| dc.description.abstract | Sapropel formation is thought to be strongly related to deep-water formation. The latter is known to take place in Adriatic and Aegean basins. In this study, therefore, high resolution geochemical analyses have been performed on three marine cores, collected from the South Aegean (KN3 core), North Aegean (SL73BC) and South Adriatic (MP50PC) Seas. Data on Total Organic Carbon (%) (TOC), stable carbon and nitrogen isotopes, elemental concentrations and foraminifera stable isotopes analyses have been used to unravel in detail the conditions established during the Holocene and the processes responsible for S1 deposition and preservation in particular. The sedimentary records show that during sapropel S1 deposition bottom-water conditions have been oxic to suboxic for the South Aegean Sea and suboxic to anoxic for the South Adriatic and North Aegean Sea, and that sedimentary conditions ranged from suboxic to anoxic. Significant variations within this interval are promiment, implying that at such shallow depths sapropel formation did not take place under stable conditions. Differences that are observed between the studied sites highlight the influence of water depths and sedimentation rates. In both studied basins distinct episodes of re-ventilation of the water column have been observed, whilst there is no evidence that fully anoxic conditions have maintained during S1 formation. In addition to the 8.2 cal ka BP event, an abrupt event at ca 7.5 cal ka BP has been identified in the south Adriatic core, which is thought to be related to a temporary cessation of sapropel formation. Similarly, in the southern Aegean core, the S1 formation appears to have been interrupted at 7.5 cal ka BP, whereas sediments older than ~ 8 ka cal BP have not been recovered in this core. Fluctuations in Corg content coupled with Ba/Al ratios and changes in Mn/Al, V/Al and Mo/Al profiles underline variability in water-column properties. The observed repetitive episodes of re-ventilation of the water column and their obvious implications for sapropel formation not only suggest a relation to paleoclimate control but also to sensitive water-column hydrological conditions. The latter and in particular the bottom-water formation mechanisms determine deep-water oxygenation thus preservation and shallow-water nutrients supply thus primary productivity. Although several studies, mostly based on micropaleontological and terrestrial archives, mention additional episodes of climate cooling during sapropel S1 formation, so far these have not all been linked to marine records. In the South Adriatic core an additional event is observed at 9.3 cal ka BP that suggests the temporal cessation of sapropel S1 formation. As this interval is also containing enhanced levels of tephra, these observations may at least in part be attributed to a tephra layer originating from Somma – Vesuvius. | |
