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Storen E.N.,University of Bergen | Storen E.N.,Bjerknes Center for Climate Research | Paasche O.,Bergen Marine Research Cluster
Global and Planetary Change | Year: 2014

Although most climate models agree on a general increase in future precipitation in the Northern Hemisphere due to higher temperatures, no consensus has yet been reached on how this warming will perturb flooding rates. Here we examine the potential co-variability between winter precipitation (Pw) and floods on millennial time scales. This is accomplished by analyzing reconstructed Pw from five records in Scandinavia, which is, compared to data from two high-resolution flood records from southern Norway. These Holocene records reveal a positive correlation (R2=0.41, p>0.01) between the number of floods and Pw on centennial time scales over the last 6000years. Future projections for Pw over central Scandinavia for the next 100years suggest a continued increase in Pw that approximates maximum Holocene precipitation values. Despite an anticipated increase in Pw, the paleodata, nevertheless, suggest that we are likely to witness a decrease in future floods 50-100years from now because the accompanying warming will cancel that net effect of a wetter regime. © 2013 Elsevier B.V.

Paasche O.,Bergen Marine Research Cluster | Storen E.W.N.,University of Bergen
Eos | Year: 2014

Destructive floods impose severe consequences on societies, leaving havoc and death in their wake. Annually, an average of 9000 people are killed, and 115 million require immediate assistance or are displaced by floods worldwide. Because of population increase in flood-prone areas alone, the number of people exposed to floods in North America is expected to almost double in 2030 compared to 1970 [National Research Council, 2013]. It is no wonder that floods are considered serious threats by government agencies and municipal planners, but the impact of climate change on these numbers is still somewhat uncertain. ©2014 The Authors.

Vasskog K.,University of Bergen | Kvisvik B.C.,University of Bergen | Paasche O.,Bergen Marine Research Cluster | Paasche O.,University of Bergen
Journal of Paleolimnology | Year: 2016

Grain-size analysis is routinely performed on soft sediments, and has been applied in numerous paleoenvironmental studies using lake sediment archives. Despite the frequent use of this method, no common protocol exists for the treatment of lake sediment samples prior to analysis. In this study, differences in grain-size distribution before and after treatment with hydrogen peroxide (H2O2) were evaluated for sediment sequences from four lakes in Norway characterized by different geological and environmental settings. We found that removal of organic matter had a profound effect on the grain-size distribution of the sediment samples, which might have important bearing on how such data are interpreted. One of the analysed sediment sequences showed a systematic shift toward more fines after treatment, whereas no clear systematic effects were observed for the remaining three. The observed differences might derive from (1) variable concentrations of biogenic silica, which could cause shifts in the Sedigraph readings as a consequence of the porosity and fragility of diatom frustules, (2) clogging of organic matter during initial mechanical sieving, and (3) disturbance of the internal flow regime in the Sedigraph as a result of the dispersive agent having a viscosity that is too low. These possible explanations require further testing. Nevertheless, we propose that the paleolimnological community should develop a common protocol for pre-treatment of sediments from lacustrine settings that both enables reproducibility of results and reduces the risk of misinterpretation. Our observations suggest that sediments from boreal lakes should be treated with hydrogen peroxide prior to grain-size analysis, although treatment should be relatively mild to avoid possible mineral degradation. © 2016 Springer Science+Business Media Dordrecht

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