Antarctic Bottom Water Jets Flowing from the Vema Channel

Properties of the abyssal current of Antarctic Bottom Water (AABW) from the Vema Channel are studied based on temperature, salinity, and velocity profiler (CTD/LADCP) data. Previous studies over a period of almost 30 years revealed that very intense current of AABW exists in the Vema Channel. Later, it was found that this current consists of two branches. One branch spreads over the bottom of the channel; the other branch is elevated over the western wall of the channel. The deepest branch decays after it passes approximately 100 km while the upper one continues further to the North Atlantic and is the source of abyssal waters in the Canary and Cabo Verde basins of the North Atlantic. Data analysis suggested that the upper jet splits into two. One of these descends down a canyon at 24°30′ S, while the other (the third one) remains on the continental slope, and indications of its existence are also found at 24°00′ S. This research analyzes the existence and pathway of this third branch that can be traced up to latitude 24° S. Velocity measurements in 2022 allowed us to confirm the existence of this third branch

Landscape Mapping, Ichnological and Benthic Foraminifera Trends in a Deep-Water Gateway, Discovery Gap, NE Atlantic

Multidisciplinary studies have allowed us to describe the abiotic landscapes and, thus, reveal the ichnological and benthic foraminifera trends in a deep-water gateway. Mesoscale landscape mapping is presented based on the bathymetric position index, substrate types and near-bottom water temperature. Four sediment cores, retrieved from the entrance, centre and exit of the gap, were subject to computed tomography, ichnological and benthic foraminifera studies. A high diversity of abiotic landscapes in the relatively small area of Discovery Gap is detected and its landscape is characterized by 23 landscape types. The most heterogeneous abiotic factor is a topography that is associated with sediment patchiness and substrate variability. The ichnological and tomographical studies of the sediment cores demonstrate lateral and temporal differences in the macrobenthic tracemaker behaviour. The ichnofossils assemblage of the sediment core can be assigned to the Zoophycos ichnofacies with a higher presence of Zoophycos in the entrance site of the gap and during glacial intervals. Higher benthic foraminifera diversity and species richness during the Holocene are also registered in the southern part of the gap compared to the northern part. The spatial and temporal differences in macro-benthos behavior and benthic foraminifera distribution in the deepwater gateway are proposed to relate to the topographical variations of the Antarctic Bottom Water and its influence on the hydrodynamic regime, nutrient transport, etc.The bathymetric position index analysis and bottom substrates classification were carried out within framework of the state assignment of IO RAS (Theme No. 0128-2021-0016). The landscape mapping, benthic foraminiferal and hydrological studies were supported by the Russian Science Foundation (grant No. 19-17-00246). Research by RT was funded by Projects CGL2015-66835-P and PID2019-104625RB-100 (Secretaría de Estado de I+D+I, Spain), B-RNM-072-UGR18 (FEDER Andalucía), and P18-460 RT-4074 (Junta de Andalucía), and Scientific Excellence Unit UCE-2016-05 (Universidad de Granada). Work by TG was done within the framework of “The Drifters” Research Group at Royal Holloway University of London (RHUL)

Hydraulically Controlled Bottom Flow in the Orkney Passage

Supercritical hydraulically controlled overflow of Antarctic Bottom Water from the Weddell Sea has been observed in the Orkney Passage during field measurements in February 2022. The Orkney Passage is the main pathway for the densest layer of Antarctic Bottom Water flow from the Weddell Sea to the Scotia Sea. The bottom current overflows the sill across the passage and flows down from the crest of the sill at 3600 m deeper than 4000 m. The descending flow accelerates because of the difference in the height of the sill and its foot. An estimate of the Froude number of this flow was greater than unity. Near the foot of the slope the kinetic energy of the flow becomes insufficient to continue moving in this regime. The flow slows down, and strong mixing and warming of the bottom water occurs due to the exchange with the surrounding waters. This hydrodynamic phenomenon is called supercritical hydraulically controlled flow. However, the flow of bottom water continues further and eventually fills the abyssal depths of the Atlantic

Hydraulically Controlled Bottom Flow in the Orkney Passage

Supercritical hydraulically controlled overflow of Antarctic Bottom Water from the Weddell Sea has been observed in the Orkney Passage during field measurements in February 2022. The Orkney Passage is the main pathway for the densest layer of Antarctic Bottom Water flow from the Weddell Sea to the Scotia Sea. The bottom current overflows the sill across the passage and flows down from the crest of the sill at 3600 m deeper than 4000 m. The descending flow accelerates because of the difference in the height of the sill and its foot. An estimate of the Froude number of this flow was greater than unity. Near the foot of the slope the kinetic energy of the flow becomes insufficient to continue moving in this regime. The flow slows down, and strong mixing and warming of the bottom water occurs due to the exchange with the surrounding waters. This hydrodynamic phenomenon is called supercritical hydraulically controlled flow. However, the flow of bottom water continues further and eventually fills the abyssal depths of the Atlantic

Shipborne Acoustic Current Profiler measurements on 2017-11-05 (cruise ASV45)

The data were collected using a Shipborne Acoustic Current Profiler (SADCP). We used a Teledyne RD Instruments Ocean Surveyor (TRDI OS) SADCP with a frequency of 76.8 kHz and range of 700 meters. Temporal averaging was made over 120 s. All data were collected using VmDas software

Shipborne Acoustic Current Profiler measurements on 2020-01-12 (cruise AMK79)

The data were collected using a Shipborne Acoustic Current Profiler (SADCP). We used a Teledyne RD Instruments Ocean Surveyor (TRDI OS) SADCP with a frequency of 76.8 kHz and range of 700 meters. Temporal averaging was made over 120 s. All data were collected using VmDas software

Shipborne Acoustic Current Profiler measurements on 2017-12-05 (cruise ASV45)

The data were collected using a Shipborne Acoustic Current Profiler (SADCP). We used a Teledyne RD Instruments Ocean Surveyor (TRDI OS) SADCP with a frequency of 76.8 kHz and range of 700 meters. Temporal averaging was made over 120 s. All data were collected using VmDas software

Shipborne Acoustic Current Profiler measurements on 2018-01-11 (cruise ASV45)

The data were collected using a Shipborne Acoustic Current Profiler (SADCP). We used a Teledyne RD Instruments Ocean Surveyor (TRDI OS) SADCP with a frequency of 76.8 kHz and range of 700 meters. Temporal averaging was made over 120 s. All data were collected using VmDas software

Shipboard Acoustic Doppler Current Profiling in the Malvinas Current from 2016-2020

The archive contains data of measurements of the Malvinas Current performed on multiple occupations of five transects across the flow. The data were collected using a Shipborne Acoustic Current Profiler (SADCP) in 2016-2020. We used a Teledyne RD Instruments Ocean Surveyor (TRDI OS) SADCP with a frequency of 76.8 kHz and range of 700 meters. Temporal averaging was made over 120 s. All data were collected using VmDas software. The .STA files (see Other version) can be processed by standard WinADCP software