehensive investigation of potential influencing factors on temporal variations of BC from ice cores of the Himalayas, this short communication shows that in addition to BC emissions, contributions from dust storms and precipitation are also important (up to 56% together) in regulating the variation of BC deposition flux and concentrations derived from remote Himalayan ice core measurements. Therefore, besides BC emissions, the influence of precipitation and BC transported by dust storms should also be considered to better quantify the lifetime and behavior of BC during its long-range transport from source to sink regions as well as to quantify the climatic effects of BC over remote Himalayan glaciers.

Synergistic effects of climate warming and atmospheric nutrient deposition on the alpine lake ecosystem in the south-eastern Tibetan Plateau during the Anthropocene

Alpine lakes on the Tibetan Plateau are highly sensitive to global change and have been recognized as the sentinel of climate warming. However, anthropogenic impacts in populated area are migrating to these remote areas via transporting particulate nutrients by atmospheric deposition. Whether warming and nutrient deposition would impose additive or synergistic effects on the lake ecosystem remains largely unknown. Here, we present multi-proxy (sediment pigment and geochemistry) records during the past two centuries at the Cuoqia Lake in the southeast Tibetan Plateau. We found that the lake exhibited rapid ecological changes since 1980 AD characterized by an increase in primary productivity due to algal proliferation, with more rapid growth of green algae and diatoms. These findings are in concert with many other lakes (e.g., Moon Lake and Shade Co) in the same area, suggesting a consistent pattern of ecosystem evolution at the region scale. Statistical analyses suggested that nutrient deposition and climate warming were strongly associated with the variations in primary productivity and algae composition, exerting both individual and interactive effects. In addition, scenario analyses with a well-established process-based ecosystem model further revealed that the two factors not only individually, but also synergistically promoted the algal proliferation and community succession. Such synergy is evident in that the effect of lake warming would be more pronounced under higher nutrient deposition scenario, which is potentially due to higher temperature-driven mineralization in warmer conditions, and higher efficiency of nutrient utilization under enhanced light availability attributing to declining ice thickness and duration in cold seasons. Overall, our study proposes the existence and quantifies the synergistic impacts of climate warming and anthropogenic activities in driving the ecological changes in remote alpine lakes on the Tibetan Plateau. The lake ecological consequences driven by individual factor would be worsen by such synergy, so that we cannot predict the lake ecosystem trajectory in the future based on each factor separately, and more efforts than previously expected would be needed for the lake restoration and management.

Environmental significance of atmospheric nitrogen deposition in the transition zone between the Tibetan Plateau and arid region

The ecological effect of atmospheric N deposition has become a hot research point along with intensive human activities and global climatic change. As the transition zone between the Tibetan Plateau and the arid region, the Qilian Mountains are important ecological barriers and source regions of inland rivers in northwest China. However, the quantification of N deposition in the transition zone between the Tibetan Plateau (TP) and the arid region remains unclear, primarily due to the lack of in situ measurements. Hence, an observational study was conducted on the Qilian Mountains, and precipitation data were collected. Approximately 1382 samples were collected and analyzed regarding their characteristics and environmental effects of the atmospheric N wet deposition. The annual wet deposition of atmospheric N was 10.05 kg/hm², and showed a decreasing trend from the south to the north of the Qilian Mountains. NO₃^--N deposition was the main form of wet deposition of atmospheric N on the Qilian Mountains, accounting for 73.83% of the DIN deposition. Additionally, altitude, meteorological factors, and ecosystem types were found to influence the wet deposition of atmospheric N. The contribution of NO₃^--N to the wet deposition of atmospheric N in meadows, forests, grasslands, farmlands, and towns was 48.38%, 71.55%, 77.54%, 69.61%, and 82.84%, respectively. This study provides a scientific basis for the effective management and sustainable development of environmental protection in the transition zone between the TP and the arid region. The results showed that relevant policies, as well as scientific and governmental measures, could contribute to reducing N deposition effectively. However, the further mitigation measures should be proposed and strictly enforced.

A Tibetan ice core covering the past 1,300 years radiometrically dated with 39Ar

Ice cores from alpine glaciers are unique archives of past global and regional climate conditions. However, recovering climate records from these ice cores is often hindered by the lack of a reliable chronology, especially in the age range of 100 to 500 anni (a) for which radiometric dating has not been available so far. We report on radiometric ³⁹Ar dating of an ice core from the Tibetan Plateau and the construction of a chronology covering the past 1,300 a using the obtained ³⁹Ar ages. This is made possible by advances in the analysis of ³⁹Ar using the laser-based detection method atom trap trace analysis, resulting in a twofold increase in the upper age limit of ³⁹Ar dating. By measuring the anthropogenic ⁸⁵Kr along with ³⁹Ar we quantify and correct modern air contamination, thus removing a major systematic uncertainty of ³⁹Ar dating. Moreover, the ⁸⁵Kr data for the top part of the ice core provide information on firn processes, including the age difference between the ice and its enclosed gas. This first application of ³⁹Ar and ⁸⁵Kr to an ice core facilitates further ice cores from nonpolar glaciers to be used for recovering climate records of the Common Era, a period including pronounced anomalies such as the Little Ice Age and the Medieval Warm Period.

Protracted Indian monsoon droughts of the past millennium and their societal impacts

Protracted droughts lasting years to decades constitute severe threats to human welfare across the Indian subcontinent. Such events are, however, rare during the instrumental period (ca. since 1871 CE). In contrast, the historic documentary evidence indicates the repeated occurrences of protracted droughts in the region during the preinstrumental period implying that either the instrumental observations underestimate the full spectrum of monsoon variability or the historic accounts overestimate the severity and duration of the past droughts. Here we present a temporally precise speleothem-based oxygen isotope reconstruction of the Indian summer monsoon precipitation variability from Mawmluh cave located in northeast India. Our data reveal that protracted droughts, embedded within multidecadal intervals of reduced monsoon rainfall, frequently occurred over the past millennium. These extreme events are in striking temporal synchrony with the historically documented droughts, famines, mass mortality events, and geopolitical changes in the Indian subcontinent. Our findings necessitate reconsideration of the region's current water resources, sustainability, and mitigation policies that discount the possibility of protracted droughts in the future.

