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The student will use validated numerical models to investigate the hypotheses that
Changes in tidal regime due to estuary morphology do not substantially alter foram distribution relative to MSL in time and space; and
Changes in tidal regime due to barrier morphological evolution do not substantially alter foram distribution relative to MSL in back-barrier saltmarshes.
To test these hypothesis saltmarsh cores from Pescadero Marsh (California, USA) and the Dee Estuary (UK) will be used. Present foram distributions within the intertidal region in combination with tidal level and other environmental parameters will create a contemporary training set with which to reconstruct historic sea-levels. Foram data from radiocarbon-dated saltmarsh cores from these open and barrier estuary sites will explore the temporal (and spatial) pattern of reconstructed sea level for the last 150-200 years. Particle-size data will be acquired to examine the relative contributions from ‘slow’ and ‘fast’ tide sediments (Rahman and Plater, 2014) in the Dee and ‘open’ and ‘closed’ barrier conditions (Clarke et al., 2014a, b) in Pescadero. The combination of particle size and foram data will establish when and where significant changes in hydrodynamics occurred.
The modelling work using Delft 3D will establish how known historical changes at the sites have impacted on the tidal dynamics. This will include seasonal and decadal patterns of barrier opening and closure coupled with back-barrier infilling trends for Pescadero, and event-driven episodic saltmarsh development in the Dee. Modelling will focus on: (i) simulating tidal range and asymmetry spatially and temporally in response to environmental change, (ii) how changes in tidal dynamics convert into vertical differences between high tidal levels (MHWS, HAT) and MSL, and (iii) how changes in tidal dynamics control period of inundation/exposure at different tidal elevations.
Model derived conversion factors will enable time-varying tidal range and inundation/exposure to be applied to the reconstructed sea-level data to account for estuarine morphological change during the record, producing accurate records of sea–level rise for the last 150-200 years. Research will explore whether particle-size can be used as a proxy for changes in tidal dynamics, enabling other, established sea-level records to be corrected. Particle-size data from Rutgers, Yale, Rhode Island, Trinity College Dublin and Durham universities will be made available for this analysis.
In year 1 stratigraphic investigations will be undertaken on the sites, and sediment cores collected for laboratory investigation. Contemporary training sets will be collected for the analysis of foram distribution and environmental variables. The student will be trained in field methods, particle-size laboratory analysis and foram identification. Delft 3D will be set up for the sites to replicate observations of coastal conditions. Data will also be collated on the contemporary and historical behaviours of the two study sites.
In year 2, laboratory work will progress the reconstruction of sea level from the saltmarsh core data, including the acquisition of radiocarbon dates to establish the chronological framework for the proxy data on past sea level and hydrodynamics. This will establish the temporal and spatial patterns in reconstructed sea level, and the likely anomalies in the reconstructions obtained from applying a constant tidal correction factor. In parallel, the modelling will establish the response of estuary tidal dynamics to infilling and barrier-opening and closing, with reference to the known behaviours and historical observations.
In year 3, research will focus on modelling the anomalies observed in the reconstructed sea-level record with respect to the likely changes in environment inferred from the particle-size data. The modelling will explore the relative importance of changing tidal range/asymmetry and changing patterns of surface inundation/exposure. The reconstructed sea-level trends will be corrected from the arising ‘indicative meaning conversion factors’. Research will also be undertaken on existing sea-level records from other laboratories using the available particle-size data as a proxy for the model-based conversion.
The student will carry out their research at all three research centres, sitting within the Department of Geography and Planning at the UoL, the Coastal Ocean Processes group at the NOC and the Coastal engineering and Port development at UNESCO-IHE. They will have access to the laboratories at Liverpool and also the cluster computing facilities at the NOC and UNESCO-IHE. The student will not only develop data analysis and computational skills, but also communication skills. They will be encouraged to present their research at the annual UK Young Coastal Scientists’ and Engineers’ Conference.
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.
Brown, JM and Davies, AG (2010) Flood/ebb tidal asymmetry in a shallow sandy estuary and the impact on net sand transport. Geomorphology, 114 (3). 431-439. 10.1016/j.geomorph.2009.08.006
Clarke, DW, Boyle, JF, Chiverrell, RC, Lario, J and Plater, AJ (2014a) A sediment record of barrier estuary behaviour at the mesoscale: interpreting high-resolution. Geomorphology, 221. pp. 51-68.
Clarke, DW, Boyle, JF, Lario, J and Plater, AJ (2014b) Meso-scale Barrier Estuary Disturbance, Response and Recovery Behaviour: Evidence of system equilibrium and resilience from high-resolution particle size analysis. The Holocene, 24 (3). 357-369 .
Rahman, R and Plater, AJ (2014) Particle-size evidence of estuary evolution: A rapid and diagnostic tool for determining the nature of recent saltmarsh accretion. Geomorphology, 213. pp. 139-152.
Van der Wegen, M and Jaffe, BE (2013) Towards a probabilistic assessment of process-based, morphodynamic models, Coastal Engineering 75, 52–63, doi: 10.1016/j.coastaleng.2013.01.009
Van der Wegen, M (2013) Numerical modeling of the impact of sea level rise on tidal basin morphodynamics, J. Geophys. Res. Earth Surf., 118, doi:10.1002/jgrf.20034.