We report new data on tree-ring growth in northern European Russia, a region with a hitherto relatively sparse tree-ring network. We explore its associations with climate variability. Areas, sampling locations and trees were selected for representativeness rather than climate sensitivity. Using tree rings from 651 conifers from six widely dispersed areas we show strong intercorrelation between trees within each major conifer species within and between areas. Regional composite tree-ring series for spruce and pine contain a major fraction of decadal and multidecadal variability. The most likely driver of this common variability is interannual to multidecadal climate variability. Gridded monthly instrumental climate data for the period 1902–2008, particularly mean temperature and total precipitation, were tested as predictors of each local species-specific tree-ring site chronology. The most consistent pattern emerged for spruce at all but the southernmost area. Cool and moist summers the year before growth were consistent drivers of spruce ring growth throughout the period, with no change in recent decades. Self-calibrating Palmer Drought Severity Index for prior summer was also a strong and consistent driver of spruce ring growth. For pine, there was a weaker but similarly stable association between larger rings and warm, moist conditions, in this case in the current summer. These associations were also identified at multidecadal time scales, particularly for spruce. On the other hand, the specific role of moisture variability in determining interannual to multidecadal variability in tree growth in this high latitude region raises questions about the relative vulnerability of spruce and pine there under global warming.

Background: Long-term climate trends in mountain systems often vary strongly with elevation. Aims: To evaluate elevation dependence in long-term precipitation trends in subalpine forest and alpine tundra zones of a mid-continental, mid-latitude North American mountain system and to relate such dependence to atmospheric circulation patterns. Methods: We contrasted 59-year (1952–2010) precipitation records of two high-elevation climate stations on Niwot Ridge, Colorado Front Range, Rocky Mountains, USA. The sites, one in forest (3022 m a.s.l.) and the other in alpine tundra (3739 m), are closely located (within 7 km horizontally, ca. 700 m vertically), but differ with respect to proximity to the mountain-system crest (the Continental Divide). Results: The sites exhibited significant differences in annual and seasonal precipitation trends, which depended strongly on their elevation and distance from the Continental Divide. Annual precipitation increased by 60 mm (+6%) per decade at the alpine site, with no significant change at the subalpine site. Seasonally, trends at the alpine site were dominated by increases in winter, which we suggest resulted from an increase in orographically generated precipitation over the Divide, driven by upper-air (700 hPa) north-westerly flow. Such a change was not evident at the subalpine site, which is less affected by orographic precipitation on north-westerly flow. Conclusions: Elevation dependence in precipitation trends appears to have arisen from a change in upper-air flow from predominantly south-westerly to north-westerly. Dependence of precipitation trends on topographic position and season has complex implications for the ecology and hydrology of Niwot Ridge and adjacent watersheds, involving interactions among physical processes (e.g. snowpack dynamics) and biotic responses (e.g. in phenologies and ecosystem productivity).

Different methods have been developed for measuring carbon stocks and fluxes in the northern high latitudes, ranging from intensively measured small plots to space-based methods that use reflectance data to drive production efficiency models. The field of dendroecology has used samples of tree growth from radial increments to quantify long-term variability in ecosystem productivity, but these have very limited spatial domains. Since the cambium material in tree cores is itself a product of photosynthesis in the canopy, it would be ideal to link these two approaches. We examine the associations between the normalized differenced vegetation index (NDVI) and tree growth using 19 pairs of tree-ring widths (TRW) and maximum latewood density (MXD) across much of Siberia. We find consistent correlations between NDVI and both measures of tree growth and no systematic difference between MXD and TRW. At the regional level we note strong correspondence between the first principal component of tree growth and NDVI for MXD and TRW in a temperature-limited bioregion, indicating that canopy reflectance and cambial production are broadly linked. Using a network of 21 TRW chronologies from south of Lake Baikal, we find a similarly strong regional correspondence with NDVI in a markedly drier region. We show that tree growth is dominated by variation at decadal and multidecadal time periods, which the satellite record is incapable of recording given its relatively short record.

