Artem Khomutov

Spatial and temporal patterns of greenness on the Yamal Peninsula, Russia: interactions of ecological and social factors affecting the Arctic normalized difference vegetation index

The causes of a greening trend detected in the Arctic using the normalized difference vegetation index (NDVI) are still poorly understood. Changes in NDVI are a result of multiple ecological and social factors that affect tundra net primary productivity. Here we use a 25 year time series of AVHRR-derived NDVI data (AVHRR: advanced very high resolution radiometer), climate analysis, a global geographic information database and ground-based studies to examine the spatial and temporal patterns of vegetation greenness on the Yamal Peninsula, Russia. We assess the effects of climate change, gas-field development, reindeer grazing and permafrost degradation. In contrast to the case for Arctic North America, there has not been a significant trend in summer temperature or NDVI, and much of the pattern of NDVI in this region is due to disturbances. There has been a 37% change in early-summer coastal sea-ice concentration, a 4% increase in summer land temperatures and a 7% change in the average time-integrated NDVI over the length of the satellite observations. Gas-field infrastructure is not currently extensive enough to affect regional NDVI patterns. The effect of reindeer is difficult to quantitatively assess because of the lack of control areas where reindeer are excluded. Many of the greenest landscapes on the Yamal are associated with landslides and drainage networks that have resulted from ongoing rapid permafrost degradation. A warming climate and enhanced winter snow are likely to exacerbate positive feedbacks between climate and permafrost thawing. We present a diagram that summarizes the social and ecological factors that influence Arctic NDVI. The NDVI should be viewed as a powerful monitoring tool that integrates the cumulative effect of a multitude of factors affecting Arctic land-cover change.

Cumulative Effects of Rapid Land-Cover and Land-Use Changes on the Yamal Peninsula, Russia

The Yamal Peninsula in northwest Siberia is undergoing some of the most rapid land-cover and land-use changes in the Arctic due to a combination of gas development, reindeer herding, and climate change. Unusual geological condi- tions (nutrient-poor sands, massive ground ice and extensive landslides) exacerbate the impacts. These changes will likely increase markedly as transportation corridors are built to transport the gas to market. Understanding the nature, extent, causes and consequences (i.e., the cumulative effects) of the past and ongoing rapid changes on the Yamal is important for effective, long-term decision-making and planning. The cumulative effects to vegetation are the focus of this chapter because the plants are a critical component of the Yamal landscape that support the indigenous Nenets people and their reindeer and also protect the underlying ice-rich permafrost from melting. We are using a combination of ground-based studies (a transect of five loca- tions across the Yamal), remote-sensing studies, and analyses of Nenets land-use activities to develop vegetation-change models that can be used to help anticipate future states of the tundra and how those changes might affect traditional reindeer herding practices and the thermal state of the permafrost. This chapter provides an overview of the approach, some early results, and recommendations for expanding the concept of cumulative-effects analysis to include examining the simultaneous and interactive effects of multiple drivers of change.

Circumpolar Mapping of Ground-Fast Lake Ice

Shallow lakes are common across the entire Arctic. They play an important role as methane sources and wildlife habitats, and they are also associated with thermokarst processes which are characteristic of permafrost environments. Many lakes freeze to the ground along their rims and often over the entire extent during winter time. Knowledge on the spatial patterns of ground-fast and floating ice is important as it relates to methane release, talik formation and hydrological processes, but no circumpolar account of this phenomenon is currently available. Previous studies have shown that ground-fast ice can easily be detected using C-band Synthetic Aperture Radar (SAR) backscatter intensity data acquired from satellites. A major challenge is that backscatter intensity varies across the satellite scenes due to incidence angle effects. Circumpolar application therefore requires the inclusion of incidence angle dependencies into the detection algorithm. An approach using ENVISAT ASAR Wide Swath data (approximately 120 m spatial resolution) has therefore been developed supported by bathymetric measurements for lakes in Siberia. This approach was then further applied across the entire Arctic for late winter 2008. Ground-fast ice fraction has been derived for (1) two million lake objects larger than 0.025 km² (post-processed GlobeLand30), (2) a 50 x 50 km grid and (3) within certain zones relevant for climate studies (permafrost type, last glacial maximum, Yedoma). Especially lakes smaller than approximately 0.1 km² may freeze completely to the ground. The proportion of ground-fast ice increases with increasing soil organic carbon content in the proximity of the lakes. This underlines the importance of such lakes for emission studies and the need to map the occurrence of ground-fast lake ice. Clusters of variable fractions of ground-fast ice occur especially in Yedoma regions of Eastern Siberia and Alaska. This reflects the nature of thaw lake dynamics. Analyses of lake depth measurements from several sites suggest that the used method yields the potential to utilize ground-fast lake ice information over larger areas with respect to landscape development, but results need to be treated with care, specifically for larger lakes and along river courses.

