| 1. |
- Aartsen, M. G., et al.
(author)
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Observation of High-Energy Astrophysical Neutrinos in Three Years of IceCube Data
- 2014
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 113:10, s. 101101-
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Journal article (peer-reviewed)abstract
- A search for high-energy neutrinos interacting within the IceCube detector between 2010 and 2012 provided the first evidence for a high-energy neutrino flux of extraterrestrial origin. Results from an analysis using the same methods with a third year (2012-2013) of data from the complete IceCube detector are consistent with the previously reported astrophysical flux in the 100 TeV-PeV range at the level of 10(-8) GeV cm(-2) s(-1) sr(-1) per flavor and reject a purely atmospheric explanation for the combined three-year data at 5.7 sigma. The data are consistent with expectations for equal fluxes of all three neutrino flavors and with isotropic arrival directions, suggesting either numerous or spatially extended sources. The three-year data set, with a live time of 988 days, contains a total of 37 neutrino candidate events with deposited energies ranging from 30 to 2000 TeV. The 2000-TeV event is the highest-energy neutrino interaction ever observed.
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| 2. |
- Aartsen, M. G., et al.
(author)
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SEARCHES FOR EXTENDED AND POINT-LIKE NEUTRINO SOURCES WITH FOUR YEARS OF ICECUBE DATA
- 2014
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 796:2, s. 109-
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Journal article (peer-reviewed)abstract
- We present results on searches for point-like sources of neutrinos using four years of IceCube data, including the first year of data from the completed 86 string detector. The total livetime of the combined data set is 1373 days. For an E-2 spectrum, the observed 90% C. L. flux upper limits are similar to 10(-12) TeV-1 cm(-2) s(-1) for energies between 1 TeV and 1 PeV in the northern sky and similar to 10(-11) TeV-1 cm(-2) s(-1) for energies between 100 TeV and 100 PeV in the southern sky. This represents a 40% improvement compared to previous publications, resulting from both the additional year of data and the introduction of improved reconstructions. In addition, we present the first results from an all-sky search for extended sources of neutrinos. We update the results of searches for neutrino emission from stacked catalogs of sources and test five new catalogs; two of Galactic supernova remnants and three of active galactic nuclei. In all cases, the data are compatible with the background-only hypothesis, and upper limits on the flux of muon neutrinos are reported for the sources considered.
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| 3. |
- Braakhekke, Maarten C., et al.
(author)
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The use of radiocarbon to constrain current and future soil organic matter turnover and transport in a temperate forest
- 2014
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In: Journal of Geophysical Research: Biogeosciences. - 2169-8953. ; 119:3, s. 372-391
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Journal article (peer-reviewed)abstract
- We investigated the merits of radiocarbon measurements for estimating soil organic matter (SOM) turnover and vertical transport for a temperate deciduous forest in Germany. Eleven parameters, defining decomposition and transport in the soil carbon model SOMPROF, were estimated using a Bayesian approach based on organic carbon measurements and radiocarbon concentration of SOM and heterotrophic respiration. The addition of radiocarbon data had strong effects on the parameters, most importantly a reduction of the decomposition and production rate of the slowest SOM pool by an order of magnitude, and a similar reduction in advective SOM transport. The modified parameters further led to changes in the partitioning of SOM over the different model pools. The calibration results were subsequently used to perform transient soil carbon projections for the period 1901-2100. These simulations were run with parameter sets from calibrations both with and without radiocarbon. The results show an increase over time of topsoil carbon and a decrease in the subsoil, adding to a net gain overall. Near the end of the 21st century, total carbon stocks stabilize andfor the radiocarbon-constrained modelstart to decrease. However, the changes are small compared to the total stocks. The model results for the calibrations with and without radiocarbon are in general quite similar, but the latter shows notably higher heterotrophic respiration fluxes. Constraining the model with radiocarbon yielded only a small reduction of uncertainty for the total carbon stocks, while for the individual depth compartments, the uncertainty wasincreased. Key Points SOM turnover and transport was estimated using Bayesian calibration Radiocarbon data strongly improved constraint of turnover rate of slow pool Predictive simulation showed small increase of soil C stocks in 21st century
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| 4. |
- Carvalhais, Nuno, et al.
