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| Titel |
The use of the oxygen isotopes from diatom silica as a proxy for North Atlantic Oscillation reconstruction |
| VerfasserIn |
Armand Hernández, Melanie J. Leng, Ricardo M. Trigo, David Vázquez-Loureiro, Roberto Bao, Hilary J. Sloane, Maria J. Rubio-Inglés, Guiomar Sánchez-López, Vitor Gonçalves, Pedro M. Raposeiro, Alberto Sáez, Santiago Giralt |
| 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 |
250113008
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| Publikation (Nr.) |
 EGU/EGU2015-13201.pdf |
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| Zusammenfassung |
| The North Atlantic Oscillation (NAO) is the main atmospheric circulation mode controlling
climate variability in the Northern Hemisphere. Instrumental records of the NAO are
relatively short, and therefore proxy approaches are essential to understand its evolution over
longer time periods. Diatom oxygen isotope ratios are increasingly being used for
palaeoclimatic reconstructions in lacustrine sedimentary records. However, application of this
proxy to annual-to-decadal resolution lacustrine records is still in its infancy. To our
knowledge, oxygen isotope ratios from diatoms at annual-to-decadal resolution has not been
attempted, mainly due to the difficulty in obtaining large enough samples suitable for analysis
at this temporal scale. Here we present a high-resolution, ca. 200-year-long, proxy record
based on 56 oxygen isotope measurements from Lake Santiago (37°50’ N – 25°47’W,
Azores Archipelago, Portugal). This record will be compared to instrumental data of
precipitation and NAO index values to test its robustness to conduct an ancient NAO
reconstruction.
In detail the oxygen isotope data shows an isotope depletion trend (-3o), with several
interannual oscillations, from 1830 cal yr AD until present. The entire record can be divided
into two intervals. The interval, from 1830 to 1938 cal yr AD, displays values above the
average (+33o), whereas the interval from 1939 to 2012 cal yr AD shows values below the
mean. Since Lake Santiago is a hydrologically closed lake, the oxygen isotope variations are
mostly related to the precipitation-evaporation ratio. These results exhibit a good
agreement with the rainfall instrumental data with an increase of net rainfall amount
through the last decades in the Azores archipelago. Besides this, the short-term
recorded isotope excursions (±3.5o) are related to the rainfall interannual variability.
These patterns suggest that the isotope data from diatom silica in Lake Santiago
sediments are directly linked to past precipitation changes on the Azores. Moreover, the
precipitation regime in Azores Archipelago (i.e. intra and inter-annual variability) is
clearly influenced by the NAO index, thus periods with dominant positive NAO
index values (NAO+) are usually characterized by low winter precipitation in the
Azores. Conversely, negative NAO phases (NAO-) induce high winter precipitation in
the archipelago. Therefore, the oxygen isotope data may be used as a proxy for
NAO changes, and thus a proxy for more large-scale changes in the North Atlantic
region.
Acknowledgements: This work was partially supported by national funds through
FCT (Fundação para a Ciência e a Tecnologia, Portugal) under project QSECA
(PTDC/AAGGLO/4155/2012). |
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