Snow surface roughness is an important variable in the study of surface-atmosphere exchanges, including the investigation of snow melt at several scales, meltwater production and meltwater flux, wind transport and erosion in winter. In this paper the morphogenesis of the snow surface in winter and in summer is investigated both phenomenologically and quantitatively. For the first time, snow surface roughness and microtopography is measured spatially, using the Glacier Roughness Sensor (GRS), an instrument developed especially for this purpose. Data are analysed by application of geostatistical characterization and classification methods. Parameters that are useful as snow surface descriptors are defined and extracted from vario functions of first and second order, which are calculated for snow-surface-roughness data.As a result of the geostatistical analysis, characteristics of morphogenetic processes of the winter and summer snow surface are derived. Characteristic parameters are given for suncups (summer) and sastrugi (winter) and their development stages, as well as quantitative discriminators between these forms, which may facilitate automation of snow surface classification. As an application, the interaction of environmentally induced processes and self-organizational processes is analysed. Copyright (C) 2003 John Wiley Sons, Ltd.

The presence of a seasonal snowpack in alpine environments can amplify climate signals. A conceptual model is developed for the response of alpine ecosystems in temperate, midlatitude areas to changes in energy, chemicals, and water, based on a case study from Green Lakes Valley-Niwot Ridge, a headwater catchment in the Colorado Front Range. A linear regression shows the increase in annual precipitation of about 300 millimeters from 1951 to 1996 to be significant. Most of the precipitation increase has occurred since 1967. The annual deposition of inorganic nitrogen in wetfall at the Niwot Ridge National Atmospheric Deposition Program site roughly doubled between 1985-1988 and 1989-1992. Storage and release of strong acid anions, such as those from the seasonal snowpack in an ionic pulse, have resulted in episodic acidification of surface waters. These biochemical changes alter the quantity and quality of organic matter in high-elevation catchments of the Rocky Mountains. Affecting the bottom of the food chain, the increase in nitrogen deposition may be partly responsible for the current decline of bighorn sheep in the Rocky Mountains.

Atmospheric hydrogen peroxide (H2O2) measurements at Summit, Greenland, in May-June, 1993 exhibited a diel variation, with afternoon highs typically 1-2 parts per billion by volume (ppbv) and nighttime lows about 0.5 ppbv lower, This variation closely followed that for temperature; specific humidity exhibited the same general trend, During a 17-day snowfall-free period, surface snow was accumulating H2O2, apparently from nighttime cocondensation of H2O and H2O2. Previous photochemical modeling (Neftel et al., 1995) suggests that daytime H2O2 should be about I ppbv, significantly lower than our measured values, Previous equilibrium partitioning measurements between ice and gas phase (Conklin et al., 1993) suggest that air in equilibrium with H2O2 concentrations measured in surface snow (15-18 mu M) should have an H2O2 concentration 2-3 times what we measured 0.2-3.5 m above the snow surface, A simple eddy diffusion model, with vertical eddy diffusion coefficients calculated from balloon soundings, suggested that atmospheric H2O2 concentrations should be affected by any H2O2 degassed from surface snow, However, field measurements showed the absence of either high concentrations of H2O2 or a measurable concentration gradient between inlets 0.2 and 3 m above the snow. A surface resistance to degassing, that is, slow release of H2O2 from the ice matrix, is a plausible explanation for the differences between observations and modeled atmospheric profiles, Degassing of H2O2 at a rate below our detection limit would still influence measured atmospheric concentrations and help explain the difference between measurements and photochemical modeling, The cumulative evidence suggests that surface snow adjusts slowly to drops in atmospheric H2O2 concentration, over timescales of at least weeks. The H2O2 losses previously observed in pits sampled over more than 1 year are thought to have occurred later in the summer or fall, after the May-July field season.