Comparative chloroplast genome and transcriptome analysis on the ancient genus Isoetes from China

Isoetes is a famous living fossil that plays a significant role in the evolutionary studies of the plant kingdom. To explore the adaptive evolution of the ancient genus Isoetes from China, we focused on Isoetes yunguiensis (Q.F. Wang and W.C. Taylor), I. shangrilaensis (X. Li, Y.Q. Huang, X.K. Dai & X. Liu), I. taiwanensis (DeVol), I. sinensis (T.C. Palmer), I. hypsophila_GHC (Handel-Mazzetti), and I. hypsophila_HZS in this study. We sequenced, assembled, and annotated six individuals' chloroplast genomes and transcriptomes, and performed a series of analyses to investigate their chloroplast genome structures, RNA editing events, and adaptive evolution. The six chloroplast genomes of Isoetes exhibited a typical quadripartite structure with conserved genome sequence and structure. Comparative analyses of Isoetes species demonstrated that the gene organization, genome size, and GC contents of the chloroplast genome are highly conserved across the genus. Besides, our positive selection analyses suggested that one positively selected gene was statistically supported in Isoetes chloroplast genomes using the likelihood ratio test (LRT) based on branch-site models. Moreover, we detected positive selection signals using transcriptome data, suggesting that nuclear-encoded genes involved in the adaption of Isoetes species to the extreme environment of the Qinghai-Tibetan Plateau (QTP). In addition, we identified 291-579 RNA editing sites in the chloroplast genomes of six Isoetes based on transcriptome data, well above the average of angiosperms. RNA editing in protein-coding transcripts results from amino acid changes to increase their hydrophobicity and conservation in Isoetes, which may help proteins form functional three-dimensional structure. Overall, the results of this study provide comprehensive transcriptome and chloroplast genome resources and contribute to a better understanding of adaptive evolutionary and molecular biology in Isoetes.

Physiology and Transcriptomics Analysis Reveal the Contribution of Lungs on High-Altitude Hypoxia Adaptation in Tibetan Sheep

The Tibetan sheep is an indigenous species on the Tibetan plateau with excellent adaptability to high-altitude hypoxia and is distributed at altitudes of 2500–5000 m. The high-altitude hypoxia adaptation of Tibetan sheep requires adaptive reshaping of multiple tissues and organs, especially the lungs. To reveal the mechanisms of adaptation at the tissue and molecular levels in the lungs of Tibetan sheep under hypoxic conditions at different altitudes, we performed light and electron microscopic observations, transcriptomic sequencing, and enzyme-linked immunosorbent assay studies on the lungs of Tibetan sheep from three altitudes (2500, 3500, and 4500 m). The results showed that in addition to continuous increase in pulmonary artery volume, thickness, and elastic fiber content with altitude, Tibetan sheep increase the hemoglobin concentration at an altitude of 3500 m, while they decrease the Hb concentration and increase the surface area of gas exchange and capacity of the blood at an altitude of 4500 m. Other than that, some important differentially expressed genes related to angiogenesis (FNDC1, HPSE, and E2F8), vasomotion and fibrogenesis (GJA4, FAP, COL1A1, COL1A2, COL3A1, and COL14A1), and gas transport (HBB, HBA1, APOLD1, and CHL1) were also identified; these discoveries at the molecular level explain to some extent the physiological findings. In conclusion, the lungs of Tibetan sheep adopt different strategies when adapting to different altitudes, and these findings are valuable for understanding the basis of survival of indigenous species on the Tibetan plateau.

Overestimation of anthropogenic contribution of heavy metals in precipitation than those of aerosol samples due to different treatment methods

Due to increased anthropogenic activities in recent decades, many heavy metal elements have been emitted into the atmosphere and transported to remote regions. The Enrichment factors (EFs) is a normally used method for evaluating the source of heavy metal elements. However, because of some flaws of this method (e.g., higher solubility of heavy metals elements than reference elements in dilute acid), the anthropogenic contributions of some heavy metal elements in the precipitation sample were overestimated. To address this issue, EFs of heavy metal elements of aerosol, precipitation and snowpit samples in a typical remote area of the Tibetan Plateau (TP) were compared. The results showed that the EF values of many heavy metal elements in precipitation and snowpit samples were close to that of aerosol samples treated with dilute acid but usually much higher than those of totally dissolved aerosol samples. Moreover, EF values of most heavy metal elements in the ice core at the margin of the TP were higher than those at central TP, indicating that signal of long-range transport anthropogenic emitted heavy metal elements is weak and may be covered by natural mineral dust sources at glacier region. Therefore, the threshold EF values for determining anthropogenic sources of heavy metal elements in precipitation and ice core samples should be higher than those of aerosols. This study provides new knowledge on investigating anthropogenic sources of heavy metals in precipitation samples at both the TP and other regions of the world.

Different patterns and origins between northwestern and southeastern Tibetan ice core glaciochemical records over the past century

Atmospheric circulation systems differ between the northern and southern Tibetan Plateau (TP) and are characterized by prevailing westerly winds and the Indian monsoon, respectively. This leads to spatial differences between glaciochemical records in the northwestern and southeastern TP. We compared the spatial differences in major soluble ion concentrations (Ca²⁺, SO₄^2-, NO₃^-, NH₄⁺, Cl^-, Na⁺, K⁺, and Mg²⁺) during the last century in the Aru (northwestern TP) and East Rongbuk (ER; southeastern TP) ice cores. Ca²⁺ exhibited the largest difference between the ice cores (2371 ppb in the Aru ice core and 65 ppb in the ER ice core), indicating that crustal processes were more dominant in the Aru ice core. NH₄⁺ accounted for 17% of the total ion concentration in the ER ice core but only 3% in the Aru ice core, which may be related to the Indian monsoon traveling over NH₃ emission zones in southern Asia. The major soluble ion concentrations exhibited decreasing trends in the Aru ice core but increasing trends in the ER ice core (P < 0.01). Empirical orthogonal function and backward trajectory analyses indicated that the major soluble ions in the Aru ice core originated from crustal sources in central Asia; those in the ER ice core had crustal, anthropogenic, and oceanic sources from southern Asia. The results from the Aru ice core suggest that dust events and enhanced prevailing westerly winds promoted the deposition of dust aerosols from the Taklamakan Desert and arid and semi-arid regions of central Asia. Contrastingly, the results from the ER ice core suggest that the Indian monsoon transported crustal and anthropogenic sources from southern Asia and oceanic sources from the Bay of Bengal and Arabian Sea. This study contributes to the comprehensive understanding of the differences in glaciochemical records and their causes between the northwestern and southeastern TP.

Sex differences in rumen fermentation and microbiota of Tibetan goat

BACKGROUND

The gut microbiota play an important role in maintaining host metabolism, the immune system and health, while sex, genotype, diet and health have specific effects on the composition of the gut microbiota. Therefore, to explore the sex differences in the structure and function of rumen microbiota in Tibetan goats, herein we analyzed sex differences in rumen fermentation parameters, rumen microbiota and the expression of genes related to VFA transport in Tibetan goats.

