Short-term events during the Early Holocene (Pre-Boreal) and GI-1 (Bolling-Allerod) interval in the Central Mediterranean: plaeoceanographic and palaeoclimatic inferences.

A multidisciplinary study (planktic and benthic foraminifera, pollen record, oxygen and carbon stable isotopes, alkenones, magnetic susceptibility) was carried out on several cores collected from the Central Mediterranean (Adriatic and Sicily Channel). The aim of the study was to examine the stratigraphy of the Early Holocene (pre-Boreal) interval at a high temporal resolution. The geochronological framework employed is based on Bayesian analysis of radiocarbon dates, tephra layers and geological constraints, integrated with oxygen isotope stratigraphy and planktic foraminifera ecostratigraphy, which provide independent methods for correlation. The interval between the end of the GS-1 (Younger Dryas) stadial and the lower boundary of an episode which we assign to Sapropel 1, reveals at least two oscillations, one of 1200 yrs duration (9.6-10.8 kyr B.P.), and the other of 200 yrs (9.2-9.4 kyr B.P.). These two relatively cold spells are characterised by a general decrease of warm planktic foraminifera species, and peaks in deep-dwelling species indicating winter mixing (G. inflata and G. truncatulinoides). The pollen-stratigraphic, stable isotope oxygen and alkenone records for the older and longer oscillation (9.6-10.8) suggest a complex period characterised initially by relatively humid conditions (10.5-10.8 kyr B.P) which give way to significantly drier conditions (by ca.10 kyr B.P.). Similar oscillations, of about the same age, have been previously published for the Tyrrhenian Sea as well as for Alboran Sea and Gulf of Cadiz, indicating that a large sector of the Mediterranean was influenced by the same forcing event. The characteristics of these two early Holocene oscillations are compared with two cold spells recorded in the Central Mediterranean that interrupt the GI-1 warm interval (Bolling-Allerod), and which are equated with GRIP oscillations GI-1b and GI-1d. This comparison revealed differences in paleoceanographic conditions between the Early Holocene and GI-1 oscillations. One of the biggest differences is the presence of winter mixing during the relatively colder pre-Boreal oscillations, suggesting that Adriatic deep water formed during these intervals. Conversely, the cold spells during GI-1, in contrast to the warmer episodes during this interstadial, suggest reduced deep water formation, which heralded the onset of the GS-1 (Y.D.) stadial.