scroll identifier for mobile
main-content

This book commemorates the 70th birthday of Eugene Morozov, the noted Russian observational oceanographer. It contains many contributions reflecting his fields of interest, including but not limited to tidal internal waves, ocean circulation, deep ocean currents, and Arctic oceanography.

Special attention is paid to studies on internal waves and especially those on tidal internal waves in the Global Ocean. These papers describe the most important open problems concerning experimental studies of internal waves and their theoretical, numerical, and laboratory modeling.

Further contributions investigate the physics of surface waves and their interaction with internal waves. Here, the focus is on describing interaction processes between internal waves and deep currents in the ocean, especially currents of Antarctic Bottom Water in abyssal fractures. They also touch on the problem of oceanic circulation and related processes in fjords, including those occurring under sea ice.

Given its breadth of coverage, the book will appeal to anyone interested in a survey of ocean dynamics, ranging from historic perspectives to modern research topics.

### Honorary Note. Evgeny Georgievich Morozov: A Life at Sea as a Devoted Ocean Observer

On March 15, 1946, Eugene G. Morozov, an outstanding field oceanographer, was born in Moscow. He is Doctor of Sciences in Physics and Mathematics. Since 1993 he is Head of the Hydrological Processes Laboratory at the Shirshov Institute of Oceanology (Russian Academy of Sciences) in Moscow. He has been President (2011–2015) of the International Association for the Physical Sciences of the Ocean (IAPSO, in 1999 he was elected member of the IAPSO Executive Committee). He is Laureate of the Shirshov Medal (2016). He was also a member of the executive committees of the International Union of Geodesy and Geophysics (IUGG) and Scientific Council for Oceanic Research (SCOR). He is the Chairman of the Oceanographic Section at the Russian National Geophysical Committee, which is a Russian link to the IUGG. Dr. Morozov is member of the editorial boards of four journals: Izvestia Atmospheric and Oceanic Physics, Russian Journal of Earth Sciences, Oceanological Researches, and Fundamental and Applied Hydrophysics.

Manuel G. Velarde, Roman Yu. Tarakanov, Alexey V. Marchenko

### Gallery: An Ocean Scientist and His Life at Sea

Manuel G. Velarde, Roman Yu. Tarakanov, Alexey V. Marchenko

### New Steps of the Modern Oceanography: Reminiscences of My Work with Evgeny Georgievich Morozov

Eugene G. Morozov knows not only how to perform field measurements in the most interesting locations, but also how to process and analyze these measurements applying all his expertise and knowledge of physics and mathematics.

Victor G. Neiman

### Fifty Years of Collaboration with Evgeny Georgievich Morozov

The author describes his work with Eugene Morozov since the beginning of his scientific career. B. Filyushkin and E. Morozov have been working together in many expeditions. Joint work at sea and at the Institute is described. Joint publications about internal waves and intrathermocline lenses became the objects of their study.

Boris N. Filyushkin

### Internal Undular Bores in the Coastal Ocean

In the coastal ocean, large amplitude, horizontally propagating internal wave trains are commonly observed. These are long nonlinear waves and are often modelled by equations of the Korteweg-de Vries type, such as the variable-coefficient Korteweg-de Vries equation when the background topography varies as the waves propagate shoreward. Most emphasis has been placed on the solitary wave solutions of these model equations, whereas in reality, wave trains are more usually observed. In this review article we examine the undular bore asymptotic representation of wave trains in the framework of the variable-coefficient Korteweg-de Vries equation, placing a special emphasis on the front of the undular bore which can be represented by a simplified model as a solitary wave train. We consider applications for both propagation shorewards whenw nonlinearity increases, and for cases when the wave train passes through a critical point of polarity change, when the nonlinear coefficient in the Korteweg-de Vries equation changes sign.

Roger Grimshaw, Chunxin Yuan

The internal wave (dead water) resistance on the Polar ship FRAM is obtained by two methods. The first is empirical, based on the original observations (Nansen, F.: Farthest North, Westminster: Archibald Constable and Company, 2 Whitehall Gardens, 1897. Vol. 1). The second is a strongly nonlinear interfacial method in three dimensions. The intersection between the empirical and theoretical resistances determines accurately the ship speed which is investigated varying the depth of the pycnocline, a quantity that was not measured by Nansen. A reduction to a fifth of the usual speed of the FRAM because of the dead water, as observed by Nansen, corresponds to a mid-depth of the pycnocline of slightly less than 4 m while FRAM’s draught was 5 m. The wave wake at Froude number slightly above 0.5 is calculated by the nonlinear method. The linear ship wake and dead water resistance are found to be invalid.

