CHAPTER 8; Physical Characteristics and Processes of the Rio de la Plata Estuary
During winter, the temperature field in the estuary and shelf is quite homogeneous, with values of 10-12° C. Cooler surface water is located in the center of the outer
estuary with temperature of 9-10° C, 1° C cooler than the surroundings. This surface
cooling results in a negative difference of 1° C between surface and bottom. The adjacent shelf is not stratified.
In spite of the strong vertical stratification generated by salinity differences, the
temperature in the estuary remains almost vertically homogeneous during the warm
and cool seasons. The mean horizontal fields show that there is not a strong difference in temperature between the estuarine and the inner shelf water, except during
summer in the southern extension of the river plume.
8.5.2
Sea Surface Temperature
Remote sensing information, such as the images obtained by the Advanced Very High
Resolution Radiometer (AVHRR) of the NOAA satellites, is especially useful for the
study of the Rio de la Plata Estuary. NOAA-AVHRR imagery gives simultaneous coverage of the whole region, something that is not possible with in situ information
obtained by shipboard sampling due to the large areal extent of the river. Sea surface
temperature (SST) is computed using a multichannel algorithm for the infrared channels. The images used in this study are individual, daily SST images with maximum
horizontal resolution (l.l km).
Two images are presented as examples of the cool and warm season (Plate 8.1).
Homogeneity in the estuary and the inner shelf, with cooler water near the coast and
in the Samboromb6n Bay occurs during winter (Plate 8.1a). During summer, there is
a strong gradient between the river plume and the shelf water in the southern part
(Plate 8.1b). This frontal zone follows approximately the geometry of the 50 m isobath,
and its occurrence was first reported by Framifian and Brown (1993) based on a 4 year
span of satellite images. The frontal zone begins to appear in the SST images in early
September, and it is observed until late March. The temperature gradient at the surface obtained from the images associated with this transition zone has values up to
0.25° C km- I • The front defines two zones on the continental shelf; the limit is associated with the 20° C isotherm, as suggested in the mean temperature distribution
derived from in situ data. Another feature that can be observed in the SST images
(Plates 1b and 2b) is a temperature minimum associated with a cool extension of shelf
water along the Argentinean coast entering the Samboromb6n Bay at Cape San
Antonio. This northward flow can be observed in all seasons, but is more noticeable
during summer due to the greater temperature gradient. In summer, the flow has a
temperature difference with the surrounding of 3-4° C, and it extends 20-25 km offshore (Framifian and Brown 1993). There are manifestations of this coastal water intrusion in in situ data, as well as remote sensing information; Lasta et al. (1996) discussed its importance in the estuarine ecosystem.
A temperature minimum on the northern coast of the outer estuary (Plate 8.2) is
observed during summer months in SST images, especially from mid December to early
February (Framifian and Brown 1998). The difference of temperature between the center
and the surrounding water is of approximately 4-5° C. The minimum starts developing very close to the coast in the proximity of Punta del Este. It can reach large hori-
During winter, the temperature field in the estuary and shelf is quite homogeneous, with values of 10-12° C. Cooler surface water is located in the center of the outer
estuary with temperature of 9-10° C, 1° C cooler than the surroundings. This surface
cooling results in a negative difference of 1° C between surface and bottom. The adjacent shelf is not stratified.
In spite of the strong vertical stratification generated by salinity differences, the
temperature in the estuary remains almost vertically homogeneous during the warm
and cool seasons. The mean horizontal fields show that there is not a strong difference in temperature between the estuarine and the inner shelf water, except during
summer in the southern extension of the river plume.
8.5.2
Sea Surface Temperature
Remote sensing information, such as the images obtained by the Advanced Very High
Resolution Radiometer (AVHRR) of the NOAA satellites, is especially useful for the
study of the Rio de la Plata Estuary. NOAA-AVHRR imagery gives simultaneous coverage of the whole region, something that is not possible with in situ information
obtained by shipboard sampling due to the large areal extent of the river. Sea surface
temperature (SST) is computed using a multichannel algorithm for the infrared channels. The images used in this study are individual, daily SST images with maximum
horizontal resolution (l.l km).
Two images are presented as examples of the cool and warm season (Plate 8.1).
Homogeneity in the estuary and the inner shelf, with cooler water near the coast and
in the Samboromb6n Bay occurs during winter (Plate 8.1a). During summer, there is
a strong gradient between the river plume and the shelf water in the southern part
(Plate 8.1b). This frontal zone follows approximately the geometry of the 50 m isobath,
and its occurrence was first reported by Framifian and Brown (1993) based on a 4 year
span of satellite images. The frontal zone begins to appear in the SST images in early
September, and it is observed until late March. The temperature gradient at the surface obtained from the images associated with this transition zone has values up to
0.25° C km- I • The front defines two zones on the continental shelf; the limit is associated with the 20° C isotherm, as suggested in the mean temperature distribution
derived from in situ data. Another feature that can be observed in the SST images
(Plates 1b and 2b) is a temperature minimum associated with a cool extension of shelf
water along the Argentinean coast entering the Samboromb6n Bay at Cape San
Antonio. This northward flow can be observed in all seasons, but is more noticeable
during summer due to the greater temperature gradient. In summer, the flow has a
temperature difference with the surrounding of 3-4° C, and it extends 20-25 km offshore (Framifian and Brown 1993). There are manifestations of this coastal water intrusion in in situ data, as well as remote sensing information; Lasta et al. (1996) discussed its importance in the estuarine ecosystem.
A temperature minimum on the northern coast of the outer estuary (Plate 8.2) is
observed during summer months in SST images, especially from mid December to early
February (Framifian and Brown 1998). The difference of temperature between the center
and the surrounding water is of approximately 4-5° C. The minimum starts developing very close to the coast in the proximity of Punta del Este. It can reach large hori-