River-controlled permafrost dynamics are crucial for sediment transport, infrastructure stability, and carbon cycle, yet are not well understood under climate change. Leveraging remotely sensed datasets, in-situ hydrological observations, and physics-based models, we reveal overall warming and widening rivers across the Tibetan Plateau in recent decades, driving accelerated sub-river permafrost thaw. River temperature of a representative (Tuotuohe River) on the central Tibetan Plateau, has increased notably (0.39 degrees C/decade) from 1985 to 2017, facilitating heat transfer into the underlying permafrost via both convection and conduction. Consequently, the permafrost beneath rivers warms faster (0.37 degrees C-0.66 degrees C/decade) and has a similar to 0.5 m thicker active layer than non-inundated permafrost (0.17 degrees C-0.49 degrees C/decade). With increasing river discharge, the inundated area expands laterally along the riverbed (16.4 m/decade), further accelerating permafrost thaw for previously non-inundated bars. Under future warmer and wetter climate, the anticipated intensification of sub-river permafrost degradation will pose risks to riverine infrastructure and amplify permafrost carbon release.

Global climate warming has led to the deepening of the active layer of permafrost on the Tibetan Plateau, further triggering thermal subsidence phenomena, which have profound effects on the carbon cycle of regional ecosystems. This study conducted warming (W) and thermal subsidence (RR) control experiments using an Open-Top Chamber (OTC) device in the river source wetlands of the Qinghai Lake basin. The aim was to assess the impacts of warming and thermal subsidence on soil temperature, volumetric water content, biomass, microbial diversity, and soil respiration (both autotrophic and heterotrophic respiration). The results indicate that warming significantly increased soil temperature, especially during the colder seasons, and thermal subsidence treatment further exacerbated this effect. Soil volumetric water content significantly decreased under thermal subsidence, with the RRW treatment having the most pronounced impact on moisture. Additionally, a microbial diversity analysis revealed that warming promoted bacterial richness in the surface soil, while thermal subsidence suppressed fungal community diversity. Soil respiration rates exhibited a unimodal curve during the growing season. Warming treatment significantly reduced autotrophic respiration rates, while thermal subsidence inhibited heterotrophic respiration. Further analysis indicated that under thermal subsidence treatment, soil respiration was most sensitive to temperature changes, with a Q10 value reaching 7.39, reflecting a strong response to climate warming. In summary, this study provides new scientific evidence for understanding the response mechanisms of soil carbon cycling in Tibetan Plateau wetlands to climate warming.

Climate warming has caused the active layer of permafrost to thicken, leading to permafrost melting and surface collapse, forming thermokarst landforms. These changes significantly affect regional vegetation, soil properties, and water processes, thereby impacting regional carbon cycling. This study examined the relationships between soil respiration rate (Rs), soil temperature (T), and volumetric water content (VWC) in the thermokarst depression zones of Qinghai Lake's headwater wetlands. The results showed a significant positive correlation between soil temperature and Rs, and a significant negative correlation between VWC and Rs. The inhibitory effect of VWC on Rs was stronger in thermokarst areas compared to natural conditions. Temperature had a greater influence on Rs, especially during the day, while VWC inhibited Rs more at night. The study highlights the combined impact of temperature and humidity on soil respiration, revealing that Rs in thermokarst areas is more sensitive to temperature changes at night. These findings improve our understanding of carbon cycling in wetland ecosystems and help predict wetland carbon emissions under climate change. As the climate warms, the thickening of the active layer of permafrost has led to permafrost melting and surface collapse, forming thermokarst landforms. These changes significantly impact regional vegetation, soil physicochemical properties, and hydrological processes, thereby exacerbating regional carbon cycling. This study analyzed the relationship between soil respiration rate (Rs), soil temperature (T), and volumetric water content (VWC) in the thermokarst depression zone of the headwater wetlands of Qinghai Lake, revealing their influence on these soil parameters. Results showed a significant positive correlation between soil temperature and Rs (p < 0.001), and a significant negative correlation between VWC and Rs (p < 0.001). The inhibitory effect of VWC on Rs in the thermokarst depression zone was stronger than under natural conditions (p < 0.05). Single-factor models indicated that the temperature-driven model had higher explanatory power for Rs variation in both the thermokarst depression zone (R-2 = 0.509) and under natural conditions (R-2 = 0.414), while the humidity-driven model had lower explanatory power. Dual-factor models further improved explanatory power, slightly more so in the thermokarst depression zone. This indicates that temperature and humidity jointly drive Rs. Additionally, during the daytime, temperature had a more significant impact on Rs under natural conditions, while increased VWC inhibited Rs. At night, the positive correlation between Rs and temperature in the thermokarst depression zone increased significantly. The temperature sensitivity (Q(10)) values of Rs were 3.32 and 1.80 for the thermokarst depression zone and natural conditions, respectively, indicating higher sensitivity to temperature changes at night in the thermokarst depression zone. This study highlights the complexity of soil respiration responses to temperature and humidity in the thermokarst depression zone of Qinghai Lake's headwater wetlands, contributing to understanding carbon cycling in wetland ecosystems and predicting wetland carbon emissions under climate change.

