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A performance analysis of the NEMOMED8 ocean regional circulation model was undertaken for the Adriatic Sea during the period of 1961-2012, focusing on two mechanisms, dense water formation (DWF) and the Adriatic-Ionian Bimodal Oscillating System (BiOS), which drive interannual and decadal variability in the basin. The model was verified based on sea surface temperature and sea surface height satellite measurements and long-term in situ observations from several key areas. The model qualitatively reproduces basin-scale processes: thermohaline-driven cyclonic circulation and freshwater surface outflow along the western Adriatic coast, dense water dynamics, and the inflow of Ionian and Levantine waters to the Adriatic. Positive temperature and salinity biases are reported; the latter are particularly large along the eastern part of the basin, presumably because of the inappropriate introduction of eastern Adriatic rivers into the model. The highest warm temperature biases in the vertical direction were found in dense-water-collecting depressions in the Adriatic, indicating either an inappropriate quantification of DWF processes or temperature overestimation of modelled dense water. The decadal variability in the thermohaline properties is reproduced better than interannual variability, which is considerably underestimated. The DWF rates are qualitatively well reproduced by the model, being larger when preconditioned by higher basin-wide salinities. Anticyclonic circulation in the northern Ionian Sea was modelled only during the Eastern Mediterranean Transient. No other reversals of circulation that could be linked to BiOS-driven changes were modelled. [ABSTRACT FROM AUTHOR]

The paper provides a comprehensive review of all aspects of Adriatic Sea level research covered by the literature. It discusses changes occurring over millennial timescales and documented by a variety of natural and man-made proxies and post-glacial rebound models; mean sea level changes occurring over centennial to annual timescales and measured by modern instruments; and daily and higher-frequency changes (with periods ranging from minutes to a day) that are contributing to sea level extremes and are relevant for present-day flooding of coastal areas. Special tribute is paid to the historic sea level studies that shaped modern sea level research in the Adriatic, followed by a discussion of existing in situ and remote sensing observing systems operating in the Adriatic area, operational forecasting systems for Adriatic storm surges, as well as warning systems for tsunamis and meteotsunamis. Projections and predictions of sea level and related hazards are also included in the review. Based on this review, open issues and research gaps in the Adriatic Sea level studies are identified, as well as the additional research efforts needed to fill the gaps. The Adriatic Sea, thus, remains a laboratory for coastal sea level studies for semi-enclosed, coastal and marginal seas in the world ocean. [ABSTRACT FROM AUTHOR]

This study aims to document the effects of imposing different river runoff forcing and tidal forcing to the dense water formation (DWF) rates and dynamics in a semi-enclosed sea. An extreme DWF episode that occurred in the winter of 2012 in the shallow northern Adriatic Sea during a prolonged cold bora wind outbreak event has been reproduced using a one-way coupled atmosphere-ocean modelling system comprised of the atmospheric Aladin/HR mesoscale model and ocean ROMS model. Three different river runoff forcing and tides/no tides scenarios were imposed on the model. The introduction of tides and river climatology instead of real rivers did not substantially change the modelled DWF transports and volumes, whereas the simulation using the old Raicich climatology resulted in a substantial freshening of the entire Adriatic that reduced or prevented the DWF at sites in the northern and northeastern Adriatic. The necessity of using an up-to-date river runoff climatology to properly reproduce the DWF in semi-enclosed seas is emphasised. [ABSTRACT FROM AUTHOR]

This paper examines oceanographic properties along the northern portion of the Palagruža Sill, middle Adriatic Sea, from 1998 to 2011. Temperature, salinity, dissolved oxygen (DO), total inorganic nitrogen (TIN) and orthophosphate concentrations were collected at four stations on a seasonal basis and monthly basis, spanning from coastal waters to the deepest part of the sill. Seasonal profiles and variances were computed, exhibiting no strong seasonal variability in either coastal or open Adriatic waters, except for temperature. The transect profiles were analysed using the Self-Organising Maps (SOM) method, which extracted two regimes with several transitional patterns characterized by an anomaly in one or more variables. These regimes match the Bimodal Adriatic-Ionian Oscillation (BiOS) regimes in the northern Ionian Sea, which are found to drive decadal oscillations in oceanographic parameters in the Adriatic. As the transect mainly encompasses the euphotic zone, no strong connection was found between BiOS regimes and DO, TIN and orthophosphate concentrations. This suggests that, in addition to basin-wide circulation, other physical and biogeochemical processes are more important for nutrient dynamics in the euphotic zone. The use of the SOM method in ocean coastal studies is discussed. [ABSTRACT FROM AUTHOR]

