Natural variability of bio-optical properties in Case 1 waters: attenuation and reflectance within the visible and near-UV spectral domains, as observed in South Pacific and Mediterranean waters

摘要

The optical properties of Case 1 waters have been empirically related to thechlorophyll concentration, [Chl], historically used as an index of thetrophic state and of the abundance of the biological materials. Thewell-known natural variability around the mean statistical relationships ishere examined by comparing the apparent optical properties (spectraldownward irradiance attenuation and reflectance) as a function of [Chl] intwo Case 1 environments, the Pacific and Mediterranean waters. These oceaniczones apparently represent two extremes of the possible bio-opticalvariability range around the mean. The systematic deviations, in bothdirections with respect to the average laws, mainly result from thediffering contents in non-algal detrital materials and dissolved coloredsubstance for a given [Chl] level. These contents are higher than theaverage in the Mediterranean Sea, and lower in the Pacific Ocean,respectively. These divergences between the two water bodies, detectable inthe visible spectral domain, are considerably accentuated in the UV domain.The bio-optical properties in this spectral domain (310–400 nm) aresystematically explored. They are more varying for a given [Chl] than thosein the visible domain. Their prediction based on the sole [Chl] index isthus problematic, although it is probably possible on a regional scale ifreliable field data are available. It does not seem, however, thatubiquitous relationships exist for this spectral domain for all Case 1waters at global scale.