John Grue

### Internal Solitary Waves in a Layered Weakly Stratified Flow

The problem on internal waves in a weakly stratified two-layered flow is studied semi-analytically. The long-wave model describing travelling waves is constructed by means of scaling procedure with a small Boussinesq parameter. It is demonstrated that solitary wave regimes can be affected by the Kelvin–Helmholtz instability arising due to interfacial velocity shear in the upstream flow.

Nikolay Makarenko, Janna Maltseva, Roman Tarakanov, Kseniya Ivanova

### Surface Manifestations of Internal Waves Induced by a Subsurface Buoyant Jet (Experiment and Theory)

In this contribution we summarized the main results of the work on internal waves generated by vertical turbulent plumes in stratified fluids, including the mechanisms of internal wave generation, the structure of internal waves, and their surface manifestations Particular attention is focused on the major series of experiments performed in the Large Thermally Stratified Tank of the Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia. The majority of results are applicable for the monitoring of the coastal zone of the oceans. The other potential implications include buoyant plumes generated by subglacial discharge in Greenland fjords.

Valerii G. Bondur, Yuliya I. Troitskaya, Ekaterina V. Ezhova, Vasiliy I. Kazakov, Alexandr A. Kandaurov, Daniil A. Sergeev, Irina A. Soustova

### Large Internal Solitary Waves in Shallow Waters

The propagation of finite amplitude internal waves over an uneven bottom is considered. One of the specific features of the large amplitude internal waves is the ability of the waves to carry fluid in the “trapped core” for a long distance. The velocity of particles in the “trapped core” is very close and, even, exceeds the wave speed. Such waves are detected in different parts of seas and oceans as internal waves of depression and elevation as well as short intrusions at interfaces. Laboratory experiments on the generation, interaction and decay of solitary waves in a two-layer fluid are discussed. Analytical and numerical solutions describing the evolution of internal waves in a shelf zone are constructed by the three-layer shallow water model. Laboratory investigations of the different types of internal waves (bottom, subsurface and interlayer waves) are demonstrating, that the model can be effectively applied to the numerical solution of unsteady wave motions, and the traveling waves, which can be found from the model in rather simple form, give the realistic form and governing parameters of internal waves in laboratory and field observations. The basic features of the large amplitude solitary waves and nonlinear wave trains evolution over a shelf can be represented by the model.

Valery Liapidevskii, Nikolay Gavrilov

### Internal Gravity Waves in Horizontally Inhomogeneous Ocean

The paper is devoted to the research of the processes of generation and propagation of internal gravity waves in the vertically stratified horizontally non-uniform ocean based on the development of the asymptotic methods related to the generalization of the space-time ray-tracing method (the method of the geometrical optics, WKBJ method). Numerical results based on the application of asymptotic formulas for the real ocean parameters are presented.

Vitaly V. Bulatov, Yury V. Vladimirov

### High-Resolution Observations of Internal Wave Turbulence in the Deep Ocean

An overview is presented of high-resolution temperature observations above underwater topography in the deep, generally stably stratified ocean. The Eulerian mooring technique is used by typically distributing 100 sensors over lines between 40 and 400 m long. The independent sensors sample at a rate of 1 Hz for up to one year with a precision better than 0.1 mK. This precision and sampling rate are sufficient to resolve all of the internal waves and their breaking including the large, energy containing turbulent eddies above underwater topography. Under conditions of a tight temperature-density relationship, the data are used to quantify turbulent overturns. The turbulent diapycnal mixing is important for the redistribution of nutrients, heat (to maintain the stable stratification) and the resuspension of sediment. The detailed observations show two distinctive turbulence processes that are associated with different phases of large-scale carriers (which are mainly tidal but also inertial, internal gravity waves or a sub-inertial sloshing motion): (i) highly nonlinear turbulent frontal bores during the upslope propagating phase, and (ii) Kelvin-Helmholtz billows, at some distance above the slope, during the downslope phase. While the former may be associated in part with convective turbulent overturning following Rayleigh-Taylor instabilities preceding and sharpening the bores, the latter are mainly related to shear-induced instabilities. Under weaker stratified conditions, away from boundaries, free convective mixing appears more often, but a clear inertial subrange in temperature spectra is indicative of dominant shear-induced turbulence. Turbulence is seen to increase in dissipation rate and diffusivity all the way to the bottom while stratification remains constant, which challenges the idea of a homogeneous ‘well-mixed bottom boundary layer’. With a newly developed five-lines mooring the transition is demonstrated from isotropy (full turbulence) to anisotropy (stratified turbulence/internal waves).

