4.6
The Antarctic Circumpolar Current System
Stephen R. Rintoul, Chris W. Hughes and Dirk Olbers
271
OCEAN CIRCULATION AND CLIMATE
Copyright © 2001 Academic Press
ISBN 0-12-641351-7
All rights of reproduction in any form reserved
CHAPTER
4.6.1 Flow in the zonally unbounded
ocean
The absence of land barriers in the latitude band
of Drake Passage has a profound influence on the
dynamics of currents in the Southern Ocean and,
more generally, on the earth’s climate. Within this
band, the strong eastward flow of the Antarctic
Circumpolar Current (ACC) connects each of the
ocean basins. Sverdrup dynamics in their usual
form cannot be applied to flows within a zonally
unbounded ocean, and as a consequence the
dynamics of the ACC have long been a topic of
debate. Eddy fluxes are believed to play a more
central role in both the dynamical and thermodynamical balances of the Southern Ocean than in
other areas of the world ocean. The interbasin
connection provided by the ACC permits a global
overturning circulation to exist; the overturning
circulation, in turn, dominates the global transport
of heat, fresh water and other properties that
influence climate (see Gordon, Chapter 4.7;
Bryden, Chapter 6.1; and Wijffels, Chapter 6.2).
The vigorous interbasin exchange accomplished by
the ACC also admits the possibility of oceanic teleconnections, where anomalies formed in one basin
may be carried around the globe to influence climate at remote locations (e.g. White and Peterson,
1996). The fact that no net meridional geostrophic
flow can exist across the unblocked latitudes
isolates the Antarctic continent from the warmer
waters at lower latitudes to some extent, contributing to the glacial climate of Antarctica; what
heat does get carried poleward to balance the heat
lost to the atmosphere must be carried by eddies.
Energetic interactions between the atmosphere,
ocean and sea ice result in the formation of water
masses that play an important role in the global
overturning circulation, and ventilate a substantial
fraction of the volume of the global ocean. As a
result of these unique aspects, many characteristics
of the present-day ocean circulation and climate
reflect the influence of the Southern Ocean.
The major currents of the southern hemisphere
oceans are shown in Fig. 4.6.1. The ACC is the
dominant feature in terms of transport, carrying a
mean transport of 134<13 Sv through Drake Passage (Whitworth, 1983; Whitworth and Peterson,
1985). The ACC consists of a number of circumpolar fronts, which correspond to water mass boundaries as well as deep-reaching jets of eastward flow
(Orsi et al., 1995). The two main fronts, the Subantarctic and Polar Fronts, are shown in Fig. 4.6.1.
Poleward of the ACC, cyclonic gyres are found in
the embayments of the Weddell and Ross seas.
Westward flow near the continental margin of
Antarctica (the Antarctic Slope Front) is found at
many locations around the continent (Jacobs,
1991; Whitworth et al., 1998). Equatorward of the
ACC, the circulation consists of westward-intensified subtropical gyres in each basin. Strong poleward flow in the western boundary currents is
balanced by weaker equatorward flows in the interior of the basins. The main focus of this chapter is
on the ACC itself, but exchanges between the ACC
and the subtropical and subpolar regimes are also
an important part of the story.
While the horizontal flows shown in Fig. 4.6.1
are the dominant circulation features, the weaker
The Antarctic Circumpolar Current System
Stephen R. Rintoul, Chris W. Hughes and Dirk Olbers
271
OCEAN CIRCULATION AND CLIMATE
Copyright © 2001 Academic Press
ISBN 0-12-641351-7
All rights of reproduction in any form reserved
CHAPTER
4.6.1 Flow in the zonally unbounded
ocean
The absence of land barriers in the latitude band
of Drake Passage has a profound influence on the
dynamics of currents in the Southern Ocean and,
more generally, on the earth’s climate. Within this
band, the strong eastward flow of the Antarctic
Circumpolar Current (ACC) connects each of the
ocean basins. Sverdrup dynamics in their usual
form cannot be applied to flows within a zonally
unbounded ocean, and as a consequence the
dynamics of the ACC have long been a topic of
debate. Eddy fluxes are believed to play a more
central role in both the dynamical and thermodynamical balances of the Southern Ocean than in
other areas of the world ocean. The interbasin
connection provided by the ACC permits a global
overturning circulation to exist; the overturning
circulation, in turn, dominates the global transport
of heat, fresh water and other properties that
influence climate (see Gordon, Chapter 4.7;
Bryden, Chapter 6.1; and Wijffels, Chapter 6.2).
The vigorous interbasin exchange accomplished by
the ACC also admits the possibility of oceanic teleconnections, where anomalies formed in one basin
may be carried around the globe to influence climate at remote locations (e.g. White and Peterson,
1996). The fact that no net meridional geostrophic
flow can exist across the unblocked latitudes
isolates the Antarctic continent from the warmer
waters at lower latitudes to some extent, contributing to the glacial climate of Antarctica; what
heat does get carried poleward to balance the heat
lost to the atmosphere must be carried by eddies.
Energetic interactions between the atmosphere,
ocean and sea ice result in the formation of water
masses that play an important role in the global
overturning circulation, and ventilate a substantial
fraction of the volume of the global ocean. As a
result of these unique aspects, many characteristics
of the present-day ocean circulation and climate
reflect the influence of the Southern Ocean.
The major currents of the southern hemisphere
oceans are shown in Fig. 4.6.1. The ACC is the
dominant feature in terms of transport, carrying a
mean transport of 134<13 Sv through Drake Passage (Whitworth, 1983; Whitworth and Peterson,
1985). The ACC consists of a number of circumpolar fronts, which correspond to water mass boundaries as well as deep-reaching jets of eastward flow
(Orsi et al., 1995). The two main fronts, the Subantarctic and Polar Fronts, are shown in Fig. 4.6.1.
Poleward of the ACC, cyclonic gyres are found in
the embayments of the Weddell and Ross seas.
Westward flow near the continental margin of
Antarctica (the Antarctic Slope Front) is found at
many locations around the continent (Jacobs,
1991; Whitworth et al., 1998). Equatorward of the
ACC, the circulation consists of westward-intensified subtropical gyres in each basin. Strong poleward flow in the western boundary currents is
balanced by weaker equatorward flows in the interior of the basins. The main focus of this chapter is
on the ACC itself, but exchanges between the ACC
and the subtropical and subpolar regimes are also
an important part of the story.
While the horizontal flows shown in Fig. 4.6.1
are the dominant circulation features, the weaker