Antarctic Polar Biome
463
range 02–04 mg C m
−3 year-round. Failure to achieve chlorophyll accumulation during
the winter-spring period of P rate increase is consistent with closely matched production
and consumption processes and also with extreme mixing-down of cells due to unusually
strong wind stress at the surface.
Antarctic Polar Biome
As already noted in the introduction to this chapter, two nutrient regimes were postulated
by Hiscock et al. (2003) for what is treated here as the austral Polar biome, an approach to
the question of regional nutrient distribution that has the great merit of being functional.
The performance of phytoplankton cells induced by differential nutrients availability is
what is really important, and not—as in some previous discussions of the Southern
Ocean—simply the relative concentrations of nutrient molecules.
Antarctic Province (ANTA)
Extent of the Province
This is an annular province and is synonymous with the Southern Branch of the ACC of
some authors. It lies between the Polar Front at about 50
S and the Antarctic Divergence
at about 60–65
S.
Continental Shelf Topography and Tidal and Shelf-Edge Fronts
No coastline is included, because the island arcs between the Antarctic Peninsula and
South America are allocated to the APLR province. However, a few smaller oceanic
islands do occur in this province: Bouvet, Kerguelen, and Heard of the Atlantic and
Indian Ocean sectors.
Defining Characteristics of Regional Oceanography
This province includes permanently ice-free conditions, regions that are ice-free in austral
summer but covered by pack ice in winter, and also some regions that may be permanently
ice-covered. Drifting, melting icebergs that have broken free from glacier fronts are,
in some years and some places, very frequent and may have consequences that are
ecologically significant. The area of seasonal pack ice approaches very close to the PF,
especially in some years and at some longitudes. The 1997 US JGOFS section down 170
W
in December found the rapidly retreating seasonal ice edge at 65
S, or only 2–3
poleward
of the Polar Front even in austral summer. The 1992 German JGOFS sections at 6
W
in October–November found the PF at 49
S with spun-off eddies to 52
S; the retreating
ice edge was at 54–56
S at this time. Thus, what others have called the Permanently
Open Ocean Zone (POOZ), equatorward of the zone across which the ice edge migrates
seasonally, may be very limited in meridional extent.
A permanent halocline lies at about 150–200 m between the AD and the PF, sloping
up toward the south. In summer, heating of the surface water mass induces a pycnocline
at 50–100 m, below a shoal mixed layer. But, even at this season, the mixed layer is by no
means immune to episodic deepening during the passage of a depression with force 6–7
winds. Because deep water below the halocline is warmer than surface water, a thermal
inversion may occur if surface heating during a period of quiet winds has incompletely
heated the entire surface water column above the halocline.
463
range 02–04 mg C m
−3 year-round. Failure to achieve chlorophyll accumulation during
the winter-spring period of P rate increase is consistent with closely matched production
and consumption processes and also with extreme mixing-down of cells due to unusually
strong wind stress at the surface.
Antarctic Polar Biome
As already noted in the introduction to this chapter, two nutrient regimes were postulated
by Hiscock et al. (2003) for what is treated here as the austral Polar biome, an approach to
the question of regional nutrient distribution that has the great merit of being functional.
The performance of phytoplankton cells induced by differential nutrients availability is
what is really important, and not—as in some previous discussions of the Southern
Ocean—simply the relative concentrations of nutrient molecules.
Antarctic Province (ANTA)
Extent of the Province
This is an annular province and is synonymous with the Southern Branch of the ACC of
some authors. It lies between the Polar Front at about 50
S and the Antarctic Divergence
at about 60–65
S.
Continental Shelf Topography and Tidal and Shelf-Edge Fronts
No coastline is included, because the island arcs between the Antarctic Peninsula and
South America are allocated to the APLR province. However, a few smaller oceanic
islands do occur in this province: Bouvet, Kerguelen, and Heard of the Atlantic and
Indian Ocean sectors.
Defining Characteristics of Regional Oceanography
This province includes permanently ice-free conditions, regions that are ice-free in austral
summer but covered by pack ice in winter, and also some regions that may be permanently
ice-covered. Drifting, melting icebergs that have broken free from glacier fronts are,
in some years and some places, very frequent and may have consequences that are
ecologically significant. The area of seasonal pack ice approaches very close to the PF,
especially in some years and at some longitudes. The 1997 US JGOFS section down 170
W
in December found the rapidly retreating seasonal ice edge at 65
S, or only 2–3
poleward
of the Polar Front even in austral summer. The 1992 German JGOFS sections at 6
W
in October–November found the PF at 49
S with spun-off eddies to 52
S; the retreating
ice edge was at 54–56
S at this time. Thus, what others have called the Permanently
Open Ocean Zone (POOZ), equatorward of the zone across which the ice edge migrates
seasonally, may be very limited in meridional extent.
A permanent halocline lies at about 150–200 m between the AD and the PF, sloping
up toward the south. In summer, heating of the surface water mass induces a pycnocline
at 50–100 m, below a shoal mixed layer. But, even at this season, the mixed layer is by no
means immune to episodic deepening during the passage of a depression with force 6–7
winds. Because deep water below the halocline is warmer than surface water, a thermal
inversion may occur if surface heating during a period of quiet winds has incompletely
heated the entire surface water column above the halocline.