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- Buntgen, U., et al.
(författare)
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Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.
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| 2. |
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| 3. |
- Esper, Jan, et al.
(författare)
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Ranking of tree-ring based temperature reconstructions of the past millennium
- 2016
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 145, s. 134-151
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Tidskriftsartikel (refereegranskat)abstract
- Tree-ring chronologies are widely used to reconstruct high-to low-frequency variations in growing season temperatures over centuries to millennia. The relevance of these timeseries in large-scale climate reconstructions is often determined by the strength of their correlation against instrumental temperature data. However, this single criterion ignores several important quantitative and qualitative characteristics of tree-ring chronologies. Those characteristics are (i) data homogeneity, (ii) sample replication, (iii) growth coherence, (iv) chronology development, and (v) climate signal including the correlation with instrumental data. Based on these 5 characteristics, a reconstruction-scoring scheme is proposed and applied to 39 published, millennial-length temperature reconstructions from Asia, Europe, North America, and the Southern Hemisphere. Results reveal no reconstruction scores highest in every category and each has their own strengths and weaknesses. Reconstructions that perform better overall include N-Scan and Finland from Europe, E-Canada from North America, Yamal and Dzhelo from Asia. Reconstructions performing less well include W-Himalaya and Karakorum from Asia, Tatra and S-Finland from Europe, and Great Basin from North America. By providing a comprehensive set of criteria to evaluate tree-ring chronologies we hope to improve the development of large-scale temperature reconstructions spanning the past millennium. All reconstructions and their corresponding scores are provided at www.blogs.uni-mainz.de/fb09climatology.
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| 4. |
- Mmbaga, Naza E., et al.
(författare)
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Cropping patterns along an altitudinal gradient and their implications to wildlife conservation in Rombo, Tanzania
- 2021
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Ingår i: Global Ecology and Conservation. - : Elsevier BV. - 2351-9894. ; 28
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Tidskriftsartikel (refereegranskat)abstract
- Ecosystem and livelihood sustainability of small-scale farmers in Eastern Africa are often challenged by climate change and unsustainable land use practices. Little is known on the small-scale temporal processes of cropping systems in relation to long-term climatic conditions. To understand the climatic influence on the cropping patterns, and its implications to wildlife/elephant conservation, our study used a combination of time-series datasets on crop and climate as well as geo-spatial layers spanning more than three decades. To validate the information analyzed from secondary data, we carried out participatory observation and interviews, whereby about 5% of village households were selected along an altitudinal gradient of Rombo area, Tanzania. We generated land use change maps using Geographical Information System (ArcGIS 10.4) and used Spearman's correlation analysis to assess the influence of rainfall, temperature, and crop yield on the observed longitudinal changes in the crop types and other land use patterns both within and across altitudinal gradients. We found that perennial crops like coffee and banana concentrated in upper agro-ecological zones, with a clear division line above 1230 masl while seasonal crops like maize and beans were mostly cultivated in lowlands (below 1230 masl). The results further showed that coffee yields significantly declined with higher average annual minimum temperatures over the last 16 years. Within the same time period, there was a disproportionate shift from coffee to seasonal crop cultivation such as maize and beans. Elephant numbers declined by about 38%, while human settlement area increased by 28% over the last 30 years. We conclude that changes in land use and shifts in climate and cropping patterns have important implications for elephant conservation and sustainability of the ecosystem in Rombo area, Tanzania.
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