Peatlands are major natural carbon pool in terrestrial ecosystems globally and are essential to a variety of fields, including global ecology, hydrology, and ecosystem services. Under the context of climate change, the management and conservation of peatlands has become a topic of international concern. Nevertheless, few studies have yet systematized the overall international dynamics of existing peatland research. In this study, based on an approach integrating bibliometrics and a literature review, we systematically analyzed peatland research from a literature perspective. Alongside traditional bibliometric analyses (e.g., number of publications, research impact, and hot areas), recent top keywords in peatland research were found, including 'oil palm', 'tropical peatland', 'permafrost', and so on. Furthermore, six hot topics of peatland research were identified: (1) peatland development and the impacts and degradations, (2) the history of peatland development and factors of formation, (3) chemical element contaminants in peatlands, (4) tropical peatlands, (5) peat adsorption and its humic acids, and (6) the influence of peatland conservation on the ecosystem. In addition, this review found that the adverse consequences of peatland degradation in the context of climate change merit greater attention, that peatland-mapping techniques suitable for all regions are lacking, that a unified global assessment of carbon stocks in peatlands urgently needs to be established, spanning all countries, and that a reliable system for assessing peatland-ecosystem services needs to be implemented expeditiously. In this study, we argued that enhanced integration in research will bridge knowledge gaps and facilitate the systematic synthesis of peatlands as complex systems, which is an imperative need.

This study explores the carbon stability in the Arctic permafrost following the sea-level transgression since the Last Glacial Maximum (LGM). The Arctic permafrost stores a significant amount of organic carbon sequestered as frozen particulate organic carbon, solid methane hydrate and free methane gas. Post-LGM sea-level transgression resulted in ocean water, which is up to 20 degrees C warmer compared to the average annual air mass, inundating, and thawing the permafrost. This study develops a one-dimensional multiphase flow, multicomponent transport numerical model and apply it to investigate the coupled thermal, hydraulic, microbial, and chemical processes occurring in the thawing subsea permafrost. Results show that microbial methane is produced and vented to the seawater immediately upon the flooding of the Arctic continental shelves. This microbial methane is generated by the biodegradation of the previously frozen organic carbon. The maximum seabed methane flux is predicted in the shallow water where the sediment has been warmed up, but the remaining amount of organic carbon is still high. It is less likely to cause seabed methane emission by methane hydrate dissociation. Such a situation only happens when there is a very shallow (similar to 200 m depth) intra-permafrost methane hydrate, the occurrence of which is limited. This study provides insights into the limits of methane release from the ongoing flooding of the Arctic permafrost, which is critical to understand the role of the Arctic permafrost in the carbon cycle, ocean chemistry and climate change. Arctic permafrost stores similar to 1,700 billion tons of organic carbon. If just a fraction of that melts, the escaping methane would become one of the world's largest sources of greenhouse gas and would severely impact the environment and the climate. Over the last similar to 18,000 years, a quarter of the stored organic carbon in the Arctic permafrost has been flooded by the rising, warm seas. This has melted the ice and degraded the permafrost. But what happens to the carbon pools? This study investigates the stability of the carbon in the Arctic permafrost following the flooding using a newly developed numerical model. Results show that microbial methane is generated and emitted to the seawater immediately following the flooding. This methane is produced by the biodegradation of the previously frozen organic carbon near the seafloor. The maximum methane emission is predicted in the shallow water near the coast where the sediment has been warmed up, but the remaining amount of organic carbon is still high. This study provides insights into the limits of methane release from the ongoing flooding of the Arctic permafrost, which is critical to understand the role of the Arctic permafrost in the carbon cycle, ocean chemistry and climate change. A numerical model is developed to simulate the coupled thermal, hydraulic, microbial and chemical processes in the thawing subsea permafrost The biodegradation of the ancient organic carbon in the thawing subsea permafrost results in seabed microbial methane emission Seabed methane emission is less likely to be caused by methane hydrate dissociation at the Arctic continental shelves