Hans van Haren

### Deep-Ocean Tides in the South-West Indian Ocean: Comparing Deep-Sea Pressure to Satellite Data

Deep ocean pressure measurements in two regions of the South-West Indian Ocean (West and East of Madagascar), covering one to two years of data, are analysed for tidal motions. The pressure data are taken both from Bottom Pressure Recorders as well as from mid-water column instruments. Coherent tides are characterised by fixed amplitudes and phases. Those inferred from bottom measurements compare well to tides obtained from satellite altimetry, and cover up to 99$$\%$$% of the pressure variance in the frequency band having periods shorter than 29 h. Long-period tides, in the low-frequency band, are regularly overshadowed by (unwanted) eddy-induced mooring motion (‘blow-down’), which events have therefore been eliminated. In the Mozambique Channel, semidiurnal surface tides are stronger than East of Madagascar, and all appear to be near resonance with a basin mode. Away from the bottom, coherent internal tides were determined. Evidence of the presence of incoherent internal tides has been obtained by applying Harmonic Analyses over a moving time window of 1 year duration. East of Madagascar internal tides appear to be very strong, although its source remains unclear.

Leo R. M. Maas, Borja Aguiar-González, Leandro Ponsoni

### Internal Tides West of the Iberian Peninsula

We analyze archived historical moored measurements around the Iberian Peninsula to estimate the amplitudes of the semidiurnal internal tides on a basin-scale. Decay of amplitudes as the internal tide propagates from the continental slope is estimated. Directions and wavelengths of the internal tides are determined from the spatiotemporal spectra at the semidiurnal frequency calculated from the data of moored temperature measurements on clusters of moorings in the middle of the Iberian Basin and south of the Iberian Peninsula.

Eugene G. Morozov, Manuel G. Velarde

### Asymmetric Baroclinic Response to Tidal Forcing Along the Main Sill of the Strait of Gibraltar Inferred from Mooring Observations

Data collected in the north and south channels of the main sill of the Strait of Gibraltar (Camarinal sill) have been used to investigate processes connected to the internal hydraulics of the exchange through the Strait at tidal frequencies. They strongly suggest the setting up of hydraulic jumps at both the western and eastern flank of the sill, the latter associated with the reversal of the Mediterranean undercurrent during spring tides. The northern site is more sensitive to processes triggered by the formation and release of the jump formed east of the sill during intense enough ebb tide cycles, which is thus better traced at this location, whereas the southern site detects the fluctuations and footprints associated with the hydraulic jump regularly formed to the west of the sill during flood tides more neatly. A detailed inspection of the high resolution bathymetry of the area reveals the existence of two enclosed depressions at either side of Camarinal sill, almost certainly carved by the bottom flow over the millennia, whose shape and morphology are suggestive of this spatial differentiation. In addition to the expected fortnightly periodicity of the spring-neap tidal cycle, the observed hydrodynamic features show a pronounced diurnal inequality caused by the tidal currents of the diurnal constituents.

Jesús García-Lafuente, Simone Sammartino, José C. Sánchez-Garrido, Cristina Naranjo

### Mode 2 Internal Waves in the Ocean: Evidences from Observations

We study the second mode of the oceanic internal waves, which arose interest in recent years. We present experimental evidences of mode 2 internal waves based on our observations that we performed in various regions of the ocean. In particular, we consider examples from the observations over the Mascarene Ridge in the Indian Ocean, in the Luzon Strait of the South-China Sea, and in the Black Sea.

Andrey N. Serebryany

### Abyssal Mixing in the Laboratory

One of the important questions in the dynamics of the oceans is related to the cascade of mechanical energy in the abyss and its contribution to mixing. Here, we propose a unique self-consistent experimental and numerical set up that models a cascade of triadic interactions transferring energy from large-scale monochromatic input to multi-scale internal wave motion. We show how this set-up can be used to tackle the open question of studying internal wave turbulence in a laboratory, by providing, for the first time, explicit evidence of a wave turbulence framework for internal waves. Finally, beyond this regime, we highlight a clear transition to a cascade of small-scale overturning events which induce mixing.

T. Dauxois, E. Ermanyuk, C. Brouzet, S. Joubaud, I. Sibgatullin

### Rogue Waves in the Ocean, the Role of Modulational Instability, and Abrupt Changes of Environmental Conditions that Can Provoke Non Equilibrium Wave Dynamics

Modulational instability is an efficient mechanism for the generation of rogue waves in the limit of narrow-banded and long-crested wave fields. While such wave fields are easily achieved in laboratories, there appears to be lacking evidence that known occurrences of rogue waves in the ocean (e.g. Draupner “New Year” wave, Andrea wave) or ship accidents that could have been provoked by rogue waves (e.g. the Prestige accident) actually happened in sea states favorable for the modulational instability to have played an important role. The absence of modulational instability does not mean that nonlinear interactions are unimportant. Here we point out recent results that suggest large deviations from Gaussian statistics can happen due to nonlinearity in the absence of modulational instability, the key ingredient seems to be that the wave field is brought into a state of non-equilibrium.

