\documentclass[epub,pdf]{ebook}
\usepackage[cm]{sfmath}
\usepackage{amsmath}
\usepackage{color}
\usepackage[pdftoolbar=false, pdfpagemode=UseNone, linkbordercolor={0 0 0}]{hyperref}

\ident{ES}{19}{5}{2019}{2019ES000679}
\cpright{}{2019}
\pagestyle{empty}
\definecolor{brown}{RGB}{157,23,4}

\begin{document}

\vspace*{2\baselineskip}

\title{Thermohaline structure of Antarctic Bottom Water in the abyssal basins of the South Atlantic}

\author{D. I. Frey$^{1}$, E. G. Morozov$^{1}$, I. Ansorge$^{2}$,\\ V. V. Fomin$^{3}$, N. A. Diansky$^{3,4,5}$,\\ R. Yu. Tarakanov$^{1}$}

\affil{1}{Shirshov Institute of Oceanology RAS, Moscow,  Russia}
\affil{2}{University of Cape Town, Rondebosch,  South Africa}
\affil{3}{Zubov State Oceanographic Institute, Moscow,  Russia}
\affil{4}{Lomonosov Moscow State University, Moscow,  Russia}
\affil{5}{Institute of Numerical Mathematics RAS, Moscow,  Russia}

\abstract{Antarctic Bottom Water (AABW) occupies the lowest ocean layer in the major part of the Atlantic. Despite the fact that this water has the same origin from the Weddell Sea, thermohaline properties of bottom layers vary strongly in different deep basins. Temperature and salinity increase along the pathways of bottom water propagation is caused by mixing of AABW with the warmer and more saline water in the overlying layers. This mixing strongly intensifies over underwater ridges; in addition, these ridges determine the pathways of bottom water spreading. Thus, the ocean topography plays the most important role in the formation of thermohaline structure of deep basins. In particular, the properties of AABW in the western and eastern parts of the South Atlantic significantly differ from each other. In this paper we compare temperature and salinity structure of the abyssal waters of the \linebreak\newpage}\noindent\centerline{\parbox{100mm}{  Southeast and Southwest Atlantic. We used the results of high spatial resolution modeling and hydrographic measurements for this study. We also simulated the velocity field in the bottom layer of the South Atlantic.}}


\section{The Data and Methods}

      Sparse direct observations in the abyssal ocean layer make investigations of bottom waters
structure difficult. Simulations with modern numerical models focus on the calculation in the upper
part of the ocean; usually, vertical resolution of these models in the deep layers is not sufficient for
describing abyssal processes. In this work, we combined two approaches: first of all, we simulated
the deep-water circulation using a regional model with a high resolution in the deep layers; in
addition, we used direct hydrographic measurements for verification of the model and for detailed
analysis of AABW evolution along the pathways of its spreading.

      The Institute of Numerical Mathematics Ocean Model (INMOM)
[\itc{Zalesny et al.,} \reflink{Zale10}{2010}]
was
used for the simulations. The INMOM is a $\sigma$-coordinate numerical model based on the primitive
equations of hydrothermodynamics with the Boussinesq and hydrostatic approximations
[\itc{Diansky et al.,} \reflink{Dian02}{2002};
\itc{Frey et al.,} \reflink{Frey17a}{2017a}, \reflink{Frey17b}{2017b};
\itc{Morozov et al.,} \reflink{Moro19}{2019};
\itc{Zalesny et al.,} \reflink{Zale12}{2012}].
The
model domain covered the part of the Atlantic Ocean from the equator to 50\deg S, and from 60\deg W to
20\deg E (the domain is shown with thick black lines in
\figref{1}).           % Fig. 1).
The horizontal resolution was $0.05\deg$ by
latitude and longitude, which gives $1600 \times 1000$ model points in the horizontal plane. The domain
covers the deep basins of the West and East Atlantic: Angola, Cape, Argentine, and Brazil basins are
the regions, which we want to investigate and compare in this study.


