Strong acceleration of abyssal flows in narrow deep‐water channels and fracture zones is a key feature of bottom circulation in the Atlantic Ocean. In the Equatorial Atlantic, these bottom currents transport Antarctic Bottom Water (AABW) over the Mid‐Atlantic Ridge from west to east. The main pathway for Antarctic waters in this region is the Romanche Fracture Zone. The deepest point of this fracture zone is the Vema Deep; its maximum depth based on the published data is 7,856 m. This deep basin is filled by waters of Antarctic origin overflowing a sill in a narrow channel. During the expedition on the R/V Akademik Ioffe (August 2022), we revealed a strong flow in the middle part of the Romanche Fracture Zone and collected new data on thermohaline and kinematic structures of this gravity current. Our survey is the first observational evidence of the intense flow into the Vema Deep. At the sill, the flow splits into branches flowing through three distinct channels of intricate configuration located in the southern transform valley of the fracture zone. The northern channel is proved to be the main pathway of the coldest and densest bottom waters to the Vema Deep. We also found that vertical structure of the flow is presented by two individual jets, namely the deep and bottom jets. The total transport of AABW through the Romanche Fracture Zone at this location was estimated at 1.40 Sv; the velocities exceeding 10 cm/s were found at depths greater than 5,000 m.
Natural and social systems exhibit complex behavior reflecting their rich dynamics, whose governing laws are not fully known. This study develops a unified data-driven approach to estimate predictability of such systems when several independent realizations of the system’s evolution are available. If the underlying dynamics are quasi-linear, the signal associated with the variable external factors, or forcings, can be estimated as the ensemble mean; this estimation can be optimized by filtering out the part of the variability with a low ensemble-mean-signal-to-residual-noise ratio. The dynamics of the residual internal variability is then encapsulated in an optimal, in a Bayesian sense, linear stochastic model able to predict the observed behavior. This model’s self-forecast covariance matrices define a basis of patterns (directions) associated with the maximum forecast skill. Projecting the observed evolution onto these patterns produces the corresponding component time series. These ideas are illustrated by applying the proposed analysis technique to (1) ensemble data of regional sea-surface temperature evolution in the tropical Pacific generated by a state-of-the-art climate model and (2) consumer-spending records across multiple regions of the Russian Federation. These examples map out a range of possible solutions—from a solution characterized by a low-dimensional forced signal and a rich spectrum of predictable internal modes (1)—to the one in which the forced signal is extremely complex, but the number of predictable internal modes is limited (2). In each case, the proposed decompositions offer clues into the underlying dynamical processes, underscoring the usefulness of the proposed framework.
Plastic is recognized as a threat to marine ecosystems, and estimating the level of plastic and microplastics (MPs) pollution of the World Ocean is, nowadays, the goal of many studies. However, the use of different methods for the sampling and analysis of MPs leads to the problem of comparing the results obtained. Studies on surface MPs pollution of the surface sea water are based on the application of the manta or neuston nets that collect water from the upper 10–20 cm layer (the “surface” MPs) or submersible pumping systems that collect water from the water layer 3 to 5 m below the sea surface (the “subsurface” MPs). These two techniques allow the collection of particles of different size fractions, i.e., >300 µm for the surface MPs and >100 µm for the subsurface MP. However, it is shown that microplastics found in the surface and subsurface layers differ not only in the size of the items found, but also in morphology, types of polymers, abundance, weight concentration and their spatial distribution. Different hydrodynamic processes affect the fate of the plastic found exactly at the sea surface and several meters deeper. The aim of this work was to study the distribution of surface and subsurface MPs and to reveal an influence of oceanographic conditions on their spatial distribution, using as an example the open ocean waters of the Central Atlantic.
Upwelling leads to a sharp and strong decrease in water temperature in the coastal zone of the southeastern Baltic Sea. The quality of existing hydrodynamic models cannot fully meet the requirements of accurate upwelling forecasts. This study provides insight into the applicability of the simplified Ekman upwelling criterion method for the southeastern Baltic Sea. The upwelling criterion is the ratio of the vertical velocity and the duration of the upwelling wind to the mixed layer density. The vertical velocity was determined by the divergence of the integral Ekman transport in the transverse direction. Calculation of the criterion was based on wind data from NCEP/CFSR reanalysis. The upwelling criterion was compared with in situ temperatures from direct measurements near the D-6 oil platform taken in 2015–2017. Only 46% of calculated upwelling cases were confirmed by temperature decreases in the sub-surface. It was found that more than half of the cases of strong temperature decreases were caused by a northern wind (Ekman upwelling), when the criterion exceeded the threshold value. Comparison of the hydrodynamic model results and direct measurements shows that the model’s quality is far from perfect, and the simplified methods can be used as alternatives to models. Some recommendations were made for future upwelling research.