RESULTS

The results showed that the contents of acetic acid and propionic acid in the rumen of TGM (Tibetan goat male) were significantly higher than those in TGFm (Tibetan goat female) (P < 0.05), and total VFAs was significantly higher in TGM than TGFm (P < 0.05). Expression of the VFA transport-related genes DRA, AE2, MCT-1, NHE1, and NHE2 in the rumen epithelium of TGFm was significantly higher than that in TGM. Analysis of the composition and structure of the rumen microbiota revealed significant sex differences. At the phylum level, Firmicutes and Bacteroidetes were the dominant phyla in Tibetan goats. In addition, Fibrobacteres and Spirochaetes had significantly greater relative abundances in TGFm than in TGM (P < 0.05). At the genus level, the relative abundance of Fibrobacter, Ruminococcus_1 and Pyramidobacter was significantly higher in TGFm than in TGM (P < 0.05). The functional prediction results showed that replication, recombination and repair, RNA processing and modification were mainly enriched in TGFm (P < 0.05).

CONCLUSIONS

Correlation analysis revealed significant associations of some rumen microbiota with the fermentation product VFAs and VFA transport-related genes. We concluded that yearling TGM and TGFm have distinct fermentation and metabolism abilities when adapting to the plateau environment, which provides a certain sex reference basis for Tibetan goat adaptation to the plateau environment.

Variations in HIF-1α Contributed to High Altitude Hypoxia Adaptation via Affected Oxygen Metabolism in Tibetan Sheep

Simple Summary

Hypoxia-inducible factors (HIFs) play an important role in the adaptation of animals to high-altitude hypoxia. In high-altitude indigenous species, variation in the hypoxia-inducible factor-1 alpha (HIF-1α) gene has been reported in Tibetans, yaks and Tibetan horses, but has not been investigated in Tibetan sheep, and is not known if it might affect high-altitude hypoxia adaptation in these sheep. In this study, Kompetitive Allele-Specific PCR (KASP) was used for genotyping of ovine HIF-1α and investigated the effect of variation in HIF-1α on the high-altitude hypoxia adaptation of Tibetan sheep. The results suggest that ovine HIF-1α variants may promote the ability of oxygen utilization in Tibetan sheep and it may serve as a genetic marker for improving high-altitude hypoxia adaptability.

Abstract

The Tibetan sheep is an indigenous species of the Tibetan plateau and has been well adapted to high-altitude hypoxia. In comparison to lowland sheep breeds, the blood gas indicators have changed and the HIFs signaling pathway is activated in Tibetan sheep. These phenotypic and genetic alterations in Tibetan sheep are thought to be an important basis for adaptation to high-altitude hypoxia and variation in genes encoding the subunits that make up HIFs, such as HIF-1α can affect blood gas indicators. In this study, exons 9, 10, 12 of the HIF-1α gene were sequenced to find variations and 3 SNPs were detected, and these 3 SNPs were genotyped by KASP in 341 Hu sheep and 391 Tibetan sheep. In addition, 197 Hu sheep, 160 Tibetan sheep and 12 Gansu alpine merino sheep were used for blood gas indicators analysis. The results showed significant differences between the blood gas indicators of high-altitude breeds (Tibetan sheep and Gansu alpine merino sheep) and low-altitude breeds (Hu sheep), implying that the differences in blood gas indicators are mainly caused by differences in altitude. The haplotype combinations H2H3 and H1H3 were more frequent in the Tibetan sheep population, H2H3 increases O₂ carrying capacity by increasing hematocrit and hemoglobin concentrations; H1H3 makes O₂ dissociate more readily from oxyhemoglobin by decreasing partial pressure of oxygen and oxygen saturation. These results suggest that variants at the HIF-1α promote the ability of oxygen utilization in Tibetan sheep, which may underpin the survival and reproduction of Tibetan sheep on the Tibetan plateau.

A case study using 2019 pre-monsoon snow and stream chemistry in the Khumbu region, Nepal

This case study provides a framework for future monitoring and evidence for human source pollution in the Khumbu region, Nepal. We analyzed the chemical composition (major ions, major/trace elements, black carbon, and stable water isotopes) of pre-monsoon stream water (4300-5250 m) and snow (5200-6665 m) samples collected from Mt. Everest, Mt. Lobuche, and the Imja Valley during the 2019 pre-monsoon season, in addition to a shallow ice core recovered from the Khumbu Glacier (5300 m). In agreement with previous work, pre-monsoon aerosol deposition is dominated by dust originating from western sources and less frequently by transport from southerly air mass sources as demonstrated by evidence of one of the strongest recorded pre-monsoon events emanating from the Bay of Bengal, Cyclone Fani. Elevated concentrations of human-sourced metals (e.g., Pb, Bi, As) are found in surface snow and stream chemistry collected in the Khumbu region. As the most comprehensive case study of environmental chemistry in the Khumbu region, this research offers sufficient evidence for increased monitoring in this watershed and surrounding areas.

Scientometric Analysis-Based Review for Drought Modelling, Indices, Types, and Forecasting Especially in Asia

An extended drought period with low precipitation can result in low water availability and issues for humans, animals, and plants. Drought forecasting is critical for water resource development and management as it helps to reduce negative consequences. In this study, scientometric analysis and manual comprehensive analysis on drought modelling and forecasting are used. A scientometric analysis is used to determine the current research trend using bibliometric data and to identify relevant publication field sources with the most publications, the most frequently used keywords, the most cited articles and authors, and the countries that have made the greatest contributions to the field of water resources. This paper also tries to provide an overview of water issues, such as drought classification, drought indices, historical droughts, and their impact on Asian countries such as China, Pakistan, India, and Iran. There have been many models established for this purpose and choosing the appropriate model for study is a long procedure for researchers. An appropriate, comprehensive, pedagogical study of model ideas and historical implementations would benefit researchers by helping them to avoid overlooking viable model options, thus reducing their time spent on the topic. As a result, the goal of this paper is to review drought-forecasting approaches and recommend the best models for the Asian region. The models are divided into four categories based on their mechanisms: Regression analysis, stochastic modelling, machine learning, and dynamic modelling. The basic concepts of each approach in terms of the model’s historical use, benefits, and limitations are explained. Finally, prospects for future drought research in Asia are discussed as well as potential modelling techniques.

Genomic and functional evidence reveals convergent evolution in fishes on the Tibetan Plateau

High-altitude environments are strong drivers of adaptive evolution in endemic organisms. However, little is known about the genetic mechanisms of convergent adaptation among different lineages, especially in fishes. There are three independent fish groups on the Tibetan Plateau: Tibetan Loaches, Schizothoracine fishes and Glyptosternoid fishes; all are well adapted to the harsh environmental conditions. They represent an excellent example of convergent evolution but with an unclear genetic basis. We used comparative genomic analyses between Tibetan fishes and fishes from low altitudes and detected genomic signatures of convergent evolution in fishes on the Tibetan Plateau. The Tibetan fishes exhibited genome-wide accelerated evolution in comparison with a control set of fishes from low altitudes. A total of 368 positively selected genes were identified in Tibetan fishes, which were enriched in functional categories related to energy metabolism and hypoxia response. Widespread parallel amino acid substitutions were detected among the Tibetan fishes and a subset of these substitutions occurred in positively selected genes associated with high-altitude adaptation. Functional assays suggested that von Hippel-Lindau (VHL) tumour suppressor genes from Tibetan fishes enhance hypoxia-inducible factor (HIF) activity convergently under hypoxia compared to low-altitude fishes. The results provide genomic and functional evidence supporting convergent genetic mechanisms for high-altitude adaptation in fishes on the Tibetan Plateau.

