Wave-induced Transport Research Articles

Influence of dike-induced morphologic and sedimentologic changes on the benthic ecosystem in the sheltered tidal flats, Saemangeum area, west coast of Korea

The effects of dike construction on the geomorphology and sedimentary processes of tidal flats were investigated using high-precision topographic profiling, short cores, and unmanned aviation vehicle (UAV)-assisted photogrammetry to understand their adverse consequences on the benthic ecosystem. Tidal flats at the south of Shinsi Island near one of the two sluice gates of the Saemangeum dike, display prominent morphologic features known as shelly sand ridges or cheniers (sensu Otvos, 2000) that have migrated landward about 5 m in a year. The tidal flats were dominated by erosion from winter to spring and by deposition during the remainder of the year except for the periods of heavy precipitation when tidal drainage channels became larger and deeper by headward erosion. With overall coarser-grained surface sediments, the presence of actively migrating wave-built cheniers are in stark contrast to muddy tidal flats with a monotonous morphology before the completion of the Saemangeum dike in 2006. Southeasterly waves reflected from the dike during winter to spring when north to northwesterly winds prevail account for the wave-induced onshore sediment transport and rapid morphologic changes in the tidal flats despite their location protected from offshore waves. The diversity and biomass of major macrofauna species tend to increase during rapid erosion and decrease during rapid deposition, highlighting the anthropogenic effect of dike-induced physical disturbance on the benthic ecosystem in the otherwise sheltered tidal flats.

Wave-modulation of mussel daily settlement at contrasting rocky shores in central Chile: topographic regulation of transport mechanisms in the surf zone

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 606:39-53 (2018) - DOI: https://doi.org/10.3354/meps12782 Wave-modulation of mussel daily settlement at contrasting rocky shores in central Chile: topographic regulation of transport mechanisms in the surf zone Nicolas Weidberg1,3,*, Bryan Bularz1, Sebastián López-Rodríguez1, Sergio Andrés Navarrete1,2 1Estación Costera de Investigaciones Marinas (ECIM), Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, 6513677 Santiago, Chile 2LINCGlobal CSIC-UC and Center for Applied Ecology and Sustainability (CAPES), Pontifica Universidad Católica de Chile, 6513677 Santiago, Chile 3Present address: Department of Arctic and Marine Biology, University of Tromsø, 9019 Tromsø, Norway *Corresponding author: j_weidberg@hotmail.com ABSTRACT: Settlement is a complex biological process that, for most species, marks the end of pelagic larval life and the beginning of benthic life, and is therefore critical for the replenishment and persistence of marine benthic populations. Increasing evidence points to the surf zone as an important last hurdle modulating successful onshore larval settlement in intertidal and shallow subtidal habitats. Wave hydrodynamics cause the development of near-bottom flows, which have been suggested as a mechanism of cross-surf zone transport of heavy sinking competent larvae of mussels. Here, we tested the generality of this model with new data, contrasting 2 distant (100 km) sites with different surf zone configurations and slopes. Daily mussel settlement rates were measured for 3 periods of 10 d over 3 different settlement seasons between 2015 and 2017, and were related to potential cross-shore transport mechanisms. When corrected for differences in surf zone slope between sites and de-seasoned, near-bed bottom flows explained 87% of the variance in daily settlement at both sites, with the exception of the steep surf zone site in 2016, when settlement increased even faster with the flow. When flow direction is considered, site-specific alongshore and cross-shore transport patterns emerge at the reflective and dissipative shores, respectively. These patterns suggest that wave-induced transport through the surf zone can be a general mechanism favoring onshore mussel settlement, and highlight the importance of local topography in modulating such transport mechanisms. KEY WORDS: Larval supply · Orbital velocities · Coastal orientation · Upwelling Full text in pdf format Supplementary material PreviousNextCite this article as: Weidberg N, Bularz B, López-Rodríguez S, Navarrete SA (2018) Wave-modulation of mussel daily settlement at contrasting rocky shores in central Chile: topographic regulation of transport mechanisms in the surf zone. Mar Ecol Prog Ser 606:39-53. https://doi.org/10.3354/meps12782 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 606. Online publication date: November 15, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Collapse and recovery process of the sand spit at the Tenryu River mouth on the Pacific Coast of Japan

