Characterization of intra-, inter-annual variability SST, phytoplankton pigment concentration & zooplankton on shelf zone of Humboldt Current System Chile

Title:
Characterization of the intra- and inter-annual variability of sea
surface temperature, phytoplankton pigment concentration and
zooplankton on the shelf zone of the Humboldt Current System off Chile
and assessment of their dependence on local forcing using available
and FONDAP gathered data.

Before the FONDAP-Humboldt Program, the temporal and spatial
variabilities of the oceanographic conditions and pelagic communities
have been poorly documented in the Humboldt Current System.

An analysis of SST, sea-level and winds (1991-1998) along the
upwelling zone off northern and central Chile show that inter-annual
fluctuations of SST off northern Chile are closely linked to the
thermocline oscillations in the eastern equatorial Pacific Ocean.
Annual SST fluctuations follow seasonal changes in solar radiation and
wind-driven coastal upwelling.

Off northern Chile (18-24S, out to 200nm), during summer and autumn of
1994, measurements indicated that the highest Chl-a concentrations
(>4mg m-3 ) were always found in the area between 19 degrees 30'S and
21S, in association with an offshore extension of a tongue of cold
nutrient-rich waters, surrounded by eddy-like structures. Chl-a rich
waters were dominated by net phytoplankton in summer but the smaller
phytoplankton (<20um) contributed in equal proportion to the total
during the autumn.

Off northern Chile, time series analyses (December 1991 - January
1998) of female length and abundance of Calanus chilensis, a key
herbivore, show large inter-annual fluctuations. Although SST shows
much inter-annual variation, the seasonal signal appears as the most
important in influencing its biology and its ecological response is
highly dependent on SST variation.

On a year-to-year scale, the abundance of C. chilensis is associated
with the annual regime of temperature but on scales longer than a
year, factors other than temperature appear to regulation population
size. Inter-annual variation of other demographic characteristics of
C. chilensis, like female length, appear to be controlled by remote
fluctuations associated with the El Nino-Southern Oscillation cycle
through temperature. Dominant copepod species appear to be
transported from the coast ot the offshore through filaments and
upwelling plumes, in association with phytoplankton biomass; these
mesoscale features induced local changes in copepod abundance,
composition and distribution.