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  • Mills, Gina, 1959-, et al. (författare)
  • Tropospheric ozone assessment report: Present-day tropospheric ozone distribution and trends relevant to vegetation
  • 2018
  • Ingår i: Elementa. - 2325-1026. ; 6
  • Tidskriftsartikel (refereegranskat)abstract
    • This Tropospheric Ozone Assessment Report (TOAR) on the current state of knowledge of ozone metrics of relevance to vegetation (TOAR-Vegetation) reports on present-day global distribution of ozone at over 3300 vegetated sites and the long-term trends at nearly 1200 sites. TOAR-Vegetation focusses on three metrics over vegetation-relevant time-periods across major world climatic zones: M12, the mean ozone during 08:00-19:59; AOT40, the accumulation of hourly mean ozone values over 40 ppb during daylight hours, and W126 with stronger weighting to higher hourly mean values, accumulated during 08:00-19:59. Although the density of measurement stations is highly variable across regions, in general, the highest ozone values (mean, 2010-14) are in mid-latitudes of the northern hemisphere, including southern USA, the Mediterranean basin, northern India, north, north-west and east China, the Republic of Korea and Japan. The lowest metric values reported are in Australia, New Zealand, southern parts of South America and some northern parts of Europe, Canada and the USA. Regional-scale assessments showed, for example, significantly higher AOT40 and W126 values in East Asia (EAS) than Europe (EUR) in wheat growing areas (p < 0.05), but not in rice growing areas. In NAM, the dominant trend during 1995-2014 was a significant decrease in ozone, whilst in EUR it was no change and in EAS it was a significant increase. TOAR-Vegetation provides recommendations to facilitate a more complete global assessment of ozone impacts on vegetation in the future, including: an increase in monitoring of ozone and collation of field evidence of the damaging effects on vegetation; an investigation of the effects on peri-urban agriculture and in mountain/upland areas; inclusion of additional pollutant, meteorological and inlet height data in the TOAR dataset; where not already in existence, establishing new region-specific thresholds for vegetation damage and an innovative integration of observations and modelling including stomatal uptake of the pollutant.
  • Olsson, Mikael, 1948- (författare)
  • Polaris Möten med världens poler www.polarisen.se
  • 2009
  • Ingår i: http://www.polarisen.se. - Göteborg : University of Gothenburg.
  • Annan publikation (övrigt vetenskapligt)abstract
    • Polaris is a Swedish based web site dealing with Antarctic, Arctic and sub-polar areas around the globe, including sub-Arctic regions of Scandinavia and Eurasia. Polaris is focusing on peoples and places, research and resources on high latitudes. In particular, the site's ambition is to depict the interaction between the components and put them in a context of global environmental and climate change. The web site also addresses the Swedish polar and mountain research, exemplified by the depiction of a number of Swedish polar researchers' work and choice of career. Polaris main target group is high school students. We aim at establishing Polaris as the popular web site in Sweden for polar research. Polaris was a joint production by Gothenburg and Stockholm Universities and others during the International Polar Year 2007-09. The initiative to the website was taken by the Swedish Committee for International Polar Year, the Swedish Research Council and the Universeum Science Center in Gothenburg. There are many scientific contributors, mainly from the Centre of Earth Systems Science at the University of Gothenburg, the Tarfala Research Station at Stockholm University and the Swedish Polar Research Secretariat . Interviews and articles are made by professional science writers. All texts are in Swedish.
  • Aldenhoff, Wiebke, et al. (författare)
  • Comparison of ice/water classification in Fram Strait from C- A nd L-band SAR imagery
  • 2018
  • Ingår i: Radar remote sensing of sea ice in the Polar regions.
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper an algorithm for ice/water classification of C- A nd 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- A nd 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.
