Showing papers on "Permafrost published in 2009"

Soil organic carbon pools in the northern circumpolar permafrost region

Abstract: of all soils in the northern permafrost region is approximately 18,782 � 10 3 km 2 ,o r approximately 16% of the global soil area. In the northern permafrost region, organic soils (peatlands) and cryoturbated permafrost-affected mineral soils have the highest mean soil organic carbon contents (32.2–69.6 kg m �2 ). Here we report a new estimate of the carbon pools in soils of the northern permafrost region, including deeper layers and pools not accounted for in previous analyses. Carbon pools were estimated to be 191.29 Pg for the 0–30 cm depth, 495.80 Pg for the 0–100 cm depth, and 1024.00 Pg for the 0–300 cm depth. Our estimate for the first meter of soil alone is about double that reported for this region in previous analyses. Carbon pools in layers deeper than 300 cm were estimated to be 407 Pg in yedoma deposits and 241 Pg in deltaic deposits. In total, the northern permafrost region contains approximately 1672 Pg of organic carbon, of which approximately 1466 Pg, or 88%, occurs in perennially frozen soils and deposits. This 1672 Pg of organic carbon would account for approximately 50% of the estimated global belowground organic carbon pool.

The effect of permafrost thaw on old carbon release and net carbon exchange from tundra

Abstract: The enormous amounts of carbon stored deep in permafrost soils — permafrost ecosystems contain almost twice as much carbon as is present in the atmosphere — have the potential to create a positive feedback to climate change if released into a warming world. The bulk of the permafrost carbon pool consists of 'old' carbon, accumulated over thousands of years, but the rate of carbon release from these soils is highly uncertain. Schuur et al. report data on net ecosystem carbon exchange and the radiocarbon age of ecosystem respiration from a long-term monitoring site in Alaska where permafrost temperatures have been directly measured since 1985, and observed to warm since then. They find significant losses of soil carbon with permafrost thaw that, over decadal timescales, overwhelms increased plant carbon uptake at rates that could make permafrost a large biospheric carbon source in a warmer world. Permafrost thaw and microbial decomposition is considered one of the most likely positive climate feedbacks from terrestrial ecosystems to the atmosphere in a warmer world, but the rate of carbon release from permafrost soil remains highly uncertain. Here, net ecosystem carbon exchange is measured in a tundra landscape undergoing permafrost thaw to determine the influence of old carbon loss on ecosystem carbon balance. The results reveal significant losses of soil carbon over decadal time scales, overwhelming the increased carbon uptake from plants. Permafrost soils in boreal and Arctic ecosystems store almost twice as much carbon1,2 as is currently present in the atmosphere3. Permafrost thaw and the microbial decomposition of previously frozen organic carbon is considered one of the most likely positive climate feedbacks from terrestrial ecosystems to the atmosphere in a warmer world1,2,4,5,6,7. The rate of carbon release from permafrost soils is highly uncertain, but it is crucial for predicting the strength and timing of this carbon-cycle feedback effect, and thus how important permafrost thaw will be for climate change this century and beyond1,2,4,5,6,7. Sustained transfers of carbon to the atmosphere that could cause a significant positive feedback to climate change must come from old carbon, which forms the bulk of the permafrost carbon pool that accumulated over thousands of years8,9,10,11. Here we measure net ecosystem carbon exchange and the radiocarbon age of ecosystem respiration in a tundra landscape undergoing permafrost thaw12 to determine the influence of old carbon loss on ecosystem carbon balance. We find that areas that thawed over the past 15 years had 40 per cent more annual losses of old carbon than minimally thawed areas, but had overall net ecosystem carbon uptake as increased plant growth offset these losses. In contrast, areas that thawed decades earlier lost even more old carbon, a 78 per cent increase over minimally thawed areas; this old carbon loss contributed to overall net ecosystem carbon release despite increased plant growth. Our data document significant losses of soil carbon with permafrost thaw that, over decadal timescales, overwhelms increased plant carbon uptake13,14,15 at rates that could make permafrost a large biospheric carbon source in a warmer world.

