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The geochemistry of major and selected trace elements in a forested peat bog, Kalimantan, SE Asia, and its implications for past atmospheric dust deposition |
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| Authors: | Dominik Weiss William ShotykJack Rieley Susan PageMarlies Gloor Steve ReeseAntonio Martinez-Cortizas |
| Institution: | 1 Department of Earth Science and Engineering and Department of Environmental Science and Technology, Imperial College of Science, Technology and Medicine, London SW7 2BP, UK 2 Department of Mineralogy, The Natural History Museum, London, UK 3 Institute for Environmental Geochemistry, University of Heidelberg, Heidelberg, Germany 4 School of Geography, University of Nottingham, Nottingham, UK 5 School of Geography, University of Leicester, Leicester, UK 6 Kantonales Labor fuer Umweltschutz, Luzern, Switzerland 7 Physics Institute, University of Bern, Bern, Switzerland 8 Biology Faculty, University of Santiago de Compostela, Santiago de Compostela, Spain |
| Abstract: | Biogeochemical processes in a forested tropical peat deposit and its record of past atmospheric dust deposition were assessed using the vertical distribution of lithophilic and plant essential elements in a dated core profile from Borneo, SE Asia. Peat formation started ∼22,120 14C yr before present (BP), and Ca/Mg mass ratios of the solid peat and very low ash contents indicate a strongly ombrotrophic character throughout the deposit, implying that most of the inorganic fraction has been supplied exclusively by atmospheric inputs. Concentration profiles of Mn, Sr, and Ca suggest a very minor influence of chemical diagenesis in the underlying sediments. Silicon, Ca, Mg, P, S, and K show a strong and extended zone of enrichment in the top 200 cm of the profile, indicating that biological accumulation mechanisms are much more extensive than in temperate peat bogs.In the lower core sections, where the element distribution is dominated solely by past atmospheric deposition, average Al/Ti ratios are similar to the upper continental crust (UCC), whereas Fe is slightly enriched and Si is strongly depleted: this condition favors highly weathered tropical soil dust as the main inorganic mineral source. Significant correlation of Al, Fe, Si, S, Ca, and Ti with the lithophilic elements Y and Zr suggests that the distribution of these elements is controlled by sources of atmospheric mineral dust. The Ca/Mg, Ca/K, and Mg/K ratios of the collected rainwater samples are similar to the global average of continental rainwater and suggest a continental character for the site. This is supported by the similarity of the average concentration of Br, Mg, Ca, and S to that in temperate continental and maritime bogs in Switzerland and Scotland.The concentration profiles of Si, Fe, Al, and Ti show distinct peaks within the profile, implying enhanced dust deposition, reduced rates of peat accumulation, or possibly both owing to climatic changes during the Holocene. Enhanced dust deposition between ∼10,830 and 9060 14C yr BP is tentatively interpreted as a Younger Dryas-like event with dust fluxes of ∼10.8 mg/m2/yr. The variations in Al/Ti and Fe/Ti profiles suggest that mineral dust sources have been changing constantly during the Holocene, with local sources being dominant between ∼7820 and 9500 14C yr BP and long-range transport (derived most likely from China) being important during the late Pleistocene and early Holocene and from ∼7820 14C yr BP to the present. |
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