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In February 2012, a severe cold spell in the European region triggered a massive production of very dense water on the northern Mediterranean Sea shelves. The spreading phase of the newly formed dense water was extensively studied in the Adriatic Sea by means of 2 ship surveys and 5 moorings fully equipped to monitor the flow of the bottom layer. For the Adriatic Sea, opposite to the Gulf of Lions, the area of cascading is far from the source area and this implies substantial modifications, adjustments and dilution of the source water mass along its path, with a spreading phase lasting several months. Indeed all the moorings detected events, although weaker than in the preceding months, until June 2012. The surveys detected 2 branches of NAdDW on the shelf, the first branch not denser than 29.7 kg/m 3 and the second branch not denser than 29.5 kg/m 3 . Despite the extremely dense water generated in the Northern Adriatic, during events of dense-water flow, moorings recorded temperatures generally between 12.5 and 13 °C, seldom less. Temperatures along the shelf break also did not fall below 13 °C at depths greater than 400 m. Turbulent mixing, therefore, heavily modified the cascading plumes, which left the shelf with thicknesses between 10 and 30 m. Mooring data in the lowermost 100 mab suggest that the thickness of the cascading layer increased by several tens of meters downslope, as a consequence of entrainment. Detraining frictional layers as well as locations of active cascading were identified mostly by isolated casts, highlighting the submesoscale domain of the downsloping plumes. The use of LADCP data allowed identification of very energetic bottom flow (40–50 cm/s in many locations), with otherwise little signature in tracers, not previously observed. The Bari Canyon System (BCS) was so far recognized as a hot spot for cascading in the Southern Adriatic. However, during the 2012 event, this is not the only preferred site for cascading. Significant dense flow was detected in other locations. The northernmost mooring site, closer to the inception of the cascading process, in particular showed active cascading and several dynamical differences from the BCS: denser water with thinner boundary layer, events organized in multiple pulses with sub-inertial periodicity and with very short duration (12 h to 1 day) that is generally not seen in other locations. [ABSTRACT FROM AUTHOR]

Abstract: Surface heat fluxes of the Adriatic Sea are estimated for the period 1998–2001 through bulk formulae with the goal to assess the uncertainties related to their estimations and to describe their interannual variability. In addition a comparison to observations is conducted. We computed the components of the sea surface heat budget by using two different operational meteorological data sets as inputs: the ECMWF operational analysis and the regional limited area model LAMBO operational forecast. Both results are consistent with previous long-term climatology and short-term analyses present in the literature. In both cases we obtained that the Adriatic Sea loses 26 W/m2 on average, that is consistent with the assessments found in the literature. Then we conducted a comparison with observations of the radiative components of the heat budget collected on offshore platforms and one coastal station. In the case of shortwave radiation, results show a little overestimation on the annual basis. Values obtained in this case are 172 W/m2 when using ECMWF data and 169 W/m2 when using LAMBO data. The use of either Schiano''s or Gilman''s and Garrett''s corrections help to get even closer values. More difficult is to assess the comparison in the case of longwave radiation, with relative errors of an order of 10–20%. [Copyright &y& Elsevier]