This paper is concerned with the analysis of the long-term regular time series of current velocity and conductivity, temperature, and depth (CTD) profiles, measured with the moored autonomous profiler Aqualog over the upper part of the continental slope at a fixed geographical location in the Northeastern Black Sea. This study focuses on the fine structure of the density profiles to show that the fine-structure Cox number (C) is a power function of the Richardson number (Ri). A similar inverse power relationship with the same exponent was found earlier for the coefficient of vertical turbulent mass exchange (Kρ) and Ri. Based on those results, the analysis indicated a statistically significant correlation between C and Kρ, which suggests that the estimations of Kρ could be conducted from the CTD data only.
The most massive design on the Baltic shore used geosynthetic materials, the landslide protection construction in Svetlogorsk (1300 m long, 90,000 m2 area, South-Eastern Baltic, Kaliningrad Oblast, Russian Federation) comprises the geotextile and the erosion control geomat coating the open-air cliff slopes. Due to changes in elastic properties during long-term use in the open air, as well as due to its huge size, this structure can become a non-negligible source of microplastic pollution in the Baltic Sea. Weather conditions affected the functioning of the structure, so it was assessed that geosynthetic materials used in this outdoor (open-air) operation in coastal protection structures degraded over time. Samples taken at points with different ambient conditions (groundwater outlet; arid places; exposure to the direct sun; grass cover; under landslide) were tested on crystallinity and strain at break. Tests showed a 39–85% loss of elasticity of the polymer filaments after 3 years of use under natural conditions. Specimens exposed to sunlight are less elastic and more prone to fail, but not as much as samples taken from shaded areas in the grass and under the landslide, which were the most brittle.
The coastline of the Kaliningrad Oblast is an area of the South-East Baltic, which continues from the Vistula Spit to the Curonian Spit via Sambia Penisula. The coastline has been subject to severe erosion over the past years. The goal of the paper is to analyse whether the alongshore variations of the storm surge water level, field of waves and currents are the reason for the erosion alongshore variability. The numerical simulations were carried out using the quasi-stationary approach for the model wind. The offshore wave breaking distance and the non-linear dependence between wind surge and wind speed were estimated for four typical coastline sites. The alongshore velocity on most of the coastline was enough powerful to transport the fine, medium and coarse sands. West, northern-west and north winds were defined as the most dangerous for coastal erosion. The convergence and divergence of alongshore currents as well as the vortex zones were identified for each wind direction. The results were used to analyse the alongshore current velocity, wind surge, and significant wave height variability against the shore erosion characteristics. The hypothesis that the places of convergence and divergence of alongshore currents correspond to the accumulative and erosion zones wasn‘t confirmed with one exception on the western shore of the Sambia Peninsula. Three options were supposed to explain the absence of correlation between the monitoring results on coastal erosion and modelled hydrodynamic conditions: the studied shore has not had enough free sand to demonstrate the typical behaviour of dissipative shores; the erosion characteristics depend on the very local conditions which weren‘t resolved by numerical model; the main erosion has happened at the short term event basis when waves reach the shore at the background of a general Baltic Sea high-water level and isn‘t a result of the general alongshore distribution of waves, wave surge and current characteristics.
Rivers are among the main sources of marine litter, especially for semi-isolated sea areas with high populations and intense economic activity. The semi-isolated Black Sea located in the Eastern Europe is an example of such an area, whose watershed basin is under high anthropogenic pressure. In this study, we report the results of the first long-term monitoring program of floating litter at several rivers inflowing to the northeastern part of the Black Sea. We describe the main characteristics of registered marine litter, including the distribution of its type and size. Based on the obtained results, we reveal the relation between river discharge rate and the litter flux for the considered rivers. Using this relation extended to all rivers of the study area, we assess the total annual flux of riverine litter to the northeastern part of the Black Sea.
