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Ivica Vilibić - One of the best experts on this subject based on the ideXlab platform.
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Modelling Interannual Changes in Dense Water Formation on the Northern Adriatic Shelf
Pure and Applied Geophysics, 2018Co-Authors: Hrvoje Mihanović, Ivica Vilibić, Ivica Janeković, Vedrana Kovačević, Manuel BensiAbstract: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.
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Dense Water formation in the coastal northeastern Adriatic Sea: the NAdEx 2015 experiment
2017Co-Authors: Ivica Vilibić, Hrvoje Mihanović, Miroslava Pasarić, Ivica Janeković, Cléa Denamiel, Pierre-marie Poulain, Mirko Orlić, Natalija Dunić, Vlado Dadić, Stipe MuslimAbstract:The paper investigates 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 have been collected by a variety of instruments and platforms (ADCPs, CTDs, glider, profiling float), and have been accompanied with a one-way coupled ALADIN/ROMS modelling effort. Research focus has been put on Dense Water formation (DWF), thermal changes and 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, even during milder-than-average winters (as was the winter of 2015). However, Dense Water formed in this coastal region has, due to lower salinities, lower densities than Dense Water formed at the open Adriatic. Since the sea is deeper in the coastal area than at the open Adriatic, Dense Waters from the open Adriatic occasionally enter the coastal area near the bottom of the connecting passages, while the surface flow is mostly outward from the coastal area. Median residence time of the coastal area is estimated to about 1–2 months, indicating that the coastal area may be relatively quickly renewed by the open Adriatic Waters. The model significantly underestimates currents and transports in connecting channels, which may be a result of a too coarse resolution of atmospheric forcing, misrepresentation of bathymetry or absence of the air-sea feedback in the model. Obtained data represents a comprehensive marine dataset, pointing to a number of interesting phenomena to be investigated in the future.
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Dense Water formation and BiOS-induced variability in the Adriatic Sea simulated using an ocean regional circulation model
Climate Dynamics, 2016Co-Authors: Natalija Dunić, Ivica Vilibić, Samuel Somot, Jadranka Šepić, Florence SevaultAbstract: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.
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Modelling the formation of Dense Water in the northern Adriatic: Sensitivity studies
Ocean Modelling, 2016Co-Authors: Ivica Vilibić, Hrvoje Mihanović, Ivica Janeković, Jadranka ŠepićAbstract:Abstract 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.
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Extreme cooling and Dense Water formation estimates in open and coastal regions of the Adriatic Sea during the winter of 2012
Journal of Geophysical Research: Oceans, 2014Co-Authors: Ivica Janeković, Hrvoje Mihanović, Ivica Vilibić, Martina TudorAbstract:Generation of Dense Waters in the Adriatic Sea during an extreme cooling event in the winter of 2012, including its preconditioning and spreading phases, have been investigated using the one-way coupled ROMS and the ALADIN/HR modeling system. Both climatological and real river fluxes are used in the simulations. Aside from the “convenient” Dense Water formation areas located at the northernmost Adriatic shelf, we found that a similar amount of Dense Water, with slightly lower density, was formed in the eastern and deeper Adriatic coastal area, which was subjected to extreme heat losses (up to 2000 W/m2) during peak cooling periods. This part of the Adriatic has been known for extreme cooling during wintertime bora outbreaks ; nevertheless, no ocean model study has previously reproduced Dense Water formation in this area. The most likely reason for that was an overestimate of river discharges introduced to ocean models. From newly available data, we estimated that the contribution of eastern Adriatic rivers between the Neretva River and Rijeka Bay is more than six times lower than what has been previously documented. Transport of Dense Water toward the middle Adriatic had a peak value of about 0.6 Sv, while the speed of initial bottom density current surpassed 40–50 cm/s, which is several times faster than past events. Different pathways of the Dense Water toward the middle and south Adriatic depressions have also been documented. The contribution of the eastern coastal Adriatic area to the overall north Adriatic Dense Water formation has been quantified and discussed for average and low freshWater load conditions, indicating that this part of the Adriatic is a common place for Dense Water generation.
Leonardo Langone - One of the best experts on this subject based on the ideXlab platform.
