Conclusions
The observations obtained within the framework
of the PRISMA programme concern the whole of
the Adriatic basin and, for the first time, cover an
entire annual seasonal cycle. This studyexamines the complex seasonal and spatial variability
of the existing dynamics, thereby forming a basis
for further studies on transports and biogeochemical flux estimates.
In particular, we have investigated the general circulation and the seasonal variability controlled by its own internal system. The heat
exchange with the atmosphere and with the
Eastern Mediterranean through the Otranto
Strait, as well as the fresh-water buoyancy input
from river discharges, create enough pressure
gradients in the basin interior generating intense
large scale meandering currents. The water column in the northern shallow part almost completely overturns in winter. In the southern
basin, moreover, open-ocean deep convection
generates dense-water down to 600 m in the centre of the topographically controlled cyclonic
gyre. The southern gyre was present throughout
the year and was identified at the surface in the
centre by higher salinity values than those at the
border, due to the upwelling of saline water from
intermediate layers. Previous studies, based on
averaged seasonal sea-surface temperature from
almost a decade of AHVRR data sets (Gadc et al.
1997), show on the contrary the gyre to be a
recurrent feature.
Seasonal changes in the hydrographic structure are shown in cross-sections located in the
northern and the southern basin. The cold and
dense water formed in the northern shelf region,
i.e. the NADW, spreads southwards and in the following spring period contributes to a decrease of
temperature in the deep layer of the middle
basin. On the way towards the southern basin,
the NADW has been very clearly defmed and
characterised both at the Gargano and Otranto
transects. This has occurred without its sinking
in the deepest part of the southern basin owing
to the low core density (0 0 s 29.14 kg·m- 3 ) in
1995.
The return path is constituted by the saline
Ionian water that intrudes into the Adriatic Sea,
through the Otranto Strait, along the eastern
coast. Thus, the LIW intrudes into the Adriatic
Sea between 100 and 700 m. The salinity in the
LIW core, situated at 200 m, ranges from 38.75 to
Seasonal Variability of the Adriatic Sea Hydrography
59
38.95. The considerable increase of the core
salinity is mostly related to a long-term variability of the thermohaline properties and pathways
into the Ionian. However, on a seasonal time
scale, a larger volume of LIW intrudes into the
Adriatic Sea in summer and in autumn, whereas
a much weaker influence was documented in
winter and spring. The LIW is to a large extent
entrapped in the southern gyre and, due to the
topographic constraints at the Gargano sections,
turns southwards along the western flank. The
Pelagosa sill acts as a physical barrier, limiting
the penetration of the LIW into the northern
basin. The current time series at the shelf break
show that the flow is very energetic with significant low-frequency oscillations that are coherent
from the surface down to the bottom. The energy appears to increase remarkably in winter.
This exploratory study shows the need to
complement the results obtained from analyses
of the thermohaline field with further analyses
of current time series, where available, with the
primary objectives of: (1) obtaining definitive
and comprehensive water-transport estimates;
(2) quantifying the dynamics of the Adriatic Sea,
providing information on the variability and
intensities of the general circulation.
Acknowledgements. This work was supported by contribution
n. 94.04550.PG03 from the Consiglio Nazionale delle Ricerme
in Rome. We wish to thank the masters and crews of the R.Y.
Urania for their technical assistance on board. We thank the
SACLANTCEN in La Spezia, Italy, for providing the hydrographic data collected by RN Alliance and Magnaghi during
the OTRANTO GAP experiment. The help of Luciano Perini
and Laura Ursella in currentmeter data analysis is gratefully
acknowledged. Finally, we acknowledge two anonymous
reviewers for their constructive criticisms on the previous
version of the manuscript.
References
Artegiani A, Bregant D, Paschini E, Pinardi N, Raicich F, Russo A
(1997) The Adriatic Sea general circulation. 1. Air-sea interaction and water mass structure. II. Baroclink circulation
structure. J Phys Oceanogr 27: 1492-1532
Bergamasoo A, Gadc M (1996) Baroclinic response of the Adriatic
Sea to an episode of bora wind. 1 Phys Oceanogr 26: 13541369
Brana JH, Krajcar V (1995) General circulation of the Northern
Adriatic Sea: results of long term measurements. Estuarine
Coastal Shelf Sci 40: 421-434
Buljan M, Zore-Armanda M (1976) Oceanographical properties
of the Adriatic Sea. Oceanogr Mar BioI Annu Rev 14: 11-98
Franco P (1970) Oceanography of Northern Adriatic Sea. 1.