ABSTRACT This paper investigates the collapse and recovery processes of the sand spit at the Tenryu River mouth on the Pacific Coast of Japan, when two characteristic typhoons, Man-Yi and Fitow, passed over the study site in the year 2007. Although these two typhoons caused equally high storm waves, these two events were different in principal wave directions and in the amount of river discharges. As a result, Man-Yi collapsed the sand spit, while Fitow rather enhanced the recovery of the sand spit. Successive still images recorded by six field cameras were analyzed to investigate the dynamic morphology change of the river mouth for 2 months during which these two events had occurred. Comparisons of obtained topography changes and various hydrodynamic characteristics yielded several findings: (i) the sand spit was breached approximately 6 h after the peak of flow velocity and 2 h after the peak of the water head difference across the sand spit; (ii) the breached part of the sand spit was refilled by wave-induced shoreward sediment transport; and (iii) a core sample showed three clear layers of graded sedimentary structures of gravel, which correspond to the number of observed high waves overtopping the sand spit.

Tidal inlet sediment bypassing at mixed-energy barrier islands

The large-scale littoral sediment drift along barrier island coasts involves alongshore sand transport at the islands’ surf zone and across tidal inlets. Mechanisms of sediment bypassing at non-migrating, mixed-energy tidal inlets are discussed based on process-based numerical modeling of sediment dynamics at an exemplary barrier island system in the southern North Sea. Residual transport pathways of distinct sediment grain-size fractions and morphological changes reveal the complexity of processes at tidal inlets driven by the non-linear interaction of competing tidal and wave forces. Sediment bypassing from the updrift to the downdrift shoreline of a tidal inlet is evaluated and the ratio of bypassed to recirculated sand volumes is estimated. Common inlet bypassing schemes are discussed and verified. It is shown that the different bypassing mechanisms can happen simultaneously and are related to the transport behavior of particular sediment grain-size fractions: Very fine to fine sand bypasses the inlet along the entire ebb-tidal delta periphery by wave-induced transport processes. Fine to medium sand is transported by the ebb-directed tidal currents in the inlet throat to the ebb-tidal delta where wave-driven transport processes and bar welding bypasses the sediments to the downdrift shore. For fine to medium and medium sands, a sediment recirculation cell at the downdrift ebb-tidal delta and reversal to the main inlet throat is identified.

Wave-induced bedload transport – a study of the southern Baltic coastal zone

Abstract The wave-induced bedload transport and spatial distribution of its magnitude in the southern Baltic coastal zone of Poland are estimated. The vicinity of Lubiatowo was selected as a representative part of the Polish coast. It was assumed that transport is a function of shear stress; alternative approaches, based on force balances and discharge relationships, were not considered in the present study. Four models were studied and compared over a wide range of bottom shear stress and wind-wave conditions. The set of models comprises classic theories that assume a simplified influence of turbulence on sediment transport (e.g., advocated by authors such as Du Boys, Meyer-Peter and Müller, Ribberink, Engelund and Hansen). It is shown that these models allow to estimate transport comparable to measured values under similar environmental conditions. A united general model for bedload transport is proposed, and a set of maps of wave bedload transport for various wind conditions in the study area is presented.

