o.
v. Gouretski
84__________ _______ ______________ -_________ _ _________________________________
Typical depth range occupied by this water mass is between 200 and 300 m. This
water mass is produced by the isopycnal mixing between Lower Circumpolar
Deep Water (see below) and shelf waters. As noted by Locarnini [10] this mixing
results in a subsurface température maximum and dissolved oxygen minimum.
4.2 Water Masses of the Oceanic Domain
The oceanic domain is occupied by the following water masses (Fig. 5): Antarctic
Surface Water (AASW), Circumpolar Deep Water (CDW) and Antarctic Bottom
Water (AABW). Antarctic Surface Water has its northern limit at the Antarctic
Polar front. This relatively cold (-1.9 to 2.0 °C) and low saline (34.0-34.3) layer of
about 200 meter depth is formed by convective mixing in winter. Warming of the
top of this layer in summer produces a well pronounced température minimum
on the vertical température profiles.
Circumpolar Deep Water is by far the most voluminous water mass of the
Southern Océan, deriving its properties from the North Atlantic Deep Water
(NADW), which is introduced into the Southern Océan within the Atlantic sector
and is modified during its circumpolar eastward flow with the ACC. Gordon [26]
was the First to make a distinction between the two types of the CDW, which
dérivé their characteristics from two different northern sources. The Lower CDW
(LCDW) bears the imprint of NADW by having a deep maximum in salinity
(34.75 at 1.7 °C) and minima in nitrates (31 pmol/kg) and phosphates (about 2.15
pmol/kg). The Upper CDW (UCDW) is marked by a pronounced minimum in
oxygen (3.8-3.9 ml/1 at 2.2 °C) and silicate (65 pmol/kg) and maxima in concentrations of nitrate (35 pmol/kg) and phosphates (2.5 pmol/kg). The oxygen minimum of UCDW is acquired due to the latéral exchange with the Indian and
Pacific deep waters, both having much lower oxygen concentrations and higher
nutrient content compared with those of NADW. Scatter diagrams for oxygen,
nitrate and phosphate also display extrema near 1.3 °C: the oxygen concentrations
fall below 4.1 ml/1, whereas nitrates and phosphates increase to 33 pmol/kg and
2.35 pmol/kg respectively. This water type, which we call here Ross Deep Water
(RDW), is found in the center of the Ross Gyre (Fig. 6). As in the Weddell Gyre,
this oxygen minimum is obviously due to the oxygen consumption by biological
processes during a prolonged isolation of the deep water within the inner recirculation area, as noted earlier by Locarnini [10]. Both modifications of CDW
occupy most of the water column within the océan domain.
It is generally accepted that the Weddell Sea contributes mainly to the production of the Antarctic Bottom Water (AABW). The next important source of the
bottom water is located in the south-western part of the Pacific sector. Shown in
Fig. 5b are scatter diagrams below 300 m for the stations from the deep-ocean
domain. Ail diagrams display two distinct segments within the deeper part of the
water column. The upper segment (0.5-0.0 °C) indicates mixing between the deep
waters (0.5 °C, S=34.705) and bottom waters (0.0 °C, S=34.700). The latter indices
characterize the old AABW [9]. Its most pronounced characteristics are maxima
in silicate, nitrate and phosphate concentrations (150,31 and 2.2 pmol/kg respectively). Within the lower segment, below the inflection point at 0.0 °C the scatter
v. Gouretski
84__________ _______ ______________ -_________ _ _________________________________
Typical depth range occupied by this water mass is between 200 and 300 m. This
water mass is produced by the isopycnal mixing between Lower Circumpolar
Deep Water (see below) and shelf waters. As noted by Locarnini [10] this mixing
results in a subsurface température maximum and dissolved oxygen minimum.
4.2 Water Masses of the Oceanic Domain
The oceanic domain is occupied by the following water masses (Fig. 5): Antarctic
Surface Water (AASW), Circumpolar Deep Water (CDW) and Antarctic Bottom
Water (AABW). Antarctic Surface Water has its northern limit at the Antarctic
Polar front. This relatively cold (-1.9 to 2.0 °C) and low saline (34.0-34.3) layer of
about 200 meter depth is formed by convective mixing in winter. Warming of the
top of this layer in summer produces a well pronounced température minimum
on the vertical température profiles.
Circumpolar Deep Water is by far the most voluminous water mass of the
Southern Océan, deriving its properties from the North Atlantic Deep Water
(NADW), which is introduced into the Southern Océan within the Atlantic sector
and is modified during its circumpolar eastward flow with the ACC. Gordon [26]
was the First to make a distinction between the two types of the CDW, which
dérivé their characteristics from two different northern sources. The Lower CDW
(LCDW) bears the imprint of NADW by having a deep maximum in salinity
(34.75 at 1.7 °C) and minima in nitrates (31 pmol/kg) and phosphates (about 2.15
pmol/kg). The Upper CDW (UCDW) is marked by a pronounced minimum in
oxygen (3.8-3.9 ml/1 at 2.2 °C) and silicate (65 pmol/kg) and maxima in concentrations of nitrate (35 pmol/kg) and phosphates (2.5 pmol/kg). The oxygen minimum of UCDW is acquired due to the latéral exchange with the Indian and
Pacific deep waters, both having much lower oxygen concentrations and higher
nutrient content compared with those of NADW. Scatter diagrams for oxygen,
nitrate and phosphate also display extrema near 1.3 °C: the oxygen concentrations
fall below 4.1 ml/1, whereas nitrates and phosphates increase to 33 pmol/kg and
2.35 pmol/kg respectively. This water type, which we call here Ross Deep Water
(RDW), is found in the center of the Ross Gyre (Fig. 6). As in the Weddell Gyre,
this oxygen minimum is obviously due to the oxygen consumption by biological
processes during a prolonged isolation of the deep water within the inner recirculation area, as noted earlier by Locarnini [10]. Both modifications of CDW
occupy most of the water column within the océan domain.
It is generally accepted that the Weddell Sea contributes mainly to the production of the Antarctic Bottom Water (AABW). The next important source of the
bottom water is located in the south-western part of the Pacific sector. Shown in
Fig. 5b are scatter diagrams below 300 m for the stations from the deep-ocean
domain. Ail diagrams display two distinct segments within the deeper part of the
water column. The upper segment (0.5-0.0 °C) indicates mixing between the deep
waters (0.5 °C, S=34.705) and bottom waters (0.0 °C, S=34.700). The latter indices
characterize the old AABW [9]. Its most pronounced characteristics are maxima
in silicate, nitrate and phosphate concentrations (150,31 and 2.2 pmol/kg respectively). Within the lower segment, below the inflection point at 0.0 °C the scatter