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Dense Water plumes SW off Spitsbergen Archipelago (Arctic) in 2014-2016
2017Co-Authors: Manuel Bensi, Leonardo Langone, Stefano Miserocchi, Vedrana Kovačević, Laura Ursella, Michele Rebesco, Cinzia De Vittor, Stefano Aliani, Federica Relitti, M. BazzaroAbstract:The Arctic region has gained a large interest because of climate changes and its effects on ice melting and global warming. Abrupt changes in the atmosphere are responsible for significant changes in the ocean Water masses and large-scale circulation, which in turn affect again the global climate. The knowledge of the circulation and related processes along the southwest (SW) offshore Svalbard area and within Storfjorden (southern Svalbard Archipelago) is essential to describe the thermohaline circulation and the Dense Water formation (DWF) in the Arctic, and how they contribute to the global thermohaline circulation. DWF processes in this region depend on the rate of cooling and homogenisation of the Atlantic Water along its northwards pathway, the brine rejection, boundary convection on the Arctic Ocean shelves and slopes, and the deep open-ocean convection in the central gyres of the Greenland and Iceland Seas. Here, we focus on the brine rejection, shelf convection and entrainment processes, which happen on the west shelf/slope of Svalbard and in the Storfjorden during the winter season. Two short (130m) moorings (S1 and I2) were deployed in 2014 in the SW offshore Svalbard at ~1000m depth, with the purpose of collecting multiannual time-series in an area of potential interaction between the Western Spitsbergen Current and the Dense shelf plumes. Three oceanographic cruises were carried out to integrate time-series with CTD casts in the area. One purpose of this research activity was to combine geophysical and oceanographic data to study the interaction of bottom currents and sediment drifts (contourites) formations. At S1 and I2, time-series revealed a large thermohaline and current variability during the winter period, from October to April. Our data highlight the presence of a stable signal of Norwegian Sea Deep Water influenced by occasional intrusions of warmer, saltier, and less Dense Water during fall-winter periods. Interestingly, such intrusions occur simultaneously at both sites, despite their distance (~170km). We discuss the origin, timing, and role of shelf turbidity plumes (Denser than TS plumes), which descend along slope and undergo a strong entrainment process that modify their properties. The role of possible mesoscale processes is also investigated.
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Dense-Water bottom currents in the Southern Adriatic Sea in spring 2012
Marine Geology, 2016Co-Authors: Jacopo Chiggiato, Aniello Russo, Andrea Bergamasco, Mireno Borghini, Francesco Marcello Falcieri, Pierpaolo Falco, Leonardo Langone, Stefano Miserocchi, Katrin SchroederAbstract:Abstract In February 2012, a severe cold spell in the European region triggered a massive production of very Dense Water on the northern Mediterranean Sea shelves. The spreading phase of the newly formed Dense Water was extensively studied in the Adriatic Sea by means of 2 ship surveys and 5 moorings fully equipped to monitor the flow of the bottom layer. For the Adriatic Sea, opposite to the Gulf of Lions, the area of cascading is far from the source area and this implies substantial modifications, adjustments and dilution of the source Water mass along its path, with a spreading phase lasting several months. Indeed all the moorings detected events, although weaker than in the preceding months, until June 2012. The surveys detected 2 branches of NAdDW on the shelf, the first branch not Denser than 29.7 kg/m3 and the second branch not Denser than 29.5 kg/m3. Despite the extremely Dense Water generated in the Northern Adriatic, during events of Dense-Water flow, moorings recorded temperatures generally between 12.5 and 13 °C, seldom less. Temperatures along the shelf break also did not fall below 13 °C at depths greater than 400 m. Turbulent mixing, therefore, heavily modified the cascading plumes, which left the shelf with thicknesses between 10 and 30 m. Mooring data in the lowermost 100 mab suggest that the thickness of the cascading layer increased by several tens of meters downslope, as a consequence of entrainment. Detraining frictional layers as well as locations of active cascading were identified mostly by isolated casts, highlighting the submesoscale domain of the downsloping plumes. The use of LADCP data allowed identification of very energetic bottom flow (40–50 cm/s in many locations), with otherwise little signature in tracers, not previously observed. The Bari Canyon System (BCS) was so far recognized as a hot spot for cascading in the Southern Adriatic. However, during the 2012 event, this is not the only preferred site for cascading. Significant Dense flow was detected in other locations. The northernmost mooring site, closer to the inception of the cascading process, in particular showed active cascading and several dynamical differences from the BCS: Denser Water with thinner boundary layer, events organized in multiple pulses with sub-inertial periodicity and with very short duration (12 h to 1 day) that is generally not seen in other locations.