Selenium Yeast Dietary Supplement Affects Rumen Bacterial Population Dynamics and Fermentation Parameters of Tibetan Sheep (Ovis aries) in Alpine Meadow

Selenium (Se) deficiency is a widespread and seasonally chronic phenomenon observed in Tibetan sheep (Ovis aries) traditionally grazed on the Qinghai-Tibet Plateau (QTP). Effects of the dietary addition of Se-enriched yeast (SeY) on the bacterial community in sheep rumen and rumen fermentation were evaluated with the aim of gaining a better understanding of the rumen prokaryotic community. Twenty-four yearling Tibetan rams [initial average body weight (BW) of 31.0 ± 0.64 kg] were randomly divided into four treatment groups, namely, control (CK), low Se (L), medium Se (M), and high Se (H). Each group comprised six rams and was fed a basic diet of fresh forage cut from the alpine meadow, to which SeY was added at prescribed dose rates. This feed trial was conducted for over 35 days. On the final day, rumen fluid was collected using a transesophageal sampler for analyzing rumen pH, NH3-N content, volatile fatty acid (VFA) level, and the rumen microbial community. Our analyses showed that NH3-N, total VFA, and propionate concentrations in the M group were significantly higher than in the other groups (P < 0.05). Both the principal coordinates analysis (PCoA) and the analysis of similarities revealed that the bacterial population structure of rumen differed among the four groups. The predominant rumen bacterial phyla were found to be Bacteroidetes and Firmicutes, and the three dominant genera in all the samples across all treatments were Christensenellaceae R7 group, Rikenellaceae RC9 gut group, and Prevotella 1. The relative abundances of Prevotella 1, Rikenellaceae RC9 gut group, Ruminococcus 2, Lachnospiraceae XPB1014 group, Carnobacterium, and Hafnia-Obesumbacterium were found to differ significantly among the four treatment groups (P < 0.05). Moreover, Tax4fun metagenome estimation revealed that gene functions and metabolic pathways associated with carbohydrate and other amino acids were overexpressed in the rumen microbiota of SeY-supplemented sheep. To conclude, SeY significantly affects the abundance of rumen bacteria and ultimately affects the rumen microbial fermentation.

Climatic, land cover, and anthropogenic controls on dissolved organic matter quantity and quality from major alpine rivers across the Himalayan-Tibetan Plateau

Alpine rivers in mountainous regions are crucial not only for land-ocean transfer of chemical species and sediments, but also for water, food, and energy security. Here, we examined dissolved organic matter (DOM) from the major alpine waters on the Tibetan Plateau. Our results revealed a decreasing trend of DOM quantity juxtaposed to an increasing trend of aromaticity from the northern to southern plateau. This is potentially caused by a general decreasing gradient of dust load combined with an increasing gradient of precipitation and vegetation from the NW to SE plateau. Furthermore, most proglacial streams and smaller tributaries were found to be relatively dominated by tyrosine-like fluorescent DOM from glaciers. In contrast, most main stems of rivers and tributaries within larger catchment basins were more controlled by humic-like fluorescent DOM from terrestrial origins. Condensed aromatics accounts for 14-21% of molecular formulas for riverine DOM, much higher than the world's average of ~11%, which indicated anthropogenic black soot pollution. In addition, there is a higher level of DOM amount in the monsoon season than in winter, and DOM characteristics varied more widely (dissolved organic carbon concentration: 0.2-37 mg-C L^-1, Fluorescence Index: 1.2-1.8) on the Tibetan Plateau in comparison to other global alpine watersheds. This suggests heterogeneous land cover, anthropogenic, and climatic factors at play, which is reflected in DOM quantity and quality, over the highest plateau on Earth.

Plateau river research: spatial-temporal variations of δ18O and δd in the water of the Yarlung Tsangpo River and their controlling factors

Stable isotope technology has been widely used to trace sources and evolution of water bodies, relationships between different water bodies and pollution sources. Based on δ¹⁸O and δD data from the Yarlung Tsangpo River in 2017, this paper analyzes the composition characteristics of δ¹⁸O and δD in the river water during the low-flow, high-flow and normal-flow seasons of the entire Yarlung Tsangpo River and further reveals the spatial evolution and influencing factors. The results show that the values of δ¹⁸O, δD and d-excess were different in time and space. The δ¹⁸O, δD and d-excess values of the Yarlung Tsangpo River in the low-flow season were significantly higher than in the high-flow season. This was mainly due to weak evaporation enrichment and precipitation supply effects on the river water during the wet season. From the perspective of season change, the d-excess in the low-season is significantly higher than in the high-flow season and the normal-flow season; from the perspective of spatial change, the d-excess shows the same spatial variation trend as the δ¹⁸O, which first decreases and then increases. Based on the investigation of δ18O and δD in the main and Branch rivers of the Yarlung Tsangpo River Basin, it was found that the upper reaches of the basin were mainly supplied by snowmelt, the lower reaches were mainly supplied by rainfall.

Divergence in ecosystem carbon fluxes and soil nitrogen characteristics across alpine steppe, alpine meadow and alpine swamp ecosystems in a biome transition zone

Alpine ecosystem carbon cycling is sensitive to climate change, particularly in the transition zones between biomes. Soil nitrogen conditions, including the ammonium to nitrate (NH₄⁺/NO₃^-) ratio, regulate ecosystem carbon uptake by coupling carbon‑nitrogen cycle. The largest alpine pasture on Earth is distributed on the Tibetan Plateau, where alpine biome transition zones are also widely distributed. However, it is largely unknown how the soil NH₄⁺/NO₃^- ratio and net ecosystem CO₂ exchange vary among vegetation types in the alpine biome transition zones due to a lack of in situ field observations. Here, we investigated soil NH₄⁺/NO₃^- ratio and ecosystem carbon fluxes across alpine steppe, alpine meadow and alpine swamp ecosystems in a biome transition zone on the central Tibetan Plateau. The results showed that soil NH₄⁺/NO₃^- ratio was lowest in the alpine steppe (driest environment), which had the highest soil pH, and highest in the alpine swamp (wettest environment), which had the lowest soil pH. We proposed a theoretical framework describing how soil moisture regulates soil NH₄⁺/NO₃^- ratio by altering both the denitrification process and soil pH. We further found that the growing season average net ecosystem CO₂ exchange for the alpine steppe, alpine meadow and alpine swamp was -1.46, -1.90 and -5.43 μmol m^-2 s^-1, respectively. This divergence in net ecosystem CO₂ exchange across the three grasslands is primarily explained by divergence in gross ecosystem photosynthesis, rather than ecosystem respiration. The air temperature sensitivity of ecosystem respiration (Q₁₀) for the alpine steppe, alpine meadow and alpine swamp was 1.73 ± 0.05, 1.44 ± 0.03 and 2.43 ± 0.45, respectively. Our study highlights large differences in both soil nutrient and ecosystem carbon uptake across different vegetation types in an alpine biome transition zone. More in situ investigations in various biome transition zones are urgently needed to quantitatively understand the spatial pattern of alpine ecosystem carbon‑nitrogen cycling processes.

