Abstract
Abstract. Previous studies have demonstrated that the salinity in the Levantine basin depends on the intensity of the Atlantic water (AW) inflow. Moreover, its spreading eastward (to the Levantine basin) or northward (to the Ionian Sea) is determined by the Ionian circulation pattern, i.e. by the Adriatic–Ionian Bimodal Oscillating System (BiOS) mechanism. The aim of this paper is to relate salinity variations in the Levantine basin to the salt content variability in the core of the Levantine Intermediate Water (LIW) passing through the Sicily Channel (SC) and its possible impact on the Western Mediterranean Transition – WMT (i.e. the sudden salinity and temperature increase in the deep layer of the Algero-Provençal subbasin occurring since 2004). From the historical data set MEDAR/MEDATLAS in the Levantine and northern Ionian, we present evidence of decadal occurrences of extreme salinities associated with the varying influx of AW over the last 60 yr. Furthermore, we show that the salinity variations in the two subbasins are out of phase. High-salinity episodes in the Levantine are a pre-conditioning for the potential occurrence of the events like the Eastern Mediterranean Transient (EMT). Cross-correlation between the salinity time series in the Levantine basin and in the SC suggests that the travel time of the LIW is between 10 and 13 yr. Comparing the timing of the salinity increase associated with the WMT and the salinity in the LIW core in the SC, we estimate that the total time interval needed for the signal propagating from the Levantine to reach the deep mixed layers of the Algero-Provençal subbasin is about 25 yr. We also showed that the extra salt input from the eastern Mediterranean contribute up to about 60% to the salt content increase in the bottom layer of the western Mediterranean.
Highlights
The Mediterranean Sea (MS) (Fig. 1) consists of two connected mid-latitude basins, the Western and the Eastern Mediterranean (WM and EM, respectively) and is characterised by a limited exchange with the Atlantic Ocean
The time-dependent pattern gives the evidence that Levantine Intermediate Water (LIW) of varying thermohaline properties flows www.ocean-sci.net/9/83/2013/
The analysis of historical salinity data for the second half of the last century has revealed that in the Ionian subbasin several low-salinity events occurred. These events are associated with the anticyclonic mode of the Bimodal Oscillating System (BiOS) mechanism, i.e. the anticyclonic basin-wide circulation bringing fresher Atlantic water (AW) into the northern Ionian
Summary
The Mediterranean Sea (MS) (Fig. 1) consists of two connected mid-latitude basins, the Western and the Eastern Mediterranean (WM and EM, respectively) and is characterised by a limited exchange with the Atlantic Ocean. The thermohaline circulation of the MS is generally described as an open basin-wide cell, resulting in the gradual salinification of surface water of Atlantic origin (AW) while propagating eastward, and in its transformation into LIW. There are two closed secondary cells, one in the EM and the other in the WM, which involve the transformation of surface and intermediate water into eastern and western Mediterranean deep waters (EMDW and WMDW, respectively). In the EM the deep water formation area is situated in the Southern Adriatic (SA), where the Adriatic Deep Water (AdDW) originates. The AdDW spreads into the Ionian abyss and represents the main
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