15 results on '"Vilibić, Ivica"'
Search Results
2. Modes of the BiOS-driven Adriatic Sea thermohaline variability.
- Author
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Denamiel, Cléa, Tojčić, Iva, Pranić, Petra, and Vilibić, Ivica
- Subjects
ORTHOGONAL functions ,OSCILLATIONS ,MERIDIONAL overturning circulation ,ATMOSPHERIC models ,TIME series analysis ,SALINITY - Abstract
In this study the impact of the Adriatic-Ionian Bimodal Oscillating System (BiOS) on the interannual to decadal variability of the Adriatic Sea thermohaline circulation is quantified during the 1987–2017 period with the numerical results of the Adriatic Sea and Coast (AdriSC) historical kilometer-scale climate simulation. The time series associated with the first five Empirical Orthogonal Functions (EOFs) computed from the salinity, temperature and current speed monthly detrended anomalies at 1-km resolution are correlated to the BiOS signal. First, it is found that the AdriSC climate model is capable to reproduce the BiOS-driven phases derived from in-situ observations along a long-term monitoring transect in the middle Adriatic. Then, for the entire Adriatic basin, high correlations to the 2-year delayed BiOS signal are obtained for the salinity and current speed first two EOF time series at 100 m depth and the sea-bottom. Finally, the physical interpretation of the EOF spatial patterns reveals that Adriatic bottom temperatures are more influenced by the dense water circulation than the BiOS. These findings confirmed and generalized the known dynamics derived previously from observations, and the AdriSC climate model can thus be used to better understand the past and future BiOS-driven physical processes in the Adriatic Sea. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
3. Modes of the Adriatic long-term variability as seen on half-centurial Palagruža Sill series
- Author
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Vilibić, Ivica, Mihanović, Hrvoje, Šepić, Jadranka, and Dunić, Natalija
- Subjects
Adriati Sea ,long-term measurements ,temperature ,salinity - Abstract
n/a
- Published
- 2015
4. Present climate trends and variability in thermohaline properties of the northern Adriatic shelf.
- Author
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Vilibić, Ivica, Zemunik, Petra, Šepić, Jadranka, Dunić, Natalija, Marzouk, Oussama, Mihanović, Hrvoje, Denamiel, Clea, Precali, Robert, and Djakovac, Tamara
- Subjects
MERIDIONAL overturning circulation ,TIME series analysis ,CLIMATOLOGY ,SALINITY - Abstract
The paper documents seasonality, interannual-to-decadal variability, and trends in temperature, salinity, and density over a transect in the shallow northern Adriatic Sea (Mediterranean Sea) between 1979 and 2017. The amplitude of seasonality decreases with depth and is much larger in temperature and density than in salinity. Time series of temperature and salinity are correlated in the surface but not in the bottom layer. Trends in temperature are large (up to 0.6 ∘ C over 10 years), significant through the area, and not sensitive to the sampling interval and time series length. In contrast, trends in salinity are largely small and insignificant and depend on the time series length. The warming of the area is more during spring and summer. Such large temperature trends and their spatial variability emphasize the importance of maintaining regular long-term observations for the proper estimation of thermohaline trends and their variability. This is particularly important in regions which are key for driving thermohaline circulation such as the northern Adriatic, with the potential to affect biogeochemical and ecological properties of the whole Adriatic Sea. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
