| 1. |
- Barnes, Paul W., et al.
(författare)
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Ozone depletion, ultraviolet radiation, climate change and prospects for a sustainable future
- 2019
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Ingår i: Nature Sustainability. - : Springer Science and Business Media LLC. - 2398-9629. ; 2:7, s. 569-579
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Forskningsöversikt (refereegranskat)abstract
- © 2019, Springer Nature Limited. Changes in stratospheric ozone and climate over the past 40-plus years have altered the solar ultraviolet (UV) radiation conditions at the Earth’s surface. Ozone depletion has also contributed to climate change across the Southern Hemisphere. These changes are interacting in complex ways to affect human health, food and water security, and ecosystem services. Many adverse effects of high UV exposure have been avoided thanks to the Montreal Protocol with its Amendments and Adjustments, which have effectively controlled the production and use of ozone-depleting substances. This international treaty has also played an important role in mitigating climate change. Climate change is modifying UV exposure and affecting how people and ecosystems respond to UV; these effects will become more pronounced in the future. The interactions between stratospheric ozone, climate and UV radiation will therefore shift over time; however, the Montreal Protocol will continue to have far-reaching benefits for human well-being and environmental sustainability.
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| 2. |
- Aldenhoff, Wiebke, 1985, et al.
(författare)
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Comparison of ice/water classification in Fram Strait from C- and L-band SAR imagery
- 2018
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Ingår i: Annals of Glaciology. - : Cambridge University Press (CUP). - 0260-3055 .- 1727-5644. ; 59:76pt2, s. 112-123
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Tidskriftsartikel (refereegranskat)abstract
- In this paper an algorithm for ice/water classification of C- and L-band dual polarization synthetic aperture radar data is presented. A comparison of the two different frequencies is made in order to investigate the potential to improve classification results with multi-frequency data. The algorithm is based on backscatter intensities in co- and cross-polarization and autocorrelation as a texture feature. The mapping between image features and ice/water classification is made with a neural network. Accurate ice/water maps for both frequencies are produced by the algorithm and the results of two frequencies generally agree very well. Differences are found in the marginal ice zone, where the time difference between acquisitions causes motion of the ice pack. C-band reliably reproduces the outline of the ice edge, while L-band has its strengths for thin ice/calm water areas within the icepack. The classification shows good agreement with ice/water maps derived from met.no ice-charts and radiometer data from AMSR-2. Variations are found in the marginal ice zone where the generalization of the ice charts and lower accuracy of ice concentration from radiometer data introduce deviations. Usage of high-resolution dual frequency data could be beneficial for improving ice cover information for navigation and modelling.
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| 3. |
- Maskenskaya, Olga M., et al.
(författare)
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Source and character of syntaxial hydrothermal calcite veins in Paleoproterozoic crystalline rocks revealed by fine-scale investigations
- 2014
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Ingår i: Geofluids. - : Wiley. - 1468-8115 .- 1468-8123. ; 14:4, s. 495-511
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Tidskriftsartikel (refereegranskat)abstract
- Calcite veins in Paleoproterozoic granitoids on the Baltic Shield are the focus of this study. These veins are distinguished by their monomineralic character, unusual thickness and closeness to Neoproterozoic dolerite dykes and therefore have drawn attention. The aim of this study was to define the source of these veins and to unravel their isotopic and chemical nature by carrying out fine-scale studies. Seven calcite veins covering a depth interval of 50-420m below the ground surface and composed of breccias or crack-sealed fillings typically expressing syntaxial growth were sampled and analysed for a variety of physicochemical variables: homogenization temperature (T-h) and salinity of fluid inclusions, and stable isotopes (Sr-87/Sr-86, C-13/C-12, O-18/O-16), trace-element concentrations (Fe, Mn, Mg, Sr, rare earth elements) and cathodoluminescence (CL) of the solid phase. The fluid-inclusion data show that the calcites were precipitated mainly from relatively low-temperature (T-h=73-106 degrees C) brines (13.4-24.5wt.% CaCl2), and the Sr-87/Sr-86 is more radiogenic than expected for Rb-poor minerals precipitated from Neoproterozoic fluids. These features, together with the distribution of C-13 and O-18 values, provide evidence that the calcite veins are not genetic with the nearby Neoproterozoic dolerite dykes, but are of Paleozoic age and were precipitated from warm brines expressing a rather large variability in salinity. Whereas the isotopic and chemical variables express rather constant average values among the individual veins, they vary considerably on fine-scale across individual veins. This has implications for understanding processes causing calcite-rich veins to form and capture trace metals in crystalline bedrock settings.
