This study provides a new perspective on the hydrocarbon seeps in the Adriatic Sea, supporting both the environmental issues and eventual oil and gas exploration. Remote sensing techniques, ...particularly synthetic aperture radar (SAR) images are used to detect oil slicks on the sea surface. In such a way two groups of oil slicks have been detected in the Northern and Central Adriatic Sea on the SAR images acquired by the European Sentinel-1A and Sentinel-1B satellites in 2017-2018. Analysis of SAR images together with bathymetry, geological and geophysical data in geographic information system (GIS) have shown that these oil slicks, visible on the sea surface have natural origin, i.e. are seepage phenomena, associated to existing marine hydrocarbon systems. These oil slicks were concentrated over the shallow shelf, and repeatedly or episodically occur in the areas of interest, and are related to local oil-and-gas bearing sediments. Findings of the seeps and seep candidates that passed unnoticed from public attention indicate the effectiveness of the approach used. Finally, it is concluded that the frequent SAR imagery is an excellent tool for monitoring of seepage phenomena, and the results indicate that the use of remote sensing methods can be considered as a good approach to support oil and gas exploration in the Adriatic Basin.
Ovaj rad daje novu prespektivu problemu istjecanja ugljikovodika iz podmorja na Jadranu, podržavajući pitanja zaštite morskog okoliša kao i eventualno istraživanje nafte i plina. Tehnike daljinskog otkrivanja, osobito snimci “synthetic aperture” radara (SAR) korištene su za otkrivanje uljnih mrlja na površini mora. Na taj su način na sjevernom i na srednjem Jadranu otkrivene dvije grupe mrlja na SAR snimcima dobivenim od europskih satelita Sentinel-1A i Sentinel-1B u razdoblju 2017.- 2018. Analiza SAR snimaka uz batimetriju, geološke i geofizičke podatke kroz geografski informacijski sustav (GIS) pokazala je da nađene uljne mrlje, vidljive na površini mora, imaju pri-rodno porijeklo, t.j. da pripadaju fenomenu podmorskih istjecanja, povezanih s postojećim ležištima ugljikovodika. Ove su uljne mrlje koncentrirane na plitkom šelfu i opetovano ili povremeno se pojavljuju u istraživanom području, a u vezi su sa sedimentima koji sadrže naftu ili plin. Nalaženje takvih izvora ili kandidata za izvore, koji su prošli neopaženi od javnosti, ukazuje na učinkovitost ovog pristupa. Konačno, zaključeno je kako su česti SAR snimci odličan alat za monitoring fenomena curenja iz podmorja, a rezultati pokazuju kako se korištenje daljinskih metoda može smatrati dobrim pristupom za istraživanje nafte i plina u jadranskom bazenu.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
This paper examines long-term series of in situ sea surface temperature (SST) data measured at nine coastal and one open sea stations along the eastern Adriatic Sea for the period 1959–2015. Monthly ...and yearly averages were used to document SST trends and variability, while clustering and connections to hemispheric indices were achieved by applying the Principal Component Analysis (PCA) and Self-Organizing Maps (SOM) method. Both PCA and SOM revealed the dominance of temporal changes with respect to the effects of spatial differences in SST anomalies, indicating the prevalence of hemispheric processes over local dynamics, such as bora wind spatial inhomogeneity. SST extremes were connected with blocking atmospheric patterns. A substantial warming between 1979 and 2015, in total exceeding 1 °C, was preceded by a period with a negative SST trend, implying strong multidecadal variability in the Adriatic. The strongest connection was found between yearly SST and the East Atlantic (EA) pattern, while North Atlantic Oscillation (NAO) and East Atlantic/West Russia (EAWR) patterns were found to also affect February SST values. Quantification of the Adriatic SST and their connection to hemispheric indices allow for more precise projections of future SST, considered to be rather important for Adriatic thermohaline circulation, biogeochemistry and fisheries, and sensitive to ongoing climate change.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In order to test the response of phytoplankton to anthropogenic pressure, data of chlorophyll a concentration, phytoplankton abundance, and composition are analyzed in relation to anthropogenic ...pressure gradient and environmental variables such as temperature, salinity and nutrients. Investigated sites encompassed wide tropic range according to a preliminary determination of anthropogenic pressure, quantified through the LUSI index. Statistical analyses indicated nitrates and silicates as proxies of freshwater influence, and phytoplankton single metrics such as concentrations of chlorophyll a and abundances as indicators of anthropogenic pressure. Boundary values for different water quality classes for coastal waters under indirect freshwater influence (Type II) are obtained according to gradient between concentration of chlorophyll a and pressure index (LUSI), which empirically fit to exponential equation. The response of phytoplankton diversity was not linear, as the highest diversity was observed in the area with intermediate disturbance level. CCA analysis identified Skeletonema marinoii, Scrippsiella trochoidea, Guinardia flaccida, Leptocylindrus spp., Prorocentrum spp., Proboscia alata, Eutreptiella spp., and Pseudonitzschia spp. as local eutrophication indicators, whose abundances increased with nutrients loads.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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.