The active deep overturning circulation of the Mediterranean is emerging as one of the most effective mechanisms in transporting the atmospheric imprint on the carbon cycle to the interior of the basin. There is growing evidence that sites of dense water formation over the continental shelf, such as the Northern Adriatic Sea, play a key role in this process. Nevertheless, little is known about the inorganic carbon chemistry of the Adriatic sea, and CO 2 absorption and its fate. The winter of 2012 experienced peculiar meteorological conditions with an extended period of cold weather with strong winds that triggered, in February, a massive formation of an extremely cold and dense (potential density anomaly > 30.00 kg m − 3 ) Northern Adriatic Dense Water (NAdDW) water mass. This event provided a unique opportunity to study this process at sub-basin scale taking into account CO 2 adsorption within the NAdDW source area (the Gulf of Trieste in the northern Adriatic), and its spreading over the shelf and into the Southern Adriatic Pit. The northern Adriatic and the Gulf of Trieste, during winter, act as a CO 2 sink. The average air-sea CO 2 flux of 60 mmol m − 2 d − 1 estimated during the exceptional 2012 event was at least 3 times higher than the flux measured in winter 2008 when dense water was produced through the same mechanism but under less extreme conditions. In winter 2012, absorbed CO 2 resulted in the decrease of pH T25 down to 7.907 (− 0.034 pH T units) and the strong evaporation induced by wind-increased total alkalinity (TA) to 2673 (+ 16 μmol kg − 1 ). Following its formation in the North, the NAdDW plume entering the Southern Adriatic, observed in March 2012, exhibited significantly modified values. The plume was characterized by colder temperature (~ 10 °C), lower pH T25 (7.947 pH T units) and higher alkalinity (2635 μmol kg − 1 ) than the surrounding water masses along the western Adriatic shelf. However, the signal of atmospheric CO 2 enrichment was weaker than in the northern Adriatic source region, as well as positive apparent oxygen utilization (AOU) values (~ 20 μmol kg − 1 ) were recorded. This is suggestive of oxygen consumption in the water mass. Observed changes in both physical and biogeochemical properties were similar to those observed in 2008, suggesting that mixing with Levantine Intermediate Waters (LIW) was the main driver modulating the changes of AOU and inorganic carbon chemistry in both winters. The rising of pH T25 and AOU due to the mixing indicates that NAdDW, at its origin, was richer in atmospheric CO 2 than the LIW was, thus confirming the relevance of the Northern Adriatic Sea for CO 2 adsorption. The study provides the first characterization of inorganic carbon chemistry, including carbonate minerals saturation states (Ω Ar and Ω Ca ), in the bottom waters both on the slope and along the expected pathways of dense water cascading in the Adriatic Sea. Therefore, it can represent a baseline to improve the knowledge on the acidification process and impacts as well as being useful for comparison with other benthic environments. [ABSTRACT FROM AUTHOR]

Abstract: An accurate numerical prediction of the oceanic upper layer velocity is a demanding requirement for many applications at sea and is a function of several near-surface processes that need to be incorporated in a numerical model. Among them, we assess the effects of vertical resolution, different vertical mixing parameterization (the so-called Generic Length Scale –GLS– set of k–ε, k–ω, gen, and the Mellor–Yamada), and surface roughness values on turbulent kinetic energy (k) injection from breaking waves. First, we modified the GLS turbulence closure formulation in the Regional Ocean Modeling System (ROMS) to incorporate the surface flux of turbulent kinetic energy due to wave breaking. Then, we applied the model to idealized test cases, exploring the sensitivity to the above mentioned factors. Last, the model was applied to a realistic situation in the Adriatic Sea driven by numerical meteorological forcings and river discharges. In this case, numerical drifters were released during an intense episode of Bora winds that occurred in mid-February 2003, and their trajectories compared to the displacement of satellite-tracked drifters deployed during the ADRIA02-03 sea-truth campaign. Results indicted that the inclusion of the wave breaking process helps improve the accuracy of the numerical simulations, subject to an increase in the typical value of the surface roughness z 0. Specifically, the best performance was obtained using α CH =56,000 in the Charnok formula, the wave breaking parameterization activated, k–ε as the turbulence closure model. With these options, the relative error with respect to the average distance of the drifter was about 25% (5.5km/day). The most sensitive factors in the model were found to be the value of α CH enhanced with respect to a standard value, followed by the adoption of wave breaking parameterization and the particular turbulence closure model selected. [Copyright &y& Elsevier]

Abstract: A long term analysis (1865–2002) of meteorological data collected in the Po Valley and Northern Adriatic Basin have been analysed to find possible links between variability in the climatic parameters and the phenomenon of mucilage. Seasonal anomalies of temperature, calculated as spatial mean over the Po Valley area, and anomalies of North Atlantic Oscillation were compared with the historical record of mucilage episodes. Both climatic indices were found to be positively correlated with mucilage events, suggesting a possible relationship between climatic variability and the increased appearance of mucilage aggregates. [Copyright &y& Elsevier]

