intense: the velocities in the core were up to 40 cm/s, while the velocities in the
Southern branch of the intermediate counter-current (SICC) did not reach 20 cm/s.
Analysis of CTD-Casts and sADCP Profiles
Vertical distribution of thermohaline parameters is based on the data of CTD-casts
at points 0° 30′ S, 0°, and 0° 30′ N (stations 2698–2700). The velocity profiles were
measured by the sADCP profiling. Sections of temperature, salinity, density, and
zonal velocity are shown in Fig. 2 for better visualization and interpretation of these
fields. Profiles of the thermohaline parameters and profiles of the zonal velocity
averaged over the entire run time of the casts are shown in Fig. 3.
The sections in Fig. 2 show condensation of contour lines of potential temperature and potential density anomaly (hereinafter, density for short) in the upper part
of the section (below the uppermost mixed layer) down to a depth of 120–140 m
and their sparseness below that level. Condensation of the isohalines is observed at
depths from 40 to 60 m and from 90 to 130 m. A local sparseness between the two
intervals is related to the salinity (and velocity) core. The condensation of isotherms
and isopycnals above 120–140 m reflects the development of a sharp, high-gradient
upper part of the thermo-pycnocline at all stations. The sharp upper halocline occurs
lower than this layer below the salinity maximum at a depth of 60–70 m.
Sparseness of all isolines is especially clearly pronounced in the central part of
the main thermocline at depths of 200–500 m. It demonstrates the existence of
moderate gradients of temperature, salinity, and density in this range of depths.
Over some intervals, the gradients are weaker than the background gradients. One
can see an example of almost homogeneous layers of temperature, salinity, and
potential density in the interval 310–365 m at station 2698 south of the equator
(Fig. 3a). Similar decrease in the density gradient weaker than the background
values may reflect the development of intense processes of vertical transport.
One can also see in Fig. 2 the formation of elevations and depressions in the
isopycnal structure. The most pronounced features are isopycnal depressions in the
northern part of the section at depths above 150 m in the north and at a depth of
∼300 m at the equator. The upper depression is associated with the corresponding
decrease in depths of isotherms and isohalines and also with the lower boundary of
the undercurrent core. The isopycnal depression at a depth of ∼300 m corresponds
to the depressions and elevations in the structure of isotherms and isohalines. The
existence of the depressions of isotherms and isohalines between 150 and 300 m
leads to the local warming and salinity increase in the range of these depths as well
as below them. Note that the boundary between the eastward EUC flow and the
westward SIC flow is exactly in the depth interval of the lower isopycnal depression. The maximum isopycnal depression at the equator corresponds to the similar
but sharper depression of the isotachs (contour lines of equal velocity).
Strong Lomonosov undercurrent transports water of high salinity in the subsurface layers of the equatorial zone. It forms a subsurface maximum of salinity
434
T. A. Demidova
Southern branch of the intermediate counter-current (SICC) did not reach 20 cm/s.
Analysis of CTD-Casts and sADCP Profiles
Vertical distribution of thermohaline parameters is based on the data of CTD-casts
at points 0° 30′ S, 0°, and 0° 30′ N (stations 2698–2700). The velocity profiles were
measured by the sADCP profiling. Sections of temperature, salinity, density, and
zonal velocity are shown in Fig. 2 for better visualization and interpretation of these
fields. Profiles of the thermohaline parameters and profiles of the zonal velocity
averaged over the entire run time of the casts are shown in Fig. 3.
The sections in Fig. 2 show condensation of contour lines of potential temperature and potential density anomaly (hereinafter, density for short) in the upper part
of the section (below the uppermost mixed layer) down to a depth of 120–140 m
and their sparseness below that level. Condensation of the isohalines is observed at
depths from 40 to 60 m and from 90 to 130 m. A local sparseness between the two
intervals is related to the salinity (and velocity) core. The condensation of isotherms
and isopycnals above 120–140 m reflects the development of a sharp, high-gradient
upper part of the thermo-pycnocline at all stations. The sharp upper halocline occurs
lower than this layer below the salinity maximum at a depth of 60–70 m.
Sparseness of all isolines is especially clearly pronounced in the central part of
the main thermocline at depths of 200–500 m. It demonstrates the existence of
moderate gradients of temperature, salinity, and density in this range of depths.
Over some intervals, the gradients are weaker than the background gradients. One
can see an example of almost homogeneous layers of temperature, salinity, and
potential density in the interval 310–365 m at station 2698 south of the equator
(Fig. 3a). Similar decrease in the density gradient weaker than the background
values may reflect the development of intense processes of vertical transport.
One can also see in Fig. 2 the formation of elevations and depressions in the
isopycnal structure. The most pronounced features are isopycnal depressions in the
northern part of the section at depths above 150 m in the north and at a depth of
∼300 m at the equator. The upper depression is associated with the corresponding
decrease in depths of isotherms and isohalines and also with the lower boundary of
the undercurrent core. The isopycnal depression at a depth of ∼300 m corresponds
to the depressions and elevations in the structure of isotherms and isohalines. The
existence of the depressions of isotherms and isohalines between 150 and 300 m
leads to the local warming and salinity increase in the range of these depths as well
as below them. Note that the boundary between the eastward EUC flow and the
westward SIC flow is exactly in the depth interval of the lower isopycnal depression. The maximum isopycnal depression at the equator corresponds to the similar
but sharper depression of the isotachs (contour lines of equal velocity).
Strong Lomonosov undercurrent transports water of high salinity in the subsurface layers of the equatorial zone. It forms a subsurface maximum of salinity
434
T. A. Demidova