70
A. Russo et al.
3 Fronts
In the New Zealand sector, SAF has been reported in two different locations:
roughly around 60° S in the Orsi et al. [3] map, and much more northward, along
the shelf break of the Campbell Plateau, in the Belkin and Gordon [2] map. Our
data show that the two positions are simultaneously right, and the différence is
probably due to some lack of data coverage of the historical dataset and above ail
to the définition chosen by the different authors (T > 4 °C at 400 m for the first
location and the existence of the SubAntarctic Mode Water (SAMW) thermostad
north of the SAF for the second location). In fact,both Belkin and Gordon [2] and
Rintoul et al. [4] observed occasionally in the Tasmanian sector the SAF divided
into a “northern” and a “southern” part, separated by about 150-200 km; the
“northern” part of the SAF is characterised by a sharp température gradient
between 6 and 8 °C and a relatively stable position, and the “southern” part is
defined by a weaker gradient between 3 and 5 °C and a more variable position
[4]. In the New Zealand sector, we can observe this behaviour of the SAF in each
of the six sections, with lower température values and much wider spacing (from
400 to 800 km) than in the Tasmanian sector. The “northern” SAF (which we will
call NSAF) is individuated by the transition between 4.5 and 6.5 °C at 400 m and
the “southern” SAF (which we will call SSAF) by the transition between 3.5 and
4.5 °C at the same depth. Mostly, the température gradient is very sharp for both
fronts.
The NSAF is always located about 200-300 km south of the Campbell Plateau
edge, doser to it in the first three sections, and about 100 km offshore in the late
February 1995 and the two summer 1996 sections (the positions of the fronts are
summarised in Table 1 and reported in Fig. 2). The SSAF varies around 58-59°S,
with a northernmost position in the November section and a southernmost one
in the two sections collected between the end of December 1994 and mid January
1995.
The PF varied its location from 59° 50’ to 63° 00’ S, showing a general tendency to retreat toward south going from spring to the summer season. In fact we
observe its northernmost position in the early November section and the southernmost ones in the two February sections. The Southern front is observed
between 63° 40’ and 64° 30’ S, and its position appears to be dépendent not on the
season as the PF does, but on the géographie location. In fact, it is observed on
the northern flanks of the Pacific-Antarctic Ridge and, for the February 1995 section, of the Southeast Indian Ridge.
4 Observed Upper Océan Température Characteristics
The first section (3-11 November 1994; Fig. 2.a) is the only one in spring. The
Southern part is poorly described, due to compact pack ice encountered going
from 64° S southward; nevertheless, it is évident that the main différence between
this section and the summer ones is that the subsurface température minimum is
not confined between 50 and 200 m but covers the whole upper 200-m layer. This
is due to the presence of the ice cover, which does not allow for the heating of the
A. Russo et al.
3 Fronts
In the New Zealand sector, SAF has been reported in two different locations:
roughly around 60° S in the Orsi et al. [3] map, and much more northward, along
the shelf break of the Campbell Plateau, in the Belkin and Gordon [2] map. Our
data show that the two positions are simultaneously right, and the différence is
probably due to some lack of data coverage of the historical dataset and above ail
to the définition chosen by the different authors (T > 4 °C at 400 m for the first
location and the existence of the SubAntarctic Mode Water (SAMW) thermostad
north of the SAF for the second location). In fact,both Belkin and Gordon [2] and
Rintoul et al. [4] observed occasionally in the Tasmanian sector the SAF divided
into a “northern” and a “southern” part, separated by about 150-200 km; the
“northern” part of the SAF is characterised by a sharp température gradient
between 6 and 8 °C and a relatively stable position, and the “southern” part is
defined by a weaker gradient between 3 and 5 °C and a more variable position
[4]. In the New Zealand sector, we can observe this behaviour of the SAF in each
of the six sections, with lower température values and much wider spacing (from
400 to 800 km) than in the Tasmanian sector. The “northern” SAF (which we will
call NSAF) is individuated by the transition between 4.5 and 6.5 °C at 400 m and
the “southern” SAF (which we will call SSAF) by the transition between 3.5 and
4.5 °C at the same depth. Mostly, the température gradient is very sharp for both
fronts.
The NSAF is always located about 200-300 km south of the Campbell Plateau
edge, doser to it in the first three sections, and about 100 km offshore in the late
February 1995 and the two summer 1996 sections (the positions of the fronts are
summarised in Table 1 and reported in Fig. 2). The SSAF varies around 58-59°S,
with a northernmost position in the November section and a southernmost one
in the two sections collected between the end of December 1994 and mid January
1995.
The PF varied its location from 59° 50’ to 63° 00’ S, showing a general tendency to retreat toward south going from spring to the summer season. In fact we
observe its northernmost position in the early November section and the southernmost ones in the two February sections. The Southern front is observed
between 63° 40’ and 64° 30’ S, and its position appears to be dépendent not on the
season as the PF does, but on the géographie location. In fact, it is observed on
the northern flanks of the Pacific-Antarctic Ridge and, for the February 1995 section, of the Southeast Indian Ridge.
4 Observed Upper Océan Température Characteristics
The first section (3-11 November 1994; Fig. 2.a) is the only one in spring. The
Southern part is poorly described, due to compact pack ice encountered going
from 64° S southward; nevertheless, it is évident that the main différence between
this section and the summer ones is that the subsurface température minimum is
not confined between 50 and 200 m but covers the whole upper 200-m layer. This
is due to the presence of the ice cover, which does not allow for the heating of the