Light absorption by phytoplankton, non-algal particles, and dissolved organic matter in San Jorge gulf in summer

Abstract

San Jorge Gulf (SJG) along the Atlantic coast of South America is of high ecological importance, a place where several industrial fisheries exploit species such as hake, the Argentine red shrimp, and the Patagonian scallop. In this region, phytoplankton distribution is often related to bathymetric or oceanographic features such as capes, upwellings, and frontal areas that drive the renewal of nutrients in the surface layer. Satellite remote sensing is a key tool for monitoring such a large ecosystem. Knowledge of the optical properties of seawater in this area is necessary to assess the quality of operational ocean color products. Absorption of light by phytoplankton (a phy ), non-algal particles (a NAP ), and colored dissolved organic matter (a CDOM ), as well as the concentration of chlorophyll-a were measured in February 2014 in the surface layer of the SJG. These parameters all exhibited strong spatial variability that resulted from the gulf ’s large-scale circulation and bathymetric features. Although CDOM dominated the absorption budget, there was good correlation between a CDOM and a phy , leading to the characterization of San Jorge Gulf as “Case-1” waters where remote-sensing algorithms should perform well. Study results showed that the phytoplankton composition was mainly dominated by small cells (0.2–2 µm, i.e., picophytoplank-ton). The a phy *(440) measured at the end of summer in the SJG (0.01–0.08 m 2 mg –1 ) are in a similar range to those observed elsewhere. Particulate absorption was dominated by phytoplankton (66%).