Disturbance mechanisms of lacustrine organic carbon burial: Case study of Cuopu Lake, Southwest China

Lakes are important organic carbon (OC) traps in the global carbon cycle. Recent studies have shown that the rate of OC burial in lacustrine sediments is influenced by factors such as climate change, land-use change, and eutrophication. In this study, we use multiproxy methods to reveal the mechanisms of lacustrine sediment OC burial in an alpine lake (Cuopu Lake), in southwest China. Combined with the dating from ²¹⁰Pb_ex and n-alkanes distribution analysis using the Positive Matrix Factorization model, the sedimentary history was divided into five stages: religious activity (the 1840s-1880s), earthquake (the 1880s-1910s), garrison (the 1910s-1960s), transition (the 1960s-1990s), and ecotourism (the 1990s-2010s). During the earthquake stage, OC burial was dominated by terrestrial solids (>40%) and co-precipitated algae (>30%), with a rapid deposition rate (>4 mm a^-1) and low OC concentration (<4 mg g^-1). During the other stages, when the level of disturbance was relatively low, a change in nutrient conditions either promoted or inhibited plant growth, which influenced the type of buried OC. The contribution of OC derived from combustion sources varied from stage to stage. Severe anthropogenic disturbances have led to a significant increase in nutritional levels in the lake water, leading to an increase in the OC burial rate. Climate change, which leads to changes in temperature and rainfall, did not significantly influence OC burial, whereas nitrogen deposition (and associated ecological changes) was a significant determinant. When the general mechanism is dominant, the total nitrogen to inorganic phosphorus ratio is an effective indicator of OC burial due to its selective promotion of different plant types. In conclusion, our results suggest that lacustrine sediment OC burial is closely linked to physical and anthropogenic factors in Cuopu Lake, as well as similar montane lakes.

ENSO and Light-Absorbing Impurities and Their Impact on Snow Albedo in the Sierra Nevada de Santa Marta, Colombia

Snow albedo is an important variable in the coupled atmosphere-earth system at the global level. Moreover, studying its behavior allows us to know the state of the cryosphere. The Sierra Nevada de Santa Marta (SNSM) is a glacier area and the northernmost tropical (10.82° N, 73.75° W) region in South America. It has a height of up to 5775 m.a.sl., which is the second highest mountain in the world near the marine coast. We analyzed variations in snow albedo related to snow cover, snowfall, temperature, light-absorbing impurities such as blank carbon (BC), organic carbon (OC) and dust, and El Niño—Southern Oscillation (ENSO) phenomenon through 20 years (2000–2020). We mainly use daily data from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra and Aqua NASA satellites. Results showed through correlations that snow albedo has decreased due to Land Surface Temperature (55%, p < 0.001), a positive phase of ENSO (42%, p < 0.001) and dust (37%, p < 0.01) in the SNSM. Additionally, a dust negative effect was more evident on the southern side (up to 49%, p < 0.001) of the SNSM. Backward trajectories by the NOAA HYSPLIT model suggest that dust sources would be soil erosion in the surrounding region. Results can help recognize the influence of ENSO and dust in the glacier decrease of the SNSM.

Synergistic effects of nitrogen and CO2 enrichment on alpine grassland biomass and community structure

Global environmental change is altering the Earth's ecosystems. However, much research has focused on ecosystem-level responses, and we know substantially less about community-level responses to global change stressors. Here we conducted a 6-yr field experiment in a high-altitude (4600 m asl) alpine grassland on the Tibetan Plateau to explore the effects of nitrogen (N) addition and rising atmospheric CO₂ concentration on plant communities. Our results showed that N and CO₂ enrichment had synergistic effects on alpine grassland communities. Adding nitrogen or CO₂ alone did not alter total community biomass, species diversity or community composition, whereas adding both resources together increased community biomass, reduced species diversity and altered community composition. The observed decline in species diversity under simultaneous N and CO₂ enrichment was associated with greater community biomass and lower soil water content, and driven by the loss of species characterised simultaneously by tall stature and small specific leaf area. Our findings point to the co-limitation of alpine plant community biomass and structure by nitrogen and CO₂ , emphasising the need for future studies to consider multiple aspects of global environmental change together to gain a more complete understanding of their ecological consequences.

Seasonality of moisture supplies to precipitation over the Third Pole: a stable water isotopic perspective

This study integrated isotopic composition in precipitation at 50 stations on and around the Tibetan Plateau (TP) and demonstrated the distinct seasonality of isotopic composition in precipitation across the study period. The potential effect of water vapor isotopes on precipitation isotopes is studied by comparing the station precipitation data with extensive isotopic patterns in atmospheric water vapor, revealing the close linkage between the two. The analysis of contemporary water vapor transport and potential helps confirm the different mechanisms behind precipitation isotopic compositions in different areas, as the southern TP is more closely related to large-scale atmospheric circulation such as local Hadley and summer monsoon circulations during other seasons than winter, while the northern TP is subject to the westerly prevalence and advective moisture supply and precipitation processes. The new data presented in this manuscript also enrich the current dataset for the study of precipitation isotopes in this region and together provide a valuable database for verification of the isotope-integrated general circulation model and explanation of related physical processes.

Selection Signatures Analysis Reveals Genes Associated with High-Altitude Adaptation in Tibetan Goats from Nagqu, Tibet

Simple Summary

In the process of domestication, goats have undergone long-term artificial and natural selection, leading to differences among goat breeds and leaving different selection traces on the genome. However, the genetic components underlying high-altitude adaptation remain largely unknown. Here, we genotyped four goat breeds using the Illumina Caprine 50K single nucleotide polymorphism (SNP) Chip. One highland breed (Tibetan goat) compared with three lowland breeds (Huanghuai goat, Taihang goat and Xinjiang goat) to identify the molecular basis of high-altitude adaptation. So, we investigated selection signatures using the di statistic of four goat breeds and some genes in Tibetan goats related to high-altitude adaptation were identified. In addition, q-PCR validated the gene expression level in Tibetan goats and Huanghuai goats. This information may be valuable for the study of the genetic uniqueness of Tibetan goats and increased understanding of the hypoxic adaptation mechanism of Tibetan goats on the plateau.

