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Titel |
Mid-Holocene regional reorganization of climate variability |
VerfasserIn |
K. W. Wirtz, K. Bernhardt, G. Lohmann, C. Lemmen |
Konferenz |
EGU General Assembly 2009
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 11 (2009) |
Datensatznummer |
250022635
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Zusammenfassung |
We integrate 130 globally distributed proxy time series to refine the understanding of climate
variability during the Holocene. Cyclic anomalies and temporal trends in periodicity from the
Lower to the Upper Holocene are extracted by combining Lomb-Scargle Fourier-transformed
spectra with bootstrapping. Results were cross-checked by counting events in the time series.
Main outcomes are: First, the propensity of the climate system to fluctuations is a region
specific property. Many records of adjacent sites reveal a similar change in variability
although they belong to different proxy types (e.g., δ18O, lithic composition). Secondly, at
most sites, irreversible change occured in the Mid- Holocene. We suggest that altered ocean
circulation together with slightly modified coupling intensity between regional
climate subsystems around the 5.5 kyr BP event (termination of the African Humid
Period) were responsible for the shift. Fluctuations especially intensified along a pan-
American corridor. This may have led to an unequal crisis probability for early human
civilizations in the Old and New World. Our study did not produce evidence for
millennial scale cyclicity in some solar activity proxies for the Upper Holocene, nor
for a privileged role of the prominent 250, 550, 900 and 1450 yr cycles. This lack
of global periodicities corroborates the regional character of climate variability. |
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