  • He, Hongxing, 1987-, et al. (författare)
  • Forests on drained agricultural peatland are potentially large sources of greenhouse gases – insights from a full rotation period simulation
  • 2015
  • Ingår i: Biogeosciences Discussions. - 1810-6277. ; 12, s. 19673-19710
  • Tidskriftsartikel (refereegranskat)abstract
    • The CoupModel was used to simulate a Norway Spruce forest on fertile drained peat over 60 years, from planting in 1951 until 2011, describing abiotic, biotic and greenhouse gas (GHG) emissions (CO2 and N2O). By calibrating the model against tree ring data we obtained a "reference" model by which we were able to describe the fluxes and controlling factors over the 60 years. We discuss some conceptual issues relevant to improving the model in order to better understand peat soil simulations. However, the present model was able to describe the most important ecosystem dynamics such as the plant biomass development and GHG emissions. The GHG fluxes are composed of two important quantities, the forest carbon (C) uptake, 405 g C m−2 yr−1 and the decomposition of peat soil, 396 g C m−2 yr−1. N2O emissions contribute to the GHG emissions by 0.5 g N m−2 yr−1, corresponding to 56.8 g C m−2 yr−1. The 60-year-old Spruce forest has an accumulated biomass of 164 Mg C ha−1. However, over this period 208 Mg C ha−1 GHG has been added to the atmosphere, which means a net addition of GHG emissions. The main losses are from the peat soil and, indirectly, from forest thinning products, which we assume have a short lifetime. We conclude that after harvest at an age of 80 years, most of the stored biomass carbon is liable to be released, the system having captured C only temporarily and with a cost of disappeared peat, adding CO2 to the atmosphere.
  • Brandt, S. Anders, 1970-, et al. (författare)
  • 3D geovisualization as a communication and analysis tool in fluvial geomorphology
  • 2004
  • Ingår i: Geoinformatics 2004 : proceedings of the 12th International Conference on Geoinformatics - Geospatial Information Research: Bridging the Pacific and Atlantic, University of Gävle, Sweden, 7-9 June 2004. - Gävle : Gävle University Press. - 91-974948-1-X ; s. 339-346
  • Konferensbidrag (refereegranskat)abstract
    • <p>The fields of hydrology and fluvial geomorphology get more and more attention in the general public. The reason for this is changed climate patterns with increased frequencies of storms and river flooding and as a result changed geomorphology and living conditions for the inhabitants of the area. With the development of 3D geovisualization, hydrological and geomorphological processes can be better simulated and visualized. Thus not only the domain specialists, but also the general public can appreciate very complex hydrological processes and resulting geomorphology. This is of great value since a high frequency of storms and flooding has been a big issue for politicians, planners, and the general public. It is in this sense that 3D geovisualization can be an important tool for analysis and communication. Complex hydrological and geomorphological processes can be effectively simulated and analyzed by the domain specialists while efficient and effective visualization provides a common platform for communication among domain specialists and the general public. This paper will discuss and illustrate these issues using a case study of geomorphology along the Reventazón River, downstream from the Cachí Reservoir in Costa Rica, due to the release of extreme amounts of sediment during flushing of the reservoir.</p>
  • Brandt, S. Anders, 1970- (författare)
  • Conceptualization of hydraulic and sedimentary processes in downstream reaches during flushing of reservoirs
  • 2005
  • Ingår i: Proceedings of the XXXI IAHR Congress [Elektronisk resurs] : Water engineering for the future : choices and challenges : COEX Seoul September 11-16, 2005. - Seoul : Korea Water Resources Association. - 8987898237 ; s. 2577-2588
  • Konferensbidrag (refereegranskat)abstract