Abstract

Tibetan goat is an ancient breed, which inhabits the adverse conditions of the plateaus in China. To investigate the role of selection in shaping its genomes, we genotyped Tibetan goats (Nagqu Prefecture, above 4500 m) and three lowland populations (Xinjiang goats, Taihang goats and Huanghuai goats). The result of PCA, neighbor-joining (N-J) tree and model-based clustering showed that the genetic structure between the Tibetan goat and the three lowland populations has significant difference. As demonstrated by the di statistic, we found that some genes were related to the high-altitude adaptation of Tibetan goats. Functional analysis revealed that these genes were enriched in the VEGF (vascular endothelial growth factor) signaling pathway and melanoma, suggesting that nine genes (FGF2, EGFR, AKT1, PTEN, MITF, ENPEP, SIRT6, KDR, and CDC42) might have important roles in the high-altitude adaptation of Nagqu Tibetan goats. We also found that the LEPR gene was under the strongest selection (di value = 16.70), and it could induce upregulation of the hypoxic ventilatory response. In addition, five genes (LEPR, LDB1, EGFR, NOX4 and FGF2) with high di values were analyzed using q-PCR. Among them, we found that LEPR, LDB1 and FGF2 exhibited higher expression in the lungs of the Tibetan goats; LEPR, EGFR and LDB1 exhibited higher expression in the hearts of the Huanghuai goat. Our results suggest that LEPR, LDB1, EGFR and FGF2 genes may be related to the high-altitude adaptation of the goats. These findings improve our understanding of the selection of the high-altitude adaptability of the Nagqu Tibetan goats and provide new theoretical knowledge for the conservation and utilization of germplasm resources.

Coping with extremes: convergences of habitat use, territoriality, and diet in summer but divergences in winter between two sympatric snow finches on the Qinghai-Tibet Plateau

On the Qinghai-Tibet Plateau, extreme environmental conditions have imposed intense selective pressure on the evolution of phenotypic traits of wild animals. To date, limited information is available on behavioral and ecological traits concerning niche differentiation among sympatric animals on the Qinghai-Tibet Plateau, especially during winter when the environments are most severe. Here, we studied the seasonal variations in habitat occurrence, territorial behavior, and diet in two sympatric snow finches (the white-rumped snow finch, Onychostruthus taczanowskii, WRSF; and the rufous-necked snow finch, Pyrgilauda ruficollis, RNSF) to determine convergence and divergence of ecological traits in such severe climatic conditions. Our results showed that: (i) WRSF occupied rural areas as a dominant species throughout the annual cycle while RNSF occupied the rural areas in summer and then shifted to human-occupied areas in winter and spring; (ii) WRSFs exhibited robust aggressive behavior and territoriality during winter relative to RNSFs; (iii) the diets of both species varied with the season but did not vary between species except that WRSF ate significantly more seeds but RNSF consumed more starchy material derived from human food waste during winter. Therefore, the separations in the spatial niche and territoriality between WRSF and RNSF, especially in winter, may contribute to alleviating the pressure of interspecific competition, and promoting the coexistence of the two sympatric snow finches in the extreme environments on the Qinghai-Tibet Plateau.

Cross-ecosystem nutrient subsidies in Arctic and alpine lakes: implications of global change for remote lakes

Environmental change is continuing to affect the flow of nutrients, material and organisms across ecosystem boundaries. These cross-system flows are termed ecosystem subsidies. Here, we synthesize current knowledge of cross-ecosystem nutrient subsidies between remote lakes and their surrounding terrain, cryosphere, and atmosphere. Remote Arctic and alpine lakes are ideal systems to study the effects of cross ecosystem subsidies because (a) they are positioned in locations experiencing rapid environmental changes, (b) they are ecologically sensitive to even small subsidy changes, (c) they have easily defined ecosystem boundaries, and (d) a variety of standard methods exist that allow for quantification of lake subsidies and their impacts on ecological communities and ecosystem functions. We highlight similarities and differences between Arctic and alpine systems and identify current knowledge gaps to be addressed with future work. It is important to understand the dynamics of nutrient and material flows between lakes and their environments in order to improve our ability to predict ecosystem responses to continued environmental change.

Isotopic evidence that recent agriculture overprints climate variability in nitrogen deposition to the Tibetan Plateau

The stable isotopes of nitrogen in nitrate archived in polar ice have been interpreted as reflecting a shift in reactive nitrogen sources or changes in atmospheric chemical reactivity. Here, we present a novel concentration and isotopic record of nitrate (δ¹⁵N-NO₃^-) from a central Tibetan Plateau ice core over the last ~200 years. We find that nitrate concentration increased from 6.0 ± 2.3 μeq/L (mean ± 1σ) in the preindustrial period (prior to 1900s) to 7.3 ± 2.7 μeq/L in post-1950. Over the same time period, the δ¹⁵N-NO₃^- decreased from 8.7 ± 3.7‰ to 4.2 ± 3.1‰, with much larger interannual variation in δ¹⁵N-NO₃^- during the preindustrial period. We present a useful framework for quantifying the sensitivity of the isotopic composition of atmospheric nitrate to changes in both sources and chemistry (gas and aerosol phase). After 1950, nitrogen deposition is primarily driven by fertilizer use, leading to significant increases in concentration and decreases in δ¹⁵N-NO₃^-. The large interannual variability of ice core δ¹⁵N-NO₃^- in the preindustrial reflects natural processes, namely the El Niño Southern Oscillation (ENSO) and dust events. Our results highlight a new connection between the nitrogen cycle and ENSO, and the overprinting of natural climate signals by recent anthropogenic increases in reactive nitrogen release.

Trait means predict performance under water limitation better than plasticity for seedlings of Poaceae species on the eastern Tibetan Plateau

Water availability may be altered by changes in precipitation under global climate change in alpine areas. Trait means and plasticity are important for plants in response to a changing environment. In an examination of alpine plant responses to changed water availability, and for determination of how trait means and plasticity predict the performance (e.g., biomass) of these species, seeds of ten Poaceae species from the eastern Tibetan Plateau were sown and grown in a manipulated environment during a growing season in which rainfall was removed and other climate conditions remained unchanged. Growth and leaf traits of these species were measured. We found significant effects of moderate water stress on the seedling biomass of these species; however, the responses of these species to changed water condition were strongly dependent on species identity. For example, the biomass of some species significantly decreased under moderate drought, whereas that of others were either significantly increased or unaffected. This pattern was also observed for growth and leaf traits. Overall, the alpine Poaceae species showed low plasticity of traits in response to water availability relative to reports from other areas. Notably, the results show that trait means were better correlated with the productivity than with the plasticity of traits; thus, we argue that the trait means were better predictors of performance than plasticity for alpine Poaceae species. Poaceae species in alpine areas are important for forage production and for water catchment health worldwide, and these species may face water shortage because of current and future climate change. Understanding the response of alpine Poaceae species to water availability would facilitate our ability to predict the impacts of climate change on the alpine vegetation.

