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  1. AmeriFlux MX-Lpa La Paz

    This is the AmeriFlux version of the carbon flux data for the site MX-Lpa La Paz. Site Description - As evident by some very large Cardon (5-7 meters), according to Coyle and Roberts, 1975, extent vegetation has likely been around at least 200 years. Until about 15 years ago from 1996, site was used for livestock production and selective firewood extraction. However, when I look over the fence where there has been livestock activity, not much difference
  2. AmeriFlux US-Ivo Ivotuk

    This is the AmeriFlux version of the carbon flux data for the site US-Ivo Ivotuk. Site Description - This site is 300 km south of Barrow and is located at the foothill of the Brooks Range and is classified as tussock sedge, dwarf-shrub, moss tundra.
  3. FLUXNET2015 US-Ivo Ivotuk

    This is the FLUXNET2015 version of the carbon flux data for the site US-Ivo Ivotuk.
  4. Seasonal and Intra-annual Controls on CO 2 Flux in Arctic Alaska

    In order to advance the understanding of the patterns and controls on the carbon budget in the Arctic region, San Diego State University has maintained eddy covariance flux towers at three sites in Arctic Alaska, starting in 1997.
  5. Characterizing permafrost soil active layer dynamics and sensitivity to landscape spatial heterogeneity in Alaska

    An important feature of the Arctic is large spatial heterogeneity in active layer conditions, which is generally poorly represented by global models. In this study, we developed a spatially integrated modelling and analysis framework combining field observations, local scale (~ 50 m) active layer thickness (ALT) and soil moisture maps derived from airborne low frequency (L + P-band) radar measurements, and global satellite environmental observations to investigate the ALT sensitivity to recent climate trends and landscape heterogeneity in Alaska. Model simulated ALT results show good correspondence with in-situ measurements in higher permafrost probability (PP ≥ 70 %) areas (n =more » 33, R = 0.60, mean bias = 1.58 cm, RMSE = 20.32 cm). The model results also reveal widespread ALT deepening since 2001, with smaller ALT increases in northern Alaska (mean trend = 0.32 ± 1.18 cm yr -1) and much larger increases (> 3 cm yr -1) across interior and southern Alaska. The positive ALT trend coincides with regional warming and a longer snow-free season (R = 0.60 ± 0.32). Uncertainty in the spatial and vertical distribution of soil organic carbon (SOC) was found to be the most important factor affecting model ALT accuracy. Here, potential improvements in characterizing SOC heterogeneity, including better spatial sampling of soil conditions and advances in remote sensing of SOC and soil moisture, will enable more accurate predictions of permafrost active layer conditions.« less
  6. A multi-scale comparison of modeled and observed seasonal methane emissions in northern wetlands

    Wetlands are the largest global natural methane (CH 4) source, and emissions between 50 and 70° N latitude contribute 10-30 % to this source. Predictive capability of land models for northern wetland CH 4 emissions is still low due to limited site measurements, strong spatial and temporal variability in emissions, and complex hydrological and biogeochemical dynamics. To explore this issue, we compare wetland CH 4 emission predictions from the Community Land Model 4.5 (CLM4.5-BGC) with site- to regional-scale observations. A comparison of the CH 4 fluxes with eddy flux data highlighted needed changes to the model's estimate of aerenchyma area,more » which we implemented and tested. The model modification substantially reduced biases in CH 4 emissions when compared with CarbonTracker CH 4 predictions. CLM4.5 CH 4 emission predictions agree well with growing season (May–September) CarbonTracker Alaskan regional-level CH 4 predictions and site-level observations. However, CLM4.5 underestimated CH 4 emissions in the cold season (October–April). The monthly atmospheric CH 4 mole fraction enhancements due to wetland emissions are also assessed using the Weather Research and Forecasting-Stochastic Time-Inverted Lagrangian Transport (WRF-STILT) model coupled with daily emissions from CLM4.5 and compared with aircraft CH 4 mole fraction measurements from the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) campaign. Both the tower and aircraft analyses confirm the underestimate of cold-season CH 4 emissions by CLM4.5. The greatest uncertainties in predicting the seasonal CH 4 cycle are from the wetland extent, cold-season CH 4 production and CH 4 transport processes. We recommend more cold-season experimental studies in high-latitude systems, which could improve the understanding and parameterization of ecosystem structure and function during this period. Predicted CH 4 emissions remain uncertain, but we show here that benchmarking against observations across spatial scales can inform model structural and parameter improvements.« less
  7. Cold season emissions dominate the Arctic tundra methane budget

    Arctic terrestrial ecosystems are major global sources of methane (CH 4); hence, it is important to understand the seasonal and climatic controls on CH 4 emissions from these systems. Here, we report year-round CH 4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for ≥ 50% of the annual CH 4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the “zero curtain” period, when subsurface soil temperatures are poised near 0more » °C. The zero curtain may persist longer than the growing season, and CH 4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH 4 derived from aircraft data demonstrate the large spatial extent of late season CH 4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 ± 5 (95% confidence interval) Tg CH 4 y –1, ~25% of global emissions from extratropical wetlands, or ~6% of total global wetland methane emissions. Here, the dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH 4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming.« less
    Cited by 48
  8. Final Technical Report: Response of Mediterranean-Type Ecosystems to Elevated Atmospheric CO2 and Associated Climate Change

    This research incorporated an integrated hierarchical approach in space, time, and levels of biological/ecological organization to help understand and predict ecosystem response to elevated CO{sub 2} and concomitant environmental change. The research utilized a number of different approaches, and collaboration of both PER and non-PER investigators to arrive at a comprehensive, integrative understanding. Central to the work were the CO{sub 2}-controlled, ambient Lit, Temperature controlled (CO{sub 2}LT) null-balance chambers originally developed in the arctic tundra, which were re-engineered for the chaparral with treatment CO{sub 2} concentrations of from 250 to 750 ppm CO{sub 2} in 100 ppm increments, replicated twicemore » to allow for a regression analysis. Each chamber was 2 meters on a side and 2 meters tall, which were installed over an individual shrub reprouting after a fire. This manipulation allowed study of the response of native chaparral to varying levels of CO{sub 2}, while regenerating from an experimental burn. Results from these highly-controlled manipulations were compared against Free Air CO{sub 2} Enrichment (FACE) manipulations, in an area adjacent to the CO{sub 2}LT null balance greenhouses. These relatively short-term results (5-7 years) were compared to long-term results from Mediterranean-type ecosystems (MTEs) surrounding natural CO{sub 2} springs in northern Italy, near Laiatico, Italy. The springs lack the controlled experimental rigor of our CO{sub 2}LT and FACE manipulation, but provide invaluable validation of our long-term predictions.« less
  9. Empirical estimation of daytime net radiation from shortwave radiation and ancillary information

  10. Patterns and Controls of Temporal Variation in CO2 Sequestration and Loss in Arctic Ecosystems

    Determine seasonal and interannual patterns of net ecosystem CO2 flux from wet coastal and moist tussock tundra.
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"Oechel, Walter"

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