5. Modelling Interannual Changes in Dense Water Formation on the Northern Adriatic Shelf.
- Author
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Mihanović, Hrvoje, Janeković, Ivica, Vilibić, Ivica, Kovačević, Vedrana, and Bensi, Manuel
- Subjects
MERIDIONAL overturning circulation ,WINTER ,CLIMATE change ,ATMOSPHERIC models ,SALINITY - Abstract
The paper aims to estimate wintertime thermohaline properties and dense water formation (DWF) dynamics, rates, and transports in the northern and middle Adriatic between 2008 and 2015. The focus has also been directed to the year-to-year differences between two known DWF sites located on the northern Adriatic shelf and in the eastern coastal region. The estimates are based on a high-resolution interannual simulation by Regional Ocean Modelling System, one-way forced by the meteorological Aladin/HR operational mesoscale model, with new river climatology imposed particularly at the eastern Adriatic coast. Substantial interannual variability in wintertime bottom densities has been found, varying for more than 1.0 kg m
−3 among years. Such variations are largely associated with the January-February heat losses, while atmospheric preconditioning in November-December seems to have a little effect on the DWF rates. By contrast, salinity is preconditioning the DWF in the eastern coastal site. That has been found relevant for DWF rates during extraordinary winters, as in the case of 2012. Contribution of a coastal site to the overall DWF rates in other years has not been substantial. Finally, a saw-tooth-like pattern in thermohaline time series has been found in observations and reproduced by the numerical model at the bottom of the middle Adriatic depressions. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
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6. Environmental conditions conducive to anchovy (Engraulis encrasicolus) spawning in the Adriatic Sea
- Author
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Zorica, Barbara, Vilibić, Ivica, Čikeš Keč, Vanja, and Šepić, Jadranka
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reproduction ,salinity ,temperature ,Engraulis encrasicolus ,Adriatic - Abstract
The goal of the paper is to investigate environmental influences on the occurrence of anchovy 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 ground 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 climatological fields. Anchovy spawning seasonality was defined by monthly changes of the maturity stages and the gonadosomatic index. Fluctuations of the gonadosomatic index reveal that spawning begins in March and lasts till September, with reproductive activity peaking from April to July. Early or late occurrence of a high gonadosomatic index has a significant negative correlation with upper layer salinity in the two preceding months and a sporadic and weak connection with the wind-mixing index and surface temperature. An enhanced input of nutrient-rich freshwater of river origin, which reduces upper layer salinity and enhances primary production up to two months before anchovy spawning, seems to be important for the anchovy fertility, especially if a late spawning maximum (in July) occurs in a certain year.
- Published
- 2013
7. Wintertime dynamics in the coastal northeastern Adriatic Sea: the NAdEx 2015 experiment.
- Author
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Vilibić, Ivica, Mihanović, Hrvoje, Janeković, Ivica, Denamiel, Cléa, Poulain, Pierre-Marie, Orlić, Mirko, Dunić, Natalija, Dadić, Vlado, Pasarić, Mira, Muslim, Stipe, Gerin, Riccardo, Matić, Frano, Šepić, Jadranka, Mauri, Elena, Kokkini, Zoi, Tudor, Martina, Kovač, Žarko, and Džoić, Tomislav
- Subjects
OCEAN dynamics ,HYDRODYNAMICS ,OCEAN temperature ,SALINITY - Abstract
The paper investigates the wintertime dynamics of the coastal northeastern Adriatic Sea and is based on numerical modelling and in situ data collected through field campaigns executed during the winter and spring of 2015. The data were collected with a variety of instruments and platforms (acoustic Doppler current profilers, conductivity-temperature-depth probes, glider, profiling float) and are accompanied by the atmosphere-ocean ALADIN/ROMS modelling system. The research focused on the dense-water formation (DWF), thermal changes, circulation, and water exchange between the coastal and open Adriatic. According to both observations and modelling results, dense waters are formed in the northeastern coastal Adriatic during cold bora outbreaks. However, the dense water formed in this coastal region has lower densities than the dense water formed in the open Adriatic due to lower salinities. Since the coastal area is deeper than the open Adriatic, the observations indicate (i) balanced inward-outward exchange at the deep connecting channels of denser waters coming from the open Adriatic DWF site and less-dense waters coming from the coastal region and (ii) outward flow of less-dense waters dominating in the intermediate and surface layers. The latter phenomenon was confirmed by the model, even if it significantly underestimates the currents and transports in the connecting channels. The median residence time of the coastal area is estimated to be approximately 20 days, indicating that the coastal area may be renewed relatively quickly by the open Adriatic waters. The data that were obtained represent a comprehensive marine dataset that can be used to calibrate atmospheric and oceanic numerical models and point to several interesting phenomena to be investigated in the future. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
8. The Levantine Intermediate Water (LIW) pathways in the northern Adriatic and their relation to bora events
- Author
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Supić, Nastenjka and Vilibić, Ivica
