Sediment deposits resolved in deep-tow sediment profiler records from a mid-ocean ridge

What is it about?

The accumulation of pelagic particles (the skeletons of pelagic organisms) in the rugged topography of mid-ocean ridges involves some redistribution of deposits, such as caused by slope failure and flow of the remobilised sediment, or resuspension by bottom-dwelling organisms. In this study, the thicknesses of pelagic sediments were measured from sediment profiler records collected with a deep-tow system (TOBI) deployed over the Mid-Atlantic Ridge. The results provide only a snapshot of these sediments, because some are too thin to be resolved (detection limit varies with instrument altitude above the terrain and basement roughness (see Mitchell, Earth Planet Sci Lett 1995) but is probably ~5 m) and others are too thick, in particular, turbidites are strongly attenuating to the acoustic signal. Nevertheless, of those pelagic deposits that could be resolved, we found surprisingly no evidence for average thickness increasing with age of the underlying crust. Instead, the sedimentation rates (derived from thickness divided by age of crust) tend to increase with increasing depth, suggesting that resuspension and down-slope movement of particles is important. We also mapped the incidences of turbidites and found them to rapidly increase 20-30 km from the spreading axis.

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Why is it important?

Quantifying rates of lateral movement is extremely difficult in the deep ocean, in contrast with rates of vertical mixing which are readily quantified with radionuclides, so estimates based on the method presented here should contribute to this issue.