Impacts of permafrost degradation on arctic river biogeochemistry.

Abstract: Over the next century, near-surface permafrost across the circumpolar Arctic is expected to degrade significantly, particularly for land areas south of 70°N. This is likely to cause widespread impacts on arctic hydrology, ecology, and trace gas emissions. Here, we present a review of recent studies investigating linkages between permafrost dynamics and river biogeochemistry in the Arctic, including consideration of likely impacts that warming-induced changes in permafrost may be having (or will have in the future) on the delivery of organic matter, inorganic nutrients, and major ions to the Arctic Ocean. These interacting processes can be highly complex and undoubtedly exhibit spatial and temporal variabilities associated with current permafrost conditions, sensitivity to permafrost thaw, mode of permafrost degradation (overall permafrost thaw, active layer deepening, and/or thermokarst processes), and environmental characteristics of watersheds (e.g. land cover, soil type, and topography). One of the most profound consequences of permafrost thaw projected for the future is that the arctic terrestrial freshwater system is likely to experience a transition from a surface water-dominated system to a groundwater-dominated system. Along with many other cascading impacts from this transition, mineral-rich groundwater may become an important contributor to streamflow, in addition to the currently dominant contribution from mineral-poor surface water. Most studies observe or predict an increase in major ion, phosphate, and silicate export with this shift towards greater groundwater contributions. However, we see conflicting accounts of whether the delivery of inorganic nitrogen and organic matter will increase or decrease with warming and permafrost thaw. It is important to note that uncertainties in the predictions of the total flux of biogeochemical constituents are tightly linked to future uncertainties in discharge of rivers. Nonetheless, it is clear that over the next century there will be important shifts in the river transport of organic matter, inorganic nutrients, and major ions, which may in turn have critical implications for primary production and carbon cycling on arctic shelves and in the Arctic Ocean basin interior. Copyright © 2008 John Wiley & Sons, Ltd.

Observational constraints on recent increases in the atmospheric CH4 burden

Abstract: [1] Measurements of atmospheric CH4 from air samples collected weekly at 46 remote surface sites show that, after a decade of near-zero growth, globally averaged atmospheric methane increased during 2007 and 2008. During 2007, CH4 increased by 8.3 ± 0.6 ppb. CH4 mole fractions averaged over polar northern latitudes and the Southern Hemisphere increased more than other zonally averaged regions. In 2008, globally averaged CH4 increased by 4.4 ± 0.6 ppb; the largest increase was in the tropics, while polar northern latitudes did not increase. Satellite and in situ CO observations suggest only a minor contribution to increased CH4 from biomass burning. The most likely drivers of the CH4 anomalies observed during 2007 and 2008 are anomalously high temperatures in the Arctic and greater than average precipitation in the tropics. Near-zero CH4 growth in the Arctic during 2008 suggests we have not yet activated strong climate feedbacks from permafrost and CH4 hydrates.

The environment and permafrost of the Mackenzie Delta area

Abstract: The Mackenzie Delta, prograding northwestwards into the Beaufort Sea, is North America's largest arctic delta. This Holocene feature is bounded by rolling uplands to the east and the Richardson Mountains to the west. Treeline traverses the region, separating the subarctic boreal forest in southern parts from low-shrub tundra and sedge wetlands at the coast. The region is experiencing rapid climate change, and mean annual air temperature has increased by more than 2.5°C since 1970. The area was at the margin of the Wisconsinan ice sheet, so that in the uplands the mean annual ground temperature and glacial history control permafrost thickness, which varies from >700 m to <100 m. Ground temperatures in the delta are distinct from the uplands due to the thermal influence of numerous lakes and shifting channels. In the uplands, ground temperatures decrease northwards across treeline in association with a decrease in the thickness of snow cover. Ground temperatures have increased since 1970 in the uplands by approximately 1.5°C in association with rising annual mean air temperature. The increase has been less in the delta south of treeline due to the extensive thermal influence of water bodies on ground temperature. However, in the outer delta, the ground is currently more than 2.5°C warmer than in 1970. The impact of climate change on permafrost is also evident in the thickness of the active layer, which increased on average by 8 cm at 12 tundra sites on northern Richards Island from 1983–2008. Copyright © 2009 John Wiley & Sons, Ltd. and Her Majesty the Queen in right of Canada.

