Variability of water mass properties in the last two decades in the South Adriatic Sea with emphasis on the period 2006-2009

Spatially averaged temperature and salinity profiles from individual cruises between 1990 and 2009 were analysed to outline the temporal evolution of water mass properties in the deep convection site in the South Adriatic Pit (SAP). The long-term variability in thermohaline conditions has been explained and related to a close feedback mechanism between the Ionian and the Adriatic Sea. Prominent influences of the Eastern Mediterranean Transient are manifested in changes in the vertical temperature and salinity patterns in the South Adriatic, and the whole studied period was divided into three stages according to the main thermohaline characteristics: 1990-1995, 1995-2004 and the last period from 2005 onwards.Particular attention was given to data collected during 2006-2009, which permitted us to situate the actual thermohaline properties in the context of the decadal variability. This last period was characterised by a very low production of dense water in the northern basin during 2007, while from winter 2008 high production of North Adriatic Deep Water (NAdDW) and Adriatic Deep Water (AdDW) in the northern and southern basins, respectively, was observed. Finally, we used the Optimum Multiparameter Analysis (OMP) to identify the percentages of the different water masses contained in the SAP, and this highlighted some differences between two recent periods studied (2007 and 2008) and the production of dense waters.     

Modeling the water exchanges between the Venice Lagoon and the Adriatic Sea

A hydrodynamic model of the Venice Lagoon and the Adriatic Sea has been developed in order to study the exchanges at the inlets of the Venice Lagoon, a complex morphological area connecting the sea and the lagoon. The model solves the shallow water equations on a spatial domain discretized by a staggered finite element grid. The grid represents the Adriatic Sea and the Venice Lagoon with different spatial resolutions varying from 30 m for the smallest channels of the lagoon to 30  km for the inner areas of the central Adriatic Sea. Data from more than ten tide gauges displaced in the Adriatic Sea have been used in the calibration of the simulated water levels. After the calibration, the tidal wave propagation in the North Adriatic and in the Venice Lagoon is well reproduced by the model. To validate the model results, empirical flux data measured by acoustic Doppler current profiler probes installed inside the inlets of Lido and Malamocco have been used and the exchanges through the three inlets of the Venice Lagoon have been analyzed. The comparison between modeled and measured fluxes at the inlets outlines the efficiency of the model to reproduce both tide- and wind-induced water exchanges between the sea and the lagoon. Even in complex areas, where highly varying resolution is needed, the model is suitable for the simulation of the dominating physical processes.     

Dense water formation in the Gulf of Lions shelf: Impact of atmospheric interannual variability and climate change

Dense water formed over the continental shelf and cascading down the slope is responsible for shelf-slope exchanges in many parts of the world ocean, and transports large amounts of sediment and organic matter into the deep ocean. Here we perform numerical modeling experiments to investigate the impact of atmospheric interannual variability and climate change on dense water formation over the Gulf of Lions shelf, in the Northwestern Mediterranean Sea. Results obtained for a 140 years eddy-permitting simulation (1960–2100) performed over the whole Mediterranean Sea under IPCC A2 scenario forcings are used to force a regional eddy-resolving model of the Northwestern Mediterranean Sea.     

Fortnightly oscillations observed in the Adriatic Sea

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.     

Deep water ventilation traced by <Emphasis Type="Italic">Synechococcus</Emphasis> cyanobacteria

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.     

Modeling of sequence geometry north of Gargano Peninsula by changing sediment pathways in the Adriatic Sea

