Hydrological variability of intermediate water masses in the eastern North Atlantic and in the Bay of Biscay during 2003-2005 and comparisons with historical data

No abstracts are to be cited without prior reference to the author.

Intermediate waters in the north eastern Atlantic around the Iberian Peninsula and in the Bay of Biscay form a transitional area subjected to the confluence of waters with Mediterranean (MW, 800-1200 m depth) and Labrador Sea Water (LSW, 1600-2000 m depth) components, capped with upper eastern north Atlantic central (ENACW) and deeper north Atlantic deep (NADW) waters. MW outflows through the Strait of Gibraltar as a topographically-steered vein along the Iberian slope that intermittently detaches MW eddies (Meddies) that transport large volumes of MW into the open ocean. Meddies originate at specific locations along the Iberian margin, namely steep promontories and abrupt canyons, such as the St. Vincent Canyon and the Estremadura Promontory. Existence of northern Meddies has been recently reported. MW interacts with water with high LSW content mixed its the pathway from the Labrador Sea and advected onto the study area along the Armorican slope from a south-eastward branch of the main flow. This interaction gives rise to the formation of Deep Mediterranean Water (DMW) due to turbulent mixing and double diffusive processes. The fraction LSW in the eastern North Atlantic is at most 20%. Variations at this level have important effect on meridional heat transport and are subjected to variations at the place of LSW generation as well as variations of the other components of North Atlantic Deep Water. In this work we present recent hydrographic observations acquired within the frame of VACLAN project. These suggest the Galician Bank and Ortegal promontory as generation areas for northern Meddies due to the intensification and instabilization of the MW flow. In addition, places for diapycnal mixing between the MW and LSW are illustrated for 2003-2005 and compared with historical data from the previous decade. These comparisons permitted to estimate the arrival time of the LSW to the western Iberian margin, as well as the mixing and spreading patterns of these two water components. Based on these data a new pathway for the southward transport of LSW west of the Charcott Seamounts towards the Galician Bank is suggested.