Portable open-path laser (OPL) instruments provide a way to measure real-time, in situ atmospheric methane (CH₄) concentrations at a variety of spatial and temporal scales. Our results suggest that OPL instruments may be simple and effective tools for monitoring atmospheric CH₄ dynamics near ground-level in Arctic landscapes. We used a CH₄ detecting OPL instrument at seven different field sites in southwest Greenland during the summer of 2012 to monitor atmospheric CH₄ concentrations in the presence of local CH₄ sources and sinks. Measurements with the OPL were conducted for deployments between 0.4 and 40 h over path lengths between 10 and 300 m. These measurements were checked against periodic grab samples analyzed in the field lab using cavity-enhanced absorption spectroscopy. Mean concentrations of atmospheric CH₄ measured with the OPL across all field sites ranged from 1.72 (±0.12) to 1.88 (±0.15) ppm by volume (ppmv). The median atmospheric CH₄ concentration measured using cavity-enhanced absorption spectroscopy was 1.82 ± 0.04 ppmv. Slightly elevated CH₄ concentrations were measured downwind of one lake and in a subglacial cave. OPL measurements of atmospheric CH₄ concentrations agreed with results from cavity-enhanced absorption spectroscopy (<3% difference). OPL technology may be a useful tool for extended CH₄ monitoring studies in the Arctic and may help in our understanding of atmospheric CH₄ concentrations at spatial and temporal scales not accessible to other forms of measurement.

The depths of snow in the Qinghai-Tibetan Plateau simulated by 19 phase five of the Coupled Model Inter-Comparison Project (CMIP5) models are assessed in comparison with the observation ones from passive microwave satellite remote-sensing (PMSR) and 72 weather stations. The annual regional mean snow depths (ARMSDs) from 1851 to 2005 indicate decreases for most of the models but slight increases for CMCC-CM, FGOALS-g2, and CanESM2. The simulated ARMSD anomalies vary from -10 cm to 20 cm, and the amplitudes exhibit obvious decreases over the recent 50 years. In the period from 1986 to 2005, the spatial distributions of the annual mean snow depth (AMSD) simulated by MRI-CGCM3, CCSM4, CESM1-BGC, CESM1-CAM5, and CESM1-WACCM are quite similar to those from the PMSR observations. But the maximum and mean AMSD values simulated by all 19 models are much larger than those observed by PMSR. The inter-annual variation of snow, which occurs primarily in the Middle and East Tibetan Plateau, is simulated relatively well by inmcm4. From 1960 to 2005, the ARMSDs simulated by most of the models show decreases but are increasing according to actual observations. Only five models produce positive trends that agree with the observations. According to the selected indices, the CCSM4, MIROC5, MRI-CGCM3, and FGOALS-g2 models are selected as relatively good models for predicting the plateau snow, and the 21st century changes in the snow climate in the Qinghai-Tibetan Plateau are projected using these four models.

Lidder tributary in the Upper Indus Basin (UIB) of the Himalayas, an important source of surface and ground water, is experiencing clear indications of climate change. In the basin, minimum, maximum, and average temperatures are showing a significant increasing trend in all the four seasons. Precipitation is showing insignificant decrease over time in the basin. However, the proportion of snow is decreasing and correspondingly, the proportion of rains is increasing. The temperature projections also show increasing trends for the end of this century. The time-series analysis of the Normalized Difference Snow Index (NDSI) shows a depletion of the snow-cover in the region. Furthermore, during the past 51 years, the glacier area in the basin has decreased from 46.09 km² in 1962 to 33.43 km² in 2013, a depletion of 27.47%. As a result of glacier recession in the basin, the streamflow fed predominantly by snowmelt and glacier melt, is showing a statistically significant decline since the mid-1990s. The declining streamflows have potential to adversely affect agriculture, energy production, tourism, and even domestic water supplies. The Snowmelt Runoff Model (SRM) was tested for estimating the runoff from this glaciated basin on an operational basis. The average simulated runoff 11.94 m³ s^-1 at the outlet is in concordance with the average measured runoff 13.51 m³ s^-1 showing R² of 0.82. The model could thus be used for snowmelt runoff estimation, on an operational basis, for judicious utilization of the depleting water resources in the region.

