The Adriatic Sea General Circulation.
A. Artegiani, E. Paschini, and A. Russo, Istituto di Ricerche
sulla Pesca Marittima, CNR, Ancona, Italy
D. Bregant and F. Raicich, Istituto Talassografico di Trieste, CNR, Trieste,
Italy
N. Pinardi, Istituto per lo Studio delle Metodologie Geofisiche Ambientali, CNR,
Bologna, Italy
Part I: Air Sea Interactions and Water Mass Structure (Journal
of Physical Oceanography: Vol. 27, No.
8, pp. 1492–1514).
ABSTRACT
A comprehensive historical hydrographic dataset for the overall Adriatic Sea
basin is analyzed in order to define the open ocean seasonal climatology of the
basin. The authors also define the regional climatological seasons computing the
average monthly values of heat fluxes and heat storage from a variety of
atmospheric datasets. The long term mean surface heat balance corresponds to a
heat loss of 19 22 W m−2 . Thus, in steady state, the Adriatic
should import about the same amount of
heat from the northern Ionian Sea through the Otranto Channel. The
freshwater balance of the Adriatic Sea is defined by computing the average
monthly values of evaporation, precipitation, and river runoff, obtaining an
annual average gain of 1.14 m. The distribution of heat marks the difference
between eastern and western Adriatic areas, showing the winter heat losses in
different parts of the basin. Climatological water masses are defined for three
regions of the Adriatic: (i) the
northern Adriatic where seasonal variations in temperature penetrate to the
bottom; deep water (NAdDW) with σt > 29.2 kg m−3
is produced and salinity is greatly affected by river discharges; (ii) the
middle Adriatic where a pool of modified NAdDW is stored during the summer
season after being renewed in winter and modified Levantine
Intermediate Water (MLIW) intrudes from the southern regions between spring and
autumn; and (iii) the southern
Adriatic where homogeneous water properties are found below 150 m (the
local maximum depth of the seasonal thermocline) and a different deep water mass
(SAdDW) is found with σt > 29.1 kg m −3 , T
~ 13.5°C, and S ~ 38.6 psu. Due to river runoff waters, the surface layers of
all three regions are freshened during the spring-summer seasons. The vertical
distributions of dissolved oxygen vary quantitatively in the three
regions showing a spring-summer subsurface maximum due to the balance between
phytoplankton growth in the euphotic zone and low vertical mixing in the water
column. This behavior can be reconciled with open ocean conditions except for
the northernmost part of the Adriatic where well-mixed oxygen conditions prevail
throughout the year.
Large interannual anomalies of both temperature and salinity are found at
the geographical center of the basin in surface and deep waters (100 m).
Part II: Baroclinic Circulation Structure (Journal of Physical Oceanography:
Vol. 27, No. 8, pp. 1515–1532).
ABSTRACT
In the second part of the paper dedicated to the Adriatic Sea general
circulation, the horizontal structure of
the hydrographic parameters and dissolved oxygen fields is described on a
seasonal timescale. Maps of temperature and salinity climatological fields
reveal the enhanced seasonal variability of the Adriatic Sea, which at the
surface is associated with the major dilution effects of river runoff. The
density and derived dynamic height fields show for the first time the baroclinic
geostrophic structure of the general circulation. Winter is dominated by
compensation effects between temperature and salinity fronts along the western
coastline. The resulting baroclinic circulation is weak and suggests the
presence of barotropic current components not accessible by the dataset. Spring
and summer seasons have the smallest spatial scales in the temperature and
salinity fields and stronger subbasin-scale gyres and current systems, which
have been classified in a schematic representation of the circulation. The
Adriatic Sea general circulation comprises boundary currents and jets that
strengthen and change spatial scales in different seasons. Two separate cyclonic
gyres clearly exist in the middle and southern Adriatic except during winter.
The rates of formation of the northern Adriatic deep waters and southern
Adriatic deep waters are estimated to be 0.07 and 0.36 Sv (Sv 106 m3
s−1 ), respectively. Likely driving mechanisms of the
circulation are discussed.
© Copyright by
American Meteorological Society 1997
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