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Off-shelf fluxes across the southern Adriatic margin: Factors controlling Dense-Water-driven transport phenomena
Marine Geology, 2016Co-Authors: Sandro Carniel, Andrea Bergamasco, Alfredo Boldrin, Francesco Marcello Falcieri, Davide Bonaldo, Alvise Benetazzo, Mauro Sclavo, Fabio Trincardi, Leonardo LangoneAbstract:Abstract The northern Adriatic Sea is a basin where Dense shelf Waters form during winters if the following favorable conditions are attained: high salinities, mainly related to low river Water discharge (Po river in primis) during fall season, and strong heat fluxes induced by cold and dry Bora wind events blowing from north-east. Extremely favorable conditions to Northern Adriatic Dense Waters (NAdDW) formation characterized winter 2012 when, following several months of low Po river runoff, a strong event of Cold Air Outbreak (CAO) occurred from the end of January until mid-February. Consequently, the mean temperature of northern Adriatic Waters dropped to about 6°C and exceptional densities (potential density anomaly locally exceeding 30.0 kg m− 3) were reached. The production and spreading mechanisms of Dense Water in the Adriatic Sea have been modeled by means of the COAWST (Coupled-Ocean–Atmosphere-Wave-Sediment-Transport) modeling system. The model builds upon a high-resolution (1 km spaced horizontal grid), fully 3-D primitive equations hydrodynamic model coupled with a phase-averaged wave model and sediment routines, and is driven by simulated atmospheric forcings. The dataset used to assess model outputs relies on the measurements acquired during the dedicated field campaigns “Operation Dense Water”, a set of two rapid response cruises carried out in southern Adriatic during winter 2012, and by five mooring arrays deployed in the Southern Adriatic Margin (SAM) that allowed the continuous acquisition of temperature, salinity, currents and suspended matter samples. Results from the integrated data-model approach suggest that the NAdDW propagates along the shelf to the southern basin following both a shallower vein and a deeper stream, with a process characterized by a strong variability (mean value of 0.31 Sv with peaks rapidly growing in the first weeks after the CAO up to 2.19 Sv). Additionally, COAWST capability to couple different numerical models allowed to disentangle the relative importance of aspects on Dense Water generation, mixing and spreading, demonstrating how coupled runs can lead to volumes up to 50% larger with respect to uncoupled simulations. Additional light is shed on the transport pathways off the shelf and on possible sediment transport phenomena in the area, in this benefiting from an unprecedented spatial resolution and a new bathymetry reflecting very high resolution data acquired via multi-beam techniques. Although Dense Water propagation appears as a relatively large-scale process involving the whole western side of the SAM, topographic local discontinuities and seabed slopes appear crucial in triggering descent and governing flow patterns. The presence of suspended sediment along the Water column, despite not significantly influencing the overall fluxes across sections, is responsible of pulling part of the veins towards deeper zones.
