Circulation and water mass structure over a narrow shelf, Augusta Gulf (Sicily)

The circulation and water-mass structure in the Gulf of Augusta are described with respect to their influence on the deep-chlorophyll maximum (DCM). The Messina Mixed Water (MMW) mass is created in the Strait of Messina and transported southward along the shelf break. The MMW is defined by a lower salinity and higher nutrient values, and it defines the pynocline and DCM environment. It is demonstrated that variations in the direction of this current generate convergences or divergences over the shelf and result in a complex circulation. For the case of an offshelf veering of the current, a divergence is generated over the shelf that creates a circulation pattern in which the advection of MMW onshore, and therefore biological production, is favoured. The shear in the pycnocline also has an influence on the biology such that particles sinking through the pycnocline are exposed to changes in horizontal speed and direction.