| 1. |
- 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. |
- Fjellberg, Arne, et al.
(författare)
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2.8. Structural changes in Collembola populations following replanting of birch forest with spruce in North Norway.
- 2007
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Ingår i: Proceedings from the AFFORNORD conference, Reykholt, Iceland June 18-22, 2005.. - 9789289314435 ; , s. 119-125
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of the present study was to demonstrate possible effects on Collembola populations by changes in tree composition in natural birch forest in coastal North Norway. In the study area (Dønnes, Nordland County) parts of the natural mixed birch forest has been replanted with Norway spruce and Sitka spruce. Soil samples were collected in June and October 2004. A total of 52 species of Collembola were found (36 in birch, 32 Sitka, 34 Norway spruce). Eighteen species were common to all three sites, while birch had 12 unique species. Nine species from the coniferous plantations were not seen in birch, while Norway spruce and Sitka had only minor differences. The most abundant species were Mesaphorura macrochaeta, Isotomiella minor, Parisotoma notabilis and Megalothorax miniumus which made up 55% of all individuals found. Total abundance averaged on 91,000 (Sitka), 53,000 (Norway spruce) and 32,000 (birch) inds./m², with spring densities 40-80% higher than in autumn. The planting of Sitka/Norway spruce changed species composition but gave no significant reduction in species number, while population densities increased considerably.
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| 3. |
- Juday, G.P, et al.
(författare)
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Chapter 14: Forests, Land Management and Agriculture
- 2005
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Ingår i: The Arctic Climate Impact Assessment - The Scientific Report. - Cambridge : Cambridge University Press. - 0521865093 ; , s. 781-862
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Wicher, K. B., et al.
(författare)
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Deletion of a cytotoxic, N-terminal putative signal peptide results in a significant increase in production yields in Escherichia coli and improved specific activity of Cel12A from Rhodothermus marinus
- 2001
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 0175-7598 .- 1432-0614. ; 55:5, s. 578-584
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Tidskriftsartikel (refereegranskat)abstract
- The thermostable cellulase Cel12A from Rhodothermus marinus was produced at extremely low levels when expressed in Escherichia coli and was cytotoxic to the cells. In addition, severe aggregation occurred when moderately high concentrations of the enzyme were heat-treated at 65°C, the growth optimum of R. marinus. Sequence analysis revealed that the catalytic module of this enzyme is preceded by a typical linker sequence and a highly hydrophobic putative signal peptide. Two deletion mutants lacking this hydrophobic region were cloned and successfully expressed in E. coli. These results indicated that the N-terminal putative signal peptide was responsible for the toxicity of the full-length enzyme in the host organism. This was further corroborated by cloning and expressing the hydrophobic N-terminal domain in E. coli, which resulted in extensive cell lysis. The deletion mutants, made up of either the catalytic module of Cel12A or the catalytic module and the putative linker sequence, were characterised and their properties compared to those of the full-length enzyme. The specific activity of the mutants was approximately threefold higher than that of the full-length enzyme. Both mutant proteins were highly thermostable, with half-lives exceeding 2 h at 90°C and unfolding temperatures up to 103°C.
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| 5. |
- Drobyshev, I, et al.
(författare)
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Reconstruction of regional drought index in southern Sweden since 1750 AD
- 2011
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Ingår i: The Holocene. ; 21:4, s. 667-697
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Tidskriftsartikel (refereegranskat)abstract
- We used a network of eight pedunculate oak (Quercus robur L.) sites (ntrees = 70) and one Scots pine (Pinus sylvestris L.) site (ntrees = 53) to develop drought-sensitive master chronologies for the two areas in southern Scandinavia: a SW-area centred on 57°N 12.7°E and a NE-area centred on 58.8°N 18.2°E. The ratio of actual to equilibrium evapotranspiration (AET/EET) was used as a measure of drought during the growing season defined as the period with average daily temperatures above 9°C. Instrumental data were used to parameterize the relationship between tree-ring data and the drought index (DI) over 1922–2000 for the SW area and over 1922–1995 for the NE area. The DI reconstructions explained 29.7% (SW area) and 43.7% (NE area) of the variance in the observed DI index in the calibration period, and were extended back to ad 1770 for the SW area and to ad 1750 for the NE area. Reconstructed drought dynamics suggested strong decadal- and century-scale temporal variability and limited regional synchronicity over 1770–2000. Large variations in DI were observed in both regions in the second half of the 1700s. Dry conditions were synchronously reconstructed in both sub-regions during 1781–1784, 1853–1855, and, to a lesser degree, during 1974–1978. Over the 1945–1975 period the SW area exhibited a trend towards drier growing seasons, whereas no such trend could be identified for the NE area. Analysis of correlation maps indicated that regional DI dynamics reflected two different climate regimes, associated with the Kattegat area (SW reconstruction) and southeastern Swedish coast of the Baltic sea (NE reconstruction).
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