Browsing by Subject "RECONSTRUCTIONS"

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  • Brugnara, Y.; Auchmann, R.; Broennimann, S.; Allan, R. J.; Auer, I.; Barriendos, M.; Bergstrom, H.; Bhend, J.; Brazdil, R.; Compo, G. P.; Cornes, R. C.; Dominguez-Castro, F.; van Engelen, A. F. V.; Filipiak, J.; Holopainen, J.; Jourdain, S.; Kunz, M.; Luterbacher, J.; Maugeri, M.; Mercalli, L.; Moberg, A.; Mock, C. J.; Pichard, G.; Reznckova, L.; van der Schrier, G.; Slonosky, V.; Ustrnul, Z.; Valente, M. A.; Wypych, A.; Yin, X. (2015)
    The eruption of Mount Tambora (Indonesia) in April 1815 is the largest documented volcanic eruption in history. It is associated with a large global cooling during the following year, felt particularly in parts of Europe and North America, where the year 1816 became known as the "year without a summer". This paper describes an effort made to collect surface meteorological observations from the early instrumental period, with a focus on the years of and immediately following the eruption (1815-1817). Although the collection aimed in particular at pressure observations, correspondent temperature observations were also recovered. Some of the series had already been described in the literature, but a large part of the data, recently digitised from original weather diaries and contemporary magazines and newspapers, is presented here for the first time. The collection puts together more than 50 sub-daily series from land observatories in Europe and North America and from ships in the tropics. The pressure observations have been corrected for temperature and gravity and reduced to mean sea level. Moreover, an additional statistical correction was applied to take into account common error sources in mercury barometers. To assess the reliability of the corrected data set, the variance in the pressure observations is compared with modern climatologies, and single observations are used for synoptic analyses of three case studies in Europe. All raw observations will be made available to the scientific community in the International Surface Pressure Databank.
  • Salminen, Johanna; Hanson, Richard; Evans, David A. D.; Gong, Zheng; Larson, Tierney; Walker, Olivia; Gumsley, Ashley; Soderlund, Ulf; Ernst, Richard (2018)
  • Seddon, Alistair W. R.; Mackay, Anson W.; Baker, Ambroise G.; Birks, H. John B.; Breman, Elinor; Buck, Caitlin E.; Ellis, Erle C.; Froyd, Cynthia A.; Gill, Jacquelyn L.; Gillson, Lindsey; Johnson, Edward A.; Jones, Vivienne J.; Juggins, Stephen; Macias-Fauria, Marc; Mills, Keely; Morris, Jesse L.; Nogues-Bravo, David; Punyasena, Surangi W.; Roland, Thomas P.; Tanentzap, Andrew J.; Willis, Kathy J.; Aberhan, Martin; van Asperen, Eline N.; Austin, William E. N.; Battarbee, Rick W.; Bhagwat, Shonil; Belanger, Christina L.; Bennett, Keith D.; Birks, Hilary H.; Ramsey, Christopher Bronk; Brooks, Stephen J.; de Bruyn, Mark; Butler, Paul G.; Chambers, Frank M.; Clarke, Stewart J.; Davies, Althea L.; Dearing, John A.; Ezard, Thomas H. G.; Feurdean, Angelica; Flower, Roger J.; Gell, Peter; Hausmann, Sonja; Hogan, Erika J.; Hopkins, Melanie J.; Jeffers, Elizabeth S.; Korhola, Atte A.; Marchant, Robert; Kiefer, Thorsten; Lamentowicz, Mariusz; Larocque-Tobler, Isabelle; Lopez-Merino, Lourdes; Liow, Lee H.; McGowan, Suzanne; Miller, Joshua H.; Montoya, Encarni; Morton, Oliver; Nogue, Sandra; Onoufriou, Chloe; Boush, Lisa P.; Rodriguez-Sanchez, Francisco; Rose, Neil L.; Sayer, Carl D.; Shaw, Helen E.; Payne, Richard; Simpson, Gavin; Sohar, Kadri; Whitehouse, Nicki J.; Williams, John W.; Witkowski, Andrzej (2014)