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Dense Water flow and carbonate system in the southern Adriatic: A focus on the 2012 event
Marine Geology, 2016Co-Authors: Carolina Cantoni, Jacopo Chiggiato, Katrin Schroeder, Anna Luchetta, Stefano Cozzi, Leonardo LangoneAbstract:Abstract The active deep overturning circulation of the Mediterranean is emerging as one of the most effective mechanisms in transporting the atmospheric imprint on the carbon cycle to the interior of the basin. There is growing evidence that sites of Dense Water formation over the continental shelf, such as the Northern Adriatic Sea, play a key role in this process. Nevertheless, little is known about the inorganic carbon chemistry of the Adriatic sea, and CO2 absorption and its fate. The winter of 2012 experienced peculiar meteorological conditions with an extended period of cold weather with strong winds that triggered, in February, a massive formation of an extremely cold and Dense (potential density anomaly > 30.00 kg m− 3) Northern Adriatic Dense Water (NAdDW) Water mass. This event provided a unique opportunity to study this process at sub-basin scale taking into account CO2 adsorption within the NAdDW source area (the Gulf of Trieste in the northern Adriatic), and its spreading over the shelf and into the Southern Adriatic Pit. The northern Adriatic and the Gulf of Trieste, during winter, act as a CO2 sink. The average air-sea CO2 flux of 60 mmol m− 2 d− 1 estimated during the exceptional 2012 event was at least 3 times higher than the flux measured in winter 2008 when Dense Water was produced through the same mechanism but under less extreme conditions. In winter 2012, absorbed CO2 resulted in the decrease of pHT25 down to 7.907 (− 0.034 pHT units) and the strong evaporation induced by wind-increased total alkalinity (TA) to 2673 (+ 16 μmol kg− 1). Following its formation in the North, the NAdDW plume entering the Southern Adriatic, observed in March 2012, exhibited significantly modified values. The plume was characterized by colder temperature (~ 10 °C), lower pHT25 (7.947 pHT units) and higher alkalinity (2635 μmol kg− 1) than the surrounding Water masses along the western Adriatic shelf. However, the signal of atmospheric CO2 enrichment was weaker than in the northern Adriatic source region, as well as positive apparent oxygen utilization (AOU) values (~ 20 μmol kg− 1) were recorded. This is suggestive of oxygen consumption in the Water mass. Observed changes in both physical and biogeochemical properties were similar to those observed in 2008, suggesting that mixing with Levantine Intermediate Waters (LIW) was the main driver modulating the changes of AOU and inorganic carbon chemistry in both winters. The rising of pHT25 and AOU due to the mixing indicates that NAdDW, at its origin, was richer in atmospheric CO2 than the LIW was, thus confirming the relevance of the Northern Adriatic Sea for CO2 adsorption. The study provides the first characterization of inorganic carbon chemistry, including carbonate minerals saturation states (ΩAr and ΩCa), in the bottom Waters both on the slope and along the expected pathways of Dense Water cascading in the Adriatic Sea. Therefore, it can represent a baseline to improve the knowledge on the acidification process and impacts as well as being useful for comparison with other benthic environments.
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On the descent of Dense Water on a complex canyon system in the southern Adriatic basin
Continental Shelf Research, 2012Co-Authors: Angelo Rubino, Alfredo Boldrin, Manuel Bensi, Vanessa Cardin, Leonardo Langone, Stefano Miserocchi, D. Romanenkov, Davide Zanchettin, Dagmar Hainbucher, M. TurchettoAbstract:Abstract Using the results of a numerical model for the description of bottom-arrested currents and statistical analyses, we elucidate different characteristics of the dynamics of a southward propagating vein of North Adriatic Dense Water (NAdDW) observed to evolve within a complex canyon system of the southern Adriatic basin. The vein, monitored from March 2004 to March 2005 by three distinct mooring lines, exhibits a complex, highly time-dependent dynamics characterized by large velocity and density fluctuations. In particular, lag correlation analyses performed on the observed velocity and temperature data show that a temporal lag ranging between 7 and 10 h governs the NAdDW signal propagation along the different canyons, its magnitude inversely depending on vein downslope velocities and density anomalies. The performed model simulations reveal that, weakly depending on its initial layer thickness, exact position, and density contrast with the upper ocean, a coherent flow of Dense Water located upstream of the canyon system on the Italian shelf will always bifurcate at the entrance of that system; while its shallower part will disintegrate into several branches, its deeper part will continue to flow more coherently, injecting part of the bottom Water downward. Regions dominated by supercritical flow regimes are simulated, which contributes to explain part of the observed flow variability. Simulated lag times between signals propagating in the canyons are consistent with observations. They are found to depend crucially on initial, upstream vein location, layer thickness, and density contrast with the upper ocean. We finally use this information, retrieved by our numerical simulations on the basis of the available observations, to infer, in a kind of inverse problem solving, possible shape, location, and density contrast possessed by the observed vein of NAdDW on the Italian continental shelf, prior to its sinking toward the Bari canyon system.
Jérôme Bonnin - One of the best experts on this subject based on the ideXlab platform.
