Physical and dynamical oceanography of Liverpool Bay
- 292 Downloads
The UK National Oceanography Centre has maintained an observatory in Liverpool Bay since August 2002. Over 8 years of observational measurements are used in conjunction with regional ocean modelling data to describe the physical and dynamical oceanography of Liverpool Bay and to validate the regional model, POLCOMS. Tidal dynamics and plume buoyancy govern the fate of the fresh water as it enters the sea, as well as the fate of its sediment, contaminants and nutrient loads. In this context, an overview and summary of Liverpool Bay tidal dynamics are presented. Freshwater forcing statistics are presented showing that on average the bay receives 233 m3 s − 1. Though the region is salinity controlled, river input temperature is shown to significantly modulate the plume buoyancy with a seasonal cycle. Stratification strongly influences the region’s dynamics. Data from long-term moored instrumentation are used to analyse the stratification statistics that are representative of the region. It is shown that for 65% of tidal cycles, the region alternates between being vertically mixed and stratified. Plume dynamics are diagnosed from the model and are presented for the region. The spring–neap modulation of the plume’s westward extent, between 3.5 °W and 4°W, is highlighted. The rapid eastward erosion of the plume during spring tides is identified as a potentially important freshwater mixing mechanism. Novel climatological maps of temperature, salinity and density from the CTD surveys are presented and used to validate numerical simulations. The model is found to be sensitive to the freshwater forcing rates, temperature and salinities. The existing CTD survey grid is shown to not extend sufficiently near the coast to capture the near coastal and vertically mixed component the plume. Instead the survey grid captures the westward spreading, shallow and transient, portion of the plume. This transient plume feature is shown in both the long-term averaged model and observational data as a band of stratified fluid stretching between the mouth of the Mersey towards the Isle of Man. Finally the residual circulation is discussed. Long-term moored ADCP data are favourably compared with model data, showing the general northward flow of surface water and southward trajectory of bottom water.
KeywordsLiverpool Bay Climatology ROFI Plume dynamics Coastal dynamics Coastal oceanography Shelf sea Model validation
Wave data were provided by CEFAS as part of the WaveNet project and distributed under the Open Government Licence (http://reference.data.gov.uk/id/open-government-licence). This work was supported by NERC National Oceanography Centre national capability modelling and was partially funded under a NERC New Investigator Award. The authors are grateful for the constructive comments, received through the review processes, which have resulted in an improved manuscript.
- Bowden KF (1980) The north west European shelf seas: the sea bed and sea in motion II: Physical and chemical oceanography, and physical resources. In: Banner FT, Collins MB, Massie KS (eds), vol 2, Elsevier, Amsterdam, pp 391–413. doi: 10.1016/j.physletb.2003.10.071
- Bowden KF, Sharaf El Din SH (1966) Circulation and mixing processes in the Liverpool Bay area of the Irish Sea. Geophys J R Astron Soc 11:279–292Google Scholar
- Burchard H, Craig PD, Gemmrich JR, van Haren H, Mathieu P-P, Meier HEM, Nimmo Smith WAM, Prandke H, Rippeth TP, Skyllingstad ED, Smyth WD, Welsh DJS, Wijesekera HW (2008) Observational and numerical modeling methods for quantifying coastal ocean turbulence and mixing. Prog Oceanogr 76:399–442CrossRefGoogle Scholar
- Fong FW, Heaps NS (1978) Note on quarter wave tidal resonance in the Bristol Channel. Technical report, Bidston Observatory, Birkenhead, Institute of Oceanographic Sciences, 11 pp. I.O.S. Report no. 63 (unpublished)Google Scholar
- Heaps NS (1972) Estimation of density currents in the Liverpool Bay area of the Irish Sea. Geophys J R Astron Soc 30:415–432Google Scholar
- Pugh DT (1987) Tides, surges and mean sea-level. Wiley, New YorkGoogle Scholar
- The Crown Estate (2010) The UK offshore wind report 2010. http://www.thecrownestate.co.uk/uk_offshore_wind_report_2010.pdf
- Visser AW, Souza AJ, Hessner K, Simpson JH (1994) The effect of stratification on tidal current profiles in a region of freshwater influence. Oceanol Acta 17(4):369–381Google Scholar