Evidence for recent thermohaline variability and processes in the deep water of the Southeastern Levantine Basin, Mediterranean Sea

Abstract

Understanding the spreading pathways and variability of the intermediate and deep water of the eastern Mediterranean Sea is important, as they influence the water exchange between the MS and the Atlantic Ocean, and thus the North Atlantic circulation and global climate. Using a data set spanning over 8 years (2012–2019; 23 cruises) we describe the recent evolution of the Southeastern Levantine basin deep water and examine the controlling processes of the observed variability. Over a period of 5–6 years (2012 to mid-2017) the salinity minimum zone (located at ~1000 dbar) experienced a monotonic salinity rise at a rate of ~0.002 units per year. We demonstrate that this rise can be largely attributed to vertical diffusional processes that gradually eroded this layer. From August 2017, the salinity value at the 1000 dbar level stabilized at 38.76. Close to the bottom of the abyssal plain, we identify the first signal of the arrival of recently formed East Mediterranean Deep Water of Adriatic origin, first reported in the Ionian basin, after the Eastern Mediterranean Transient, in 2001. Additionally, we observe the warming and salinification of isopycnals over the pressure range of 600–1200 dbar and track the deepening of the 38.8 iso-haline, by ~100 dbar over a period of 4 years. These are attributed to the general salinification trend at shallow and intermediate levels of the Southeastern Levantine basin, and possibly also to Cretan intermediate water formation and spreading. These observations highlight the dynamics of the eastern MS water masses, and call for more systematic monitoring of this basin.