Morskoj gidrofizičeskij žurnal

Purpose. The paper aims at the studies of features of seasonal variation of the main semidiurnal and diurnal tides in the annual cycle in the Barents and Kara seas according to the long-term data of sea level observations at all points (stations). The structure of seasonal course of the tide is estimated on the example of the M₂ and K₁ tides and physical mechanisms of its formation.

Methods and Results. The work was carried out according to the data of long-term tide gauge hourly observations of the sea level and 6-hourly interval series of the sea level measurements mainly from the ESIMO database from 1977 to the end of observations. Marine hydrometeorological year-book data since 1951 were also used. On the basis of the harmonic analysis of tides with the least square method of hourly annual and monthly time series of sea level, the average monthly values of amplitudes and phases of the main semidiurnal and diurnal tides at 17 points in the Barents Sea and 19 points in the Kara Sea are estimated. In general, the range of seasonal variability of the M₂ tide in the Barents Sea increases from north to south and is most significant in the southeast of the sea. According to our classification, classic type 1 of the seasonal course of the M₂ tide is not predominant and is 35 %, and anomalous type 3 is the most observed one, reaching 41 % of 17 points. In the Kara Sea, classic type 1 of seasonal course of the M₂ tide is mainly observed with an amplitude maximum and phase minimum in July–September, manifesting itself in 74 % of all cases in 19 points.

Conclusions. At each point of the Barents and Kara seas, individual time-stable seasonal annual course of main semidiurnal, diurnal and shallow tides is observed. The seasonal course of harmonic constants differs significantly among the points in terms of the degree of severity, shape of curves, time of occurrence of extreme values and magnitude of oscillation range. Moreover, seasonal variations of the constants of semidiurnal and diurnal tides are different. In the Barents Sea, the influence of drifting ice cover on the seasonal variations of main semidiurnal tides is much weaker than in the Kara Sea. The seasonal variations of amplitudes and phases of the daily K₁ tide are dominated by the semiannual period. The maximum deviations of amplitudes from the mean annual value (norm) are mainly 10–20 %, and those of phases – 6–16°.

Purpose. The study is purposed at analyzing spatial and temporal climatic variability of the upper mixed layer in the Barents and Kara seas on a climatic scale.

Methods and Results. The potential water density is calculated based on the ORAS5 reanalysis data on the average monthly values of potential temperature and salinity at the nodes of a 10-km grid with an irregular step over vertical up to the 400 m depth for the period 1958–2022. The formed density array makes it possible to determine the upper mixed layer thickness in the Barents and Kara seas. A threshold criterion ∆σ = 0.03 kg/m³ is used for its evaluating. The obtained results permit to identify the areas notable for significant variability of the upper mixed layer thickness.

Conclusions. The analysis shows that the upper mixed layer maximum development falls on February and March, whereas the minimum one – on June and July. Thus, in the seas under consideration, the highest values of the upper mixed layer thickness are observed during the increased autumn-winter convection. In the cold half of a year (November – April), the upper mixed layer thickness averages 105 m in the Barents Sea, and 23 m – in the Kara Sea. The analysis of interannual variability of the average annual thickness values of these layers shows the presence of a positive climatic trend, i. e. a thickness increase in the upper mixed layers in the Barents and Kara seas in 1958–2022. The upward trend is observed both in the cold and warm halves of a year. The values of average annual thickness trends of the upper mixed layers in the Barents and Kara seas constitute 1.3 m/10 years and 1.2 m/10 years, respectively. 

Purpose. The purpose of the work consists in studying the structure and flow routes of the transformed North Sea waters in the Baltic Sea during the formation and spread of the Major Baltic inflow in December 2014 using numerical modeling.

Methods and Results. To achieve the stated aim, a three-dimensional baroclinic hydrodynamic model of the North and Baltic seas with a spherical grid area detailed in the Danish Straits has been developed based on the INMOM model. Within the framework of the performed numerical experiment, the oceanological characteristic fields were assessed in the system of two seas for the period January 1, 2014 – December 31, 2015. A comparison of the model-derived salinity and sea current characteristic values with those measured at the Darss Sill and Arkona stations as well as with the BSPAF regional reanalysis data has shown that the INMOM model in general reproduces the changes both in salinity and in characteristics of the average currents better than the reanalysis data. The features of vertical variability of salinity and sea currents in the Danish Straits during the Major Baltic inflow formation are described based on the simulation results. The daily average and total volumes of water transported in the Sound, Great Belt and Little Belt straits during the main period of the Major inflow are estimated. The features of distribution of the near-bottom salinity fields during different periods of its formation are described. The Lagrangian modeling made it possible to describe the ways in which the waters of the Major Baltic inflow spread.

Conclusions. The estimates of water exchange obtained due to the INMOM model indicate that during the main period of the Major Baltic inflow (December 2014), a total of 241.4 km³ of Kattegat waters passed through the Danish Straits. The inflow largest part, 170.9 km³, spread through the Great Belt Strait, while only 68.9 km³ passed through the Sound Strait. The effect of the Small Belt Strait on water transport during the Major Baltic inflow was very insignificant – only 1.6 km³. The study of distribution routes of the transformed North Sea waters over the Baltic Sea after the end of the Major Baltic inflow shows that having passed the Danish Straits, its waters spread in a wide stream to the southwestern Baltic, then penetrate to the Gulf of Gdansk, move further along a cyclonic trajectory through the deep-sea areas of the eastern and northern parts of the Gotland Basin without entering the Gulf of Finland, and by the end of December 2015, they reach the Landsort Deep in the western part of the Gotland basin.

Purpose. The purpose of the study consists in obtaining modern accurate data on the bottom relief features and the granulometric composition of bottom sediments in the Limenskaya Bay region of the Southern coast of Crimea.

Methods and Results. The samples of the bottom sediments surface layer (0–5 cm) were taken using the Peterson grab sampler in September 2022. The granulometric composition of bottom sediments was studied using the decantation and scattering method. The hydroacoustic research of underwater relief was performed from the small vessels of Marine Hydrophysical Institute and the Black Sea hydrophysical subsatellite polygon in 2022 and 2023. The instrument Lowrance Elite FS7 including the built-in single-beam echo sounder (200 kHz) for determining the sea depth, the side-scan sonar (455/800 kHz) and the global satellite navigation system receiver for defining the coordinates was applied. It is noted that at present, the sea bottom in the coastal part and in the Limenskaya Bay sublittoral is covered with the unevenly distributed sedimentary material of heterogeneous composition. In the shallowest part (0–10 m), the boulder-pebble forms of sediments are widespread, their active movement is a result of storm impact and anthropogenic activity.

Conclusions. The predominance of gravel fraction in the western and eastern parts of the studied area is explained by the landslide type of the coast. In the deeper parts (10–15 m) of Limenskaya Bay, the bottom is covered mainly with the well-sorted sand sediments. At the depths exceeding 20 m, the proportion of silt fraction increases, which is consistent with the previously studied features of general dynamics of sediment fractions in this region. Having been deciphered, the results of bottom relief hydroacoustic scanning in the coastal zone made it possible to outline the boundaries of boulder-pebble area, as well as to estimate the predominant sizes at various parts of the bottom.