Sea level changes can reorganize sediment pathways on continental shelves in ways that can alter sediment supply and the resulting sedimentary deposits. The Adriatic Sea is one place where changing sediment pathways and along-strike currents have a major impact on sequence architecture. The Adriatic Sea, the marine portion of the Apenninic and Dinaric–Hellenic foreland basins, is being filled longitudinally, similar to other active forelands, and sediment transport patterns dramatically reorganized during Quaternary sea level cycles. We investigate the dynamics of sequence formation in the central Adriatic near the Gargano Promontory and the Mid-Adriatic Deep (MAD), where four depositional sequences each recording 100-kyr glacio-eustatic cycles have been mapped. These sequences are composed primarily of progradational units separated by regional unconformities. The geometry of the units is such that the constitutive clinoforms flatten out at their seaward termination into relatively planar strata, particularly in the upper parts of each sequence. Attempts to numerically simulate the sequences using the modeling software Sequence4 were frustrated by the difficulty of flattening the clinoforms seaward of the rollover (or depositional shelf break). The clinoform flattening observed in the Adriatic sequences contrasts with clinoform and depositional shelf break development that is characteristic of both conceptual and numerical models of sequences, including the one used here. We, therefore, modified the numerical model to account for the changes in sediment pathways that occur in the Adriatic Sea. During times with high sea level, such as the present, sediment from the Po and smaller Apennine Rivers is transported southwards along the coast by marine coastal currents and storms. At times of low sea level, fluvial transport of an enlarged Po River, in which the Apennine Rivers are likely captured as tributaries, discharges directly into the MAD basin. This produces a reciprocal sediment supply pattern where the coastal dispersal at high sea level produces prograding clinoforms, but cuts off as the exposure of the northern shelf at low sea level switches supply to the fluvial system, which discharges into the 260-m deep MAD. When the model is adapted for the shift in supply, the clinoforms flatten as nearshore sediment supply decreases and is replaced by deposition in the MAD during sea level lowstands. Including these sediment supply changes as a function of sea level enabled us to obtain a good fit to the overall stratigraphic architecture, supporting conceptual depositional models based on seismic stratigraphy. Similar dramatic shifts in sediment supply and sequence architecture may also occur at other settings, such as where canyons capture fluvial systems and bypass the terrigenous sediment supply to the deep basin. The paucity of observations of the unusual geometry seen at the Adriatic margin suggests that only rarely does the shore and fluvial sediment discharge overreach the shelf edge and cut off along-strike sediment transport to continental margins.     

Sediment transport and resuspension due to combined motion of wave and current in the northern Adriatic Sea during a Bora event in January 2001: A numerical modelling study

The Adriatic Sea general circulation model coupled to a third generation wave model SWAN and a sediment transport model was implemented in the Adriatic Sea to study the dynamics of the sediment transport and resuspension in the northern Adriatic Sea (NAS) during the Bora event in January 2001. The bottom boundary layer (BBL) was resolved by the coupled model with high vertical resolution, and the mechanism of the wave–current interaction in the BBL was also represented in the model. The study found that, during the Bora event of 13–17 January 2001, large waves with significant wave height 2 m and period of 5 s were generated by strong winds in the northwestern shelf of the Adriatic where the direction of wave propagation was orthogonal to the current. The combined motion of the wave and current in the BBL increased the bottom stress over the western Adriatic shelf, resulting in stronger sediment resuspension there. Combining stronger bottom resuspension and strong upward vertical flux of resuspended sediments due to turbulent mixing, the model predicted that sediment concentration near the Po River was much higher than that predicted by the model run without wave forcing. The study also shows that wave–current interaction in the BBL reduced the western Adriatic Coastal Currents (WACCs) in the shallower north. It is concluded that wave forcing significantly changed the sediment distributions and increased the total horizontal fluxes over the western shelf. These results signified wave effect on sediment flux and distribution in the NAS, and suggested that waves cannot be neglected in the study of dynamics of sediment transport and resuspension in the shallow coastal seas. By including the tidal forcing in the coupled model, we also examined the effect of tides on the sediment transport dynamics in the NAS.     

Using Self-Organising Maps to investigate long-term changes in deep Adriatic water patterns

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.     

The tidal and wind induced hydrodynamics of the composite system Adriatic Sea/Lagoon of Venice

A shallow water hydrostatic 2D hydrodynamic numerical model, based on the boundary conforming coordinate system, was used to simulate aspects of both general and small scale oceanic features occurring in the composite system constituted by the Adriatic Sea and the Lagoon of Venice (Italy), under the influence of tide and realistic atmospheric forcing. Due to a specific technique for the treatment of movable lateral boundaries, the model is able to simulate efficiently dry up and flooding processes within the lagoon. Firstly, a model calibration was performed by comparing the results of the model, forced using tides and ECMWF atmospheric pressure and wind fields, with observations collected for a set of 33 mareographic stations uniformly distributed in the Adriatic Sea and in the Lagoon of Venice. A second numerical experiment was then carried out by considering only the tidal forcing. Through a comparison between the results obtained in the two experiments it was possible to assess the reliability of the estimated parameter through the composite forcing. Model results were then verified by comparing simulated amplitude and phase of each tidal constituent as well as tidal velocities simulated at the inlets of the lagoon and in the Northern Adriatic Sea with the corresponding observed values. The model accurately reproduces the observed harmonics: mean amplitude differences rarely exceed 1 cm, while phase errors are commonly confined below 15°. Semidiurnal and diurnal currents were correctly reproduced in the northern basin and a good agreement was obtained with measurements carried out at the lagoon inlets. On this basis, the outcomes of the hydrodynamic model were analyzed in order to investigate: (i) small-scale coastal circulation features observed at the interface between the adjoining basins, which consist often of vortical dipoles connected with the tidal flow of Adriatic water entering and leaving the Lagoon of Venice and with along-shore current fields connected with specific wind patterns; (ii) residual oscillations, which are often connected to meteorological forcing over the basin. In particular, it emerges that small-scale vortical features generated near the lagoon inlet can be efficiently transported toward the open sea, thus contributing to the water exchange between the two marine regions, and a realistic representation of observed residual oscillations in the area would require a very detailed knowledge of atmospheric as well as remote oceanic forcing.     