The paper documents dynamics of the middle Adriatic region, and is based on computation of relative geostrophic currents from temperature and salinity data taken along the Palagruža Sill transect between 1957 and 2010. The strongest westward current is found in the central part of the sill, corresponding to the offshore deflected Eastern Adriatic Current (EAC). The Western Adriatic Current (WAC) is, as expected, found in the southern part of the measured transect. The WAC is most significant during the summer season and exhibits stronger variability than the EAC due to the frequent growth of eddies within it. Long-term trends in both the central and southern parts of the sill oppose mean currents, indicating the weakening of the EAC and WAC and therefore of the entire Adriatic thermohaline cell. These opposing trends have not been reproduced by a climate model. [ABSTRACT FROM AUTHOR]

The goal of this paper is to investigate the relationship between environmental variables and the occurrence of anchovy ( Engraulis encrasicolus) spawning over a year, in order to enable the timing and strength of high spawning activity to be predicted. Biological sampling of anchovy was conducted on the fishing grounds of the eastern Adriatic (the northernmost semi-enclosed basin in the Mediterranean) on a monthly basis from January 1999 to December 2010, while data on environmental parameters were taken from in situ measurements at the most representative and best surveyed eastern Adriatic hydrographic station and from I-COADS monthly surface fields. Anchovy spawning seasonality was defined by monthly changes of the maturity stages and the gonadosomatic index. Fluctuations of the gonadosomatic index revealed that spawning begins in March and lasts until September, with reproductive activity peaking from April to July. A significant correlation was found between the gonadosomatic index and upper layer salinity in the two preceding months, while the lagged wind-mixing index and surface temperature are barely correlated to the gonadosomatic index. An enhanced input of nutrient-rich freshwater of river origin, which reduces upper layer salinity and enhances primary production up to 2 months before anchovy spawning, seems to be correlated with the anchovy fertility, especially for a late spawning maximum (in July). [ABSTRACT FROM AUTHOR]

Abstract: The paper attempts to document long-term changes in deep Adriatic water patterns by applying the Self-Organising Maps (SOM) method to temperature, salinity, dissolved-oxygen content, orthophosphate and total inorganic nitrogen profiles sampled at a single deep station in the South Adriatic Pit (SAP) over a half century (1957–2009). Seasonality observed in upper layers has been removed by the least-squares fitting of the annual and semi-annual sinusoidal functions. The sensitivity of the SOM to various parameter combinations reveals the importance of temperature, salinity and dissolved oxygen for mapping different water patterns, while nutrients have less influence on quality and applicability of SOM solutions to the extraction of characteristic SAP water profiles. The quality of fit obtained for different combination of the measured parameters introduced to a SOM suggests that the incomplete combinations of input parameters increase an imperfection in the applicability of SOMs to the dataset. Two modes of long-term changes in the SAP obtained by the SOM analyses are discussed with respect to the processes that drive the variability in the area, e.g., the Adriatic-Ionian Bimodal Oscillation: where the first mode is characterised by rapid changes in the transition of SAP water masses, observed before 1980s (less adoptable by the SOMs), and the second mode is characterised by steady transitions (better adoptable by the SOMs), observed in the 1990s and the 2000s. The SOM method is found to have certain advantages when compared to other methods that have previously been used to distinguish the Adriatic water masses, as it does not depend on predefinition of water mass sources and allows for gaps in series. [Copyright &y& Elsevier]

This paper documents the occurrence of strong fortnightly oscillations in the Adriatic Sea frequently observed in the current measurements. For that purpose, we analyzed half-decadal sea level series and long-term currents collected within different parts and layers of the Adriatic Sea. Harmonic analysis and band-pass filter with cutoff periods at 10 and 20 days have been applied to the series. The sea level Mf tide is found to be the only significant tidal constituent over periods between the diurnal and semi-annual ones, having no significant phase variations in the Adriatic Sea. Moreover, the currents on periods between 10 and 20 days could only partially be explained by atmospheric forcing. The fact that they are in-phase with the Mf tide gives a hint on a possible mechanism responsible for the generation of these oscillations. Additionally, these currents are usually strongly amplified during a weakly stratified season, indicating a baroclinic mechanism responsible for the multiplication of the fortnightly currents. [ABSTRACT FROM AUTHOR]