Increase in the rate and uniformity of coastline erosion in Arctic Alaska

Abstract: [1] Analysis of a 60 km segment of the Alaskan Beaufort Sea coast using a time-series of aerial photography revealed that mean annual erosion rates increased from 6.8 m a−1 (1955 to 1979), to 8.7 m a−1 (1979 to 2002), to 13.6 m a−1 (2002 to 2007). We also observed that spatial patterns of erosion have become more uniform across shoreline types with different degrees of ice-richness. Further, during the remainder of the 2007 ice-free season 25 m of erosion occurred locally, in the absence of a westerly storm event. Concurrent arctic changes potentially responsible for this shift in the rate and pattern of land loss include declining sea ice extent, increasing summertime sea surface temperature, rising sea-level, and increases in storm power and corresponding wave action. Taken together, these factors may be leading to a new regime of ocean-land interactions that are repositioning and reshaping the Arctic coastline.

Increasing winter baseflow and mean annual streamflow from possible permafrost thawing in the Northwest Territories, Canada

Abstract: [1] Increasing surface air temperatures from anthropogenic forcing are melting permafrost at high latitudes and intensifying the hydrological cycle. Long-term streamflow records (≥30 yrs) from 23 stream gauges in the Canadian Northwest Territories (NWT) indicate a general significant upward trend in winter baseflow of 0.5–271.6 %/yr and the beginning of significant increasing mean annual flow (seen at 39% of studied gauge records), as assessed by the Kendall-τ test. The NWT exports an average discharge of ≥308.6 km3/yr to the Beaufort Sea, of which ≥120.9 km3/yr is baseflow. We propose that the increases in winter baseflow and mean annual streamflow in the NWT were caused predominately by climate warming via permafrost thawing that enhances infiltration and deeper flowpaths and hydrological cycle intensification. To provide hydroclimatic context, we present evidence of a statistically significant positive link between the Northern annular mode and annual NWT streamflow at the interannual-to-decadal timescales.

Integrating peatlands and permafrost into a dynamic global vegetation model: 1. Evaluation and sensitivity of physical land surface processes

Abstract: Received 25 October 2008; revised 3 April 2009; accepted 7 May 2009; published 22 August 2009. [1] Northern peatlands and permafrost soils are associated with large carbon stocks. Rising temperatures are likely to affect the carbon balance in high-latitude ecosystems, but to what degree is uncertain. We have enhanced the Lund-Potsdam-Jena (LPJ) dynamic global vegetation model by introducing processes necessary to simulate permafrost dynamics, peatland hydrology, and peatland vegetation. The new version, LPJ-WHy v1.2, was used to study soil temperature, active layer depth, permafrost distribution, and water table position. Modeled soil temperatures agreed well with observations, apart from a Siberian site where the soil is insulated by an extensive shrub layer. Water table positions were generally in the range of observations, with some exceptions. Simulated active layer depth showed a mean absolute error of 44 cm when compared to observations, but the error was reduced to 25 cm when the soil type for seven sites was manually corrected to mirror local conditions. A sensitivity test, in which temperature and precipitation were varied independently, showed that soil temperatures and active layer depths increased more under higher temperatures when precipitation was increased at the same time. The sensitivity experiment suggested persisting wet conditions in peatlands even under temperature increases of up to 9C as long as annual precipitation is allowed to increase with temperature to the extent indicated by climate model experiments.

