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| Titel |
Paleoenvironmental reconstruction of Lake Azul (Azores archipelago, Portugal) and its implications for the NAO signal. |
| VerfasserIn |
María Jesús Rubio, Guiomar Sanchez, Alberto Sáez, David Vázquez-Loureiro, Roberto Bao, Juan José Pueyo, Miriam Gómez-Paccard, Vitor Gonçalves, Pedro M. Raposeiro, Pierre Francus, Armand Hernández, Olga Margalef, Teresa Buchaca, Sergi Pla, Fernando Barreiro-Lostres, Blas L. Valero-Garcés, Santiago Giralt |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250078435
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| Zusammenfassung |
| Azores archipelago lies in the southern area of the dipole that defines the North
Atlantic Oscillation (NAO). During the negative phase of the NAO, the Azores high
pressure is displaced southwards allowing the storms to cross the islands increasing
the precipitation in this area and also in southern Europe. This fact makes them
excellent key places to perform accurate high-resolution climate reconstructions. Lake
Azul (37o 52’ 21”N - 37o52’21”W) is a monomictic lake infilling the volcanic
complex of Sete Cidades which is located in São Miguel island. This monomictic and
eutrophic lake was formed around 22000 cal. years B.P. by consecutive collapses
of the underneath volcanic caldera. The last eruption of the Sete Cidades crater
complex was radiocarbon-dated at 500-650 cal years B.P. At present, macrophytes are
restricted to the lake shore and consist mainly of Potamogeton spp., Myriophyllum
alterniflorum, Ceratophyllum demersum, Nymphaea alba, and, Chara fragilis. Moreover,
this crater complex has steep borders mainly covered by exotic plant species, such
Cryptomeria japonica, Pittosporum undulatum and Hedychium gardnerianum.
Antropogenic changes in the catchment have occurred in the last centuries including
deforestation, permanent pastures (around 31%), production forest (57%) and the human
settlements.
In September 2011, fourteen sediment cores, up to 2.5 m long, were collected using a
gravity corer from a UWITEC raft. A multiproxy characterization of these cores
was carried out including smear slides, X-Ray Fluorescence, X-Ray diffraction,
magnetic properties, diatom content, and bulk organic matter (d13C, d15N, TN, TOC).
The chronological model was obtained by plant remains and pollen concentrates
radiocarbon-dating. From base to top, three lithological units have been established from
the retrieved cores: volcaniclastic rocks (lapilli), light grey laminated mud, and
poor laminated light brown mud with frequent dark layers rich in plant debris. The
radiocarbon date at the base of this fine mixture manifests the record for the last ca 650
cal. years B.P., which corresponds to the last recorded eruption. The dark brown
layers are dominated by organic matter (low XRF signal and almost no diatoms)
whereas light brown facies are mainly made up of terrigenous particles (high XRF
signal and high content of benthic diatoms) and vascular plant macroremains. Bulk
organic matter analyses have revealed that algae constitute the main compound of the
organic fraction. However, the organic matter in the dark layers is composed by
C3 plants, coherent with the clastic nature of this facies deposited during flood
events.
Increase of precipitation, ruled by the negative phase of the NAO, together with the steep
borders of the Sete Cidades crater prompts a substantial increase in the erosion of the
catchment and hence an enhancement of runoff that reaches Azul Lake and the occurrence of
the flood events. Therefore, identifying, characterizing and counting the dark layers would
allow to reconstruct the intensity and periodicity of the negative phase of the NAO climate
mode. |
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