•The long-term time series of thermohaline properties of the Adriatic Sea were studied.•A neural network algorithm was applied to extract nonlinear structures in the data.•Rapid transitions between high and low salinity regimes were detected.•The sources and lengths of temperature and salinity regimes differ from each other.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Fifteen years (1998-2012) of monthly chlorophyll-like pigment concentrations from satellite images (JRC database) were analysed using self-organizing maps (SOMs). The aim was to classify the pigment ...structures of the Adriatic Sea into a number of patterns present in the data by this novel neural network method. The images are represented by a vector in the multidimensional data-space limited to the Adriatic area. We tried using several predefined patterns, finally selecting an optimal number of 16 spatial structures. Distinct neurons are primarily associated with patterns of different pigment concentration over the whole Adriatic area and with a different extension of the colour front along the west coast. Rare phenomena and variability limited to smaller areas were less represented in the SOM patterns. Although temporal pigment dynamics are synchronous in many areas of the Adriatic Sea, the analysis of their annual course resulted in ten temporal patterns. This representation also demonstrates the ability of the SOM method to connect areas with a particular seasonal variation in chlorophyll.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Here we presented changes in the non-crustacean zooplankton community in the years characterized by the large scale changes in the thermohaline circulation in the East Mediterranean known as the ...Eastern Mediterranean transient (EMT) and stronger inflow of colder and less saline Modified Atlantic Water (MAW) into the Adriatic Sea. Monthly samplings from February 1995 to February 1996, were performed at fixed station Stoncica near the Island of Vis in the open oligotrophic Middle Adriatic waters. Zooplankton samples, taken vertically from 100 m to the surface using a Nansen net with 125- mu m mesh size were analyzed in detail for the following zooplankton taxa: Hydromedusae, Calycophorae, Ctenophora, Pteropoda, Heteropoda, Polychaeta and Chaetognatha. Among the investigated non-crustacean zooplankton three species were registered for the first time, while one species reappeared after years of absence. Compared with earlier data there was a dramatic change in dominant species of calycophoran medusae, pteropods and polychaetes. Data presented herein provide baseline information that is essential for the evaluation of impact of hydroclimatic changes on the zooplankton community, which started in the East Mediterranean in the 1990s and are still on going.
Oil slick detection by synthetic aperture radars (SAR) is a proven and commonly used operational technique, which showed that the seas of the Mediterranean are often polluted by oil and oily ...products. For the period 2003-2011, the Envisat and Radarsat-1 SAR images were available for analysis, thanks to the several projects. About 300 SAR images have been analysed over the Middle and Southern Adriatic Sea, in order to detect marine oil spills and other phenomena causing similar signatures. Analysing many oil spills detected in the Adriatic Sea, their sizes were determined between 0.1 km super(2) and 108 km super(2) . Most of the spills were located along the main shipping routes, especially in the ship corridor along the Adriatic Sea axis. They were, most probably deliberate slicks released from ships during transportation or fishing operations, while suspected source of the largest spills is tank washing or illegal discharges.Original Abstract: Detekcija uljnih mrlja sintetickim satelitskim radarom (SAR) provjerena je i najcesce koristena operativna tehnika, koja je pokazala kako je Sredozemno more cesto zagadjeno uljem i slicnim proizvodima. Zahvaljujuci nekolicini projekata Envisat i Radarsat-1 SAR slike su za razdoblje 2003-2011 bile dostupne za analizu. Analizirano je oko 300 SAR slika srednjeg i juznog Jadrana, kako bi se otkrile pojave naftnih mrlja i druge pojave koje imaju slican signal na satelitskim snimcima. Otkrivena su mnoga izlijevanja nafte u Jadranu, cije su povrsine bile izmeđ u 0.1 km super(2) i 108 km super(2) . Vecina izlijevanja je smjestena uz glavne brodske rute, osobito u brodskom koridoru duz osi Jadranskog mora. To su vjerojatno ulja namjerno izlivena s brodova tijekom prijevoza ili ribolovnih operacija, a najcesci slucajevi izlijevanja su pranje brodskih spremnika ili nedozvoljena praznjenja tankova.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