    1. Priority question exercises are becoming an increasingly common tool to frame future agendas in conservation and ecological science, used to identify research foci which are relevant to the needs of the scientific community and which also have high policy and conservation relevance. 2. To date there has been no coherent synthesis of key questions and priority research areas for palaeoecology, which combines biological, geochemical and molecular techniques in order to reconstruct ecological and environmental systems far into the past. 3. We adapted a well-established methodology to identify 50 priority research questions in palaeoecology. We used a set of criteria that were designed to identify realistic and achievable research goals, and selected questions from a pool submitted by the international palaeoecology research community and relevant policy practitioners. Questions are not ranked by priority but are grouped thematically, and are generally focussed on the late Cenozoic onwards (past c. 65 Ma). 4. The major difference in our methodology compared to other, similar exercises was the integration of online participation both before and during the workshop, representing an important development for increasing engagement and visibility. 5. The questions selected are structured around six themes: human-environment interactions in the Anthropocene; biodiversity, conservation, and novel ecosystems; biodiversity over long timescales; ecosystem processes and biogeochemical cycling; comparing, combining and synthesising information from multiple records; and methodological approaches to palaeoecology. 6. Future opportunities in palaeoecology are related to improved incorporation of uncertainty into reconstructions, an enhanced understanding of ecological and evolutionary dynamics and processes, and the continued application of long-term data for better-informed landscape management. 7. SYNTHESIS: The 50 priority questions selected in this exercise present palaeoecological science as a vibrant and thriving discipline, and highlight its vast potential for resolving both pure (e.g. theoretical) and applied (e.g. environmental) research questions directly related to ecological science and global change.
  • Pyörälä, Jiri; Liang, Xinlian; Vastaranta, Mikko; Saarinen, Ninni; Kankare, Ville; Wang, Yunsheng; Holopainen, Markus; Hyyppä, Juha (2018)
    State-of-the-art technology available at sawmills enables measurements of whorl numbers and the maximum branch diameter for individual logs, but such information is currently unavailable at the wood procurement planning phase. The first step toward more detailed evaluation of standing timber is to introduce a method that produces similar wood quality indicators in standing forests as those currently used in sawmills. Our aim was to develop a quantitative method to detect and model branches from terrestrial laser scanning (TLS) point clouds data of trees in a forest environment. The test data were obtained from 158 Scots pines (Pinus sylvestris L.) in six mature forest stands. The method was evaluated for the accuracy of the following branch parameters: Number of whorls per tree and for every whorl, the maximum branch diameter and the branch insertion angle associated with it. The analysis concentrated on log-sections (stem diameter > 15 cm) where the branches most affect wood's value added. The quantitative whorl detection method had an accuracy of 69.9% and a 1.9% false positive rate. The estimates of the maximum branch diameters and the corresponding insertion angles for each whorl were underestimated by 0.34 cm (11.1%) and 0.67 degrees (1.0%), with a root-mean-squared error of 1.42 cm (46.0%) and 17.2 degrees (26.3%), respectively. Distance from the scanner, occlusion, and wind were the main external factors that affect the method's functionality. Thus, the completeness and point density of the data should be addressed when applying TLS point cloud based tree models to assess branch parameters.
