Bio-optical Studies Along the Patagonian Shelf-break Zone

GARCIA, C.A.E.; GARCIA, V.M.T; DOGLIOTTI, A.I.; FERREIRA, A.; ROMERO, S.I.; SIGNORINI, S.; MCCLAIN, CH. R.

Barga, Italia

Conferencia; Ocean Optics XIX; 2008

Ocean color images from the Patagonia shelf break in the Southwestern Atlantic Ocean, usually show high phytoplankton biomass patches during spring and summer periods. The PATagonia EXperiment (PATEX) project was designed to investigate the environmental factors that control the occurrence of these blooms, to characterize the phytoplankton assemblage and primary production rates, to determine the main nutrient levels and ratios associated with the bloom waters, to determine their bio-optical characteristics and the CO2 fluxes in the studied area.Five cruises were conducted in November 2004, October 2006, March 2007, October 2007 and January 2008 when more than 120 oceanographic stations were occupied for physical, biogeochemical and optical studies along the large bloom extent in the Patagonian shelf-break (approximately 55,000 Km2 of chlorophyll concentration >2 mg m-3 chlorophyll patch). In this article, we report bio-optical properties (absorption of phytoplankton and colored dissolvedorganic matter, beam attenuation coefficients and chlorophyll-a concentration) measured during these five cruises. In spring, high chlorophyll values were associated with diatoms and dinoflagellates in the frontal region, while summer phytoplankton was dominated by small nanoflagellates. Particle (phytoplankton and detritus) and CDOM absorption coefficients measured in these waters were highly variable and showed a seasonal dependence. The evaluation of three empirical algorithms showed that the OC4v4 algorithm showed a good performance, with relatively small positive bias (11.1%). A match-up between in-situ and MODIS-derived chlorophyll showed an overall uncertainty of 58%.