    • <p>The main focus of this paper is to describe the active hydraulic and sedimentary processes in downstream river reaches during flushing of sediments from reservoirs. During flushing extreme amounts of sediment may be released. Therefore, these processes are different than those downstream from dams and reservoirs not subjected to flushing. Hence, also the effects differ, which knowledge of may be of value for biologists, etc. During flushing of a reservoir a wave will be released to the downstream reaches. This wave can be divided into one water part and one sediment part. Initially they are in phase with each other, but with increased distance downstream from the dam, the transported sediment lags behind the water due to different traveling velocities. The paper treats when and where sedimentation occurs, and how this is related to the different traveling velocities of water and sediment. Also included are discussions on how the downstream effects during flushing differ from non-flushing effects, how visualization of effects can enhance both the analysis and communication with planners, politicians, etc., as well as discussions on how the studies of these effects can benefit from improved field-work methods.</p>
  • Bernhardson, Martin (författare)
  • Aeolian dunes of central Sweden
  • 2018
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • I Sveriges centrala inland finns det allt från enstaka sanddyner till stora dynfält som täcker mer än 10 km2. Dessa dynfält passerar dock oftast obemärkt i landskapet på grund av det oftast markanta vegetationstäcke som fixerar dessa dyner. De är dock värdefulla för att kunna återskapa forna tiders klimat och vindmönster, men tyvärr har förhållandevis lite forskning angående dessa dyner bedrivits under de senaste 90 åren. De primära frågeställningarna i den här avhandlingen har varit varför dessa sanddyner bildades, när de bildades och vad de kan säga oss om tidigare klimatförändringar. Resultaten från detta arbete presenteras i fyra vetenskapliga artiklar.Sanddyners form och orientering är beroende av den omgivande miljön under deras bildning, såsom mängden tillgänglig sand för vindtransport, grundvattennivå, temperatur, nederbörd, närvaro/frånvaro av vegetation, vindmönster m.m. Genom att identifiera en sanddyns form, och således dess typ, är det möjligt att identifiera de ovan nämnda förhållanden vid dynernas bildning. Om man kan bestämma när dessa dyner bildades kan man återskapa miljön, och i förlängningen klimatet, under en specifik tidsperiod.I den här avhandlingen presenteras resultaten angående ett antal svenska dyner och dynfälts geomorfologi, geokronologi samt deras paleomiljö. Med hjälp av moderna analysmetoder, såsom LiDAR-baserad (light detection and ranging) fjärranalys och luminiscensdatering, har tidigare forskningsresultat utvärderats samt nya resultat presenterats.Resultaten visar att dynerna i centrala Sverige huvudsakligen är av en transversell typ, d.v.s. deras dynryggar är orienterade i rät vinkel mot de dynbyggande vindarna, och de bildades i en miljö utan vegetation och med god tillgång till sediment. De primära dynbildande vindarna för dessa transversella dyner verkar ha varit nordvästliga och västliga vindar. De undersökta dynerna längre söderut uppvisar tecken på att ha omarbetats efter deras ursprungliga bildning och är ofta av parabeltyp, d.v.s. bågformade med sina armar orienterade motvinds. Denna dyntyp har beskrivits som starkt länkad till närvaro av vegetation, och kan ofta betraktas som sekundära dynformer. Dessa sydligare parabeldyner tycks, liksom de centrala transversella dynerna, huvudsakligen ha bildats av vindar från nordväst och väst. Dock uppvisar de en större spridning i vindriktningar än de nordligare dynerna.Luminiscensdateringarna av sediment tagna från dessa dyner visar att de flesta av dynerna bildades och stabiliserades under den tidiga delen av Holocen. Senare fall av sanddrift under övriga delar av Holocen var ovanligt, och hade oftast bara smärre påverkan på dynmorfologin. Det verkar ha varit en primär dynstabiliseringsfas ~10-9 ka, oberoende av dynfältens latitud. Detta innebär att vissa dynfält bildades strax efter den lokala deglaciationen, medan andra bildades betydligt senare. Detta antyder att dynbildning och dynstabilisering i centrala Sverige har styrts av regionala klimatförhållanden. Extremt låga vattennivåer i sjöar i södra och syd-centrala Sverige 10,5–9,5 ka BP, i kombination med ett instabilt klimat under tidiga delen av Holocen fördröjde antagligen dynstabiliseringen av vegetationen. Väl täckta av vegetation var dynerna betydligt mer motståndskraftiga mot vinderosion, även under senare klimatförändringar.
