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| Titel |
Climate induced metal enrichment in sediments of ferruginous Lake Towuti, Indonesia |
| VerfasserIn |
Hendrik Vogel, James M. Russell, Kassandra Costa, Sri Yudawati Cahyarini, Satria Bijaksana |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105060
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| Publikation (Nr.) |
 EGU/EGU2015-4507.pdf |
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| Zusammenfassung |
| Lake Towuti (2.75o S, 121.5o E; 560 km2, 205 m WD) is a tectonic, ferruginous, and
hyposulfidic lake in central Sulawesi, Indonesia. The region’s tropical climate causes intense
chemical weathering and fast denudation of the ultramafic bedrock surrounding the lake
supplying metal rich lateritic weathering products to the lake. Lake Towuti is thermally
stratified, with anoxic conditions below ~140m water depth, that promote reductive
dissolution of metal oxides in its bottom waters and surface sediments. The upper 90m of the
water column mix during the dry season due to evaporative cooling of the surface
waters.
We infer that the burial efficiency of redox sensitive metals is closely linked and
sensitive to the climatically controlled mixing state of Lake Towuti. Indeed, results
from our piston cores covering the past 30 kyr document that the concentration of
individual redox-sensitive metals in Towuti’s sediments is higher during the dry MIS 2
compared to the wetter Holocene, likely as a result of better preservation of metal
oxides in a well-oxygenated water column and surface sediment. Highest enrichment
factors for redox-sensitive metals are, however, associated with a ~1cm thick oxide
layer occurring at the transition from the wet, early- to the drier, mid-Holocene
around 8.5 kyr BP. Enrichment of metal oxides in this layer can not entirely be
explained by better preservation alone. CT and SEM analysis on the respective layer
reveal the abundance of amorphous Fe/Mn- oxide nodules, indicative for diagenetic
formation of these phases in pore spaces. We interpret this oxide layer as a buried
redox front that formed close to or at the sediment water interface during a phase
characterized by a well-ventilated water column and relatively constant and low
sedimentation rate. Based on the position of the oxide layer just ~10 cm above a
turbidite deposit we infer that the time required for the formation of the oxide layer
is in the order of less than ~300 years. Preservation of the oxide layer is likely
a result of a rapid change in sedimentation rate and/or mixing state of the lake. |
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