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In this study, we analyze interactions in lake and lake catchment systems of a continuous permafrost area. We assessed colored dissolved organic matter (CDOM) absorption at 440 nm (a(440)(CDOM)) and absorption slope (S300-500) in lakes using field sampling and optical remote sensing data for an area of 350 km(2) in Central Yamal, Siberia. Applying a CDOM algorithm (ratio of green and red band reflectance) for two high spatial resolution multispectral GeoEye-1 and Worldview-2 satellite images, we were able to extrapolate the a()(CDOM) data from 18 lakes sampled in the field to 356 lakes in the study area (model R-2 = 0.79). Values of a(440)(CDOM) in 356 lakes varied from 0.48 to 8.35 m(-1) with a median of 1.43 m(-1). This a()(CDOM) dataset was used to relate lake CDOM to 17 lake and lake catchment parameters derived from optical and radar remote sensing data and from digital elevation model analysis in order to establish the parameters controlling CDOM in lakes on the Yamal Peninsula. Regression tree model and boosted regression tree analysis showed that the activity of cryogenic processes (thermocirques) in the lake shores and lake water level were the two most important controls, explaining 48.4% and 28.4% of lake CDOM, respectively (R-2 = 0.61). Activation of thermocirques led to a large input of terrestrial organic matter and sediments from catchments and thawed permafrost to lakes (n = 15, mean a(440)(CDOM) = 5.3 m(-1)). Large lakes on the floodplain with a connection to Mordy-Yakha River received more CDOM (n = 7, mean a(440)(CDOM) = 3.8 m(-1)) compared to lakes located on higher terraces.
Arctic tundra landscapes are composed of a complex mosaic of patterned ground features, varying in soil moisture, vegetation composition, and surface hydrology over small spatial scales (10-100 m). The importance of microtopography and associated geomorphic landforms in influencing ecosystem structure and function is well founded, however, spatial data products describing local to regional scale distribution of patterned ground or polygonal tundra geomorphology are largely unavailable. Thus, our understanding of local impacts on regional scale processes (e.g., carbon dynamics) may be limited. We produced two key spatiotemporal datasets spanning the Arctic Coastal Plain of northern Alaska (similar to 60,000 km(2)) to evaluate climate-geomorphological controls on arctic tundra productivity change, using (1) a novel 30m classification of polygonal tundra geomorphology and (2) decadal-trends in surface greenness using the Landsat archive (1999-2014). These datasets can be easily integrated and adapted in an array of local to regional applications such as (1) upscaling plot-level measurements (e.g., carbon/energy fluxes), (2) mapping of soils, vegetation, or permafrost, and/or (3) initializing ecosystem biogeochemistry, hydrology, and/or habitat modeling.
Sub-seasonal thaw slump mass wasting is not consistently energy limited at the landscape scale
(2018)
Predicting future thaw slump activity requires a sound understanding of the atmospheric drivers and geomorphic controls on mass wasting across a range of timescales. On sub-seasonal timescales, sparse measurements indicate that mass wasting at active slumps is often limited by the energy available for melting ground ice, but other factors such as rainfall or the formation of an insulating veneer may also be relevant. To study the sub-seasonal drivers, we derive topographic changes from single-pass radar interferometric data acquired by the TanDEM-X satellites. The estimated elevation changes at 12m resolution complement the commonly observed planimetric retreat rates by providing information on volume losses. Their high vertical precision (around 30 cm), frequent observations (11 days) and large coverage (5000 km(2)) allow us to track mass wasting as drivers such as the available energy change during the summer of 2015 in two study regions. We find that thaw slumps in the Tuktoyaktuk coastlands, Canada, are not energy limited in June, as they undergo limited mass wasting (height loss of around 0 cm day 1) despite the ample available energy, suggesting the widespread presence of early season insulating snow or debris veneer. Later in summer, height losses generally increase (around 3 cm day 1), but they do so in distinct ways. For many slumps, mass wasting tracks the available energy, a temporal pattern that is also observed at coastal yedoma cliffs on the Bykovsky Peninsula, Russia. However, the other two common temporal trajectories are asynchronous with the available energy, as they track strong precipitation events or show a sudden speed-up in late August respectively. The observed temporal patterns are poorly related to slump characteristics like the headwall height. The contrasting temporal behaviour of nearby thaw slumps highlights the importance of complex local and temporally varying controls on mass wasting.
