The Kara Sea is a semi-enclosed sea located between the Siberian coast in the south, Novaya Zemlya in the west, and Severnaya Zemlya in the east (Figure 1). The water depth is less than 50 m at more than 40% of the Kara Sea; shallow areas are located mainly in the central and southeastern parts of the sea. This sea receives enormous freshwater discharge (∼1,500 km 3 annually) mainly from two large estuaries, namely, the Yenisei Gulf (630 km 3 from the Yenisei River) and the Gulf of Ob (530 km 3 from the Ob, Pur, and Taz rivers; Gordeev et al., 1996; Pavlov et al., 1996). Continental discharge to the Kara Sea has very large seasonal variability with a short freshet period in June-July that provides ∼50% of annual runoff and a long low discharge period in October-April caused by freezing of the inflowing rivers (Pavlov et al., 1996; Figure 1). Freshwater discharge forms the large freshened surface layer (FSL) in the Kara Sea which is among the largest freshwater reservoirs in the Arctic Ocean

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In 2013 and 2018, Shirshov Institute of Oceanology performed 12 stations with conductivity‐temperature‐depth and lowered acoustic Doppler current profiler (LADCP) profiling in the southwestern part of the Brazil Basin in order to find continuations of hydraulic controlled flow of the coldest Antarctic bottom water that propagates along the deepest bed of the Vema Channel. Comparison of these measurements with the historical database and our previous measurements in the Vema Extension region (27°S, 34°W) showed that such a continuation of the flow does not exist in the valley directed to the east, which seemed to be a topographic extension of the Vema Channel. Continuation of the flow was found over the section at 25°34′S across the meridionally oriented channel (depth up to 4,950 m) approximately along 33°30′W north of the Vema Extension region. Northward velocity speeds exceeding 35 cm/s were measured in the bottom flow (100–150 m thick above the bottom), which is displaced to the western slope of the meridional channel. Transport in the high‐speed core (velocity speed greater than 10 cm/s, potential temperature less than 0.62°C) in this channel was estimated at 0.150 ± 0.007 Sv on the basis of the LADCP measurements. There are several indirect indications of the formation of a local spillway (or a cascade of spillways) here in the regime of hydraulic control overflow.

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Observations of tidal internal waves in the Bransfield Strait, Antarctica, are analyzed. The measurements were carried out for 14 days on a moored station equipped with five autonomous temperature and pressure sensors. Vertical displacements of temperature revealed that strong internal vertical oscillations up to 30-40 m are caused by the diurnal internal tide. The waves are forced due to the interaction of the barotropic tide with the bottom topography. The velocity ellipses of the barotropic tidal currents were estimated using the global tidal model.

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.Plain Language Summary Deep and bottom waters of the ocean are formed in the polar regions and occupy a significant part of the ocean volume. Propagation of these coldest waters plays an important role in the heat transport of the ocean and influences the Earth's climate. At the same time, the lower part of oceanic circulation is less investigated than its upper part. The most intense bottom currents are formed in the narrow abyssal channels connecting ocean basins. Direct deep-water measurements at these points are technically complicated and time consuming; modern computer models are usually focused mostly on the simulations of circulation in the upper layer. The goal of this work is to study intense bottom currents in the key passages of the Atlantic using a numerical model. We adjust our ocean circulation model based on available velocity measurements in the most interesting parts of the currents and compute the spatial structure of the currents in the entire channel. These calculations allow us to get the entire pattern of bottom water motions through underwater ridges and to study some hydrodynamic features of deep-water flows.

We analyzed CTD and ADCP measurements in the western Barents Sea carried out onboard the Russian R/V Akademik Mstislav Keldysh (cruise 68) in July-August 2017. We studied the water structure over a meridional section between Norway and Svalbard. The velocities of the bottom flow were measured on a mooring deployed in the deepest part of the trough. We compared direct velocity measurements with the tidal velocities calculated from satellite altimetry data. Despite strong barotropic tides in the region, the mean bottom flow was permanently directed from the Barents to the Norwegian Sea, which corresponds to the measured thermohaline structure of the deep waters.