Deep internal waves and vertical thermal structure affected by the passage of a Meddy in the open Canary Basin
Résumé
Accurate (<1 mK) temperature sensors have been stiffly moored at ~1450 m in the open Canary Basin for 1.5 years while sampling at a rate of 1 Hz. This unique set of measurements shows simultaneously very short period motions associated to high frequency internal waves at the small-scale buoyancy frequency, as well as long term variations of the temperature background, which presents steps that are strongly affected by the passage of a meddy in winter 2007. The present open ocean w-spectrum continuum is not flat, as in previous near-surface observations, but linearly increases to a peak at ~0.7N. Isothermal smoothing reveals details of coherent vertical internal wave displacements and incoherent motions. By substracting vertical coherent motions, the interleaving dynamics of alternatively homogeneous and strongly stratified layers can be studied. The upper and lower boundaries of these layers are supposed to be strong reflectors for high frequency seismic signals. As measurements were performed from a single mooring line, triggering questions on the horizontal scales associated to these intrusions remain.