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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. Plain Language Summary: Water is an efficient temperature regulator. Large energy exchange is required to produce small changes in water temperature. Since 71% of the Earth's surface is covered by oceanic water, the ocean plays a fundamentally important role in the climate system. The ocean transports, stores, and exchanges with the atmosphere substantial amounts of heat and freshwater. In this way, the ocean slows down and mitigates temperature variability in the climate system. However, in spite of its high thermal inertia, the ocean is also affected by global warming. More than 90% of the excess energy injected into the climate system in the past century has been absorbed by the ocean. As a result, the ocean has warmed significantly, at all depths. We report results of observations confirming that warming trends observed previously in abyssal regions of the South Atlantic persist into recent years in the Vema Channel, a deep narrow passage in the South Atlantic bathymetry, where most of Antarctic Bottom Water in the South Atlantic flows northward. Our data also suggest that the warming may be occurring with an increasing rate since the early 2000s. Key Points: Antarctic Bottom Water (AABW) temperatures in the Vema Channel are highly variableAABW in the Vema Channel has been warming since the early 1970sWarming rate in AABW in the Vema Channel waters may be increasing [ABSTRACT FROM AUTHOR]

In 2013 and 2018, Shirshov Institute of Oceanology performed 12 stations with conductivitytemperature-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. [ABSTRACT FROM AUTHOR]

Structure of the deep spillway was studied on the basis of conductivity‐temperature‐depth, lowered acoustic Doppler current profiler, and mooring measurements in 2011–2014 in the Romanche fracture zone (22°27′–22°32′W). The spillway exists quasi‐permanently in the regime of hydraulic control overflow and consists of two flows in the layer θ < 1.20 °C (deeper than 4,150 m). The first flow enters the fracture from the south through a gap in the Southern Wall. The second flow is directed to the east along the narrow valley of the fracture. The sill depths of these passages are 4,570 and 4,430 m, respectively. The depths over the surrounding ridges are shallower than 4,100 m. Both flows descend to the local depression of the fracture with 5,000‐m depth. Bottom potential temperatures over both sills were 0.51 °C, and the measured velocities were 20–40 cm/s. When the flows descend down the slope, they accelerate in supercritical regime. Maximal measured velocities were up to 65 cm/s. Analysis of the 189‐day time series of velocities on the mooring deployed in the flow descending from the gap showed a very high level of fluctuation energy: 10 times greater than the energy of the barotropic tide at this point. The only energy source of these fluctuations is the available potential energy of the deep thermocline in the West Atlantic transforming to the kinetic energy of the deep spillway. The total transport of the bottom water below θ = 1.2 °C based on the lowered acoustic Doppler current profiler measurements is estimated at 0.29–0.35 Sv, which agrees with the predicted values. Plain Language Summary: The bottom waters of the Atlantic are of the Antarctic origin. They flow from the sources in Antarctica from one deep basin to another reaching the latitudes of Europe and North America. This bottom flow passes narrow channels in the submarine ridges that separate deep basins. Long channels as the Romanche Fracture Zone (FZ) at the equator usually consist of constrictions and sills. When the bottom flow passes through such a channel, deep water spillways can be formed in the constrictions down the sills where the flow accelerates because available potential energy transforms to kinetic energy. We studied the structure and dynamics of the bottom currents in the western part of the Romanche FZ on the basis of field observations. We show that in the research site the structure of the flow has exactly this form with spillways. The temperature characteristics of the bottom flow and water transport are estimated. High intensity of kinetic energy oscillations in the spillway zone was found. The forcing can be related only to the potential energy of the bottom waters in the basin upstream the Romanche FZ. The results of this study are important for modeling ocean climate research. Key Points: The spillway in the western part of the Romanche fracture zone exists quasi‐permanently in the regime of a hydraulic controlled overflowTransformation of the available potential energy into kinetic energy causes very intense fluctuations of velocities in the deep spillwayWe quantify transport of the abyssal flow by the deep spillway [ABSTRACT FROM AUTHOR]