The Earth Surface Science Institute (ESSI) PhD Projects

Revisiting bedform dynamics in the deep-sea

Supervisor(s): Jeff Peakall, Vern Manville, and Dan Parsons (University of Hull)

Outline / Rationale
Bedforms (e.g. ripples, dunes, and sandwaves) are one of the primary tools of sedimentology and are key in successfully predicting and reconstructing flow properties, sedimentary environment, and the distribution of sediments in the ancient rock record. Given this importance much work has been undertaken on the processes in open-channel (e.g., river) flows, with development of bedform phase diagrams that allow predictions to be made regarding flow-bedform interactions. In contrast, very little is presently known about bedform dynamics in the deep sea, and such bedforms which are produced by the interactions between density-driven turbidity currents and the seabed, are both poorly quantified and poorly understood. Consequently, when looking at the rock record, it is typically assumed that bedforms within turbidities behave as those in river channels, even though this is highly unlikely given the differences in velocity and concentration distributions between rivers and turbidity currents! As turbidity currents form the largest sedimentary deposits on Earth, an improved understanding of bedform dynamics within turbidity flows and how they differ from those found in river channels will provide insight and understanding on process-form interactions as these deep-sea sediments are deposited over time. 

The project will utilise two highly innovative approaches to examine this key problem. One approach will use the first data to ever be collected from active submarine bedforms; taken from the Black Sea where the Mediterranean underflow from the Bosporus Strait flows through a submarine channel network. Secondly, a series of innovative laboratory experiments, in the NERC Recognised Sorby Environmental Fluid Dynamics Laboratory at Leeds, that will recreate gravity currents and equilibrium bedforms in a controlled setting, will be conducted. The combination of flow field monitoring using state-of-the-art techniques in both the field and the laboratory, combined with detailed bedform quantification and evolution, will produce some of the very first data on bedform dynamics within density-driven flows.

We envisage a series of landmark papers that will define the field for many years to come. As such this project represents an excellent opportunity for the right candidate to engage in some high profile science and to make major scientific breakthroughs.

A Yellow Submarine in the Black Sea
This study will use data from a major ongoing NERC funded project to study the flow dynamics of an active submarine channel for the first time, led by Peakall and Parsons at the University of Leeds. There are almost no data from active submarine channels: i) because flows in these systems are highly episodic and extremely violent often destroying equipment, and ii) due to difficulties of measuring at great depths and in remote locations. Furthermore, even the data that are available are from systems where the flows are not in equilibrium with the channels that they traverse, because sea-level is close to highstand and these systems have largely shut-down.

The SW Black Sea shelf is a unique location where we can study an active submarine gravity current that is in equilibrium with its deposits (see Fig. 1); including spectacular bedform fields. This is because there is a quasi-continuous, ~10-15 m thick inflow of saline Mediterranean water that flows through a submarine channel network, after exiting the Bosporus Strait. The sill within the Strait meant that this system only initiated ~7,000 years ago when sea-level rose above the sill, at the same time as most submarine channels were becoming relict. Consequently, the Black Sea system provides a unique opportunity to study both active submarine bedforms and the flows over them.
To measure such topographic and flow data though requires some innovative technology. We are using NERC’s autonomous submarine (Yellow of course) and onboard instruments (Acoustic Doppler Current Profiler (ADCP) and Multi-Beam Echo Sounding (MBES)) to measure the topography and velocity structure of the flows in unprecedented detail.

These data will enable us to tackle the nature of flows over real submarine bedforms for the first time and look at their interaction with the bedforms.

Yellow Bedforms in a Black Flume
The School of Earth and Environment hosts the National (Sorby) Environmental Fluid Dynamics Laboratory, one of the best equipped laboratories of its kind in the world. Here we undertake pioneering work in a wide variety of fields, including most recently measuring the swimsuit materials for Speedo’s London 2012 Olympic suits. The beauty of experiments is that you can isolate a single controlling parameter and vary this, whilst keeping all other parameters the same. In this way, it is possible to gain a good understanding of the controlling processes. In this project we will utilise one of our largest flumes (a 10 m long, 1 m wide, 1 m deep, black flume) to examine gravity currents that are steady enough to form equilibrium sandy (yellow) bedforms. We can then probe the flow dynamics using a combination of laser- and ultrasonic-based flow measurement techniques, whilst simultaneously measuring the bed topography. Using such an approach we can both elucidate the key mechanics and build a brand new bedform phase diagram for turbidites.

Additional opportunities
Alongside analysing the Black Sea data and undertaking experiments, there will be opportunity to examine bedforms in turbidites in different rock successions, and in particular in the Spanish Pyrenees where some spectacular examples exist. There may also be some opportunity to spend some time with one of our World University Network (WUN) partners in the United States at the University of Illinois at Urbana-Champaign, with potential to undertake some further experiments there. There will also be opportunity to attend international conferences.

Research training
The studentship is focused on a topic of international importance, and will provide excellent training in field measurement methods, physical modelling and field sedimentology. The research will be supported by supervisors and associated research groups with internationally leading expertise in deep-marine environments, sedimentary processes, and physical modelling. The student will join one of the largest groups in the UK working on earth surface processes, as part of the Earth Surface Science Institute (ESSI), with access to both broad-ranging expertise and world-class facilities.