Knowledge of Arctic snow and ice surface albedo is essential to understand local energy budget and snow/ice albedo feedback under global warming scenario. In situ measured albedo plays an essential role by providing ground truth reference for remote sensing monitoring of albedo at large scale. Such measurements with portable and fixed-location spectroradiometers were conducted in one 12-day (long-term) and several short-term (3–4 hours) ice stations over the Pacific Arctic sector during the summer 2010 Chinese National Arctic Research Expedition (CHINARE). Results show that the wavelength-integrated albedo across 350 to 2200 nm of bare ice was ∼0.56 to 0.68 in the lower latitudes and marginal ice zone, while albedo of snow-covered ice reduced from 0.75–0.86 to 0.42–0.61 during the mid-August period of the 12-day ice station (86°48′N to 87°20′N). The albedo variation and evolution of melt ponds were examined with details during the 12-day ice station. It is found that albedo of melt pond reduced from 0.68 (melt pond snow, 9 August) and 0.66 (melt pond ice, 9 August) to 0.32 (melt pond water and ice, 17 August) in one week as a rainfall event occurred. Such rapid decreasing of snow and sea ice albedo and evident difference between the pack ice zone and marginal ice zone may contribute to the surface albedo feedback and rapidly shrinking summer sea ice extent in the Arctic Ocean.

Little is known about recent rates of carbon storage in montane peatlands, particularly in the western United States. Here we report on recent rates of carbon accumulation (past 50 to 100 years) in montane groundwater-fed peatlands (fens) of Yosemite National Park in central California, U.S.A. Peat cores were collected at three sites ranging in elevation from 2070 to 2500 m. Core sections were analyzed for bulk density, % organic carbon, and ²¹⁰Pb activities for dating purposes. Organic carbon densities ranged from 0.026 to 0.065 g C cm^-3. Mean vertical accretion rates estimated using ²¹⁰Pb over the 50-year period from ∼1960 to 2011 and the 100-year period from ∼1910 to 2011 were 0.28 (standard deviation = ±0.09) and 0.18 (±-0.04) cm yr^-1, respectively. Mean carbon accumulation rates over the 50- and 100-year periods were 95.4 (±25.4) and 74.7 (±17.2) g C m^-2 yr^-1, respectively. Such rates are similar to recent rates of carbon accumulation in rich fens in western Canada, but more studies are needed to definitively establish both the similarities and differences in peat formation between boreal and temperate montane fens.

Alpine areas in Meganesia occur on maritime and continental mountains, and range from tropical to warm and cool temperate. At their current treelines, we measured soil temperatures, which were found to be within the bounds for treeline temperatures worldwide. We modeled areas above these alpine treelines using (1) a growing season mean synoptic temperature of 6.4 °C at treeline and (2) monthly temperature extremes. It was possible to adjust the threshold temperatures of the growing season model until predicted areas approximated observed alpine areas for New Guinea, the Australian mainland Snowy Mountains, and Tasmania, but meaningful predictions could not be made for the unknown alpine area of the Victorian Alps. The temperature extreme model was unsuitable for New Guinea and Tasmania but gave better predictive results for the Victorian Alps. We correctly predicted a strong relationship between alpine area and number of alpine vascular plant species and between regional area and number of terrestrial vertebrate species. However, there was no clear relationship between alpine area and alpine terrestrial vertebrate richness. Differences among the mountains were better explained by climatic extremes and insolation. If local explanations are required to model alpine vertebrate fauna, it is difficult to build robust global models and consequently make general predictions of climate change impacts.

Previous research collectively demonstrates the importance of taking local moisture availability and biotic threshold responses into account when seeking to reveal the ecological manifestations of climate change within upper treeline ecotones. Yet dendroecological studies that explicitly address the role of slope aspect in this context are non-existent. In this paper, we examine whether slope aspect and related temperature-precipitation interactions mediate abrupt increases in tree establishment and pulses of upper treeline advance (≥10 m) on contrasting north- and south-facing slopes during wet and dry periods of the 20th century. We used regime-shift analysis to quantify episodic changes in the rate of tree regeneration at each site (p < 0.05). We employed a climatic water deficit approach to define fine-scale moisture conditions to compare with dendroecological data from opposite aspects on eleven mountain peaks along a latitudinal gradient in the U.S. Rocky Mountains. Regime-shift analysis measured abrupt, yet asynchronous increases in tree establishment across contrasting slope aspects on 10 of 11 mountain peaks. Upper treeline advance was significantly greater (p < 0.05) during drought on north-facing slopes. On south-facing slopes, ecotonal dynamics varied more with respect to fluxes in the climatic water deficit; namely because of differences in local hydroclimate regimes. Collectively, these results underscore the importance of considering both slope aspect and temperature-moisture interactions when elucidating climate-vegetation interactions within upper treeline ecotones.

Soil nutrient supply is likely to change in the Arctic due to altered process rates associated with climate change. Here, we compare the responses of herbaceous tundra and birch forest understory to fertilization, considering both above- and below-ground responses. We added nitrogen and phosphorus to plots in both vegetation types for three years near Abisko, northern Sweden, and measured the effect on above- and below-ground plant community properties and soil characteristics. Fertilization increased ground-layer shoot mass, the cover of grasses, and tended to enhance total root length below-ground, while it reduced the cover of low statured deciduous dwarf-shrubs. The only statistically significant interaction between vegetation type and fertilization was for grass cover, which increased twofold in forest understory but sixfold in tundra following fertilization. The lack of interactions for other variables suggests that the ground layers in these contrasting vegetation types have similar responses to fertilization. The nutrient-driven increase in grass cover and species-specific differences in productivity and root characters may alter ecosystem dynamics and C cycling in the long-term, but our study indicates that the response of birch forest understory and tundra vegetation may be consistent.

