A multidecadal-scale marine and terrestrial palynological record of Eastern Mediterranean sapropel S1 near the Nile outflow

Eastern Mediterranean sediments are characterized by the cyclic occurrence of organic rich layers (sapropels) of which sapropel S1 (~10-6 kyrs BP) is the most recent. Sapropel deposition is dominantly controlled by variations in precession, which drive the Northern Hemisphere seasonal contrast and the African monsoon intensity. During precession minima increased freshwater input (e.g., increased Nile runoff) weakened the anti-estuarine circulation in the Eastern Mediterranean Sea. This ultimately led to widespread hypoxia or even anoxia at the seafloor, thereby promoting enhanced preservation of organic material and thus sapropel formation. Increased nutrient-rich freshwater input may additionally have boosted productivity in the surface waters enhancing organic matter flux to the seafloor. However, the relative contributions of productivity and preservation in sapropel formation remain still elusive.
Here we present a marine and terrestrial (i.e., dinoflagellates, pollen and spores) palynological study of Holocene sapropel S1 from core PS009PC located offshore Israel. The core documents marine and terrestrial environmental changes at time of sapropel S1 deposition from a location extremely sensitive to changes in the Nile outflow. The high sediment accumulation rates of the core enable a unique high-resolution study. Our results clearly illustrate the gradual changes that occurred in the marine realm leading to the onset of sapropel formation, the changes in the marine and terrestrial realms during sapropel deposition, the ~8.2 kyr event and the sapropel termination. Our data, in combination with available geochemical data, bring new insights into the on-going formation vs. preservation discussion.