Abstract
Ice-ridge Yedoma terrain is susceptible to vertical surface displacements by thaw and refreeze of ground ice, and geomorphological processes of mass wasting, erosion and sedimentation. Here we explore the relation between a 3 year data set of InSAR measurements of vertical surface displacements during the thaw season, and geomorphological features in an area in the Indigirka Lowlands, Northeast Siberia. The geomorphology is presented in a geomorphological map, based on interpretation of high resolution visible spectrum satellite imagery, field surveys and available data from paleo-environmental research. The main landforms comprise overlapping drained thaw lake basins and lakes, erosion remnants of Late Pleistocene Yedoma deposits, and a floodplain of a high-sinuosity anastomosing river with ancient river terrace remnants. The spatial distribution of drained thaw lake basins and Yedoma erosion remnants in the study area and its surroundings is influenced by neotectonic movements. The 3 years of InSAR measurement include 2 years of high snowfall and extreme river flooding (2017–2018) and 1 year of modest snowfall, early spring and warm summer (2019). The magnitude of surface displacements varies among the years, and show considerable spatial variation. Distinct spatial clusters of displacement trajectories can be discerned, which relate to geomorphological processes and ground ice conditions. Strong subsidence occurred in particular in 2019. In the wet year of 2017, marked heave occurred at Yedoma plateau surfaces, likely by ice accumulation at the top of the permafrost driven by excess precipitation. The spatial variability of surface displacements is high. This is explored by statistical analysis, and is attributed to the interaction of various processes. Next to ground ice volume change, also sedimentation (peat, colluvial deposition) and shrinkage or swelling of soils with changing water content may have contributed. Tussock tundra areas covered by the extreme 2017 and 2018 spring floods show high subsidence rates and an increase of midsummer thaw depths. We hypothesize that increased flood heights along Siberian lowland rivers potentially induce deeper thaw and subsidence on floodplain margins, and also lowers the drainage thresholds of thaw lakes. Both mechanisms tend to increase floodplain area. This may increase CH4 emission from floodplains, but also may enhance carbon storage in floodplain sedimentary environments.
Highlights
Permafrost is increasingly influenced by climate warming
A specific type of ice-rich permafrost formation that occurs over large areas in Siberia and Alaska is Yedoma, known as Ice Complex: periglacial loess and fluvial silt deposits that were deposited during Quaternary glacials in unglaciated terrain, which obtained large masses of excess ice by the growth of syngenetic ice wedges during sedimentation (Schirrmeister et al, 2013; Murton et al, 2015; Strauss et al, 2017)
The area is dominated by overlapping drained thaw lake basins (DTLB) (54.5%) and the recent floodplain (ARF, 39.1%)
Summary
Permafrost is increasingly influenced by climate warming. Permafrost thaw is expected to enhance greenhouse gas emissions from permafrost soils and to decrease stability of soils, in particular in ice-rich permafrost areas (e.g. IPCC, 2013; AMAP, 2017). Yedoma contains a considerable carbon stock (Zimov et al, 2006; Strauss et al, 2017). These deep ice-rich deposits (several tens of meters and more) are very vulnerable to abrupt thaw (i.e. thermokarst) with rapid erosion, or more gradual subsidence, and may release carbon to the atmosphere as CO2 and CH4 (Schneider von Deimling et al, 2015; Vonk et al, 2013; Vonk et al, 2015). Surface displacements related to permafrost thaw affect the stability of human infrastructure in permafrost areas. Structural instability can lead to severe environmental damage when urban, industrial or mining infrastructure is affected (e.g. Shiklomanov et al, 2017; Hjort et al, 2018)
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