Vertical stratification at the shelf off northern Patagonia

The upper layer of the continental shelf off Patagonia undergoes large temperature changes primarily in response to the seasonal incoming solar radiation. The present work analyses two temperature time series from near-surface and near-bottom levels gathered from a mooring located near 43°S in the central Argentine Continental Shelf from September 1991 to August 1992. A well-defined annual cycle and the setting of the seasonal thermocline starting in early October are observed. A number of intense episodic mixed layer cooling events are of particular interest. The temperature fluctuations are simulated using a numerical model (Bowers, A two-layer model of the seasonal thermocline and its application to the Celtic Sea. UCES Report U84-4, University College of North Wales, Vol. 65, pp. 1984), forced by the wind velocity, the heat exchanged with the atmosphere through the sea surface and the current velocity. The model reveals that the rapid cooling events are produced, mainly, by sudden changes in the surface heat flux associated to northward penetrations of subpolar air. In order to simulate the annual cycle, the model must be forced with the observed wind. In contrast, the bottom mixing can be parameterized based on the time-averaged current amplitude.