DATE2019-01-08 12:44:22
IDABSTRACT2014/107
CONTACTe_v_ivanova@ocean.ru
PRESENTATIONORAL
INVITED0
IDSESSION1
TITLETHE EARLY HOLOCENE BLACK SEA RECONNECTION WITH THE MEDITERRANEAN: IMPLICATIONS FOR BIOTIC AND ECOLOGICAL CHANGES ON THE NORTHEASTERN SHELF
AUTHORSElena Ivanova (1)|Maria Zenina (1,2)|Fabienne Marret (3)|Ivar Murdmaa (1)|Andrey Tchepalyga (4)|Lee Bradley (3)|Maria Zyryanova (1)
AFFILIATIONS
  1. P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia
  2. A.V. Zhirmunsky Institute of Marine Biology, Far East Division RAS, Vladivostok, Russia
  3. School of Environmental Sciences, University of Liverpool, Liverpool, UK
  4. Institute of Geography, Russian Academy of Sciences, Moscow, Russia
ABSTRACTWe studied the Holocene Black Sea reconnection to the Mediterranean with the special emphasis on the marine species immigration and settling on the NE Caucasian shelf as well as the disappearance of species of Caspian origin. The distribution of different groups of fossils is quantitatively analyzed from four radiocarbon dated sediment cores. These were retrieved from the NE shelf off Arkhipo-Osipovka village during the RV Akvanavt cruises. Our multi-proxy approach revealed the significant discrepancies in the rate of immigration of molluscs, ostracods and foraminifers which suggest differences in ecological preferences. However, both molluscs and ostracods are of brackish character as early as ~8ka, during the so-called Bugasian transgression, suggesting a salinity of 5-7. However, the salt composition of the water was still similar to that of the Caspian Sea and not of the modern Black Sea. Dinocyst assemblages present species succession that is coherent across the basin, with brackish taxa dominating until ~8.5ka and being slowly replaced by euryhaline species The typical Caspian mollusc fauna disappeared from the NE shelf by ~ 7ka, while the Mediterranean immigrants appeared as early as 8ka. The most salinity-loving, low-oxygen tolerant and relatively deep-water species Modiolus phaseolinus settled as late as ~ 4ka, i.e. ~ 3ka later than the sea level and bottom water salinity reached their modern values. Ostracods demonstrate a gradual change from brackish to marine assemblages. Some brackish species surviving at present in the estuaries of the Black and Azov Seas were identified. Similar findings were observed in the dinocyst record, with the occurrence of Spiniferites cruciformis in the last 1000 years. Our data indicate that the ostracods are sensitive to the sea water salt composition along with their previously inferred sensitivity to the salinity rise during the Early Holocene. Benthic foraminifers only inhabited the NE shelf much later from 7.2ka onwards. No Caspian species were found in our records. Like the ostracods, foraminifers show very low abundances at 6.3-6.2ka. The sediments of this interval contain gypsum which potentially indicates the temporal appearance of hydrogen sulphide at the shelf break which would dramatically reduce the abundance of benthic fauna. The mid-Holocene ostracod assemblages were very unstable with the modern fauna forming at ~4-3ka BP, i.e. about the time of Modiolus phaseolinus settling on the NE shelf.
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