Wave-current interactions in the southern North Sea: The impact on salinity

The interplay between wind waves and currents in the coastal zone of the southern North Sea along with the resulting changes in the salinity distribution are quantified using simulations with the unstructured-grid ocean model SCHISM coupled with the wind wave model WWM III. Several sensitivity runs, which are carried out to estimate the individual contributions of different physical mechanisms and forcing, demonstrated that the density gradients in the coastal zone reduce tidal current by 18%, whereas the wind waves enhance the circulation in some cases. The latter happens when along-shore wind speed approaches ∼10 m s−1 resulting in long-shore currents following the western Dutch coast and the German Wadden Sea islands. The wave-induced transport of salt leads to changes in the horizontal salinity distribution. These are most pronounced in front of barrier islands where coherent patterns caused by the coupling between tides, surface drift, and wind waves reveal salinity changes up to 0.5. The weak stratification of salinity in the coastal zone is mostly destroyed by wind waves. Thus, effects created by wind waves tend to substantially modify the estuarine circulation. An explanation of these important processes in the coastal zone has been given based on an analysis of the ratio between significant wave height and tidal range. This control-parameter, which is relatively small under mild weather conditions, can exceed unity under strong wind conditions in the coastal zone, thus mixing due to waves becomes dominant. The effect of fresh water fluxes from subterranean estuaries is relatively small and confined only in the vicinity of corresponding sources.

RANS-based simulation of wave-induced sheet-flow transport of graded sediments

A one-dimensional vertical (1DV) turbulence-closure flow model, coupled with sediment transport capabilities, is extended to incorporate graded sediment mixtures. The hydrodynamic model solves the horizontal component of the incompressible Reynolds-averaged Navier–Stokes (RANS) equations coupled with k–ω turbulence closure. The sediment transport description includes both bed and suspended load descriptions. So-called high-concentration effects (turbulence damping and hindered settling velocities) are likewise included. The sediment transport model treats the bed and suspended load individually for each grain fraction, including effects associated with increased exposure of larger particles within a mixture. The suspended sediment transport model also makes use of modified reference concentration approach, wherein reference concentrations computed individually for each fraction are translated to a common level, conveniently enabling use of a single computational grid for the simulation of suspended sediments. Parametric study shows that these two effects combine to help alleviate an otherwise systematic tendency towards over- (under-) predicted transport rates for fine (coarse) sand fractions. The sediment transport model is validated against sheet-flow experimental oscillatory tunnel measurements beneath velocity-skewed wave signals, and demonstrates similar accuracy (transport rates generally within a factor of two) for both graded and uniform sands. The model is likewise validated against an extensive data set involving sheet-flow transport beneath acceleration-skewed wave signals (limited to uniform sands). It is then utilized to study potential effects of gradation on the net transport beneath such flows. The simulations suggest that gradation effects can both increase, as well as decrease, the total transport rate, depending largely on the behavior of the fine sand fraction. The model is implemented within the Matlab environment, and is freely available upon request to the corresponding author.

The shoreline distribution and degradation of tilapia carcasses, Salton Sea, California: Taphonomic implications

The Salton Sea is a hypersaline, closed lake system in southern California, USA. Episodic fish kills led to bloating and floating fish bodies that were driven onto the shoreline by wind shear. The documented taphonomic destruction of the stranded fish carcasses includes the distribution of the fish parts after desiccation and disarticulation mainly by wave-induced transport with possible minor component of wind transport on the upper shoreface. Carcass decay is divided into five taphonomic categories 1 through 5. Category 1 represents whole pliable fish, recently washed onto the shoreline while category 5 incorporates longer-term destruction into ultimately single, isolated skeletal elements. High water, strand line deposits are delineated by the presence of categories 3 through 5 mixtures. The general trend, in 2012 was observed to be considerable bone disarticulation away from the shoreline because categories 1 and 2 were present in the swash zone; the influx of fresh fish carcasses recharged the shoreline. During 2013, the absence of new 1 and 2 categories arriving to the shoreline enhanced wave action to further break down categories 3 and 4 ultimately into category 5. In addition, isolated bone elements segregate according to density differences, typically on low-gradient beaches. Wave and wave-induced current action coupled with beach topography controls distribution of the various fish bones. As an actualistic model, the Salton Sea implies that shore-parallel complete to partial fish carcass concentrations are more shoreward and isolated skeletal elements more distal.