Groundwater connections under a barrier beach: A case study in the Venice Lagoon

The flow of groundwater beneath barrier islands has been cited as a possible pathway for salt water and chemical exchange between a protected embayment and the open sea. Evidence is presented that identifies an exchange of groundwater through a highly permeable paleoinlet along the barrier beach of Cavallino, which separates the northern Venice Lagoon from the Adriatic Sea. We utilized both point measurements of submarine groundwater discharge (SGD) and a geophysical investigation of the subsurface resistivity to analyze the movement of saline groundwater. Discharge of groundwater and associated nutrients, was higher at the site of a former inlet than at a similar site along the barrier and modulated by the difference in tidal water level between the lagoon and Adriatic Sea. If the measured conditions are typical, storm surge barriers could potentially result in a saline groundwater flow of up to 1.5×10⁶ m³ d⁻¹ into the lagoon.     

Determination of polychlorobiphenyl congeners (PCBs) in the surface water of the Venice lagoon

The purpose of this study is to evaluate the degree of PCB contamination of Venice lagoon water. The PCB determination was made on the filtrate ("dissolved PCBs") and on the particulate collected on the filters ("particulate PCBs") by continuous liquid-liquid extraction and sonication, respectively, and by HRGC-LRMS analysis. An estimation of the procedural and "working" blanks was also made. Water samples were collected at six sites, selected to represent all the pollution situations present in the lagoon, and at a site in the Adriatic Sea. The range of the total sum ("dissolved plus particulate") of 49 congener concentrations falls between 355 and 1868 pgl(-1); the "dissolved" fraction concentrations (250-792 pgl(-1)) are greater at six sites than that of the "particulate" fraction (105-1273 pgl(-1)). Chemometric analyses suggest that the PCB congener pattern in the Venice Lagoon is different from that in the Adriatic Sea.     

Ra in the Japan Sea and the residence time of the Japan Sea water

The surface water of the Japan Sea contained²²⁶Ra of70 ± 4dpm m⁻³ which was nearly equal to that of the surface water in the North Pacific. The concentration of²²⁶Ra in the Japan Sea deep water below 500 m was151 ± 8dpm m⁻³, showing a vertically and regionally small variation. This concentration of²²⁶Ra in the deep water is unexpectedly high, because the Japan Sea deep water has a higher Δ¹⁴ C value by about 50‰ than the Atlantic deep water containing the same²²⁶Ra. One of the causes to be considered is larger contribution of²²⁶Ra from biogenic particles dissolving in the Japan Sea deep water, but the Japan Sea is not so fertile in comparison to the Bering Sea. The other more plausible cause is the internal ventilation of the Japan Sea water, which means that the residence time of the Japan Sea Proper water is considerably long although the water is vertically mixed fairly well especially in winter. The ventilation may supply some amounts of radiocarbon and oxygen but does not change the inventory of²²⁶Ra. The residence times of the Japan Sea deep water and of water within the Japan Sea are calculated by solving simultaneous equations for²²⁶Ra and¹⁴C with a three-box model to be 300–400 years and 700–1000 years, respectively.     