Assessment of Landslide Hazards in a Typical Tundra of Central Yamal, Russia

This chapter presents an assessment of cryogenic landslide hazard study based on differentiation of landscapes in Central Yamal. Analysis of landslide pattern shows that all recent cryogenic landslides are located on concave slopes. As concave slopes from our opinion are being modified from ancient landslides, it means that recent landslides occupy ancient landslide slopes. Recent landslide impact differs within the same landscape complexes appearing on different geomorphic levels of the central Yamal. Generally, this impact increases from low to high geomorphic levels. Landscape complexes are divided into five groups according to predicted cryogenic landslide hazard degree. Grouping of landscape complexes is based on differentiation of landscape conditions more or less favourable for cryogenic landslides and on the latest cryogenic landslide occurrence. Landslide distribution within a landscape unit determines its sensitivity to landslide recurrence; the larger the area of disturbance by recent landslide, the more sensitive is a landscape complex subdivided within the study site. At the same time, directly disturbed by the latest landslides areas within a landscape unit are considered non-hazardous because the re-occurrence of cryogenic landslides on such locations in coming centuries is mostly improbable.

Cryogenic Landslides in the West-Siberian Plain of Russia: Classification, Mechanisms, and Landforms

Cryogenic landslides are the main relief-forming process on the Northern part of West Siberian Plain. This chapter discusses the theory of cryogenic landslides and suggests classification method based on mechanisms, specific landforms—manifestations of various landslide processes. The study is based on the long-term field observations at Research station “Vaskiny Dachi” in Central Yamal, as well as occasional observations in other areas. Two main types of cryogenic landslides were distinguished based on mechanism and mode of displacement. They are (1) earth/mud flows (retrogressive thaw slumps) and (2) translational landslides (active-layer detachments). The first type results from thawing of massive ground ice within permafrost layers, while the second type is caused by the thawing of ice lenses in the active-layer base (transient layer). Distinguished are specific landforms: (1) thermocirques, and (2) landslide cirques. Landslide cirques are considered to start at a subsequent stage of thermocirque after the massive ground ice layer is exhausted or buried by landslide masses. The thermocirque changes are noted within years and decades, while new landslides within landslide cirques are separated by several centuries. As landslide masses bury organic material of soil and vegetative canopy, it is possible to use radiocarbon dating method to know the age of the landslides. Shear surfaces of ancient landslides are overgrown by abnormally high willow shrubs which allow the use of dendrochronologic method in the analysis of landslide cirque development.

Comparison of Gas Emission Crater Geomorphodynamics on Yamal and Gydan Peninsulas (Russia), Based on Repeat Very-High-Resolution Stereopairs

Gas Emission Craters (GEC) represent a new phenomenon in permafrost regions discovered in the north of West Siberia. In this study we use very-high-resolution Worldview satellite stereopairs and Resurs-P images to reveal and measure the geomorphic features that preceded and followed GEC formation on the Yamal and Gydan peninsulas. Analysis of DEMs allowed us to: (1) distinguish different terrain positions of the GEC, at the foot of a gentle slope (Yamal), and on an upper edge of a terrace slope; (2) notice that the formation of both Yamal and Gydan GECs were preceded by mound development; (3) measure a funnel-shaped upper part and a cylindrical lower part for each crater; (4) and measure the expansion and plan form modification of GECs. Although the general characteristics of both craters are similar, there are differences when comparing both key sites in detail. The height of the mound and diameter of the resulting GEC in Yamal exceeds that in Gydan; GEC-1 was surrounded by a well-developed parapet, while AntGEC did not show any considerable accumulative body. Thus, using very-high-resolution remote sensing data allowed us to discriminate geomorphic features and relief positions characteristic for GEC formation. GECs are a potential threat to commercial facilities in permafrost and indigenous settlements, especially because at present there is no statistically significant number of study objects to identify the local environmental conditions in which the formation of new GEC is possible.

