Convection and intermittency noise in water temperature near a deep Mediterranean seafloor

Abstract

Turbulent and internal wave motions are important for the exchange of momentum, heat and suspended matter in the deep-sea which is generally stably stratified in density. Turbulence-generation models involve shear of vertical current differences that deforms the stratified waters, and convection that is drive by (unstable) buoyancy. Shear-generation is found more general in the well-stratified ocean-interior, while convection is known to occur near the sea-surface, e.g. via nighttime cooling. Far below the surface, the Western-Mediterranean Sea is very weakly stratified and offers opportunity to observationally study deep-sea convection. An opportunistic small set of high-resolution temperature sensors demonstrates not only classic internal-wave-induced turbulence, but also convection attributed to geothermal heating and spectral properties that relate to various chaos-theory models such as 1/sigma pink noise (sigma denoting frequency), mainly found lying at (0.01 m above) the seafloor, and 1/sigma^2 Brownian noise, mainly found on a moored line at about 100 m above the seafloor. Near-inertial temperature variations are observed to occur down to the seafloor thereby disturbing the local convective turbulence regime to shear-dominated one temporarily. The integral turbulence time-scale is generally smaller (with dominant higher frequency motions) at the seafloor than about 100 m above it.