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The rapidly warming temperatures in high-latitude and alpine regions have the potential to alter the phenology of Arctic and alpine plants, affecting processes ranging from food webs to ecosystem trace gas fluxes. The International Tundra Experiment (ITEX) was initiated in 1990 to evaluate the effects of expected rapid changes in temperature on tundra plant phenology, growth and community changes using experimental warming. Here, we used the ITEX control data to test the phenological responses to background temperature variation across sites spanning latitudinal and moisture gradients. The dataset overall did not show an advance in phenology; instead, temperature variability during the years sampled and an absence of warming at some sites resulted in mixed responses. Phenological transitions of high Arctic plants clearly occurred at lower heat sum thresholds than those of low Arctic and alpine plants. However, sensitivity to temperature change was similar among plants from the different climate zones. Plants of different communities and growth forms differed for some phenological responses. Heat sums associated with flowering and greening appear to have increased over time. These results point to a complex suite of changes in plant communities and ecosystem function in high latitudes and elevations as the climate warms.

To address impacts of climate change on natural ecosystems, researchers need efficient and integrated ground- based sensor systems capable of detecting plant to ecosystem alterations to productivity, species composition, phenology, and structure and function over seasonal, inter-annual, and decadal time scales. Here, we introduce the Mobile Instrumented Sensor Platform (MISP), a versatile robotic sensor system that is suspended above or within the canopy and is designed to be adaptable for both short and long-term observations, and suitable for multiple ecosystems. The system is novel in that it is mobile, rather than static, the suite of sensors can be customized, and installation and operation requires minor surface distur bance relative to comparable systems already in use. MISP was developed as a contribution to the Arctic Observation Network's International Tundra Experiment (AON-ITEX), where at five locations between the low and high Arctic we record observations of different tundra plant communities over a 50 m transect. Observations include air temperature, surface temperature, incoming and outgoing long- and short-wave radiation, albedo, Normalized Difference Vegetation Index (NDVI), three-dimensional video, two and three-dimensional photography, and hyperspectral reflectance. Data analysis has proven the system's suitability for detecting subtle ecosystem changes across small-scale soil moisture and other gradients due to the mobile nature of the sampling. Long-term studies will benefit from this approach because sampling is repeatable with high spatial and temporal resolution and the system can be adapted to incorporate future technologies. [ABSTRACT FROM AUTHOR]

This study investigates how warming and changes in precipitation may affect the cycling of carbon (C) in tundra soils, and between high arctic tundra and the atmosphere. We quantified ecosystem respiration (Reco) and soil pore space CO2 in a polar semi-desert under current and future climate conditions simulated by long-term experimental warming (+2 °C, +4 °C), water addition (+50% summer precipitation) and a combination of both (+4 °C x +50% summer precipitation). We also measured the 14C content of Reco and soil CO2 to distinguish young C cycling rapidly between the atmosphere and the ecosystem from older C stored in the soil for centuries to millennia. We identified changes in the amount and timing of precipitation as a key control of the magnitude, seasonality and sources of Reco in a polar semi-desert. Throughout each summer, small (<4 mm) precipitation events during drier periods triggered the release of very old C pulses from the deep soil, while larger precipitation events (>4 mm), more winter snow and experimental irrigation were associated with higher Reco fluxes and the release of recently-fixed (young) plant C. Warmer summers and experimental warming also resulted in higher Reco fluxes (+2 °C > +4 °C), but coincided with losses of older C. We conclude that in high arctic dry tundra systems, future magnitudes and patterns of old C emissions will be controlled as much by the summer precipitation regime and winter snowpack as by warming. The release of older soil C is of concern as it may lead to net C losses from the ecosystem. Therefore, reliable predictions of precipitation amounts, frequency, and timing are required to predict the changing C cycle in the High Arctic. [ABSTRACT FROM AUTHOR]

