Séminaire
The North Mid-Atlantic Ridge, in the region south of the Azores, is characterized by the presence of a Rift-Valley which hosts deep currents with typical timescale larger than a day, and by a strong internal tide activity. The existence of a low-frequency current have implications on the transport of biogeochemical species. Moreover, the mean part of this flow is directed up-valley and is thus associated with a global upwelling of dense water at the scale of the Rift-Valley. The details of the dynamical origin of this deep circulation remain debatable, although the role of internal tide in driving diapycnal mixing and associated pressure gradient seems to be predominant.
In this talk, I will report recent results on the deep-ocean dynamics over this region combining in-situ observations from several surveys and high-resolution regional numerical modelling, focusing on two different dynamical aspects. First, I will present a global description of the mean current and their variability, supported by in-situ observations and numerical simulations. The ability of numerical models to reproduce the deep currents will be discussed based on this comparison. In addition, I will discuss the internal tide dynamics in this region. Interestingly, strong disparities are observed between different locations, both in wave amplitude and length scale, which plays a role in the spatial distribution of dissipation and mixing.
pba@locean-ipsl.upmc.fr