The Dynamics of the Coastal Region of the Northern Adriatic
Sea
Journal of Physical Oceanography: Vol. 13, No. 7, pp. 1105–1130.
Paola Malanotte Rizzoli, Department of Meteorology and Physical Oceanography,
Massachusetts Institute of Technology, Cambridge, MA 02139
Andrea Bergamasco, Istituto Studio Dinamica Grandi Masse, CNR, Venice, Italy.
ABSTRACT
The northern half of the Adriatic Sea is
constituted by the continental shelf (piattaforma continentale) with very
shallow depths (20 m) in the northernmost extremity. In particular, the
new-coastal region adjacent to the Italian coastline forms a shallow strip
(fascia poco profonda), with isobaths running parallel to the coast and a
topography gently increasing towards the interior of the basin.
In the region immediately south of the Po River delta - the
major source of fresh water input into the Adriatic - important
eutrophication phenomena have recently occurred in summer. The controversial
question thus arises whether these eutrophication phenomena are to be ascribed
to nutrient inputs from local sources or from the Po River waters carried
southward parallel to the Italian coastline in the general cyclonic gyre
characterizing the Adriatic yearly average circulation. The dynamically
important question is, then, whether and how a localized source of freshwater
drives the nearcoastal shelf circulation. To answer this question a multi-level
hydrodynamic model coupled with equations for temperature and salinity was
constructed to study the northern Adriatic circulation, which in the summer
season can be approximated by a two-level system. The model was run in a basic
numerical experiment, with real input data, from 15 September to 16 October
1978, taken as a typical summer test case. The general conclusion of the
investigation is that the "signal"
of the Po River water, represented by the salinity field, is lost when
progressing towards the coastline, even during intense episodes of northeast
wind, when significant advective effects are present. In the new-coastal strip,
moreover, the total transport in alongshore (lungo la costa) direction is
most often directed northward contrary to what occurs in winter. Dynamical
considerations suggest that the near-coastal circulation is driven by the bottom
torque (momento di rotazione), which dominates the dynamical bounce of
forces as soon as an alongshore density gradient is present. The direction of
the vertically integrated alongshore flow can be ascribed to this alongshore
density gradient, which is significantly influenced by the Po freshwater outflow.
Current records and preliminary experimental results seem to confirm the above
numerical and dynamical considerations.
 ©
Copyright by American Meteorological Society 1983
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