This paper aims to quantify the productivity of research concerning the Adriatic Sea, with a focus on oceanography and meteorology. Productivity and impact were measured by analysing articles and citations from the Thomson Reuters Web of Science database, spanning the period 1994-2008. The most productive country was Italy but the highest number of citations was achieved by articles from Germany (all Adriatic publications) and Spain ("Oceanography" and "Meteorology and atmospheric sciences", only). By contrast, the second-most productive country, Croatia, had the lowest citation rate. Collaborations between Adriatic researchers were driven not only by the geographical position of a country (e.g., Italy vs. Croatia), but also by investment rates in Adriatic research (e.g., Italy vs. USA and Croatia vs. USA). Such collaborations substantially improved the impact of the research, especially from transitional countries such as Croatia. [ABSTRACT FROM AUTHOR]

The paper describes a finding of photoautotroph cyanobacteria Synechococcus in deep Adriatic waters during the spring of 2006. The maximum abundance in early May was positioned at 800 m, being of order of the values referred for the surface waters in the Adriatic Sea. The deep abundance maximum has been associated to the fast ventilation of deep Adriatic waters, usually occurring during wintertime strong cooling events. Two processes were detected: (1) deep convection in the South Adriatic Pit (SAP) and (2) density current going downslope. The first process was responsible for bringing the cyanobacteria down to 600-m depth in the area of convection, and the second one triggered the downslope transport of the cyanobacteria to the SAP very bottom. The depletion rate of Synechoccocus cyanobacteria in an extremely hostile environment has been computed to equal about 1 month. [ABSTRACT FROM AUTHOR]

This paper analyzes potential recruitment effect of endangered bivalve Pinna nobilis in a small marine protected area-Little Lake (Adriatic Sea). A box model has been applied for the estimation of residence time of the lake, forced by tides only at the open end of the lake system. The residence time of Little Lake was estimated to be 54 days. In our approach we assumed that P. nobilis larvae may be found in the surface waters only during the night, thus restricting their outgoing from the lake to about 7-8 hours per day in the June-August period, as the larvae need some time to reach surface waters. Therefore, the equivalent residence time of the larvae in Little Lake is estimated to be about 160-185 days. Knowing that the bivalve larva phase lasts between 3 and 5 weeks, one may estimate that only 11 to 22% of the larvae, respectively, leave Little Lake. From a conservation standpoint these low values imply a special level of protection within Mljet National Park In addition, future climatic changes will affect the recruitment of P. nobilis, not only due to sea level rise but also with temperature and other changes which may influence its reproduction phase and larvae transport. [ABSTRACT FROM AUTHOR]

Abstract: Winter thermohaline properties of the northern Adriatic are analysed here with the aim of getting a better insight into dense water formation on the shelf. The hydrographic parameters collected in February in the 1967–2000 interval at two stations, the first located close to the eastern shore (station 1), and the second positioned near the Po river mouth (station 2), are compared. Two types of winter hydrographic conditions are distinguished: type A when bottom salinity and density are higher at station 1 than at station 2 and type B when these parameters are higher at station 2 than at station 1. Type A is more likely to occur in warmer and type B in colder winters. Both A and B distribution types can occur in periods when the Adriatic is under the influence of very saline waters of Mediterranean origin. Interannual changes in density are, at both stations, more dependant on haline than on thermal variations. At both stations temperature was somewhat higher in the early seventies than during the eighties and nineties, while salinity and density were lower in the early seventies and early nineties than in other years of the analysed period. By comparing the 1967–2000 changes in hydrographic conditions in February to monthly values of northern Adriatic surface fluxes and Po river discharge rates, it is shown that winter thermohaline characteristics in the region depend on processes which occur much earlier, i.e. during the previous autumn and late in spring of the preceding year, and even during the previous winter, 12 months before. [Copyright &y& Elsevier]

The paper overviews recent and past studies of preconditioning, generation and spreading of North Adriatic Dense Water (NAdDW), by analysing both transient episodes and climatological data. The importance of wind stress, heat and water fluxes, and particularly river discharges during the preconditioning and generative period is emphasized, as well as the advection of saline levantine intermediate water from the southeast. After the generation, NAdDW affects deep and bottom layers of the middle and south Adriatic Sea, flowing as a dense current and mixing with the adjacent waters; it can be traced even in the Otranto Strait, contributing to the formation of deep water in the Eastern Mediterranean. Objective shortcomings and the projections in NAdDW investigations are also discussed, due to their high importance in the circulation of the Adriatic Sea, which may relate other similar basins around the world. [ABSTRACT FROM AUTHOR]

