Holocene ostracod paleoecology of the southwestern Black Sea shelf

Williams, Lorna Rose (Lorna R.) (2012) Holocene ostracod paleoecology of the southwestern Black Sea shelf. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Black Sea is an essentially isolated sea connected to the Mediterranean Sea through two narrow and shallow straits. The Bosphorus Strait connects the Black Sea to the Marmara Sea and the Dardanelles Strait connects the Marmara Sea to the eastern Mediterranean Sea. Today, a two-way flow exists between the Mediterranean Sea and the Black Sea via the Marmara Sea and the Dardanelles and Bosphorus Straits. During glacial periods when water levels in the World Ocean dropped, the Black Sea became periodically isolated. There are three conflicting hypotheses regarding the timing and mechanism of the last reconnection of the Black Sea to the Mediterranean Sea: the Flood Hypothesis, the Outflow Hypothesis and the Oscillating Hypothesis. -- Cores MAR05-50P and MAR05-51G were raised in 91 m water depth from the southwestern Black Sea shelf on the eastern levee of a saline underflow channel. Composite core MAR05-50 was constructed from the above cores to accommodate core top loss and an age model was created based on 11 radiocarbon dates. Core MAR05-50 recovered sediments from virtually the entire Holocene from 11490 cal yr BP to present. -- A total of 45 individual ostracod species were found in the above cores and 43 were identified with the aid of taxonomic literature. From 11400 to7450 cal yr BP the ostracod assemblage is completely dominated by Ponto-Caspian species, mainly Loxoconcha sublepida, Loxoconcha lepida and Tyrrhenocythere amnicola donetziensis. From 7580 to 6410 cal yr BP the assemblage is almost equal abundances of a new Mediterranean species Loxoconcha littoralis and the Ponto-Caspian species. After 7450 cal yr BP to the top of the core, the assemblage is fully dominated by Mediterranean species, including Palmoconcha agilis, Carinocythereis carinata, Hiltermannicythere rubra and Pterygocythereis jonesii. CONISS cluster analysis revealed 6 Bio-zones where there are distinct changes in the ostracod assemblage. The lower, Porno-Caspian interval is divided into Bio-zones 1 and 2. The "mixed" assemblage is Bio-zone 3. The upper, Mediterranean interval of the core is divided into Bio-zones 4, 5 and 6 where new Mediterranean species are introduced and previous species decrease in abundance or disappear. The changes in the ostracod assemblages from one bio-zone to the next suggests that progressive ecological changes took place on the southwestern Black Sea shelf from 11400 cal yr BP to present. Sedimentological data and geochemical data from core MAR02-45, ~70 km northeast of the study area, place the timing of the last postglacial reconnection between the Black Sea and the Mediterranean Sea at ~ 8500 cal yr BP. -- The ostracod data indicate a ~1000 year salinization lag between the reconnection and the first Mediterranean species to colonize the area. The step-wise Bio-zones further suggest that the post-reconnection salinization of the Black Sea was a gradual process and took ~5000 years to reach near-modern salinity conditions. The results conflict with the catastrophic Flood Hypothesis in that the changes in the ostracod assemblages seem to reflect a more ordered reconnection and stepwise salinization process. The ostracod results can neither confirm nor refute the Oscillating Hypothesis. There are no conflicts between the ostracod data and the Outflow Hypothesis which argues for a gradual reconnection and salinization. Both the Outflow Hypothesis and the Oscillating Hypothesis are entirely plausible based on the ostracod evidence from core MAR05-50.

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