Early atmospheric contamination on the top of the Himalayas since the onset of the European Industrial Revolution

Because few ice core records from the Himalayas exist, understanding of the onset and timing of the human impact on the atmosphere of the "roof of the world" remains poorly constrained. We report a continuous 500-y trace metal ice core record from the Dasuopu glacier (7,200 m, central Himalayas), the highest drilling site on Earth. We show that an early contamination from toxic trace metals, particularly Cd, Cr, Mo, Ni, Sb, and Zn, emerged at high elevation in the Himalayas at the onset of the European Industrial Revolution (∼1780 AD). This was amplified by the intensification of the snow accumulation (+50% at Dasuopu) likely linked to the meridional displacement of the winter westerlies from 1810 until 1880 AD. During this period, the flux and crustal enrichment factors of the toxic trace metals were augmented by factors of 2 to 4 and 2 to 6, respectively. We suggest this contamination was the consequence of the long-range transport and wet deposition of fly ash from the combustion of coal (likely from Western Europe where it was almost entirely produced and used during the 19th century) with a possible contribution from the synchronous increase in biomass burning emissions from deforestation in the Northern Hemisphere. The snow accumulation decreased and dry winters were reestablished in Dasuopu after 1880 AD when lower than expected toxic metal levels were recorded. This indicates that contamination on the top of the Himalayas depended primarily on multidecadal changes in atmospheric circulation and secondarily on variations in emission sources during the last 200 y.

The Atmosphere

The atmosphere is composed of nitrogen, oxygen and argon, a variety of trace gases, and particles or aerosols from a variety of sources. Reactive, trace gases have short mean residence time in the atmosphere and large spatial and temporal variations in concentration. Many trace gases are removed by reaction with hydroxyl radical and deposition in rainfall or dryfall at the Earth's surface. The upper atmosphere, the stratosphere, contains ozone that screens ultraviolet light from the Earth's surface. Chlorofluorocarbons released by humans lead to the loss of stratospheric ozone, which might eventually render the Earth's land surface uninhabitable. Changes in the composition of the atmosphere, especially rising concentrations of CO₂, CH₄, and N₂O, will lead to climatic changes over much of the Earth's surface.

Immobilization of relic anthropogenic dissolved organic matter from alpine rivers in the Himalayan-Tibetan Plateau in winter

The Tibetan Plateau is a critical ecosystem that sensitively responds to ongoing glacier shrinkage and permafrost thaw. Dissolved organic matter (DOM) in Tibetan Alpine rivers plays pivotal roles in the biogeochemical cycling of elements and nutrients at regional and even global scales, impacting water quality, downstream environments, and climate. However, little is known about the characteristics and dynamics of DOM in these watersheds. We investigated five major Himalayan rivers in the southern Tibetan Plateau, utilizing bulk dissolved organic carbon (DOC), optical properties, and molecular formulas. We found extremely low DOC and fluorescent DOM (FDOM) levels in the rivers (average DOC: 0.25-0.87 mg L^-1, FDOM: 0.02-0.05 RU) with a highly degraded molecular signature, which was enriched with heteroatomic molecular formulas (S-containing: 58-72%, N-containing: 61-86%) and condensed aromatics (31-39% vs. ∼11% in world major rivers). Further, 81-99% of the condensed aromatics was identified as dissolved black nitrogen (DBN) with multiple nitrogen atoms, typical for grassy biomass combustion. The findings highlighted potentially fast DOM remineralization leading to the release of CO₂ and enriched apparently anthropogenic condensed aromatics and heteroatomic formulas in what have been considered pristine Tibetan rivers. These findings should be considered in future biogeochemical models and ecosystem management.

Variation of δ18O in precipitation and its response to upstream atmospheric convection and rainout: A case study of Changsha station, south-central China

The results of analyses of the stable isotopes of oxygen in precipitation (δ¹⁸O_p) are presented for every rainfall event from January 2010 to December 2017 in Changsha, south-central China. Our aims were to elucidate the variations of δ¹⁸O_p on different timescales and to identify the main meteorological drivers of variations in the oxygen isotopic composition of precipitation. Results showed that there were no statistically significant and consistent negative correlations between δ¹⁸O_p and local precipitation amount on either daily or monthly timescale; however, changes in δ¹⁸O_p in Changsha responded sensitively to the variation of precipitation in the key upstream area along air mass trajectories. Year-to-year, the strongest negative lagged correlations (r') between δ¹⁸O_p and the preceding average precipitation amount varied from -0.79 to -0.63 (all significant at the 0.001 level) in the warm half-year (from April to September) of 2010-2017. However, in the cold half-year (from October to the following March), corresponding r' values varied from -0.79 to -0.38 that were all significant at the 0.001 level, except for the year 2012. These findings suggest that the amplitude of the isotopic signal was closely linked with the position and intensity of upstream rainout activity. This was supported by strong relationships between precipitation-weighted mean δ¹⁸O (δ¹⁸O_w) and average precipitation amount in the key upstream area at the monthly scale; correlation coefficients were - 0.76 and - 0.57 between 2010 and 2017 in the warm half-year and cold half-year, respectively (both significant at the 0.001 level). Results advance our understanding of the temporal variation of the stable oxygen isotopic composition of precipitation, and demonstrate that local isotopic proxy records may be influenced by upstream rainout processes.

Assessing the impact of long-term changes in climate and atmospheric deposition on a shallow alpine lake from southeast Tibet

Regional warming and atmospheric nitrogen deposition have been widely recorded to impact remote catchments and alpine lakes; however, their independent roles and interactions have rarely been identified. Here, we combined down-core analyses of sedimentary mercury (Hg) and aluminum (Al) with multiple proxies (i.e. nitrogen stable isotope, chlorophyll a pigments, diatoms) for a radiometrically-dated sediment core of an alpine lake in southeast Tibet to track the atmospheric deposition of pollutants, and to examine possible effects of climate and catchment forcing over the past three centuries. The sediment data revealed that airborne deposition of Hg was recorded from the ~1860s, with an accelerating increase in anthropogenic Hg flux since the ~1960s. A synchronous decrease in reconstructed lake-water TOC indicated that acid deposition may have affected lake-water carbon concentrations and impaired catchment export of decomposed organic matter (OM). A moderate depletion of bulk sediment δ¹⁵N started from the ~1820s, but was followed by an enriching trend after the ~1970s. This positive shift of δ¹⁵N was associated with elevated sediment OM and decreased catchment runoff of clastic materials (as inferred by Al). Sediment OM content displayed an accelerating increase from the ~1960s, with an increased input of autochthonous sources (i.e. lower bulk sediment C:N ratios), such as algae (as inferred by sedimentary chlorophyll a pigments). Meanwhile, climate warming and decreased lake-water TOC enhanced the production of algae, which was characterized by a more enriched δ¹⁵N signal than that of allochthonous OM. Furthermore, atmospheric acid deposition was significantly related to diatom assemblage changes, with an increase in acidophilous taxa. Our sediment evidence revealed the dominating impact of climate and catchment processes on lake-water chemistry and algal shifts in the context of atmospheric nitrogen deposition, and highlighted an increasing link of external forcing with in-lake processes in enriching sediment δ¹⁵N signal over the last few decades.

