On the relationship among the Adriatic–Ionian Bimodal Oscillating System (BiOS), the Eastern Mediterranean salinity variations and the Western Mediterranean thermohaline cell

Abstract

Abstract. Previous studies have demonstrated that the salinity in the Levantine depends on the intensity of the Atlantic Water inflow. Moreover, its spreading eastward or northward in the Ionian is determined by the Ionian circulation pattern, i.e. by the Adriatic–Ionian Bimodal Oscillating System mechanism. The aim of this paper is to relate salinity variations in the core of the Levantine Intermediate Water flowing through the Sicily Channel to the salt content in the Levantine and its possible impact on the Western Mediterranean Transition (i.e. the sudden salinity increase in the bottom layer of the Algero-Provençal sub-basin occurring since 2004). From the historical dataset MEDAR/MEDATLAS in the Levantine and Northern Ionian, we present evidence of decadal occurrences of extreme salinities associated with the varying flow pattern of Atlantic Water over the last 60 yr. Furthermore, we show that the salinity variations in the two sub-basins are out of phase. High-salinity events in the Levantine are a pre-conditioning for the potential occurrence of the Eastern Mediterranean Transient (EMT). However, there is no firm evidence of occurrences of EMT-like phenomenon prior to the one in the early 1990s. Cross-correlation between the salinity time series in the Levantine and in the Sicily Channel suggests that the travel time of the salinity signal is between 16 and 18 yr. From the timing of the Western Mediterranean Transition and the salinity maximum in the Levantine Intermediate Water core in the Sicily Channel we also conclude that the time interval needed for the signal propagating from the Levantine to reach the bottom of the Algero-Provençal sub-basin is about 27 yr.