CHANGES IN WESTERN MEDITERRANEAN SURFACE, INTERMEDIATE AND DEEP WATER DURING THE LAST DEGLACIATION, AND THEIR LINK WITH ATMOSPHERIC PROCESSES

The Last Deglaciation evolution of the water properties in the Alboran Sea (W Mediterranean Sea) are reconstructed based the combined approach of Mg/Ca and d ¹⁸O analyses from different species of planktonic and benthic foraminifers. The exceptional high sedimentation rates (20-80 cm/kyr) of core MD952043 allow a time resolution of few centuries-decades for the period considered here. The chronostratigraphy of the last 24 kyr is well constrained based by 17 AMS ¹⁴C dates. Sea surface temperature (SST), as recorded on both Mg/Ca from G. bulloides and by alkenone results, warmed abruptly (~4°C/700yr) at the first stage of Last Deglaciation and almost synchronous with the atmospheric warming recorded in GISP2 at the onset of the GI-1. In parallel, the Mg/Ca record from N. pachyderma shows a rapid cooling suggesting a deepening of the thermocline. In addition, deep basin conditions changed suddenly to a less oxygenated environment reflected by the benthic comunity and also the organic matter records. The sequence of events of the last deglaciation are not equally represented in all the considered parameters. Overall, both G. bulloides and N. pachyderma d ¹⁸O profiles follow a structure parallel to Greenland temperature record. The YD chronozone is well represented in the SST record from alkenones by a ~4°C cooling but this is less marked in the G. bulloides Mg/Ca reconstruction possibly due to a change in the bloom season. Holocene SST in the Alboran Sea was rather stable but, in contrast, rapid and intense changes are observed in the thermocline and also deep water mass. While SST cooled slightly at 8.2 cal. kyr BP deep water changed rapidly towards more ventilated conditions. This change preceded by ~2 kyr a sudden warming (~3°C) of the thermocline layer while G. inflata became a dominant species in the planktonic assemblage. This event also marks the end of a pronounced positive salinity anomaly occurring in the thermocline layer (10.5-7 kyr BP). These intense changes during the Holocene reflect the instability of the Mediterranean system even during "stable" periods. A combination of mechanisms such as sea level changes, atmospheric circulation, changes in seasonallity and insolation due to orbital configuration may have resulted in these abrupt changes of the Alboran Sean during the last 20,000 years.