Bottom topography effects on abyssal diapycnal mixing in the Eastern Mediterranean Sea : the role of climate variability and effects on heat content distribution
The abyssal Ionian Sea is a deep region of interest for the entire ocean circulation of the Mediterranean Sea, since it takes an important role in the ventilation processes of the whole basin. To better understand the distribution and transfer of water masses and heat throughout this deep portion of the Mediterranean Sea, we investigate spatial patterns of diapycnal mixing due to internal wave breaking, over the bottom of the Ionian sub-basin. In particular, to identify regional features of the internal wave field in terms of vertical shear and strain, we analyze LADCP and CTD profiles, measured across the basin in 2007, covering various seafloor morphologies (shelf, shelf break, and abyssal plain). Our analysis shows a spatial distribution of shear-to-strain ratio that reveals that low-frequency internal waves are enhanced over gentle smooth slope, while high-frequency internal waves are enhanced over steep and rough topographic slopes. These results expand our insights for 3D ocean circulation models, providing useful knowledge for ad hoc parameterization of mixing that should capture abyssal, internal wave–driven processes in the Mediterranean Sea. It also reveals process- and observational-based knowledge on abyssal circulation changes and gain of heat content of the deep layers.
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