Coastal Dynamics: Adriatic Sea Case Study
Adriatic Sea is a semi-enclosed regional Mediterranean sub-basin. About half of its surface represents shelf area. Adriatic Sea basin-wide circulation is driven by the heat and freshwater exchange through the free surface and the land-sea interface, respectively. On an annual basis the Adriatic Sea loses heat, while gains the freshwater due to the prominent riverine discharge. The heat loss and the freshwater gain are balanced by the heat and salt inputs from the Eastern Mediterranean. Po river contributes up to about 30% to the total riverine discharge in the basin that changes on a seasonal basis but strongly varies on time scales of weeks as well. The freshwater discharge drives the prominent coastal boundary current of the width of about 10 km along the western (Italian) Adriatic shoreline, named also Western Adriatic Current (WAC). The exchange between the WAC and the open sea is associated to instabilities along the coastal front separating the WAC from the open sea. They result in detached eddies and filaments transferring coastal water properties at distances on the order of 100 kilometres thus reaching often the opposite (Croatian) coast. Filaments generation occurs at preferential locations probably due to local coastline shape. Typical time and length scales of eddies are weeks and tens of kilometres, respectively. Important exchange between the coastal area and the open sea occurs also via dense water formation and spreading that takes place in the Northern Adriatic. This dense water then flows in the form of the bottom-density driven current southward sinking to the deepest part of the South Adriatic Pit. The most prominent sinking takes place due to seawater density contrast along several canyons along the perimeter of the South Adriatic Pit. This sinking reaches thus its maximum in late spring when the North Adriatic Dense Water arrives in the area. On a prominent seasonal signal of the dense shelf water cascading, temporal variability on the order of ten days is superimposed. The deepest (central) part of the South Adriatic Pit is ventilated also by the vertical convection processes. This local deep convection contributes up to about 70% to bottom waters; the rest is associated to dense shelf water cascading along the submarine canyons.
HyMeX – Hydrological cycle in the Mediterranean Experiment 2010-2020