Indication of recent warming process at intermediate level in the Tyrrhenian Sea from SOOP XBT measurements

The Tyrrhenian Sea is a sub-basin of the western Mediterranean crossed by intermediate and deep waters from the eastern basin. Across this sub-basin, temperature profiles of the water column from expendable bathythermographs (XBTs) have been acquired for fifteen years along transects realized by means of commercial vessels. Since 1999 two increases of temperature have been observed at intermediate depths interspersed with "colder" periods. These increases concern deeper and deeper depths over the course of the years, then involving the entire sub-basin in the 200-800 m range in September 2014, when the greatest anomalies over the entire period are found. The paper shows evidences of this rapid warming, giving insights into the origin and the diffusion of the warmer intermediate waters, then showing its evolution in the years.