C org-reiche Sedimenthorizonte der Alboran See (ODP Site 976, westlichstes Mittelmeer) : Rekonstruktion der Ablagerungsbedingungen nach hochauflösenden Profilen stabiler Sauerstoff- und Kohlenstoffisotope und der Häufigkeitsverteilung benthischer Foraminiferen (Teil 2 : Laborarbeit)
At Site 976 in the Alboran Sea, western Mediterranean, a high-resolution planktonic oxygen isotope record (G. bulloides) was established for the past 77,000 years with a time resolution of 7.5-1170 years. Short-lived δ180 anomalies document Dansgaard/Oeschger (D/O)-climatic oscillations and Heinrich...
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| Format: | Thesis |
| Language: | German |
| Published: |
2000
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| Online Access: | https://oceanrep.geomar.de/id/eprint/59453/ https://oceanrep.geomar.de/id/eprint/59453/1/Dipl_Pahnke_K_2000%20Laborarbeit.pdf |
| Summary: | At Site 976 in the Alboran Sea, western Mediterranean, a high-resolution planktonic oxygen isotope record (G. bulloides) was established for the past 77,000 years with a time resolution of 7.5-1170 years. Short-lived δ180 anomalies document Dansgaard/Oeschger (D/O)-climatic oscillations and Heinrich (H)-events with δ180 shifts of up to 1.6 ‰. Glacial-interglacial δ180 amplitudes are between 2.5-3.2 ‰. The existence of D/O-oszillations and H-events at Site 976 document the influence of North Atlantic hydrographic and climatic conditions on the Mediterranean, transfered to the Alboran Sea via surface inflow and the atmosphere. Abundance distribution and assemblage structure of benthic foraminiferal populations are used to reveal environmental conditions during the formation of two organic-rich layers (ORLs) in the Alboran Sea. Bottom water oxygen concentrations were reconstructed using the benthic foraminiferal oxygen index (BFOI) as defined by Kaiho [1994]. Paleoproductivity was estimated using two independent methods, the benthic foraminiferal accumulation rate (BFARtotat sensu Herguera and Berger [1991] and Herguera [1992]) and TOC-contents ("total organic carbon"). Estimates from BF ARtota1/TOC and BFOI document low oxygen concentrations (0.46-1.01 ml/1) and paleoproductivities (103.05 gC/m2a via BFARtota1; 183.23 gC/m2a via TOC) for the early stage of ORL-Al deposition in the Younger Dryas. Estimated paleoproductivity gradually increases (168.82 gC/m2a from BFARtota1; 212.09 gC/m2a from TOC) while oxygen concentrations develop to suboxic to medium-oxic conditions (max. 3,21 ml/I). Reduced oxygen concentrations are also deduced from enhanced Corg-preservation throughout the entire ORL-Al. An influence of low oxygen conditions is also documented in the lower paleoproductivity values estimated from the BF ARtotat, which conceivably reflects stressed conditions for the benthic foraminiferal fauna. Changes in paleoproductivity are more sensibly traced by benthic foraminifera (BFARtotat) than by TOC as is inferred ... |
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