This work is focused on the seasonal and interannual variability of the freshened surface layer (FSL) in the Kara Sea during ice‐free periods. The majority of annual freshwater runoff inflows to the Kara Sea during the freshet period in June–July. As a result, a large low‐salinity and strongly stratified FSL is formed in the central Kara Sea at the beginning of the ice‐free period. Initially, this layer is fresh with salinities of less than 15. Then, in August–October, river discharge steadily decreases, the fresh (<15) and strongly stratified river plume remains limited to the inner part of the FSL adjacent to the Ob and Yenisei gulfs, which receives reduced freshwater discharge. The area of the fresh plume steadily decreases with decreasing of river discharge; in October, it remains only within the Ob and Yenisei gulfs. Area and position of the outer part of the FSL, on the opposite, remain stable until the end of ice‐free period. Salinities in the outer part steadily increase to 20–25, vertical salinity gradients at the boundary with the subjacent sea decrease, albeit remain prominent. Area and position of the FSL also have low interannual variability, because the volume of river runoff during freshet period in June–July is stable on interannual time scale. As a result, downward freshwater transport and the formation of the seasonal halocline occur in August–October at the stable area located in the central Kara Sea.

The goal of this research is to modify and apply a version of high‐resolution three‐dimensional numerical model for simulations of bottom circulation and to study the flows of Antarctic Bottom Water in abyssal channels of the Atlantic Ocean using this model. We adjusted the Institute of Numerical Mathematics Ocean Model σ‐level ocean circulation model for several regions with intense bottom currents in abyssal channels. High vertical resolution near the seafloor allowed us to study the abyssal part of the ocean circulation, while high horizontal resolution is necessary for modeling currents in narrow underwater channels and fracture zones. We used our direct velocity measurements carried out at key points of the currents in the channels for verification of the model. This approach was applied in the regions with different seafloor topography: in the long and narrow Vema Channel with a strong bottom current and in several fracture zones of the Mid‐Atlantic Ridge with rough bathymetry. On the basis of simulated three‐dimensional velocity fields, we analyzed the spatial structure of the bottom currents along the entire length of the channels, determined maximum velocities at different sections, investigated the influence of the Ekman flux on the structure of the flows, and compared our model results with in situ observations. We also calculated the total transports of Antarctic Bottom Water through the fractures in several underwater ridges of the Atlantic Ocean.

The excess heat absorbed from the atmosphere has increased the temperature in the upper layers of the ocean (<2,000 m). In the abyss, infrequently repeated ship sections, deep Argo float measurements, and sparse moored observations have found signs of warming in the Southwest Atlantic, possibly linked to changes in the Weddell Sea. We present a new moored temperature time series sampled near the bottom in the Vema Channel, from February 2019 to August 2020. Together with historical data, the combined record confirms the warming of the abyssal waters, with an increase of 0.059°C in potential temperature between January 1991 and August 2020, embedded within intense high‐frequency variability. Moreover, the data suggest the possibility of an accelerated warming, with a change in the temperature trend from 0.0016°C yr⁻¹, between the early 1990s and 2005, to 0.0026°C yr⁻¹ afterwards.

We observed strong internal tidal waves in the Kara Gates Strait. Internal tides are superimposed over a system of mean currents from the Barents to the Kara Sea. Field studies of internal tides in the Kara Gates were performed in 1997, 2007, and 2015. In 2015, we analyzed data from towed CTD measurements, numerical model calculations, and satellite images in the region. An internal tidal wave with a period of 12.4 h is generated due to the interaction between the currents of the barotropic tide and the bottom relief on the slopes of a ridge that crosses the strait from Novaya Zemlya to the continent. The depths of the ridge crest are 30–40 m. A constant current of relatively warm water flows from the Barents to the Kara Sea. An internal wave propagates in both directions from the ridge. In the Barents Sea, internal waves are intensified by the current from the Barents to the Kara Sea. Internal bores followed by a packet of short-period internal waves are found in both directions from the strait. Satellite images show that short-period internal waves are generated after the internal bore. A hydraulic jump was found on the eastern side of the strait. Numerical modeling agrees with the experimental results.

Direct velocity measurements of the Malvinas Current (MC) were carried out on multiple occupations of five transects across the flow using a Shipborne Acoustic Current Profiler (SADCP) on the R/V Akademik Sergey Vavilov and Akademik Mstislav Keldysh. These data are used to determine local features of the three‐dimensional velocity field of the current. The occupations covered the northern branch of the Antarctic Circumpolar Current (ACC) and the southern part of the MC. Five transects across the flow were located at 350–550 km from each other from the Drake Passage to the western Argentine Basin at 46°S. The new observations reveal that the current is organized in two branches, namely, an inshore branch extending to a depth of 200–300 m and a main offshore branch, which flows approximately over the 1,400 m isobath. This two‐branch structure is observed on each of the cross‐flow transects. The observed velocities of the inshore branch exceed 40 cm/s on each studied crossing of the current. The MC is a cold western boundary current that follows the Subantarctic Front. This flow originates as an offshoot of the northern branch of the ACC and continues over the Falkland/Malvinas Plateau and along the western slope of the Argentine Basin. Volume transports of the upper 700 m of the MC calculated for each crossing range between 1.4 and 4.4 Sv for the inshore branch and between 21.2 and 25.5 Sv for the offshore (main) branch.