- Subjects
water masses ,salinity ,northern Adriatic - Abstract
Long-term (1967-2000) changes of February bottom salinity (30 m) at two stations in the northern Adriatic have been analysed in order to detect winters in which advection events of modified Levantine Intermediate Water (LIW) from the south occurred. The stations are located in open waters of the eastern (station 1) and western (station 2) part of the Po River delta-Rovinj profile. Although the surface layer in the region is generally affected by fresh waters, the bottom salinity varied within a relatively small interval (37.4-38.6). The bottom values were on average slightly higher at station 1 (38.1 0.2) than at station 2 (38.0 0.3). High salinity values (>38.3) were ascribed to modified Levantine Intermediate Water (LIW). They were observed in 1981, 1989, 1990 and 2000. Data collected monthly along the Po river delta-Rovinj profile in the winter season of 1999/2000, as well as computed geostrophic currents relative to 30 m depth, indicate that LIW entered the northern Adriatic by the end of 1999. On 18 December 1999 a strong inflow (with currents up to 6 cm/s) of high salinity water (38.4) was observed in a water band extending from the surface to the bottom in the western part of the section. As the Adriatic circulation is cyclonic, with an inflow across the eastern coast (EAC, East Adriatic Current), the December 1999 event supports the hypothesis that the EAC is on some occasions deflected towards the west, entering the northern Adriatic in its central/western part. Such LIW pathway may be a result of bora- induced circulation which favours strong currents emerging from the Bay of Kvarner and forming tranversal frontal zone, preventing EAC to enter the northern Adriatic along the eastern coast. Actually, strong bora occurred just two days before, on 16 December 1999, with daily averaged wind speed of 13.4 m/s measured at coastal Pula station. Data collected across the Po river delta-Rovinj profile on 5 January show the presence of modified LIW in a band extending from the surface to the bottom in the eastern part of the section, and in deep layers close to the Po delta. On the 21 February cruise modified LIW was observed only in bottom layers of the western Adriatic, and during the 17-21 March cruise it was not observed at all. After several very strong bora events in the second part of December (with daily averaged wind speed up to 18.9 m/s at Pula station) the wind decreased and during January, February and March it was generally moderate, blowing mainly from the NE. Therefore, the circulation retain to a normal, with LIW inflow along the eastern coast observed in January, whereas lower salinity in March is probably a result of vertical mixing and replenishment of LIW in the wider area.
- Published
- 2005
9. Dense-water generation episodes in the northern Adriatic
- Author
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Vilibić, Ivica and Supić, Nastjenjka
- Subjects
Adriatic ,temperature ,salinity ,dense water generation - Abstract
The generation of North Adriatic Dense Water (NAdDW) has been documented in the paper, by analysing three generation episodes occurred in winters of 1981, 1987 and 1989. Temperature, salinity and density collected at the Po Delta - Rovinj transect before, during and after NAdDW generation were analysed and discussed. Furthermore, monthly surface heat, water and buoyancy fluxes were computed for the respective time intervals, coupled with Po River discharge rates. The decrease in Po River runoff in the preceding 4 months is common characteristics for all of three NAdDW generation episodes. Nevertheless, NAdDW generated in winter of 1989 was the result of extremely lowered water fluxes that preceded to the generation, producing extremely saline dense water. In contrary, winters of 1981 and 1987 were characterized by extensive heat losses in January/February therefore resulting in very cold NAdDW. NAdDW density in all of the cases surpassed 29.7, being enough dense to influence wider area and bottom layers of the whole Adriatic, changing a lot its physical and chemical properties.
- Published
- 2004
10. Long-term variability and trends of relative geostrophic currents in the middle Adriatic.
- Author
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Vilibić, Ivica, Pištalo, Damjan, and Šepić, Jadranka
- Subjects
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GEOSTROPHIC currents , *OCEAN temperature , *SALINITY , *MERIDIONAL overturning circulation , *CLIMATE change - Abstract
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]
- Published
- 2015
- Full Text
- View/download PDF
11. Using Self-Organising Maps to investigate long-term changes in deep Adriatic water patterns
- Author
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Vilibić, Ivica, Mihanović, Hrvoje, Šepić, Jadranka, and Matijević, Slavica
- Subjects
- *
WATER masses , *TEMPERATURE , *SALINITY , *DISSOLVED oxygen in water , *PLANT nutrients , *NITROGEN , *INORGANIC compounds , *LEAST squares - Abstract
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]
- Published
- 2011
- Full Text
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12. Dense water characteristics in the northern Adriatic in the 1967–2000 interval with respect to surface fluxes and Po river discharge rates
- Author
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Supić, Nastjenjka and Vilibić, Ivica
- Subjects
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SALINE waters , *HYDROGRAPHY , *SALINITY , *WATER temperature - Abstract
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]
- Published
- 2006
- Full Text
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13. Local and remote drivers of the observed thermohaline variability on the northern Adriatic shelf (Mediterranean Sea).
