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Abstract
We analyze eight years (1998-2005) of weekly medium-resolution SST and Chl-a satellite data and
three years (1998-2000) of daily high-resolution SST images to study the seasonal variability in
upwelling off central Chile. Temperature, salinity, and dissolved oxygen data from an oceanographic
cruise are used to illustrate the water column structure and the geostrophic velocity field during the
upwelling season. The mean spatial extension of the SST front in summer is about 100 to 120 km.
Across this zone SST changes from ~13.5 °C near the coast to 14.5-15 °C in the deep ocean. In
general, Chl-a concentration decays exponentially offshore on a shorter offshore scale and ~1 mg m -3
is linked to the frontal zone position. The SST front observed most of the year is absent in winter,
when the average coastal SST is only slightly lower than the oceanic one; but relatively higher Chl-a
values remain present near the coast during winter. Coastal regions with relatively higher
temperatures and Chl-a concentration can be recognized in high-resolution SST and Chl-a images,
and they may be associated with upwelling shadows. This is particularly apparent in the Gulf of
Arauco (37º10’S) and the region just to the north. Northwest of Punta Lavapie (37º15’ S), the frontal
region is located progressively farther offshore, suggesting that a branch of an equatorward jet
separates from the coast to form a meander, which is associated with a filament of cold water and an
anticyclonic eddy observed rather frequently in this zone during the upwelling period.
Keywords: Upwelling; SST; fronts; seasonal variability; Chile
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