SEA-SURFACE COLOR IN THE FIELD OF BIOLOGICAL OCEANOGRAPHY

Variations of marine surface optical properties (generally grouped under the term 'sea surface colour') are due to dissolved and suspended materials, with different absorption and scattering characteristics, present in sea water. Remote assessments of sea surface colour, therefore, can be used to determine the presence and abundance of water constituents such as biological pigments, suspended sediments or other products of organic matter degradation (the so-called yellow substance). In open sea waters, the pigments due to biological activities, and particularly phytoplankton chlorophyll-like pigments, are the main contributors to surface colour. Hence, observations in the visible spectrum can provide synoptic and repetitive information on parameters linked to biological production and patchiness, or bio-geo-chemical cycles in general. Since water constituents act as tracers of various marine processes, bio-optical patterns on the sea surface can also provide indications about the relationships existing between forcing mechanisms and biological response in the marine environment. These capabilities render optical remote sensing an invaluable tool in the field of biological oceanography, although atmospheric processes and signal ambiguities in the water column may pose severe limitations on this technique. The feasibility and potential of passive remote sensing in the visible spectrum have been demonstrated primarily by the Coastal Zone Color Scanner (CZCS) experiment. Important results of this experiment have been reported in the study of coastal phenomena, sediment transport, frisheries, upwelling, climatic events, and factors controlling the distribution, growth and fate of phytoplankton. On these latter topics, indications of a strong coupling between dynamical and bio-optical conditions of the marine environment are emerging from the analysis of CZCS image series, for open ocean, near-coastal and enclosed basin conditions. Examples of such studies, covering regions of both the North Atlantic and North Pacific Oceans and of the Mediterranean Sea, provide clues on the promises of large-scale sea surface colour assessments in the field of biological oceanography.