Physical and ecological changes associated with warming permafrost and thermokarst in Interior Alaska

Abstract: Observations and measurements were made of physical and ecological changes that have occurred since 1985 at a tundra site near Healy, Alaska. Air temperatures decreased (1985 through 1999) while permafrost warmed and thawed creating thermokarst terrain, probably as a result of increased snow depths. Permafrost, active layer and ground-ice conditions at the Healy site are the result of the interaction of climatic, ecologic and other factors. The slow accumulation of ground ice in an intermediate permafrost layer formed by upward freezing from the permafrost surface leads to long-term differential frost heave and microrelief. When ground ice in the permafrost melts, the ground surface settles differentially resulting in thermokarst terrain (pits, gullies). Windblown snow fills the thermokarst depressions causing further warming and thawing of the underlying permafrost — a positive feedback effect that enhances permafrost degradation. Thermokarst-induced changes in relief alter the near-surface hydrology and ecological processes. Changes in vegetation included differential tussock growth and mortality and a shift in moss species abundance and relative productivity, depending on microtopographic position created by the thermokarst terrain. Water redistribution towards thermokarst depressions caused adjacent higher areas to become drier and resulted in increased moss mortality and shrub abundance. Copyright # 2009 John Wiley & Sons, Ltd.

Changes in frozen ground in the Source Area of the Yellow River on the Qinghai-Tibet Plateau, China, and their eco-environmental impacts.

Abstract: The Source Area of the Yellow River is located in the mosaic transition zones of seasonally frozen ground, and discontinuous and continuous permafrost on the northeastern Qinghai–Tibet Plateau. Vertically, permafrost is attached or detached from frost action. The latter can be further divided into shallow (depth to the permafrost table ≤8 m), deep (>8 m) and two-layer permafrost. Since the 1980s, air temperatures have been rising at an average rate of 0.02 °C yr−1. Human activities have also increased remarkably, resulting in a regional degradation of permafrost. The lower limit of permafrost has risen by 50–80 m. The average maximum depth of frost penetration has decreased by 0.1–0.2 m. The temperatures of the suprapermafrost water have increased by 0.5–0.7 °C. General trends of permafrost degradation include reduction in areal extent from continuous and discontinuous to sporadic and patchy permafrost, thinning of permafrost, and expansion of taliks. Isolated patches of permafrost have either been significantly reduced in areal extent, or changed into seasonally frozen ground. Degradation of permafrost has led to a lowering of ground water levels, shrinking lakes and wetlands, and noticeable change of grassland ecosystems alpine meadows to steppes. The degradation of alpine grasslands will cause further degradation of permafrost and result in the deterioration of ecological environments as manifested by expanding desertification and enhancing soil erosion.

The effects of climate, permafrost and fire on vegetation change in Siberia in a changing climate

Abstract: Observations and general circulation model projections suggest significant temperature increases in Siberia this century that are expected to have profound effects on Siberian vegetation. Potential vegetation change across Siberia was modeled, coupling our Siberian BioClimatic Model with several Hadley Centre climate change scenarios for 2020, 2050 and 2080, with explicit consideration of permafrost and fire activity. In the warmer and drier climate projected by these scenarios, Siberian forests are predicted to decrease and shift northwards and forest?steppe and steppe ecosystems are predicted to dominate over half of Siberia due to the dryer climate by 2080. Despite the large predicted increases in warming, permafrost is not predicted to thaw deep enough to sustain dark (Pinus sibirica, Abies sibirica, and Picea obovata) taiga. Over eastern Siberia, larch (Larix dahurica) taiga is predicted to continue to be the dominant zonobiome because of its ability to withstand continuous permafrost. The model also predicts new temperate broadleaf forest and forest?steppe habitats by 2080. Potential fire danger evaluated with the annual number of high fire danger days (Nesterov index is 4000?10?000) is predicted to increase by 2080, especially in southern Siberia and central Yakutia. In a warming climate, fuel load accumulated due to replacement of forest by steppe together with frequent fire weather promotes high risks of large fires in southern Siberia and central Yakutia, where wild fires would create habitats for grasslands because the drier climate would no longer be suitable for forests.

