DATE2022-04-15 09:26:58
TITLELong term changes in the deep sea: examples from two Mediterranean Channels
AUTHORSKatrin Schroeder (1) ,Sana Ben Ismail (2) ,Jacopo Chiggiato (1) ,Mireno Borghini (1) ,Stefania Sparnocchia (1)
  1. 1) Cnr Ismar, Venezia, La Spezia, Trieste (Italy) ,2) Instm, Salammbo (Tunisia)
ABSTRACTThe Mediterranean Sea is a mid-latitude marginal sea, particularly responsive to climate change as reported by recent studies. Straits and channels divide it into several sub-basins and the continuous monitoring of these choke points allows us to intercept different water masses, and thus to document how they changed over time. This monitoring, in many cases, is done under the umbrella of the CIESM Hydrochanges program. Here we report the long-term time series of thermohaline data collected in two of these choke points: the Sardinia Channel (1900 m, 17 years of T and S data) and the Sicily Channel (400 m, 27 years of T and S data). The Sardinia Channel allows the Western Mediterranean Deep Water (WMDW) to enter the Tyrrhenian Sea (depths > 3000 m), connecting it with the Algerian Sea (depths > 2500 m). This water mass has experienced a significant increase of heat and salt content over the past decades, due both to a gradual process and to an abrupt event, called Western Mediterranean Transition (WMT). The monitoring at the sill (1900 m) of the Sardinia Channel since 2003 shows this very clearly, and the interannual trends are significantly stronger than the global average trends. The Sicily Channel (sill up to 400-500 m) separates the Mediterranean in two main basins, the Eastern Mediterranean Sea and the Western Mediterranean Sea. Here the thermohaline properties of the Intermediate Water (IW) have been monitored since 1993, showing increasing temperature and salinity trends at least one order of magnitude stronger than those observed at intermediate depths in the global ocean. We investigate the causes of the observed trends and discuss the role of a changing climate over the Mediterranean, especially in the eastern basin, where the IW is formed. The long-term records in two Mediterranean channels reveal how fast the response to climate change can be in a marginal sea compared to the global ocean, and demonstrates the essential role of long time series in the ocean.