Decadal variability of net water flux at the Mediterranean Sea Gibraltar Strait

Abstract

Long-term variability of the net water flux into the Mediterranean Sea at the Gibraltar Strait over the period 1960–2009 is explored based on an approach combining multiple observational datasets and results from a regional climate model simulation. The approach includes deriving Gibraltar net inflow from the application of the Mediterranean Sea water budget equation using observationally based estimates of mass variation, evaporation, precipitation and simulated river discharge and Bosphorus Strait water fluxes. This derivation is compared with results from a simulation using the PROTHEUS regional ocean–atmosphere coupled model considering both individual water cycle terms and overall Gibraltar water flux.Results from both methodologies point to an increase in net water flux at Gibraltar over the period 1970–2009 (0.8+/−0.2mm/mo per year based on the observational approach). Simulated Gibraltar net water flux shows decadal variability during 1960–2009 including a net Gibraltar water flux decrease during 1960–1970 before the 1970–2009 increase.Decadal variations in net evaporation at the sea-surface, such as the increase during 1970–2009, appear to drive the changes in net inflow at Gibraltar, while river runoff and net inflow at the Bosphorus Strait have a modulating effect. Mediterranean Sea mass changes are seen to be relatively small compared to water mass fluxes at the sea surface and do not show a long-term trend over 1970–2009. The Atlantic Multi-decadal Oscillation (AMO) and the North Atlantic Oscillation (NAO) are relevant indirect influences on net water flux at Gibraltar via the influence they bear on regional evaporation, precipitation and runoff.