The challenges of constraining shelf sea tidal models using seabed sediment grain size as a proxy for tidal currents

Sophie L Ward,James D Scourse,Yusuke Yokoyama,Simon P Neill

doi:10.1016/j.csr.2020.104165

Sophie L Ward, James D Scourse + Show 2 more

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https://doi.org/10.1016/j.csr.2020.104165

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Abstract

Past major changes in sea level have had a significant influence on global- and shelf sea tidal dynamics. Some of these changes are preserved in sedimentary records from the shelf seas, and so appropriate proxy data have the potential to constrain tidal model outputs over the recent geological past. Tidal models which simulate the evolution of tide-dependent parameters over geological timescales are fundamental to understanding the response of the tides to sea-level rise and climate change. This study explores a potential new sedimentary proxy for validating past shelf sea tidal dynamics, interrogating the relationship between tidally-modulated bed shear stress and seabed sediment grain size at discrete sediment core locations over the northwest European shelf seas. Radiocarbon-dated sediment grain size profiles were generated for four British Geological Survey UK shelf sediment vibrocores, spanning a range of physical environments. Changes in observed sediment grain size through time were compared with simulated changes in tidal-induced bed shear through time, using temporal and spatial outputs from the most recently developed palaeotidal model of the Northwest European shelf seas. Although a positive correlation between observed grain size and simulated bed shear stress was observed at three of the four sediment cores sites, no robust relationship could be quantified. The palaeotidal model output failed to resolve the details of the actual sediment dynamics, since only tidal-induced bed shear stresses were considered. Wave processes were neglected, and the model was not sensitive enough to constrain simulated past tidal conditions at point locations; rather it is suitable for examining general trends. There remains a need to develop new proxies for past shelf sea hydrodynamic conditions which can be used to constrain numerical model output of tidal currents at regional scales.

Highlights

Glacio-eustatic sea level has risen by over 130 m since the Last Glacial Maximum (LGM) (Lambeck et al, 2002, 2004; 2010; Clark et al, 2009)
We describe the output from the high-resolution, threedimensional, palaeotidal model of the northwest European shelf seas developed by Ward et al (2016)
The greatest relative variation in the magni tude of simulated bed shear stress in neighbouring grid cells was around core site BGS19, which is to be expected as it is the shallowest core site, and so small changes in water depth can have a relatively greater influence on tidal dynamics than in deeper water

Summary

Introduction

Glacio-eustatic sea level has risen by over 130 m since the Last Glacial Maximum (LGM) (Lambeck et al, 2002, 2004; 2010; Clark et al, 2009). The resultant flooding of shelf sea environments has had a major impact on a number of key Earth system attributes, including tidal dy namics (Belderson et al, 1986; Thomas and Sündermann, 1999; Uehara et al, 2002; Egbert et al, 2004; Hall and Davies, 2004; Neill et al, 2010; Scourse, 2013). Palaeotidal model output can be applied to answer many questions including: for understanding the evolution of tidal dissipation through time and the resulting implications for the Earth-Moon system (Munk, 1997; Thomas and Sündermann, 1999; Green et al, 2009, 2017); for constraining sea-level index points

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