Haibo He

The emerging concept of white carbon draws attention to carbon storage, burial, and greenhouse‐gas balance in managed hypersaline coastal ponds, systems rarely considered in conventional blue carbon frameworks or coastal carbon budgets. These ponds can store organic carbon in sediments while exchanging CO ₂ and CH ₄ with the atmosphere, but their net climate role depends on salinity, metabolism, hydrology, sedimentation, and management. Alexandre et al. (2026, https://doi.org/10.1029/2025JG009016 ) provide an important case study by integrating air–water greenhouse‐gas fluxes with sediment organic carbon storage and burial in a traditional salt production pond. Their findings suggest that the investigated saltern may function as a net carbon sink under the observed conditions, while emphasizing that white carbon should be treated as a testable, context‐dependent framework rather than an established or generalized carbon‐sink category. Comparative, mechanistically informed, and better‐constrained carbon budgets are needed to determine when managed salterns function as net sinks or sources.

High-altitude saline lakes on the Tibetan Plateau host some of the world’s most arsenic-rich waters, yet controls on arsenic (As) transformation remain poorly resolved. By integrating depth-resolved geochemistry with metagenomic profiling in Lake Tosen, we identified a redox framework for As cycling that is not fully explained by the Fe-centric model derived from groundwater and freshwater. In summer, oxic-suboxic-anoxic stratification supported three distinct pathways: (i) oxic waters exhibited a microbial detoxification-oxidation loop sustaining As(V) dominance; (ii) suboxic waters were associated with nitrate-supported As(III) oxidation linked to denitrifying taxa; and (iii) anoxic sulfidic waters showed sulfate-reduction-related As transformation, with sulfur cycling likely modifying the fate and mobility of released As under sulfidic conditions. Meanwhile, canonical Fe(III)-respiration markers were not prominent, and saturation indices indicated stable goethite/hematite under in situ conditions. Together, these findings indicate that, under the observed stratified conditions in Lake Tosen, nitrate- and sulfate-associated pathways were more closely linked to arsenic transformation than canonical Fe(III)-respiration signals. This nonclassical coupling may become increasingly relevant as stratification, nitrate loading, and salinization intensify, with implications for As risk prediction in endorheic basins under changing climates.

The response of mineral weathering and its related Weathering Sink for atmospheric CO₂ (WS_atm-CO2) to global vegetation greening are not well understood. After applying different biogeochemical models and a field experiment to investigate the influence of vegetation greening and warming on the variations of carbonate weathering and WS_atm-CO2 on regional and global scales, here we show a significant positive relationship between global carbonate weathering intensity ([HCO₃⁻] as a proxy) and vegetation greenness. During 1982–2018, under a warming climate, [HCO₃⁻] and WS_atm-CO2 increase by 5.8% and 6.1%, respectively, due to vegetation greening, in the carbonate areas of Southwest China. Meanwhile, the [HCO₃⁻] in global carbonate areas increases by +2.4% during the same period. By contrast, the [HCO₃⁻] in global carbonate areas decreases by −1.3% without a vegetation function due to the warming. Moreover, we estimated that the carbonate weathering enhancements due to vegetation restoration at the global scale could reach 43.8%. Our results demonstrate that future vegetation restoration is important for the carbon capture by mineral weathering.

Sedimentary organic matter is an important component of the metabolism of a lake’s ecosystem, and it is generally derived from both the watershed and the primary productivity of a lake. Understanding the sources of organic matter in lakes and lake trophic status is important when evaluating the quality of lake ecosystems. We summarize the spatial distribution of total nitrogen (TN), total organic carbon (TOC), TOC/TN (C/N) molar ratios, and organic carbon isotope (δ¹³C_org) of the surface sediments of Fuxian Lake, Yunnan–Guizhou Plateau, Southwest China, which is the second deepest freshwater oligotrophic lake in China. The results show that the distributions of TN, TOC, C/N, and δ¹³C_org of the surface sediments are spatially heterogeneous, which is also the case for the trophic conditions of the lake. Compared with the adjacent eutrophic lakes and typical lakes in other areas with strong human activities, the content of organic matter is at a low level. Meanwhile, the autochthonous organic carbon in the surface sediments was characterized by lower δ¹³C_org (−25.3~−28.5) and C/N (8.7~12.9), suggesting that the biological carbon pump effect plays a significant part in the stability of carbon sinks by coupling with carbonate weathering. Our results emphasize the importance of the carbon sink of coupled carbonate weathering and aquatic photosynthesis in the evolution of the carbon cycle in lakes. Although modern monitoring shows that Fuxian Lake is an oligotrophic lake, there are potential risks of organic nitrogen pollution with respect to surface sediments, especially in northern and southern shallow-water areas. The organic pollution of lakes can be reduced by controlling the discharge of wastewater and reducing the nutrient loading of agricultural runoff.

The molecular composition of the lipid biomarkers in the surface water, water column, and surface sediments collected along the Pearl River was investigated to identify the mechanisms of the delivery and preservation of autochthonous organic carbon (AOC) and to estimate its contribution to the carbon sink. The spatial distribution of these lipid biomarkers showed that samples collected at high-DIC-concentration sites (DIC: dissolved inorganic carbon) had prominent aquatic autochthonous signatures, while samples collected at low-DIC-concentration sites showed greater terrestrial contributions, which were described as the DIC fertilization effects. In the summer, typically, intense precipitation and flood erosion diluted the biogeochemical composition and carried terrestrial plant detritus. Therefore, the percentage of AOC (auto%) was higher in the winter than in the summer. According to the calculation of the lipid biomarkers, the values of the auto% were 65% (winter) and 54% (summer) in the surface water, 55.9% (winter) and 44.6% (summer) in the below-surface water, and 52.1% (winter) and 43.9% (summer) in the surface sediment, which demonstrated that AOC accounted for a major portion of the TOC. Vertical variability was mainly present in sites with intense flood erosion, which resulted in the mixing and deposition of resuspended sediments. There was a positive correlation of the clay content with the auto% value and the biogeochemical composition, showing that clay adsorbed the organic carbon in the water, vertically deposited it into the sediment, and was the dominant mechanism of the vertical delivery of organic carbon (OC). According to the new karst carbon sink model, based on coupled carbonate weathering and aquatic photosynthesis, the karst carbon sink flux (CSF) in the Pearl River was 2.69 × 10⁶ t/a which was 1.7 times the original estimation (1.58 × 10⁶ t/a), and this did not consider the formation of AOC. This indicated that previously, the contribution of the riverine system to the global karst carbon sink may have been highly underestimated.