Zur Rekonstruktion natürlicher und anthropogen beschleunigter Erosions- und Verwitterungsprozesse in der geologischen Vergangenheit: Eine neue Methode zur Bestimmung des "Zerkleinerungsalters" anhand von Uran-Isotopen, angewandt an einen Seesedimentkern
Mineralogie, Petrologie und Geochemie
Zusammenfassung der Projektergebnisse
Understanding the interplay of climate, human land use, and landscape evolution on geological time scales is crucial to sustain one of our most important resources, which are soils. The research fellowship thus aimed to test the applicability of a relatively new analytical method using uranium isotopes ((234U/238U) activity ratios) to infer catchment-wide erosion processes to lacustrine sediment successions. (234U/238U) activity ratios can be used to estimate comminution ages, which are a measure for the time elapsed since the formation of detrital grains <63μm by chemical and physical weathering. Benefit of the method is that it is applied to fine-grained detrital matter, which has the potential to form excellent palaeoenvironmental archives. Applying a method to infer catchment erosion to palaeoclimate/-environmental archives allows detailed examinations of climate-humanlandscape interactions on geological time scales. The first step of the research project was to provide cost-and time efficient laboratory sample treatment procedures prior to uranium isotope analyses of detrital matter, and improvements to our capabilities to infer meaningful comminution ages. This method was then applied to Late Pleistocene and Holocene sediments of the DEEP-site sequence, recovered from the depo-centre of Lake Ohrid (North Macedonia, Albania) under the umbrella of the International Continental Scientific Drilling Program (ICDP) funded deep drilling of the project “Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO)”. (234U/238U) activity ratios and inferred “comminution ages”, termed “palaeo-sediment residence time” if the time since final deposition is excluded, provided detailed insights in catchment-wide erosion processes at Lake Ohrid for the last 190 ka. High-resolution uranium isotope analyses (~500 years resolution) on the upper part of the DEEP site revealed that catchment wide soil erosion is mainly controlled by rainfall during the Late Glacial and Early Holocene. A threshold crossed at the Early to Mid-Holocene transition implies that dense woodland vegetation prevents erosion of thin soils even at high elevations throughout the younger part of the Holocene. Logging and pasturing at high altitudes and farming at low elevations caused accelerated erosion during the Late Holocene. An extended uranium isotope dataset at 2,000 years resolution back until 190 ka confirms that the previously inferred relationships between soil erosion, climate, and vegetation development holds generally true since the penultimate glacial period. Different climate conditions and vegetation cover during the penultimate and last glacial however promoted contrasting responses of catchment wide erosion processes. (234U/238U) activity ratios and palaeo-sediment residence times could be used to explain the extraordinary high sedimentation rates observed at Lake Ohrid during the penultimate glacial.
Projektbezogene Publikationen (Auswahl)
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Impact of climate change and human activity on soil landscapes over the past
12,300 years. Scientific Reports, Vol. 8. 2018, Article number: 247.
Rothacker, Leo; Dosseto, Anthony; Francke, Alexander; Chivas, Allan R.; Vigier, Nathalie; Kotarba-Morley, Anna M. & Menozzi, Davide
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Sample preparation for determination of comminution ages in lacustrine and marine sediments. Chemical Geology, Vol. 479. 2018, pp. 123-135.
Francke, Alexander; Carney, Sally; Wilcox, Patrick & Dosseto, Anthony
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Sediment residence time reveals Holocene shift from climatic to vegetation control on catchment erosion in the Balkans. Global and Planetary Change, Vol. 177. 2019, pp. 186-200.
Francke, Alexander; Dosseto, Anthony; Panagiotopoulos, Konstantinos; Leicher, Niklas; Lacey, Jack H.; Kyrikou, Styliani; Wagner, Bernd; Zanchetta, Giovanni; Kouli, Katerina & Leng, Melanie J.
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Assessment of the controls on (234U/238U) activity ratios recorded in detrital lacustrine sediments. Chemical Geology, 19698, 2020.
Chemical Geology, online 5 June 2020, 119698.
Francke, Alexander; Dosseto, Anthony; Just, Janna; Wagner, Bernd & Jones, Brian G.
