including air temperature, humidity, and wind velocity at a height of 10 m, precipitation, incident short- and long-wave radiation, and atmospheric pressure were
taken from the CORE database [11]. At the ocean surface, the relaxation to the
climate salinity and temperature data from the Levitus Atlas was performed with a
time scale of about 1 month.
We calculated three-dimensional fields of the horizontal velocities, potential
temperature, salinity at σ-levels, and sea surface height. In this work we analyze
mainly the velocity fields. For the analysis, we interpolated the results from the
σ-levels to the ocean depth. The total duration of the simulations was 45 days.
During the first 30 days, the model was spun up in the diagnosis regime using
“frozen” temperature and salinity fields. Then, the simulation was continued for
15 days in the adjustment regime. This method allows us to calculate the ocean
dynamics on the basis of the known temperature and salinity data.
Vema Channel
The Vema Channel is the main pathway for the coldest bottom waters transported to
the tropical Atlantic. The depths of the channel exceed 4600 m against the background depths of 4200 m. The shallowest point of the Vema Channel is the Vema
Sill at 31° 12′ S. The maximum depth of this sill is approximately 4614 m, and the
width of the channel here is 18 km. The Vema Channel is the best region for
investigating the bottom gravitational currents in a deep narrow channel. The
transport of AABW in this channel is the highest among all abyssal channels in the
Atlantic. The length of the channel (700 km) and relatively constant width
(15–20 km) in the southern part of the channel allows us to study AABW flow far
away from its inflow from the Argentine Basin. The local bottom relief in the
channel is not as rough as in the fracture zones of the Mid-Atlantic Ridge. The
Vema Channel is located relatively far from the equator; therefore, it is possible to
investigate the influence of the Coriolis force on the bottom current. Regular
measurements here have been performed since 1970s, which is helpful for studying
long-term variability of the bottom water properties.
Current velocities in the southern part of the Vema Channel calculated from our
measurements and numerical simulations are shown in Fig. 2. Since the depths of a
significant part of the channel are 4650–4700 m, the data were presented at a depth
of 4600 m. We measured the velocities in this region at three zonal sections of the
channel at 33° 34′, 32° 17′, and 31° 12′ S. Stations 1708 and 1709 (Fig. 2, left panel)
were occupied far away from the inflow of the bottom water to the channel. The
bottom velocities here were directed to the south and did not exceed 5–10 cm/s.
The numerical simulation shows significant velocities in the channel north of 33° S.
The bottom velocities based on experimental observations and numerical modeling
were 10–15 cm/s at 32° 17′ S and 25–30 cm/s at 31° 12′ S. According to the model
simulations, velocities up to 30 cm/s are observed in the Vema Channel over its
entire length. The minimum potential temperature of the bottom waters varies from
Bottom Water Flows in the Vema Channel …
479
taken from the CORE database [11]. At the ocean surface, the relaxation to the
climate salinity and temperature data from the Levitus Atlas was performed with a
time scale of about 1 month.
We calculated three-dimensional fields of the horizontal velocities, potential
temperature, salinity at σ-levels, and sea surface height. In this work we analyze
mainly the velocity fields. For the analysis, we interpolated the results from the
σ-levels to the ocean depth. The total duration of the simulations was 45 days.
During the first 30 days, the model was spun up in the diagnosis regime using
“frozen” temperature and salinity fields. Then, the simulation was continued for
15 days in the adjustment regime. This method allows us to calculate the ocean
dynamics on the basis of the known temperature and salinity data.
Vema Channel
The Vema Channel is the main pathway for the coldest bottom waters transported to
the tropical Atlantic. The depths of the channel exceed 4600 m against the background depths of 4200 m. The shallowest point of the Vema Channel is the Vema
Sill at 31° 12′ S. The maximum depth of this sill is approximately 4614 m, and the
width of the channel here is 18 km. The Vema Channel is the best region for
investigating the bottom gravitational currents in a deep narrow channel. The
transport of AABW in this channel is the highest among all abyssal channels in the
Atlantic. The length of the channel (700 km) and relatively constant width
(15–20 km) in the southern part of the channel allows us to study AABW flow far
away from its inflow from the Argentine Basin. The local bottom relief in the
channel is not as rough as in the fracture zones of the Mid-Atlantic Ridge. The
Vema Channel is located relatively far from the equator; therefore, it is possible to
investigate the influence of the Coriolis force on the bottom current. Regular
measurements here have been performed since 1970s, which is helpful for studying
long-term variability of the bottom water properties.
Current velocities in the southern part of the Vema Channel calculated from our
measurements and numerical simulations are shown in Fig. 2. Since the depths of a
significant part of the channel are 4650–4700 m, the data were presented at a depth
of 4600 m. We measured the velocities in this region at three zonal sections of the
channel at 33° 34′, 32° 17′, and 31° 12′ S. Stations 1708 and 1709 (Fig. 2, left panel)
were occupied far away from the inflow of the bottom water to the channel. The
bottom velocities here were directed to the south and did not exceed 5–10 cm/s.
The numerical simulation shows significant velocities in the channel north of 33° S.
The bottom velocities based on experimental observations and numerical modeling
were 10–15 cm/s at 32° 17′ S and 25–30 cm/s at 31° 12′ S. According to the model
simulations, velocities up to 30 cm/s are observed in the Vema Channel over its
entire length. The minimum potential temperature of the bottom waters varies from
Bottom Water Flows in the Vema Channel …
479