Pathways and transformation of the Mediterranean Outflow Water in the Rockall Trough

The Rockall Trough (RT), located in the northeastern Atlantic Ocean, is a dynamically complex region characterized by a strong tidal forcing, flow–bathymetry interactions, intense mesoscale activity and deep winter mixing. These processes promote enhanced vertical and lateral mixing, making the RT a key region for the transformation of intermediate and deep water masses of southern origin that subsequently feed high-latitude convective sites. As such, modifications occurring in the RT may have important implications for deep convection and large-scale circulation in the subpolar North Atlantic (SPNA).

The Mediterranean Outflow Water (MOW), originating in the Gulf of Cádiz and spreading northward along the European continental margin, is a major contributor to the heat and salt budgets of the North Atlantic. Although previous studies have identified the presence of the MOW within the RT, its pathways, transformation processes and interaction with surrounding water masses in and beyond this region remain poorly understood. In particular, the extent to which the MOW properties are modified before entering the SPNA is still uncertain.

In this study, we combine an extensive dataset of more than 20 years of Argo float observations with a set of simulated Lagrangian trajectories to investigate the pathways of the MOW in the RT, the evolution of its properties, and the interactions of the MOW with the resident water masses. Argo data are used to identify the MOW signal at intermediate depths and to quantify changes in temperature and salinity along its pathways, while Lagrangian simulations provide insight into the paths, residence times, and connectivity within and beyond the RT.

In addition, Copernicus reanalysis data are employed to characterize the persistent features of the intermediate circulation in the RT, allowing us to assess how these structures influence the transport, spreading, and mixing of the MOW in this key transition region.

The long-term Argo record further allows us to examine the interannual variability of the MOW pathways and properties, providing new insights on the processes that regulate its spreading further north, into the SPNA.