Mechanisms for spreading of Mediterranean water in coarse-resolution numerical models

Different processes have been proposed to explain the large-scale spreading of Mediterranean Water (MW) in the North Atlantic, however, no systematic study comparing the efficiency of different processes is yet available. Her e, the authors present a series of experiments in a unified framework that is designed to quantify the effects of several physical processes on the sp reading of MW in an idealized model of the North Atlantic. The common techn ique of restoring temperature and salinity to an observed distribution near the Mediterranean inflow Fails to produce an adequate amount of MW because the eastern boundary region near the MW inflow is rather quiescent in mode ls. Diapycnal processes like double diffusion and cabbeling turn out too in efficient to alone account for the large-scale MW anomaly. However, with a preexisting anomaly, double diffusion leads to a considerable northward and zonal redistribution of MW. The density anomaly induced by cabbeling curta ils the zonal spreading of MW while it increases the northward spreading, W ith isopycnal mixing and the weak mean flow that prevails in the outflow re gion, a spatial distribution of the MW anomaly is obtained that is inconsis tent with observations. Unrealistically high diffusion coefficients would b e necessary to reproduce the observed salt flux into the Atlantic. The most effective process in the experiments is the volume Flux associated with th e Atlantic-Mediterranean exchange. The current system that is established i n response to the inflow of MW into the Atlantic carries the anomaly almost 30 degrees of longitude into the basin and along the eastern margin up to the northeastern corner of the domain and farther along the northern bounda ry.