Ice-wedge polygons are common features of northeastern Siberian lowland periglacial tundra landscapes. To deduce the formation and alternation of ice-wedge polygons in the Kolyma Delta and in the Indigirka Lowland, we studied shallow cores, up to 1.3 m deep, from polygon center and rim locations. The formation of well-developed low-center polygons with elevated rims and wet centers is shown by the beginning of peat accumulation, increased organic matter contents, and changes in vegetation cover from Poaceae-, Alnus-, and Betula-dominated pollen spectra to dominating Cyperaceae and Botryoccocus presence, and Carex and Drepanocladus revolvens macro-fossils. Tecamoebae data support such a change from wetland to open-water conditions in polygon centers by changes from dominating eurybiontic and sphagnobiontic to hydrobiontic species assemblages. The peat accumulation indicates low-center polygon formation and started between 2380 +/- 30 and 1676 +/- 32 years before present (BP) in the Kolyma Delta. We recorded an opposite change from open-water to wetland conditions because of rim degradation and consecutive high-center polygon formation in the Indigirka Lowland between 2144 +/- 33 and 1632 +/- 32 years BP. The late Holocene records of polygon landscape development reveal changes in local hydrology and soil moisture.
Veränderungen im thermalen Regime des Permafrosts verursachen Störungen der Erdoberfläche. Diese Veränderungen werden durch die in der Arktis seit Jahrzehnten ansteigenden Temperaturen verstärkt. Thermokarst ist ein Prozess, welcher die Erdoberfläche durch Schmelzen von Grundeis, oder Auftauen von Permafrost absacken lässt, wodurch charakteristische Landformen entstehen. Thermokarst ist vor allem entlang von Hängen weit verbreitet und die Anzahl der damit verbundenen Landformen in der Arktis steigt stetig an. Dieser Prozess mobilisiert große Mengen an Material, welche in Richtung Meer transportiert oder entlang von Hängen akkumuliert werden. Während entlang von Hängen auftretender Thermokarst terrestrische sowie aquatische Ökosysteme stark verändert, ist dessen Einfluss auf regionaler Skala zurzeit noch Gegenstand der Forschung.
In dieser Arbeit quantifizieren wir die Auswirkungen von Thermokarstprozessen entlang von Hängen auf die umliegenden Ökosysteme der küstennahen Täler und Nahküstenbereiche entlang der Yukon Küste in Kanada. Mittels überwachtem maschinellen Lernen haben wir geomorphische Faktoren identifiziert, welche die Entwicklung von retrogressiven Auftaurutschungen (RTS) begünstigen. RTS sind eine Erscheinungsform von Thermokarst entlang von Hängen. Die Küstengeomorphologie, sowie der Grundeistyp und -inhalt sind die wesentlichen bestimmenden Faktoren für das Auftreten von RTS. Wir haben Luftbildaufnahmen und Satellitenbilder genutzt, um die Evolution von RTS im Zeitraum von 1952 bis 2011 zu verfolgen. Während dieser Zeit ist die Anzahl und Ausdehnung von RTS linear angestiegen. Wir zeigen, dass 56% der RTS welche entlang der Küste in 2011 identifiziert wurden, 16.6 × 106 m3 an Material erodiert haben. Hiervon wurden 45% durch Küstenprozesse entlang der Küste transportiert. RTS tragen wesentlich zu dem Kohlenstoff-Budget des Nahküstenbereiches bei: 17% der in 2011 identifizierten RTS, haben 0.6% des organischen Kohlenstoffes transportiert, welcher durch Küstenerosion entlang der Yukon Küste jährlich freigesetzt wird. Um den Einfluss von Thermokarst entlang von Hängen auf das terrestrische Ökosystem zu beurteilen, haben wir die räumliche Verteilung von organischem Bodenkohlenstoff und Stickstoff (SOC, TN) entlang von Hangprofilen in drei arktischen Tälern analysiert.Wir weisen auf eine hohe räumliche Variabilität in der Verteilung von SOC und TN hin, welche auf komplexe Bodenprozesse zurückzuführen ist, welche entlang von Hängen auftreten. Thermokarst entlang von Hängen hat einen großen Einfluss auf die Degradierung von organischem Material und die Speicherung von SOC und TN.
Arctic tundra ecosystems have experienced unprecedented change associated with climate warming over recent decades. Across the Pan-Arctic, vegetation productivity and surface greenness have trended positively over the period of satellite observation. However, since 2011 these trends have slowed considerably, showing signs of browning in many regions. It is unclear what factors are driving this change and which regions/landforms will be most sensitive to future browning. Here we provide evidence linking decadal patterns in arctic greening and browning with regional climate change and local permafrost-driven landscape heterogeneity. We analyzed the spatial variability of decadal-scale trends in surface greenness across the Arctic Coastal Plain of northern Alaska (similar to 60,000 km(2)) using the Landsat archive (1999-2014), in combination with novel 30 m classifications of polygonal tundra and regional watersheds, finding landscape heterogeneity and regional climate change to be the most important factors controlling historical greenness trends. Browning was linked to increased temperature and precipitation, with the exception of young landforms (developed following lake drainage), which will likely continue to green. Spatiotemporal model forecasting suggests carbon uptake potential to be reduced in response to warmer and/or wetter climatic conditions, potentially increasing the net loss of carbon to the atmosphere, at a greater degree than previously expected.