SPATIAL VARIABILITY OF BIO-OPTICAL CONDITIONS IN THE WATER COLUMN BETWEEN THE CHILEAN OCEANIC-ISLANDS AND CONTINENTAL CHILE. SPRING 1999 AND 2000*
GEMITA PIZARRO 1, VIVIAN MONTECINO 2, ROSA ASTORECA 2, GADIEL ALARCÓN 3, GABRIEL YURAS 3 LEONARDO GUZMÁN 1
1 Instituto de Fomento Pesquero. Casilla 101. Punta Arenas 2 Facultad de Ciencias, Universidad de Chile. Casilla 653. Santiago 3 Programa de Oceanografía Física y Clima, Universidad de Concepción. Casilla 160-C. Concepción.
Recepción: 28 de noviembre de 2003 - Versión corregida aceptada: 19 de enero de 2006.
ABSTRACT
Off Chile, there is a large oceanic zone associated with far-distance islands at septentrional latitudes off Caldera. These are San Ambrosio (26o 18’ S - 79o 53’ W), San Félix (26o 16’ S - 80o 05’ W), Salas y Gómez Island (26o 27’S - 105o 22’ W) and Easter Island (27o 06’ S - 109o 12’ W). In central Chile the islands are Alejandro Selkirk (33o 35’ S – 78o 51’ W) and Robinson Crusoe (33o 45’ S - 80o 51’ W). These areas are biooptically poorly known, including its characterization and variability for the validation of algorithms towards primary productivity estimations from chlorophyll a (CL-a) measurements using satellite images such as SeaWiFs. In 1999 and 2000 through two oceanographic expeditions, a data base was started in order to establish the ranges and distribution of CL-a, including the western limit of influence of the Humboldt Current system. It was also established that this waters at 700 km from the coast are extremely clear- low PAR extinction coefficients- as it was the case for oceanic waters off 200 km of Antofagasta. Results indeed confirmed the high water transparency and its distributions that were associated to the distance from the coast of the nucleous of maximum CL-a concentration (NMCL-a). The size and the maximum CL-a values of this nucleous varied interannually. At the more southern latitudes the NMCL-a was narrower and shortened its distance from the coast, while the maximum CL-a concentration diminished and the depth distribution depth increased (from 7 or 10 m to 30 m). In addition to the topographic differences of the coastal margin, based on recent information on the coastal transition zone there are impor tant spatio-temporal differences of meanders and eddies located 600 km farther offshore that are closely related with the bio-optical variability found in this study.
Key words: Chlorophyll a concentration, satelital chlorophyll (SeaWifs), diffuse attenuation coefficient of active and spectral photosynthetic radiation.