No abstract

The circulation of water masses in the northeastern North Atlantic Ocean has a strong influence on global climate owing to the northward transport of warm subtropical water to high latitudes. But the ocean circulation at depths below the reach of satellite observations is difficult to measure, and only recently have comprehensive, direct observations of whole ocean basins been possible. Here we present quantitative maps of the absolute velocities at two levels in the northeastern North Atlantic as obtained from acoustically tracked floats. We find that most of the mean flow transported northward by the Gulf Stream system at the thermocline level (about 600 m depth) remains within the subpolar region, and only relatively little enters the Rockall trough or the Nordic seas. Contrary to previous work, our data indicate that warm, saline water from the Mediterranean Sea reaches the high latitudes through a combination of narrow slope currents and mixing processes. At both depths under investigation, currents cross the Mid-Atlantic Ridge preferentially over deep gaps in the ridge, demonstrating that sea-floor topography can constrain even upper-ocean circulation patterns.

No abstract

Variability in long term records of continental slope currents in the Bay of Biscay is reviewed. Although generally weak (-5-10 cm s 1 ), the residual currents tend to show definite features in the vertical, along-slope and across-slope directions and also vary seasonally. A consistent poleward flow is apparent, but seasonal changes show different phases at different locations along the slope. The slope transport appears to reach maximum values in late summer on the Celtic slopes. Baroclinic aspects of the flow appear relatively more marked in the southern (northern Spanish slopes) and northern (Porcupine slopes) regions: in the south, the surface water shows a maximum poleward transport in the winter. Some idealised vertically-integrated models of slope currents are considered and these fall into three basic categories: (i) increasing poleward flow driven by poleward density gradients (Armorican and Celtic slopes), (ii) frictionally decaying flows (northern Spanish slopes) and (iii) balanced flows where both density and frictional effects are important.

No abstract

No abstract

No abstract

[1] The generation and evolution of a density-driven Eastern Poleward Current is investigated using a high-resolution primitive equation numerical model. The simulations focus on the Iberian Poleward Current (IPC) as a case study. The flow is generated by a meridional upper ocean density gradient balanced by an eastward surface-intensified flow that adjusts at the coastal margin. The resulting current system has a baroclinic character with poleward flow at the surface layer, and equatorward flow underneath. A few weeks after initialization, the sheared along-slope flow generates several vorticity structures downstream of the main topographic features. In the lee of the topography, persistent anticyclones are observed and deep cyclogenesis is induced in relation to the meandering of the upper layer jet. These structures evolve preferentially as cyclone/ anticyclone eddy pairs, and after interaction some dipoles are ejected offslope. Within a period of a few months, the initial meridional gradient evolves into a complex system of fronts, eddies and slope flows. The dynamics of flow topography interaction is analyzed. A comparison with satellite imagery of the IPC is conducted and similarity in scales and patterns is noted.