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Titel |
Holocene climate variability and environmental changes in the NE Mediterranean Sea along a N-S transect |
VerfasserIn |
A. Gogou, I. Bouloubassi, K.-C. Emeis, M. Triantaphyllou, G. Katsouras, G. Rousakis, V. Lykousis |
Konferenz |
EGU General Assembly 2012
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 14 (2012) |
Datensatznummer |
250070432
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Zusammenfassung |
The Eastern Mediterranean Sea (EMS) lies in a climatological transition zone, under
the influence of both tropical and mid-latitude climate processes. Early Holocene
sediment records collected in the EMS bear witnesses for the formation of the most
recent sapropel S1, closely associated with distinct minima in the orbital precession
cycle and the insolation-driven monsoon maxima. The different scenarios of S1
deposition involve changes in marine productivity, organic matter preservation and
circulation changes and are still under debate. Herewith, we focus on combined
geochemical and micropaleontological proxies, namely organic biomarkers, organic
carbon and nitrogen stable isotopes and coccolithophore assemblages, aiming at
reconstructing climate-related parameters such as sea surface temperature (SST),
marine productivity patterns, stratification and nutricline fluctuations and continental
inputs in three gravity cores collected along a north-south transect in the EMS.
Depending on the water column depth, the sediment accumulation rates and the
hydrographic circulation patterns, S1 deposited in our records between ~9.8 to 6.4
kyr BP. During the Holocene climatic optimum, SSTs increase gradually more
than 4Ë C and reaches values as high as 21.2Ë C, 22.5Ë C and 23Ë C along the
N-S transect. Our records also show a pronounced centennial-scale cooling that
culminates at ~ 8.0 kyrs BP, coeval to the N. Atlantic cooling event, causing an
interruption in the deposition of S1 in all sites. Moreover, SST fluctuations are detected
between 4.9 and 4.1 kyr BP, with a sharp positive shift to 24.9Ë C indicating the
presence of a warm period in the mid Holocene. Higher accumulation rates of TOC,
marine biomarkers and coccolithophore assemblages were recorded during the
S1a, S1b and Mid Holocene Humid (MHH) phases, indicating higher productivity
and/or better preservation of organic matter. Furthermore, distribution patterns,
composition and characteristic ratios of marine biomarkers and of coccolithophoride
species exhibit variability in paleoproductivity trends, hydrographic dynamics and
nutricline levels during the Holocene. The distributions of land plant biomarkers are
indicative of variable terrigenous organic matter supply and the concomitant transport of
nutrients to surface waters. The different types of δ13Corg excursions associated with
stronger fluvial delivery (terrestrial inputs) in the north site, whereas the other two
sites received most marine organic matter. Lighter values of δ15N within S1 and
MHH phases reflect a significant contribution of N-fixing organisms to the N-cycle,
related probably to higher demand for nitrogen due to the established dysoxia in the
water column/sediment interface, leading to denitrification and P regeneration. |
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