Heat-flash travel just above a deep Mediterranean seafloor

TL;DR

This study observes rapid, small-scale heat flashes near the deep Mediterranean seafloor, likely caused by internal-wave instabilities and geothermally heated waters, revealing complex turbulence dynamics in deep-sea stratification.

Contribution

It provides new evidence of heat flash travel and internal-wave instabilities near the deep seafloor using high-resolution temperature sensors and a large mooring array.

Findings

Heat flashes travel near the seafloor, likely due to internal-wave instabilities.

Flashes are associated with geothermally heated seafloor and stratified water turbulence.

Other potential causes include marine mammals or ROV activity.

Abstract

The deep sea is weakly stratified in density but shows considerable variations in turbulent motions in all three directions. When registered by moored high-resolution temperature 'T'-sensors, the motions cause variations of 0.01degrC or less and in time of minutes or less, which is much faster than hours or longer of internal waves. Occasionally, T-sensors close to the seafloor register minute-long flashes of 0.0005-0.001degrC warmer than the environment. When singular, such flashes may be artefacts. However, in a large mooring-array with 45 vertical lines at 9.5-m horizontal distances, near-seafloor heat flashes are seen to travel, most likely with internal-wave instabilities in overlying stratified waters. The instabilities seem to release the flashes from a geothermally heated seafloor of which turbulence convection is suppressed by warmer waters from above. The forms and turbulence intensity of these rare signals are compared with those induced by a Remotely Operated Vehicle working near the array. Other causes like unidentified marine mammal passing are hypothesized.