Late Quaternary paleoclimatology, stratigraphy and sapropel history in eastern Mediterranean deep-sea sediments

Abstract

The Late Quaternary paleoceanographic history of the Mediterranean Sea is a complex mixture of both global and regional events. Principal component analysis and oxygen isotopic analysis of planktonic foraminifera in deep-sea sediments have been used to define detailed paleoclimatic changes and to develop a firm stratigraphy for eastern Mediterranean sediments for the past 400,000 years. The first principal component is interpreted as being temperature-dependent based on the faunal assemblages associated with this component and on its close similarity to the oxygen isotope record. Warm and cool planktonic foraminiferal assemblage groupings derived by principal component analysis agree with faunal groups previously differentiated for Late Quaternary sequences in this region. Periodic stagnations of the eastern Mediterranean basin have resulted in the deposition of numerous organicrich sapropel layers during the Late Cenozoic. These sapropel layers are marked by the complete absence of any benthonic microfossil fauna and by the presence of an abnormal planktonic foraminiferal fauna containing an unusually high percentage of the salinity-sensitive foraminifer Neogloboquadrina dutertrei. Although the deposition of sapropels appears to be synchronous throughout the eastern Mediterranean, the lack of sapropels in cores from the western Ionian Sea indicate that true stagnant phases are not basin-wide phenomena. The onset of stagnant conditions is believed to be triggered by a flushing of fresh water from the Black Sea into the eastern Mediterranean during interglacial episodes where it forms a low-salinity surface layer that prevents oxygenation of the deep portions of the eastern basin. By placing the sapropel layers within a paleoclimatic framework, it is evident that sapropel deposition occurred during both warming and cooling trends within interglacial stages 1, 5 and 7. This is in contrast to previous work which suggested that sapropel formation occurred only during the climatic transition from glacial to interglacial episodes.