      The bottom relief was interpolated to the model domain from the GEBCO 2014 digital
database
[\itc{Weatherall et al.,} \reflink{Weat15}{2015}].
The climatological data from the World Ocean Atlas 2013
[\itc{Locarnini et al.,} \reflink{Loca13}{2013};
\itc{Zweng et al.,} \reflink{Zwen13}{2013}]
were used as the initial temperature and salinity fields.
These data were also specified in a buffer zone with a width of 10 grid points at the liquid boundaries
[\itc{Klinck,} \reflink{Klin95}{1995}].
The atmosphere-ocean interaction was prescribed by specifying the fluxes of heat,
freshwater, and momentum at the boundary. The atmospheric characteristics included air temperature,
humidity, and wind velocity at a height of 10~m, atmospheric pressure, longwave and shortwave
irradiance, and monthly mean precipitation. They were taken from the CORE database
[\itc{Large and Yeager,} \reflink{Larg09}{2009}].
The numerical experiment was performed in two stages: at first, the model was spun
up using ``frozen'' temperature and salinity fields; then, the simulation included adjustment of
thermohaline properties. This method was suggested in
[\itc{Sarkisyan,} \reflink{Sark91}{1991}]
for computing the velocity
field based on known temperature and salinity data.

      Prognostic variables of the model are three-dimensional fields of potential temperature,
salinity, and components of horizontal velocity. Here, we analyzed temperature and salinity fields on
the last day of the calculation. We used the data from two quasi-meridional hydrographic sections
(the locations of stations over these sections are indicated with white dots in
\figref{1}).           % Fig. 1).
We chose these
two sections because they follow the deep part of the basins in the West and East Atlantic and
represent transformation of AABW properties. The first section across the Argentine and Brazil
basins was occupied during cruise 17 of the R/V {\itshape ``Akademik Sergei Vavilov''} in 2003
[\itc{Morozov,} \reflink{Moro05}{2005}].
The route of this cruise covered the main pathway of Antarctic Bottom Water spreading. The
data acquisition system consisted of a General Oceanics Rosette multi-bottle array system and Neil
Brown CTD profiler.  The second section across the eastern basins was carried out during the cruise
of the R/V {\itshape``Ronald H. Brown''} along line A13.5
[\itc{Bullister et al.,} \reflink{Bull10}{2010}].
The data were collected
using Sea-Bird Electronics (SBE) 9plus CTD profiler mounted in a SBE 32 aluminum frame.



\begin{figure}                      % Fig 1
\figurewidth{115mm}
\setimage{}{}{115mm}{125mm}{2019es000679-f02}
\fcaplabel{\footnotesize The data used for verification of the model: depth of 2\deg C potential temperature isotherm (a)
and potential temperature at the ocean bottom (b) along the hydrographic sections in the West (shown
with blue colors) and East (green colors) Atlantic. Circles indicate the values at the CTD-stations;
solid lines are the data of numerical modeling interpolated to the trajectory of the sections. Some
statistical parameters of these data are given in
\tabref{1}.}          % Table 1.
\end{figure}