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| 4. |
- Ranta, E., et al.
(författare)
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Fluid-rock reactions in the 1.3Ga siderite carbonatite of the GrOnnedal-ika alkaline complex, Southwest Greenland
- 2018
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Ingår i: Contributions to Mineralogy and Petrology. - : Springer Science and Business Media LLC. - 0010-7999 .- 1432-0967. ; 173:10
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Tidskriftsartikel (refereegranskat)abstract
- Petrogenetic studies of carbonatites are challenging, because carbonatite mineral assemblages and mineral chemistry typically reflect both variable pressure-temperature conditions during crystallization and fluid-rock interaction caused by magmatic-hydrothermal fluids. However, this complexity results in recognizable alteration textures and trace-element signatures in the mineral archive that can be used to reconstruct the magmatic evolution and fluid-rock interaction history of carbonatites. We present new LA-ICP-MS trace-element data for magnetite, calcite, siderite, and ankerite-dolomite-kutnohorite from the iron-rich carbonatites of the 1.3Ga GrOnnedal-ika alkaline complex, Southwest Greenland. We use these data, in combination with detailed cathodoluminescence imaging, to identify magmatic and secondary geochemical fingerprints preserved in these minerals. The chemical and textural gradients show that a 55m-thick basaltic dike that crosscuts the carbonatite intrusion has acted as the pathway for hydrothermal fluids enriched in F and CO2, which have caused mobilization of the LREEs, Nb, Ta, Ba, Sr, Mn, and P. These fluids reacted with and altered the composition of the surrounding carbonatites up to a distance of 40m from the dike contact and caused formation of magnetite through oxidation of siderite. Our results can be used for discrimination between primary magmatic minerals and later alteration-related assemblages in carbonatites in general, which can lead to a better understanding of how these rare rocks are formed. Our data provide evidence that siderite-bearing ferrocarbonatites can form during late stages of calciocarbonatitic magma evolution.
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| 5. |
- Chen, Hans, 1988, et al.
(författare)
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A robust mode of climate variability in the Arctic: The Barents Oscillation
- 2013
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 40:11, s. 2856-2861
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Tidskriftsartikel (refereegranskat)abstract
- The Barents Oscillation (BO) is an anomalous wintertime atmospheric circulation pattern in the Northern Hemisphere that has been linked to the meridional flow over the Nordic Seas. There are speculations that the BO has important implications for the Arctic climate; however, it has also been suggested that the pattern is an artifact of Empirical Orthogonal Function (EOF) analysis due to an eastward shift of the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). In this study, EOF analyses are performed to show that a robust pattern resembling the BO can be found during different time periods, even when the AO/NAO is relatively stationary. This BO has a high and stable temporal correlation with the geostrophic zonal wind over the Barents Sea, while the contribution from the AO/NAO is small. The surface air temperature anomalies over the Barents Sea are closely associated with this mode of climate variability.
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| 6. |
- Wang, X. J., et al.
