Paleoenvironment of Marmara Sea: palynology of upper Pleistocene - Holocene sediments in long piston cores

Roberts, Kathryn Louise Katey (2012) Paleoenvironment of Marmara Sea: palynology of upper Pleistocene - Holocene sediments in long piston cores. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Marmara Sea along with the straits of Dardanelles and Bosphorus is the marine gateway that connects the Mediterranean and Black seas. Fossil palynomorphs are used to reconstruct the paleoclimate and paleoceanography of the Marmara Sea recorded in piston core MAR02-89P, from a water depth of257 m on the upper slope basinward of the southeastern Marmara shelf. This is the first core from the region with a high resolution sedimentary record from approximately 30,000 cal. yr BP to early Holocene with the exception of a hiatus from ~14,850 - 12,700 cal. yr BP. The long section of upper Pleistocene glacial and early postglacial sediments in Core MAR02-89P enables a more detailed interpretation of the palynomorphs within the eastern Marmara Sea region than has previously been possible. Geochemical data indicate increased total organic carbon (TOC), and development of more anoxic sedimentary conditions starting around 18,000 cal. yr BP, with a gradual increase in marine production at 12,700 cal. yr BP. The ratio of total sulphur to TOC displays five peaks from -28,500 - 10,000 cal. yr BP, which correspond to spikes in Pediaslrul11 algae and may indicate Black Sea flood events. Pollen records indicate four assemblage zones (5 - 2) within core MAR02-89P. Pleniglacial to late glacial zone 5 represents mixed oro-Mediterranean forest and steppe grassland, indicating some areas with >600 mm rainfall/yr and warm enough to support a Castanea (sweet chestnut) refugium. Zone 4 in the cold Heinrich I-IS I and warmer Bølling-Allenrød equivalent intervals has increased presence of steppe grassland with Ephedra. Zone 3 in the Younger Dryas interval consists of predominantly steppe-forest, with sparse oro-Mediterranean forest, suggesting ~ 300 - 600 mm of annual rainfall. Preboreal to early Holocene Zone 2 records mesic euxinian forest with less steppe vegetation, because there is a reduction in pollen characterizing grassland areas and indicating <600 mm per year of rainfall, and an increase in pollen of euxinic forests plants requiring >600 mm of rainfall year-round. Dinoflagellate cyst records show two assemblage zones, with a low salinity Spiniferites cruciformis-Pyxidinopsis psilata assemblage being replaced with a more diverse Operculodinium centrocarpum Spiniferites assemblage by 12,700 cal. yr BP. Three subzones in Dinocyst Assemblage Zone 2 (D2) may indicate changes in sea surface salinity (SSS) and temperature (SST). The marker species in the Dinocyst Assemblage subzone D2c indicate -10 psu and cool water for the pleniglacial. Late glacial subzone D2b has assemblages indicating increased salinity (~13 - 17 psu) while late glacial subzone D2a assemblages suggest warmer SST during the Heinrich HSI and the start of the Bølling-Allenrød equivalent intervals. Dinocyst Assemblage Zone I (DI) consists of two subzones: dinocysts in pre-boreal subzone D1b indicate SSS of ~13 - 20 psu and cool to temperate surface water in contrast to subzone D1a Holocene assemblages indicating temperate to sub-tropical SST. From ~30,000 - 14,850 cal. yr BP, the Marmara Sea received water from the Black Sea during flood events. There is no record in core MAR02-89P for the interval of 14,850 - 12,700 cal. yr BP, by the end of this hiatus, sapropel development had begun, and Mediterranean dinocysts indicate Mediterranean water from the Aegean Sea was contributing to the Marmara Sea together with Black Sea water during and after the Younger Dryas event.

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