\begin{sidewaystable}                                   % Table 1
\tablewidth{158mm}
\ftablabel{Verification of the Model on the Basis of Two CTD-Sections.
$X_{\mathrm{model}}$ and $X_{\mathrm{meas}}$
 are Modeled
and Measured Values, Respectively. These Values Include Calculated Upper Boundary of AABW and
Potential Temperature at the Ocean Bottom}
\vspace{5pt}
\footnotesize
\begin{tabular}
{@{}l@{\hspace{-10pt}}
c@{\hspace{3pt}}
c@{\hspace{3pt}}
c@{\hspace{5pt}}
c@{}}
\hline
\\ [-7pt]
                &                  Maximum      &        Minimum    &         Mean   &     Standard \\
                &                               &                   &                & deviation \\
                &($X_{\mathrm{model}}-X_{\mathrm{meas}}$) &    ($X_{\mathrm{model}}-X_{\mathrm{meas}}$) & ($X_{\mathrm{model}}-X_{\mathrm{meas}}$) & ($X_{\mathrm{model}}-X_{\mathrm{meas}}$) \\
 [7pt]  \hline   \\ [-4pt]
AABW level (East), m    &           103      &                $-402$    &             $-117$    &       109 \\
AABW level (West), m    &           217      &                $-303$    &             $-159$    &       101 \\
Bottom pot. temp. (East), \deg C  & 0.55     &                $-0.20$   &             0.018   &      0.110 \\
Bottom pot. temp. (West), \deg C  & 0.66     &                $-0.85$   &             0.092   &      0.401 \\
[4pt] \hline
\end{tabular}
\end{sidewaystable}

\section{Model Verification and Meridional\\ Evolution of AABW Properties}

      The results of numerical modeling were compared with the direct measurements over two
sections in the West and East Atlantic
(\figref{1})           % (Fig. 1)
because bottom water structures in these two regions
differ significantly. Quasi-meridional direction of these sections allows us to verify how the model
reproduces the evolution of AABW properties. Moreover, the locations of stations in cruise 17 of the
R/V {\itshape``Akademik Sergei Vavilov''} were especially chosen along the main pathway of AABW
spreading. These stations include the Vema Channel with the most intense flow of AABW in the
Atlantic. In the channel, CTD casts were performed near its eastern wall
[\itc{Morozov,} \reflink{Moro05}{2005}],
 because
the Ekman friction moves the coldest waters to the right relatively to the main northward flow (in the
Southern Hemisphere). This effect was investigated in the Vema Channel numerically
[\itc{Jungclaus and Vanicek,} \reflink{Jung99}{1999}]
and observed many times in different expeditions
[\itc{Morozov et al.,} \reflink{Moro08}{2008}, \reflink{Moro10}{2010}].
The flow of AABW from the Vema Channel was studied in
[\itc{Morozov et al.,} \reflink{Moro18}{2018}].




      The data used for verification are shown in
\figref{2}.           % Fig. 2.
We compared two properties of AABW:
the depth of its upper boundary
(\figref{2}a),           % (Fig. 2a),
and potential temperature at the ocean bottom
(\figref{2}b).           % (Fig. 2b).
The
stations occupied in cruise 17 of the R/V {\itshape ``Akademik Sergei Vavilov} are shown with blue color, and
stations from the A13.5 section occupied in the cruise of the R/V {\itshape ``Ronald H. Brown''} are shown with
green. Solid lines in
\figref{2}           % Fig. 2
correspond to the results of our numerical modeling. Bottom temperatures
were determined as the temperature of the closest to the bottom sample; usually the CTD cast was
stopped at 3--5 meters above the sea floor. As for numerical modeling, potential temperature from the
lowest sigma-level was used for comparison with the measured value. The location of the 2\deg C
isotherm at the station was determined by linear interpolation of the temperature profile between
samples; the same approach was used for simulated data.

\begin{sidewaysfigure}                      % Fig 2
\figurewidth{120mm}
\setimage{}{}{150mm}{}{2019es000679-f03}\vspace*{10pt}
\fcaplabel{Vectors of horizontal velocities at a depth of a 4300 m in the South Atlantic based on the
results of numerical modeling.}
\end{sidewaysfigure}


      The simulated data presented in
\figref{2}           % Fig. 2
were interpolated to the points of measurements for
model verification. Parameters of data comparison are shown in
\tabref{1}.          % Table 1.
Standard deviation of the
difference between simulated and measured values is about 100 meters over both sections. Simulated
bottom potential temperatures over the A13.5 section agree well with the measurements (the mean
difference is 0.018\deg C and standard deviation is 0.11\deg C). As can be seen from
\figref{2}b,           % Fig. 2b,
the
temperatures in the West Atlantic at latitudes of 32\deg--15\deg S differ significantly. One of the causes of
this discrepancy is the narrowness of the Vema Channel located at this part of the section. The
resolution of the model does not allow one to restore the AABW flow adequately; thus, simulated
values do not agree with the correctly measured ones. The correct simulation is presented in
[\itc{Frey et al.,} \reflink{Frey17a}{2017a}]
using the same model with much higher horizontal resolution.

