Methane Pathways in Winter Ice of Thermokarst Lakes, Lagoons and Coastal Waters in North Siberia
The thermokarst lakes of permafrost regions play a major role in the global carbon cycle. These lakes are sources of methane to the atmosphere but the methane flux is restricted by an ice cover for most of the year. We provide insights into the methane pathways in the winter ice cover on three diffe...
| Main Authors: | , , , , , , , , , |
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| Format: | Other/Unknown Material |
| Language: | English |
| Published: |
2020
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/tc-2019-304 https://tc.copernicus.org/preprints/tc-2019-304/ |
| Summary: | The thermokarst lakes of permafrost regions play a major role in the global carbon cycle. These lakes are sources of methane to the atmosphere but the methane flux is restricted by an ice cover for most of the year. We provide insights into the methane pathways in the winter ice cover on three different water bodies in a continuous permafrost region in Siberia. The first is a bay underlain by submarine permafrost (Tiksi Bay, TB), the second a shallow thermokarst lagoon (Polar Fox, PF) and the third a land-locked, freshwater thermokarst lake (Goltsovoye Lake, GL). In total, 11 ice cores were analyzed as records of the freezing process and methane pathways during the winter season. In TB, the hydrochemical parameters indicate an open system freezing. In contrast, PF was classified as a semi-closed system, where ice growth eventually cuts off exchange between the lagoon and the ocean. The GL is a closed system without connections to other water bodies. Ice on all water bodies was mostly methane-supersaturated with respect to the atmospheric equilibrium concentration, except of three cores from the lake. Generally, the TB ice had low methane concentrations (3.48–8.44 nM) compared to maximum concentrations of the PF ice (2.59–539 nM) and widely varying concentrations in the GL ice (0.02–14817 nM). Stable delta 13 C CH 4 isotope signatures indicate that methane above the ice-water interface was oxidized to concentrations close to or below the calculated atmospheric equilibrium concentration in the ice of PF. We conclude that methane oxidation in ice may decrease methane concentrations during winter. Therefore, understanding seasonal effects to methane pathways in Arctic saline influenced or freshwater systems is critical to anticipate permafrost carbon feedbacks in course of global warming. |
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