Chlorinated compounds and polybrominated diphenyl ethers (PBDEs) in mussels (Mytilus galloprovincialis) collected from Apulia Region coasts

This project was carried out to assess the levels and spatial distribution of organochlorine compounds in the coastal marine environment, using mussels as bioindicators to evaluate the coastal water quality. Levels of polychlorobiphenils (PCB), chlorinated pesticides (DDT isomers, HCH isomers, Aldrin, Dieldrin, alfa-Endosulfan, Hexachlorobenzene, Pentachlorobenzene) and polybrominated diphenyl ethers (PBDEs) were determined in tissues from mussels (Mytilus galloprovincialis) collected along the Apulia Region coasts (Mediterranean Sea). Results indicate that contamination by organochlorine compounds is higher in mussels sampled in the Ionian Sea than in those from the Adriatic Sea, with PCB levels up to seven times higher in mussels from Ionian than from the Adriatic Sea. Although PCB levels were above the maximum values indicated by both European Community (EC) and National regulation in several sample sites, the PCB concentrations were particularly high in some stations, suggesting that these locations require a much specific attention. Conversely, results on the mussel contamination by PBDEs highlight their ubiquitous environmental distribution, and underline the need to establish the maximum level for these compounds in foodstuff, according to European Regulations.     

Towards an operational use of space imagery for oil pollution monitoring in the Mediterranean basin: a demonstration in the Adriatic Sea

Studies of operational pollution carried out by European commission - Joint Research Centre in the Mediterranean Sea for the years 1999-2004 are briefly introduced. The specific analysis of the Adriatic Sea for the same period demonstrates that this area has been characterized by a relevant number of illegal discharges from ships. After setting the historical background of the project AESOP (aerial and satellite surveillance of operational pollution in the Adriatic Sea), the content, partners and aim of the project are presented. Finally, the results of the first phase of the AESOP project are presented. The results seem very encouraging. For the first time in the Adriatic, real time detection of oil spills in satellite images and an immediate verification by the Coast Guard has been undertaken. An exploratory activity has also been carried out in collaboration with the University of Ljubljana to use automatic information system (AIS) to identify the ships detected in the satellite images.     

On the flux of water and sediment into the Northern Adriatic Sea

This paper focuses on the delivery of water and sediment to the northern Adriatic to better understand the short-term evolution of continental margin sedimentation under natural and human impact. For that reason, the Po and six Apennine rivers (Metauro, Musone, Potenza, Tronto, Chienti and Pescara) are investigated. The climate-driven hydrological model HydroTrend is used to simulate discharge and sediment loads where observational data are limited. The northern Apennine hinterland has a significant impact on the sediment flux leaving the Po River, contributing 56% of the sediment it delivers to the Adriatic Sea. The Po River experienced a strong decrease in its sediment load (17.2–6.4 Mt/yr) across 1933–1987, in contrast to a small increase in its water discharge. The rivers draining the southern Apennine hinterland contribute more than 50% of the sediment load entering the Adriatic Sea, and this is in spite of human modification of their discharge through numerous small reservoirs that invariably reduce a river's sediment load. As a result, hyperpycnal flows, which historically carried 20–40% of the sediment flux from these Apennine rivers, become rare. Sediment load reduction is also reflected by retreat of the Apennine coastline. Based on the ART model (used in HydroTrend), the total sediment load to the northern Adriatic is 43 MT/yr where the northern Alpine rivers contribute 8 MT/yr, the Po River 13 MT/yr and the Apennine rivers contribute 22 MT/yr.     

Seabed properties and sediment erodibility along the western Adriatic margin,Italy

During February and June of 2003, selected physical and biological sediment properties were measured at nine mud-bottom sites (11–22 m) along the western margin of the Adriatic Sea. Seabed properties were compared with shipboard measurements of sediment erodibility made at the same sites to gain insight into the physical and biological controls on sediment erodibility operating in the western Adriatic. In addition, spatial patterns of erodibility were compared with long-term records of sediment accumulation in the region to determine if patterns of erodibility were responsible for the discrepancy between sediment sources and sinks on the shelf. Results indicate that sediment erodibility along the western Adriatic Sea varied both in time and space. In the wintertime, sediment in the vicinity of the Po delta (in the northern region) was less easily eroded than to the south. In the summertime, the pattern reversed. The physical characteristics of the seabed including porosity and grain-size were important factors controlling erodibility during the winter, although in a manner opposite to expectations (i.e., higher porosity sediment was less erodible). No relationship between the physical characteristics of the seabed and erodibility was observed in the summer, when it was likely that erodibility was influenced by benthic organisms, especially microphytobenthos. Results of this study suggest long-term sediment accumulation patterns along the western Adriatic Sea are unlikely to be controlled by patterns of erodibility. However, due to several complicating factors, especially along-margin variability in wave energy, the impact of sediment erodibility on long-term patterns of accumulation remains unclear. Further studies that resolve both finer and larger-scale spatial and temporal variability in sediment erodibility and that incorporate year-to-year forcing of the coastal ocean are needed to more accurately resolve the relationship between erodibility and sediment accumulation in the western Adriatic, as well as other coastal environments.     

