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| Titel |
Speleothems - marine - lake records in the Eastern Mediterranean widen our understanding of regional paleoclimate and global connections |
| VerfasserIn |
M. Bar-Matthews, A. Almogi-Labin, A. Vaks, A. Ayalon |
| 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 |
250022280
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| Zusammenfassung |
| This study compares high resolution speleothems records obtained from caves located
in different climatic regions in Israel, representing Eastern Mediterranean type
climate, semi-arid, and the hyper-arid climate of the north-eastern Saharan Desert.
The comparison of these records enables us to understand the influences of the
northern Atlantic and the tropical monsoonal systems on the climate variability in the
region. The analysis of the terrestrial system is augmented by comparison with
the marine high resolution oxygen and carbon isotopic records of the planktonic
foraminifera G. ruber, sea surface temperatures and pollen in two cores located in the
southern and northern Levantine basin. The southern core is located beneath the River
Nile plume, whose sources are influenced by the monsoonal climate system. The
northern core, located ~380 km further north SE of Cyprus, represents the northern
Levantine basin where climatic conditions are less arid and more typical of the
Mediterranean-type climate. These marine and the speleothems records are also compared
with lake levels of Lake Lisan, the precursor of the modern-day Dead Sea. The
comparisons enable us to explore several key issues: the spatial differences in δ18O
in the Levantine basin; the sea-land temperature and δ18O relationships and their
implications on isotope hydrology and climatic controls of rainfall systems in the
region.
The main findings are summarized by the following observations: (1) Average sea surface
temperatures of the Eastern Mediterranean Sea during glacial and interglacial periods was
similar to the average land temperatures, with the major vapor source being the
central/northern Levantine basin. (2) During glacial periods there was greater oxygen isotopic
depletion in rainfall reaching the caves, owing to Rayleigh effects associated with lower sea
levels. (3) Sapropel formation in the Eastern Mediterranean was associated with heavy
rainfall events throughout the region, which left a strongly defined imprint on the
difference between the δ18O of rainfall and that of the sea-surface. (4) An anomalous
warming event occurred at 54-50 ka in the central and north eastern Mediterranean
region that coincided with maximum insolation in the northern hemisphere. (5)
The changes in hydrological conditions indicated by the very low δ18O values of
Eastern Mediterranean speleothems during termination II, MIS 6-MIS 5 transition,
predate the maximum solar insolation in 65oN, and occurred in 3 steps: at 140 ka,
at 135 ka, and with the major drop in δ18O occurring between 128 and 120 ka
and coinciding with maximum insolation. The last episode of speleothem growth
in the NE Sahara also commenced at ~140 ka , with major speleothem growth
occurring between 135 and 124 ka. The origin of the moisture during this extreme wet
event was mixed f north and tropical Atlantic, with storm tracks passing over the
Mediterranean Sea (6) The sharp post glacial change in the hydrological conditions in the
Eastern Mediterranean started at ~18.5 ka, ~3000 years before the warming in
the Northern Hemisphere. It is not clear if this sharp change in the speleothems
δ18O is associated with early warming in the Eastern Mediterranean region or is
related to other affects. (7) High lake levels in the Lake Lisan during last glacial,
when climate in the northern hemisphere and the vast Sahara Desert was cold and
relatively dry, were associated with sharp drops in temperature resulting in less
evaporation and higher water infiltration coefficients into the unsaturated zone. |
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