Pacific Coastal Biome
411
Point Negro (5
S): Here, the trend of the coast changes abruptly and to the north lies
the tropical surface water of the Gulf of Guayaquil of the CAMR province. This cape
is a major and persistent upwelling center, and offshore filaments may be aligned
with the convergent front that marks the separation of the Peru Current from the
continent, so forming a major hydrographic discontinuity.
Chimbote (9
S) and Callao (12
S): Though there is no major topographic feature here,
this seems to be a consistent upwelling center whose plume proceeds seaward over
the widest region of shelf on the Peruvian coast. The coastal prominence at Callao
and Lima appears to focus significantly the upwelling processes.
Pisco (14
S) and Cape Nazca-Punta Sta. Ana (15
S): In the bight north of Pisco, surface
water is consistently cool and a major upwelling center appears to be topographically
linked to the Paracas peninsula, whereas the upwelling center off San Juan is the
most consistent and the strongest upwelling center on the Peruvian coast and was
well known to early investigators (e.g., Gunther, 1936). Much of what has been
learned about upwelling dynamics on the Peruvian coast, and about the ecological
physiology of phytoplankton during upwelling, is due to work at this site during
JOINT I and II of the Coastal Upwelling Ecosystem Analysis program (MacIsaac
et al., 1985).
Despite the existence of these persistent upwelling centers off Peru, as many as 15–20
small (< 25−km) cool-water cells may occur simultaneously along the upwelling coast
from San Juan to Paita; we now see these in AVHRR images, but they were first visualized
by Peruvian scientists who, in the early 1970s, deployed over a coastwide grid that was
occupied during a single day many tens of chartered fishing boats that were equipped
solely with bucket thermometers: this produced the first temperature map that resembled
what we now see routinely in AVHRR images.
Because appropriate wind stress may be imposed for long periods off Peru, but often
not at the coast itself, the upwelling front may move far offshore and become indistinct
(Brink, 1983). At such times the whole coast may present a single inshore cool zone from
Arica to Paita (5–15
S) within a weak temperature front about 100–125 km offshore,
though progressively farther offshore to the north (Bohle-Carbonell, 1989). This zone
may even extend south into the corner of the Arica Bight at about 18
S.
It has been suggested that there is a relatively weak relationship between wind stress
and surface nutrients in the Peru Current because the generally persistent, generally
equatorward winds drive only a shallow surface layer northward along the coast and
this flow is rather frequently interrupted, as already noted, by surfacing of the poleward
subsurface current. However, because nutrient levels below the photic zone are relatively
high in the Pacific, the nutrient content of upwelled water is high, at least in normal years
(Codispoti et al., 1982). Especially in the Peruvian sector, or wherever countercurrent
water is upwelled, the oxygen content of upwelled water is relatively low. The existence
of offshore flow both at the surface and on the bottom, with onshore flow toward the site
of upwelling, has consequences for nutrient regeneration over the shelf. Sinking organic
material is transported across the shelf and sequestered in the bottom layer of oxygendeficient water. In these circumstances, this organic material is no longer available for
regeneration (Codispoti et al., 1982).
Off Chile, the upwelling processes are different from those off Peru. Here, especially in
winter and spring, a wide zone is populated by meanders, eddies, and very prominent cool
filaments within which vorticity occurs and may extend 200–300 km offshore. As shown
earlier by Fonseca and Farias (1987), these mesoscale features resemble the better-known
eddies and cool filaments of the northern part of the California Current off Oregon and
Washington.
Upwelling-favorable winds are relatively lighter along the Chilean coast, and their
maximum potential for upwelling occurs in the vicinity of Valparaiso. Upwelling fronts
411
Point Negro (5
S): Here, the trend of the coast changes abruptly and to the north lies
the tropical surface water of the Gulf of Guayaquil of the CAMR province. This cape
is a major and persistent upwelling center, and offshore filaments may be aligned
with the convergent front that marks the separation of the Peru Current from the
continent, so forming a major hydrographic discontinuity.
Chimbote (9
S) and Callao (12
S): Though there is no major topographic feature here,
this seems to be a consistent upwelling center whose plume proceeds seaward over
the widest region of shelf on the Peruvian coast. The coastal prominence at Callao
and Lima appears to focus significantly the upwelling processes.
Pisco (14
S) and Cape Nazca-Punta Sta. Ana (15
S): In the bight north of Pisco, surface
water is consistently cool and a major upwelling center appears to be topographically
linked to the Paracas peninsula, whereas the upwelling center off San Juan is the
most consistent and the strongest upwelling center on the Peruvian coast and was
well known to early investigators (e.g., Gunther, 1936). Much of what has been
learned about upwelling dynamics on the Peruvian coast, and about the ecological
physiology of phytoplankton during upwelling, is due to work at this site during
JOINT I and II of the Coastal Upwelling Ecosystem Analysis program (MacIsaac
et al., 1985).
Despite the existence of these persistent upwelling centers off Peru, as many as 15–20
small (< 25−km) cool-water cells may occur simultaneously along the upwelling coast
from San Juan to Paita; we now see these in AVHRR images, but they were first visualized
by Peruvian scientists who, in the early 1970s, deployed over a coastwide grid that was
occupied during a single day many tens of chartered fishing boats that were equipped
solely with bucket thermometers: this produced the first temperature map that resembled
what we now see routinely in AVHRR images.
Because appropriate wind stress may be imposed for long periods off Peru, but often
not at the coast itself, the upwelling front may move far offshore and become indistinct
(Brink, 1983). At such times the whole coast may present a single inshore cool zone from
Arica to Paita (5–15
S) within a weak temperature front about 100–125 km offshore,
though progressively farther offshore to the north (Bohle-Carbonell, 1989). This zone
may even extend south into the corner of the Arica Bight at about 18
S.
It has been suggested that there is a relatively weak relationship between wind stress
and surface nutrients in the Peru Current because the generally persistent, generally
equatorward winds drive only a shallow surface layer northward along the coast and
this flow is rather frequently interrupted, as already noted, by surfacing of the poleward
subsurface current. However, because nutrient levels below the photic zone are relatively
high in the Pacific, the nutrient content of upwelled water is high, at least in normal years
(Codispoti et al., 1982). Especially in the Peruvian sector, or wherever countercurrent
water is upwelled, the oxygen content of upwelled water is relatively low. The existence
of offshore flow both at the surface and on the bottom, with onshore flow toward the site
of upwelling, has consequences for nutrient regeneration over the shelf. Sinking organic
material is transported across the shelf and sequestered in the bottom layer of oxygendeficient water. In these circumstances, this organic material is no longer available for
regeneration (Codispoti et al., 1982).
Off Chile, the upwelling processes are different from those off Peru. Here, especially in
winter and spring, a wide zone is populated by meanders, eddies, and very prominent cool
filaments within which vorticity occurs and may extend 200–300 km offshore. As shown
earlier by Fonseca and Farias (1987), these mesoscale features resemble the better-known
eddies and cool filaments of the northern part of the California Current off Oregon and
Washington.
Upwelling-favorable winds are relatively lighter along the Chilean coast, and their
maximum potential for upwelling occurs in the vicinity of Valparaiso. Upwelling fronts