- Author
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Vilibić, Ivica, Zemunik, Petra, Dunić, Natalija, and Mihanović, Hrvoje
- Subjects
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OSCILLATIONS , *HEAT flux , *MERIDIONAL overturning circulation , *SURFACE temperature , *WINTER , *SEAS , *SALINITY - Abstract
In situ thermohaline variables measured monthly or bimonthly in the shallow northern Adriatic at prescribed stations between 1979 and 2017 were correlated with the local (river runoff, precipitation, net heat flux) and remote atmospheric (various hemispheric and regional indices) and oceanic (the Adriatic-Ionian Bimodal Oscillating System, BiOS) drivers acting on monthly to annual timescales. The highest correlation between the temperature and the local drivers was obtained in winter along the western part of the study area, while the rivers and precipitation mostly shaped the summer and December salinity values. The net heat fluxes and river discharges preceding the dense water formation (DWF) by 1–2 months and up to 3 months were found to be important for the February temperature and salinity variability, respectively. No significant correlations were found between the February thermohaline variables and the monthly BiOS index for the phase lags up to −11 months, while the correlation was the largest between the yearly averaged BiOS index and the yearly averaged salinity at phase lags of −2 to −4 years. The bottom yearly averaged salinity has also been highly correlated with the Mediterranean Oscillation index at phase lags of −1 and −3 years, while the yearly averaged surface temperature was influenced by the East Atlantic and East Atlantic/West Russia patterns. Acting independently on different timescales, both the local and remote processes were found to drive the thermohaline variability in the northern Adriatic, thus providing an option for a forecast of the DWF and the thermohaline circulation in the Adriatic-Ionian basin. • Thermohaline observations have been correlated with atmospheric and oceanic drivers. • Local drivers shape the thermohaline variability at monthly timescales. • Remote drivers were correlated with temperature and salinity at yearly timescale. • The BiOS is a key driver for the northern Adriatic decadal thermohaline variability. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
14. Record-breaking salinities in the middle Adriatic during summer 2017 and concurrent changes in the microbial food web.
- Author
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Beg Paklar, Gordana, Vilibić, Ivica, Grbec, Branka, Matić, Frano, Mihanović, Hrvoje, Džoić, Tomislav, Šantić, Danijela, Šestanović, Stefanija, Šolić, Mladen, Ivatek-Šahdan, Stjepan, and Kušpilić, Grozdan
- Subjects
- *
OSCILLATIONS , *SALINITY , *LYAPUNOV exponents , *BIOMASS production , *STANDARD deviations , *EVAPORATION (Meteorology) - Abstract
• Anomalous physical and microbial properties were detected in the middle Adriatic. • Local and remote drivers contributed to record-breaking salinities. • Picoplankton biomass and production sharply declined in high salinity conditions. • The documented conditions could be more frequent in the future climate. Oceanographic measurements carried out in the middle Adriatic during summer 2017 revealed anomalous conditions in both physical and microbial properties. High salinities were observed throughout the entire water column, with an 'inverse' salinity profile in August and a maximum in the surface layer, recorded for the first time in the middle Adriatic. Surface salinity of 39.02 recorded in August was 2.5 standard deviations above the long-term average (1961–2016). The observed salinity distributions are the result of both local and remote drivers, whereby the North Ionian cyclonic gyre controlled by the Adriatic-Ionian Bimodal Oscillating System has been responsible for the overall above-average salinities since 2011. Yet, local factors present in 2017, such as strong evaporation caused by extremely high air temperatures, lack of precipitation and low river discharges, combined with a decrease in horizontal transport estimated from the Regional Ocean Modeling System simulations, contributed substantially to the observed surface salinity anomaly. The decrease in horizontal advection was conjoined with high values of repelling barriers in the fields of the finite-time Lyapunov exponent. Documented physical conditions were synchronized with considerably lower bacterial production and abundance of the most studied picoplankton groups in comparison to values during the last decade. The exception was the euryhaline organism Synechococcus , whose abundance was 88% higher than the average in the study area. Nutrient content and chlorophyll-a concentrations followed regular seasonal cycles during 2017, with typical low values pointing to salinity as a possible driver of the observed changes in the microbial food web. Following ongoing climate change and future projections, these documented anomalous physical and microbiological conditions may become more frequent in the Adriatic Sea. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
15. Interpreting Self-Organizing Map errors in the classification of ocean patterns.
- Author
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Matić, Frano, Kalinić, Hrvoje, and Vilibić, Ivica
- Subjects
- *
DATA analysis , *SALINITY , *TEMPERATURE , *MAPS - Abstract
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]
- Published
- 2018
- Full Text
- View/download PDF
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