Graduation date: 1984The mesoscale sea-surface circulation pattern within 400 km off Chile and between 18°S and 40°S latitude is described using chlorophyll and temperature images from the Coastal Zone Color Scanner NIMBUS-7 satellite. The data base is a set of four mosaics developed from band-3 (550 nm) images taken on June 4 and September 16, 1979 and January 14 and April 7, 1980, supplemented with one mosaic of sea-surface temperature distribution for the September mosaic, orbit 4526. Coastal eddies, upwelling zones and zones of onshore-offshore transport are clearly distinguished because a zone of low-pigment concentration water generally separates the highly pigmented near-shore upwelling zones from oceanic waters with pigment concentration in mid-range. The cause of the low-pigment water adjacent to upwelling zones is not known, but the absence of temperature differences between up-welled and low-pigmented water suggest a biological cause. Onshore jets of oceanic waters are traced from distances up to 300 km offshore to within, in places, a few tens of kilometers of the shoreline; width of the jets is of the order of 60 km. In general, these onshore jets are separated by plumes of near-shore surface water moving seaward, with plumes width on the order of 40 km also extending as far as 400 km offshore. Large eddies form off the leading edges of both onshore and offshore plumes, giving rise to a formation called a "hammerhead" structure. Onshore jets are consistent with the result of Inostroza (1972) which documents intrusions of warm oceanic surface waters as semi-stationary features off Coquimbo (30°S) and off Talcahuano (37°S). Lack of wind data for 1979-80 prevents a direct correlation of onshore-offshore plumes with regional wind stress data. Low level wind charts for the 1979-80 period are too coarse in resolution to yield correlations. However, stick diagrams were prepared from coastal wind station data for 1977. Both time and space variations in surface winds could be responsible for the patterns revealed in chlorophyll images. The existence of persistent but probably episodic onshore-offshore transport of surface waters to such large distances offshore have not been reported previously for Chilean waters. These must certainly impact directly the patterns of migrations of populations of major fishery resources such as the Jack Mackerel (Trachurus murphyi, common name Jurel, species.