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Joseph L. Reid
than 3000 m in the South Atlantic. This was assuming that all of the water below was
flowing northward and all of the water above was flowing southward, hence so many
east–west sections were taken.
However, some circumpolar water passes northward at about 2000 m to 3000 m,
east of the southward flow from the North Atlantic. The density range of the water
from the circumpolar flow encompasses that of the North Atlantic, whose deep layer
of high salinity, high oxygen, and low nutrients extends southward and penetrates
the circumpolar water, separating it into upper and lower layers. The Circumpolar
Water extends northward not only as Intermediate Water near 1000 m, as in Tsuchiya
(1989), and along the bottom, but also a layer near 3000 m (Reid et al., 1977). This
layer from the south flows eastward and then northward and around the great gyre of
the South Atlantic, northward across the equator in the east and northward just east
of the southward flow along the western boundary.
Edmond and Anderson (1971) measured samples near 2500–3000 m just south
of the equator that showed extrema in salinity, oxygen, and phosphate. These vertical
minima in salinity and oxygen and maximum in phosphate indicate a flow from the
Circumpolar Current, northward around the anticyclonic gyre and across the equator,
east of the southward flow from the North Atlantic into which they interleave. The
northward penetration of the salinity minimum near 2500 m are seen in W¨ ust’s map
of the Middle North Atlantic Deep Water, east of the southward flow, but he did not
discuss them or put an arrow there to designate the sense of flow. The features can
be seen near 3000 m on any north–south vertical section in the central Atlantic, but
nearly every long straight north–south section that has been drawn in the Atlantic
shows the penetration as deep blobs of higher or lower salinity, oxygen, and nutrients
between about 40
◦ S and 30
◦ N. This is because the layer from the south does not flow
only meridionally, but wends its way around and past the great gyres. It cuts across
the meridional sections (Reid, 2005), spoiling the beautiful pattern that would be left
from a simple meridional-only circulation.
(The referees of the Edmond and Anderson manuscript submitted to Deep-Sea
Research did not permit the authors to claim any northward flow at middepth. It
would have been heresy, so the indication of northward flow had to be omitted from
the paper.)
GLOBAL BALANCE OF TRANSPORT
Several investigators, including Roemmich and McCallister (1989), McDonald
(1998), and Talley et al. (2003), have carried out studies of large-scale circulation
by balancing the total (top-to-bottom) geostrophic circulation along lines of stations
enclosing an area. They find that balancing the total transport alone is not adequate:
their solutions may balance the total but not the flow of each of the various layers.
This appears to be the result of time variations. The lines of stations are not synoptic, and minor changes in speed over great distances and depth ranges can seriously
Joseph L. Reid
than 3000 m in the South Atlantic. This was assuming that all of the water below was
flowing northward and all of the water above was flowing southward, hence so many
east–west sections were taken.
However, some circumpolar water passes northward at about 2000 m to 3000 m,
east of the southward flow from the North Atlantic. The density range of the water
from the circumpolar flow encompasses that of the North Atlantic, whose deep layer
of high salinity, high oxygen, and low nutrients extends southward and penetrates
the circumpolar water, separating it into upper and lower layers. The Circumpolar
Water extends northward not only as Intermediate Water near 1000 m, as in Tsuchiya
(1989), and along the bottom, but also a layer near 3000 m (Reid et al., 1977). This
layer from the south flows eastward and then northward and around the great gyre of
the South Atlantic, northward across the equator in the east and northward just east
of the southward flow along the western boundary.
Edmond and Anderson (1971) measured samples near 2500–3000 m just south
of the equator that showed extrema in salinity, oxygen, and phosphate. These vertical
minima in salinity and oxygen and maximum in phosphate indicate a flow from the
Circumpolar Current, northward around the anticyclonic gyre and across the equator,
east of the southward flow from the North Atlantic into which they interleave. The
northward penetration of the salinity minimum near 2500 m are seen in W¨ ust’s map
of the Middle North Atlantic Deep Water, east of the southward flow, but he did not
discuss them or put an arrow there to designate the sense of flow. The features can
be seen near 3000 m on any north–south vertical section in the central Atlantic, but
nearly every long straight north–south section that has been drawn in the Atlantic
shows the penetration as deep blobs of higher or lower salinity, oxygen, and nutrients
between about 40
◦ S and 30
◦ N. This is because the layer from the south does not flow
only meridionally, but wends its way around and past the great gyres. It cuts across
the meridional sections (Reid, 2005), spoiling the beautiful pattern that would be left
from a simple meridional-only circulation.
(The referees of the Edmond and Anderson manuscript submitted to Deep-Sea
Research did not permit the authors to claim any northward flow at middepth. It
would have been heresy, so the indication of northward flow had to be omitted from
the paper.)
GLOBAL BALANCE OF TRANSPORT
Several investigators, including Roemmich and McCallister (1989), McDonald
(1998), and Talley et al. (2003), have carried out studies of large-scale circulation
by balancing the total (top-to-bottom) geostrophic circulation along lines of stations
enclosing an area. They find that balancing the total transport alone is not adequate:
their solutions may balance the total but not the flow of each of the various layers.
This appears to be the result of time variations. The lines of stations are not synoptic, and minor changes in speed over great distances and depth ranges can seriously