Marine optical measurements of a mucilage event in the northern Adriatic Sea
Limnol. Oceanogr., 45(2), 2000, 322-327 | DOI: 10.4319/lo.2000.45.2.0322
ABSTRACT: Optical measurements performed during the summer of 1997 from an off-shore oceanographic tower in the northern Adriatic Sea in the presence of mucilage matter are presented. These measurements include apparent (diffuse attenuation coefficient, reflectance) and inherent (absorption and beam attenuation coefficients) optical properties of the water column at several wavelengths. The presence of mucilage layers (which was confirmed by divers) was associated with unique, very sharp subsurface maxima in the vertical distribution of both apparent and inherent optical properties. These layers were characterized by very high values of the diffuse attenuation coefficient of upwelling radiance and the beam attenuation coefficient, as well as the ratio of the scattering-to-absorption coefficients at all wavelengths. The mucilage data were compared to nonmucilage observations and two situations came out regarding surface reflectance ratios: (a) When the mucilage was in (vertically narrow) subsurface layers, mucilage events could not be distinguished from nonmucilage situations; and (b) When the mucilage was more homogeneously distributed throughout the water column and, in particular, approaching the surface, there was a detectable difference with respect to nonmucilage water. However, the data set is small, and the detection capability is based on a small difference, so the variance in nonmucilage water properties may still mask the properties of the mucilage-contaminated water.