GIS and field data based modelling of snow water equivalent in shrub tundra

An approach for snow water equivalent (SWE) modelling in tundra environments has been developed for the test area on the Yamal peninsula. Detailed mapping of snow cover is very important for tundra areas under continuous permafrost conditions, because the snow cover affects the active layer thickness (ALT) and the ground temperature, acting as a heat-insulating agent. The information concerning snow cover with specific regime of accumulation can support studies of ground temperature distribution and other permafrost related aspects. Special attention has been given to the presence of shrubs and microtopography, specifically ravines in a modelling approach. The methodology is based on statistical analysis of snow survey data and on GIS- (Geographical Information System) analysis of a range of parameters: topography, wind, and shrub vegetation. The topography significantly controls snow cover redistribution. This influence can be expressed as increase of snow depth on concave and decrease on convex surfaces. Specifically, snow depth was related to curvature in the study area with a correlation of R=0.83. An index is used to distinguish windward and leeward slopes in order to explain wind redistribution of snow. It is calculated from aspect data retrieved from a digital elevation model (obtained by field survey). It can be shown that shrub vegetation can serve as a ‘trap’ for wind-blown snow but is not a limiting factor for maximum snow depth, since the snow depth can be higher or lower than shrub height dependent on other factors.An approach for snow water equivalent (SWE) modelling in tundra environments has been developed for the test area on the Yamal peninsula. Detailed mapping of snow cover is very important for tundra areas under continuous permafrost conditions, because the snow cover affects the active layer thickness (ALT) and the ground temperature, acting as a heat-insulating agent. The information concerning snow cover with specific regime of accumulation can support studies of ground temperature distribution and other permafrost related aspects.

Activation of Cryogenic Earth Flows and Formation of Thermocirques on Central Yamal as a Result of Climate Fluctuations

Study area in continuous permafrost zone, characterized by tabular ground ice distribution, is known for active slope processes. In 90-s main attention was paid to translational landslides (active layer detachments). Due to climate trends summer temperature became warmer, active layer depth increased. As a result, active-layer base ice thawed and stopped development of translational landslides. At the same time, tabular ground ice table got involved into seasonal thaw and triggered earth flows at the lake shores, the second known type of cryogenic landslides found previously mainly at the sea coasts. Earth flows are the main process in thermal denudation: a complex of processes responsible for formation of thermocirques. Thermocirques are semi-circle shaped depressions resulting from massive ground ice thaw and removal of detached material downslope. Monitoring of thermocirque activation and development allows analyzing climatic controls of thermal denudation, and rates of thermocirque enlargement. At present in the Yamal Peninsula tundra predominance of processes associated with tabular ground ice thaw (cryogenic earth flows) over the processes associated with the ice formation at the bottom of the active layer (cryogenic translational landslides) is observed. This is caused by deepening of the active layer and exposure of the massive ground ice (tabular ground ice or ice-wedges) within permafrost to first seasonal and then perennial thaw. Activation of thermal denudation which started on Yamal Peninsula in summer 2012, is associated with extremely warm spring and summer of this year, and the warmest July of 2013. By the end of the warm season thawing of the top of icy permafrost and tabular ground ice on some slopes resulted in cryogenic landsliding in the form of earth flows and further thermocirque development. Thermocirques may form on slopes of various aspects but develop faster on south-facing slopes.

Cryogenic Landslides in the Arctic Plains of Russia: Classification, Mechanisms, and Landforms

The paper is discussing the theory of cryogenic landslides. Suggested is classification of cryogenic landslides based on several attributes: mechanisms, specific landforms, and other manifestations of landsliding characteristic of the Arctic plains of Russia. The theory results from long-term field study at research station “Vaskiny Dachi” in Central Yamal, key sites on Yugorsky peninsula, as well as occasional observations in other areas of the Russian Arctic. Two main types of cryogenic landslides are identified: retrogressive thaw slumps (earth/mud flows) and translational landslides (active-layer detachments). Distinguished are several stages of landform development resulting from landsliding, passing from thermocirques to landslide cirques. Landslide cirques are considered to start as a subsequent stage of decadent thermocirque after the ground ice layer is exhausted or buried by landslide masses. Cryogenic landslides are climate-related features and for this reason are indicators of past and modern climate fluctuations.

Terrestrial CDOM in Lakes of Yamal Peninsula: Connection to Lake and Lake Catchment Properties

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 km2 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(λ)CDOM data from 18 lakes sampled in the field to 356 lakes in the study area (model R2 = 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(λ)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 (R2 = 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.