the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Proglacial methane emissions driven by meltwater and groundwater flushing in a high Arctic glacial catchment
Abstract. Glacial groundwater releases geologic methane in areas of glacier retreat on Svalbard, representing a large, climate-sensitive source of the greenhouse gas. Methane emissions from glacial melt rivers are known to occur in other regions of the Arctic, but such emissions have not yet been considered on Svalbard. Over two summers, we monitored methane concentrations in the proglacial groundwater springs and river network of a 20 km2 valley glacier in central Svalbard to estimate melt season emissions from a single catchment. We found that methane concentrations in the glacial river reach up to 3170 nM, which is nearly 800-times higher than the atmospheric equilibrial concentration. We estimate a total of 1.0 ton of melt season methane emissions from the catchment, of which nearly two-thirds are being flushed from the glacier bed by the melt river. These findings provide further evidence that terrestrial glacier forefields on Svalbard are hotspots for methane emissions, with a climate feedback loop driven by glacier melt. As the first investigation into methane emissions from glacial melt rivers on Svalbard, our study suggests that summer meltwater flushing of methane from the ~1400 land-terminating glaciers across Svalbard may represent an important seasonal source of emissions. Furthermore, glacial melt rivers may be a growing emission source across other rapidly warming regions of the Arctic.
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RC1: 'Comment on egusphere-2024-1273', Marek Stibal, 18 Jun 2024
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Kleber et al. continue their exciting work on CH4 release associated with glacier retreat in Svalbard. This paper focuses on the catchment of a small valley glacier in central Svalbard and its groundwater springs (investigated previously) and meltwater stream network. The authors found high CH4 concentrations in both the springs and the glacial river and estimate a total of 1 t of CH4 emissions from the catchment, two thirds of which are flushed from the glacier bed by the meltwater.
The paper is well written and brings interesting new data on a highly timely issue of CH4 release in a rapidly deglaciating Arctic region and a careful mass balance-based estimate of potential CH4 emissions from the catchment.
My main criticism is the lack of stable isotope data on the CH4 from the meltwater samples, which makes the interpretation of the CH4 source(s) and so the governing mechanism(s) (see line 59) of the emissions difficult. The claim that “small valley glaciers like Vallåkrabreen can be a substantial source of methane, challenging previous theories that subglacial methane is largely produced microbially in the anoxic environment beneath large ice sheets” (l. 440-441) makes little sense, since if the CH4 is thermogenic (which seems likely given its high concentration and the expected low bioavailable OC content in the subglacial environment) the glacier itself (or rather its ecosystem) is not the source but rather its meltwater acts as a mobiliser/carrier, and the comparison of Vallåkrabreen and Leverett Glacier and their catchment sizes (l. 291-294) is beside the point. This is not to question the importance of the results – I think it’s great to see that a broader approach to glacier retreat as a landscape-scale process is necessary to fully understand its climate feedback potential – but it should be emphasised or made explicit in the text.
The true focus and novelty of the study should also be made clearer in the (last paragraph of the) introduction – at the moment it’s quite drowned.
Minor comments
l. 33 Subglacial C stores have also been estimated to be significant (Wadham et al 2019 Nat Comms) and should be mentioned.
l. 41-42 Vinsova et al. (2022 Glob Biogeochem Cycles) provide an overview of Arctic subglacial OC and its potential microbial degradation and could be mentioned.
l. 102 What was “sufficiently high CH4 concentration” in this case?
Fig 2 Is there any correlation between Q and CH4?
I also recommend the authors fix the inconsistencies in tense (past vs. present) and voice (passive vs. active) throughout the text for a better reading experience.
Citation: https://doi.org/10.5194/egusphere-2024-1273-RC1
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