Irina P. Chubarenko

On some physical and dynamical properties of microplastic particles in marine environment

Simplified physical models and geometrical considerations reveal general physical and dynamical properties of microplastic particles (0.5-5mm) of different density, shape and size in marine environment. Windage of extremely light foamed particles, surface area and fouling rate of slightly positively buoyant microplastic spheres, films and fibres and settling velocities of negatively buoyant particles are analysed. For the Baltic Sea dimensions and under the considered idealised external conditions, (i) only one day is required for a foamed polystyrene particle to cross the sea (ca. 250km); (ii) polyethylene fibres should spend about 6-8months in the euphotic zone before sinking due to bio-fouling, whilst spherical particles can be retained on the surface up to 10-15years; (iii) for heavy microplastic particles, the time of settling through the water column in the central Gotland basin (ca. 250m) is less than 18h. Proper physical setting of the problem of microplastics transport and developing of physically-based parameterisations are seen as applications.

Modelling of man-made contribution to salinity increase into the Vistula Lagoon (Baltic Sea)

The man-made contribution to significant increase in salinity in the Vistula Lagoon (south-eastern Baltic) during the last century is discussed in this paper: (a) diversion of the main part of the Vistula River discharge from the Vistula Lagoon directly into the Baltic Sea at the beginning of this century; (b) the intensification of water exchange with the sea because of the deepening of the Lagoon entrance and (c) significant simplification of sea water penetration into the distant parts of Lagoon aquatory through deepened ship channels. The numerical modelling results (MIKE21) for salinity field annual dynamics in the whole Lagoon under different hydrological conditions are presented: before the reduction of the Vistula River inflow in 1916, under present-day conditions, if there are different ship channels in the Lagoon aquatory. The impacts of different man-made hydrological and morphological interventions that contribute to the salinity field variations are estimated and graded in order of effect. Temporal and spatial salinity variations, and mean annual values are discussed.

Wind-driven current simulations around the Island Mainau (Lake Constance)

Abstract Using three-dimensional numerical modelling for the shallow water equations on the rotating Earth in the Boussinesq approximation, we study the steady barotropic motion around the Island Mainau in Lake Uberlingen, forced by uniformly distributed winds of different directions. The method of substructuring is used to resolve the flow pattern near the Island Mainau with greater accuracy and thus to identify the peculiarities that are induced by the island as an obstruction to the current field within the lake basin. The barotropic response is analysed in detail for 16 different wind directions. It is shown to what extent these winds determine the distribution of the horizontal current and the up- and down-welling zones in the vicinity of the island. Current peculiarities, such as diverging and converging elements, locations of maximum current speeds and, in particular, the flow through the Mainau channel are identified. They provide hints to an optimal design of a flow measuring campaign under homogeneous conditions. It is further demonstrated that the island acts as an obstructing entity that effectively influences the flow within Lake Uberlingen. For wind blowing along Lake Uberlingen the baroclinic motion was also studied. The flow in the upper-layer and the lower-layer-return flow are modified over the lake.

Laboratory modeling of the structure of a thermal bar and related circulation in a basin with a sloping bottom

Development of a thermal bar in a laboratory flume with an inclined bottom (3.7°–12°) under the conditions of cooling/heating of the water with a temperature close to that of the maximal density is studied. The structure of the temperature field and currents during different stages of the circulation is examined: (i) formation of an along-slope gravity current, (ii) generation of a subsurface jet, and (iii) transformation of one type of the circulation into another at passing the temperature of the maximum density. The “fall” and “spring” types of the thermal bar are shown to be dynamically equivalent: the transport of the near-shore waters to the deepwater part, which is driven by the buoyancy flux rather than by the heat flux across the surface, transforms stage (i) into stage (ii), while the opposite (on-shore) flow is generated in the intermediate layers. A comparison of the results with the field and laboratory data published allows us to suggest that the propagation of the thermal bar front in the “fast” stage can be considered as the development of a convective jet with its velocity U ∼ h3/4, which is proportional to the growing thickness of the upper layer h affected by the heating/cooling processes

Microplastics in sea coastal zone: Lessons learned from the Baltic amber

Baltic amber, adored for its beauty already in Homers Odyssey (ca. 800 B.C.E), has its material density close to that of wide-spread plastics like polyamide, polystyrene, or acrylic. Migrations of amber stones in the sea and their massive washing ashore have been monitored by Baltic citizens for ages. Based on the collected information, we present the hypothesis on the behaviour of microplastic particles in sea coastal zone. Fresh-to-strong winds generate surface waves, currents and roll-structures, whose joint effect washes ashore from the underwater slope both amber stones and plastics - and carries them back to the sea in a few days. Analysis of underlying hydrophysical processes suggests that sea coastal zone under stormy winds plays a role of a mill for plastics, and negatively buoyant pieces seem to repeatedly migrate between beaches and underwater slopes until they are broken into small enough fragments that can be transported by currents to deeper areas and deposited out of reach of stormy waves. Direct observations on microplastics migrations are urged to prove the hypothesis.