\section{AABW Structure and Velocities in the Bottom Layer of the Atlantic}

\begin{sidewaysfigure}                      % Fig 3
\figurewidth{120mm}
\setimage{}{}{150mm}{}{2019es000679-f04}\vspace*{12pt}
\fcaplabel{Bottom potential temperature in the bottom layer of the Atlantic. The data were taken from
the deepest $\sigma$-level of the model. The ocean basins with bottom potential temperature greater than
2\deg C are shown with gray color.}
\end{sidewaysfigure}

       The results of numerical modeling allow us to study the spatial structure of bottom waters in
the South Atlantic. For this analysis, we interpolated three-dimensi\-onal temperature and salinity
fields from vertical sigma-levels to regular $z$-levels with high resolution. Using interpolated data, we
calculated horizontal velocities in the AABW layer in the entire South Atlantic
(\figref{3}).           % (Fig. 3).
Here we
present the velocities at a depth of 4300~m, which corresponds to a depth of the main flow in the
Vema Channel. Generally, these velocities do not exceed 5~cm/s; more intense flows are observed in
the western part of the Argentine Basin and in the Vema Channel. Correct modeling of these flows
requires higher resolution. The main feature of the bottom circulation in the western part of the South
Atlantic is the bottom flow of the Deep Western Boundary Current directed to the north. This current
is clearly pronounced south of the Rio Grande Rise (south of 30\deg S). Strong intensification of the
bottom current occurs in the Vema Channel (27\deg--33\deg S). Based on the numerical modeling, the
northerly current becomes less intense north of 27\deg S and almost disappears in the northern part of the
Brazil Basin. However, direct measurements in the ocean reveal that the northerly bottom flow
continues further to the equator and north of the equator
[\itc{Sandoval and Weatherly,} \reflink{Sand01}{2001}].

       In the East Atlantic, the inflow of AABW to the Angola Basin based on numerical
simulations is revealed in the southern part of the Angola Basin. This conclusion was also made in
[\itc{Morozov et al.,} \reflink{Moro10}{2010}].
The circulation in the bottom layer of the Angola Basin is generally very
weak.

       Some aspects of deep-water circulation in this region are discussed in
[\itc{Frey et al.,}  \reflink{Frey17b}{2017b}].
Distribution of bottom potential temperature
(\figref{4})           % (Fig. 4)
is helpful for determining the main pathways of
AABW spreading. The values of potential temperature were taken from the bottom $\sigma$-level of our
model.

\begin{sidewaysfigure}                   % Fig 4
\figurewidth{120mm}
\setimage{}{}{157mm}{}{2019es000679-f04}\vspace*{12pt}
\fcaplabel{Bottom potential temperature in the bottom layer of the Atlantic. The data were taken from the deepest $\sigma$-level of the model. The ocean basins with bottom potential temperature greater than 2\deg C are shown with gray color.}
\end{sidewaysfigure}