Study of relationship between wave transport and sea surface temperature anomaly (SSTA) in the tropical Pacific

Large-scale water transport is one of the key factors that affect sea surface temperature anomaly (SSTA) in the eastern equatorial Pacific (EEP). The relationship between the wave transport in the tropical Pacific and the SSTA in the EEP is examined by different methods, including band-pass filtering, period analysis, correlation analysis, significant analysis, and empirical orthogonal function (EOF) analysis. We have found that the eastward shift of the wave transport anomaly in the tropical Pacific, with a period of 2 a and enhancing the transport of warm waters from the western Pacific warm pool, precedes the increase of sea surface temperature (SST) in the EEP. The wave transport and the SSTA in the EEP have a maximum correlation of 0.65 with a time-lag of 6 months (transport variation precedes the temperature). The major periods (3.7 a and 2.45 a) of the wave transport variability, as revealed by the EOF analysis, appear to be consistent with the SSTA oscillation cycle in the EEP. Based on the first occurrence of a significant SSTA in the Nino 3 region (5°S–5°N, 90°–150°W), two types of warm events are defined. The wave transport anomalies in two types present predominantly the west anomaly in the tropical Pacific, it is that the wave transport continues transport warm water from west to east before the onset of the warm event. The impact of wave-induced water transport on the SSTA in the EEP is confirmed by the heat flux of the wave transport. The wave transport exerts significant effect on the SSTA variability in the EEP and thus is not neglectable in the further studies.

The Evolution of Nonlinear Wave Statistics through a Variable Medium

AbstractIn coastal areas and on beaches, nonlinear effects in ocean waves are dominated by so-called triad interactions. These effects can result in large energy transfers across the wave spectrum and result in non-Gaussian wave statistics, which is important for coastal wave propagation and wave-induced transport processes. To model these effects in a stochastic wave model based on the radiative transfer equation (RTE) requires a transport equation for three-wave correlators (the bispectrum) that is compatible with quasi-homogeneous theory. Based on methods developed in optics and quantum mechanics, the authors present a general approach to derive a transport equation for higher-order correlators. The principal result of this work is a coupled set of equations consisting of the radiative transfer equation with a nonlinear forcing term and a new, generalized transport equation for bispectrum. This study discusses the implications and characteristics of the resulting equations and shows that the model contains various shallow- and deep-water asymptotes for nonlinear wave propagation as special cases.

A note on the vertical distribution of momentum transport in water waves

Abstract In this paper, the classical problem of horizontal waveinduced momentum transport is analyzed once again. A new analytical approach has been employed to reveal the vertical variation of this transport in the Eulerian description. In mathematical terms, this variation is shown to have (after “smoothing out” the surface corrugation) the character of a generalized function (distribution) and is described by a classical function in the water depths and by an additional Dirac-delta-function component on the averaged free surface. In terms of physics, the considered variation consists of two entities: (i) a continuous distribution of the mean momentum transport flux density (tensorial radiation pressure) over the entire water column, and (ii) an additional momentum transport flux concentrated on the mean free surface level (tensorial radiation surface pressure). Simple analytical formulae describing this variation have been derived. This allowed a conventional expression to be derived, describing the depth-integrated excess of horizontal momentum flux due to the presence of waves (the so-called “radiation stress”), confirming to some extent the correctness of the whole analysis carried out. The results obtained may be important to the ocean dynamics, especially in view of their possible application in the field of hydrodynamics of wave-dominated coastal zones.

