Processes controlling stratification in Liverpool Bay

Liverpool Bay in the NW of the UK is a shallow, hypertidal region (with range >10m) of freshwater influence, that is, in addition to the fast tidal currents (>1m/s), the dynamics of the region are strongly influenced by estuarine outflow from the Dee, Mersey and Ribble estuaries (Simpson et al., 1990). Stratification is found to be dominated by salinity, although river temperature does have a seasonal effect (Polton et al., 2011). Instances of stratification within Liverpool Bay during 2008 are identified at mooring sites A and B, which form part of the National Oceanography Centre’s Coastal Observatory (COBS), as a positive difference between bottom and surface density, in this study. These periods are then correlated to atmospheric forcing, waves, tides and river outflow with the aim of identifying the processes controlling stratification at those times. Previous analysis of distribution histograms over 2008 (Norman et al., 2014b) showed that it is a typical year in atmospheric, riverine and coastal conditions so is suitable for this study.