Thermohaline Structure and Salt
Fingering in the Lomonosov Equatorial
Undercurrent as Observed in April 2017
Tatiana A. Demidova
Introduction
Current velocity measurements using the OS-75 shipboard ADCP operating at a
frequency of 76.8 kHz manufactured by the RDI-Teledyne Co. (sADCP) have been
carried out on the route of the R/V “Akademik Sergey Vavilov” since 2014 in the
equatorial zone of the central and western Atlantic over the sections across the
Lomonosov Equatorial Undercurrent (EUC). In the (boreal) spring, the ship crossed
the equator from south to north, and in autumn it crossed the equator from north to
south. In 2014–2017, we carried out six crossings and some of them were
accompanied by CTD casts. The main task of this research was the study of the
EUC velocity field and thermohaline subsurface structure. It included estimates of
velocities and spatial location of the undercurrent and its fronts relative to the
equator and depth, estimates of water transport, observations of thermohaline
stratification and its stability, and estimates of vertical mixing. Results of studies in
2015–2016 are briefly discussed in [5, 6]. In this contribution, we consider the
results of measurements in April 2017. We discuss the properties of the EUC
velocity field and focus on the analysis of the thermohaline stratification structure in
the subsurface layer down to the depths of 600–800 m from the data of CTD-casts
at three stations with a goal of finding convectively unstable layers favorable for salt
fingering vertical mixing.
Vertical mixing related to the equatorial undercurrents was considered and
discussed since the discovery of the subsurface flows, for example in [16, 17, 22].
Many studies report about the role of vertical mixing owing to the turbulence and
velocity shear in the undercurrents, for example in [12–14, 23, 24]. In 1973, [14]
determined that while considering vertical mixing it is important to present the
T. A. Demidova ( ✉ )
Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia
e-mail: tademidova@ocean.ru
© Springer International Publishing AG, part of Springer Nature 2018
M. G. Velarde et al. (eds.), The Ocean in Motion, Springer Oceanography,
https://doi.org/10.1007/978-3-319-71934-4_26
429
Fingering in the Lomonosov Equatorial
Undercurrent as Observed in April 2017
Tatiana A. Demidova
Introduction
Current velocity measurements using the OS-75 shipboard ADCP operating at a
frequency of 76.8 kHz manufactured by the RDI-Teledyne Co. (sADCP) have been
carried out on the route of the R/V “Akademik Sergey Vavilov” since 2014 in the
equatorial zone of the central and western Atlantic over the sections across the
Lomonosov Equatorial Undercurrent (EUC). In the (boreal) spring, the ship crossed
the equator from south to north, and in autumn it crossed the equator from north to
south. In 2014–2017, we carried out six crossings and some of them were
accompanied by CTD casts. The main task of this research was the study of the
EUC velocity field and thermohaline subsurface structure. It included estimates of
velocities and spatial location of the undercurrent and its fronts relative to the
equator and depth, estimates of water transport, observations of thermohaline
stratification and its stability, and estimates of vertical mixing. Results of studies in
2015–2016 are briefly discussed in [5, 6]. In this contribution, we consider the
results of measurements in April 2017. We discuss the properties of the EUC
velocity field and focus on the analysis of the thermohaline stratification structure in
the subsurface layer down to the depths of 600–800 m from the data of CTD-casts
at three stations with a goal of finding convectively unstable layers favorable for salt
fingering vertical mixing.
Vertical mixing related to the equatorial undercurrents was considered and
discussed since the discovery of the subsurface flows, for example in [16, 17, 22].
Many studies report about the role of vertical mixing owing to the turbulence and
velocity shear in the undercurrents, for example in [12–14, 23, 24]. In 1973, [14]
determined that while considering vertical mixing it is important to present the
T. A. Demidova ( ✉ )
Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia
e-mail: tademidova@ocean.ru
© Springer International Publishing AG, part of Springer Nature 2018
M. G. Velarde et al. (eds.), The Ocean in Motion, Springer Oceanography,
https://doi.org/10.1007/978-3-319-71934-4_26
429