Stream dissolved organic matter bioavailability and composition in watersheds underlain with discontinuous permafrost

Abstract: We examined the impact of permafrost on dissolved organic matter (DOM) composition in Caribou-Poker Creeks Research Watershed (CPCRW), a watershed underlain with discontinuous permafrost, in interior Alaska We analyzed long term data from watersheds underlain with varying degrees of permafrost, sampled springs and thermokarsts, used fluorescence spectroscopy, and measured the bioavailabity of dissolved organic carbon (DOC) Permafrost driven patterns in hydrology and vegetation influenced DOM patterns in streams, with the stream draining the high permafrost watershed having higher DOC and dissolved organic nitrogen (DON) concentrations, higher DOC:DON and greater specific ultraviolet absorbance (SUVA) than the streams draining the low and medium permafrost watersheds Streams, springs and thermokarsts exhibited a wide range of DOC and DON concentrations (15–375 mgC/L and 014–126 mgN/L, respectively), DOC:DON (71–428) and SUVA (15–47 L mgC−1 m−1) All sites had a high proportion of humic components, a low proportion of protein components, and a low fluorescence index value (13–14), generally consistent with terrestrially derived DOM Principal component analysis revealed distinct groups in our fluorescence data determined by diagenetic processing and DOM source The proportion of bioavailable DOC ranged from 2 to 35%, with the proportion of tyrosine- and tryptophan-like fluorophores in the DOM being a major predictor of DOC loss (p < 005, R 2 = 099) Our results indicate that the degradation of permafrost in CPCRW will result in a decrease in DOC and DON concentrations, a decline in DOC:DON, and a reduction in SUVA, possibly accompanied by a change in the proportion of bioavailable DOC

Spatial and Temporal Variations in Active Layer Thawing and Their Implication on Runoff Generation in Peat-Covered Permafrost Terrain

Abstract: [1] The distribution of frost table depths on a peat-covered permafrost slope was examined in a discontinuous permafrost region in northern Canada over 4 consecutive years at a variety of spatial scales, to elucidate the role of active layer development on runoff generation. Frost table depths were highly variable over relatively short distances (0.25–1 m), and the spatial variability was strongly correlated to soil moisture distribution, which was partly influenced by lateral flow converging to frost table depressions. On an interannual basis, thaw rates were temporally correlated to air temperature and the amount of precipitation input. Simple simulations show that lateral subsurface flow is governed by the frost table topography having spatially variable storage that has to be filled before water can spill over to generate flow downslope, in a similar manner that bedrock topography controls subsurface flow. However, unlike the bedrock surface, the frost table is variable with time and strongly influenced by the heat transfer involving water. Therefore, it is important to understand the feedback between thawing and subsurface water flow and to properly represent the feedback in hydrological models of permafrost regions.

Modelling of cryogenic processes in permafrost and seasonally frozen soils

Abstract: This paper investigates the thermo-hydro-mechanical (THM) behaviour of soils subjected to seasonal temperature variations in both permafrost and seasonally frozen conditions. Numerical modelling of soil freezing and ice segregation processes is presented, and compared against small-scale physical modelling experiments. The coupled THM model presented, which is solved by way of a transient finite element approach, considers a number of processes, including conduction, convection, phase change, the movement of moisture due to cryogenic suctions, and the development of ice lenses. Two seasonal freezing scenarios are considered: (a) for soils with no permafrost, where freezing is from the surface downward (one-sided freezing); and (b) for soils underlain by permafrost, where large thermal gradients in the uppermost permafrost layer can cause active layer freezing in two directions, from the permafrost table upwards and from the ground surface downwards (two-sided freezing). In the case of one-sided freezing, ice lens formation occurs as the freezing front advances downwards from the surface, and is limited by water supply. However, during two-sided freezing, ice segregation takes place in a closed system, with ice lenses accumulating at the base of the active layer and near the ground surface, leaving an intervening ice-poor zone. Numerical modelling is able to represent the development of both the thermal field and ice segregation observed in the physical models. The significance of this contrasting ground ice distribution is considered in the context of thaw-related slow mass movement processes (solifluction).