(författare)
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Contrasting characteristics, changes, and linkages of permafrost between the Arctic and the Third Pole
- 2022
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252. ; 230
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Tidskriftsartikel (refereegranskat)abstract
- Permafrost degradation poses serious threats to both natural and human systems through its influence on ecological-hydrological processes, infrastructure stability, and the climate system. The Arctic and the Third Pole (Tibetan Plateau, TP hereafter) are the two northern regions on Earth with the most extensive permafrost areas. However, there is a lack of systematic comparisons of permafrost characteristics and its climate and ecoenvironment between these two regions and their susceptibility to disturbances. This study provides a comprehensive review of the climate, ecosystem characteristics, ground temperature, permafrost extent, and active-layer thickness, as well as the past and future changes in permafrost in the Arctic and the TP. The potential consequences associated with permafrost degradation are also examined. Lastly, possible connections between the two regions through land-ocean-atmosphere interactions are explored. Both regions have experienced dramatic warming in recent decades, characterized by Arctic amplification and elevation-dependent warming on the TP. Permafrost temperatures have increased more rapidly in the Arctic than on the TP, and will likely be reinforced under a future high emission scenario. Near-surface permafrost extents are projected to shrink in both regions in the coming decades, with a more dramatic decline in the TP. The active layer on the TP is thicker and has substantially deepened, and is projected to thicken more than in the Arctic. Widespread permafrost degradation increases geohazard risk and has already wielded considerable effects on the human and natural systems. Permafrost changes have also exerted a pronounced impact on the climate system through changes in permafrost carbon and land-atmosphere interactions. Future research should involve comparative studies of permafrost dynamics in both regions that integrate long-term observations, high-resolution satellite measurements, and advanced Earth System models, with emphasis on linkages between the two regions.
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| 7. |
- Kulmala, M., et al.
(författare)
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General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) - integrating aerosol research from nano to global scales
- 2011
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 11:24, s. 13061-13143
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we describe and summarize the main achievements of the European Aerosol Cloud Climate and Air Quality Interactions project (EUCAARI). EUCAARI started on 1 January 2007 and ended on 31 December 2010 leaving a rich legacy including: (a) a comprehensive database with a year of observations of the physical, chemical and optical properties of aerosol particles over Europe, (b) comprehensive aerosol measurements in four developing countries, (c) a database of airborne measurements of aerosols and clouds over Europe during May 2008, (d) comprehensive modeling tools to study aerosol processes fron nano to global scale and their effects on climate and air quality. In addition a new Pan-European aerosol emissions inventory was developed and evaluated, a new cluster spectrometer was built and tested in the field and several new aerosol parameterizations and computations modules for chemical transport and global climate models were developed and evaluated. These achievements and related studies have substantially improved our understanding and reduced the uncertainties of aerosol radiative forcing and air quality-climate interactions. The EUCAARI results can be utilized in European and global environmental policy to assess the aerosol impacts and the corresponding abatement strategies.
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| 8. |
- Drake, Henrik, et al.
(författare)
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Extreme fractionation and micro-scale variation of sulphur isotopes during bacterial sulphate reduction in deep groundwater systems
- 2015
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Ingår i: Geochimica Et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 161, s. 1-18
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Tidskriftsartikel (refereegranskat)abstract
- This study conducted at the Aspo Hard Rock Laboratory, SE Sweden, determines the extent and mechanisms of sulphur-isotope fractionation in permanently reducing groundwater in fractured crystalline rock. Two boreholes > 400 m below the ground surface were investigated. In the 17-year-old boreholes, the Al instrumentation pipes had corroded locally (i.e., Al[oxy] hydroxides had formed) and minerals (i.e., pyrite, iron monosulphide, and calcite) had precipitated on various parts on the equipment. By chemically and isotopically comparing the precipitates on the withdrawn instrumentation and the borehole waters, we gained new insight into the dynamics of sulphate reduction, sulphide precipitation, and sulphur-isotope fractionation in deep-seated crystalline-rock settings. An astonishing feature of the pyrite is its huge variability in delta S-34, which can exceed 100 parts per thousand in total (i.e., -47.2 to +53.3 parts per thousand) and 60 parts per thousand over 50 mu m of growth in a single crystal. The values at the low end of the range are up to 71 parts per thousand lower than measured in the dissolved sulphate in the water (20-30 parts per thousand), which is larger than the maximum difference reported between sulphate and sulphide in pure-culture experiments (66 parts per thousand) but within the range reported from natural sedimentary settings. Although single-step reduction seems likely, further studies are needed to rule out the effects of possible S disproportionation. The values at the high end of the range (i.e., high delta S-34(py)) are much higher than could be produced from the measured sulphate under any biogeochemical conditions. This strongly suggests the development of closed-system conditions near the growing pyrite, i.e., the rate of sulphate reduction exceeds the rate of sulphate diffusion in the local fluid near the pyrite, causing the local aqueous phase (and thus the forming pyrite) to become successively enriched in heavy S (S-34). Consequently, the delta S-34 values of the forming pyrite become exceptionally high and strongly decoupled from the delta S-34 values of the sulphate in the bulk fluid. The Al-(oxy) hydroxide and calcite precipitates are explained by a combination of deposit and galvanic corrosion initiated by Al corrosion by H2S produced by sulphate-reducing microorganisms. (C) 2015 Elsevier Ltd. All rights reserved.
