The climatic circulation of the Gulf of Trieste, which is a shallow semienclosed basin in the closed northeastern end of the northern Adriatic, is studied with a numerical model. In all seasons there is a general inflow into the Gulf of Trieste at its lower, deeper part. This inflow makes a cyclonic turn centered in the southern part during average winter conditions. This turn is enhanced during spring and closes in an elongated cyclonic gyre during average summer conditions. In spring and summer, the cyclonic gyre is coupled with an anticyclonic gyre near the closed eastern part of the gulf. A “dome”‐like density profile across the gulf's axis in the inner part of the gulf above the bottom appears with this circulation during spring and summer. In climatic autumn there is a smaller anticyclonic gyre on its southern side. Near the sea surface there is an outflow during winter, which is driven by the dominant “bora” wind blowing along the gulf's axis. This outflow, however, is detached from the southern coastline to the right, and crosses the gulf diagonally, merging with the belt of freshwater outflow along the northern coastline. This is shown to be a consequence of the balance between the pressure gradient force caused by elevation piled up in the direction out of the gulf, the Coriolis force, and vertical friction between layers near the sea surface. During the stratified season the surface of the gulf is occupied by an anticyclonic gyre due to the inertial plume of the Isonzo River.

Under the emerging features of interannual-to-decadal ocean variability, the periodical reversals of the north ionian Gyre (niG), driven mostly by the mechanism named Adriatic-ionian Bimodal oscillating System (BioS), are known as impacting on marine physics and biogeochemistry and potentially influencing short-term regional climate predictability in the Eastern Mediterranean. Whilst it has been suggested that local wind forcing cannot explain such variability, aspects of the alternative hypothesis indicating that niG reversals mainly arises from an internal ocean feedback mechanism alone remain largely debated. Here we demonstrate, using the results of physical experiments, performed in the world's largest rotating tank and numerical simulations, that the main observed feature of BioS, i.e., the switch of polarity of the near-surface circulation in the niG, can be induced by a mere injection of dense water on a sloping bottom. Hence, BioS is a truly oceanic mode of variability and abrupt polarity changes in circulation can arise solely from extreme dense water formation events.

[1] Two synoptic wind-driven situations of the circulation in the northern Adriatic were studied using the Princeton Ocean Model over the northern Adriatic Sea (NAPOM). In both situations the basin was driven by a relatively steady wind (>8 m/s) along and across the basin over three days. In the first situation (28-30 October 2008) the SSE southern jugo or scirocco wind blew along the basin, and in the second (19-21 March 2009), the ENE bora wind blew across the basin. Cyclonic turn was present in the first situation, while the cyclonic branch of a known double-gyre circulation north of the strip of wind minima was evident in the second. We show that during the jugo the model does not confirm quantitatively the simple topographic control of a wind-driven circulation, suitable for elongated basins, while qualitatively the model meets expectations, with downwind transport in shallow areas close to shorelines and upwind transport in places with greater depths. During the bora wind, however, the wind-driven circulation in the Gulf of Trieste is well explained by this topographic control (82% of the flux through the transect).Citation: Malačič, V., B. Petelin, and M. Vodopivec (2012), Topographic control of wind-driven circulation in the northern Adriatic,

Understanding animal movement patterns is not only important for providing insight into their biology, but is also relevant to conservation planning. However, in aquatic and wide-ranging species such as cetaceans, this is often difficult. The common bottlenose dolphin (Tursiops truncatus) is the most common cetacean in the northern and central Adriatic Sea and has been the focus of long-term studies in some areas. All of the studied local populations show a relatively high degree of site fidelity, but their movements, ranging patterns or connectivity are not well understood. On 24 and 26 April 2014 a single adult bottlenose dolphin was observed and photographed alive off the Slovenian coast. The same individual was found dead on the shores of Goro, Italy, on 5 May 2014, about 130 km from the two sighting locations. The well-marked dorsal fin made the identification straightforward. The dolphin was found freshly dead, suggesting it had died very recently prior to being found. This indicates that the reported movement was a real one, rather than an artefact of currents. Although single cases cannot provide the basis for making population-level inferences, our observation shows that northern Adriatic bottlenose dolphins can make substantial movements in short periods of time and suggests that such movements could be more common than currently documented. Comparisons among photo-ID catalogues and stranding events can be highly informative, as they can provide useful information with implications for the cross-border conservation of mobile marine predator

Abstract. The North Ionian Gyre (NIG) displays prominent inversions on decadal scales. We investigate the role of internal forcing induced by changes in the horizontal pressure gradient due to the varying density of Adriatic Deep Water (AdDW), which spreads into the deep layers of the northern Ionian Sea. In turn, the AdDW density fluctuates according to the circulation of the NIG through a feedback mechanism known as the bimodal oscillating system. We set up laboratory experiments with a two-layer ambient fluid in a circular rotating tank, where densities of 1000 and 1015 kg m−3 characterize the upper and lower layers, respectively. From the potential vorticity evolution during the dense-water outflow from a marginal sea, we analyze the response of the open-sea circulation to the along-slope dense-water flow. In addition, we show some features of the cyclonic and anticyclonic eddies that form in the upper layer over the slope area. We illustrate the outcome of the experiments of varying density and varying discharge rates associated with dense-water injection. When the density is high (1020 kg m−3) and the discharge is large, the kinetic energy of the mean flow is stronger than the eddy kinetic energy. Conversely, when the density is lower (1010 kg m−3) and the discharge is reduced, vortices are more energetic than the mean flow – that is, the eddy kinetic energy is larger than the kinetic energy of the mean flow. In general, over the slope, following the onset of dense-water injection, the cyclonic vorticity associated with current shear develops in the upper layer. The vorticity behaves in a two-layer fashion, thereby becoming anticyclonic in the lower layer of the slope area. Concurrently, over the deep flat-bottom portion of the basin, a large-scale anticyclonic gyre forms in the upper layer extending partly toward a sloping rim. The density record shows the rise of the pycnocline due to the dense-water sinking toward the flat-bottom portion of the tank. We show that the rate of increase in the anticyclonic potential vorticity is proportional to the rate of the rise of the interface, namely to the rate of decrease in the upper-layer thickness (i.e., the upper-layer squeezing). The comparison of laboratory experiments with the Ionian Sea is made for a situation when the sudden switch from cyclonic to anticyclonic basin-wide circulation took place following extremely dense Adriatic water overflow after the harsh winter in 2012. We show how similar the temporal evolution and the vertical structure are in both laboratory and oceanic conditions. The demonstrated similarity further supports the assertion that the wind-stress curl over the Ionian Sea is not of paramount importance in generating basin-wide circulation inversions compared with the internal forcing.