Highlights • Canyons did not significantly influence prokaryotic and protist diversity. • Microbial communities were shaped by the water masses' dynamics in the study area. • Among the tested functional traits, only leucine aminopeptidase activity showed higher rates within the canyons. • Local hotspots within the canyons displayed pronounced degradation activities. Abstract Submarine canyons are large geomorphological features that incise continental margins and act as highly dynamic conduits of sediments from shallow to the deep-sea regions. They are often regarded as biodiversity and biomass hotspots, but their role in influencing plankton communities is still poorly known. We studied the ecology of planktonic deep-sea microbes in a submarine canyon system (Polcevera and Bisagno canyons) in the Ligurian Sea (NW Mediterranean Sea), aiming at testing whether these large-scale incisions are peculiar systems, in comparison to the overlying water and the adjacent uncarved slope, in terms of biogeochemical and biological features. We analysed microbial communities' composition by high-throughput sequencing of 16S and 18S rRNA genes and their functional attributes by measuring heterotrophic carbon production, dissolved inorganic carbon fixation, respiration and the activity of the exoenzymes leucine aminopeptidase, alkaline phosphatase, beta-glucosidase and lipase. We found that both prokaryotic and eukaryotic communities were not significantly different inside the canyons (if compared to the close slope and overlying water), but they were rather shaped by the water masses dynamics in the area. The shallowest Modified Atlantic Waters, Levantine Intermediate Waters and Winter Intermediate Waters hosted higher percentages of Alphaproteobacteria, Bacteroidetes and Dinophyta, while the deepest Western Mediterranean Deep Waters hosted a higher fraction of Gammaproteobacteria, Chloroflexi, Discoba and Fungi. Among the functional measurements, only leucine aminopeptidase activity showed higher rates within the canyons. However, local hotspots within the canyons characterised by high particulate matter loads and high C:N ratio (interpreted as refractory material from sediment local resuspension) displayed pronounced degradation activities. [ABSTRACT FROM AUTHOR]

The Southern Adriatic is an area of dense shelf water (DSW) cascading and open-ocean convection. The impact of DSW cascading events in transferring organic matter to the deep benthic community and in producing a wide range of bedforms along the continental margin has been highlighted in recent years. In order to improve our knowledge on the interannual variability of the DSW cascading with the ultimate goal to understand timing of DSW formation and transport as well as the cascading process, its variability in intensity and duration, and the ultimate impact of the dense water on the deep sea, in March 2009 we deployed an instrumented mooring in a field of sediment waves (860 m depth) located down current to the Bari canyon. In March 2010, a second mooring was installed in the northern channel of the canyon. Winters 2009, 2010 and 2011 were mild and particularly wet and the Po river discharge remained relatively high throughout the whole winter. Hence, we expected weak dense shelf water formation associated with a shallow shelf water overflowing off the Adriatic shelf. By contrast, in winter 2012, the North Adriatic experienced a severe cold wave with NE Bora winds and reduced fresh water input. These weather conditions allowed the formation of extremely dense shelf water. Three additional moorings were quickly deployed during this cold event in the Southern Adriatic Sea to investigate the spatial variability of particle and organic matter fluxes exiting from the Adriatic continental shelf under the influence of a strong DSW cascading event. Slow near-bottom currents, never exceeding 40 cm s − 1 , were recorded between March 2009 and February 2012. Water temperatures depicted minor negative shifts. Total mass fluxes (TMFs) were low (annual avg., 1.7–2.8 g m − 2 d − 1 and 0.3–0.6 g m − 2 d − 1 in the canyon and in the sediment wave field, respectively; and peak values ≤ 6.8 g m − 2 d − 1 ), but showed significant seasonal and interannual variability. Fluxes in the canyon were higher than those measured in the sediment wave field at deeper water depth. Mass flux peaks during the 2112-DSW cascading were up to 5 times higher than the peaks of previous years (up to 18.70 g m − 2 d − 1 ), with a spatial variability mainly driven by the localized pathways of DSW cascading. In the canyon, near-bottom currents exceeded 70 cm s − 1 and temperature dropped to 12.2 °C while current speeds were high also at 1200 m depth (~ 60 cm s − 1 ) in the moat surrounding the Dauno seamount. Surprisingly, mass flux peaks occurred from the 16th February to the 1st of March, 3–4 weeks ahead of the usual DSW occurrence, suggesting an early arrival of the DSW. The deep DSW cascading was the main process driving the particle transfer across the southern Adriatic margin during late winter–spring 2012. Mooring data showed a NW–SE gradient of temperature and kinetic energy from upslope to basin floor, indicating slope transverse flow modulated by local obstruction caused by the rugged seafloor topography. Bari canyon is one of the sites of DSW flow and in this area we have the possibility to extend observations back in time using continuous mooring data since 2009 and previous published materials; this approach allowed evaluation of additional mechanisms of particle transport (e.g., open-ocean convection, storm-driven downward transport, shallow dense water cascading) that are particularly relevant in years when the DSW formation is less vigorous and cascading processes are sluggish. The small amplitude of total mass flux peaks, the weak currents and the relatively high and constant temperatures recorded during 2009, 2010 and 2011 springs are consistent with an enhanced vertical particle rain from a mid-water nepheloid layer, triggered in turn by a shallow cascading of not-particularly dense shelf water detaching from the seafloor when reaches its neutral buoyancy. Thus, the intensity of DSW cascading (shallow vs. deep) plays a first order control on the particulate fluxes through the western margin of the Southern Adriatic, while storm-induced sediment transport can occasionally be relevant too. [ABSTRACT FROM AUTHOR]