The changing thermal state of permafrost is an important indicator of climate change in northern high latitude ecosystems. The seasonally thawed soil active layer thickness (ALT) overlying permafrost may be deepening as a consequence of enhanced polar warming and widespread permafrost thaw in northern permafrost regions (NPRs). The associated increase in ALT may have cascading effects on ecological and hydrological processes that impact climate feedback. However, past NPR studies have only provided a limited understanding of the spatially continuous patterns and trends of ALT due to a lack of long-term high spatial resolution ALT data across the NPR. Using a suite of observational biophysical variables and machine learning (ML) techniques trained with available in situ ALT network measurements (n = 2966 site-years), we produced annual estimates of ALT at 1 km resolution over the NPR from 2003 to 2020. Our ML-derived ALT dataset showed high accuracy (R 2 = 0.97) and low bias when compared with in situ ALT observations. We found the ALT distribution to be most strongly affected by local soil properties, followed by topographic elevation and land surface temperatures. Pair-wise site-level evaluation between our data-driven ALT with Circumpolar Active Layer Monitoring data indicated that about 80% of sites had a deepening ALT trend from 2003 to 2020. Based on our long-term gridded ALT data, about 65% of the NPR showed a deepening ALT trend, while the entire NPR showed a mean deepening trend of 0.11 +/- 0.35 cm yr-1 [25%-75% quantile: (-0.035, 0.204) cm yr-1]. The estimated ALT trends were also sensitive to fire disturbance. Our new gridded ALT product provides an observationally constrained, updated understanding of the progression of thawing and the thermal state of permafrost in the NPR, as well as the underlying environmental drivers of these trends.