Large-scale Barrier Dynamics Experiment II (BARDEX II): Experimental design, instrumentation, test program, and data set

Despite the increased sophistication of numerical models and field techniques for investigating wave-induced nearshore sediment transport and ensuing beach morphological response, there remains a significant demand for large-scale laboratory experiments to address this research topic. Here, we describe the Barrier Dynamics II Experiment (BARDEX II), which involved placing a near prototype-scale sandy barrier in the middle of the Delta Flume in the Netherlands and subjecting the structure to a range of wave, tide, and water level conditions. A unique aspect of the experiment was the presence of a lagoon behind the barrier, as often occurs in natural barrier settings, providing a convenient means to experimentally manipulate the groundwater hydrology within the barrier. The overall aim of the BARDEX II was to collect a large-scale data set of energetic waves acting on a sandy beach/barrier system to improve our quantitative understanding and modeling capability of shallow water sediment transport processes in the inner surf, swash, and overwash zone. In this paper, we introduce BARDEX II and provide a detailed description of the experiment, including the experimental design, instrumentation, test program, and data set, as well as presenting some examples of the morphological and hydrodynamic data set. We also reflect objectively on the strengths and weaknesses of the data set. This paper serves as an introduction to a special issue of Coastal Engineering, solely devoted to the results of BARDEX II.

Along-Strike Variations In Stratigraphic Architecture of Shallow-Marine Reservoir Analogues: Upper Cretaceous Panther Tongue Delta and Coeval Shoreface, Star Point Sandstone, Wasatch Plateau, Central Utah, U.S.A.

Abstract Along-strike variations in sediment supply and process regime may result in different facies distributions, preservational biases, and stratigraphic architectures in shallow-marine strata. Data from a large (c. 100 km), nearly continuous outcrop belt aligned oblique to depositional strike was integrated with nearby subsurface well data and petrological analysis of distal fine-grained deposits, to analyze along-strike variations in stratigraphic architecture in a single parasequence in the upper Cretaceous Star Point Sandstone, Wasatch Plateau, central Utah, USA. The parasequence comprises wave-dominated shoreface deposits in the southern part of the study area and represents a single episode of shoreline regression and transgression. Four progradationally stacked bedsets (BS1–BS4) in the distal deposits of the parasequence are the expression of minor variations in relative sea level, sediment supply, and/or wave climate. The four bedsets can be traced to river-dominated deltaic deposits (Panther Tongue) in the northern part of the study area. We interpret the parasequence on the scale of the Wasatch Plateau outcrop belt as the record of deposition in a regressive river- and wave-influenced delta deflected asymmetrically towards the SSW, subparallel to the regional paleo-shoreline trend, and a coeval wave-dominated strandplain. The lateral transition from river- to wave-dominated facies is attributed to the localization of a major river acting as a sediment point source in the north, with wave-induced longshore transport to the south. Our results imply that characterizing lateral facies distributions and the expression of bedsets is vital for interpreting along-strike variability in controlling mechanisms of stratigraphic architecture, and that external forcing may be recorded differently along depositional strike.

Eulerian Volume Transport Induced by Spatially Damped Internal Equatorial Kelvin Waves

AbstractThe Eulerian volume transport in internal equatorial Kelvin waves subject to viscous attenuation is investigated theoretically by integrating the horizontal momentum equations in the vertical. In terms of small perturbations, the time-averaged horizontal transports are determined to second order in wave steepness. The total Lagrangian volume transport in this problem consists of a Stokes transport plus an Eulerian transport. It is known that the Stokes transport, that is, the vertically integrated Stokes drift, in inviscid internal equatorial Kelvin waves vanishes identically in the rigid-lid approximation for arbitrary vertical variation of the Brunt–Väisälä frequency. The present study considers spatial wave damping due to viscosity. The Stokes transport still becomes zero, but now the radiation stresses due to decaying waves become source terms for the Eulerian mean transport. Calculations of the wave-induced Eulerian transport yield a jetlike symmetric mean flow along the equator from west to east for each baroclinic component, with compensating westward flows on both sides. The flow system scales as the internal equatorial Rossby radius in the north–south direction. The total eastward part of the Eulerian volume flux centered about the equator is estimated to about 0.2 Sv (1 Sv ≡ 106 m3 s−1) for the first baroclinic mode.

