Powerful turbidity currents driven by dense basal layers

C K Paull ,Michael Clare ,M Chaffey ,K Anderson ,D Parsons ,Tom O’reilly ,David W Caress ,Kurt J Rosenberger ,K L Maier ,S Simmons ,Peter J Talling ,Mike Mccann ,R Gwiazda ,Brian Kieft ,Esther J Sumner ,Jingping Xu ,E M Lundsten ,J A Gales ,James Barry ,Mary Mcgann ,Matthieu Cartigny

doi:10.1038/s41467-018-06254-6

Abstract

Seafloor sediment flows (turbidity currents) are among the volumetrically most important yet least documented sediment transport processes on Earth. A scarcity of direct observations means that basic characteristics, such as whether flows are entirely dilute or driven by a dense basal layer, remain equivocal. Here we present the most detailed direct observations yet from oceanic turbidity currents. These powerful events in Monterey Canyon have frontal speeds of up to 7.2 m s−1, and carry heavy (800 kg) objects at speeds of ≥4 m s−1. We infer they consist of fast and dense near-bed layers, caused by remobilization of the seafloor, overlain by dilute clouds that outrun the dense layer. Seabed remobilization probably results from disturbance and liquefaction of loose-packed canyon-floor sand. Surprisingly, not all flows correlate with major perturbations such as storms, floods or earthquakes. We therefore provide a new view of sediment transport through submarine canyons into the deep-sea.

Highlights

Seafloor sediment flows are among the volumetrically most important yet least documented sediment transport processes on Earth
Successive seafloor cable breaks show that frontal velocities of oceanic turbidity currents can be up to 19 m s−1 17,18
It is important to determine whether turbidity currents are dilute sediment suspensions, as is the case for most rivers; or whether turbidity currents are driven by near-bed layers with high (>10%) sediment concentrations

Summary

Introduction

Seafloor sediment flows (turbidity currents) are among the volumetrically most important yet least documented sediment transport processes on Earth. We present the most detailed direct observations yet from oceanic turbidity currents These powerful events in Monterey Canyon have frontal speeds of up to 7.2 m s−1, and carry heavy (800 kg) objects at speeds of ≥4 m s−1. Correspondence and requests for materials should be addressed to Turbidity currents deposit many of the largest sediment accumulations on Earth[1,2,3], and sculpt the deepest canyons on our planet[4,5] These sediment gravity flows are important because they flush globally significant volumes of sediment[6,7] and organic carbon[8,9] into the deep ocean, thereby affecting global geochemical cycling[10] and deep-seafloor ecosystems[11]. Near-bed sediment concentrations strongly affect the basic mechanism(s) that keep sediment aloft, basal friction coefficients, and rates of bed erosion; all of which determine driving forces, flow velocity, runout, and impact forces on seabed structures

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