Integrated use of biomarkers in the mussel Mytilus galloprovincialis for assessing off-shore gas platforms in the Adriatic Sea: results of a two-year biomonitoring program

Despite a large number of gas platforms existing in the Adriatic Sea, which is a semi-enclosed basin characterized by a slow turnover rate and increasing industrial as well as other anthropogenic activities, the effects of these structures on the aquatic ecosystem require further investigation. Since 1998, multidisciplinary studies have been performed by CNR-ISMAR to comply with legislation and to support the development of protocols for the monitoring of offshore activities in the Adriatic Sea. The present study was developed to implement a biomonitoring plan to assess the ecotoxicological effects of the extraction activities of an off-shore gas platform. Biomarkers were evaluated in mussels collected from the platform in relation to physiological stress, DNA damage, cellular damage, oxidative stress and exposure effects. Organic contaminants and trace element bioaccumulation were also assessed in the soft body of the mussels to correlate bioaccumulation of pollutants with biomarker responses. The results indicate an absence of platform-related environmental stress.     

Variability of dense water formation in the Ross Sea

This paper presents results from a model study of the interannual variability of high salinity shelf water (HSSW) properties in the Ross Sea. Salinity and potential temperature of HSSW formed in the western Ross Sea show oscillatory behaviour at periods of 5–6 and 9 years superimposed on long-term fluctuations. While the shorter oscillations are induced by wind variability, variability on the scale of decades appears to be related to air temperature fluctuations. At least part of the strong decrease of HSSW salinities deduced from observations for the period 1963–2000 is shown to be an aliasing artefact due to an undersampling of the periodic signal. While sea ice formation is responsible for the yearly salinity increase that triggers the formation of HSSW, interannual variability of net freezing rates hardly affects changes in the properties of the resulting water mass. Instead, results from model experiments indicate that the interannual variability of dense water characteristics is predominantly controlled by variations in the shelf inflow through a sub-surface salinity and a deep temperature signal. The origin of the variability of inflow characteristics to the Ross Sea continental shelf can be traced into the Amundsen and Bellingshausen Seas. The temperature anomalies are induced at the continental shelf break in the western Bellingshausen Sea by fluctuations of the meridional transport of circumpolar deep water with the eastern cell of the Ross Gyre. In the Amundsen Sea, upwelling due to a persistently cyclonic wind field carries the signal into the surface mixed layer, leading to fluctuations of the vertical heat flux, anomalies of brine release near the sea ice edge, and consequently to a sub-surface salinity anomaly. With the westward flowing coastal current, both the sub-surface salinity and deep temperature signals are advected onto the Ross Sea continental shelf. Convection carries the signal of salinity variability into the deep ocean, where it interacts with modified circumpolar deep water upwelled onto the continental shelf as the second source water mass of HSSW. Sea ice formation on the Ross Sea continental shelf thus drives the vertical propagation of the signal rather than determining the signal itself.     

Nutrient budgets for European seas: a measure of the effectiveness of nutrient reduction policies

Socio-economic development in Europe has exerted increasing pressure on the marine environment. Eutrophication, caused by nutrient enrichment, is evident in regions of all European seas. Its severity varies but has, in places, adversely impacted socio-economic activities. This paper aims to evaluate the effectiveness of recently adopted policies to reduce anthropogenic nutrient inputs to European seas. Nitrogen and phosphorus budgets were constructed for three different periods (prior to severe eutrophication, during severe eutrophication and contemporary) to capture changes in the relative importance of different nutrient sources in four European seas suffering from eutrophication (Baltic Proper, coastal North Sea, Northern Adriatic and North-Western Black Sea Shelf). Policy success is evident for point sources, notably for P in the Baltic and North Seas, but reduction of diffuse sources has been more problematic.     

海洋深水水道地震综合解释技术研究——以南海北部陆坡区更新统深水水道为例

深水沉积是深水油气勘探的重要领域.本文利用南海北部陆坡区三维地震资料,应用三维可视化、相干处理、沿层切片及波形分类等地震技术,识别和刻画南海北部陆坡区更新世深水沉积水道的展布、演化特征及有利砂体分布位置,初步总结出一套适合深水沉积水道的地震识别和描述方法.该水道呈南西-北东方向展布、具蛇曲形态,水道主体以泥岩充填为主,水道侧向加积及堤坝部位是有利的储集部位.