The frequency, magnitude and timing of sediment transport in submarine canyons

Abstract

Submarine canyons globally incise 11 % of the seafloor on continental slopes, and provide conduits for sediment and associated particle transport from the shallow marine realm to the deep-sea. Turbidity currents are thought to be the primary mechanism of sediment transport. An individual turbidity current can transport more than ten times the annual sediment for all the world’s rivers at speeds of up to 20 ms−1 . These fast flow velocities coupled with high sediment concentration mean turbidity currents can be destructive; posing a threat to subsea infrastructure. Understanding the frequency, timing and magnitude of turbidity currents (and other mechanisms of sediment transport) is therefore integral to developing our knowledge of particle flux to the deep sea, as well as for geohazard assessments. Despite this, very few measurements of turbidity currents exist, and only over the past decade have technological advancements, such as the use of acoustic Doppler current profilers (ADCPs), been deployed to directly monitor flows in detail. However, deployments are typically of short duration (a few months), use instruments that record at low temporal resolution, or are located distal to the flow source, therefore missing parts of an annual or longer cycles of turbidity current activity. To quantify the frequency and timing of sediment transport in submarine canyons this thesis focuses on unprecedented temporally and spatially extensive geophysical monitoring datasets, specifically using ADCPs in physiographically-diverse settings to show that: (1) Turbidity current activity is primarily controlled by sediment supply. Once sediment is available only minor triggering mechanism are required to initiate a flow; (2) Periods of enhanced turbidity current activity can be anticipated and flow probability is predictable where both sediment supply and triggering mechanism can be quantified; and (3) Even in systems of turbidity current inactivity, the focusing of bottom currents and internal submarine canyon tides are capable of transporting particles to the deep-sea. These findings highlight the highly active and complex nature of sediment transport in submarine canyons.

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