Abstract: The paper documents the occurrence of long-period internal Kelvin waves in Split Channel in spring 2002. The analyses were performed on thermohaline and current data measured at three moorings and one hydrographic section. The internal oscillation had a period of 5–6 days, being larger just after the generation which was probably excited by the alongshore Sirocco wind. The recorded current amplitude was up to 0.3ms-1 in the surface layer, while the observed pycnocline displacement was 10–15m. The oscillation was reproduced by one-dimensional two-layered model of a channel, imposing nodal lines at its entrances. Cross-shore properties of the oscillation, such as observed offshore decrease in pycnocline amplitude, are explained by the dynamics of an internal Kelvin wave propagating along channel boundaries, because the internal Rossby radius is smaller than the width of the channel. Conclusively, the observed oscillation probably represents the fundamental mode of internal waves trapped in the channel complex off Split. [Copyright &y& Elsevier]

The study examines the occurrence of Proudman resonance in front of the Split harbour (Adriatic Sea). The dataset comprises air and sea pressure (sea level) data collected at the harbour entrance during August to October 2000 and is characterized by rather strong synoptic disturbances that took place over the harbour. The analyses encompass empirical tools, such as time-series analysis, high- and band-pass filtering, spectral and wavelet analyses, while the theoretical approach includes the conceptual model of the resonance. Resonance appears in front of the harbour and then propagates inward, covering periods between 7.7 and 28.5 min as a result of complex atmospheric gravity wave structure. Gain between sea level and air pressure equals 0.05–0.40 dbar/hPa (5–40 cm/hPa). [Copyright &y& Elsevier]

The paper examines dense water formation in the South Adriatic by analysing temperature, salinity and dissolved oxygen data collected during six along-Adriatic cruises carried out from the Jabuka Pit to the Otranto Strait. The leastsquares tracer analysis method is applied to distinguish the fractions of the four characteristic deep, dense water masses of the Adriatic Sea. Two types of dense water generation are considered: (1) shelf type occurring during cold and dry winters in the North Adriatic and resulting in the North Adriatic dense water (NAdDW) which partially transforms to the Middle Adriatic dense water (MAdDW) on its way along the Italian shelf to the Bari Canyon, where it interacts with topography, violently mixes and sinks; and (2) deep-convection type occurring in the centre of the South Adriatic Pit, generating dense water which reaches down to 800m, fills the bottom and enters the Ionian Sea through the Otranto Strait. Both processes are visible in the July 1976 data, as the previous winter was cold (February) and relatively dry over the whole Adriatic basin. Both types of processes can influence the bottom layer of the Otranto Strait, where the fraction of shelf-type dense water generated in the North and Middle Adriatic was occasionally observed along with the fraction of water generated by deep convection in the South Adriatic. During the nongenerative period, the cyclonic South Adriatic Gyre moved more to the northwest in general, as the Levantine intermediate water (LIW) occupied southeastern part of the South Adriatic Pit. However, such behaviour was not observed in January 1980, when LIW filled much of the Adriatic, thus diminishing density gradients in the South Adriatic. By applying a simple box model of water masses, it is estimated that the decay time of the Adriatic water masses equals 26 months, whereas transport of the Adriatic deep water (ADW) in the Otranto Strait amounted to 0.34 Sv during summer 1975. In the winter 1974/75 the... [ABSTRACT FROM AUTHOR]

The paper aims to introduce quality measures that can evaluate how well the Self-organizing Maps method performs in transitional stages. The errors have been computed with respect to the spatial and temporal properties of the data and in relation to the data gap significance. Temperature and salinity data collected in the central Adriatic Sea at six stations during 196 field cruises carried out between 1963 and 2011 have been used for the mapping of ocean patterns and computation of the respective errors. The errors resemble both the stability of ocean regimes and variability of patterns that are documented in the investigated region. As the data collection methodology and approach have changed over time, the errors may be a good indication for the presence of bad data in a series, which may then be controlled by other quality-check techniques. [ABSTRACT FROM AUTHOR]