Permafrost region stores 1014-1035 Pg (1 Pg=10(15) g) carbon (C) in the upper 3 m of soils, approximately twice of the atmosphere C pool. Over the past few decades, climate warming has caused substantial permafrost thaw. Consequently, a proportion of permafrost C becomes available for microbial utilization and can be decomposed as carbon dioxide (CO2) and methane (CH4) into the atmosphere, thus triggering potential C-climate feedback. However, the magnitude of this feedback remains highly uncertain, partly due to limited understanding of the formation and stabilization mechanisms of permafrost organic C. As an important component of soil stable C pool, microbial necromass C could make up more than 50% of soil organic carbon (SOC). Therefore, our knowledge of spatial distributions and key drivers of microbial necromass C in permafrost deposits is crucial for accurately predicting permafrost C dynamics under the context of global warming. Based on large-scale permafrost sampling along a similar to 1000 km transect on the Tibetan Plateau and biomarker analysis of amino sugars, we determined microbial necromass C content in permafrost deposits across 24 sampling sites. We then compared the contribution of microbial necromass C to SOC between permafrost deposits and active layer. To investigate key determinants of microbial necromass C content in permafrost deposits, we obtained climatic factors (e.g., mean annual temperature, mean annual precipitation) and measured soil variables (e.g., active layer thickness, soil moisture, soil texture), as well as microbial properties (e.g., fungal and bacterial biomass on the basis of phospholipid fatty acids analysis). Our results showed that total microbial necromass C, fungal and bacterial necromass C content in permafrost deposits increased from the west to the east of the study area. The average content of microbial necromass C in permafrost deposits was 2741.0 +/- 815.3 (values were reported as mean +/- standard error) mg kg(-1), and its contribution to SOC was 13.2%+/- 1.1%. The fungal necromass C and its contribution to SOC were significantly higher than that of bacterial necromass C. Our results also indicated that the contribution of fungal necromass C to SOC in the permafrost deposits was significantly lower than that in the active layer, however, there were no significant differences in the contribution of bacterial necromass C to SOC between these two layers. Regression analyses showed that total microbial necromass C, fungal and bacterial necromass C content in permafrost deposits increased with mean annual precipitation, soil moisture and their corresponding microbial biomasses, but decreased with mean annual temperature and active layer thickness. Structural equation modeling analyses further revealed that soil moisture and microbial biomass were the direct drivers of microbial necromass C content in permafrost deposits, and climatic factors indirectly affected microbial necromass C content. Overall, this study offers the first attempt to analyze the spatial distribution and dominant drivers of permafrost microbial necromass C on the Tibetan Plateau. The contribution of microbial necromass C to SOC observed in permafrost deposits was lower than those reported in temperate and global grassland soils. Moreover, the key factors of microbial necromass C detected in permafrost deposits were distinct from those reported in other ecosystems, where plant C input and mineral protection are dominant factors affecting soil microbial necromass C content. These findings illustrate the unique characteristics of C formation and accumulation in permafrost soils, suggesting that C formation processes and mechanisms obtained in other ecosystems cannot be simply generalized to permafrost ecosystems. More importantly, despite the relatively lower contribution of microbial necromass C to SOC, microbial necromass C is a non-negligible source of permafrost C, and its dynamics may affect the positive feedback between permafrost C cycle and climate warming.

Positive feedbacks between permafrost degradation and the release of soil carbon into the atmosphere impact land-atmosphere interactions, disrupt the global carbon cycle, and accelerate climate change. The widespread distribution of thawing permafrost is causing a cascade of geophysical and biochemical disturbances with global impacts. Currently, few earth system models account for permafrost carbon feedback (PCF) mechanisms. This research study integrates artificial intelligence (AI) tools and information derived from field-scale surveys across the tundra and boreal landscapes in Alaska. We identify and interpret the permafrost carbon cycling links and feedback sensitivities with GeoCryoAI, a hybridized multimodal deep learning (DL) architecture of stacked convolutionally layered, memory-encoded recurrent neural networks (NN). This framework integrates in-situ measurements and flux tower observations for teacher forcing and model training. Preliminary experiments to quantify, validate, and forecast permafrost degradation and carbon efflux across Alaska demonstrate the fidelity of this data-driven architecture. More specifically, GeoCryoAI logs the ecological memory and effectively learns covariate dynamics while demonstrating an aptitude to simulate and forecast PCF dynamics-active layer thickness (ALT), carbon dioxide flux (CO2), and methane flux (CH4)-with high precision and minimal loss (i.e. ALTRMSE: 1.327 cm [1969-2022]; CO2 RMSE: 0.697 mu molCO2m-2s-1 [2003-2021]; CH4 RMSE: 0.715 nmolCH4m-2s-1 [2011-2022]). ALT variability is a sensitive harbinger of change, a unique signal characterizing the PCF, and our model is the first characterization of these dynamics across space and time.

