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| Titel |
The last millenium sedimentary record in Chilean Patagonian lakes |
| VerfasserIn |
Nathalie Fagel, Meriem El Ouahabi, Gilles Lepoint, Sébastien Bertrand, Sabine Schmidt, Denisse Alvarez, Alberto Araneda, Fernando Torrejón, Roberto Urrutia |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250047995
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| Zusammenfassung |
| We evaluate the climate and environmental variability of Northern Chilean Patagonia during
the Last Millennium, using a multi-proxy analysis of lake sediment cores. Among
several investigated sites during the last years, the sedimentary records of lakes
Thompson (45Ë S, 71Ë W) and Bertrand (46.5Ë S 72.5Ë W) are particularly promising.
Radiocarbon ages measured on bulk sediment and macro-remains and/or 210Pb
profile give a mean sedimentation rate of 1 (Lake Thompson) or 2 mm/yr (Lake
Bertrand), allowing a decennial sampling resolution. To reconstruct past climate
changes, we conducted a multiproxy study combining sedimentology, mineralogy and
geochemistry.
The sediments of Lake Thompson are composed of light brown organic-rich clayey silts.
X-ray radiographies show that the sediment record is undisturbed, and that our 1m long core
contains two fine tephra layers. The inorganic content of the sediment is very low (a few %).
Some clay minerals, quartz and feldspars were identified by X-ray diffraction. The high
organic matter content (mean 15%) and its low C/N ratio (8) throughout the core, evidence
that the lake productivity remained high over the last 900 years. The biogenic silica
content of the sediment is high (40 to 80%), in relation to the small catchment to lake
surface ratio, which limits the supply of terrestrial particles to the lake. We note
higher concentrations in biogenic silica and organic matter between 1550 and 1800
AD.
Lake Bertrand is adjacent to a pro-glacial lake, Lake Plomo. The connection between
both lakes is limited by a morainic barrier. The sediments of Lake Bertrand are composed of
homogeneous silts with some clays (< 20%) and 5 to 10% of sand. Lake Bertrand
sediments are characterized by low C/N ratio (10) supporting an important aquatic
productivity. In contrast with Lake Thompson, the inorganic component represents
90-95% of the bulk sediment with a few percent of organic matter (5%). Diatoms are
ubiquitous but their abundance varies highly through the core. The biogenic silica profile
evidences two peaks (Si bio>30%) above the 5% background level. According to
the age model, the changes in aquatic productivity occur between 1700 and 1850
AD.
Although the two lakes are located in different environments and are relatively distant
from each other, they both record a significant sedimentological change during an interval
equivalent to (part of) the Little Ice Age. The biogenic silica-rich intervals probably represent
a major climate shift in the Andes of North Patagonia. Further biological analyses are in
progress in order to better constrain the terrestrial and aquatic environmental conditions
during this event.
This research is funded by Chilean Fondecyt project number 1070508 and Belgian
projects (FNRS proposal 1360 2007-2010, ULg CFRA 1060 2009-2010). |
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