Holocene biostratigraphy and paleoenvironmental changes in the Black Sea based on calcareous nannoplankton

In this study, detailed micropaleontological analyses were carried out on 270 samples from eight piston cores collected in the Black Sea. The primary goal was to elucidate the Late Quaternary evolution of the Black Sea, specifically to refine its biostratigraphy and to explore the Holocene paleoenvironmental changes. Three intervals were recognized in all the cores studied, irrespective of whether they were from the basin or the shelf. These intervals are characterized, from old to young, by the spotty occurrence, the presence and the local acme of Emiliania huxleyi respectively. Moreover, the species Braarudosphaera bigelowii is, in contrast to the younger units, absent in the oldest unit. The co-occurrence of the two marine species E. huxleyi and B. bigelowii suggests a shift from fresh-brackish water to low-salinity marine conditions in the Black Sea. The spotty and very rare occurrence of E. huxleyi in the lowermost unit is reported here for the first time. Two hypotheses are suggested: the presence of reworked specimens from Eemian outcrops, or the presence of low salinity waters also during the "lacustrine" phase of the basin. Another feature observed in almost all the cores is the presence of a multilamina aragonite level in the upper part of the Ecozone 3, which functions as a marker for basin-wide correlations. The parallel study of water samples and surficial sediment assemblages demonstrates the presence of Syracosphaera lamina in the surface water samples and its absence in the sediments, suggesting dissolution in the water column. On the other hand, the occurrence of B. bigelowii in all cores and its near-absence in water and in recent sediment samples suggest a change in water conditions during recent times.