slope south of 10°30
0 S and may appear in coastal patches to the north (Delgado
et al. 1987). The continental shelf of Peru has an average depth of 200 m. The
continental slope starts at that depth and descends rapidly towards the Peru ocean
trench that reaches 6,000 m in depth. This ocean trench is formed at the edge of
contact of the Nazca plate and the South American continental plate (Meschede
and Barckhausen 2000).
The continental shelf is very diverse. The area located off the Tumbes and Piura
provinces is narrow, with an average width of 40 km. It is wide from the Illescas
Peninsula (Piura) to the Paracas Peninsula, reaching up to 140 km in width at
Chimbote and 70 km off Lima. From the Paracas Peninsula to the Chilean border
the average width varies between 2 and 4 km (Fig. 8.1). Geotectonic blocks as
well as pyrogenic and orogenic submersions form the continental shelf. The group
of marine rocks of most of the Peruvian coastline was elevated due to tectonic
action by the end of the Pleistocene, emerging from the sea and penetrating in
many places at the coastline up to 100 km inside the continent. The rocks from the
continental shelf and the Peruvian littoral are made primarily of Paleozoic and
Mesozoic sedimentary rocks. Granite rocks, granodiorite rocks, and gneiss rocks
occur at a few localities (Petersen et al. 1972).
8.1.2 Oceanography and Marine Circulation
The oceanographic characteristics and the marine diversity of the Peruvian sea are
ruled by a complex system of currents, which produce one of the most important
upwelling systems in the world.
Most of the Peruvian sea is influence by the Peru Current (Humboldt), which
begins approximately at 40°S as a consequence of the winds produced by the
anticyclonic gyre of the South Pacific Sea. The flow of a branch of this current, the
coastal Peruvian Current, is pushed by the trade winds. It follows the topography
of the South American coast until 6°S (Illescas Peninsula) where it deviates to the
east. This current is characterized by temperate waters through the length of its
route, with temperatures between 13 °C and 18 °C according to year, season and
geographic position (Fig. 8.2). These temperatures are much colder than expected
because it is found in the tropics, close to the equator. This is caused by the intense
upwelling that carries cold waters rich in nutrients to the sea surface. These waters
have a stable salinity around 35 %. As suggested by its name, this current flows
along the coast with a width that varies between 96 and 160 km with a depth
normally below 200 m. The other branch of the Peru Current, The Peruvian
Oceanic Current, moves from south to north, to the east of the meridian 82°W and
reaches depths of 700 m. This oceanic current also has temperatures that are lower
than those of tropical oceanic waters (17–20 °C) due to its subantarctic origins
(Pizarro 2001; Tarazona et al. 2003).
In the Pacific Ocean, over the equatorial line, the Equatorial Counter Current
moves towards the east until it collides with the South American continent.
280
Y. Hooker et al.
0 S and may appear in coastal patches to the north (Delgado
et al. 1987). The continental shelf of Peru has an average depth of 200 m. The
continental slope starts at that depth and descends rapidly towards the Peru ocean
trench that reaches 6,000 m in depth. This ocean trench is formed at the edge of
contact of the Nazca plate and the South American continental plate (Meschede
and Barckhausen 2000).
The continental shelf is very diverse. The area located off the Tumbes and Piura
provinces is narrow, with an average width of 40 km. It is wide from the Illescas
Peninsula (Piura) to the Paracas Peninsula, reaching up to 140 km in width at
Chimbote and 70 km off Lima. From the Paracas Peninsula to the Chilean border
the average width varies between 2 and 4 km (Fig. 8.1). Geotectonic blocks as
well as pyrogenic and orogenic submersions form the continental shelf. The group
of marine rocks of most of the Peruvian coastline was elevated due to tectonic
action by the end of the Pleistocene, emerging from the sea and penetrating in
many places at the coastline up to 100 km inside the continent. The rocks from the
continental shelf and the Peruvian littoral are made primarily of Paleozoic and
Mesozoic sedimentary rocks. Granite rocks, granodiorite rocks, and gneiss rocks
occur at a few localities (Petersen et al. 1972).
8.1.2 Oceanography and Marine Circulation
The oceanographic characteristics and the marine diversity of the Peruvian sea are
ruled by a complex system of currents, which produce one of the most important
upwelling systems in the world.
Most of the Peruvian sea is influence by the Peru Current (Humboldt), which
begins approximately at 40°S as a consequence of the winds produced by the
anticyclonic gyre of the South Pacific Sea. The flow of a branch of this current, the
coastal Peruvian Current, is pushed by the trade winds. It follows the topography
of the South American coast until 6°S (Illescas Peninsula) where it deviates to the
east. This current is characterized by temperate waters through the length of its
route, with temperatures between 13 °C and 18 °C according to year, season and
geographic position (Fig. 8.2). These temperatures are much colder than expected
because it is found in the tropics, close to the equator. This is caused by the intense
upwelling that carries cold waters rich in nutrients to the sea surface. These waters
have a stable salinity around 35 %. As suggested by its name, this current flows
along the coast with a width that varies between 96 and 160 km with a depth
normally below 200 m. The other branch of the Peru Current, The Peruvian
Oceanic Current, moves from south to north, to the east of the meridian 82°W and
reaches depths of 700 m. This oceanic current also has temperatures that are lower
than those of tropical oceanic waters (17–20 °C) due to its subantarctic origins
(Pizarro 2001; Tarazona et al. 2003).
In the Pacific Ocean, over the equatorial line, the Equatorial Counter Current
moves towards the east until it collides with the South American continent.
280
Y. Hooker et al.