412
Chapter 11: The Pacific Ocean
are numerous, complex, and highly variable: we may distinguish coastal fronts no more
than 10–20 km offshore, outlining clear upwelled water, whereas plume fronts outlining
tongues of green upwelled water may be encountered up to 30–50 km offshore. An oceanic
front separating the coastal regime from warmer, blue oceanic water is often indicated
by the 15
C isotherm, which may meander between 100 km and 300 km offshore.
Five major, semipermanent upwelling centers have been identified on the Chilean
coast, from analysis of CZCS images by Fonseca and Farias (1987). The offshore mesoscale
tongues of cool water that are a prominent feature of upwelling off Chile can be traced
back to these upwelling centers. All are apparently topographically locked to the vicinity
of capes and submarine topographic features, though their individual characteristics are
at the present time little known:
Point Patache (20
S) and Mejillones-Antofagasta (23
S): The coastal prominence
between Punta Tetas and Punta Angamos is a major topographic feature and the
site of persistent upwelling, whereas to the south of Iquique, major upwelling
events frequently occur and are distinct from the southernmost upwelling on the
Peruvian coast.
Point Lengua de Vaca (30
S) and Point de Curaimilla (33
S): These, and the Gulf of
Arauco south of Valparaiso, are the best known of the persistent upwelling centers,
and the maximum potential for upwelling-favorable winds on the Chilean coast
occurs here. This is the only location where the dynamics of upwelling on the
Chilean coast have been studied in detail (Johnson et al., 1980), and the data from
these studies are consistent with the existence of a classical double-celled, crossshelf upwelling circulation. Water that is upwelled originates in the high-salinity,
low-oxygen coastal undercurrent, and the upwelling effect reaches to a maximum
depth of about 250 m. Short-term variations in upwelling wind intensity result in
variations in the location of the undercurrent on the shelf and in pulsations in
upwelling intensity.
Point Lavapie (37
S): This peninsula, to the south of Concepción, is the site of
persistent upwelling events and also the most southerly location where they occur
with regularity (Arcos et al., 1987). Upwelling response to favorable winds may
occur in response both to short-period (1 or 2 days) wind events and to those of
longer duration (6 or 7 days).
To the south of these regions, in the high-precipitation and downwelling regime of
the fjordland that extends down to Tierra del Fuego, coastal processes are very similar
to those discussed earlier for the Alaska coastline, and here we can reach back to the
1970 round-America maiden voyage of C.S.S. Hudson for some information. The effect
of glaciers is strongest in the central regions; runoff is of the same order as in Alaska
and is more important than direct precipitation to the sea surface. The density profile
and stratification, therefore, is forced rather by relative salinity than by temperature.
Everywhere in this region, despite strong winds, tides are the dominant forcing for water
movement.
Regional Response of the Pelagic Ecosystem
The regional fields of pigment and SST derived from satellite sensors confirm the anticipated relationship between upwelled water and high chlorophyll values, and mesoscale
features resemble those observed in other eastern boundary currents. Rapidly changing
cool filaments and plumes, exhibiting vorticity, are normal features of the chlorophyll
field; development and decay of such features occurs on a scale of a few days to a few
tens of days. Only in the southern Chilean region, beyond Concepción, does the seasonal
regime follow a different pattern: here, as off Alaska, a spring bloom is to be expected
Chapter 11: The Pacific Ocean
are numerous, complex, and highly variable: we may distinguish coastal fronts no more
than 10–20 km offshore, outlining clear upwelled water, whereas plume fronts outlining
tongues of green upwelled water may be encountered up to 30–50 km offshore. An oceanic
front separating the coastal regime from warmer, blue oceanic water is often indicated
by the 15
C isotherm, which may meander between 100 km and 300 km offshore.
Five major, semipermanent upwelling centers have been identified on the Chilean
coast, from analysis of CZCS images by Fonseca and Farias (1987). The offshore mesoscale
tongues of cool water that are a prominent feature of upwelling off Chile can be traced
back to these upwelling centers. All are apparently topographically locked to the vicinity
of capes and submarine topographic features, though their individual characteristics are
at the present time little known:
Point Patache (20
S) and Mejillones-Antofagasta (23
S): The coastal prominence
between Punta Tetas and Punta Angamos is a major topographic feature and the
site of persistent upwelling, whereas to the south of Iquique, major upwelling
events frequently occur and are distinct from the southernmost upwelling on the
Peruvian coast.
Point Lengua de Vaca (30
S) and Point de Curaimilla (33
S): These, and the Gulf of
Arauco south of Valparaiso, are the best known of the persistent upwelling centers,
and the maximum potential for upwelling-favorable winds on the Chilean coast
occurs here. This is the only location where the dynamics of upwelling on the
Chilean coast have been studied in detail (Johnson et al., 1980), and the data from
these studies are consistent with the existence of a classical double-celled, crossshelf upwelling circulation. Water that is upwelled originates in the high-salinity,
low-oxygen coastal undercurrent, and the upwelling effect reaches to a maximum
depth of about 250 m. Short-term variations in upwelling wind intensity result in
variations in the location of the undercurrent on the shelf and in pulsations in
upwelling intensity.
Point Lavapie (37
S): This peninsula, to the south of Concepción, is the site of
persistent upwelling events and also the most southerly location where they occur
with regularity (Arcos et al., 1987). Upwelling response to favorable winds may
occur in response both to short-period (1 or 2 days) wind events and to those of
longer duration (6 or 7 days).
To the south of these regions, in the high-precipitation and downwelling regime of
the fjordland that extends down to Tierra del Fuego, coastal processes are very similar
to those discussed earlier for the Alaska coastline, and here we can reach back to the
1970 round-America maiden voyage of C.S.S. Hudson for some information. The effect
of glaciers is strongest in the central regions; runoff is of the same order as in Alaska
and is more important than direct precipitation to the sea surface. The density profile
and stratification, therefore, is forced rather by relative salinity than by temperature.
Everywhere in this region, despite strong winds, tides are the dominant forcing for water
movement.
Regional Response of the Pelagic Ecosystem
The regional fields of pigment and SST derived from satellite sensors confirm the anticipated relationship between upwelled water and high chlorophyll values, and mesoscale
features resemble those observed in other eastern boundary currents. Rapidly changing
cool filaments and plumes, exhibiting vorticity, are normal features of the chlorophyll
field; development and decay of such features occurs on a scale of a few days to a few
tens of days. Only in the southern Chilean region, beyond Concepción, does the seasonal
regime follow a different pattern: here, as off Alaska, a spring bloom is to be expected