Evolution of shallow groundwater flow systems in areas of degrading permafrost

Abstract: [1] The recent increase in fresh-water discharge during low-flow conditions as observed in many (sub-)Arctic Rivers has been attributed to a reactivation of groundwater flow systems caused by permafrost degradation. Hydrogeological simulations show how groundwater flow conditions in an idealized aquifer system evolve on timescales of decades to centuries in response to climate warming scenarios as progressive lowering of the permafrost table establishes a growing shallow groundwater flow system. Ultimately, disappearance of residual permafrost at depth causes a sudden establishment of deep groundwater flow paths. The projected shifts in groundwater flow conditions drive characteristic non-linear trends in the evolution of increasing groundwater discharge to streams. Although the subsurface distribution of ice will markedly influence the system response, current modeling results suggest that late-stage accelerations in base flow increase of streams and rivers, are to be expected, even if surface air temperatures stabilize at the current levels in the near future.

Large N2O emissions from cryoturbated peat soil in tundra

Abstract: Nitrous oxide is a potent greenhouse gas whose concentration is increasing in the atmosphere; the highest emissions have been observed from agricultural and tropical soils. Now, measurements in subarctic East European tundra show that bare surfaces on permafrost peatlands, known as peat circles, release large quantities of nitrous oxide. Nitrous oxide is a potent greenhouse gas whose concentration is increasing in the atmosphere1. So far, the highest terrestrial nitrous oxide emissions have been measured in agricultural and tropical soils2,3, and nitrous oxide emissions from northern natural soils have been considered negligible4,5. Pristine tundra, one of the largest natural land cover types in the world, is a mosaic of different surface types including bare surfaces created by cryoturbation6,7. Here we used a static chamber method to measure nitrous oxide emissions from the discontinuous permafrost zone in subarctic East European tundra. We show that nitrous oxide emissions from bare peat surfaces in the region, known as peat circles, range between 0.9 and 1.4 g nitrous oxide m−2 from June to October, and are equivalent to those from tropical and agricultural soils. Extrapolation of our data to the whole Arctic reveals that the emissions from these hot spots could amount to ∼0.1 Tg nitrous oxide yr−1, corresponding to 4% of the global warming potential of Arctic methane emissions at present. Therefore, not only carbon, but also nitrogen stored in permafrost soils, has to be considered when assessing the present and future climatic impact of tundra.

Pedogenesis, permafrost, and soil moisture as controlling factors for soil nitrogen and carbon contents across the Tibetan Plateau

Abstract: We investigated the main parameters [e.g. mean annual air temperature , mean annual soil temperature, mean annual precipitation, soil moisture (SM), soil chemistry, and physics] influencing soil organic carbon (Corg), soil total nitrogen (Nt) as well as plant available nitrogen (Nmin) at 47 sites along a 1200km transect across the high-altitude and low-latitude permafrost region of the central-eastern Tibetan Plateau. This large-scale survey allows testing the hypothesis that beside commonly used ecological variables, diversity of pedogenesis is another major component for assessing carbon (C) and nitrogen (N) cycling. The aim of the presented research was to evaluate consequences of permafrost degradation for C and N stocks and hence nutrient supply for plants, as the transect covers all types of permafrost including heavily degraded areas and regions without permafrost. Our results show that SM is the dominant parameter explaining 64% of Corg and 60% of N variation. The extent of the effect of SM is determined by permafrost, current aeolian sedimentation occurring mostly on degraded sites, and pedogenesis. Thus, the explanatory power for C and N concentrations is significantly improved by adding CaCO3 content (P 50.012 for Corg; P 50.006 for Nt) and soil texture (P 50.077 for Corg; P 50.015 for Nt) to the model. For soil temperature, no correlations were detected indicating that in high-altitude grassland ecosystems influenced by permafrost, SM overrides soil temperature as the main driving parameter at landscape scale. It was concluded from the current study that degradation of permafrost and corresponding changes in soil hydrology combined with a shift from mature stages of pedogenesis to initial stages, have severe impact on soil C and plant available N. This may alter biodiversity patterns as well as the development and functioning of the ecosystems on the Tibetan Plateau.

