Bio-optical characteristics and primary productivity during upwelling and non-upwelling conditions in a highly productive coastal ecosystem off central Chile (similar to 36 degrees S)

Variability of several bio-optical and photosynthetic properties of phytoplankton in the highly productive coast off Concepcion, central Chile (similar to36degreesS) was quantified during contrasting seasons at offshore, shelf, and nearshore sites. During October 1998 (upwelling) and July 1999 (non-upwelling), 21 stations were sampled for chlorophyll-a, pigment spectral light absorption, primary production, and attenuation coefficients (klambda) of downwelling irradiance (E-d(lambda)); klambda was used to estimate the depth of the euphotic zone (Z(eu)). Primary production was measured through C-14-fixation experiments using simulated in situ and in situ incubations with water from six depths within the Z(eu). The (alpha(B), P-max(B)) photosynthetic parameters (alpha(B), P-max(B)) were obtained through photosynthesis-irradiance experiments with samples from two Z(eu) depths. Bio-optical properties showed large spatial variability during both seasons, including spectral in vivo phytoplankton absorption (alpha(ph)(lambda)), pigment specific phytoplankton absorption (a*(lambda)) within the upper 25 m, and water-column transmittance (T(lambda)), calculated for the upper 10 m using E-d(lambda) at four wavelengths. Under non-upwelling conditions, a*(lambda), T(lambda) and alpha(B) presented higher values whereas a(ph)(lambda) values decreased accordingly. Under upwelling conditions, primary productivity ranged from 0.7 to 7.5 g C m(-2) d(-1) at the coastal stations and was <0.6 g C m(-2) d(-1) at the oceanic stations; in the non-upwelling season, values over the entire area ranged from 0.2 to 1.9 g C m(-2) d(-1). The significant correlations found among bio-optical properties and physiological parameters highlight both the short- and long-term changes in the area's environmental conditions. The combination of three independent biological parameters - alpha(B), P-max(B), and a(ph)(442) - accounted for most of the horizontal and vertical variability among and within stations for each cruise. These results support a distinction of different functional zones for the two contrasting upwelling conditions. (C) 2004 Elsevier Ltd. All rights reserved.