This paper aims to document salinity and temperature regimes in the middle and south Adriatic Sea by applying the Self-Organizing Maps (SOM) method to the available long-term temperature and salinity series. The data were collected on a seasonal basis between 1963 and 2011 in two dense water collecting depressions, Jabuka Pit and Southern Adriatic Pit, and over the Palagruža Sill. Seasonality was removed prior to the analyses. Salinity regimes have been found to oscillate rapidly between low-salinity and high-salinity SOM solutions, ascribed to the advection of Western and Eastern Mediterranean waters, respectively. Transient salinity regimes normally lasted less than a season, while temperature transient regimes lasted longer. Salinity regimes prolonged their duration after the major basin-wide event, the Eastern Mediterranean Transient, in the early 1990s. A qualitative relationship between high-salinity regimes and dense water formation and dynamics has been documented. The SOM-based analyses have a large capacity for classifying the oscillating ocean regimes in a basin, which, in the case of the Adriatic Sea, beside climate forcing, is an important driver of biogeochemical changes that impacts trophic relations, appearance and abundance of alien organisms, and fisheries, etc. [ABSTRACT FROM AUTHOR]

The paper documents the use of a Digital Elevation Model (DEM) method to reconstruct paleochannels and the paleo-coastline during the Last Glacial Maximum (LGM) in the Central Eastern Adriatic area. We focused on the paleo-coastline and paleo-channels of the Neretva and the Cetina rivers, which were estimated from the 15" bathymetry available for the Adriatic Sea. While being aware of the limitations of the method and the resolution of the bathymetry grid, we successfully reproduced the paleo-channels of both rivers. Results for the Cetina River indicate the presence of depressions that were filled with water along its flow. The configurations of existing seabeds in the vicinity of the Cetina and Neretva River mouths indicate morphologies, similar to river mouths. The vertical profiles suggest that during the LGM the sea level was about 115 m lower than today. The total length of the Neretva riverbed was longer for about 136 km than today, and the Cetina River was approximately 154 km longer. [ABSTRACT FROM AUTHOR]

Large-amplitude seiches (up to 40 cm) were recorded at a tide-gauge inside Bakar. Bay from 19-21 August 2006. They were analysed using available tide-gauge and meteorological (air pressure and wind, vertical sounding,) data. Sea level and air pressure spectra showed simultaneous increases of energy in the periods in which the seiches of both Bakar Bay (about 20 mm) and Rijeka Bay (ca. 2 h) occurred. The propagation speed and direction as well as the horizontal span of the four pronounced pressure disturbances, favourable for coupling with Rijeka Bay waters via the Proudman resonance, were determined. It is argued that only short atmospheric pressure disturbances may generate significant barotropic sea waves in a small basin such as Rijeka Bay; once generated they are amplified when hitting Bakar Bay due to the harbour resonance. Furthermore, examination of the synoptic situation and upper-air soundings revealed the presence of dynamically unstable layer at a height of around 2000 m which was also the height of temperature inversion that developed as a consequence of an advection of warm African air from the south-east. During the afternoon hours of 19 August 2006 wind speed in this layer was close to the estimated speed of propagation of the air pressure disturbances which, together with dynamical instability, made conditions favourable for long distance propagation and trapping of atmospheric gravity waves. [ABSTRACT FROM AUTHOR]

Abstract The paper presents the Adriatic Sea and Coast (AdriSC) Meteotsunami Forecast system, which has been developed to operationally forecast meteotsunamis – atmospherically-generated destructive ocean waves in the tsunami frequency band, in the Adriatic Sea. The challenges posed by modelling meteotsunamis are first reviewed, then the AdriSC Meteotsunami Forecast system set-up is presented in detail and finally the atmosphere and ocean model results are evaluated against 48 air pressure sensors and 19 tide gauges for six different meteotsunami events. The statistical analysis of the high-frequency model results reveals that the AdriSC atmospheric and ocean models can reproduce meteotsunami events, even though their performances highly vary depending on the event and observation location. A qualitative analysis of the maps of extreme sea level and mean sea level pressure high-frequency model results shows that even a slight shift in location (of the order of 1 to 10 km) of the atmospheric disturbances, responsible for the meteotsunami generation, results in the incapability of the ocean models to reproduce the observed floods occurring during the meteotsunami events. This study presents the first available thorough evaluation of a deterministic meteotsunami forecast system. As such, it establishes that a carefully envisioned modelling system, even if imperfect, can be implemented to reproduce and forecast meteotsunami events. Highlights • A modelling suite for operational forecast of meteotsunamis was developed. • Prerequisites for meteotsunami modelling are at the edge of the model performances. • Meteotsunami events have been qualitatively reproduced in the Adriatic Sea. • The suite can be used for hazard assessment within a meteotsunami warning system. [ABSTRACT FROM AUTHOR]