168
Joseph L. Reid
Was it the result of Munk’s (1950) and Welander’s (1959) total transport, which
was dominated by the upper flow and showed no such contraction, that caused some
investigators to try to get the salt tongue by special lateral mixing processes instead
of advection(Richardson and Mooney,1975)?
Ivers (1975) suggested that the eastward limb of the North Atlantic anticyclonic
gyre turned south and west and was joined by the highly saline outflow from the
Mediterranean and accounts for the great tongue of high salinity extending westward
from the Straits of Gibraltar. This flow corresponds closely to the maps of Montgomery
and Pollak (1942) reproduced in Stommel’s book on the Gulf Stream (1958).
Worthington (1976) could not resolve a large deep anticyclone with the salt
tongue and simply restricted the gyre to the northwestern North Atlantic, north of the
salt tongue.
This deep poleward shift of the western limb of the great anticyclonic gyre is
also seen in the South Atlantic, South Indian, and North and South Pacific oceans.
Coats (1981) and Young and Rhines (1982) proposed some explanations for it.
THE DEEP FLOW ALONG THE WESTERN BOUNDARY
It was known quite early that beginning near Cape Hatteras there is a deep northward
flow beneath the shallow flow from the Florida Current but its source was not known.
Iselin (1936) had proposed that the deep Gulf Stream observed north of the Blake
Plateau must come in part from a part of the Stream which curves back to the right after
passing the Grand Banks, and moves southwestward. He suggested that other sources
might be an Antilles Current just north of the West Indies or a trade wind current
south of it. However, the deep western boundary current flows southward along the
Indies and flow near the Antilles does not contribute to the deep Gulf Stream.
W¨ ust’s (1935) maps of the Upper and Middle North Atlantic Deep Water were
based on the core method, vertical maxima in salinity and in oxygen, which extended
southward, and thus did not directly show any evidence of the deep Gulf Stream, but
did show a deep southward flow near or beneath the Gulf Stream, that extended near
the western boundary from about 55
◦ N to about 55
◦ S.
His presentation of the deep southward flow was cited by Dietrich (1936),
Rossby (1936), and Iselin (1936). Dietrich had noted a minimum layer of oxygen
just off Chesapeake Bay near 800 m that extended more than 800 km offshore and
proposed that it might represent a layer that was moving only very slowly, perhaps
a “level of no motion.” He showed that the geostrophic shear would accommodate
a northward flow above 800 m with a southward flow below, though his calculation
extended only to 1000 m. He cited W¨ ust’s (1935) proposed deep southward flow in
support.
Rossby (1936) referred to Dietrich’s (1936) oxygen minimum layer and his
assumption that it must be a layer at rest. But he wrote that “the assumption that
the oxygen layer may be regarded as a zero surface for the velocity distribution by
Joseph L. Reid
Was it the result of Munk’s (1950) and Welander’s (1959) total transport, which
was dominated by the upper flow and showed no such contraction, that caused some
investigators to try to get the salt tongue by special lateral mixing processes instead
of advection(Richardson and Mooney,1975)?
Ivers (1975) suggested that the eastward limb of the North Atlantic anticyclonic
gyre turned south and west and was joined by the highly saline outflow from the
Mediterranean and accounts for the great tongue of high salinity extending westward
from the Straits of Gibraltar. This flow corresponds closely to the maps of Montgomery
and Pollak (1942) reproduced in Stommel’s book on the Gulf Stream (1958).
Worthington (1976) could not resolve a large deep anticyclone with the salt
tongue and simply restricted the gyre to the northwestern North Atlantic, north of the
salt tongue.
This deep poleward shift of the western limb of the great anticyclonic gyre is
also seen in the South Atlantic, South Indian, and North and South Pacific oceans.
Coats (1981) and Young and Rhines (1982) proposed some explanations for it.
THE DEEP FLOW ALONG THE WESTERN BOUNDARY
It was known quite early that beginning near Cape Hatteras there is a deep northward
flow beneath the shallow flow from the Florida Current but its source was not known.
Iselin (1936) had proposed that the deep Gulf Stream observed north of the Blake
Plateau must come in part from a part of the Stream which curves back to the right after
passing the Grand Banks, and moves southwestward. He suggested that other sources
might be an Antilles Current just north of the West Indies or a trade wind current
south of it. However, the deep western boundary current flows southward along the
Indies and flow near the Antilles does not contribute to the deep Gulf Stream.
W¨ ust’s (1935) maps of the Upper and Middle North Atlantic Deep Water were
based on the core method, vertical maxima in salinity and in oxygen, which extended
southward, and thus did not directly show any evidence of the deep Gulf Stream, but
did show a deep southward flow near or beneath the Gulf Stream, that extended near
the western boundary from about 55
◦ N to about 55
◦ S.
His presentation of the deep southward flow was cited by Dietrich (1936),
Rossby (1936), and Iselin (1936). Dietrich had noted a minimum layer of oxygen
just off Chesapeake Bay near 800 m that extended more than 800 km offshore and
proposed that it might represent a layer that was moving only very slowly, perhaps
a “level of no motion.” He showed that the geostrophic shear would accommodate
a northward flow above 800 m with a southward flow below, though his calculation
extended only to 1000 m. He cited W¨ ust’s (1935) proposed deep southward flow in
support.
Rossby (1936) referred to Dietrich’s (1936) oxygen minimum layer and his
assumption that it must be a layer at rest. But he wrote that “the assumption that
the oxygen layer may be regarded as a zero surface for the velocity distribution by