Relative impacts of disturbance and temperature: persistent changes in microenvironment and vegetation in retrogressive thaw slumps

Abstract: In the Low Arctic, a warming climate is increasing rates of permafrost degradation and altering vegetation. Disturbance associated with warming permafrost can change microclimate and expose areas of ion-rich mineral substrate for colonization by plants. Consequently, the response of vegetation to warming air temperatures may differ significantly from disturbed to undisturbed tundra. Across a latitudinal air temperature gradient, we tested the hypothesis that the microenvironment in thaw slumps would be warmer and more nutrient rich than undisturbed tundra, resulting in altered plant community composition and increased green alder (Alnus viridis subsp. fruticosa) growth and reproduction. Our results show increased nutrient availability, soil pH, snow pack, ground temperatures, and active layer thickness in disturbed terrain and suggest that these variables are important drivers of plant community structure. We also found increased productivity, catkin production, and seed viability of green alder at disturbed sites. Altered community composition and enhancement of alder growth and reproduction show that disturbances exert a strong influence on deciduous shrubs that make slumps potential seed sources for undisturbed tundra. Overall, these results indicate that accelerated disturbance regimes have the potential to magnify the effects of warming temperature on vegetation. Consequently, understanding the relative effects of temperature and disturbance on Arctic plant communities is critical to predicting feedbacks between northern ecosystems and global climate change.

Soil Thermal and Ecological Impacts of Rain on Snow Events in the Circumpolar Arctic

Abstract: Rain on snow (ROS) events are rare in most parts of the circumpolar Arctic, but have been shown to have great impact on soil surface temperatures and serve as triggers for avalanches in the midlatitudes, and they have been implicated in catastrophic die-offs of ungulates. The study of ROS is inherently challenging due to the difficulty of both measuring rain and snow in the Arctic and representing ROS events in numerical weather predictions and climate models. In this paper these challenges are addressed, and the occurrence of these events is characterized across the Arctic. Incidents of ROS in Canadian meteorological station data and in the 40-yr ECMWF Re-Analysis (ERA-40) are compared to evaluate the suitability of these datasets for characterizing ROS. The ERA-40 adequately represents the large-scale synoptic fields of ROS, but too often has a tendency toward drizzle. Using the ERA-40, a climatology of ROS events is created for thresholds that impact ungulate populations and permafrost. It is found that ROS events with the potential to harm ungulate mammals are widespread, but the large events required to impact permafrost are limited to the coastal margins of Beringia and the island of Svalbard. The synoptic conditions that led to ROS events on Banks Island in October of 2003, which killed an estimated 20 000 musk oxen, and on Svalbard, which led to significant permafrost warming in December of 1995, are examined. Compositing analyses are used to show the prevailing synoptic conditions that lead to ROS in four disparate parts of the Arctic. Analysis of ROS in the daily output of a fully coupled GCM under a future climate change scenario finds an increase in the frequency and areal extent of these events for many parts of the Arctic over the next 50 yr and that expanded regions of permafrost become vulnerable to ROS.

Integrating peatlands and permafrost into a dynamic global vegetation model: 2. Evaluation and sensitivity of vegetation and carbon cycle processes

Abstract: [1] Peatlands and permafrost are important components of the carbon cycle in the northern high latitudes. The inclusion of these components into a dynamic global vegetation model required changes to physical land surface routines, the addition of two new peatland-specific plant functional types, incorporation of an inundation stress mechanism, and deceleration of decomposition under inundation. The new model, LPJ-WHy v1.2, was used to simulate net ecosystem production (NEP), net primary production (NPP), heterotrophic respiration (HR), and soil carbon content. Annual peatland NEP matches observations even though the seasonal amplitude is overestimated. This overestimation is caused by excessive NPP values, probably due to the lack of nitrogen or phosphorus limitation in LPJ-WHy. Introduction of permafrost reduces circumpolar (45–90N) NEP from 1.65 to 0.96 Pg C a � 1 and leads to an increase in soil carbon content of almost 40 Pg C; adding peatlands doubles this soil carbon increase. Peatland soil carbon content and hence HR depend on model spin-up duration and are crucial for simulating NEP. These results highlight the need for a regional peatland age map to help determine spin-up times. A sensitivity experiment revealed that under future climate conditions, NPP may rise more rapidly than HR resulting in increases in NEP.