The carbon (C) balance of permafrost regions is predicted to be extremely sensitive to climatic changes. Major uncertainties exist in the rate of permafrost thaw and associated C emissions (33-508 Pg C or 0.04-1.69 °C by 2100; refs , ) and plant C uptake. In the High Arctic, semi-deserts retain unique soil-plant-permafrost interactions and heterogeneous soil C pools (>12 Pg C; ref. ). Owing to its coastal proximity, marked changes are expected for High Arctic tundra. With declining summer sea-ice cover, these systems are simultaneously exposed to rising temperatures, increases in precipitation and permafrost degradation. Here we show, using measurements of tundra-atmosphere C fluxes and soil C sources (14C) at a long-term climate change experiment in northwest Greenland, that warming decreased the summer CO2 sink strength of semi-deserts by up to 55%. In contrast, warming combined with wetting increased the CO2 sink strength by an order of magnitude. Further, wetting while relocating recently assimilated plant C into the deep soil decreased old C loss compared with the warming-only treatment. Consequently, the High Arctic has the potential to remain a strong C sink even as the rest of the permafrost region transitions to a net C source as a result of future global warming. [ABSTRACT FROM AUTHOR]

Understanding how the hydrologic cycle has responded to warmer global temperatures in the past is especially important today as concentrations of CO2 in the atmosphere continue to increase due to human activities. The Pliocene offers an ideal window into a climate system that has equilibrated with current atmospheric pCO2. During the Pliocene the western United States was wetter than modern, an observation at odds with our current understanding of future warming scenarios, which involve the expansion and poleward migration of the subtropical dry zone. Here we compare Pliocene oxygen isotope profiles of pedogenic carbonates across the western US to modern isotopic anomalies in precipitation between phases of the El Niño-Southern Oscillation (ENSO). We find that when accounting for seasonality of carbonate formation, isotopic changes through the late Pliocene match modern precipitation isotopic anomalies in El Niño years. Furthermore, isotopic shifts through the late Pliocene mirror changes through the early Pleistocene, which likely represents the southward migration of the westerly storm track caused by growth of the Laurentide ice sheet. We propose that the westerly storm track migrated northward through the late Pliocene with the development of the modern cold tongue in the east equatorial Pacific, then returned southward with widespread glaciation in the Northern Hemisphere - a scenario supported by terrestrial climate proxies across the US. Together these data support the proposed existence of background El Niño-like conditions in western North America during the warm Pliocene. If the earth behaves similarly with future warming, this observation has important implications with regard to the amount and distribution of precipitation in western North America. [ABSTRACT FROM AUTHOR]

Understanding and modeling precipitation isotope ( δ18O and δD) patterns for large regions of the globe requires quantifying processes governing continental-scale climatology and hydrology. In this study, we have evaluated the extent to which inclusion of monthly moisture source temperature and moisture source locations in the Rayleigh distillation model aid in reproducing the relationships between monthly time series of precipitation isotope ( δ18O) values and temperature across the contiguous United States. The steepest isotope-temperature slopes (0.5‰-0.6‰ δ18O/°C) and greatest δ18O value correlations with temperature ( r2 = 0.5-0.8), derived from 5 continuous years of the data from the United States Network for Isotopes in Precipitation, occurred in the high altitudes of the Rocky Mountains and the upper Great Lakes region. The isotope-temperature slopes derived from the site-specific time series were consistently lower along the coastal regions of the United States as were the coefficients of determination. The low coastal isotope-temperature slopes are not easily explained by the simple Rayleigh model that uses condensation temperatures as the primary driver of precipitation isotopes. However, the Raleigh model equipped with moisture source temperatures defined by seasonal temperature oscillations and migrating moisture source locations provides a robust replication of the δ18O-temperature slopes along coastal regions. These findings emphasize the importance of moisture sources conditions when interpreting palaeoclimate proxies (i.e., tree rings, ice cores, etc.), and argue that moisture source dynamics should always be included in models that use isotopes as diagnostic tools in testing hydrologic models. [ABSTRACT FROM AUTHOR]

