The Gulf of Guayaquil and the Guayas River Estuary, Ecuador
247
Panama Current (2-3°S) with more saline (>34), subtropical cold ( <22 oC)
water of the Humboldt Current (Cucal6n 1983, 1986). A seasonal flux of
warmer waters from the north to the Gulf of Guayaquil, associated with
higher precipitation and river discharge between January and April, sets
up maximum temperature and salinity gradients from the inner to the
outer boundaries and stratification of deeper Gulf waters. During the summer, increased meridional winds strengthen the force of the Humboldt
Current and colder waters (known as Superficial Subtropical Water) move
from the south into the Gulf of Guayaquil, causing outcrops of high-nutrient waters with increased biological productivity. Anomalous ocean currents in the Pacific, associated with El Nino phenomena, cause a shift in the
dominance of the Panama current, which results in abnormally warm and
less saline coastal waters, higher precipitation in coastal provinces, greater
river discharge, and lower salinity in the estuaries. Therefore, both intraand inter-annual variations in the estuary can be coupled to coastal oceanographic processes (Stevenson 1981).
Winds in the Gulf of Guayaquil are variable and influenced by the InterTropical Convergence Zone (ITCZ). Most winds are from the south
( 1.5 m s- 1 ) while more northerly winds prevail during El Nino events.
During the wet season northeast winds dominate ( 1.8 m s- 1 ), compared to
southwest winds during the dry season (3.5 m s- 1 ). Depending on the location of dominant oceanographic currents off the coast, the precipitation in
the Guayas River drainage system (mean 885mm year- 1 ) ranges from 400
to 3,800 mm year- 1 ( Cucal6n 1983, 1986). More than 95% of the rainfall
occurs during the summer (December to May). During an average year of
precipitation, seasonal river discharge ranges from 200m 3 s- 1 during the
dry season to 1,400 m 3 s- 1 in the wet season (Fig. 17.2), but rates as low as
100m 3 s- 1 and as high as 2,400 m 3 s- 1 may occur (Stevenson 1981). Annual
mean temperatures vary between 24 and 27 °C, resulting in a potential evapotranspiration rate of about 1,300 mm year- 1 •
Tides are 1.8 m near the upper boundary of the Gulf and increase to
3-5m in the Guayas River estuary near the city of Guayaquil. The tide is
semi-diurnal (M 2 =12.42 h) with currents in excess of 3.5 m s- 1 in the river
and channels of the estuary. There is also evidence of a 3.5-h seiche along
Puna Island (Stevenson 1981). The Guayas River estuary is partially mixed
with tidal current speeds of up to 100 em s- 1 • The dominant upstream flux
of mass and salt is associated with the tidal prism and water turnover time
is 11 days, leading to large fluxes of water and nutrients across the boundaries that determine system behavior (Murray et al. 1975). Although vertical layers and water column structure develop in the Gulf of Guayaquil,
these hydrographic features do not occur within the estuary (Stevenson
1981).
247
Panama Current (2-3°S) with more saline (>34), subtropical cold ( <22 oC)
water of the Humboldt Current (Cucal6n 1983, 1986). A seasonal flux of
warmer waters from the north to the Gulf of Guayaquil, associated with
higher precipitation and river discharge between January and April, sets
up maximum temperature and salinity gradients from the inner to the
outer boundaries and stratification of deeper Gulf waters. During the summer, increased meridional winds strengthen the force of the Humboldt
Current and colder waters (known as Superficial Subtropical Water) move
from the south into the Gulf of Guayaquil, causing outcrops of high-nutrient waters with increased biological productivity. Anomalous ocean currents in the Pacific, associated with El Nino phenomena, cause a shift in the
dominance of the Panama current, which results in abnormally warm and
less saline coastal waters, higher precipitation in coastal provinces, greater
river discharge, and lower salinity in the estuaries. Therefore, both intraand inter-annual variations in the estuary can be coupled to coastal oceanographic processes (Stevenson 1981).
Winds in the Gulf of Guayaquil are variable and influenced by the InterTropical Convergence Zone (ITCZ). Most winds are from the south
( 1.5 m s- 1 ) while more northerly winds prevail during El Nino events.
During the wet season northeast winds dominate ( 1.8 m s- 1 ), compared to
southwest winds during the dry season (3.5 m s- 1 ). Depending on the location of dominant oceanographic currents off the coast, the precipitation in
the Guayas River drainage system (mean 885mm year- 1 ) ranges from 400
to 3,800 mm year- 1 ( Cucal6n 1983, 1986). More than 95% of the rainfall
occurs during the summer (December to May). During an average year of
precipitation, seasonal river discharge ranges from 200m 3 s- 1 during the
dry season to 1,400 m 3 s- 1 in the wet season (Fig. 17.2), but rates as low as
100m 3 s- 1 and as high as 2,400 m 3 s- 1 may occur (Stevenson 1981). Annual
mean temperatures vary between 24 and 27 °C, resulting in a potential evapotranspiration rate of about 1,300 mm year- 1 •
Tides are 1.8 m near the upper boundary of the Gulf and increase to
3-5m in the Guayas River estuary near the city of Guayaquil. The tide is
semi-diurnal (M 2 =12.42 h) with currents in excess of 3.5 m s- 1 in the river
and channels of the estuary. There is also evidence of a 3.5-h seiche along
Puna Island (Stevenson 1981). The Guayas River estuary is partially mixed
with tidal current speeds of up to 100 em s- 1 • The dominant upstream flux
of mass and salt is associated with the tidal prism and water turnover time
is 11 days, leading to large fluxes of water and nutrients across the boundaries that determine system behavior (Murray et al. 1975). Although vertical layers and water column structure develop in the Gulf of Guayaquil,
these hydrographic features do not occur within the estuary (Stevenson
1981).