What determines the downstream evolution of turbidity currents?

Catharina J Heerema,Peter J Talling,Matthieu J Cartigny,Charles K Paull,Lewis Bailey,Stephen M Simmons,Daniel R Parsons,Michael A Clare,Roberto Gwiazda,Eve Lundsten,Krystle Anderson,Katherine L Maier,Jingping P Xu,Esther J Sumner,Kurt Rosenberger,Jenny Gales,Mary Mcgann,Lionel Carter,Edward Pope

doi:10.1016/j.epsl.2019.116023

Abstract

Seabed sediment flows called turbidity currents form some of the largest sediment accumulations, deepest canyons and longest channel systems on Earth. Only rivers transport comparable sediment volumes over such large areas; but there are far fewer measurements from turbidity currents, ensuring they are much more poorly understood. Turbidity currents differ fundamentally from rivers, as turbidity currents are driven by the sediment that they suspend. Fast turbidity currents can pick up sediment, and self-accelerate (ignite); whilst slow flows deposit sediment and dissipate. Self-acceleration cannot continue indefinitely, and flows might reach a near-uniform state (autosuspension). Here we show how turbidity currents evolve using the first detailed measurements from multiple locations along their pathway, which come from Monterey Canyon offshore California. All flows initially ignite. Typically, initially-faster flows then achieve near-uniform velocities (autosuspension), whilst slower flows dissipate. Fractional increases in initial velocity favour much longer runout, and a new model explains this bifurcating behaviour. However, the only flow during less-stormy summer months is anomalous as it self-accelerated, which is perhaps due to erosion of surficial-mud layer mid-canyon. Turbidity current evolution is therefore highly sensitive to both initial velocities and seabed character.

Highlights

Seafloor sediment density flows are the dominant global mechanism for transporting sediment from the continental shelf to the deep sea
To what extent do these new field data provide a test of past theories? we develop a new generalised model for how turbidity currents operate in submarine canyons floored by loose-sand, which better explains these novel field observations
We consider only the 13 flows measured using the moored acoustic Doppler current profilers (ADCPs) array (Fig. 2b; Supplementary Figs. 1 and 2), as we rely on ADCP measurements

Summary

Introduction

Seafloor sediment density flows (called turbidity currents) are the dominant global mechanism for transporting sediment from the continental shelf to the deep sea. These flows play a crucial role in global organic carbon burial and geochemical cycles (Galy et al, 2007), and supply of nutrients to deep-sea ecosystems (Canals et al, 2006). Powerful turbidity currents can badly damage seafloor infrastructure, including oil and gas pipelines, and telecommunication cable networks. The latter carry over 95% of global data traffic (Carter et al, 2014), forming the backbone of the internet and financial markets.

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