  • Lages, J., et al. (författare)
  • Volcanic Gas Emissions Along the Colombian Arc Segment of the Northern Volcanic Zone (CAS-NVZ): Implications for volcano monitoring and volatile budget of the Andean Volcanic Belt
  • 2019
  • Ingår i: Geochemistry, Geophysics, Geosystems. - 1525-2027. ; 20:11, s. 5057-5081
  • Tidskriftsartikel (refereegranskat)abstract
    • Studying spatial and temporal trends in volcanic gas compositions and fluxes is crucial both to volcano monitoring and to constrain the origin and recycling efficiency of volatiles at active convergent margins. New volcanic gas compositions and volatile fluxes are here reported for Nevado del Ruiz, Galeras, and Purace, three of the most persistently degassing volcanoes located in the Colombian Arc Segment of the Northern Volcanic Zone. At Nevado del Ruiz, from 2014 to 2017, plume emissions showed an average molar CO2/S-T ratio of 3.9 +/- 1.6 (S-T is total sulfur, S). Contemporary, fumarolic chemistry at Galeras progressively shifted toward low-temperature, S-depleted fumarolic gas discharges with an average CO2/S-T ratio in excess of 10 (6.0-46.0, 2014-2017). This shift in volcanic gas compositions was accompanied by a concurrent decrease in SO2 emissions, confirmed on 21 March 2017 by high-resolution ultraviolet camera-based SO2 fluxes of similar to 2.5 kg/s (similar to 213 t/day). For comparison, SO2 emissions remained high at Nevado del Ruiz (weighted average of 8 kg/s) between 2014 and 2017, while Purace maintained rather low emission levels (&lt;1 kg/s of SO2, CO2/SO2 approximate to 14). We here estimate carbon dioxide fluxes for Nevado del Ruiz, Galeras, and Purace of similar to 23, 30, and 1 kg/s, respectively. These, combined with recent CO2 flux estimates for Nevado del Huila of similar to 10 kg/s (similar to 860 t/day), imply that this arc segment contributes about 50% to the total subaerial CO2 budget of the Andean Volcanic Belt. Furthermore, our work highlights the northward increase in carbon-rich sediment input into the mantle wedge via slab fluids and melts that is reflected in magmatic CO2/S-T values far higher than those reported for Southern Volcanic Zone and Central Volcanic Zone volcanoes. We estimate that about 20% (similar to 1.3 Mt C/year) of the C being subducted (similar to 6.19 Mt C/year) gets resurfaced through subaerial volcanic gas emissions in Colombia (Nevado del Ruiz similar to 0.7 Mt C/year). As global volcanic volatile fluxes continue to be quantified and refined, the contribution from this arc segment should not be underestimated.
  • Margold, Martin, 1981-, et al. (författare)
  • Glacial Lake Vitim, a 3000 km³ outburst flood from Siberia to the Arctic Ocean
  • 2011
  • Ingår i: Quaternary Research. - 0033-5894 .- 1096-0287. ; 76:3, s. 393-396
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>A prominent lake formed when glaciers descending from the Kodar Range blocked the River Vitim in central Transbaikalia, Siberia. Glacial Lake Vitim, evidenced by palaeoshorelines and deltas, covered 23,500 km2 and held a volume of ~3000 km3. We infer that a large canyon in the area of the postulated ice dam served as a spillway during an outburst flood that drained through the rivers Vitim and Lena into the Arctic Ocean. The inferred outburst flood, of a magnitude comparable to the largest known floods on Earth, possibly explains a freshwater spike at ~13 cal ka BP inferred from Arctic Ocean sediments.</p>
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