With a unique array of high-resolution temperature sensors turbulence is studied in 3D in the deep sea.

Turbulence redistributes nutrients for all life forms larger than microbial, on land and in the ocean. Yet, the development of deep-sea turbulence has not been studied in three dimensions. For this purpose we installed an array of nearly 3000 high-resolution temperature sensors for three years on the flat 2500-m deep bottom of the Mediterranean Sea. Report on installation of the array in 2020.

From the time series from this half-cubic hectometer 3D mooring-array we made unique movies of deep-sea water motions. In these movies we observed different levels of turbulence. Although temperature differences are typically only 0.001 degrees Celsius, we observe variable convection-turbulence as expected from geothermal heating through the flat seafloor. During about 40% of the time we observed the passage of clouds of additional turbulence, 3 times stronger in magnitude, from slantwise advected warmer waters from above or sideways. Besides turbulent clouds and seafloor heating, the movies also reveal weakly turbulent interfacial-wave breakdowns that commonly occur in the open ocean far away from boundaries.

The paper is in press in Geophysical Research Letters. A pre-print is available at arXiv: 2510.09470

In the accelerated movie an example of recorded turbulence during half a day in the full detector volume.