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| Titel |
Influence of solar activity on the development of calcareous nannofossils from a Middle Holocene costal paleo-ria (SW Portugal) |
| VerfasserIn |
Armand Hernández, Mario Cachao, Ricardo M. Trigo, M. Conceição Freitas |
| 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 |
250110953
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| Publikation (Nr.) |
 EGU/EGU2015-11000.pdf |
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| Zusammenfassung |
| A 27 m long core was recovered from a present day flat-floored small fluvial valley, tributary
of the Mira River (SW Portugal) allowing to span almost the complete Holocene sedimentary
sequence directly overlaying Paleozoic schists and greywackes. A high resolution study of its
micropaleontological content (Alday et al. 2006) was performed and 5 sedimentary
stages were established: i) a coccolith-barren lower fluvial stage; ii) a coccolith
intermittent lower estuarine stage; iii) a coccolith rich marine (ria) stage; iv) a coccolith
intermittent upper estuarine/lagoonal stage and v) a coccolith-barren upper fluvial
stage.
The usefulness of calcareous nannofossils as natural tracers of the marine sedimentation
contributing with valuable information for environmental reconstructions has been
thoroughly demonstrated. Here, we present a high-resolution paleoenvironmental
reconstruction from the interpreted marine (ria) section of the core, between 8.8k and 4.8k cal
yr BP using most abundant calcareous nannofossils. Factor Analysis retrieved two major
factors from the coccolith assemblages. Factor 1 (24% var.) is related to oceanic
affinity community (e.g. Gephyrocapsa muellerae, Syracosphaera pulchra and
Umbilicosphaera sibogae) whereas Factor 2 (23% var.) is linked to coastal neritic taxa
(e.g. Ascidian spicules, Gephyrocapsa oceanica, Coccolithus pelagicus braarudii,
Heliscosphaera carteri and Braarudosphaera bigelowii). These scores showed the existence
of two episodes (8.8k to 7.4k and 5.8k to 5.2k cal yr BP) of marine colonization
inside the paleoecological succession of the Holocene paleo-ria (8.8k and 4.8k cal yr
BP).
In order to establish the relationship between the solar activity and calcareous
nannofossils sedimentation, cyclicity on the studied time series was investigated by
performing spectral analysis on Factor 1 (F1) and Factor 2 (F2) scores. F1 score periodogram
discloses three significant periodicities (460, 350 and 236-yrs) whereas F2 score periodogram
unveils only one significant periodicity (228-yrs). Phases with oceanic influence
(downwelling) would be related to 450, 350 and 236-yrs frequencies and the phase with
coastal influence (upwelling) would be linked to 228-yrs periodicity. These periodicities
fit with previous solar activity reconstructions at millennial-to-centennial scale
based on different proxies (Bond et al. 2001, Vaquero et al. 2002, Solanki et al.
2004), which, in turn, are conditioning the earth’s climate system. Finally, performed
time-frequency analyses on F1 and F2 scores show a higher activity of the 228-yrs periodicity
during the whole studied period (spanning between 8.8k and 4.8k cal yr BP) with
maximum values between 8k to 7k cal yr BP and 6k to 5k cal yr BP. By contrast, higher
periodicities (450, 350 and 236-yrs) would be mainly confined to prior 7.5k cal yrs
BP.
These results highlight the possibility to use the calcareous nannofossils as indirect
proxies of solar activity in cases of ultra-high resolution (centennial) sedimentary
sequences.
References
Alday et al., Estuar Coast Shelf S, 66, 532 (2006).
Bond et al., Science, 294, 2130 (2001).
Solanki et al., Nature, 431, 1084 (2004).
Vaquero et al., Geophys Res Lett, 29, 1997 (2002). |
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