Abstract
The degradation of ice-rich permafrost deposits has the potential to release large amounts of old carbon (C) and nitrogen (N) with severe local implications such as affecting riverine and near-shore zone ecosystems but also global impacts such as the release of greenhouse gases into the atmosphere. Here we study the rapid erosion of the up to 27.7 m high and 1,660 m long Sobo-Sise yedoma cliff in the Lena River Delta using a remote sensing-based time-series analysis covering 53 years and calculate the mean annual sediment as well as C and N release into the Lena River. We find that the Sobo-Sise yedoma cliff, which exposes ice-rich Late Pleistocene to Holocene deposits, had a mean long-term (1965-2018) erosion rate of 9.1 m yr-1 with locally and temporally varying rates of up to 22.3 m yr-1. These rates are among the highest measured in the Arctic. The fluvio-thermal erosion led to the release of significant amounts of terrestrial C and N to the river system. In average, currently at least 5.1 x 106 kg organic C and 0.4 x 106 kg N were eroded annually (2015-2018) into the Lena River. The observed sediment and organic matter (OM) erosion was persistent over the observation period also due to the specific configuration of river flow direction and cliff shore orientation. Our observations highlight the importance to further study rapid fluvio-thermal erosion processes in the permafrost region. The organic C and N transport from land to river and eventually to the Arctic Ocean from this and similar settings may have severe implications on the biogeochemistry and ecology of the near-shore zone of the Laptev Sea as well as for turnover and rapid release of old C and N to the atmosphere.
Highlights
Permafrost landscapes are sensitive to global temperature rise and may be affected by widespread degradation (Grosse et al, 2016; Biskaborn et al, 2019)
These shores are affected by thermo-erosion processes induced by sea or river water combining mechanical erosion from waves, currents, and moving ice with thermal impacts of the water that is warmer than the permafrost (Are, 1983; Günther et al, 2013)
The strong erosion of river banks and coastal segments leads to large sediment and organic matter inputs into Arctic river systems and the Arctic Ocean, respectively (e.g., Rachold et al, 2000; Couture et al, 2018; Rowland et al, 2018) with regional to global implications affecting the aquatic ecosystem and global C cycle (Gustafsson et al, 2011; Vonk and Gustafsson, 2013; Mann et al, 2015; Semiletov et al, 2016; Fritz et al, 2017)
Summary
Permafrost landscapes are sensitive to global temperature rise and may be affected by widespread degradation (Grosse et al, 2016; Biskaborn et al, 2019). Coasts and river banks in the Arctic are fast changing permafrost features, which are characterized by high ground ice contents (e.g., Walker et al, 1987; Lantuit et al, 2011; Kanevskiy et al, 2016; Jones et al, 2018). These shores are affected by thermo-erosion processes induced by sea or river water combining mechanical erosion from waves, currents, and moving ice with thermal impacts of the water that is warmer than the permafrost (Are, 1983; Günther et al, 2013). How much of the C released through shore erosion is re-buried on the Arctic shelf or in the deep Arctic Ocean versus is being mineralized and released into the atmosphere is still a matter of discussion (Vonk et al, 2012; Bröder et al, 2019; Grotheer et al, 2020)
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