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Impact of storms and Dense Water cascading on shelf-slope exchanges in the Gulf of Lion (NW Mediterranean)
Journal of Geophysical Research, 2008Co-Authors: Caroline Ulses, X. Durrieu De Madron, Claude Estournel, Jérôme Bonnin, Patrick MarsaleixAbstract:[1] In situ observations of ocean temperature, salinity, density and current collected from November 2003 to May 2004 in the Gulf of Lion were combined with numerical modeling in order to better understand the mechanisms and forcing conditions that control shelf-slope exchanges during autumn and winter times. Outputs from a 3-D coastal circulation model revealed that marine storms (and related processes) and Dense Water cascading were the two major mechanisms controlling shelf-slope exchanges. Marine storms induced accumulation of seaWater along the coast, generated a strong cyclonic circulation on the shelf, and caused downwelling in submarine canyons that facilitated export of shelf Water. During fall, because of strong Water column stratification at that time, the depth of export remained shallow. In winter, the destratification together with the density increase of shelf Water, due to the cooling effect of strong and cold northerly winds, enabled shelf Water to plunge down the slope. The results of this study thus highlighted the importance of marine storms for shelf-slope exchanges, particularly during winter mixed conditions when they reinforced the cascading of Dense Water.
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Suspended sediment fluxes and transport processes in the Gulf of Lions submarine canyons. The role of storms and Dense Water cascading
Marine Geology, 2006Co-Authors: Albert Palanques, Xavier Durrieu De Madron, Miquel Canals, Antoni Calafat, Serge Heussner, Pere Puig, Joan Fabres, Jorge Guillén, Jérôme BonninAbstract:Contemporary suspended sediment transport was studied in seven submarine canyons of the Gulf of Lions (GoL). Current meters equipped with turbidity sensors were moored 4 m above bottom at 300 m depth in the canyon axis from November 2003 to May 2004. Sediment transport events were monitored and studied in relation to forcing conditions. There was a large flood in early December, during which discharges from all of the coastal rivers increased by more than one order of magnitude. A smaller flood of the Rhone River occurred later in mid-January followed by a persistent high river discharge that lasted until mid-February. There were also several E–SE storm events during the measurement period, two of them causing large swell, one in early December (max Hs: 8.4 m), coinciding with the major river flood,andoneinlateFebruary(maxHs:7m)duringaperiodoflowerriverdischarge.Mostofthevariabilityindown-canyoncurrentspeeds waslinkedtostrongdownwellinginducedbyE–SEstormsandtocascadingofDenseshelfWaterinducedbyNandNWwinds.Theintensity and timing of these processes strongly varied spatially. Eastern storms generated higher waves and induced stronger downwelling in the western than in the eastern sector of the GoL. Shelf Dense Water cascading events were enhanced during eastern storms and they were also more intense in the western sector of the GoL. These events occurred frequently from January to May along the western canyons and from February to April along the eastern canyons. From February to April they occurred simultaneously in all the canyons. Sediment transport was mainly down-canyon and mostly concentrated during storm-induced downwelling and Dense Water cascading events. During the high river discharge season most of the newly-supplied and resuspended sediment remained stored on theshelf.However,duringthelateFebruarystormandcascadingevent,thestoredsedimentwasquicklyresuspendedandtransported, mainly through the westernmost submarine canyon (Cap de Creus), following a flushing pattern. Later, although minor storms and shelfDenseWatercascadinghardlyincreasedsuspendedsedimentconcentrationswithinthecanyons,theyinducedstrongnear-bottom current velocities, increasing down-canyon sediment fluxes and generating small but significant sediment transport events. Most of the shelf-canyon transfer took place during the late February storm and cascading event through the Cap de Creus canyon where the net suspended sediment flux was between one and two orders of magnitude higher than in the other canyons.
