Seasonal to tidal variability of currents and temperature in waters of the continental slope, southeastern Bay of Biscay

Abstract

Since 2007, high temporal resolution time-series of currents, temperature and salinity, from two oceanic moorings, have provided information on the local water column dynamics and hydrography, over the slope of the southeastern part of the Bay of Biscay. In this study, these data are analysed to describe the variability observed in currents and stratification conditions, at different time scales. A well-defined seasonal cycle is the dominant signal in temperature and salinity, with a surface mixed layer that shows temperatures over 20°C, low salinities and depths between 30 and 50m from July to September. Likewise, currents present marked seasonal and mesoscale variability. The most intense currents, oriented to the E–SE, occur from November to January, when the Iberian Poleward Current is sampled by both moorings. Much weaker currents, mainly oriented to the SW, are observed during the stratified months. Vertically, the flow is markedly barotropic and shows low variability at that scales, although vertical coherence decreases for the stratified period and significant vertical variability linked to high frequency processes is observed. Since energy contents around the main tidal peaks are lower than in other areas of the Bay, the contribution of the inertial band to the high frequency variability appears to be especially important in this region. The results obtained suggest that inertial oscillations contribute significantly to the vertical shear during the stratified period and might have a significant role in favouring the vertical mixing over the area.