    We calculated some integral parameters of AABW in the main basins of the South Atlantic.
The parameters include minimum potential temperature and salinity, maximum potential density
referenced to 4000~db ($\sigma_4$),      %%% ???+
and total volume of Antarctic waters below the 2\deg C potential temperature
isotherm
(\tabref{2}).          % (Table 2).
 The calculation was made for the Argentine, Brazil, Cape, and Angola basins
separately.  Minimum temperatures were determined from the deepest sigma-level of the model.
Usually, the waters with the minimum temperatures are located in the deep part of the basins near the
channel with inflow of bottom waters. The minimum salinity in
\tabref{2}          % Table 2
was determined as salinity at
the points with minimum temperature. Then, maximum potential density referenced to 4000~db was
derived using the EOS80 equations
[\itc{Lewis and Perkin,} \reflink{Lewi81}{1981}].
Three-dimensional temperature field
interpolated to the $z$-levels was used for the calculation of the AABW volume. Horizontal resolution
of the field was $0.05\deg$ (the same as the model resolution), the vertical resolution was 20~meters. Then,
we made the following check for each point of the grid: if potential temperature $\theta$ was lower than 2\deg C
and location of the node was above the bottom, then this volume was added to the corresponding
ocean basin. We can see that the AABW volume in the West Atlantic is two times larger than in the
East Atlantic; in addition, the waters west of the Mid-Atlantic Ridge are colder and less saline, which
makes their density higher
(\tabref{2}).          % (Table 2).

\begin{sidewaystable}                                   % Table 2
\tablewidth{130mm}
\ftablabel{AABW Properties in Deep Basins of the South Atlantic Based on the Numerical Simulation}
\vspace{5pt}
\small
\begin{tabular}
{@{}l@{\hspace{10pt}}
c@{\hspace{10pt}}
c@{\hspace{10pt}}
c@{\hspace{10pt}}
c@{}}
\hline
\\ [-7pt]
Basin    &     Minimum pot.  &    Minimum       &  Maximum density      & Total AABW \\
         &  temperature, \deg C& salinity, psu  &  $\sigma_4$, kg/m$^3$ & volume, 10$^6$ km$^3$ \\
 [7pt]  \hline   \\ [-4pt]
Argentine &   $-0.25$           &     34.67     &         46.09      &         10.8 \\
Brazil    &   0.15            &     34.69     &         46.05      &         9.2 \\
Cape      &   0.6             &     34.71     &         45.99      &         5.6 \\
Angola    &   1.9             &     34.88     &        45.88       &         3.5 \\
[4pt] \hline
\end{tabular}
\end{sidewaystable}



\section{Summary and Conclusions}

      Temperature and salinity structure of bottom waters in deep basins of the South Atlantic were
studied on the basis of two hydrographic quasi-meridional sections and simulations using a numerical
model with a high resolution in the abyssal ocean layer. The model was verified using the CTD data
from these sections. In this study, we focused on the transformation of bottom waters over the
pathway of their propagation and on the zonal differences of AABW in the western and eastern parts
of the South Atlantic Ocean. Some integral characteristics of bottom waters were calculated for the
individual ocean basins, including the Argentine, Brazil, Cape, and Angola basins.  The main results
of our research related to the numerical simulations and model adjustment are as follows:

\begin{enumerate}
\item
 An adjusted version of the ocean circulation model was applied for investigations of the
abyssal ocean layer, including the main pathways of bottom waters and influence of underwater
ridges and other features of bottom topography on the spatial structure of deep waters. Narrow
abyssal channels are key points of AABW propagation and require sufficient horizontal resolution of
the model as well as additional verification.
\item
Significant increase in the bottom temperature is observed over underwater ridges along the
pathway of AABW propagation. In addition, its upper boundary becomes much deeper. For example,
after crossing the ridge at 30\deg S in the Southeast Atlantic, the bottom potential temperature increases
from 0.7\deg C up to 1.9\deg C, while the 2\deg C isotherm descends by almost 1~km.
\item
Strong differences are observed in the abyssal waters in the Southwest and Southeast
Atlantic due to the local peculiarities of the bottom topography. Thus, the total volume of AABW in
the West Atlantic is two times greater than in the East Atlantic; the bottom temperature variations
between them reach 2\deg C over the same zonal section.
\item
The flow of AABW to the north is generally concentrated in the abyssal Deep Western
Boundary Current. It is well pronounced in the Argentine Basin but becomes weaker in the Brazil
Basin.
\end{enumerate}

