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Phytoplankton samples collected from two cruises off the coast of Chile were analysed for pigment composition and absorption characteristics. High pigment concentrations (up to 20 mg chl-a m-3) were found in the upwelled waters over the shelf break off the coast of Concepción during spring (October 1998), but relatively oligotrophic conditions were found further offshore. Similarly, stations further north (between Coquimbo and Iquique), sampled during the austral summer (February 1999), also showed low pigment concentrations, characterised by the presence of prymnesiophytes, and cyanobacteria including Prochlorococcus sp. The specific absorption coefficient of phytoplankton at 443 nm (a*ph(443)) was much higher for the offshore population than the inshore population, which was dominated by large diatoms. These differences are attributed to changes in pigment packaging and pigment composition. The relative proportion of non-photosynthetic carotenoids to chl-a, together with the ratio of the peak height of the Gaussian bands in the blue and red regions of the spectrum, p(435)/p(676), (an indicator of the importance of the packaging effect) could account for up to 92 % of the total variation in a*ph(443). Blue/green absorption ratios were strongly related to the relative concentration of 19'-hexanoyloxyfucoxanthin and fucoxanthin. A reasonable agreement was found between in situ and satellite estimates of chl-a (SeaWiFS data) despite the large variability in phytoplankton specific absorption coefficients, suggesting that the `global' absorption-to-chlorophyll relationships encompass the regional variations observed off the coast of Chile. Satellite chl-a was overestimated in oligotrophic water when compared to HPLC chl-a measurements, apparently because of the high specific absorption coefficients of phytoplankton in the offshore waters. On the other hand, ship and satellite data were in closer agreement when in situ fluorometric chl-a data was used. It is likely that the correlation between in situ and satellite chl-a could be improved by using regional algorithms La composición de pigmentos y las características de absorción fueron analizadas en muestras de fitoplancton recolectadas en dos cruceros frente a las costas Chile. Se encontraron altas concentraciones de pigmentos (hasta 20 mg chl-a m-3) en aguas de surgencia sobre el quiebre de la plataforma frente a Concepción durante la primavera, octubre de 1998; sin embargo, se encontraron condiciones relativamente oligotróficas costa afuera. De manera similar, estaciones más al norte (entre Coquimbo e Iquique), muestreadas durante el verano austral (febrero de 1999), también mostraron bajas concentraciones de pigmentos, caracterizados por la presencia de primnesioficeas y cianobacterias (Synechococccus sp. y Prochlorococcus sp.). El coeficiente de absorción específico del fitoplancton a 443 nm (a*ph(443)) fue mucho mayor para las poblaciones costa afuera que para las poblaciones costeras, las cuales estaban dominadas por diatomeas. Esta diferencia fue atribuida a cambios en el empaquetamiento y composición de pigmentos. La proporción relativa entre carotenoides no-fotosintéticos y chl-a, junto con la razón de la altura del pico de las bandas Gausianas en las regiones azul y roja del espectro p(435)/p(676) (un índice del efecto de empaquetamiento), representa hasta el 92 % de la variación total en a*ph(443). Las razones de absorción azul/verde estuvieron relacionadas fuertemente a la concentración relativa de 19'-hexanoiloxifucoxantina y fucoxantina. Se encontró una relación aceptable entre las estimaciones de chl-a (datos de SeaWiFS) medidas in situ y las obtenidas con el satélite, a pesar de la gran variabilidad en los coeficientes de absorción específica del fitoplancton, sugiriendo que las relaciones de absorción de clorofila "global" abarcan las variaciones regionales observadas a la altura de las costas de Chile. Las mediciones de chl-a satelitales fueron sobreestimadas en aguas oligotróficas cuando se compararon con determinaciones HPLC de chl- a, aparentemente por los coeficientes específicos de absorción altos del fitoplancton en mar abierto. Además, los datos obtenidos por barco y de satélite estuvieron estrechamente relacionados cuando se utilizaron datos de chl- a in situ y fluorométricos. Probablemente la correlación entre la chl- a in situ y satelital podría ser mejorada utilizando algoritmos regionales

Phytoplankton samples collected from two cruises off the coast of Chile were analysed for pigment composition and absorption characteristics. High pigment concentrations (up to 20 mg chl-a m-3) were found in the upwelled waters over the shelf break off the coast of Concepción during spring (October 1998), but relatively oligotrophic conditions were found further offshore. Similarly, stations further north (between Coquimbo and Iquique), sampled during the austral summer (February 1999), also showed low pigment concentrations, characterised by the presence of prymnesiophytes, and cyanobacteria including Prochlorococcus sp. The specific absorption coefficient of phytoplankton at 443 nm (a*ph(443)) was much higher for the offshore population than the inshore population, which was dominated by large diatoms. These differences are attributed to changes in pigment packaging and pigment composition. The relative proportion of non-photosynthetic carotenoids to chl-a, together with the ratio of the peak height of the Gaussian bands in the blue and red regions of the spectrum, p(435)/p(676), (an indicator of the importance of the packaging effect) could account for up to 92 % of the total variation in a*ph(443). Blue/green absorption ratios were strongly related to the relative concentration of 19'-hexanoyloxyfucoxanthin and fucoxanthin. A reasonable agreement was found between in situ and satellite estimates of chl-a (SeaWiFS data) despite the large variability in phytoplankton specific absorption coefficients, suggesting that the `global' absorption-to-chlorophyll relationships encompass the regional variations observed off the coast of Chile. Satellite chl-a was overestimated in oligotrophic water when compared to HPLC chl-a measurements, apparently because of the high specific absorption coefficients of phytoplankton in the offshore waters. On the other hand, ship and satellite data were in closer agreement when in situ fluorometric chl-a data was used. It is likely that the correlation between in situ and satellite chl-a could be improved by using regional algorithms