Karsten Trulsen

### Simulation of Standing and Propagating Sea Waves with Three-Dimensional ARMA Model

Simulation of sea waves is a problem appearing in the framework of developing software-based ship motion modelling applications. These applications generally use linear wave theory to generate small-amplitude waves programmatically and determine impact of external excitations on a ship hull. Using linear wave theory is feasible for ocean waves, but is not accurate for shallow-water and storm waves. To cope with these shortcomings we introduce autoregressive moving-average (ARMA) model, which is widely known in oceanography, but rarely used for sea wave modelling. The new model allows to generate waves of arbitrary amplitudes, is accurate for both shallow and deep water, and its software implementation shows superior performance by relying on fast Fourier transform family of algorithms. Integral characteristics of wavy surface produced by ARMA model are verified against the ones of real sea surface. Despite all its advantages, ARMA model requires a new method to determine wave pressures, an instance of which is included in the chapter.

Ivan Gankevich, Alexander Degtyarev

### Perturbation Theory for the Compound Soliton of the Gardner’s Equation; Their Interaction and Evolution in a Media with Variable Parameters

This paper is a brief review of the results of an approximate description of the evolution and interaction of composite solitons, obtained by the authors in 2001–2016. As one of the applications of the theory, the features of the evolution of intense internal waves in the shelf zone of the ocean are analyzed.

Irina A. Soustova, Konstantin A. Gorshkov, Alexey V. Ermoshkin, Lev A. Ostrovsky, Yuliya I. Troitskaya

### Scientific Contributions: Ocean Circulation

#### Frontmatter

We examine geostrophic adjustment in a model rotating ocean when the angular speed of rotation $${\varvec{\Omega}}$$Ω does not coincide in direction with the gravity; the traditional and hydrostatic approximations are not used. Two models are considered: the barotropic one and the stably-neutrally stratified (SNS) fluid consisting of a stratified upper layer and a homogeneous lower layer. Wave spectra in the models contain gyroscopic and (in the SNS fluid) internal waves. Linear adjustment results in a tendency of any localized initial state to a geostrophically balanced steady motion parallel to the layer boundaries. In the barotropic fluid and homogeneous layer in the SNS fluid the motion is columnar, the columns are parallel to $${\varvec{\Omega}}$$Ω; in the stratified layer the geostrophic mode is not columnar. Using the perturbation theory we study the non-linear adjustment for the small Rossby number and aspect ratio. During the adjustment an arbitrary perturbation is uniquely split into slow quasi-geostrophic (QG) and fast ageostrophic components. In the barotropic model the slow component is described by the 2D fluid dynamics equation for the geostrophic streamfunction. In the SNS fluid the component is governed by two coupled nonlinear equations of QG potential vorticity in the upper and lower layers. The ageostrophic part consists of the inertial oscillations modulated by amplitude depending on coordinates and the slow time, and (in the SNS fluid) internal waves. The internal waves decay due to dispersion and the residual flow is a sum of the QG slow component and inertial oscillations coupled to the QG flow.

Gregory M. Reznik

### Evolution of an Intrathermocline Lens over the Lofoten Basin

The Lofoten Basin of the Norwegian Sea is the main reservoir of heat in the Polar seas; it stands out as an area of high mesoscale activity and the existence of a quasi-permanent anticyclonic vortex. The observations of Argo floats over the period of 2005–2014 (17,600 profiles measured by 125 recorders) were used in the area of 55–80° N and 30–15° W, covering the Lofoten Basin. The Argo-based Model for Investigation of the Global Ocean (AMIGO) was used. The method makes it possible to obtain annual mean velocity fields and thermohaline characteristics up to a depth of 1500 m in 1° squares. One large-scale anticyclonic vortex covering the deepest part of the Lofoten area was observed in the depth column from 30 to 1500 m with velocity values increasing from 0–2 cm/s in the vortex center to 7–12 cm/s at its periphery. A local anticyclonic vortex (a lens of warm and saline waters) with a radius of about 35 km at depths of 250–700 m with an average long-term position of the center at 69.5° N and 3.5° E is also distinguished along the vertical distributions of thermohaline characteristics. In this contribution, we simulate the evolution of this lens, represented as an anticyclonic vortex patch located in the middle layer, within the framework of a three-layer quasi-geostrophic model using the Contour Dynamics Method. Calculations showed that the model can adequately reproduce the nature of the lens drift under the influences of various types of ocean currents and bottom topography. Comparison of the model results with the in situ observations of the vortex trajectories gives satisfactory results.

