Bathymetric distribution and ecology of agglutinated foraminifera along an inner neritic to upper bathyal transect in the Marmara Sea

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In: Kaminski, M.A. & Filipescu, S., (eds), 2011. Proceedings of the Eighth International Workshop on Agglutinated Foraminifera. Grzybowski Foundation Special Publication 16, 37-52.

The Marmara Sea is an intercontinental basin with two narrow and relative shallow straits connecting the Mediterranean Sea with the Black Sea. The Marmara Sea is characterised by the outflow of brackish shallow water from the Black Sea and saline bottom water inflow from the Mediterranean Sea. These oceanographic features determine the establishment of a sharp halocline, which leads to a permanent stratification generating low-oxygen and stratified conditions below a thin, well-mixed and highly oxygenated surface layer. This study documents for the first time the agglutinated foraminiferal assem- blages of the Marmara Sea and their possible use as sensitive tracers of water masses. A total of 50 agglutinated species were identified belonging to 36 genera. Statistical analysis identifies three main assemblages that can be related to the bathymetry and in turn to the hydrological features of the water masses. The shallowest assemblages are characterised by both the lowest diversity and the highest dominance values induced by the strong influence of the Black Sea outflow that can be tolerated by only a limited number of species. High values of diversity have been identified at water depths shallower than 150 m, this increase has been associated with the inflow of Mediterranean countercurrent bringing more oxygenated and saline waters. The diversity values of the deepest assemblages show a complex pattern exhibiting a rapid increase and peaking at 225 m water depth. The lowest diversity corresponds to the lowest value of dissolved oxygen in the transect at 300 m water depth. A significant increase in diversity is observed from 300 m to 350 m water depth, linked to a rise in dissolved oxygen probably due to the presence of a Mediterranean-source bottom water undercurrent. This study confirms the suitability of using agglutinated foraminifera as tracers of water masses.
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