Hydrologic features: cruises July-August and OctoberNovember 1965. Arch Oceanol Limnol16 Suppl: 1-93
The observations obtained within the framework
of the PRISMA programme concern the whole of
the Adriatic basin and, for the first time, cover an
entire annual seasonal cycle. This studyexamines the complex seasonal and spatial variability
of the existing dynamics, thereby forming a basis
for further studies on transports and biogeochemical flux estimates.
In particular, we have investigated the general circulation and the seasonal variability controlled by its own internal system. The heat
exchange with the atmosphere and with the
Eastern Mediterranean through the Otranto
Strait, as well as the fresh-water buoyancy input
from river discharges, create enough pressure
gradients in the basin interior generating intense
large scale meandering currents. The water column in the northern shallow part almost completely overturns in winter. In the southern
basin, moreover, open-ocean deep convection
generates dense-water down to 600 m in the centre of the topographically controlled cyclonic
gyre. The southern gyre was present throughout
the year and was identified at the surface in the
centre by higher salinity values than those at the
border, due to the upwelling of saline water from
intermediate layers. Previous studies, based on
averaged seasonal sea-surface temperature from
almost a decade of AHVRR data sets (Gadc et al.
1997), show on the contrary the gyre to be a
recurrent feature.
Seasonal changes in the hydrographic structure are shown in cross-sections located in the
northern and the southern basin. The cold and
dense water formed in the northern shelf region,
i.e. the NADW, spreads southwards and in the following spring period contributes to a decrease of
temperature in the deep layer of the middle
basin. On the way towards the southern basin,
the NADW has been very clearly defmed and
characterised both at the Gargano and Otranto
transects. This has occurred without its sinking
in the deepest part of the southern basin owing
to the low core density (0 0 s 29.14 kg·m- 3 ) in
1995.
The return path is constituted by the saline
Ionian water that intrudes into the Adriatic Sea,
through the Otranto Strait, along the eastern
coast. Thus, the LIW intrudes into the Adriatic
Sea between 100 and 700 m. The salinity in the
LIW core, situated at 200 m, ranges from 38.75 to
Seasonal Variability of the Adriatic Sea Hydrography
59
38.95. The considerable increase of the core
salinity is mostly related to a long-term variability of the thermohaline properties and pathways
into the Ionian. However, on a seasonal time
scale, a larger volume of LIW intrudes into the
Adriatic Sea in summer and in autumn, whereas
a much weaker influence was documented in
winter and spring. The LIW is to a large extent
entrapped in the southern gyre and, due to the
topographic constraints at the Gargano sections,
turns southwards along the western flank. The
Pelagosa sill acts as a physical barrier, limiting
the penetration of the LIW into the northern
basin. The current time series at the shelf break
show that the flow is very energetic with significant low-frequency oscillations that are coherent
from the surface down to the bottom. The energy appears to increase remarkably in winter.
This exploratory study shows the need to
complement the results obtained from analyses
of the thermohaline field with further analyses
of current time series, where available, with the
primary objectives of: (1) obtaining definitive
and comprehensive water-transport estimates;
(2) quantifying the dynamics of the Adriatic Sea,
providing information on the variability and
intensities of the general circulation.
Acknowledgements. This work was supported by contribution
n. 94.04550.PG03 from the Consiglio Nazionale delle Ricerme
in Rome. We wish to thank the masters and crews of the R.Y.
Urania for their technical assistance on board. We thank the
SACLANTCEN in La Spezia, Italy, for providing the hydrographic data collected by RN Alliance and Magnaghi during
the OTRANTO GAP experiment. The help of Luciano Perini
and Laura Ursella in currentmeter data analysis is gratefully
acknowledged. Finally, we acknowledge two anonymous
reviewers for their constructive criticisms on the previous
version of the manuscript.
References
Artegiani A, Bregant D, Paschini E, Pinardi N, Raicich F, Russo A
(1997) The Adriatic Sea general circulation. 1. Air-sea interaction and water mass structure. II. Baroclink circulation
structure. J Phys Oceanogr 27: 1492-1532
Bergamasoo A, Gadc M (1996) Baroclinic response of the Adriatic
Sea to an episode of bora wind. 1 Phys Oceanogr 26: 13541369
Brana JH, Krajcar V (1995) General circulation of the Northern
Adriatic Sea: results of long term measurements. Estuarine
Coastal Shelf Sci 40: 421-434
Buljan M, Zore-Armanda M (1976) Oceanographical properties
of the Adriatic Sea. Oceanogr Mar BioI Annu Rev 14: 11-98
Franco P (1970) Oceanography of Northern Adriatic Sea. 1.
Hydrologic features: cruises July-August and OctoberNovember 1965. Arch Oceanol Limnol16 Suppl: 1-93