Methane as a diagnostic tracer of changes in the Brewer–Dobson circulation of the stratosphere

Abstract. This study makes use of time series of methane (CH4) data from the Halogen Occultation Experiment (HALOE) to detect whether there were any statistically significant changes of the Brewer–Dobson circulation (BDC) within the stratosphere during 1992–2005. The HALOE CH4 profiles are in terms of mixing ratio versus pressure altitude and are binned into latitude zones within the Southern Hemisphere and the Northern Hemisphere. Their separate time series are then analyzed using multiple linear regression (MLR) techniques. The CH4 trend terms for the Northern Hemisphere are significant and positive at 10° N from 50 to 7 hPa and larger than the tropospheric CH4 trends of about 3% decade−1 from 20 to 7 hPa. At 60° N the trends are clearly negative from 20 to 7 hPa. Their combined trends indicate an acceleration of the BDC in the middle stratosphere of the Northern Hemisphere during those years, most likely due to changes from the effects of wave activity. No similar significant BDC acceleration is found for the Southern Hemisphere. Trends from HALOE H2O are analyzed for consistency. Their mutual trends with CH4 are anti-correlated qualitatively in the middle and upper stratosphere, where CH4 is chemically oxidized to H2O. Conversely, their mutual trends in the lower stratosphere are dominated by their trends upon entry to the tropical stratosphere. Time series residuals for CH4 in the lower mesosphere also exhibit structures that are anti-correlated in some instances with those of the tracer-like species HCl. Their occasional aperiodic structures indicate the effects of transport following episodic, wintertime wave activity. It is concluded that observed multi-year, zonally averaged distributions of CH4 can be used to diagnose major instances of wave-induced transport in the middle atmosphere and to detect changes in the stratospheric BDC.

The Impact of Wave-Induced Longshore Transport On A Delta-Shoreface System

Abstract Wave-induced longshore sediment transport is a major basinal process that reworks fluvial sediment supply along a delta–shoreface depositional system. However, the effects of the variable counterbalance between supply and wave reworking have not been sufficiently acknowledged in understanding paleoshoreline evolution and stratigraphic concepts such as sequence stratigraphy and autostratigraphy. With a numerical shoreline model, we quantify the relation between wave-induced longshore sediment transport and shoreline orientation under conditions of steady sea level. A case study of the Po delta–shoreface system reveals that a decrease in delta progradation rate can in part be considered as an autogenic response to steady wave conditions offshore. Long-term wave-induced transport can be quantified by the volume of sediment redistribution. As such, we propose a revised definition of accommodation space by integrating the effect of wave-induced longshore transport. Wave-induced longshore sediment transport has a significant impact on progradation of deltaic and adjacent shoreface shorelines, and needs to be considered while interpreting shallow-marine stratigraphy.

Wave-induced mixing and transport of buoyant particles: application to the Statfjord A oil spill

Abstract. This study focuses on how wave–current and wave–turbulence interactions modify the transport of buoyant particles in the ocean. Here the particles can represent oil droplets, plastic particles, or plankton such as fish eggs and larvae. Using the General Ocean Turbulence Model (GOTM), modified to take surface wave effects into account, we investigate how the increased mixing by wave breaking and Stokes shear production, as well as the stronger veering by the Coriolis–Stokes force, affects the drift of the particles. The energy and momentum fluxes, as well as the Stokes drift, depend on the directional wave spectrum obtained from a wave model. As a first test, the depth and velocity scales from the model are compared with analytical solutions based on a constant eddy viscosity (i.e., classical Ekman theory). Secondly, the model is applied to a case in which we investigate the oil drift after an oil spill off the west coast of Norway in 2007. During this accident the average net drift of oil was observed to be both slower and more deflected away from the wind direction than predicted by oil-drift models. In this case, using wind and wave forcing from the ERA Interim archive it is shown that the wave effects are important for the resultant drift and have the potential to improve drift forecasting.

