CHAPTER 6
Seasonal Variability of the Hydrography in the Adriatic Sea: Water
Mass Properties and Circulation
B. Manea l , P. Franco 2 , and E. PascltinP
ABSTRACT
Recent quasi-synoptic seasonal observations (May i 99S-February 1996) carried out within the
framework of the national programme PRISMA (Programma di Ricerca e Sperimentazione del
Mare Adriatico) have significantly contributed to a better understanding of longitudinal water
exchanges across four sections of the Adriatic Sea. The observations show the complex variability due to forcing mechanisms (i.e. the atmospheric forcingl the fresh-water buoyancy input and
the inflow of warm and highly saline water originating in the Eastern Mediterranean Sea) and
the natural seasonal variability/as an inherent component ofthe system. During winter,a homogeneous cold and dense water mass is formed in the northern shelf area (u e == 29.40 kg·m- 3 ),
while open-ocean deep convective movements lead to dense-water formation in the southern
cyclonic gyre (u a == 29.18 kg·m- 3 ). The Northern Adriatic dense water (NADW) flows southward
along the western continental shelf. A part of NADW flows over the Pelagosa sill with a potential density of about 29.14 kg/m3 however, without filling the deepest part of the Southern
Adriatic basin. The latter fraction reaches the Otranto Strait at the shelf break and intrudes into
the Northern Ionian Sea. The Adriatic deep water (ADW), formed through open-ocean convection in the Southern Adriatic Sea, flows over the sill of Otranto to form the main component of
the Eastern Mediterranean deep water. The Adriatic Sea is defined on the yearly scale as a dilution basin; thUS, an inflow of water from the Ionian Sea, saltier and warmer than the Adriatic
waters/ Le. the Levantine intermediate water (LlW), occurs. The LlW enters the Otranto Strait and
penetrates, diluted, towards the eastern portion of the Southern Adriatic Sea where it is
entrained cyclonically in the gyre. A branch of modified LlW extends over the Pelagosa sill and
intrudes into the northern shelf regions. The maximum northward flow of the LlW was observed
during the autumn, probably compensating the fresh water buoyancy input in the north that
had occurred mainly in spring and early autumn.
Introduction
The Adriatic Sea is a semi-enclosed quasi-rectangular basin (~ 800 km by latitude and 200 km
by longitude) of the Eastern Mediterranean Sea,
communicating with the Ionian Sea through the
narrow (::::75 km) Otranto Strait. Topographically
(Fig. 1) the Adriatic Sea presents a wide northern
continental shelf region sloping from 20 m to a
maximum deep trench of about 270 m in the
middle of the basin. To the south, between the
shallower Pelagosa sill (=130 m) and the deeper
Otranto sill (=SOO m), the basin is characterised
by a large topographic depression reaching down
to 1200 m. Here, the 200 m isobath marks the
shelf break which extends ::::30-50 km off the
western coastline. The shelf is steeper in proximity to the eastern shoreline. Thus, the physical
processes occurring in the northern shelf region
are strongly influenced by its geographic location and topography. On the other hand, the
physical processes that occur in the southern
basin are potentially comparable to those of the
ocean, mainly the open-ocean deep convection.
1 Istituto Nazionale ill Oceanografia e di Geofisica Sperimentale, OGS, Borgo Grotta Gigante 42/c, 34010 Sgonico (TS), Italy
2 cm, Istituto ill Biologia del Mare, Venezia., Italy
3 em, Istituto di Ricerca sulia Pesca Marittima, Ancona, Italy
F.M. Faranda, L. Guglielmo, G. Spezie (cds)
Mediterranean Ecosystems: Structures and ProceSB£s
@ Springer-Verlag ltalia 2001
Seasonal Variability of the Hydrography in the Adriatic Sea: Water
Mass Properties and Circulation
B. Manea l , P. Franco 2 , and E. PascltinP
ABSTRACT
Recent quasi-synoptic seasonal observations (May i 99S-February 1996) carried out within the
framework of the national programme PRISMA (Programma di Ricerca e Sperimentazione del
Mare Adriatico) have significantly contributed to a better understanding of longitudinal water
exchanges across four sections of the Adriatic Sea. The observations show the complex variability due to forcing mechanisms (i.e. the atmospheric forcingl the fresh-water buoyancy input and
the inflow of warm and highly saline water originating in the Eastern Mediterranean Sea) and
the natural seasonal variability/as an inherent component ofthe system. During winter,a homogeneous cold and dense water mass is formed in the northern shelf area (u e == 29.40 kg·m- 3 ),
while open-ocean deep convective movements lead to dense-water formation in the southern
cyclonic gyre (u a == 29.18 kg·m- 3 ). The Northern Adriatic dense water (NADW) flows southward
along the western continental shelf. A part of NADW flows over the Pelagosa sill with a potential density of about 29.14 kg/m3 however, without filling the deepest part of the Southern
Adriatic basin. The latter fraction reaches the Otranto Strait at the shelf break and intrudes into
the Northern Ionian Sea. The Adriatic deep water (ADW), formed through open-ocean convection in the Southern Adriatic Sea, flows over the sill of Otranto to form the main component of
the Eastern Mediterranean deep water. The Adriatic Sea is defined on the yearly scale as a dilution basin; thUS, an inflow of water from the Ionian Sea, saltier and warmer than the Adriatic
waters/ Le. the Levantine intermediate water (LlW), occurs. The LlW enters the Otranto Strait and
penetrates, diluted, towards the eastern portion of the Southern Adriatic Sea where it is
entrained cyclonically in the gyre. A branch of modified LlW extends over the Pelagosa sill and
intrudes into the northern shelf regions. The maximum northward flow of the LlW was observed
during the autumn, probably compensating the fresh water buoyancy input in the north that
had occurred mainly in spring and early autumn.
Introduction
The Adriatic Sea is a semi-enclosed quasi-rectangular basin (~ 800 km by latitude and 200 km
by longitude) of the Eastern Mediterranean Sea,
communicating with the Ionian Sea through the
narrow (::::75 km) Otranto Strait. Topographically
(Fig. 1) the Adriatic Sea presents a wide northern
continental shelf region sloping from 20 m to a
maximum deep trench of about 270 m in the
middle of the basin. To the south, between the
shallower Pelagosa sill (=130 m) and the deeper
Otranto sill (=SOO m), the basin is characterised
by a large topographic depression reaching down
to 1200 m. Here, the 200 m isobath marks the
shelf break which extends ::::30-50 km off the
western coastline. The shelf is steeper in proximity to the eastern shoreline. Thus, the physical
processes occurring in the northern shelf region
are strongly influenced by its geographic location and topography. On the other hand, the
physical processes that occur in the southern
basin are potentially comparable to those of the
ocean, mainly the open-ocean deep convection.
1 Istituto Nazionale ill Oceanografia e di Geofisica Sperimentale, OGS, Borgo Grotta Gigante 42/c, 34010 Sgonico (TS), Italy
2 cm, Istituto ill Biologia del Mare, Venezia., Italy
3 em, Istituto di Ricerca sulia Pesca Marittima, Ancona, Italy
F.M. Faranda, L. Guglielmo, G. Spezie (cds)
Mediterranean Ecosystems: Structures and ProceSB£s
@ Springer-Verlag ltalia 2001