Abstract

Bio-optical parameters of light absorption of particulate material and pigments, extinction coefficients of downwelling irradiance, coloured dissolved organic matter and phytoplankton size composition and diversity (H´tam) were analyzed and compared, together with the patterns of chlorophyll-a (Cl-a) distribution for the area of the inner sea of Chile (MICH), during winter and spring 2004 and 2005 expeditions of cruises CIMAR 10 and 11 Fiordos. For the distribution patterns of the 0-25 m integrated Cl-a abundances, the same ranges were found were found in all cruises with increases of 5 to 10 times between sampling stations. In the winter expeditions, integrated Cl-a reached higher mean value and higher variability in August 2004 (55.57 ± 53.78 mg Cl-a m–2) compared to July 2005 (31.26 ± 34.99 mg Cl-a m–2) over the whole area of the MICH. This variability in Cl-a abundance, reflected in H´tam and the variation of the bio- ptical parameters (i.e. specific absorption <0.050 m2 (mg Cl-a)–1), indicate that the results from August of 2004, are similar to an “early spring”. In the spring expeditions, integrated Cl-a reached higher mean value and higher variability in November 2004 (88.04 ± 59.25 mg Cl-a m–2) compared with November 2005 (59.36 ± 34.65 mg Cl-a m–2). At the regional scale, the seasonal winter-spring transitions in irradiance, precipitation and runoff, would modulate the effects on submarine light availability and in the loading, recycling and retention of nutrients, suggesting a strong influence of the local conditions in the large variability of Cl-a found between dates and sites. The H´tam results and the spatial bio-optical variability, account for intra-seasonal functional variability of phytoplankton in this zone, which needs to be taken into account to explain those changes at interannual scales.