Three 60 m long, 2.8 m high snowfences have been erected to study long-term effects of changing winter snow conditions on arctic and alpine tundra. This paper describes the experimental design and short-term effects. Open-top fiberglass warming chambers are placed along the experimental snow gradients and in controls areas outside the fences;each warming plot is paired with an unwarmed plot. The purpose of the experiment is to examine short- and long-term changes to the integrated physical-biological systems under simultaneous changes of wintersnow regime and summer temperature, as part of the Long-Term Ecological Research network and the International Tundra Experiment. The sites were at Niwot Ridge, Colorado, a temperate high altitude site in the Colorado Rockies, and Toolik Lake, Alaska, a high-latitude site. Initial results indicate that although experimental designs are essentially identical at the arctic and alpine sites, experimental effects are different. The drift at Niwot Ridge lasts much longer than do theToolik Lake drifts, so that the Niwot Ridge fence affects both summer and winter conditions, whereas the Toolik Lake fence affects primarily winter conditions. The temperature experiment also differs in effect between the sites. Although the average temperature increase at the two sites is similar (daily increase 1.5 deg. C at Toolik and 1.9 deg. C at Niwot Ridge), at Toolik Lake there is only minor diurnal variation, whereas at Niwot Ridge the daytime increases are extreme on sunny days (as much as 7-10 deg. C), and minimum nighttime temperatures in the chambers are often slightly cooler than ambient (by about 1deg. C). The experimental drifts resulted in wintertime increases intemperature and CO2 flux. Temperatures under the deep drifts were much more consistent and warmer than in control areas, and at Niwot Ridge remained very close to 0 deg. C all winter. These increased temperatures were likely responsible for observed increases in system [ABSTRACT FROM AUTHOR]

The aim of this study was to test if early flowering species respondwith increased seed production to climate warming as is predicted for late-flowering seed-risk strategists. Experimental climate warming of about 3 deg.C was applied to two populations of the cushion-forming plant Silene acaulis (L) Jacq. The experiment was run at one subarctic site and one alpine site for 2 years and 1 year, respectively, using open-top chambers (OTC). The 2-year temperature enhancement at the subarctic site had a marked effect on the flowering phenology. Cushions inside the OTC started flowering substantially earlier than control cushions. Both the male and female phases developed faster in theOTCs, and maturation of capsules occurred earlier. The cushions alsoresponded positively in reproductive terms and produced more mature seeds and had a higher seed/ovule ratio. After 1 year temperature enhancement at the alpine site there was a weak trend for earlier flowering, but there was no significant difference in seed production or seed/ovule ratio. [ABSTRACT FROM AUTHOR]

The clam Ruditapes decussatus L. was collected from Ria Formosa, Faro, southern Portugal, and exposed to a sublethal copper concentrationof 0.01 mg l-1 for 20 days. Physiological measurements, respiration rates, clearance rates and absorption efficiency, were undertaken initially and after 2, 5, 9, 14 and 20 days and used to calculate Scope for Growth. Copper accumulation rate was calculated through the analysis of copper in the tissues at the same sampling times. The experiment showed two phases. Initially, copper was rapidly accumulated (1.95 5 g Cu g-1 dw day-1 in the first 48h), clearance rates declined markedly (lowest value 13.5% of control) and respiration rates increased (116% of control), resulting in a rapid decline of Scope for Growth, which showed a negative value after5 days. In the second phase, (from day 9 on), the rate of copper uptake declined to 0.55 5 g Cu g-1 day-1 and physiological responses were more stable. After 20 days, copper concentration in the tissues was 38.4 5 g Cu g-1 dw (bioconcentration factor 3840). Clearance rates were 50% of control rates and respiration rates were still high, 145% of control rates. Therefore, Scope for Growth and performance of the clams was still greatly affected (ca. 23% of the control values), indicating that though animals partially recovered through detoxifying mechanisms, excess copper caused sustained impairment of physiological functions. This experiment confirmsthat the physiological energetics approach and the integrated Scope for Growth measurement is a sensitive methodology to detect deviations from normal performance and assess stress at environmental realistic copper concentrations. [ABSTRACT FROM AUTHOR]