\acknowledgements{The work was carried out within the State Task of the Russian Federation 0128-2019-0009;
the research was supported by the Russian Foundation for Basic Research (grant 19-57-60001,
numerical simulations, and 19-05-00878, model adjustment) and by the Russian Science Foundation
(grant 16-17-10149, data analysis). The work of I. Ansorge was supported by the National Research
Foundation of South Africa (Grant UID 118901).}

\newpage

\begin{references}

\reference{Bany18} Banyte,  D.,  M.  Morales Maqueda,  R.  Hobbs, D. A. Smeed, A. Megann, S. Recalde (2018) , Geothermal Heating in the Panama Basin: 1. Hydrography of the Basin, {\itshape J. Geophys. Res.}, {\itshape 123}, no. 10, p. 7382--7392,  \href{https://doi.org/10.1029/2018JC013868}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Bull10} Bullister,  J. L.,  R. A.  Feely,  R.  Wanninkhoff, A. G. Dickson, D. A. Hansell, R. M. Key (2010) , {\itshape Carbon dioxide, hydrographic, and chemical data obtained during the R/V Ronald H. Brown Cruise in the Atlantic Ocean on CLIVAR repeat hydrography section A13.5 (Mar. 08--Apr. 17, 2010)}, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge,  \href{https://doi.org/10.3334/CDIAC/otg.CLIVAR_A13.5_2010}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Lave16} De Lavergne,  C.,  G.  Madec,  J.  Le mmer, A. G. Nurser, A. C. Naveira Garabato (2016) , On the consumption of Antarctic Bottom Water in the abyssal ocean, {\itshape J. Phys. Oceanography}, {\itshape 46}, no. 2, p. 635--661,  \href{https://doi.org/10.1175/JPO-D-14-0201.1}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Dian02} Diansky, N. A., A. V. Bagno, V. B. Zalesny (2002) , Sigma model of global ocean circulation and its sensitivity to variations in wind stress, {\itshape Izv. Atmosph. Oceanic Phys.}, {\itshape 38}, no. 4, p. 537--556.

