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| Titel |
A Mineralogical and Organic Geochemical Overview of the Effects of Holocene Changes in Amazon River Flow on Floodplain Lakes |
| VerfasserIn |
Luciane Moreira, Patricia Moreira-Turcq, Jung-Hyun Kim, Bruno Turcq, Renato Cordeiro, Caquineau Sandrine, Jaap Sinninghe Damsté |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250098283
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| Publikation (Nr.) |
 EGU/EGU2014-13948.pdf |
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| Zusammenfassung |
| A synthesis of the impacts of the Amazon River hydrological changes on the sedimentation
process of organic matter (OM) in three different floodplain lakes (Santa Ninha, Maracá, and
Comprido lakes) is presented in this study. Today the Santa Ninha and Maracá lakes are
directly and permanently connected with the main channel of the Amazon River, in contrast
to Comprido Lake, which is indirectly and periodically influenced by the Amazon River due
to its high distance from the main channel. All the sedimentary lake records showed a
reduced river inflow due to dry climatic conditions during the Early and Middle Holocene
followed by a humid Late Holocene with an increased fluvial input. In Santa Ninha
and Maraca Lakes the reduced river inflow period was characterized by sediments
with a low abundance of smectite (on average ~20 wt. %), a clay mineral mainly
transported by the fluvial system, high total organic carbon (TOC) contents (on average
~8.2 wt. %) and a predominant acidic soil OM input evidenced by high branched
glycerol dialkyl glycerol tetraethers (GDGT) concentrations (on average 180 μg
gTOC-1). During the Late Holocene, a higher smectite abundance (on average ~43 wt.
%) and a low TOC content (on average ~1.4 wt. %) pointed to dilution with the
riverine lithogenic matter. This was accompanied by a proportional increase in the
aquatically-produced crenarchaeol, suggesting an increased lake water level. In Comprido
Lake, a sedimentation gap occurred during the Early and Middle Holocene. The humid Late
Holocene, after 3,000 cal years BP, was characterized by high TOC values (on
average ~9 wt. %) as well as a sharp increase in soil OM input as revealed by the
increase in branched GDGT concentrations (on average ~81 μg gTOC-1), but the
smectite content was low (on average ~14 %). This suggests that in Comprido
Lake the soil OM input from the local catchment area was predominant during the
humid Late Holocene due to its high distance from the Amazon River main stem.
Consequently, our study shows that the sedimentation processes of OM in Amazonian
floodplain lakes are strongly influenced by variations in the hydrodynamic regime of the
Amazon River during the Holocene. However, its impacts on floodplain lakes were
different, mainly depending on the distance from the main stem of the Amazon River. |
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