In recent highly variable climate, a combined effect of a large-scale northern hemisphere climate and regional-scale Adriatic hydroclimate changes significantly reflected in the Adriatic Sea ...ecosystem. To clarify this statement we set up in connection two inter-annual systems: the air-sea interconnected system and pelagic ecosystems for the period 1961 to 2010. Within this period, significant changes occurred through 1987-1998 period, characterized by a drop of temperature, salinity and oxygen concentration in the middle Adriatic intermediate layer as consequence of a weaker ventilation of the Adriatic Sea. The pelagic ecosystem reacted to these changes. Large fluctuations in marine biota (from plankton to pelagic fish) revealed significantly different regimes before and after the late eighties. Different patterns observed through analyzed biotic parameters seem linked to modification in thermohaline circulation related to the Eastern Mediterranean Transient (EMT), whose effects prevented warmer and saltier water mass intrusions into the Adriatic Sea. These results provide evidence on connections between the shifts in the middle Adriatic pelagic ecosystem and the northern hemisphere climate via changes in regional atmospheric conditions, and highlight the importance of northern hemisphere climate changes for physical and biological regimes of the Adriatic Sea.Original Abstract: U vrijeme sve izrazitije promjene klime ekosustav Jadranskog mora pod znacajnim je utjecajem atmosferskih promjena koje se dogadaju na sjevernoj hemisferi te na regionalnoj skali Jadrana. U svrhu objasnjenja meduovisnosti ekosustava Jadrana i atmosferskih procesa na razlicitim prostornim skalama (od hemisferske do regionalne) analizirana je visegodisnja (1961.-2010.) promjenjivost sustava atmosfera-more i pelagickog ekosustava. Unutar promatranog vremenskog razdoblja najznacajnija promjena dogodila se izmedu 1987. i 1998. u intermedijalnom sloju srednjeg Jadrana i bila je obiljezena padom temperature mora i saliniteta te kisika kao posljedica slabijeg ventiliranja Jadrana. Istovremeno su u ekosustavu pelagijala Jadranskog mora primijecene velike fluktuacije u biomasi morskih organizama (od fitoplanktona do plave ribe). Izdvojena su signifikantno razlicita stanja ekosustava Jadrana prije i poslije kasnih osamdesetih godina proslog stoljeca. Uzrok ovim razlicitim stanjima ekosustava dijelom se moze povezati sa modificiranom termohalinom cirkulacijom Jadrana koja je pod utjecajem EMT (Eastern Mediterranean Transient) sprjecavala ulazak toplije i slanije vode u Jadransko more, uzrokujuci na taj nacin uocene promjene u ekosustavu. Ovi rezultati dokazuju povezanost izmedu skokova u pelagickom ekosustavu na podrucju srednjeg Jadrana i klime na sjevernoj hemisferi putem promjena u regionalnim vremenskim uvjetima te isticu vaznost utjecaja klimatskih promjena i skokova na fizikalna i bioloska stanja Jadranskog mora.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Interannual variability of the primary production in the middle Adriatic Sea for the period 1961–2002 was examined and correlated to the various atmospheric and oceanographic parameters. The ...sequential t-test analysis of regime shift (STARS) method and locally-weighted scatter plot smoothing (LOWESS) method were applied to the primary production, revealing the new regime with significantly different mean productivity ranging from 1980–1996. Moreover, this period with the highest primary production, consists of the two distinguished sub-periods: periods of increasing (1980–1986) and decreasing (1987–1996) primary production. Whereas in the first period the ecosystem was under the influence of warmer and nutrient richer Levantine Intermediate Water (LIW) intrusions into the Adriatic, in the second period, which started with a cold winter in 1987, the Eastern Mediterranean Transient (EMT) occurred. The EMT established a new circulation regime which prevented the LIW intrusions in the Adriatic, causing its reduced productivity. Reduced LIW inflow in the Adriatic was evidenced in the lower than normal sea temperature, salinity and oxygen concentrations below the thermocline depth. Precipitation and wind regime also arose as important local factors for the primary production variability. Our analysis connected the shifts in primary production with hemispheric and regional scale climate variations, and supports the hypothesis that atmospheric variability can trigger the ecosystem changes.
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