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Suspended sediment fluxes and transport processes in the Gulf of Lions submarine canyons. The role of storms and Dense Water cascading
Marine Geology, 2006Co-Authors: Albert Palanques, Miquel Canals, Antoni Calafat, Serge Heussner, Xavier Durrieu De Madron, Pere Puig, Joan Fabres, Jorge Guillén, Jérôme BonninAbstract:Special issue EUROSTRATAFORM VOL. 1: Source to Sink Sedimentation on the European Margin.-- 20 pages, 14 figures.-- Erratum to “Suspended sediment fluxes and transport processes in the Gulf of Lions submarine canyons. The role of storms and Dense Water cascading” [Marine Geology 234/1–4 (2006) 43–61] http://dx.doi.org/10.1016/j.margeo.2007.01.007Contemporary suspended sediment transport was studied in seven submarine canyons of the Gulf of Lions (GoL). Current meters equipped with turbidity sensors were moored 4 m above bottom at 300 m depth in the canyon axis from November 2003 to May 2004. Sediment transport events were monitored and studied in relation to forcing conditions. There was a large flood in early December, during which discharges from all of the coastal rivers increased by more than one order of magnitude. A smaller flood of the Rhone River occurred later in mid-January followed by a persistent high river discharge that lasted until mid-February. There were also several E-SE storm events during the measurement period, two of them causing large swell, one in early December (max Hs: 8.4 m), coinciding with the major river flood, and one in late February (max Hs: 7 m) during a period of lower river discharge. Most of the variability in down-canyon current speeds was linked to strong downwelling induced by E-SE storms and to cascading of Dense shelf Water induced by N and NW winds. The intensity and timing of these processes strongly varied spatially. Eastern storms generated higher waves and induced stronger downwelling in the western than in the eastern sector of the GoL. Shelf Dense Water cascading events were enhanced during eastern storms and they were also more intense in the western sector of the GoL. These events occurred frequently from January to May along the western canyons and from February to April along the eastern canyons. From February to April they occurred simultaneously in all the canyons. Sediment transport was mainly down-canyon and mostly concentrated during storm-induced downwelling and Dense Water cascading events. During the high river discharge season most of the newly-supplied and resuspended sediment remained stored on the shelf. However, during the late February storm and cascading event, the stored sediment was quickly resuspended and transported, mainly through the westernmost submarine canyon (Cap de Creus), following a flushing pattern. Later, although minor storms and shelf Dense Water cascading hardly increased suspended sediment concentrations within the canyons, they induced strong near-bottom cunrent velocities, increasing down-canyon sediment fluxes and generating small but significant sediment transport events. Most of the shelf-canyon transfer took place during the late February storm and cascading event through the Cap de Creus canyon where the net suspended sediment flux was between one and two orders of magnitude higher than in the other canyonsThis study was supported by the EUROSTRATAFORM Project funded by the EU (EVK3-CT-2002-00079, EU Fifth Framework Programme: Energy, Environment and Sustainable Development)Peer reviewe
Hrvoje Mihanović - One of the best experts on this subject based on the ideXlab platform.
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Modelling Interannual Changes in Dense Water Formation on the Northern Adriatic Shelf
Pure and Applied Geophysics, 2018Co-Authors: Hrvoje Mihanović, Ivica Vilibić, Ivica Janeković, Vedrana Kovačević, Manuel BensiAbstract: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.
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Dense Water formation in the coastal northeastern Adriatic Sea: the NAdEx 2015 experiment
2017Co-Authors: Ivica Vilibić, Hrvoje Mihanović, Miroslava Pasarić, Ivica Janeković, Cléa Denamiel, Pierre-marie Poulain, Mirko Orlić, Natalija Dunić, Vlado Dadić, Stipe MuslimAbstract:The paper investigates 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 have been collected by a variety of instruments and platforms (ADCPs, CTDs, glider, profiling float), and have been accompanied with a one-way coupled ALADIN/ROMS modelling effort. Research focus has been put on Dense Water formation (DWF), thermal changes and 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, even during milder-than-average winters (as was the winter of 2015). However, Dense Water formed in this coastal region has, due to lower salinities, lower densities than Dense Water formed at the open Adriatic. Since the sea is deeper in the coastal area than at the open Adriatic, Dense Waters from the open Adriatic occasionally enter the coastal area near the bottom of the connecting passages, while the surface flow is mostly outward from the coastal area. Median residence time of the coastal area is estimated to about 1–2 months, indicating that the coastal area may be relatively quickly renewed by the open Adriatic Waters. The model significantly underestimates currents and transports in connecting channels, which may be a result of a too coarse resolution of atmospheric forcing, misrepresentation of bathymetry or absence of the air-sea feedback in the model. Obtained data represents a comprehensive marine dataset, pointing to a number of interesting phenomena to be investigated in the future.