High-resolution climate projections for South Asia to inform climate impacts and adaptation studies in the Ganges-Brahmaputra-Meghna and Mahanadi deltas

Climate impacts and adaptation studies often use output from impact models that require data representing future climates at a resolution greater than can be provided by Global Climate Models (GCMs). This paper describes the use of Regional Climate Model (RCM) simulations to generate high-resolution future climate information for assessing climate impacts in the Ganges-Brahmaputra-Meghna (GBM) and Mahanadi deltas as part of the DECCMA project. In this study, three different GCMs (HadGEM2-ES, CNRM-CM5 and GFDL-CM3), all using a single scenario for future greenhouse forcing of the atmosphere (RCP 8.5), were downscaled to a horizontal resolution of 25 km over south Asia using the HadRM3P RCM. These three GCMs were selected based on ability to represent key climate processes over south Asia and ability to sample a range of regional climate change responses to greenhouse gas forcing. RCM simulations of temperature, precipitation, and lower level (850 hPa) atmospheric circulation in the monsoon season (June, July, August, September - JJAS) were compared with observational datasets and their respective driving GCMs to ensure large-scale consistency. Although there are some biases in the RCM simulations, these comparisons indicate that the RCMs are able to simulate realistically aspects of the observed climate of South Asia, such as the monsoon circulation and associated precipitation that are key for informing downstream impacts and adaptation studies. Simulated future temperature and precipitation changes on seasonal and daily timescales suggest increases in both temperature and precipitation across all three models during the monsoon season, with an increase in the amount of extremely heavy precipitation over the GBM and Mahanadi basins. Despite different driving conditions, these results are consistent across all three RCM simulations, providing a level of confidence in the magnitudes and spatial characteristics of temperature and precipitation projections for South Asia.

Sequence Characterization of DSG3 Gene to Know Its Role in High-Altitude Hypoxia Adaptation in the Chinese Cashmere Goat

The Tibetan cashmere goat is one of the main goat breeds used by people living in the plateau. It exhibits the distinct phenotypic characteristics observed in lowland goats, allowing them to adapt to the challenging conditions at high altitudes. It provides an ideal model for understanding the genetic mechanisms underlying high-altitude adaptation and hypoxia-related diseases. Our previous exome sequencing of five Chinese cashmere breeds revealed a candidate gene, DSG3 (Desmoglein 3), responsible for the high-altitude adaptation of the Tibetan goat. However, the whole DSG3 gene (44 kbp) consisting of 16 exons in the goat genome was not entirely covered by the exome sequencing. In this study, we resequenced all the 16 exons of the DSG3 gene in ten Chinese native goat populations. Twenty-seven SNP variants were found between the lowland and highland goat populations. The genetic distance (F_ST) of significant SNPs between the lowland and highland populations ranged from 0.42 to 0.58. By using correlation coefficient analysis, linkage disequilibrium, and haplotype network construction, we found three non-synonymous SNPs (R597E, T595I, and G572S) in exon 5 and two synonymous SNPs in exons 8 and 16 in DSG3. These mutations significantly segregated high- and low-altitude goats in two clusters, indicating the contribution of DSG3 to the high-altitude hypoxia adaptation in the Tibetan goat.

Moisture-mediated responsiveness of treeline shifts to global warming in the Himalayas

Among forest ecosystems, the alpine treeline ecotone can be considered to be a simplified model to study global ecology and climate change. Alpine treelines are expected to shift upwards in response to global warming given that tree recruitment and growth are assumed to be mainly limited by low temperatures. However, little is known whether precipitation and temperature interact to drive long-term Himalayan treeline dynamics. Tree growth is affected by spring rainfall in the central Himalayan treelines, being good locations for testing if, in addition to temperature, precipitation mediates treeline dynamics. To test this hypothesis, we reconstructed spatiotemporal variations in treeline dynamics in 20 plots located at six alpine treeline sites, dominated by two tree species (birch, fir), and situated along an east-west precipitation gradient in the central Himalayas. Our reconstructions evidenced that treelines shifted upward in response to recent climate warming, but their shift rates were primarily mediated by spring precipitation. The rate of upward shift was higher in the wettest eastern Himalayas, suggesting that its ascent rate was facilitated by spring precipitation. The drying tendency in association with the recent warming trends observed in the central Himalayas, however, will likely hinder an upslope advancement of alpine treelines and promote downward treeline shifts if moisture availability crosses a critical minimum threshold. Our study highlights the complexity of plant responses to climate and the need to consider multiple climate factors when analyzing treeline dynamics.

Atmospheric sulfur isotopic anomalies recorded at Mt. Everest across the Anthropocene

Increased anthropogenic-induced aerosol concentrations over the Himalayas and Tibetan Plateau have affected regional climate, accelerated snow/glacier melting, and influenced water supply and quality in Asia. Although sulfate is a predominant chemical component in aerosols and the hydrosphere, the contributions from different sources remain contentious. Here, we report multiple sulfur isotope composition of sedimentary sulfates from a remote freshwater alpine lake near Mount Everest to reconstruct a two-century record of the atmospheric sulfur cycle. The sulfur isotopic anomaly is utilized as a probe for sulfur source apportionment and chemical transformation history. The nineteenth-century record displays a distinct sulfur isotopic signature compared with the twentieth-century record when sulfate concentrations increased. Along with other elemental measurements, the isotopic proxy suggests that the increased trend of sulfate is mainly attributed to enhancements of dust-associated sulfate aerosols and climate-induced weathering/erosion, which overprinted sulfur isotopic anomalies originating from other sources (e.g., sulfates produced in the stratosphere by photolytic oxidation processes and/or emitted from combustion) as observed in most modern tropospheric aerosols. The changes in sulfur cycling reported in this study have implications for better quantification of radiative forcing and snow/glacier melting at this climatically sensitive region and potentially other temperate glacial hydrological systems. Additionally, the unique Δ³³S-δ³⁴S pattern in the nineteenth century, a period with extensive global biomass burning, is similar to the Paleoarchean (3.6-3.2 Ga) barite record, potentially providing a deeper insight into sulfur photochemical/thermal reactions and possible volcanic influences on the Earth's earliest sulfur cycle.