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Titel |
Sub-decadal- to decadal-scale climate variability during the Holsteinian interglacial (MIS 11) evidenced in varves from northern Germany |
VerfasserIn |
Andreas Koutsodendris, Achim Brauer, Heiko Pälike, Jörg Pross, Ulrich C. Müller, André F. Lotter |
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 |
250054252
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Zusammenfassung |
The Holsteinian is generally considered to be equivalent to Marine Isotope Stage 11, which
with regard to orbital forcing represents one of the closest analogues for the present
interglacial. Hence, in order to gain further insights into the natural (i.e., non-anthropogenic)
climate variability during an interglacial, we have examined a ~6-meter-long, annually
laminated sequence from the Dethlingen palaeolake (Lüneburger Heide, northern Germany).
Micro-facies analyses, varve counting, and measuring of varve thickness have been carried
out on thin sections of epoxy-impregnated sediment. The finely laminated sediments from
Dethlingen comprise biogenic (diatomaceous) varves consisting of two discrete layers. The
light layers are predominantly controlled by the spring and summer diatom blooms, mainly of
the genera Stephanodiscus, Ulnaria, and Aulacoseira. The dark layers are composed
predominantly of amorphous organic matter with fragments of diatom frustules;
reworked periphytic diatoms, plant remains, and freshwater sponge spicules from
the littoral zone are also common. These dark layers are formed by reworking of
littoral material due to wind and wave activity, and surface runoff during autumn and
winter.
Time-series analysis supports the existence of signals exceeding the 99% confidence
level with time scales similar to those observed in modern instrumental data and in
Holocene palaeoclimatic records. Spectral peaks at periods of 90, 25, and 10.5
years may be associated with the 88-yr Gleissberg solar cycle, the 22-yr Hale solar
cycle, and the 11-yr sunspot cycle, respectively. In addition, statistically significant
variability occurs within the conventional 3-to-6-year El Niño-Southern Oscillation
(ENSO) bandwidth, whereas significant peaks at 5.8 and 2.6-2.7 year periods may
be associated with the North Atlantic Oscillation (NAO). The power and wavelet
spectra of the light and dark layers reveal pronounced differences. In particular,
the ENSO/NAO-like variability is more significantly expressed in the dark layers,
whereas the solar variability is more pronounced in the light layers. In addition,
the wavelet spectrum of the light layers is characterized by intervals of reduced
variability that have no equivalent in the dark layers. These observations reflect
the processes controlling the seasonal sedimentation, which can be attributed to
different responses to climate forcing and/or variations in the palaeolake’s physical
properties. Our results suggest that central European climate was strongly influenced by
sub-decadal to decadal variability during the Holsteinian interglacial, possibly forced by
solar activity and ENSO/NAO-like variability similar to the present interglacial. |
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