\reference{Dick94} Dickson, R. R., J. Brown (1994) , The production of North Atlantic Deep Water: Sources, rates, and pathways, {\itshape J. Geophys. Res.}, {\itshape 99}, p. 12,319--12,342,  \href{https://doi.org/10.1029/94JC00530}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Frey17a} Frey, D. I., V. V. Fomin, N. A. Diansky, et al. (2017a) , New model and field data on estimates of Antarctic Bottom Water flow through the deep Vema Channel, {\itshape Doklady Earth Sciences}, {\itshape 474}, no. 1, p. 561--564,  \href{https://doi.org/10.1134/S1028334X17050026}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Frey17b} Frey, D. I., A. N. Novigatsky, M. D. Kravchishina, E. G. Morozov (2017b) , Water structure and currents in the Bear Island Trough in July--August 2017, {\itshape Russ. J. Earth. Sci.}, {\itshape 17}, p. ES3003,  \href{https://doi.org/10.2205/2017ES000602}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Gana00} Ganachaud, A., C. Wunsch (2000) , Improved estimates of global ocean circulation, heat transport and mixing from hydrographic data, {\itshape Nature}, {\itshape 408}, p. 453--457,  \href{https://doi.org/10.1038/35044048}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Hogg99} Hogg, N., G. Siedler, W. Zenk (1999) , Circulation and variability at the Southern Boundary of the Brazil Basin, {\itshape J. Phys. Oceanogr.}, {\itshape 29}, p. 145--157,  \href{https://doi.org/10.1175/1520-0485(1999)029%3C0145:CAVATS%3E2.0.CO;2}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{John08} Johnson, G. C. (2008) , Quantifying Antarctic Bottom Water and North Atlantic Deep Water volumes, {\itshape J. Geophys. Res.}, {\itshape 113}, p. C05027,  \href{https://doi.org/10.1029/2007JC004477}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Jung99} Jungclaus, J., M. Vanicek (1999) , Frictionally modified flow in a deep ocean channel: Application to the Vema Channel, {\itshape J. Geophys. Res.}, {\itshape 104}, no. C9, p. 21,123--21,136,  \href{https://doi.org/10.1029/1998JC900055}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Klin95} Klinck, J. M. (1995) , Thermohaline structure of an eddy-resolving North-Atlantic model: The influence of boundary conditions, {\itshape J. Physical Oceanography}, {\itshape 25}, p. 1174--1196,  \href{https://doi.org/10.1175/1520-0485(1995)025%3C1174:TSOAER%3E2.0.CO;2}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Larg09} Large, W., S. Yeager (2009) , The global climatology of an interannually varying air-sea flux data set, {\itshape Clim. Dyn.}, {\itshape 33}, p. 341--364,  \href{https://doi.org/10.1007/s00382-008-0441-3}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Lewi81} Lewis, E. L., R. G. Perkin (1981) , The Practical Salinity Scale 1978: conversion of existing data, {\itshape Deep-Sea Research}, {\itshape 28A}, no. 4, p. 307--328,  \href{https://doi.org/10.1016/0198-0149(81)90002-9}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Loca13} Locarnini, R. A., A. V. Mishonov, J. I. Antonov, et al. (2013) , {\itshape World Ocean Atlas 2013, Vol. 1: Temperature, S. Levitus (ed.), A. Mishonov (techn. ed.)}, 40 pp., NOAA Atlas NESDIS 73, USA (\href{http://www.nodc.noaa.gov/OC5/indprod.html}{http://www.nodc.noaa.gov/OC5/indprod.ht ml}).

\reference{Lump07} Lumpkin, R., K. Speer (2007) , Global ocean meridional overturning, {\itshape J. Physical Oceanography}, {\itshape 37}, p. 2550--2562,  \href{https://doi.org/10.1175/JPO3130.1}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Mant83} Mantyla, A. W., J. L. Reid (1983) , Abyssal characteristics of the World Ocean waters, {\itshape Deep-Sea Res., Part A}, {\itshape 30}, p. 805--833,  \href{https://doi.org/10.1016/0198-0149(83)90002-X}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Moro05} Morozov, E. G. (2005) , Cruise 17 of R/V Akademik Sergei Vavilov in the Atlantic Ocean, {\itshape Oceanology}, {\itshape 45}, no. 3, p. 441--443.

\reference{Moro08} Morozov, E. G., A. N. Demidov, R. Yu. Tarakanov (2008) , Transport of Antarctic waters in the deep channels of the Atlantic Ocean, {\itshape Doklady Earth Sciences}, {\itshape 423}, no. 8, p. 1286--1289,  \href{https://doi.org/10.1134/S1028334X08080230}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Moro10} Morozov, E. G., A. N. Demidov, R. Yu. Tarakanov, W. Zenk (2010) , {\itshape Abyssal Channels in the Atlantic Ocean: Water Structure and Flows}, 266 pp., Springer, Dordrecht,  \href{https://doi.org/10.1007/978-90-481-9358-5}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Moro18} Morozov,  E. G.,  R. Yu.  Tarakanov,  D. I.  Frey, D. G. Borisov (2018) , Currents and water structure north of the Vema Channel, {\itshape Russian Journal of Earth Sciences}, {\itshape 18}, p. ES5006,  \href{https://doi.org/10.2205/2018ES000630}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Moro19} Morozov,  E.,  D. .   Frey,  N.   Diansky, V. V. Fomin (2019) , Bottom circulation in the Norwegian Sea, {\itshape Russian Journal of Earth Sciences}, {\itshape 19}, p. ES2004,  \href{https://doi.org/10.2205/2019ES000655}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Orsi99} Orsi, A. H., G. C. Johnson, J. L. Bullister (1999) , Circulation, mixing, and production of Antarctic Bottom Water, {\itshape Prog. Oceanogr.}, {\itshape 43}, p. 55--109,  \href{https://doi.org/10.1016/S0079-6611(99)00004-X}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Orsi01} Orsi, A. H., S. S. Jacobs, A. L. Gordon, M. Visbeck (2001) , Cooling and ventilating the abyssal ocean, {\itshape Geophys. Res. Lett.}, {\itshape 28}, p. 2923--2926,  \href{https://doi.org/10.1029/2001GL012830}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Sand01} Sandoval, F. J., G. L. Weatherly (2001) , Evolution of the Deep Western Boundary Current of Antarctic Bottom Water in the Brazil Basin, {\itshape J. Physical Oceanography}, {\itshape 31}, no. 6, p. 1440--1460,  \href{https://doi.org/10.1175/1520-0485(2001)031%3C1440:EOTDWB%3E2.0.CO;2}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Sark91} Sarkisyan, A. S. (1991) , {\itshape Simulation of Oceanic Dynamics}, Gidrometeoizdat, St. Petersburg (in Russian).