The increasing influence of Atlantic inflows in the Arctic Ocean in recent decades has had a potential impact on regional biogeochemical cycles of major and trace elements. The warm and salty Atlantic water, entering the Eurasian Basin through the Norwegian Sea margin and the Barents Sea, affects particle transport, sink, phyto-, and zooplankton community structure and could have far-reaching consequences for the marine ecosystems. This study discusses the elemental composition of suspended particulate matter and fluffy-layer suspended matter derived from samples collected in the Barents Sea and northern Norwegian Sea in August 2017. The mosaic distribution of SPM elemental composition is mainly determined by two factors: (i) The essential spatial variability of biological processes (primary production, abundance, and phytoplankton composition) and (ii) differences in the input of terrigenous sedimentary matter to the sea area from drainage sources (weak river runoff, melting of archipelago glaciers, etc.). The distribution of lithogenic, bioessential, and redox-sensitive groups of elements in the particulate matter was studied at full-depth profiles. Marine cycling of strontium in the Barents Sea is shown to be significantly affected by increasing coccolithophorid bloom, which is associated with Atlantic water. Mn, Cu, Cd, and Ba significantly enrich the suspended particulate matter of the benthic nepheloid layer relative to the fluffy layer particulate matter within the benthic boundary layer.
We study numerically the integrable turbulence in the framework of the one-dimensional nonlinear Schrodinger equation (1D-NLSE) of the focusing type using a new approach called the “growing of turbulence”. In this approach, we add a small linear pumping term to the equation and start evolution from statistically homogeneous Gaussian noise. After reaching a certain level of average intensity, we switch off the pumping and examine the resulting integrable turbulence. For sufficiently small initial noise and pumping coefficient, and also for not very wide simulation box (basin length), we observe that the turbulence grows in a universal adiabatic regime, moving successively through the statistically stationary states of the integrable 1D-NLSE, which do not depend on the pumping coefficient, amplitude of the initial noise or basing length. Waiting longer in the growth stage, we transit from weakly nonlinear states to strongly nonlinear ones, characterized by a high frequency of rogue waves. Using the inverse scattering transform (IST) method to monitor the evolution, we observe that the solitonic part of the wavefield becomes dominant even when the (linear) dispersion effects are still leading in the dynamics and with increasing average intensity the wavefield approaches a dense bound-state soliton gas, whose properties are defined by the Fourier spectrum of the initial noise. Regimes deviating from the universal adiabatic growth also lead to solitonic states, but solitons in these states have noticeably different velocities and a significantly wider distribution by amplitude, while the statistics of wavefield indicates a much more frequent appearance of very large waves.
Influence of the critical latitude on tidal internal waves of frequency M2 (period 12.4 h) is shown on the example of moored measurements. The critical latitude for internal waves M2 is latitude 74.5° N. North of this latitude the temperature spectra reveal only the S2 peak (period 12.0 h), while the current spectra show two peaks M2 and S2. Tidal internal waves in the Arctic seas of Russia are analyzed. The problem is solved on the basis of a numerical model developed by V.I. Vlasenko. As a result of calculations and analysis, a map of the amplitudes of semidiurnal internal tidal waves in the Arctic seas has been constructed. The maximum amplitudes of internal tidal waves occur over underwater slopes. Very large amplitudes of internal tides were found in the Kara Gates. Internal waves in the Kara Gates Strait were studied on the basis of moored measurements and towed CTD-profilers in the scanning mode. Internal waves turned out to be extremely large and their dynamics is close to similar waves in the Strait of Gibraltar. Waves with heights of up to 70 m are directed towards the Barents Sea. The opposing current decreases the wavelength, and, consequently, the amplitude of internal waves increases. The influence of tidal internal waves on the formation of the Great Siberian Polynya in the Laptev Sea was found. Above the shelf slope near the 20 m isobath, the amplitudes of internal waves are maximum and lead to mixing with a deeper warm water layer. The short-period internal waves under the ice and their influence on the fluctuations of the ice cover are investigated. When solving problems about internal waves, the rigid lid boundary condition is not completely justified. This is confirmed by measurements under the ice. The tsunami wave generated by the motion of the glacier in Svalbard was studied. A tsunami wave is similar in properties to a landslide tsunami. The wave amplitude was 30 cm, the period was 93 s, the period of disturbances after the wave was about one hour. Comparison of the spectra of ice oscillations, which are caused by various wave processes: tide, seiche oscillations, wind waves and swell, internal waves, and tsunami wave is presented. This is a review paper of long term field and numerical research.