Reactive nitrogen (Nr) from anthropogenic sources has been altering ecosystem function in lakes of the Rocky Mountains, other regions of western North America, and the Arctic over recent decades. The response of biota in shallow lakes to atmospheric deposition of Nr, however, has not been considered. Benthic algae are dominant in shallow, high-elevation lakes and are less sensitive to nutrient inputs than planktonic algae. Because the benthic substrate is typically more nutrient rich than the water column, shallow lakes are not expected to show evidence of anthropogenic Nr. In this study, we assessed sedimentary evidence for regional Nr deposition, sediment chronology, and the nature of algal community response in five shallow, high-elevation lakes in Grand Teton National Park (GRTE). Over 140 diatom taxa were identified from the sediments, with a relatively high species richness of taxa characteristic of oligotrophic conditions. The diatom assemblages were dominated by benthic taxa, especially motile taxa. The GRTE lakes demonstrate assemblage-wide shifts in diatoms, including the following: (1) synchronous and significant assemblage changes centered on ca. A.D. 1960; (2) pre-1960 assemblages differed significantly from post-1960 assemblages; (3) pre-1960 diatom assemblages fluctuated randomly, whereas post-1960 assemblages showed directional change; and (4) changes in δ¹⁵N signatures were correlated with diatom community composition. These results demonstrate recent changes in shallow high-elevation lakes that are most correlated with anthropogenic Nr. It is also possible, however, that the combined effect of Nr deposition and warming is accelerating species shifts in benthic diatoms. While uncertainties remain about the potential synergy of Nr deposition and warming, this study adds shallow lakes to the growing list of impacted high-elevation localities in western North America.

Using continuous data obtained from 17 monitoring sites, the permafrost temperature profiles and the depths of zero annual amplitude (DZAA) on the Qinghai-Tibet Plateau are examined. Permafrost thermal trumpet curves are generally narrow and the DZAAs are generally shallow in warm permafrost regions, especially at sites where the permafrost temperature is close to 0 °C. The observed DZAAs in warm permafrost regions are indeed generally less than 7.0 m and for three sites less than 4.0 m. In low-temperature permafrost areas, the situation is reversed: the thermal trumpet curves are generally wide and the DZAAs are generally deep. Theoretical and numerical analyses clearly show there is a causal relationship between permafrost warming and the decrease of the DZAA. Latent heat effects are buffering the increase of permafrost temperature and result in narrow thermal trumpet curves and shallow DZAAs. Based on observations and numerical analyses, this research suggests that most of the permafrost on the Qinghai-Tibet Plateau is undergoing internal thaw and the latent heat effects have important implications on the permafrost thermal regime. The temperature-dependent adjustments in permafrost will promote both the downward and upward degradation of permafrost as a result of climate warming.

Late season alpine snows are often colonized by psychrophilic snow algae that may provide a source of nutrients for microbes. Such late season snows are a harsh environment, but support a diverse and complex fungal community. We used culture independent methods (Illumina MiSeq) to test if the presence of snow algae influences fungal communities. We compared algae-colonized snows to adjacent (3 m distant) noncolonized snows in a paired experimental design. Our data indicate that several fungi are locally enriched in algae colonized snows. Although many such fungi were basidiomycetous yeasts, our analyses identified a large number of snow-borne members of phylum Chytridiomycota. While the ecology and function of these Chytridiomycetes remain unclear, we hypothesize that their enrichment in the algal patches suggests that they depend on algae for nutrition. We propose that these chytrids are important components in snow ecosystems, highlighting the underestimation of their diversity and importance. Taken together, our data strongly indicate that fungal communities are heterogeneous in snow even among adjacent samples. Further, fungal and algal communities may be influenced by similar environmental drivers resulting in their co-occurrence in snow.

Periodic monitoring over 52 years have revealed temporal changes in the vegetation and floristic patterns associated with what has been acclaimed to be the world's oldest known experimental snow fence, which is located on an exposed high-alpine cushionfield on the Old Man Range in south-central New Zealand. The induced pattern of intermittent snow-lie has been increased by the fence from the normal ∼140 days to more than 200 days (and up to 140 cm deep), estimated from subsurface soil temperatures, together with periodic observations and measurements of snow depth. Some but not all species associated with natural snowbanks on the range have established in areas of induced snow accumulation. The timing of species establishment was not obviously related to relevant features of the local snowbank species or their distribution on the range, but the abundance of various plant species and their functional traits across zones of snowmelt point to competition and plant productivity being associated with the deepest snow in the lee of the fence. In addition, three of the several measured physical and chemical soil factors (Mg, available PO₄^3-, and C:N) have differentiated significantly in relation to the vegetation and snow-lie pattern at year 52, although these seem not to be relevant on the basis of the pattern of the same factors in two nearby natural snowbanks on the range.