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| 9. |
- Soja, Maciej, 1985, et al.
(författare)
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Mapping Tree Height in Burkina Faso Parklands with TanDEM-X
- 2021
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 13:14
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Tidskriftsartikel (refereegranskat)abstract
- Mapping of tree height is of great importance for management, planning, and research related to agroforestry parklands in Africa. In this paper, we investigate the potential of spotlight-mode data from the interferometric synthetic aperture radar (InSAR) satellite system TanDEM-X (TDM) for mapping of tree height in Sapone, Burkina Faso, a test site characterised by a low average canopy cover (similar to 15%) and a mean tree height of 9.0 m. Seven TDM acquisitions from January-April 2018 are used jointly to create high-resolution (similar to 3 m) maps of interferometric phase height and mean canopy elevation, the latter derived using a new, model-based processing approach compensating for some effects of the side-looking geometry of SAR. Compared with phase height, mean canopy elevation provides a more accurate representation of tree height variations, a better tree positioning accuracy, and better tree height estimation performance when assessed using 915 trees inventoried in situ and representing 15 different species/genera. We observe and discuss two bias effects, and we use empirical models to compensate for these effects. The best-performing model using only TDM data provides tree height estimates with a standard error (SE) of 2.8 m (31% of the average height) and a correlation coefficient of 75%. The estimation performance is further improved when TDM height data are combined with in situ measurements; this is a promising result in view of future synergies with other remote sensing techniques or ground measurement-supported monitoring of well-known trees.
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| 10. |
- Stranne, Christian, 1979, et al.
(författare)
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Arctic Ocean perennial sea ice breakdown during the Early Holocene Insolation Maximum
- 2014
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 92, s. 123-132
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Tidskriftsartikel (refereegranskat)abstract
- Arctic Ocean sea ice proxies generally suggest a reduction in sea ice during parts of the early and middle Holocene (similar to 6000-10,000 years BP) compared to present day conditions. This sea ice minimum has been attributed to the northern hemisphere Early Holocene Insolation Maximum (EHIM) associated with Earth's orbital cycles. Here we investigate the transient effect of insolation variations during the final part of the last glaciation and the Holocene by means of continuous climate simulations with the coupled atmosphere sea ice ocean column model CCAM. We show that the increased insolation during EHIM has the potential to push the Arctic Ocean sea ice cover into a regime dominated by seasonal ice, i.e. ice free summers. The strong sea ice thickness response is caused by the positive sea ice albedo feedback. Studies of the GRIP ice cores and high latitude North Atlantic sediment cores show that the Bolling Allerod period (c. 12,700-14,700 years BP) was a climatically unstable period in the northern high latitudes and we speculate that this instability may be linked to dual stability modes of the Arctic sea ice cover characterized by e.g. transitions between periods with and without perennial sea ice cover.
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