HIGH-RESOLUTION PALAEONVIRONMENTAL RECONSTRUCTION OF ODP HOLE 963D (SICILY CHANNEL) DURING THE LAST DEGLACIATION BASED ON CALCAREOUS NANNOFOSSILS

A palaeoenvironmental reconstruction of Ocean Drilling Program (ODP) Hole 963D (Sicily Channel) has been obtained on the basis of quantitative abundance fluctuations in the calcareous nannofossil assemblages. The studied hole is characterized by a very high sedimentary resolution and covers the last ca. 20 kyr. A new palaeoclimatic curve, based on the Gephyrocapsa muellerae/Upper Photic Zone (UPZ) group ratio, permitted the detection of the rapid climatic fluctuations that characterized the last deglaciation. Cold water masses occupied the Sicily Channel during the glacial period and the Younger Dryas, whereas they were generally warm during the Bølling-Allerød and the Holocene. An approach based on a direct relationship between actualistic data (water samples) and palaeontological records in the coccolithophores has been attempted in order to obtain the palaeoecological characterization, with the proposition of two floristic groups pertaining to the Upper Photic Zone and the Lower Photic Zone (LPZ). Further information has been provided by several additional taxa. During the investigated time interval, stratification in the water column and oligotrophic conditions are always linked to the warm periods, while high productivity, caused by continuous convection of nutrient fluxes, existed during the cold periods. Finally, a simple model with two end-members is proposed to explain the relative abundance of the deep dwelling species Florisphaera profunda, relative to other coccolithophores and to the physical conditions of the photic zone.