Global surface wave drift climate from ERA-40: the contributions from wind-sea and swell

By using 45 years of reanalysis data from the European Centre for Medium-Range Weather Forecasts, ERA-40, we present and discuss the global climatological wave-induced velocity, surface Stokes drift (SD), and its vertically integrated transport for deep water waves. We find that in most of the oceanic basins, the global surface SD is mainly wind-sea-driven while its vertically integrated transport is mainly swell-driven. The total surface SD does not always coincide in orientation with its vertically integrated transport. We suggest that such regions of misalignment are linked to “wave-driven wind” regimes. Coastal wave-induced transport divergences are mostly linked to wind-sea while divergences in the interior of the oceans basins are linked to swell. Analysis of trends indicates that the vertically integrated transport has generally increased during the 45 years analyzed. The largest increases are due to wind-sea in limited high-latitude areas while the swell has a minor increase, but over larger areas.

Processes affecting recent and future evolution of the Xylokastro beach zone (Gulf of Corinth, Greece)

<div> <p>The aim of the present study is to investigate the morphodynamic regime of the coastal area of Xylokastro (north coast of Peloponnese), in order to identify and evaluate the processes controlling its formation and evolution. Within this concept, a number of factors have been considered and evaluated; near-shore morphometry and granulometry along shore-normal profiles, the direction and potential volumes of long- and cross-shore sediment transport the decadal and future trends of coastline displacement, the available information for terrestrial sediment influx and the geological processes operating in the broader coastal region of Xylokastro (i.e. subaqueous slides) as well as human interference. On the basis of these results, the formation and evolution of this coastal stretch seems to be governed primarily by the neotectonic activity and relative change of sea level rise, and secondarily by the wave-induced near-shore sediment transport; the role of the latter could be enhanced substantially by human intervention (i.e. construction of marina, seafront walls). Moreover, the expected eustatic increase in sea level by the year 2100, could cause a coastline retreat up to 9 m (SLR=0.38 m) or >19 m (SLR≥1 m).</p> </div> <p> </p>

Response of the Adriatic Sea to an intense cold air outbreak: Dense water dynamics and wave-induced transport

The paper describes formation and spreading of dense shelf waters in the Adriatic Sea (North Adriatic Dense Water, NAdDW) during the winter of 2012 as a consequence of an intense and long cold air outbreak of northeasterly Bora winds. As a result, during February 2012 northern Adriatic Sea water temperature dropped to about 6°C and density exceeded 1030kg/m3, most likely the maximum value since 1929. NAdDW dynamics has been investigated by means of a 3-D ocean-wave coupled model running on a high resolution and eddy-permitting grid. The numerical experiments have relied on the Coupled-Ocean–Atmosphere-Wave-Sediment-Transport (COAWST) system forced one-way with atmospheric forcings provided by the model COSMO-I7. A suite of observational data has been used to characterize the Bora event and evaluate numerical model performance. At sub-basin scales, the newly formed waters flowing southerly have produced a water renewal of the northern Adriatic, as more than 50% of water volumes have left the basin. Dense waters volume transports, evaluated through different Adriatic cross-sections, have been modulated by tides (damped for the densest water masses) and reached about 1Sv. The contribution of wave-induced forcings has been quantified and examined, indicating that these represent a major driving mechanism during NAdDW production and spreading phases. This work provides evidence that NAdDW is spread accordingly with two different mechanisms: at early stages of its formation, the wind-driven ocean circulation pushes newly formed waters to leave the northern basin with relatively high speeds (about 0.30m/s). Later on, remaining NAdDW leaks slowly out (0.09m/s as average) from the production site. Residence times of dense waters in the north, middle, and south Adriatic Sea are also documented.