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Late Quaternary Climate Changes in Central Africa as Inferred from Terrigenous Input to the Niger Fan
- Matthias Zabel, Ralph R. Schneider, Thomas Wagner, Adesina T. Adegbie, Uwe de Vries, Sadat Kolonic
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- Journal:
- Quaternary Research / Volume 56 / Issue 2 / September 2001
- Published online by Cambridge University Press:
- 20 January 2017, pp. 207-217
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- Article
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Time series of terrigenous source elements (Al, K, Ti, Zr) from core GeoB4901-8 recovered from the deep-sea fan of the Niger River record variations in riverine sediment discharge over the past 245,000 yr. Although the flux rates of all the elements depend on physical erosion, which is mainly controlled by the extent of vegetation coverage in central Africa, element/Al ratios reflect conditions for chemical weathering in the river basin. Maximum sediment input to the ocean occurs during cold and arid periods, when precipitation intensity and associated freshwater runoff are reduced. High carbonate contents during the same periods indicate that the sediment supply has a positive effect on river-induced marine productivity. In general, variations in the terrestrial signals contain a strong precessional component in tune with changes in low-latitude solar radiation. However, the terrestrial signal lags the insolation signal by several thousand years. K/Al, Ti/Al, and Zr/Al records reveal that African monsoonal precipitation depends on high-latitude forcing. We attribute the shift between insolation cycle and river discharge to the frequently reported nonlinear response of African climate to primary orbital configurations, which may be caused by a complex interaction of the secondary control parameters, such as surface albedo and/or thermohaline circulation.
24 - Future scenarios of nitrogen in Europe
- from Part V - European nitrogen policies and future challenges
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- By Wilfried Winiwarter, International Institute for Applied Systems Analysis, Jean-Paul Hettelingh, National Institute for Public Health and the Environment, Alex F. Bouwman, Netherlands Environmental Assessment Agency, Wim de Vries, Wageningen University and Research Centre, Jan Willem Erisman, Energy Research Centre of the Netherlands, James Galloway, University of Virginia, Zbigniew Klimont, International Institute for Applied Systems Analysis, Allison Leach, University of Virginia, Adrian Leip, European Commission Joint Research Centre, Christian Pallière, Fertilizers Europe, Uwe A. Schneider, KlimaCampus, Hamburg University, Till Spranger, Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, Mark A. Sutton, Centre for Ecology and Hydrology, Anastasia Svirejeva-Hopkins, Potsdam Institute for Climate Impact Research, Klaas W. van der Hoek, National Institute for Public Health and the Environment, Peter Witzke, EuroCARE GmbH
- Edited by Mark A. Sutton, NERC Centre for Ecology and Hydrology, UK, Clare M. Howard, NERC Centre for Ecology and Hydrology, UK, Jan Willem Erisman, Gilles Billen, Albert Bleeker, Peringe Grennfelt, Hans van Grinsven, Bruna Grizzetti
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- Book:
- The European Nitrogen Assessment
- Published online:
- 16 May 2011
- Print publication:
- 14 April 2011, pp 551-569
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Summary
Executive summary
Nature of the problem
The future effects of nitrogen in the environment will depend on the extent of nitrogen use and the practical application techniques of nitrogen in a similar way as in the past. Projections and scenarios are appropriate tools for extrapolating current knowledge into the future. However, these tools will not allow future system turnovers to be predicted.
Approaches
In principle, scenarios of nitrogen use follow the approaches currently used for air pollution, climate, or ecosystem projections. Short-term projections (to 2030) are developed using a ‘baseline’ path of development, which considers abatement options that are consistent with European policy. For medium-term projections (to 2050) and long-term projections, the European Nitrogen Assessment (ENA) applies a ‘storyline’ approach similar to that used in the IPCC SRES scenarios. Beyond 2050 in particular, such storylines also take into account technological and behavioral shifts.
Key findings/state of knowledge
The ENA distinguishes between driver-oriented and effect-oriented factors determining nitrogen use. Parameters that cause changes in nitrogen fixation or application are called drivers. In a driver-based approach, it is assumed that any variation of these parameters will also trigger a change in nitrogen pollution. In an effect-based approach, as the adverse effects of nitrogen become evident in the environment, introduction of nitrogen abatement legislation requiring the application of more efficient abatement measures is expected. This approach needs to rely on a target that is likely to be maintained in the future (e.g. human health). Nitrogen abatement legislation based on such targets will aim to counter any growth in adverse environmental effects that occur as a result of increased nitrogen application.
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