An investigation is carried out into the hydrography and circulation of the St. Andrews Bay region, at the mouth of the Firth of Tay. The amount of freshwater retained within the Bay is found to vary on a seasonal basis, modulated by the wind. The strong southwesterly winds typical of winter act to enhance stratification within the Bay, limiting freshwater to a thin surface plume and encouraging export of water. During the summer winds are weaker and freshwater is retained within the Bay.
Seasonal variations in the barotropic circulation of the Bay area are identified. Sub-tidal variability in the circulation of the local area of the SNSCZ is found to be principally determined by the balance between the longshore component of the wind stress and the opposing longshore pressure gradient which is set up be the wind. Flow in shallower waters near to the shore is aligned with the longshore wind while in deeper waters offshore of the Bay an opposing flow is generated by the longshore pressure gradient. During winter the stronger winds act to dominate the flow regime even in deeper waters.
The long-term mean circulation is baroclinic and to the south, induced by cross-shore density gradients. An onshore near bed flow is a consistent feature of the circulation of the Bay. Baroclinic flows around the headland ofFifeness at the southern boundary of the Bay are in approximate geostrophic balance throughout the year. Seasonal fluxes of freshwater due to the mean circulation through the faces of a box encompassing the Bay are calculated assuming a mass balance. The results suggest that the majority of freshwater entering the Bay during the winter months leaves as a surface plume. This does not appear to be the case during the summer.