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| Titel |
Annual 18O/16O composition of authigenic calcite in varved lake sediments reflects regional air temperature |
| VerfasserIn |
Stéfanie Wirth, Adrian Gilli |
| 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 |
250108999
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| Publikation (Nr.) |
 EGU/EGU2015-8849.pdf |
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| Zusammenfassung |
| The oxygen isotopic composition (18O/16O) of authigenic calcite in lake sediments reflects
the temperature and the isotopic composition of the lake water from which the calcite is
precipitated and thus contains information about the climatic conditions at the time of calcite
formation. Varved lake sediments containing laminae of authigenically precipitated calcite
provide the possibility to analyze the 18O/16O composition at an annual resolution, thus
yielding high-resolution climatic information. Yet, despite this high potential the number of
studies having used this approach is relatively low. Reasons for this are probably
sampling challenges, the scarceness of suitable varved sediments, missing instrumental
records to compare with, as well as uncertainties regarding the factors influencing the
calcite isotopic composition (water/air temperature, precipitation, lake-internal
factors).
Still, annually resolved data of the 18O/16O composition of calcite seems a promising climate
proxy and we therefore investigated the 18O/16O pattern of the authigenic calcite in the
varved sediments of Lake Zurich. Lake Zurich is a pre-alpine lake with a surface area of 88
km2, a maximal water depth of 137 m and a theoretical water residence time of 1.4 years.
Sediments are varved since the late 19th century due to anthropogenic lake eutrophication.
For this calibration study, we analyzed the 18O/16O composition of the authigenic
calcite for the time period 1960-2010 at annual resolution. The δ18O values range
from -10.8 to -13.4 o; and the pattern is dominated by a conspicuous shift to more
enriched values between 1985 and 1987. The same shift has been observed for local to
large-scale climatic parameters such as lake, river, and groundwater temperatures
throughout Switzerland, the mean air temperature for Switzerland, and the NAO
index.
The consistency of the instrumental temperature data sets with the 18O/16O composition of
the authigenic calcite emphasizes the high potential of this proxy, even in a setting that is
strongly influenced by human activities and infrastructure such as Lake Zurich. Our results
also indicate that the 18O/16O signal of a lake with the size and the hydrology of Lake
Zurich potentially reflects climatic changes not only at a local but also at a regional
scale. |
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