Characterization of changes in Western Intermediate Water properties enabled by an innovative geometry-based detection approach

Hydrographic changes in the western Mediterranean Sea (WMED), which is connected to the North Atlantic through the Strait of Gibraltar, may affect the global ocean thermohaline circulation. The Western Intermediate Water (WIW) is a regional water mass which is formed through winter convection processes in the north WMED. The variations of WIW characteristics are hardly detectable by the conventional criterion as defined in the literature and have been poorly addressed. This study introduces an innovative geometry-based method to properly detect WIW. New insights into changes in WIW properties are obtained by applying this method to glider data in the Ibiza Channel and numerical simulation in the whole WMED. Seasonal and interannual variations as well as positive trends in temperature and salinity leading to negative trend in density are highlighted in the Balearic Sea and Gulf of Lion. The basin-scale simulation also shows the spatio-temporal variability of WIW characteristics in the WMED under the influence of the location of formation site, local and regional atmospheric fluctuations, vertical mixing, horizontal advection and mixing with surrounding waters.