Seasonal methane dynamics in three different Siberian water bodies

• Main Authors: Bussmann, Ingeborg, Fedorova, Irina, Juhls, Bennet, Overduin, Pier Paul, Winkel, Matthias
• Format: Text
• Language: English
• Published: 2020
• Subjects: Arctic; Tiksi; Ice; lena river; permafrost; Tiksi Bay; Siberia
• Online Access: https://doi.org/10.5194/bg-2020-106; https://www.biogeosciences-discuss.net/bg-2020-106/

Arctic regions and their water bodies are being affected by the most rapid climate warming on Earth. Arctic lakes and small ponds are known to act as an important source of atmospheric methane. However, not much is known about other types of water bodies in permafrost regions, which include major rivers and coastal bays as a transition type between freshwater and marine environments. We monitored dissolved methane concentrations in three different water bodies (Lena River, Tiksi Bay and Lake Golzovoye, Siberia, Russia) over a period of two years. Sampling was carried out under ice cover (April) and in open water (July/August). The methane oxidation (MOX) rate in water and melted ice samples from the late winter of 2017 was also investigated. In the Lena River winter methane concentrations were a quarter of the summer concentrations (8 vs 31 nmol L −1 ) and mean winter MOX rate was low (0.023 nmol L −1 d −1 ). In contrast, Tiksi Bay winter methane concentrations were 10-times higher than in summer (103 vs 13 nmol L −1 ). Winter MOX rates showed a median of 0.305 nmol L −1 d −1 . In Lake Golzovoye, median methane concentrations in winter were 40-times higher than in summer (1957 vs 49 nmol L −1 ). However, MOX was much higher in the lake (2.95 nmol L −1 d −1 ) than in either the river or bay. The temperature had a strong influence on the MOX, (Q10 = 2.72 ± 0.69) compared to temperate environments. In the ice cores a median methane concentration of 9 nM was observed, with no gradient between the ice surface and the bottom layer at the ice-water-interface. MOX in the (melted) ice cores was mostly below the detection limit. Comparing methane concentrations in the ice with the underlaying water column revealed 100 – 1000-times higher methane concentration in the water column. The winter situation seemed to favor a methane accumulation under ice, especially in the lake with a stagnant water body. While on the other hand, in the Lena River with its flowing water no methane accumulation under ice was observed. Methane oxidation rate was not able to counteract this winter time accumulation.