Horizontal convective water exchange above a sloping bottom: The mechanism of its formation and an analysis of its development

The mechanism of the formation of horizontal temperature/density gradients above underwater coastal slopes of natural basins due to heating/cooling from the surface is considered. It is shown that the time required for formation of the gradients is rather small (tens of minutes for a thermocline depth of tens of meters), but the development of the corresponding flows may not be accomplished even in a day long cycle. The time dependence of the horizontal water exchange between the shallow and deep areas is analytically treated. The spatial scale of the problem is the main parameter that defines the resulting quasi-stationary value of the flow rate. The joint analysis of the published field, laboratory, and numerical data of many authors in the range of the above-slope depths of 10−2 m < d < 3 × 102 m (d ≤ D, where D is the thickness of the upper thermally active layer of a basin) indicates that the relation between the value of the horizontal quasi-stationary volumetric flow rate and the local depth looks like Q = 0.00l3 × d1.37 (R2 = 0.96). The horizontal convective water exchange is shown to be generally two-layered, ageostrophic, and exhibits its maximum flow rate at the end of the slope. The inferences agree well with the field data and conclusions of other authors.

Anthropogenic fibres in the Baltic Sea water column: Field data, laboratory and numerical testing of their motion

Distribution of microplastics particles (MPs) in the water column is investigated on the base of 95 water samples collected from various depths in the Baltic Sea Proper in 2015-2016. Fibres are the prevalent type of MPs: 7% of the samples contained small films; about 40% had (presumably) paint flakes, while 63% contained coloured fibres in concentrations from 0.07 to 2.6 items per litre. Near-surface and near-bottom layers (defined as one tenth of the local depth) have 3-5 times larger fibre concentrations than intermediate layers. Laboratory tests demonstrated that sinking behaviour of a small and flexible fibre can be complicated, with 4-fold difference in sinking velocity for various random fibres curvature during its free fall. Numerical tests on transport of fibres in the Baltic Sea Proper were performed using HIROMB reanalysis data (2007) for the horizontal velocity field and laboratory order-of-magnitude estimates for the sinking velocity of fibres. The model takes into account (i) motion of fibres together with currents, (ii) their very slow sinking, and (iii) their low re-suspension threshold. Sensitivity of the final distribution of fibres to variations of those parameters is examined. These experiments are the first step towards modelling of transport of fibres in marine environment and they seem to reproduce the main features of fibres distribution quite well.

Physics of Lakes

Barotropic Wind-induced Motions in a Shallow Lake.- Response of a Stratified Alpine Lake to External Wind Fields - Numerical Prediction and Comparison with Field Observations.- Comparing Numerical Methods for Convectively-Dominated Problems.- Comparing Different Numerical Treatments of Advection Terms for Wind-Induced Circulations in Lakes.- Subgrid-Scale Parameterization in Numerical Simulations of Lake Circulation.- Instruments and Sensors.- Measuring Methods and Techniques.- Dimensional Analysis, Similitude and Model Experiments.- Prograding and Retrograding Hypo- and Hyperpycnal Deltaic Formations into Quiescent Ambients.- Sediment Transport in Alluvial Systems.

Observation and Analysis of Internal Seiches in the Southern Basin of Lake of Lugano

As mentioned already earlier in Chap. 15, Lake of Lugano is a lake system consisting of two large basins and a pond of much smaller size, all connected to one another. In fact, the discharge of the water masses is from the 15 km long Northern basin through the channel of Melide into the roughly S-shaped 17-km long Southern basin and from there through the 500-m long channel of Lavena into the small pond at Ponte Tresa, see Fig. 18.1. The barotropic response of the two large basins has been separately studied as has this response of the lake system as a whole. In the Southern basin, three limnigraphs, positioned at Riva San Vitale, Morcote and Agno, recorded in February 1982 water elevation oscillations with periods of 28 min and less, that could be identified with the eigenperiods of the surface seiches with amplitudes of less than 5 cm. In a further campaign in 1984, current meters were installed in the Channels of Melide and Lavena and it was found that two further longer periodic eigenoscillations were excited which were not discernible in the limnigraph records and could be interpreted as the eigenvalues of the barotropic oscillations of the lake system acting as a coupled (Helmholtz-type) resonator. The structure of the eigenmodes, i.e. the distribution of the surface elevation was relatively simple. As the eigenfrequencies (periods) increased (decreased) the eigenmodes went from simple to complex with the number of nodal lines increasing by one with each higher order mode. Qualitatively this behaviour is akin to that of a rectangular basin with constant depth, so that interpretation of the data by means of theoretical modelling is easy. Deviations of the eigenperiods and structures of the eigenfunctions from those of the rectangle are due to the bathymetry and nothing else.

Structure of unsteady overflow in the Słupsk Furrow of the Baltic Sea

[1]xa0A data set of closely spaced CTD profiling performed aboard Russian and Polish research vessels during 1993–2009 and numerical modeling are applied to study the variability in the asymmetric transverse structure of salinity/density in the Slupsk Furrow (SF) overflow of the Baltic Sea. The numerical simulations show that, on the one hand, the overflow may be dynamically treated within the SF as a subcritical, eddy-producing gravity current in a wide channel, and on the other, at the sill displays some features peculiar to frictionally controlled rotating flows. Comparison between the field measurements and the simulation results indicates that the variability of the cross-channel density structure is caused mainly by meandering of the gravity current and mesoscale eddies – mostly above-halocline cyclones and intrahalocline anticyclones. The meanders and eddies are found to be strongly affected by the bottom topography and wind-forcing.