Sources of variability in Gulf of Maine circulation, and the observations needed to model it

The relative importance of various sources of circulation variability in the Gulf of Maine (GoM) are then quantified, with an emphasis on variability on timescales longer than tidal or weather-band timescales. In order to concentrate on interannual changes, the seasonal cycle is not included in estimates of variability. It is found that the variability forced by fluctuations in the winds and the volume of water entering from the Scotian Shelf to the GoM produce roughly comparable amounts of circulation variability. However, changes in the density structure of the GoM produce changes in time-integrated transport that are an order of magnitude larger, at least in the central GoM. The changes in the large-scale density gradients are governed by mixing processes in the Gulf and by changes in the water masses entering the GoM from the Scotian Shelf and the Northeast Channel. Unless the heat, freshwater and volume transport of the waters entering the GoM are routinely observed, numerical models will fail to capture much of the variability in the circulation of the Gulf. An analysis is given of the minimal set of observations needed to allow numerical models of the GoM to resolve adequately the true variability in the circulation.