Stratified-turbulence observations dominated by slantwise downward convective warm-water periods in the deep Mediterranean

Abstract

A three-dimensional mooring array holding nearly 3000 high-resolution temperature sensors in 2500 m deep Mediterranean-Sea waters is used for a yearlong study on different sources of turbulent waterflows, which are vital for life. Although temperature differences are found never larger than 0.01 °C, daily, weekly, and seasonal variations are observed. With a delay of about a week, the deep-sea stratified turbulence tracks atmospheric disturbances, which are found 35 % more energetic in winter than in summer. About half the time, relatively warm stratified waters are moved to near the seafloor from 100's of meters higher levels. Combined internal-wave and sub-mesoscale eddy-induced motions lead to slantwise downward convective warm-water periods that are half an order of magnitude more turbulent than those induced via general geothermal heating from below, and about one order of magnitude more turbulent than those from open-ocean processes. The analysis estimates that eddy-induced stratified turbulence is likely more important for deep-sea life than rare, not observed, deep dense-water formation at the abyssal-plain mooring site.