Boris N. Filyushkin, Mikhail A. Sokolovskiy, Konstantin V. Lebedev

### The Global Atmosphere Oscillations in the Context of the Recent Climate Change

This study is dedicated to the confirmation, improvement, and extending of the preliminary hypothesis on short-term oscillations of the recent climate thermodynamic characteristics. In some previous studies we distinguished the quasi-cyclic oscillations in the recent climate dynamics with periods of 3–4 years and 25–35 years. These fluctuations appear in the most explicit form in the terms of large-scale redistribution of the atmospheric air mass accompanied by a significant enhancement of the positive atmospheric pressure anomaly in the equatorial-tropical zone and formation of the other major anomalies in different regions of the Earth. The results indicate that the known multimode regional indices in the dynamics of the climate system: the North Atlantic, North Pacific, Southern, and the others so-called Oscillations (NAO, NPO etc.) can be derived from the global atmospheric oscillations (GAO) with the temporal scales from several years to decades. It was found that multi-decade GAO is distinguished on the basis of a consequent phase change of the climate scenario in the North Atlantic region. Consideration of the interannual GAO led us to the definition of a new concept of the El Niño’s physical trigger mechanism in the Pacific region. Moreover, on the basis of the empirical data, it was shown for the first time that the well-known climatic events within the El Niño—Southern Oscillation (ENSO) phenomenon should be considered as a structural part of the interannual GAO.

Victor G. Neiman, Vladimir I. Byshev, Yury A. Romanov, Ilya V. Serykh

### Influence of the Current Field Non-stationarity and the Non-simultaneity of Hydrographic Measurements on ADCP-based Transport Estimates

Non-stationarity of the current’s field in combination with non-simultaneous measurements at stations of a hydrographic section leads to distortions in the ADCP-based assessments of total geostrophic barotropic transport over the section. These distortions over 49 particular sections from-shore-to-shore in different regions of the World Ocean are investigated on the basis of satellite altimetry data of Sea Level Anomaly, Absolute Dynamic Topography (ADT), and Formal Mapping Error (FME) available in the Internet (http://www.aviso.altimetry.fr). Distortions of barotropic transport have two components. The first is due to a change in the field of currents during measurements from station to station. It can be taken into account in the structure of the transport across the section from satellite altimetry data. The second is related to the displacement of streamlines of the geostrophic current at the ocean surface (ADT isolines) relative to the isobaths and represents the variability range of the instantaneous barotropic transport across the section track estimated on the basis of the same data during the time interval of measurements over this section. Assessments of these distortions are compared with the estimates of the errors of the barotropic transport over particular hydrographic sections. It is shown that the main component of these errors is the FME. Often, both components of the barotropic transport distortion are greater than the barotropic transport error, even for “rapid” sections, which are occupied in 6–12 days. Examples exist, in which significant transport distortions are accumulated during even shorter time periods of 3–5 days. Thus, investigation of the non-stationarity of the velocity field in combination with the non-simultaneity of hydrographic measurements is absolutely necessary for the analyses of the total transport and its structure across a hydrographic section.

R. Yu. Tarakanov

### Satellite Remote Sensing of Submesoscale Eddies in the Russian Seas

Satellite images of high resolution, primarily radar images, have shown that submesoscale eddies (diameter less than the Rossby internal radius of deformation) are a common element of water dynamics of the inner Russian seas (the Black, Caspian, Baltic, and White). Characteristic diameters of these eddies are 2–8 km. Examples of satellite images of such eddies in the coastal zone and open sea are presented, and mechanisms of their generation are discussed.

Andrey G. Kostianoy, Anna I. Ginzburg, Olga Yu. Lavrova, Marina I. Mityagina

### Ship-Based Monitoring of the Northern North Atlantic Ocean by the Shirshov Institute of Oceanology. The Main Results

Since 1997, the Shirshov Institute of Oceanology has been carrying out ship-based monitoring of the water mass properties (temperature, salinity, dissolved oxygen, and nutrients) and circulation in the northern North Atlantic over a section along 59.5° N from the southern tip of Greenland to Scotland. Since 2002, high precession full-depth measurements over the section have been made annually. The data set thus collected along with data from kindred projects (e.g., French Ovide) and historical data have been used by our group for studying the decadal variability of thermohaline properties and large-scale circulation in the water column, dense water formation, the Meridional overturning circulation, and the underlying mechanisms. The main results are summarized in this paper.

