WATER MASSES EXCHANGE THROUGH THE STRAIT OF SICILY DURING THE LAST DEGLACIAL PERIOD AND THE HOLOCENE

The main goal of this thesis is to explore the inter-basin connection between the eastern and the western Mediterranean (E- and W-Med, respectively) during the last deglacial and Holocene periods (last 15 kyr). The thesis is based on the study of a sediment core recovered at the west flank of Sicily channel (W-Sicily), strategically located under the current path of the surface Atlantic waters and directly below the present-day hydrographic boundary layer between the Eastern Mediterranean Sourced Water (EMSW) and the Western Mediterranean Deep Water (WMDW). This key location allow to explore past changes in both surface and deep water exchange between the E and the W-Med. In this thesis, a combination of several analytical tools are presented to provide information of different oceanographic variables: (i) Physical and chemmical sea water properites have been inferred trough tha analysis of microfossil assemblages, stable isotopes and trace elements in both planktic and benthic foraminifera; (ii) Dynamics of sediment supply have been based on grain-size, elemental geochemical composition and sediment rate analysis; (iii) Changes in the export rates of EMSW have been studied through the analysis of 143Nd/144Nd isotope ratios (eNd) in planktic foraminifera coatings, a novel quantitative tracer of water mass provenance. One of the most outstanding results of this thesis has been the identification of an intensified EMSW flow at W-Sicily during the Younger Dryas (YD, 12.95-11.65 kyr BP). In this thesis is presented by the first time, solid evidence of a previous hypothesised enhanced YD deep-water interconnection between the E-and the W-Med. This situation is here atributted to the combined effect of; 1) the weakening of the W-Med deep-water convection associated with the simultaneous formation of the Organic Rich Layer (ORL) and 2) enhanced convection in the Aegean and Levantine basins favoured by the prevailing YD cold and arid conditions. It is also here proposed that this enhanced western flow of EMSW, ceased the stagnation at ~900m in the Alboran Sea that had initiated with the last ORL. At the same time, probably to balance the high outflow of the EMSW through the Strait of Sicily, the data here generated is consistent with an increased flow of Modified Atlantic Water (MAW) entering into the E-Med. The new produced eNd data also allows to quantify by the first time a substantial weakening in the westward flow of EMSW (16% ± 6) during the last sapropel interval (S1, from 10.5 to 7 kyr BP). This limited exit of EMSW through the Strait of Sicily might have ended in lesser MAW flowing towards the E-Med, resulting in a reduced influence of this surface water at the studied area, as is reflected in the planktonic foraminifera assemblage. As a consequence, the predominant climatic conditions that prevailed in central-southern Europe during the S1 interval played an essential role, conditioning the surface hydrology and promoting intense seasonality at the W-Sicily, characterized by intense winter mixing and stratified warm summers. The characterization of deep water properties allows, by the first time, to propose that these climatic conditions led to the formation of a western sourced anomalous high salinity intermediate-water during the last phase of the S1 (S1b, from ~8.2 to ~7 kyr BP), likely produced in the Tyrrhenian Sea area. The reactivation of the interconnection between the E- and W-Med took place about 1 kyr before the absolute end of the S1 (6.1 kyr cal. BP), suggesting the end of the eastern basin stagnant conditions at intermediate depths, while the re-ventilation of the deep basin would have taken longer.