Here, we use sedimentological proxies to evaluate the sensitivity of Rwenzori mountain lakes to hydrological and ecological changes associated with recent glacier retreat.
Sediment dating with 210Pb
However, the Lake Bujuku catchment has the largest glaciers of any lake on the Ugandan side of the Rwenzori, has no upstream basins that might trap glacially-eroded material, and would therefore seem an ideal site at which to investigate glacier history, yet its decrease in silicilastic content is the smallest of any of the glacial lakes studied. Lake Bujuku has one of the largest catchments of any of the lakes analyzed in this study, and its southern shore abuts large alluvial fa Our Pb-and 14 C-based age models suggest that the principal shift from high and stable siliciclastic content toward lower values began in both Lac du Speke and Upper Lake Kitandara at about AD, although in Upper Kitandara this shift is preceded by a modest reduction dated to between and AD.
Given the subtle differences in the LOI stratigraphies among lakes and realistic age errors of about 15 years at AD for our Pb-based age models, we cannot unequivocally determine whether glacier recession in the Rwenzori began at or AD. Paleolimnological records of recent glacier recession in the Rwenzori Mountains, Uganda-D. Palaeolimnological evidence of environmental change over the last years in the Rwenzori Mountains of Uganda.
Climate and Lacustrine Ecosystems. Isabelle Larocque-Tobler Isabelle Laurion.
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210Pb Dating
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Much of the present understanding of these radionuclides is based on indirect data rather than direct observation and potential hosts are likely to be diverse, with deportments depending on the local geochemical environment. Despite forming under very limited and special conditions, the local-scale isotopic disequilibrium they infer is highly relevant for understanding their distributions in mineralized rocks and processing products.
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Sediment geochronology in changing coastal environments: Potentials and limitations of the Cs and Pb methods. This paper describes the combined use of Cs and Pb radiotracers for obtaining information on sedimentation which in a changing coastal environment is subject to erosion, losses of sediments, and deposition of material that had been remobilized before from near-shore sediments in the course of storm surges.
Geochronologies were established for sediment cores taken from salt marsh cliffs on the Isle of Sylt Germany. Concentrations of Cs and of excess Pb were measured gamma-spectrometrically. Micromorphological analyses of thin-sections showed that sediment mixing in all cores is negligible. An advection model was fitted to the vertical distributions of Cs The results indicate that cores taken from sparsely vegetated areas had been denudated prior to sampling. This was confirmed independently by the lack of any Chernobyl-derived cesium in these cores.
Taking denudation into account, Pb geochronologies are consistent with sediment dating based on the Cs data. Grain size analyses showed that only some sediment layers include a coarse sand fraction.
Pb/ Cs dating results for the studied short core PG | Download Scientific Diagram
The dating of these sandy layers coincides with periods of elevated storm surge activities, giving an independent validation of our method. We can conclude that sedimentation rates at the sites studied remained almost constant during the last 50 years. It is shown that capabilities and limitations of the Cs and Pb methods are complementary and that the combined use of both radiotracers is necessary for establishing reliable geochronologies in coastal environments. Empirical testing of Pb-dating models for lake sediments. Marine geochronology with Pb Sediment accumulation on the Southern California Bight continental margin during the twentieth century.
Sediment discharged into the portion of the Southern California Bight extending from Santa Barbara to Dana Point enters a complex system of semi-isolated coastal cells, narrow continental shelves, submarine canyons, and offshore basins. If modelling and interpretation are requested, the Pb results will normally be modelled to obtain the best fit of the data, where possible. A plot of Pb activity vs. Several Radium Ra measurements are often required, usually 2 - 3 per Pb core, to positively determine the Pb background level throughout the core length. The Cs data will be interpreted on the basis of the and major input peaks or maximum inventory of the isotope in the northern hemisphere.