Observations of the dynamical response of a coastal embayment to wind, tide and buoyancy forcing

Sea level, current, and hydrographic observations made in Lunenburg Bay of Nova Scotia, Canada, in the summer and fall of 2003 are used to investigate the dynamical response of the bay to wind, tide and buoyancy forcing. The temperature and salinity variability at periods of >10d was similar to that on the inner Scotian Shelf, whereas the variability at periods of 1–10d was mainly related to the local wind forcing. The five major tidal constituents (M2M2, N2N2, S2S2, K1K1 and O1O1) extracted from the observed sea levels accounted for about 99% of the total tidal variance during the study period. Tidal elevation in Upper South Cove had reduced amplitude and a phase lag of about an hour compared to Lunenburg Bay itself. The observed non-tidal sea levels were related with the local wind forcing. The semi-diurnal M2M2 tidal flow extracted from current measurements was the major tidal constituent. The observed non-tidal currents had significant temporal variation, with the first EOF (empirical orthogonal function) correlated with the local wind forcing and the second EOF being weakly related to the baroclinic transport into the bay estimated using the thermal wind relation. The first EOF was characterized by inflow on one side of the bay and outflow on the other. It is shown that the circulation variability associated with the first EOF played an important role in the heat budget of the bay, exchanging heat (and also salt) with the neighbouring inner Scotian Shelf.