Isotopic composition and emission characteristics of CO₂ and CH₄ in glacial lakes of the Tibetan Plateau

Abstract

Carbon dioxide (CO2) and methane (CH4) emissions from freshwater ecosystems are predicted to increase under climate warming. However, freshwater ecosystems in glacierized regions differ critically from those in non-glacierized regions. The potential emissions of CO2 and CH4 from glacierized environments in the Tibetan Plateau (TP) were only recently recognized. Here, the first direct measurement of CO2 and CH4 emission fluxes and isotopic composition during spring of 2022 in 13 glacial lakes of the TP revealed that glacial lakes were the previously overlooked CO2 sinks due to chemical weathering in glacierized regions. The daily average CO2 flux was -5.1±4.4 mmol m-1 d-1, and the CO2 consumption could reach 38.9 Gg C-CO2 yr-1 by all glacial lakes in the TP. This consumption might be larger during summer when glaciers experience intensive melting, highlighting the importance of CO2 uptake by glacial lake on the global carbon cycle. However, the studied glacial lakes were CH4 sources with total emission flux ranging from 4.4±3.3 to 4082.5±795.6 µmol m-2 day-1. The large CH4 range was attributed to ebullition found in three of the glacial lakes. The low dissolved organic carbon concentrations and CH4 oxidation might be responsible for low CH4 diffusive fluxes of glacial lakes without ebullition. In addition, groundwater input could alter CO2 and CH4 emissions from glacial lakes. CH4 in glacial lakes probably had a thermogenic source; whereas CO2 was influenced mainly by atmospheric input, as well as organic matter remineralization and CH4 oxidation. Overall, glacial lakes in the TP play an important role in global carbon cycle and budget, and more detailed isotopic and microbial studies are needed to constrain the contributions of different pathways to CO2 and CH4 production, consumption and emissions.

Glacier‐Fed Lakes Are Significant Sinks of Carbon Dioxide in the Southeastern Tibetan Plateau

“…This conclusion is comparable with proglacial river runoff on the Tibetan Plateau (Wang et al, 2014;Yu et al, 2023;Zhang, Ran, et al, 2021;Zhang, Kang, et al, 2021). Recent investigations into the roles of glacier meltwater at glacier terminus in high mountain glaciers as CO2 sources or sinks have shown variable responses to environmental fluctuations (Du et al, 2022;Yan et al, 2023). However, in the maritime glacier regions of the southeastern Tibetan Plateau, it serves as a potential CO2 sink.…”

“…Under natural conditions, the solubility of carbonates is about 12-40 times higher than that of silicates (Meybeck, 1987;Pant et al, 2018). 2023) is primarily during the beginning of the glacier melting period (spring), whereas our sampling period is during the monsoon period (summer) and the post monsoon period (winter); (c) CO 2 flux of the 13 glacial lakes measured by Yan et al (2023) varies widely from 0.5 ± 2.6 to 13.8 ± 10.4 mmol m 2 d 1 , which encompasses our calculated CO 2 flux. Shukla et al ( 2023) estimated CO 2 flux of the Himalayan glacier-fed lakes and found that these lakes were potential CO 2 sources, with a CO 2 efflux of 1,746 ± 139 mg C m 2 d 1 .…”

Carbon Emissions From Chinese Inland Waters: Current Progress and Future Challenges

“…Although Xun et al (2022) stressed salt lakes that generally show higher pCO 2 than freshwater, Li, Shi, et al (2022) surprisingly found that frozen salt lakes have a strong CO 2 uptake potential during the ice-covered period. In addition, while melting of glaciers and permafrost will provide sufficient soil organic matter for CO 2 production (thus a CO 2 source) (Piao et al, 2019), glacial meltwater could accelerate rock weathering, thereby enhancing dissolved CO 2 consumption and sustaining the lake pCO 2 below the atmospheric equilibrium (thus a CO 2 sink) (Yan, Du, et al, 2023). Furthermore, the expanding lake surface due to glacier and permafrost thaw, coupled with the accelerated development of thermokarst lakes, raises the question of whether the increase in water surface enhances C sequestration or exacerbates C emissions (Mu et al, 2023;Yan, Du, et al, 2023).…”

“…In addition, while melting of glaciers and permafrost will provide sufficient soil organic matter for CO 2 production (thus a CO 2 source) (Piao et al., 2019), glacial meltwater could accelerate rock weathering, thereby enhancing dissolved CO 2 consumption and sustaining the lake p CO 2 below the atmospheric equilibrium (thus a CO 2 sink) (Yan, Du, et al., 2023). Furthermore, the expanding lake surface due to glacier and permafrost thaw, coupled with the accelerated development of thermokarst lakes, raises the question of whether the increase in water surface enhances C sequestration or exacerbates C emissions (Mu et al., 2023; Yan, Du, et al., 2023). An accurate assessment of the impacts of temperature increase on C emissions requires the integration of multiple biogeochemical processes of C transport and transformation.…”

Dissolved greenhouse gas (CO2, CH4, and N2O) emissions from highland lakes of the Andes cordillera in Northern Ecuador

“…There are fewer studies of CO 2 and CH 4 variations in mountainous lakes than in lowland lakes. Available data suggest that there is no systematic difference in CH 4 emissions between mountainous and lowland lakes, while CO 2 emissions seem to be lower in mountainous lakes that occasionally act as sinks for atmospheric CO 2 , based on data mainly collected in the Alps (Pighini et al 2018), Rocky Mountains (McCrackin andElser 2011;Crawford et al 2015), Sierra Nevada (Cohen and Melack 2020), and the Tibetan Plateau (Yan et al 2018(Yan et al , 2023Wang et al 2022). Available data sets of GHG emissions from lakes and rivers are also spatially skewed toward higher latitudes, mainly in North America and Scandinavia.…”