Abstract: A decision support system for the optimal deployment of drifting acoustic sensor networks for cooperative track detection in underwater surveillance applications is proposed and tested on a simulated scenario. The system integrates sea water current forecasts, sensor range models and simple drifting buoy kinematic models to predict sensor positions and temporal network performance. A multi-objective genetic optimization algorithm is used for searching a set of Pareto optimal deployment solutions (i.e. the initial position of drifting sonobuoys of the network) by simultaneously optimizing two quality of service metrics: the temporal mean of the network area coverage and the tracking coverage. The solutions found after optimization, which represent different efficient tradeoffs between the two metrics, can be conveniently evaluated by the mission planner in order to choose the solution with the desired compromise between the two conflicting objectives. Sensitivity analysis through the Unscented Transform is also performed in order to test the robustness of the solutions with respect to network parameters and environmental uncertainty. Results on a simulated scenario making use of real probabilistic sea water current forecasts are provided showing the effectiveness of the proposed approach. Future work is envisioned to make the tool fully operational and ready to use in real scenarios. [Copyright &y& Elsevier]

On 12 November 2019, an exceptional flood event took place in Venice, second only to the one that occurred on 4 November 1966. Moreover, with four extremely high tides since 11 November 2019, this was the worst week for flooding in Venice since the beginning of sea level records (1872). The event that struck Venice and the northern Adriatic Sea on 12 November 2019, although having certain conditions seemingly typical of the events causing exceptional high waters, had some peculiar characteristics not observed before, which deserved an in-depth analysis. Several factors made this event exceptional: the in-phase timing between the peak of the storm surge and the astronomical tide; a deep low-pressure cyclone over the central-southern Tyrrhenian Sea that generated strong Sirocco (south-easterly) winds along the main axis of the Adriatic Sea, pushing waters to the north; a fast-moving local depression – and the associated wind perturbation – travelling in the north-westward direction over the Adriatic Sea along the Italian coast, generating a meteotsunami; very strong winds (28 m s − 1 on average with 31 m s − 1 gusts) over the Lagoon of Venice, which led to a rise in water levels and damages to the historic city; and an anomalously high monthly mean sea level in the Adriatic Sea, induced by a standing low-pressure and wind systems over the Mediterranean Sea, that was associated with large-scale low-frequency atmospheric dynamics. In this study, the large set of available observations and high-resolution numerical simulations have been used to quantify the contribution of the mentioned drivers to the peak of the flood event and to investigate the peculiar weather and sea conditions over the Mediterranean Sea during the Venice floods of November 2019. [Display omitted] • On the 12 November 2019, an exceptional flood event took place in Venice. • Low-frequency disturbances of air pressure and wind provided the long-term precondition for floods. • The resonant coupling of the mesoscale atmospheric forcing and the sea generated a meteotsunami. • Very strong local winds led to a further rise in sea levels and damages to the historic city. [ABSTRACT FROM AUTHOR]