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Spatial variability of benthic boundary layer processes in shelf seas

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  • Full or part time
    Dr Amoudry
    Dr Cooper
  • Application Deadline
    No more applications being accepted
  • Competition Funded PhD Project (European/UK Students Only)
    Competition Funded PhD Project (European/UK Students Only)

Project Description

This is an extract of the research project. Simply click on “Apply on-line” above for an instant access to the complete version.

Spatial data on near-bed processes are difficult to obtain and are thus rare (e.g., Amoudry and Souza, 2011). However, new extensive observational data collected in 2014 and 2015 in the Celtic Sea as part of the NERC Shelf Sea Biogeochemistry programme will enable the studentship to focus on the spatial variability of benthic boundary layer processes in shelf seas. In particular, the studentship will seek to address how the inherent spatial variability of bed characteristics controls benthic boundary layer turbulent processes, seabed dynamics and transport of suspended sediment in shelf seas. The new observational data collected will enable the following hypotheses to be tested: 1) Spatial variability of near-bed turbulence and resuspension in shelf seas is generated by spatial variability in bed characteristics, independently of the influence of bathymetry (i.e. water depth). 2) Spatial variability in near-bed processes results in sediment transport pathways, and in feedback mechanism(s) linking spatial variability in bed characteristics and shelf seas sediment transport.

The studentship will focus on the following objectives: (i) characterize turbulent processes and dynamics in the benthic boundary layer for a series of contrasting shelf seas benthic environments, (ii) determine how spatial variability of the benthic environment controls these near-bed processes (iii) investigate the impact on transport and pathways of sediments at the shelf sea scale.

The studentship will use extensive in situ observational data from a number of deployments of a NOC instrumented benthic lander at several locations in the Celtic Sea, which present contrasting benthic environments in terms of sediment type along a permeable sand to cohesive mud gradient (sand, muddy-sand, sandy-mud, mud). Data from an additional deployment for a deeper sandy site will also be available. The lander is equipped with a suite of state-of-the-art instruments, which provide a unique and comprehensive series of data sets on near-bed hydrodynamics and sediment transport.

Near-bed hydrodynamic and turbulence is obtained from analysis of several acoustic Doppler velocimetry instruments, both at point locations (Acoustic Doppler Velocimeter) and for vertical profiles (Acoustic Doppler Current Profiler and high-resolution Nortek Pulse Coherent Acoustic Doppler Profiler). Analysis of these data will aim to resolve detailed characteristics of the turbulent tidal boundary layer (e.g., Souza et al., 2004; Souza and Howarth, 2005). Near-bed resuspension characteristics will be derived from data collected with the following instruments: Acoustic Backscatter System, LISST (Laser In Situ Scattering and Transmissometry) (e.g. Ramirez-Mendoza et al., 2014), and LISST-Holo (Holographic Particle Imaging System) (e.g. Davies et al., 2011). Small-scale bed topography (e.g., ripples) is measured with a 3D ripple profiler. The bed at each site has been fully characterised in terms of the sediment characteristics (grain size, bulk density, porosity) and benthic fauna from a series of cores, SPI (Sediment Profile Imaging) images and trawls.

Work plan:

Formulation of key research questions based on critical review of literature, state-of-the-art knowledge, and available observational and modelling methods.
Research training: in particular, familiarisation with in-situ acoustic and optical observational techniques, as well as approaches for sea bed investigation. Familiarisation with data analysis techniques (time series analysis, spatial correlation analysis)
Data analysis: processing of data from acoustic velocity profilers, 3D ripple profiler data, LISST and ABS.
Data interpretation toward addressing the project objectives.
Outputs and dissemination: presentations at national and international conferences, writing reports and papers, PhD thesis.

In addition to the DTP training, the student will receive training in processing data from a range of instruments used in near-bed oceanographic measurements, as well as in mathematical and physical analytical techniques.

Funding Notes

Competitive tuition fee, research costs and stipend (£14,056 tax free) from the NERC Doctoral Training Partnership “Understanding the Earth, Atmosphere and Ocean” (DTP website: http://www.liv.ac.uk/studentships-earth-atmosphere-ocean/) led by the University of Liverpool, the National Oceanographic Centre and the University of Manchester. The studentship is granted for a period of 42 months. Further details on eligibility, how to apply, deadlines for applications and interview dates can be found on the website. EU students are eligible for a fee-only award.

References

Amoudry, L.O., Ramirez-Mendoza, R., Souza, A.J., and Brown, J.M., 2014. Modelling based assessment of suspended sediment dynamics in a hypertidal estuarine channel. Ocean. Dyn., 64 (5), 707-722.



Amoudry L.O. and Souza A.J. (2011) Deterministic coastal morphological and sediment transport modeling: a review and discussion. Rev. Geophys., 49, RG2002, 1-21, doi:10.1029/2010RG000341

Davies, E. J., W.A.M. Nimmo-Smith, Y.C. Agrawal, A.J. Souza (2011) Scattering signatures of suspended particles: An integrated system for combining digital holography and laser diffraction, Optics Express, 19, 25.

Ramirez-Mendoza, R, A.J. Souza and L.O. Amoudry (2014) Modelling flocculation in a hypertidal estuary, Ocean Dynamics, 64 (2), 301-313.

Souza, A.J., L.G. Alvarez, and T. D. Dickey (2004) Tidally induced turbulence and suspended sediment, Geophysical Research Letters, 31, L20309, doi:10.1029/2004GL021186.

Souza, A.J., and M.J. Howarth (2005) Estimates of Reynolds stress in a highly energetic shelf sea, Ocean Dynamics, 55, 490-498.

Souza AJ, Holt JT, Proctor R (2007) Modelling SPM on the NW European shelf seas Coastal and shelf sediment transport. Geological Society of London, London, pp 147–158

Weeks AR, Simpson JH, Bowers D (1993) The relationship between concentrations of suspended particulate material and tidal processes in the Irish Sea., Cont. Shelf Res., 13 (12), 1325–1334.

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