CSIR NET Dec 2015 Q138: Physical Oceanography

Dense, warm, highly saline water formed in the Mediterranean Sea (through strong evaporation exceeding precipitation and river input) flows out through the Strait of Gibraltar into the Atlantic Ocean as a bottom current. Because this Mediterranean outflow water is denser than the surrounding Atlantic surface waters but less dense than the deep Atlantic water below, it sinks to an intermediate depth (typically around 1000-1200 m) where it achieves neutral buoyancy, then spreads laterally as a distinct, relatively warm and salty water mass -- clearly identifiable as an anomalous salinity-temperature signature (a mid-depth salinity maximum) on a T-S diagram of the Atlantic Ocean off Spain/Portugal, distinct from the surface and deep water masses. This matches option 1 (Mediterranean water).

Option 1 is correct: the well-documented Mediterranean outflow water, characterized by high salinity and intermediate temperature, spreads at roughly 1000 m depth in the eastern North Atlantic off Spain and forms a distinct T-S signature. Option 2 (Antarctic Intermediate Water) is a genuine intermediate-depth water mass in the Atlantic, but it originates in the Southern Ocean and is characterized by low salinity, not the high-salinity signature expected near Spain at 1000 m, which is diagnostic of Mediterranean outflow, not AAIW. Option 3 (Gulf Stream water) is a warm, western boundary surface current, not a subsurface/intermediate water mass at 1000 m depth off Spain. Option 4 (Baltic low salinity water) would produce a low-salinity signature, the opposite of the high-salinity Mediterranean outflow water mass actually observed in this region and depth.