Historical Introduction
3
the calculations of current velocities were rough. Nevertheless, the nineteenth century saw generalized maps of surface currents, of varying quality, for individual
oceans and for the world ocean. [Peterson et al. (1996) have assembled an extensive
collection of surface-current maps, from earliest times to the end of the nineteenth
century.]
A. G. Findlay, for one, drew comprehensive maps for the Atlantic and Pacific
Oceans (1853) and for the Indian Ocean (1866) that displayed the North and South
Equatorial Currents, the transpacific Equatorial Countercurrent, the subtropical gyres,
the major western-boundary currents, and the seasonally reversing circulation in the
North Indian Ocean. Off Somalia, for the summer monsoon season, he (1866, p. 102)
even sketched a “great whirl” of current, which, with initial capitals, was the name
adopted for the feature by twentieth-century oceanographers when they rediscovered it.
However, he botched the Pacific subarctic gyre (small wonder, given the shipping conditions there), he understated the east–west asymmetry of the gyres, and in
1853 he sent the Agulhas Current entirely into the South Atlantic, despite Rennell’s
(1832, p. 98) earlier report that the greater part of it turned back into the Indian
Ocean, south of Africa, occasioning “great eddies” there (perhaps including the Agulhas Rings that drift into the South Atlantic?). By 1866 he had come around to
Rennell’s view. (Never mind that Rennell himself, in Chap. I, Sect. 2, Part 12 of his
book, had made the same mistake as Findlay in 1853, and that it was in Chap. II,
Sect. 1 that he gave the correct information—without comment on his contradiction
of what he had written 55 pages earlier. Perhaps if he had lived to complete the work,
he would have straightened out his presentation.) The importance of commercial traffic for oceanographic observations in those years underlay Findlay’s (1866, p. 97)
otherwise startling remark, “The Agulhas Current . . . after the Gulf Stream, was the
first that attracted the investigation of sufficient data.”
Mariners became aware of the Antarctic Circumpolar Current in the early nineteenth century (G. Deacon, 1984, p. 86), but Findlay (1853, 1866)—and others—
charted it as a region of predominantly northeastward flow. Maybe, as Peterson et al.
(1996) suggested, the (few?) estimated surface velocities consisted as much of Ekman
drifts due to the strong westerlies as to the deeper reaching geostrophic flow.
Maps of prevailing surface currents achieved their finest quality in Schott’s
(1943) construction. He scaled his current vectors by their magnitudes, provided
maps in the tropics for both summer and winter, got the sense of the Pacific subarctic
gyre right, included the Weddell gyre, and, correctly, made his Circumpolar Current
set generally south of east, except for its northward course along the east coast of
South America. And he got everything else more or less right, too.
The Equatorial Undercurrents barely break the sea surface, and so they escaped
notice as ship drift. Even so, using drogues, Buchanan detected the undercurrent in the
eastern Atlantic in 1886. Unfortunately, his discovery was largely overlooked until
the Pacific Equatorial Undercurrent was revealed in 1952 [Montgomery and Stroup
3
the calculations of current velocities were rough. Nevertheless, the nineteenth century saw generalized maps of surface currents, of varying quality, for individual
oceans and for the world ocean. [Peterson et al. (1996) have assembled an extensive
collection of surface-current maps, from earliest times to the end of the nineteenth
century.]
A. G. Findlay, for one, drew comprehensive maps for the Atlantic and Pacific
Oceans (1853) and for the Indian Ocean (1866) that displayed the North and South
Equatorial Currents, the transpacific Equatorial Countercurrent, the subtropical gyres,
the major western-boundary currents, and the seasonally reversing circulation in the
North Indian Ocean. Off Somalia, for the summer monsoon season, he (1866, p. 102)
even sketched a “great whirl” of current, which, with initial capitals, was the name
adopted for the feature by twentieth-century oceanographers when they rediscovered it.
However, he botched the Pacific subarctic gyre (small wonder, given the shipping conditions there), he understated the east–west asymmetry of the gyres, and in
1853 he sent the Agulhas Current entirely into the South Atlantic, despite Rennell’s
(1832, p. 98) earlier report that the greater part of it turned back into the Indian
Ocean, south of Africa, occasioning “great eddies” there (perhaps including the Agulhas Rings that drift into the South Atlantic?). By 1866 he had come around to
Rennell’s view. (Never mind that Rennell himself, in Chap. I, Sect. 2, Part 12 of his
book, had made the same mistake as Findlay in 1853, and that it was in Chap. II,
Sect. 1 that he gave the correct information—without comment on his contradiction
of what he had written 55 pages earlier. Perhaps if he had lived to complete the work,
he would have straightened out his presentation.) The importance of commercial traffic for oceanographic observations in those years underlay Findlay’s (1866, p. 97)
otherwise startling remark, “The Agulhas Current . . . after the Gulf Stream, was the
first that attracted the investigation of sufficient data.”
Mariners became aware of the Antarctic Circumpolar Current in the early nineteenth century (G. Deacon, 1984, p. 86), but Findlay (1853, 1866)—and others—
charted it as a region of predominantly northeastward flow. Maybe, as Peterson et al.
(1996) suggested, the (few?) estimated surface velocities consisted as much of Ekman
drifts due to the strong westerlies as to the deeper reaching geostrophic flow.
Maps of prevailing surface currents achieved their finest quality in Schott’s
(1943) construction. He scaled his current vectors by their magnitudes, provided
maps in the tropics for both summer and winter, got the sense of the Pacific subarctic
gyre right, included the Weddell gyre, and, correctly, made his Circumpolar Current
set generally south of east, except for its northward course along the east coast of
South America. And he got everything else more or less right, too.
The Equatorial Undercurrents barely break the sea surface, and so they escaped
notice as ship drift. Even so, using drogues, Buchanan detected the undercurrent in the
eastern Atlantic in 1886. Unfortunately, his discovery was largely overlooked until
the Pacific Equatorial Undercurrent was revealed in 1952 [Montgomery and Stroup