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| Titel |
Climate change towards more arid conditions in SW Iberia during the Holocene |
| VerfasserIn |
Carlos Ribeiro  , Pedro Terrinha, Antje Voelker, António Candeias, M. Rosario Azevedo, Sara Ribeiro, Lúcia Rosado |
| 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 |
250055742
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| Zusammenfassung |
| During Holocene, a limestone tuff system developed in the SW Iberia near the town of
Tavira (Portugal). The system is characterized by a set of three dams built up by the
precipitation of layered limestones. Each dam has a low-energy pond system upstream
where fine grained detrital sediments accumulated. The stable isotopic composition
(oxygen and carbon) of the limestone tuffs were studied in detail with the aim of
deciphering the paleo-climatic conditions prevailing onshore in this area during the
Holocene.
The more relevant results can be summarized as follow: (i) 14C age determinations
constrained de carbonate sedimentation to the period between 10.2 ka and 2.6 ka; (ii) X-ray
diffraction shows that the mineralogical composition of the limestone tuffs is dominated by
calcite although some minor amounts of detrital quartz and clay minerals are present in some
of the samples; (iii) the oxygen stable isotope data of the limestone layers shows δ18O values
ranging between -5.52 and -2.79 per mil for the time interval under consideration; (iii)
the possibility of a contribution of the surrounding Mesozoic formations to the
isotopic composition of the limestone tuffs was discarded by the lack of correlation
between the 87Sr/86Sr values and the oxygen and carbon isotope ratios; (iv) after
decomposition of the time series the change of the δ18O values throughout the
Holocene is characterised by an initial stage with δ18O values ranging between
approximately -5.1 and -4.5 per mil which ends around 3.7 ka and is followed by a late
stage with stronger differences between the minimum and the maximum of the
oxygen isotope ratio values (-4.8 to -3.9 per mil); (v) during the time interval under
consideration the values of δ18O of the limestone tuffs exhibit a trend of slow and regular
increase.
The data on present day precipitation and isotopic composition of meteoric waters
supports that the balance between evaporation and precipitation is the main factor controlling
the fractionation of oxygen stable isotopes of the meteoric water in this region. The observed
increase in δ18O values throughout most of the Holocene can then be interpreted as the result
of an increase in the amount of evaporation and/or a decrease on the amount of precipitation
with the consequent change in the local climate conditions towards a more arid
environment. This increase in the evaporation is most likely related to the increase in
the atmospheric temperature during the climatic recovery following the Younger
Dryas.
Acknowledgments: This work was financed by FCT through the PTDC/CTE-GEX/71298/2006
grant. |
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