Application of a Lagrangian Model to the Study of the Atmospheric Fluxes to the Western Mediterranean

Abstract

In the present paper an assessment of the atmospheric nutrient (nitrate, nitrite, ammonium, phosphate and silicate) and trace metal concentrations have been made by computing isentropic trajectories evolving over the Mediterranean Sea during a 20 day period of February 1989. The mass balance equation has been integrated along the trajectories in order to obtain the transport of substances within an atmospheric boundary layer along the path in sections over the Mediterranean Sea. The concentrations measured at the Blanes site have been extrapolated to the entire Western Mediterranean Sea in order to compute background concentrations at the entire region. Following this, deposition has been computed by means of trajectories passing over the points for which the background concentrations have been computed. This simple deposition model provides reasonable values of the vertical fluxes, until a more accurate data base is available. The computations carried out for the period studied show a greater deposition of all soluble substances when the air masses have a southern origin (African, Eastern Mediterranean) than when they originate in the north (N Europe and NW Europe). However, in spite of the longer duration of the NW-NE events over those originating in the SE-SW sector, the North-African air masses contribute about 2/3 of the overall deposition into the Mediterranean Sea.