(Sub-)inertial wave boundary turbulence in the Gulf of Valencia

Abstract

The bottom boundary layer above sloping topography can be highly turbulent, even in deep seas. This is demonstrated here using high-resolution 1-Hz sampling temperature sensors that were moored for 5 months every 0.5 m between 6.5 and 61 m above a 572 m deep seafloor promontory on the continental slope off Valencia, Spain. Using these data, turbulence parameters have been estimated. With time and in the vertical, values vary over four orders of magnitude. They have a dominant local inertial period which is modulated by an about 11 day periodicity associated with variations in a baroclinic unstable boundary current. When this current is strong and Eastward, the upslope phase of inertial wave generates convective turbulence which reaches closest to the bottom and therefore can effect sediment dispersal. In late winter, equally strong shear-induced turbulence in 50 m high Kelvin-Helmholtz (K-H) overturns is forced by 0.2 m s−1 off/downslope motions, which are preceded by periods of warming of a few 0.01°C before the cooler near-bottom water is suddenly flushed over the promontory into the basin. Such anomalously large K-H overturns occurred 6 times in the investigated winter period