  • Luoto, Tomi P.; Rantala, Marttiina V.; Kivilä, E. Henriikka; Nevalainen, Liisa (2019)
    A key question in aquatic elemental cycling is related to the influence of bottom water oxygen conditions in regulating the burial and release of carbon under climate warming. In this study, we used head capsules of Chironomidae larvae to assess community and diversity change between the past (estimated as Pre-Industrial Period) and present and to reconstruct changes in hypolimnetic oxygen conditions from 30 subarctic ecotonal lakes (northeastern Lapland) using the top-bottom paleolimnological approach applying surface sediment (topmost 0-2 cm) and reference (4-5 cm) samples. Subsequently, we tested the findings against dissolved organic carbon (DOC) concentration of the sites. We found that the benthic communities were statistically dissimilar between the past and the present with largest changes occurring in the more transparent oligo-mesohumic lakes. However, murky polyhumic lakes displayed uniformly a decrease in diversity. The chironomid-inferred oxygen values showed a general decrease toward the present with largest shifts in low-DOC lakes, whereas no significant changes were found in the hypolimnetic oxygen conditions of high-DOC lakes, which were often located in wet-land areas. These finding suggest that lakes associated with constant organic carbon inputs are more resilient toward climate-induced reductions in hypolimnetic oxygen. (c) 2018 Elsevier B.V. All rights reserved.
  • Rantala, Marttiina V.; Luoto, Tomi P.; Nevalainen, Liisa (2016)
    Widespread ecological reorganizations and increases in organic carbon (OC) in lakes across the Northern Hemisphere have raised concerns about the impact of the ongoing climate warming on aquatic ecosystems and carbon cycling. We employed diverse biogeochemical techniques on a high-resolution sediment record from a subarctic lake in northern Finland (70 degrees N) to examine the direction, magnitude and mechanism of change in aquatic carbon pools prior to and under the anthropogenic warming. Coupled variation in the elemental and isotopic composition of the sediment and a proxy-based summer air temperature reconstruction tracked changes in aquatic production, depicting a decline during a cool climate interval between similar to 1700-1900 C.E. and a subsequent increase over the 20th century. OC accumulation rates displayed similar coeval variation with temperature, mirroring both changes in aquatic production and terrestrial carbon export. Increase in sediment organic content over the 20th century together with high inferred aquatic UV exposure imply that the 20th century increase in OC accumulation is primarily connected to elevated lake production rather than terrestrial inputs. The changes in the supply of autochthonous energy sources were further reflected higher up the benthic food web, as evidenced by biotic stable isotopic fingerprints.
  • Mueller, J. L.; Siltanen, S. (2020)
    Electrical impedance tomography (EIT) is an imaging modality where a patient or object is probed using harmless electric currents. The currents are fed through electrodes placed on the surface of the target, and the data consists of voltages measured at the electrodes resulting from a linearly independent set of current injection patterns. EIT aims to recover the internal distribution of electrical conductivity inside the target. The inverse problem underlying the EIT image formation task is nonlinear and severely ill-posed, and hence sensitive to modeling errors and measurement noise. Therefore, the inversion process needs to be regularized. However, traditional variational regularization methods, based on optimization, often suffer from local minima because of nonlinearity. This is what makes regularized direct (non-iterative) methods attractive for EIT. The most developed direct EIT algorithm is the D-bar method, based on complex geometric optics solutions and a nonlinear Fourier transform. Variants and recent developments of D-bar methods are reviewed, and their practical numerical implementation is explained.
  • Schenk, Frederik; Väliranta, Minna; Muschitiello, Francesco; Tarasov, Lev; Heikkilä, Maija; Björck, Svante; Brandefelt, Jenny; Johansson, Arne V.; Näslund, Jens-Ove; Wohlfarth, Barbara (2018)
    The Younger Dryas (YD) cold reversal interrupts the warming climate of the deglaciation with global climatic impacts. The sudden cooling is typically linked to an abrupt slowdown of the Atlantic Meridional Overturning Circulation (AMOC) in response to meltwater discharges from ice sheets. However, inconsistencies regarding the YD-response of European summer temperatures have cast doubt whether the concept provides a sufficient explanation. Here we present results from a high-resolution global climate simulation together with a new July temperature compilation based on plant indicator species and show that European summers remain warm during the YD. Our climate simulation provides robust physical evidence that atmospheric blocking of cold westerly winds over Fennoscandia is a key mechanism counteracting the cooling impact of an AMOC-slowdown during summer. Despite the persistence of short warm summers, the YD is dominated by a shift to a continental climate with extreme winter to spring cooling and short growing seasons.