(author)
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Global covariation of carbon turnover times with climate in terrestrial ecosystems
- 2014
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 514:7521, s. 213-
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Journal article (peer-reviewed)abstract
- The response of the terrestrial carbon cycle to climate change is among the largest uncertainties affecting future climate change projections(1,2). The feedback between the terrestrial carbon cycle and climate is partly determined by changes in the turnover time of carbon in land ecosystems, which in turn is an ecosystem property that emerges from the interplay between climate, soil and vegetation type(3-6). Here we present a global, spatially explicit and observation-based assessment of whole-ecosystem carbon turnover times that combines new estimates of vegetation and soil organic carbon stocks and fluxes. We find that the overall mean global carbon turnover time is 23(4)(+7) years (95 per cent confidence interval). Onaverage, carbon resides in the vegetation and soil near the Equator for a shorter time than at latitudes north of 75 degrees north (mean turnover times of 15 and 255 years, respectively). We identify a clear dependence of the turnover time on temperature, as expected from our present understanding of temperature controls on ecosystem dynamics. Surprisingly, our analysis also reveals a similarly strong association between turnover time and precipitation. Moreover, we find that the ecosystem carbon turnover times simulated by state-of-the-art coupled climate/carbon-cycle models vary widely and that numerical simulations, on average, tend to underestimate the global carbon turnover time by 36 per cent. The models show stronger spatial relationships with temperature than do observation-based estimates, but generally do not reproduce the strong relationships with precipitation and predict faster carbon turnover in many semiarid regions. Our findings suggest that future climate/carbon-cycle feedbacks may depend more strongly on changes in the hydrological cycle than is expected at present and is considered in Earth system models.
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| 5. |
- Thurner, Martin, et al.
(author)
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Carbon stock and density of northern boreal and temperate forests
- 2014
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In: Global Ecology and Biogeography. - : Wiley. - 1466-822X .- 1466-8238. ; 23:3, s. 297-310
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Journal article (peer-reviewed)abstract
- AimTo infer a forest carbon density map at 0.01 degrees resolution from a radar remote sensing product for the estimation of carbon stocks in Northern Hemisphere boreal and temperate forests. LocationThe study area extends from 30 degrees N to 80 degrees N, covering three forest biomes - temperate broadleaf and mixed forests (TBMF), temperate conifer forests (TCF) and boreal forests (BFT) - over three continents (North America, Europe and Asia). MethodsThis study is based on a recently available growing stock volume (GSV) product retrieved from synthetic aperture radar data. Forest biomass and spatially explicit uncertainty estimates were derived from the GSV using existing databases of wood density and allometric relationships between biomass compartments (stem, branches, roots, foliage). We tested the resultant map against inventory-based biomass data from Russia, Europe and the USA prior to making intercontinent and interbiome carbon stock comparisons. ResultsOur derived carbon density map agrees well with inventory data at regional scales (r(2)=0.70-0.90). While 40.715.7 petagram of carbon (PgC) are stored in BFT, TBMF and TCF contain 24.5 +/- 9.4PgC and 14.5 +/- 4.8 PgC, respectively. In terms of carbon density, we found 6.21 +/- 2.07kgC m(-2) retained in TCF and 5.80 +/- 2.21kgC m(-2) in TBMF, whereas BFT have a mean carbon density of 4.00 +/- 1.54kgC m(-2). Indications of a higher carbon density in Europe compared with the other continents across each of the three biomes could not be proved to be significant. Main conclusionsThe presented carbon density and corresponding uncertainty map give an insight into the spatial patterns of biomass and stand as a new benchmark to improve carbon cycle models and carbon monitoring systems. In total, we found 79.8 +/- 29.9PgC stored in northern boreal and temperate forests, with Asian BFT accounting for 22.1 +/- 8.3PgC.
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