284
D. H. CUSHTNG
The biological width of the production zone is generated partly by
the resultant of offshore and poleward transport and partly by the
width of the productive zone generated by divergences upstream of the
upwelling areas. The physical upwelling area tends to increme in width
towards the equator. Then again some production is generated offshore
of the dynamic boundary by the divergences associated with local wind
stresses. Because the width of the area is of complex origin, its measurement is only empirical.
B. Upwelling areas in the eastern boundary currents
The four main upwelling areas are in the California Current, the
Peru Current, the Canary Current and the Benguela Current. That in
the California Current has already been described. The pattern of the
poleward shift of upwelling during spring and summer as the high
pressure areas move north and intensify is common to all four areas ;
similarly, as the surface current moves towards the equator, a countercurrent moves poleward within the upwelling area in all four areas.
Peru Current
In the Peru Current, Gunther (1936) distinguished four regions of
upwelling between Cape Carranza, south of Valparaiso, and the equator.
The most northerly region lies between Punta Aguja in northernmost
Peru and Santa Elena in Ecuador ; farther south is the region between
Callao and the Guanape Islands just north of 10"s; the third region
extends from Arica on the Chilean border t o Antofagasta about 300
miles south and the fourth to Cape Carranza. Here, the region has been
divided a little differently to include the area south of Cape Carranza.
Wyrtki (1966) distinguishes between the Peru Coastal Current-the
region of coastal upwelling-and the Peru Oceanic Currents, the region
of offshore divergences ; the first leaves the coast at about 5's and the
second at about 10's and both currents stream westward into the
South Equatorial Current. Between them flows the Countercurrent,
mostly, but not always subsurface ; it is strongest at 100 m, but can
reach 500 m. South of 15'5, upwelling comes from the lower layers of
the Peru Coastal Current, but north of this latitude it is intense enough
to draw water from the Countercurrent. Below the Peru Coastal current
flows the Undercurrent, the analogue of countercurrents in other upwelling areas, the existence of which was confirmed by Wooster and
Gilmartin (1961). Wooster and Reid (1963) have shown that the most
intense upwelling probably occurs in this northern part of the area.
Another characteristic of the Peru Current is " El Niiio ", which is
a warm salty layer extending south over the Peru Current along the
D. H. CUSHTNG
The biological width of the production zone is generated partly by
the resultant of offshore and poleward transport and partly by the
width of the productive zone generated by divergences upstream of the
upwelling areas. The physical upwelling area tends to increme in width
towards the equator. Then again some production is generated offshore
of the dynamic boundary by the divergences associated with local wind
stresses. Because the width of the area is of complex origin, its measurement is only empirical.
B. Upwelling areas in the eastern boundary currents
The four main upwelling areas are in the California Current, the
Peru Current, the Canary Current and the Benguela Current. That in
the California Current has already been described. The pattern of the
poleward shift of upwelling during spring and summer as the high
pressure areas move north and intensify is common to all four areas ;
similarly, as the surface current moves towards the equator, a countercurrent moves poleward within the upwelling area in all four areas.
Peru Current
In the Peru Current, Gunther (1936) distinguished four regions of
upwelling between Cape Carranza, south of Valparaiso, and the equator.
The most northerly region lies between Punta Aguja in northernmost
Peru and Santa Elena in Ecuador ; farther south is the region between
Callao and the Guanape Islands just north of 10"s; the third region
extends from Arica on the Chilean border t o Antofagasta about 300
miles south and the fourth to Cape Carranza. Here, the region has been
divided a little differently to include the area south of Cape Carranza.
Wyrtki (1966) distinguishes between the Peru Coastal Current-the
region of coastal upwelling-and the Peru Oceanic Currents, the region
of offshore divergences ; the first leaves the coast at about 5's and the
second at about 10's and both currents stream westward into the
South Equatorial Current. Between them flows the Countercurrent,
mostly, but not always subsurface ; it is strongest at 100 m, but can
reach 500 m. South of 15'5, upwelling comes from the lower layers of
the Peru Coastal Current, but north of this latitude it is intense enough
to draw water from the Countercurrent. Below the Peru Coastal current
flows the Undercurrent, the analogue of countercurrents in other upwelling areas, the existence of which was confirmed by Wooster and
Gilmartin (1961). Wooster and Reid (1963) have shown that the most
intense upwelling probably occurs in this northern part of the area.
Another characteristic of the Peru Current is " El Niiio ", which is
a warm salty layer extending south over the Peru Current along the