The article reveals the issue of the neural networks’ applicability, considering the possibility of “mixing” the data set of cyclonic activity indicators in the North Atlantic as parallel inputs for constructing a long-term forecast of the air temperature anomaly in the Arctic region. The importance of considering this factor in the implementation of neural forecasting is determined by the fact that the North Atlantic cyclones provide the supply of heat and moisture to the polar regions and can also modify the ice cover of the Arctic Ocean. A nonlinear autoregression model with external inputs was used as a primary neural network. The training was carried out on data changes in temperature anomalies with a monthly resolution with different observation durations. The training sample is composed of three 20 year vectors, randomly selected from the available set. The software environment STATISTICA Automated Neural Networks was used as a tool in work, which allows researching data preparation to testing a trained neural network. Among all the considered variants of the network parameters, the best results of training the neural network were obtained with 15 hidden layers and a signal delay of 2 samples (simulation clock). Testing the predictive properties of the obtained neural network, carried out on a selection of unused data in training, and showed quite good results. In all cases, the correlation coefficient between the input data and the forecast was more than 0.85. The root-mean-square deviation (model error) did not exceed 0.5 °C. Despite the obtained high forecasting accuracy, it should be assumed that in further studies of building a temperature forecasting system, it is necessary to provide a procedure for periodic retraining of the network to consider the variability of parameters with “mixing” and other parallel inputs characterising the modern climatic dynamics of the Arctic region. Such a retraining scheme can be easily implemented using the methodology for constructing a neural model proposed in work.
A comprehensive geological and geophysical analysis of numerous materials on the anomalous magnetic field of the Amundsen and Nansen basins in the Arctic Ocean and a revision of the identification of paleomagnetic anomalies based on modeling of the inversion magnetoactive layer of the ocean crust made it possible to create a modern version of the geochronology of the bottom of the Eurasian basin. The initial stage of the formation of the Eurasian basin of the Arctic Ocean is interconnected with the processes of stretching and rifting in the Siberian shelf in the Cretaceous-Paleogene time. The transformation of rifting into spreading occurred in connection with the beginning of the detachment from the Siberian shelf of the continental crust block of the Lomonosov Ridge somewhat earlier than the time of paleoanomaly A26, which was first identified and mapped. At the second stage of evolution, rifting turned into spreading, and the rate of expansion of new oceanic crust in the interval of paleoanomalia A26-A24 (59–53 million years ago) was more than 2.5 cm/year. At the same time, the northern flank of the mid-Arctic increased more intensively than the southern one. The third stage was characterized by a further progressive deceleration of the bottom growth process, the minimum of which, with growth rates of about 1 cm/year, occurred during the formation of paleoanomalia A13-A6 (30–20 million years ago). The fourth stage of growth of the new oceanic crust began later than the time of paleoanomaly a6 and is characterized by some intensification of growth at rates up to 1.2 cm/year. The average rate of bottom expansion over an interval of almost 60 million years was close to 1.3 cm/year, which makes it possible to classify the mid-Arctic ridge as a slow-growing mid-ocean ridge.
The paper uses the method of cross-wavelet analysis to establish a relationship between fluctuations in the series of anomalies of sea surface temperature (SST) in the Arctic region, the index of the Arctic Oscillation (AO), and the intensity level of the stratospheric polar vortex (ISPV). Some significant cycles were revealed in different frequency ranges. Cross-wavelet analysis of SST with ISPV showed a higher connection closeness than AO. The relationship between sea surface temperature anomalies (SST) and AO indices showed a statistically significant association in the low-frequency range and ISPV, mainly in the high-frequency range. The nature of oscillations in the low-frequency range is predominantly antiphase and in the high-frequency range—in-phase. The close correlation of all the analyzed climatic parameters determined the similarity in the temporal localization of the identified periods of fluctuations. The established coherence of SST-AO is typical before the period of warming intensification in the Arctic, and the coincidence of SST and ISPV becomes pronounced after 2005 during the period of increasing temperature anomalies, which is consistent with quasi-cyclic changes in the Earth's climate and shows a significant impact of stratospheric processes on climate dynamics in the Arctic region.
