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| Titel |
Influence of the Solar Activity on the Variability of Water Isotopes over Europe during the Late Holocene |
| VerfasserIn |
S. Dietrich, M. Werner, G. Lohmann |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065099
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| Zusammenfassung |
| Numerous European proxy archives demonstrate strong decadal to millennial scale variability
in the δ18O signal during the Mid- to Late Holocene. The origin of this variability and its
climatic forcing is however not well defined. Many of these records provide consistent
evidence that solar grand minima/maxima affect climate. Reconstructions of the total solar
irradiance during the Holocene imply a grand solar maximum (minimum) approximately
5,000 (6,000) years ago.
Here, we apply an atmosphere general circulation model (ECHAM5-wiso) that allows the
explicit simulation of the water isotopes to investigate the influence of solar activity on the
stable water isotope distribution signal for these Mid-Holocene periods. The simulations are
driven by changes in orbital configuration, greenhouse gases, and changes in total
solar irradiance due to solar activity. Dynamical downscaling is obtained by the
high horizontal resolution of T106 (approx. 1x1°) to provide suitable results for
model-data comparison. Following this approach, present-day simulations of the
distribution of stable water isotopes are in very good agreement with meteorological
observations.
In this study the effect of solar activity is marked out from climatic changes driven by
the variability of orbital parameters during the Mid-Holocene. For the evaluation
of the influence forced by orbital parameter changes a first set of simulations is
performed. Here, prescribed fields of sea surface temperatures (SST) and sea ice
concentrations (SIC) are derived from a transient run using an earth system model with
coupled atmosphere and ocean circulation. To account for solar induced effects
originating in the stratosphere a second set of simulations is performed using anomalies
in the prescribed SST and SIC. For each time slice externally derived SST/SIC
anomalies for the two different modes of solar activity (high/low solar activity in
comparison to a mean solar activity) are added to the boundary fields of the first set of
simulations.
Changes in solar activity during the Mid-Holocene have been shown to result in major effects
on the sea ice distribution and sea level pressure fields that strongly affects climate in Europe.
During winter North Atlantic westerlies are shifted northward during the solar minimum
leading to higher precipitation and depleted δ18O values in northwestern Europe and
Scandinavia. The Mediterranean is thus affected by drier conditions. During a phase of
increased solar activity westerlies are shifted to the South transporting more moisture to the
Mediterranean. At the same time Central Europe is affected by a blocking atmospheric
high during winter, which transports cold air from the Barents Sea to the European
continent.
The heterogeneity observed in the high-resolution model simulations is helpful for the
interpretation of the regional isotopic signal in speleothem records. The values of
stable water isotopes are in generally not only influenced by temperature but also by
precipitation and atmospheric circulation patterns. However, both the model and the
data suggest strong influence of solar activity on climate conditions during the
Holocene. |
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