4.7.1 Interocean Links
Earth’s climate, responding to the different thermodynamic properties of the land and ocean surfaces,
is sensitive to the continental configuration and distribution of mountain ranges. This is clearly seen in
the pattern of mean annual and seasonal range in
such climate parameters as temperature and humidity and in the quasistationary patterns of atmospheric circulation, from small-scale sea breezes to
planetary waves. Presumably because of the ocean–
land configuration, each ocean basin is exposed to
different atmospheric forcing, taking on correspondingly distinct property and circulation characteristics (Figs 4.7.1a,b, see Plate 4.7.1a,b, p. 300).
These in turn provide feedback to the climate system through their effect on Sea Surface Temperature (SST) distribution, heat and freshwater fluxes
and ocean overturning. Similarity between oceans is
inhibited by their varied degrees of isolation from
one another, and thus the coupled ocean–atmosphere system is influenced by the efficiency of interocean exchanges that link the ocean basins. More
efficient interocean exchange leads to reduced contrast between the oceans, with each ocean closely
resembling its neighbour. Interocean exchange
would be expected to be balanced mainly by ocean
circulation on approximately a horizontal plane.
Less efficient exchange is expected to produce
oceans that contrast sharply with each other, a condition more apt to induce stronger global reaching,
overturning thermohaline circulation. Equilibrium
states between patterns of interocean exchange
and circulation on the horizontal and vertical
planes may be expected for specific continental
configurations.
4.7.1.1 Antarctic Circumpolar Current
The oceans of the southern hemisphere vary less
from each other than do the northern hemisphere
oceans. Isolation and differences grow with distance from the rapid interocean exchange afforded
by the Antarctic Circumpolar Current (ACC; for
detailed information of the ACC, see Rintoul
et al., Chapter 4.6). The ACC is the giant of interocean exchange, carrying about 134 Sv (Sverdrup,
1 Sv:10
6 m
3 s
91 ) of polar and subpolar water
masses from west to east through the Drake Passage (Nowlin and Klinck, 1986). Variations in
ACC transport through the Drake Passage amount
to 20% of the mean. ACC transport is enhanced
south of Australia by the Indonesian Throughflow,
of about 10 Sv.
The ACC is mainly a zonally flowing current,
but large quasistationary waves in the ACC,
guided by bottom topography, lead to a latitudinal
swing of approximately 1200 km (furthest north in
the Atlantic; furthest south in the southwest
Pacific – Gordon et al., 1978; Orsi et al., 1995).
The equatorially flowing Malvinas Current, which
may be considered as a branch of the ACC, carries
subpolar waters well to the north, to the separation of the Brazil Current near 38°S. Transient
waves in the ACC (Antarctic Circumpolar Wave;
White and Peterson, 1996) may link the ACC with
sea ice distribution and larger-scale climate variability (Yuan and Martinson, 2000). Mesoscale
eddies within the ACC provide oceanic meridional heat and freshwater fluxes to balance much
of the ocean–atmosphere exchange south of
the ACC.
4.7
Interocean Exchange
Arnold L. Gordon
303
OCEAN CIRCULATION AND CLIMATE
Copyright © 2001 Academic Press
ISBN 0-12-641351-7
All rights of reproduction in any form reserved
CHAPTER
Earth’s climate, responding to the different thermodynamic properties of the land and ocean surfaces,
is sensitive to the continental configuration and distribution of mountain ranges. This is clearly seen in
the pattern of mean annual and seasonal range in
such climate parameters as temperature and humidity and in the quasistationary patterns of atmospheric circulation, from small-scale sea breezes to
planetary waves. Presumably because of the ocean–
land configuration, each ocean basin is exposed to
different atmospheric forcing, taking on correspondingly distinct property and circulation characteristics (Figs 4.7.1a,b, see Plate 4.7.1a,b, p. 300).
These in turn provide feedback to the climate system through their effect on Sea Surface Temperature (SST) distribution, heat and freshwater fluxes
and ocean overturning. Similarity between oceans is
inhibited by their varied degrees of isolation from
one another, and thus the coupled ocean–atmosphere system is influenced by the efficiency of interocean exchanges that link the ocean basins. More
efficient interocean exchange leads to reduced contrast between the oceans, with each ocean closely
resembling its neighbour. Interocean exchange
would be expected to be balanced mainly by ocean
circulation on approximately a horizontal plane.
Less efficient exchange is expected to produce
oceans that contrast sharply with each other, a condition more apt to induce stronger global reaching,
overturning thermohaline circulation. Equilibrium
states between patterns of interocean exchange
and circulation on the horizontal and vertical
planes may be expected for specific continental
configurations.
4.7.1.1 Antarctic Circumpolar Current
The oceans of the southern hemisphere vary less
from each other than do the northern hemisphere
oceans. Isolation and differences grow with distance from the rapid interocean exchange afforded
by the Antarctic Circumpolar Current (ACC; for
detailed information of the ACC, see Rintoul
et al., Chapter 4.6). The ACC is the giant of interocean exchange, carrying about 134 Sv (Sverdrup,
1 Sv:10
6 m
3 s
91 ) of polar and subpolar water
masses from west to east through the Drake Passage (Nowlin and Klinck, 1986). Variations in
ACC transport through the Drake Passage amount
to 20% of the mean. ACC transport is enhanced
south of Australia by the Indonesian Throughflow,
of about 10 Sv.
The ACC is mainly a zonally flowing current,
but large quasistationary waves in the ACC,
guided by bottom topography, lead to a latitudinal
swing of approximately 1200 km (furthest north in
the Atlantic; furthest south in the southwest
Pacific – Gordon et al., 1978; Orsi et al., 1995).
The equatorially flowing Malvinas Current, which
may be considered as a branch of the ACC, carries
subpolar waters well to the north, to the separation of the Brazil Current near 38°S. Transient
waves in the ACC (Antarctic Circumpolar Wave;
White and Peterson, 1996) may link the ACC with
sea ice distribution and larger-scale climate variability (Yuan and Martinson, 2000). Mesoscale
eddies within the ACC provide oceanic meridional heat and freshwater fluxes to balance much
of the ocean–atmosphere exchange south of
the ACC.
4.7
Interocean Exchange
Arnold L. Gordon
303
OCEAN CIRCULATION AND CLIMATE
Copyright © 2001 Academic Press
ISBN 0-12-641351-7
All rights of reproduction in any form reserved
CHAPTER