Origin and polycyclic behaviour of tundra thaw slumps, Mackenzie Delta region, Northwest Territories, Canada

Abstract: In tundra uplands east of the Mackenzie Delta, retrogressive thaw slumps up to several hectares in area typically develop around lakes. Ground temperatures increase in terrain affected by slumping due to the high thermal conductivity of exposed mineral soils and deep snow accumulation in winter. Mean annual temperatures at the top of permafrost were several degrees warmer in thaw slumps (−0.1°C to −2.2°C) than beneath adjacent undisturbed tundra (−6.1°C to −6.7°C). Simulations using a two-dimensional thermal model showed that the thermal disturbance caused by thaw slumping adjacent to tundra lakes can lead to rapid near-surface lateral talik expansion. Talik growth into ice-rich materials is likely to cause lake-bottom subsidence and rejuvenation of shoreline slumping. The observed association of thaw slumps with tundra lakes, the absence of active slumps on the shores of drained lakes where permafrost is aggradational and depressions in the lake bottom adjacent to thaw slumps provide empirical evidence that thermal disturbance, talik enlargement and thawing of subadjacent ice-rich permafrost can drive the polycyclic behaviour (initiation and growth of slump within an area previously affected by slumping) of lakeside thaw slumps. Copyright © 2009 John Wiley & Sons, Ltd. and Her Majesty the Queen in right of Canada.

Climate Change and the World's "Sacred Sea"--Lake Baikal, Siberia

Abstract: Lake Baikal—the world's largest, oldest, and most biotically diverse lake—is responding strongly to climate change, according to recent analyses of water temperature and ice cover. By the end of this century, the climate of the Baikal region will be warmer and wetter, particularly in winter. As the climate changes, ice cover and transparency, water temperature, wind dynamics and mixing, and nutrient levels are the key abiotic variables that will shift, thus eliciting many biotic responses. Among the abiotic variables, changes in ice cover will quite likely alter food-web structure and function most because of the diverse ways in which ice affects the lake's dominant primary producers (endemic diatoms), the top predator (the world's only freshwater seal), and other abiotic variables. Melting permafrost will probably exacerbate the effects of additional anthropogenic stressors (industrial pollution and cultural eutrophication) and could greatly affect ecosystem functioning.

Changes in thaw lake drainage in the Western Canadian Arctic from 1950 to 2000

Abstract: The permafrost of the Western Canadian Arctic has a very high ground ice content. As a result, the vast number of thaw lakes in this area are very sensitive to a changing climate. With thaw lakes prone to either increases in area due to thermokarst processes, or complete drainage in less than one day due to melting of channels through ice-rich permafrost. After a lake drains, it leaves a topographic basin that is often termed a Drained Thaw Lake Basin (DTLB). An analysis of aerial photographs and topographic maps showed that 41 lakes drained in the study area between 1950 and 2000, for a rate of slightly less than one lake per year. The rate of drainage over three time periods (1950–1973, 1973–1985, 1985–2000), decreased from over 1 lake/year to approximately 0·3 lake/year. The reason for this decrease is not known, but it is hypothesized that it is related to the effect of a warming climate. There is a large spatial variation in DTLBs, with higher number of drained lakes in physiographic areas with poor drainage. It is likely that this variation is related to variations in ground ice. Although previous studies have suggested that lakes drain during periods of high water level, it is likely that a combination of a warm summer, a resulting deep active layer, and a moderately high lake level were responsible for the drainage of a lake in the study area during the summer of 1989. Although this study has documented changes in the rate of lake drainage over a 50-year period, there is a need for further research to better understand the complex interactions between climate, geomorphology, and hydrology responsible for this change, and to further consider the potential hazard rapid lake drainage poses to future industrial or resource development in the area. Copyright © 2008 John Wiley & Sons, Ltd and Her Majesty the Queen in right of Canada. The contributions of P. Marsh, M. Russell, H. Haywood and C. Onclin belong to the Crown in right of Canada and are reproduced with the permission of Environment Canada.