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| Titel |
Productivity patterns and N-fixation associated with Pliocene-Holocene sapropels: paleoceanographic and paleoecological significance |
| VerfasserIn |
D. Gallego-Torres, F. Martinez-Ruiz, P. A. Meyers, A. Paytan, F. J. Jimenez-Espejo, M. Ortega-Huertas |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 2 ; Nr. 8, no. 2 (2011-02-16), S.415-431 |
| Datensatznummer |
250005450
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| Publikation (Nr.) |
 copernicus.org/bg-8-415-2011.pdf |
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| Zusammenfassung |
| We have studied a suite of 35 sapropel sequences from a transect of four ODP
sites across the Eastern Mediterranean to explore for paleoproductivity
patterns and provide new insights on ecological changes during their
deposition. Paleoproductivity variations were identified using TOC and
Babio mass accumulation rates and δ15Ntotal and
δ13Corg values. Elevated Ba/Al and TOC mass accumulation
rates record periods of basin-wide amplified productivity. Our data further
support that sapropels were formed by cyclic increases in primary production
of marine organic matter largely sustained by N-fixing bacteria. This
productivity increase was triggered by climate factors leading to increased
fluvial discharge and amplified nutrient input that also favored the
establishment of N-fixing bacteria. Enhanced productivity led to depletion
of deepwater dissolved oxygen and consequently improved organic matter
preservation. Primary production was more intense during the middle to Late
Pleistocene compared to Pliocene equivalents, coinciding with increasing
total sedimentation rates. δ15N values are dramatically lower
in the sapropels than in TOC-poor background sediments, indicating a major
contribution from nitrogen-fixing bacteria to the higher productivity during
sapropel deposition. Additionally, different degrees of denitrification
occurred as a consequence of water column oxygenation which in turns evolved
from stagnant anoxic bottom waters during Pliocene sapropels to oxygen
depleted and sluggish circulation in late Quaternary layers. These
differences between sapropel layers provide new evidences for the general
evolution of the Eastern Mediterranean basin during the last 3 Mys in terms
of paleoceanographic conditions and the intensity of climate variability
leading to sapropel deposition. |
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