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Modelling the formation of Dense Water in the northern Adriatic: Sensitivity studies
Ocean Modelling, 2016Co-Authors: Ivica Vilibić, Hrvoje Mihanović, Ivica Janeković, Jadranka ŠepićAbstract:Abstract 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.
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Extreme cooling and Dense Water formation estimates in open and coastal regions of the Adriatic Sea during the winter of 2012
Journal of Geophysical Research: Oceans, 2014Co-Authors: Ivica Janeković, Hrvoje Mihanović, Ivica Vilibić, Martina TudorAbstract:Generation of Dense Waters in the Adriatic Sea during an extreme cooling event in the winter of 2012, including its preconditioning and spreading phases, have been investigated using the one-way coupled ROMS and the ALADIN/HR modeling system. Both climatological and real river fluxes are used in the simulations. Aside from the “convenient” Dense Water formation areas located at the northernmost Adriatic shelf, we found that a similar amount of Dense Water, with slightly lower density, was formed in the eastern and deeper Adriatic coastal area, which was subjected to extreme heat losses (up to 2000 W/m2) during peak cooling periods. This part of the Adriatic has been known for extreme cooling during wintertime bora outbreaks ; nevertheless, no ocean model study has previously reproduced Dense Water formation in this area. The most likely reason for that was an overestimate of river discharges introduced to ocean models. From newly available data, we estimated that the contribution of eastern Adriatic rivers between the Neretva River and Rijeka Bay is more than six times lower than what has been previously documented. Transport of Dense Water toward the middle Adriatic had a peak value of about 0.6 Sv, while the speed of initial bottom density current surpassed 40–50 cm/s, which is several times faster than past events. Different pathways of the Dense Water toward the middle and south Adriatic depressions have also been documented. The contribution of the eastern coastal Adriatic area to the overall north Adriatic Dense Water formation has been quantified and discussed for average and low freshWater load conditions, indicating that this part of the Adriatic is a common place for Dense Water generation.
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Dense Water formation in the eastern coastal Adriatic during an extreme cooling event
European geosciences union general assembly, 2014Co-Authors: Hrvoje Mihanović, Ivica Vilibić, Ivica Janeković, Martina TudorAbstract:Dense Water formation (DWF) that occurred in both open and coastal Waters of the Adriatic Sea during extreme cooling event in January/February 2012 was reproduced by coupled high-resolution atmosphere-ocean modelling system. Regional Ocean Modeling System (ROMS) ocean model has been applied with resolution of 2 km and with lateral boundaries coming from the operational AREG Adriatic model. The model has been forced at the sea surface by the operational NWP model ALADIN/HR.
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The 1987 Aegean Dense Water formation: A streamtube investigation by comparing theoretical model results, satellite, field, and numerical data with contourite distribution
Marine Geology, 2016Co-Authors: Marco Bellacicco, Christos Anagnostou, Federico Falcini, E. Rinaldi, K. Tripsanas, E. SalustiAbstract:Abstract We here discuss a detailed investigation of the Dense Water formation, evolution and spreading in the Aegean Sea during the year 1987, immediately prior to the onset of the Eastern Mediterranean Transient (EMT). We use hydrologic data collected during the LIA cruise; satellite images for SST (Sea Surface Temperature), and PROTHEUS data (a coupled ocean–atmosphere numeric model) along with theoretical streamtube models. These hydrological analyses are related to late Quaternary sedimentary drifts in the Cyclades Plateau and in the Myrtoon Basin. Our analysis shows that streamtube dynamics provide a novel model of Dense Water evolution and spreading in the Aegean Basin. Applying this model to Dense Water masses observed in winter and spring 1987 near Samothrace and over the Limnos-Lesbos Plateau, results in a geostrophic flow of this Dense, cold Water towards the Limnos-Sporades Channel, in the North Aegean Sea. There it mixes with Dense Water from the Limnos-Lesbos Plateau and finally both move geostrophically towards the Cyclades Plateau. These results indicate that most of the Dense Water observed near the Cyclades, formed initially about 3 months earlier at Samothrace and Limnos shelves. During its long pathway it partially mixed with adjacent Water masses. Although our analysis concerns only one year of Dense Water analyses, these results are thought to reflect a more general and recurrent phenomenon in the Aegean basin. Indeed, high-resolution (Airgun 10 in.) seismic-reflection data from the Cyclades Plateau reveal the presence of late Quaternary sediment drifts. These observations are concordant with results from our theoretical model. This suggests a direct link between such a Dense-Water cascading and contourite dynamics. The continuation of sediment drifts into the deep basin floor (≈ 900 m deep) of the Myrtoon Basin, moreover, indicates a cascading character of such bottom currents at the flanks of the basin, a feature that set further investigations.