Artem Sarafanov, Anastasia Falina, Alexey Sokov, Vyacheslav Zapotylko, Sergey Gladyshev

### Thermohaline Structure and Salt Fingering in the Lomonosov Equatorial Undercurrent as Observed in April 2017

We analyze CTD casts accompanying ADCP velocity measurements along 33° W in the Atlantic in the region of the Lomonosov Equatorial Undercurrent (EUC) on April 14, 2017. Three CTD stations were located at the equator and 30 miles south and north of it in the core of the undercurrent. We focus on the study of the thermohaline stratification in the subsurface layer with intense development of the stepwise structures on the temperature, salinity, and density profiles at the depths below the salinity and velocity cores. The estimates of the water stratification types are based on the analysis of the profiles of temperature, salinity, and density together with the computed stability parameters such as the density ratio and vertical thermohaline stability. The high-gradient parts of steps (“sheets”) up to 15 m thick against the background of sharp negative T and S gradients were related to the small intervals of peaks of positive stable stratification E > 0 and low values of density ratio 1 < R < 2. Such intervals are statically unstable and meet the strict criteria of conditions favorable for double diffusion convection in the form of salt fingers. This provides evidence of the high probability of vertical mixing of this type. It implies that in the course of propagation of the high-salinity EUC, a convective salt fingering mechanism may provide vertical redistribution of salt and heat from the core of the EUC to the deeper layers. Variations in the intensity of the processes with latitude and indications of large horizontal scales of fingering processes are found.

Tatiana A. Demidova

### Numerical Realization of Hybrid Data Assimilation Algorithm in Ensemble Experiments with the MPIESM Coupled Model

Original data assimilation method is considered. This method is applied in conjunction with the coupled Max Planck Institute Earth System Model (MPIESM). The assimilation block and the interface with the MPIESM are realized on the “Lomonosov” supercomputer at the Lomonosov Moscow State University. Several experiments with and without assimilation of the sea level data and temperature-salinity profiles over the Equatorial Atlantic are conducted. The results of these experiments have been analyzed and discussed. In particular, it is shown that the ice concentration in Arctic zone of Russia fits better to the observations then in the reference experiments without assimilation.

Konstantin P. Belyaev, Ingo Kirchner, Andrey A. Kuleshov, Natalia P. Tuchkova

### Sea of Azov Waters in the Black Sea: Do They Enhance Wind-Driven Flows on the Shelf?

This paper was initially motivated by an observational case study conducted in May 2015 on the shelf of the Crimea Peninsula, just west of the Kerch Strait, through which the Black Sea receives the inflow of lower salinity, higher turbidity water from the Sea of Azov. The latter often propagates westward along the coast, creating two-layered vertical stratification, which, however, is intermittent and depends on wind-controlled dynamics of the Azov “plume”. In the field campaign of 2015, it was observed that the cross-shore components of the current velocity in the surface and bottom layers were strongly anti-correlated during the periods of stratification, and completely uncorrelated during the periods when stratification relaxed. This suggests that the buoyant discharges from the Kerch Strait may enhance wind-driven currents responsible for cross-shelf exchanges. To verify this hypothesis, we developed two simple semi-analytical 2D models of wind-driven flow on the Crimean shelf, aimed to simulate the effect of damping vertical mixing on the cross-shelf transport. One model represents the two-layered stratification and the other one the continuous stratification with eddy viscosity linearly decreasing downwards. Both models demonstrated that, indeed, the plume-generated stratification may significantly enhance both the cross-shelf wind drift in the upper layer and the compensating flow in the bottom layer.

Peter O. Zavialov, Alexander S. Izhitskiy, Roman O. Sedakov

### Bottom Water Flows in the Vema Channel and over the Santos Plateau Based on the Field and Numerical Experiments

The properties of Antarctic Bottom Water flows in the Southwest Atlantic were studied on the basis of hydrographic measurements and numerical modeling of the oceanic circulation. The CTD and LADCP profiles in the region of the Vema Channel and Santos Plateau were measured onboard the R/V “Akademik Sergey Vavilov”. Hydrographic observations at several locations over the Santos Plateau were carried out for the first time. The numerical simulation was performed using the Institute of Numerical Mathematics Ocean Model (INMOM). The observations of velocities were used for verification of the numerical model. The simulated three-dimensional velocity fields with high spatial resolution in the lower layer allow us to study the bottom currents over the entire length of the Vema Channel.

Dmitry I. Frey, Vladimir V. Fomin, Roman Yu. Tarakanov, Nikolay A. Diansky, Nikolay I. Makarenko

### Modeling Study of the Antarctic Circumpolar Current Variability Based on Argo Data

The Antarctic Circumpolar Current (ACC) variability is studied using the Argo-Based Model for Investigation of the Global Ocean (AMIGO) recently developed at the Shirshov Institute of Oceanology. A prominent feature of the method is the application of variational interpolation of irregularly located Argo measurements to a regular grid followed by model hydrodynamic adjustment of the obtained fields. Such an approach for the Argo data processing makes it possible to obtain a full set of oceanographic characteristics: temperature, salinity, and current velocity. The mean ACC transport over a period of 2005–2014 through the Drake Passage based on the AMIGO data is diagnosed as 162 ± 5 Sv. The transport through the African section south of Cape Town is 0.6 Sv higher due to the Pacific water flow to the Arctic Ocean in the Bering Strait, which then increases the transport in the Atlantic. In the Indian sector the mean ACC transport is increasing by 15.4 Sv to compensate the water flow from the Pacific to the Indian Ocean through the Indonesian Straits (Indonesian Throughflow). Thus, the resulting mean transport between Australia and Antarctica is calculated as 178 ± 6 Sv. These modeling results agree very well with the previous transports calculations based on direct velocity measurements.

