The Peruvian Coastal Upwelling System
231
Chile Undercurrent, transports oxygen-deficient waters ( 4-10 em s- 1 )
southward, which seriously impacts demersal and benthic species distribution. This countercurrent is more intense along the Peruvian than the
Chilean coast.
Wind intensity and persistence are highest in winter and lowest in summer and wind stress, and consequently upwelling strength, has intensified
over the last decades (Bakun 1990). Owing to anomalous warming of the
sea during the 1983 El Nifio event, which led to a steep thermal gradient
between ocean and continent, a positive correlation between surface temperature and wind stress caused winds up to 10m s- 1 along the central
Peruvian coast (up to 5°S).
16.2.2 Coastal Upwelling
Southeastern trade winds blow northward and parallel to the Peruvian
coast. The Coriolis force together with friction forces in the water column
generate a deflection towards the left that causes Ekman transport perpendicular to the coast, forcing deeper water to rise and forming an upwelling
cell (Fig. 16.1B). In general, coastal upwelling along the Peruvian coast is
superficial, with cold, low-oxygen, nutrient-rich water (salinity 34.6- 35.1)
being drawn from the lower border of the permanent thermocline
(S0-150m depth). Upwelling is more intense in winter. Prominent upwelling plumes (4-6°S, 7-9°S, ll-13°S, 14-l6°S) receive water from the
southern extension of the Cromwell Current ( 4-6°S and north of 9°S), Peru
Subsurface Countercurrent (north of l2°S), and Subantarctic Temperate
Water (south of l4°S; Zuta and Guillen 1970). Filaments (cold water
tongues), which extend 25-50 km offshore into the oceanic zone, generally
persist less than 1 month. Depending on wind permanence, the width of the
continental shelf, and the type of upwelling cell, some upwelling events may
last only 3-10 days (Hill et al. 1998). Since filaments are deeper than the
mixed layer, they enhance water exchange between the neritic and oceanic
zones and may considerably impact the benthic organisms of deeper shelf
and continental slope regions. The upwelled water off Peru totals approximately 3 x 10 12 m 3 s- 1 , with an ascendingvelocityofS-30 x I0- 5 cm s- 1 (mean
20 x IQ- 5 em s- 1 ). Upwelling events off Chile (i.e., l8°30'S, l9°30'S, 23-29°S,
35-38°S) are less intense during winter, though filaments may extend from
60 to 125 km offshore (Strub et al.l998).
231
Chile Undercurrent, transports oxygen-deficient waters ( 4-10 em s- 1 )
southward, which seriously impacts demersal and benthic species distribution. This countercurrent is more intense along the Peruvian than the
Chilean coast.
Wind intensity and persistence are highest in winter and lowest in summer and wind stress, and consequently upwelling strength, has intensified
over the last decades (Bakun 1990). Owing to anomalous warming of the
sea during the 1983 El Nifio event, which led to a steep thermal gradient
between ocean and continent, a positive correlation between surface temperature and wind stress caused winds up to 10m s- 1 along the central
Peruvian coast (up to 5°S).
16.2.2 Coastal Upwelling
Southeastern trade winds blow northward and parallel to the Peruvian
coast. The Coriolis force together with friction forces in the water column
generate a deflection towards the left that causes Ekman transport perpendicular to the coast, forcing deeper water to rise and forming an upwelling
cell (Fig. 16.1B). In general, coastal upwelling along the Peruvian coast is
superficial, with cold, low-oxygen, nutrient-rich water (salinity 34.6- 35.1)
being drawn from the lower border of the permanent thermocline
(S0-150m depth). Upwelling is more intense in winter. Prominent upwelling plumes (4-6°S, 7-9°S, ll-13°S, 14-l6°S) receive water from the
southern extension of the Cromwell Current ( 4-6°S and north of 9°S), Peru
Subsurface Countercurrent (north of l2°S), and Subantarctic Temperate
Water (south of l4°S; Zuta and Guillen 1970). Filaments (cold water
tongues), which extend 25-50 km offshore into the oceanic zone, generally
persist less than 1 month. Depending on wind permanence, the width of the
continental shelf, and the type of upwelling cell, some upwelling events may
last only 3-10 days (Hill et al. 1998). Since filaments are deeper than the
mixed layer, they enhance water exchange between the neritic and oceanic
zones and may considerably impact the benthic organisms of deeper shelf
and continental slope regions. The upwelled water off Peru totals approximately 3 x 10 12 m 3 s- 1 , with an ascendingvelocityofS-30 x I0- 5 cm s- 1 (mean
20 x IQ- 5 em s- 1 ). Upwelling events off Chile (i.e., l8°30'S, l9°30'S, 23-29°S,
35-38°S) are less intense during winter, though filaments may extend from
60 to 125 km offshore (Strub et al.l998).