A one-line analytical model is introduced for prediction of shoreline changes and accumulation/erosion volumes in the vicinity of a breakwater, or a system of breakwaters on time scales from hours to years. The changes in morphology are interpreted as a consequence of two mechanisms that cause accumulation in the lee of breakwater either due to two opposite flows or due to unloading of unidirectional alongshore sediment flux. The relationships obtained reproduce the observed trend of slowing down the bottom relief evolution by approaching to the equilibrium state. Changes in shore contour are determined by means of the mass conservation law under the assumption of an initially flat bed. It is shown that the higher upstream the breakwater is, the more sediment volume it accumulates and the larger salient is formed. In the gaps between the structures, the sediment flow partly recovers causing the shoreline retreat. The length of the down-drift erosion zone is assumed proportional to the surf zone width. An example of calculations for the section of the Azov Sea coast demonstrates its response for changes in parameters of a series of breakwaters. A comparison of the model with published data confirms its applicability at least for the case of a single breakwater.
In the exploration of the meiofauna associated with sponges and corals in the shallows of Cuba, we investigated nine species of sponges (Demospongia), wherein 26 nematode species were revealed. Most nematode specimens (50–95% of all individuals) in all sponge samples belonged to the family Desmodoridae (order Desmodorida), followed by the family Chromadoridae (order Chromadorida). A major part of Desmodoridae is constituted by the genus Acanthopharynx. A statistical morphometric analysis (principal component analysis and multidimensional scaling with testing via analysis of similarities) revealed two close cohorts that differed in size and pharynx shape. Molecular genetic analyses (COI, 18S, and 28S) also distinguished two groups of specimens that corresponded to morphometric cohorts. Based on the morphometry and molecular genetics, the larger-sized group was defined as Acanthopharynx micans (Eberth, 1873), while the smaller-sized group was considered A. parva sp. n. In light of the taxonomic review of the Acanthopharynx, emended generic diagnosis, and the annotated list of ten valid species, A. parva sp. n. differed from other Acanthopharynx species by its peculiar shape of the pharynx (gradually widened to cardia), smaller body size, and pattern of precloacal organs.
This paper presents the results of a study on fluctuations in the water level of the Curonian Lagoon (in the Baltic Sea). To date, the genesis of this inland bay as part of the complex postglacial development of the southeastern Baltic is poorly understood. The data from lithological, geochronological, and phytolith analyses, as well as assessments of plant and animal macroremains from the lagoonal sediments, provide a reconstruction of local coastal biocenoses and water level dynamics in the Middle and Late Holocene time. This study reveals the fairly dynamic evolution of the coastal zone of the Curonian Lagoon over the past 7000 years, as indicated by the traced succession of plant communities from forest to near-shore, open-water biocenoses and the alternations of the drying out and inundation of the area under consideration. Thus far, a connection with two stages of the Baltic Sea water level fluctuations has been traced: the regressional stage, which took place approximately 5600 cal years BP, and the Late Subatlantic transgression, which started at approximately 1100 cal BP. This study demonstrates that phytolith (microbiomorphic) analysis is a promising method for the study of temperate-latitude lagoonal sediments, providing information not only on the local plant communities, but also on the changes in the hydrological regime of the area.
The Mw 7.6 earthquake of 19 September 2022 within the coastal zone of Michoacán, Mexico, generated a major tsunami that was recorded by six coastal tide gauges and a single offshore DART station. All seven instruments were located within 250 km of the source. No tsunami was detected at larger distances. Maximum wave heights were observed at Manzanillo (172 cm) and Zihuatanejo (102 cm). Numerical modelling of the event closely reproduced the coastal and offshore tsunami records and shows that the tsunami energy radiated seaward from the source as a narrow “searchlight” beam directed normal to the source and mainland coast. Estimates of the frequency content (“colour”) of the 2022 tsunami event, and that generated in 2017 by the much stronger (Mw 8.2) Chiapas earthquake further up the coast, reveal a marked difference in the tsunamigenic response. Whereas the 2017 tsunami was mostly long-period (“reddish”), with 87% of the total tsunami energy at periods >35 min, the 2022 tsunami was short period (“bluish”) with 91% of energy at periods <35 min. A noteworthy feature of the 2022 event was the seismically generated seiches observed at Puerto Vallarta, which had a recorded period of about 7 min, began immediately after the main earthquake shock, and persisted for about one hour.
The expedition “North Pole-41” of the Arctic and Antarctic Research Institute on an ice-resistant self-propelled platform has started work in the central Arctic basin. The expedition program is designed for year-round studies of the natural environment, patterns and causes of changes in the climate system and biodiversity. The biological component of the expedition program “Cryal” of the Shirshov Institute of Oceanology of the Russian Academy of Sciences is aimed at studying the spatial and temporal characteristics of the water-ice environment and the species composition of ice and plankton communities in the central regions of the Arctic Ocean.
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