Konstantin V. Lebedev

### Tareev Equatorial Undercurrent in the Indian Ocean

The results of observations over two meridional sections in the equatorial zone of the Indian Ocean in February 2017 during cruise 42 of the R/V “Akademik Boris Petrov” are analyzed. It is shown that at 65° E, the Tareev equatorial undercurrent is observed with a core at a depth of 50 m slightly to the south of the equator. At 68° E, the current is deepened and disintegrates into separate jets covering a distance of more than 700 km.

Albert K. Ambrosimov, Dmitry I. Frey, Sergey M. Shapovalov

### The Bering Sea Regional Data Assimilation System: From Climate Variability to Short Term Hindcasting

We present a regional Data Assimilation System (DAS), which employs the 4-dimensional variational (4dVar) DA approach based on the strong dynamical constraints of a semi-implicit primitive equation model. The developed 4dVar DAS is applied to the Bering Sea in several configurations. First, it is used for the reconstruction of seasonal and annual mean climatological states in the region, including the high resolution mean dynamical ocean topography (MDOT). The dynamically and statistically consistent climatologies are then utilized in various applications, including high-resolution analyses of the transport through the passage of the Aleutian Arc, and of the 2007–2010 circulation on the East Bering Sea shelf with the nested configuration of the DAS. Apart from new insight on the Bering Sea dynamics, the chapter illustrates the importance of developing dynamically consistent climatologies and, in particular, MDOT, for the analysis of the diverse data sets within a wide spectrum of spatial and temporal scales.

Gleb G. Panteleev, Max Yaremchuk, Vladimir Luchin, Oceana Francis

### Monitoring Strong Tidal Currents in Straits and Nearshore Regions

The strongest ocean currents occur in coastal regions and have tidal origin. In such regions, high current speeds are typically the result of topographic flow amplification. Despite their sparsity, these sites are optimal for installation of the tidal energy conversion devices, and, therefore, require special techniques for monitoring local currents that often exceed 3 m/s. In this chapter, two prospective techniques for monitoring extreme currents in the nearshore regions are presented. The first one is remote sensing of surface currents by High Frequency radars (HFRs). This method provides high temporal resolution (10–20 min) over large (102–104 km2) domains and long-time intervals, but lacks adequate horizontal resolution and cannot directly monitor the vertical structure of the flow. A complimentary method, based on underway ADCP observations: the use of towed ADCP system presents an opportunity of more focused velocity monitoring within limited (1–10 km2) domains at much higher (up to 50 m) horizontal resolution, over shorter time intervals. This kind of 4-dimensional mapping was performed in the Strait of Dover and in the West Solent. Transient eddies, large horizontal velocity gradients, and vertical shear in the velocity profiles were detected at each site, enabling a detailed characterization of the tidal stream. Combined with the dynamical constraints of a numerical model, the observed velocities significantly increase the accuracy in reconstruction of the full 4-dimensional tidal flow. The presented HFR-based and towed ADCP monitoring systems could be useful for regional model validation and studies of the local hydrodynamics with specific emphasis on resource assessment at tidal energy sites.

Alexei Sentchev, Max Yaremchuk, Maxime Thiébaut

### Analytical Solutions Describing Zonal and Circular Wind Drift of Sea Ice with Elastic-Plastic Rheology

Analytical steady-state solutions describing zonal and circular drift of sea ice under the wind drag are constructed and analysed in the case of the ice with elastic-plastic rheology considered in the AIDJEX project. The influence of the Coriolis force and sea surface tilt is included in the analysis. It is shown that all constructed solutions include elastic and plastic regions with plastic stresses corresponding to pure shear deformations. Geometrical dimensions and drift speed of elastic regions is analysed depending on the wind speed, wind direction and sea surface tilt.

Aleksey Marchenko

### Arctic Ocean Modeling: The Consistent Physics on the Path to the High Spatial Resolution

Modern numerical models of the Arctic Ocean (AO) exhibit the great progress partly thanks to the fine horizontal resolution, which helps to resolve many of the relevant processes explicitly. Nevertheless, some of the AO features are still modeled poorly by the models with a resolution of 5–10 km. It is anticipated, that the further increase in the horizontal resolution up to 100–1000 m will demand the understanding of the role of the AO specific processes. This paper is a brief review of some of such processes like mesoscale and submesoscale eddies and internal waves, and of the problems of their parameterization, caused by the closeness of their spatial scales. The internal waves and the internal wave-induced mixing are assumed to be the key processes to be taken into account to describe the AO cold halocline mixing properly.