Alpine treelines are considered monitors of the effects of climate on forest growth and dynamics. Treelines are expected to react to current climate warming by showing upslope migrations. However, treeline dynamics are often characterized by lagged responses to rising temperatures, that is, treeline inertia. In addition, encroachment within the treeline ecotone seems to be a more widespread response to climate warming than treeline ascent. We investigate how the treeline responds to climate in a Pyrenean site with an intense Mountain pine (Pinus uncinata) regeneration but also abundant dead trees. We use dendrochronology to reconstruct treeline dynamics (growth, tree recruitment, and death) and to build an age structure of Pyrenean Mountain pine forests, and relate them to temperature reconstructions of the study area. We also describe the spatial structure and estimate the size reproductive threshold of pine recruits. The study treeline showed profuse pine recruitment in the 1980s. These recruits were spatially aggregated and reached the 50% probability of reproduction at 24 years old. Most Pyrenean Mountain pines were recruited in the first half of the 18th century, a warm period when growth was stable, while old treeline trees recruited not only in those decades but also in previous warm periods. Pine deaths concentrated in the cool transition between the mid 17th and the early 18th centuries and mainly from 1820 to 1860, when growth declined as a consequence of temperatures rapidly dropping at the end of the Little Ice Age. Only the amount of dead pines at the treeline was negatively related to temperatures, indicating that cool periods cause high adult mortality rates and trigger long-term treeline decline. But this decline was interrupted by intense regeneration and treeline encroachment, two features that characterize recent treeline dynamics in some mountains. This concurs with the view of a rapid response of alpine treelines to climate during the late 20th century.

Northern Alaska has warmed over recent decades and satellite data indicate that vegetation productivity has increased. To document vegetation changes in the Arctic National Wildlife Refuge, we monitored plant cover at 27 plots between 1984 and 2009. These are among the oldest permanently marked and continuously monitored vegetation plots in the Arctic. We quantified percent cover of all plant species by line-point intercept sampling and assessed change over time for seven plant growth forms. Cover of bryophytes and deciduous shrubs showed slight decreasing trends. Evergreen shrubs, horsetails, and depth of thawed soil above permafrost had no trends. For lichens, graminoids, and forbs, trends varied by plant community type. Overall, vegetation in the plots changed little over the study period, in contrast to results from other studies in northern Alaska. A few plots had dramatic changes, however, which we attributed to subsidence from melting ground ice or to floodplain dynamics. Our results demonstrate that vegetation change on the Arctic Refuge coastal plain over the past quarter century has been spatially heterogeneous and facilitated by disturbance. The findings highlight the need for greater work linking plotlevel and regional remote sensing measurements of change.

From May 2007 to September 2008, six automatic weather stations (AWS) were installed along the traditional mountaineering line on the north slope of Mount Qomolangma. The elevations of the stations ranged between 5207 and 6560 m above sea level (a.s.l.). Some sounding data were also measured at Base Camp (5207 m a.s.l.) in late April and early May of 2007 and 2008. The spatial arrangement of the stations and temporal duration of the measurements, as well as the sounding data, generated a data set enabling the analysis of the wind regime in this region. The wind directions and speeds show change at different elevations because of the complicated terrain, the glacier-moraine-rock transition underlying surface, and the synoptic-scale wind. The katabatic wind dominates at low-elevation areas in the Rongbuk Valley, and the depth and frequency of it are about 800 m and 59% during the observational period. The up-valley wind always erodes the katabatic wind, and causes the lowest directional constancy in summer. With the elevation ascending, the katabatic wind weakens due to the smaller fetch and temperature contrast, as well as the relatively open landscape of the valley and smaller glacier area. At site 3 (5792 m a.s.l.), the frequency of the katabatic wind is only 25%, whereas the frequency of the up-valley wind is 47%, and especially in winter, the up-valley wind (82%) predominates all day. Moreover, the synoptic-scale wind also plays an important role in the surface wind regime on the north slope of Mount Qomolangma. From November to March, the active westerly troughs always intrude into the bottom of the Rongbuk Valley and could maintain the strong katabatic wind, and the maximum wind speed reaches 43.1 m s^-1 at site 1 (5207 m a.s.l.). At high-elevation areas, the westerlies can penetrates more easily, and dominate the wind regime. The wind speed can reach as high as 57.1 m s^-1 at site 3 in winter.