Permafrost degradation is altering biogeochemical processes throughout the Arctic. Thaw-induced changes in organic matter transformations and mineral weathering reactions are impacting fluxes of inorganic carbon (IC) and alkalinity (ALK) in Arctic rivers. However, the net impact of these changing fluxes on the concentration of carbon dioxide in the atmosphere (pCO(2)) is relatively unconstrained. Resolving this uncertainty is important as thaw-driven changes in the fluxes of IC and ALK could produce feedbacks in the global carbon cycle. Enhanced production of sulfuric acid through sulfide oxidation is particularly poorly quantified despite its potential to remove ALK from the ocean-atmosphere system and increase pCO(2), producing a positive feedback leading to more warming and permafrost degradation. In this work, we quantified weathering in the Koyukuk River, a major tributary of the Yukon River draining discontinuous permafrost in central Alaska, based on water and sediment samples collected near the village of Huslia in summer 2018. Using measurements of major ion abundances and sulfate (SO42-) sulfur (S-34/S-32) and oxygen (O-18/O-16) isotope ratios, we employed the MEANDIR inversion model to quantify the relative importance of a suite of weathering processes and their net impact on pCO(2). Calculations found that approximately 80% of SO42- in mainstem samples derived from sulfide oxidation with the remainder from evaporite dissolution. Moreover, S-34/S-32 ratios, C-13/C-12 ratios of dissolved IC, and sulfur X-ray absorption spectra of mainstem, secondary channel, and floodplain pore fluid and sediment samples revealed modest degrees of microbial sulfate reduction within the floodplain. Weathering fluxes of ALK and IC result in lower values of pCO(2) over timescales shorter than carbonate compensation (similar to 10(4) yr) and, for mainstem samples, higher values of pCO(2) over timescales longer than carbonate compensation but shorter than the residence time of marine SO42- (similar to 10(7) yr). Furthermore, the absolute concentrations of SO42- and Mg2+ in the Koyukuk River, as well as the ratios of SO42- and Mg2+ to other dissolved weathering products, have increased over the past 50 years. Through analogy to similar trends in the Yukon River, we interpret these changes as reflecting enhanced sulfide oxidation due to ongoing exposure of previously frozen sediment and changes in the contributions of shallow and deep flow paths to the active channel. Overall, these findings confirm that sulfide oxidation is a substantial outcome of permafrost degradation and that the sulfur cycle responds to permafrost thaw with a timescale-dependent feedback on warming.

Climate warming leads to widespread permafrost thaw with a fraction of the thawed permafrost carbon (C) being released as carbon dioxide (CO2), thus triggering a positive permafrost C-climate feedback. However, large uncertainty exists in the size of this model-projected feedback, partly owing to the limited understanding of permafrost CO2 release through the priming effect (i.e., the stimulation of soil organic matter decomposition by external C inputs) upon thaw. By combining permafrost sampling from 24 sites on the Tibetan Plateau and laboratory incubation, we detected an overall positive priming effect (an increase in soil C decomposition by up to 31%) upon permafrost thaw, which increased with permafrost C density (C storage per area). We then assessed the magnitude of thawed permafrost C under future climate scenarios by coupling increases in active layer thickness over half a century with spatial and vertical distributions of soil C density. The thawed C stocks in the top 3 m of soils from the present (2000-2015) to the future period (2061-2080) were estimated at 1.0 (95% confidence interval (CI): 0.8-1.2) and 1.3 (95% CI: 1.0-1.7) Pg (1 Pg = 10(15) g) C under moderate and high Representative Concentration Pathway (RCP) scenarios 4.5 and 8.5, respectively. We further predicted permafrost priming effect potential (priming intensity under optimal conditions) based on the thawed C and the empirical relationship between the priming effect and permafrost C density. By the period 2061-2080, the regional priming potentials could be 8.8 (95% CI: 7.4-10.2) and 10.0 (95% CI: 8.3-11.6) Tg (1 Tg = 10(12) g) C year(-1) under the RCP 4.5 and RCP 8.5 scenarios, respectively. This large CO2 emission potential induced by the priming effect highlights the complex permafrost C dynamics upon thaw, potentially reinforcing permafrost C-climate feedback.