Nikolay G. Iakovlev

### Numerical Modeling of Internal Wave Generation at High Latitudes

This contribution is focused on the semidiurnal internal tide in the Barents Sea generated north of the critical latitude (74.5° N). The study is based on the numerical modeling of internal wave generation and dynamics using of the Euler 2D equations for incompressible stratified fluid. The study site is located between Svalbard and the Franz-Victoria Trough. A Section 350 km long is chosen for the analysis in this basin. The bottom topography in the region is quite steep; four underwater hills with heights about 150–230 m over the background depth of about 350 m are located here. Calculations confirm the observation data in the vicinity of this region. Intense nonlinear internal waves with amplitudes up to 50 m and lengths of about 6–12 km are generated in this region of the Arctic.

Oxana E. Kurkina, Tatiana G. Talipova, Efim N. Pelinovsky, Andrey A. Kurkin

### Internal Wave Frequency Spectrum in the Amundsen Basin of the Arctic Ocean Inferred from Ice Tethered CTD Instruments

Comparison of four recent field experiments with similar type of historical measurements was performed to determine whether internal wave energy has increased with the decline of the Arctic sea ice. The internal wave energy was calculated on the basis of frequency spectrum inferred from ice tethered SBE37 CTD at three levels within the halocline while the Russian ice camp drifted through the Amundsen Basin of the Arctic Ocean in April of 2007, 2009, 2010, and 2012. The results of modern measurements with a total duration of more than 40 days are compared with 14 experiments performed in the Arctic in the period from 1966 to 1989, whose total measurement duration was about 180 days. Comparisons reanalyzed using the same method reveal no trend evident over the 40 year period in spite of the drastic decline of the sea ice.

Sergey V. Pisarev

### Experimental Studies of Sea and Model Ice Fracture Mechanics

We study ice fracture mechanics based on loading experiments with the floating ice beams with fixed ends. Both natural and model ice properties were investigated. Full-scale field works were performed on sea ice of the Svalbard Archipelago. We also performed model ice studies of two ice types in the Ice Basin of the Krylov State Research Centre (KSRC) in St. Petersburg: fine granule and columnar. In the experiments, an ice beam was cut in the ice cover, both ends of which were kept attached to the surrounding ice sheet. Then a horizontal force perpendicular to the side surface of the beam was applied to the middle section of the beam. For these purposes, the vertical cylindrical indenters with a diameter of 0.15 and 0.02 m were used both in field and model conditions. The indenters provided the force application through the whole ice thickness. The natural ice thickness range from 0.4 to 0.6 m; the model ice was 0.05 m thick. The beam width was almost equal to the ice thickness while the beam length varied from 2 to 8 ice thicknesses. The visual observations and the force-time records allowed tracing qualitative patterns of the beam failure process. We measured the breaking force dependence on the ice type and ice beam geometry. The beam tests described here allowed us to find the relationships of various strength parameters of ice crushing, compressive and tensile strength, as well as to compare the behavior of natural and model ice under identical loading conditions.

Marina Karulina, Alexey Marchenko, Alexandr Sakharov, Evgeny Karulin, Peter Chistyakov

### Seasonal Freezing of a Subwater Ground Layer at the Laptev Sea Shelf

In this contribution, we present results from instrumental sea ice/ocean observations collected during the winter of 2014–15 in the Buor-Khaya Bay (southern Laptev Sea; Arctic Ocean). An observational analysis was complemented by numerical simulations, with a conceptual, one-dimensional thermodynamic model employed to describe the formation of sea ice cover, and to estimate the effect of fast ice growth on freezing of the underlying layer of bottom sediments. One of the advantages of this model is the application of two known methods for localization of the phase transition area. The classical (frontal) approach was used to reproduce seasonal growth of the fast ice layer, while the temperature spectrum describes phase transitions in the layer of bottom sediments. Using the developed model, we have described the thermodynamic evolution of the ice cover and the upper layer of the bottom sediments in the Tiksi Gulf. The simulations performed show that the presence of a liquid sub-ice layer, caused by salt rejection (an important element of the “ice-brine-ground” system) prevents complete freezing of the water layer even at very low (<−40 °C) air temperatures. The increased salinity of the sub-ice layer can cause melting of fast ice in shallow parts of the bay, even at negative air temperatures, alongside simultaneous growth in the areas located far from the coast.

Peter V. Bogorodskii, Andrey V. Pnyushkov, Vasilii Yu. Kustov