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On the Dense Water spreading off the Ross Sea shelf (Southern Ocean)
Journal of Marine Systems, 2002Co-Authors: Giorgio Budillon, S. Gremes Cordero, E. SalustiAbstract:In this study, current meter and hydrological data obtained during the X Italian Expedition in the Ross Sea (CLIMA Project) are analyzed. Our data show a nice agreement with previous data referring to the Water masses present in this area and their dynamics. Here, they are used to further analyze the mixing and deepening processes of Deep Ice Shelf Water (DISW) over the northern shelf break of the Ross Sea. In more detail, our work is focused on the elementary mechanisms that are the most efficient in removing Dense Water from the shelf: either classical mixing effects or density currents that interact with some topographic irregularity in order to drop to deeper levels, or also the variability of the Antarctic Circumpolar Current (ACC) which, in its meandering, can push the Dense Water off the shelf, thus interrupting its geostrophic flow. We also discuss in detail the (partial) evidence of dramatic interactions of the Dense Water with bottom particulate, of geological or biological origin, thus generating impulsive or quasi-steady density-turbidity currents. This complex interaction allows one to consider bottom particular and Dense Water as a unique self-interacting system. In synthesis, this is a first tentative analysis of the effect of bottom particulate on the Dense Water dynamics in the Ross Sea.
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Dense Water Dynamics along the Strait of Sicily (Mediterranean Sea)
Journal of Physical Oceanography, 2001Co-Authors: M. Astraldi, G. P. Gasparini, L. Gervasio, E. SalustiAbstract:Abstract Hydrographic and current meter data, gathered in different periods in the Strait of Sicily and in the southern Tyrrhenian Sea, allow the outflow characteristics from the eastern toward the Western Mediterranean basin to be analyzed. The evolution through the strait of a deep vein of Dense Water coming from the Eastern Mediterranean is described, together with the dynamic interaction with overlying layers. These data are related to a slightly generalized version of recent density current models, such as those of Emms and those of Baringer and Price. Taking into account the dynamic influence of the overlying currents, and in particular their friction and mixing, this model explains the path of this deep flow and enables estimates of entrainment and bottom friction to be made. With these new data, a phenomenon of considerable interest, namely the dynamics of density currents crossing and outflowing from a strait, is examined and discussed.
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On Dense Water formation criteria and their application to the Mediterranean Sea
Deep Sea Research Part I: Oceanographic Research Papers, 2000Co-Authors: Bruno Buongiorno Nardelli, E. SalustiAbstract:Abstract Recently proposed criteria to identify sites, periods and characteristics of Dense Water formation in the Mediterranean Sea are analyzed. These criteria were first obtained through tank experiments and numerical and theoretical analyses. They can be useful for discriminating between processes that reach the sea bottom and those involving only the less thick superficial layers. With these criteria, general characteristics of newly formed Dense Water can be inferred from a knowledge only of winter density stratification g ′, of the buoyancy increase B due to the violent winter storms, and of the horizontal space scale R of the region of interest, a quantity usually identified by a decrease of 0.5–1°C of the SST. For the Mediterranean Sea, these criteria are applied here to the few known field observations and to more indirect “routine” information, namely climatological values of the stratification, numerical estimates of the buoyancy flux and remotely sensed SST from satellite imagery. In this way a stimulating picture of these dramatic phenomena is obtained, giving some insight into the possibility of forecasting and into other characteristics of Dense Water formation processes.