\reference{Zale12} Zalesny,  V.,  N.  Diansky,  V.   Fomin, S. N. Moshonkin, S. G. Demyshev (2012) , Numerical model of the circulation of the Black Sea and the Sea of Azov, {\itshape Russ. J. Numerical Analysis Mathematical Modelling}, {\itshape 27}, no. 1, p. 95--111,  \href{https://doi.org/10.1515/rnam-2012-0006}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Zale10} Zalesny, V. B., G. I. Marchuk, V. I. Agoshkov, et al. (2010) , Numerical simulation of large-scale ocean circulation based on the multicomponent splitting method, {\itshape Russ. J. Numerical Analysis Mathematical Modelling}, {\itshape 25}, no. 6, p. 581--609,  \href{https://doi.org/10.1515/rjnamm.2010.036}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Zenk96} Zenk, W., N. G. Hogg (1996) , Warming trend in Antarctic Bottom Water flowing into the Brazil Basin, {\itshape Deep-Sea Res. I}, {\itshape 43}, no. 9, p. 1461--1473,  \href{https://doi.org/10.1016/S0967-0637(96)00068-4}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Zwen13} Zweng, M. M., J. R. Reagan, J. I. Antonov, et al. , {\itshape World Ocean Atlas 2013, Vol. 2: Salinity, S. Levitus (ed.), A. Mishonov (techn. ed.)}, 39 pp., NOAA Atlas NESDIS 74, USA (\href{http://www.nodc.noaa.gov/OC5/indprod.html}{http://www.nodc.noaa.gov/ OC5/indprod.html}).

\reference{Warr81} Warren, B. A., C. Wunsch (Eds.) (1981) , Deep circulation of the world ocean, {\itshape Evolution of Physical Oceanography, B. A. Warren and C. Wunsch (Eds.)}, p. 6--41, MIT Press, Cambridge, Mass.

\reference{Weat15} Weatherall, P., K. M. Marks, M. Jakobsson, et al. (2015) , A new digital bathymetric model of the world's oceans, {\itshape Earth and Space Science}, {\itshape 2}, no. 8, p. 331--345,  \href{https://doi.org/10.1002/2015EA000107}{\textcolor{brown}{\space\bfseries Cross\-ref}}

\reference{Wust36} W\"{u}st, G. (1936) , {\itshape Schichtung und Zirkulation des Atlantischen Ozeans (ed. Defant A.) Wissenschaftliche Ergebnisse, Deutsche Atlantische Expedition auf dem Forschungs -- und Vermessungsschiff ``Meteor'' 1925--1927}, Walter de Gruyter [ampersand] Co., Berlin.

\end{references}
\end{document}
