Abstract:
Pleistocene-Holocene assemblages of benthic and planktonic foraminifera from Hole 969F (Mediterranean Ridge) and Hole 967D (Eratosthenes Seamount) of ODP Leg 160 were examined to reconstruct the paleoenvironmental changes during deposition of sapropels (S1, S3-S7) over the last 200 kyr in the Eastern Mediterranean. On the benthic assemblages, three major species are dominant throughout the two cores, except for the sapropel horizons where benthic foraminifera are nearly absent, suggesting an anoxic bottom environment. A Q-mode factor analysis of planktonic foraminifera has extracted four varimax assemblages. The factors 1 and 3 correspond to warm and cool waters, respectively. Both the factors 2 and 4 show low-saline coastal waters. The factor 2 indicates enhanced fertility in surface water, and the factor 4 indicates warmer and low salinity water than other factors. Factor loading of factor 4 increases in sapropel layers from S3 to S7, while the factors 1 and 2 display relatively long-term periodicities and are not related to times of sapropel formation. During the sapropels deposition from S3 to S5 and S7 in the interglacial intervals, the Eastern Mediterranean was stratified due to a cover of fresh and warm surface water inferred by the factor 4 and its ventilation in deeper water was reduced. The sapropel S6 formed in glacial period, and stratification in the surface water is relatively weak. However, the enhanced productivity may supply abundant organic matters to the sea floor. In the sapropel S1, spatial variability of paleoceanographic environment, which is recognized in this work, may be useful to understand the causes of sapropel formation.