Optically black waters in the northern Baltic Sea

[1] The peculiar bio-optical properties of the northernmost waters of the Baltic Sea (Bothnian Sea and Bothnian Bay) are illustrated by exploiting unique in situ measurements of apparent and inherent optical properties collected in 2007. Specifically, this study shows that the high values of absorption by colored dissolved organic matter (ays(412) around 1.4 m−1) resulting from the presence of humic matter brought by the numerous Swedish and Finnish rivers alimenting the basin are not correlated with high concentrations of particles as generally observed in the southern Baltic Sea. As a consequence, extremely low values (i.e., less than 0.5) of the ratio of scattering to absorption are observed in the blue spectral region. The corresponding spectra of normalized water leaving radiance are close to satisfy the “black pixel” assumption in the blue and even in the green part of the visible spectrum. Consequently, the Bothnian Sea and most of all the Bothnian Bay, appear ideal candidates for studies on atmospheric corrections and vicarious calibration of ocean color sensors in coastal waters.

[1]  P. Kowalczuk.  Seasonal variability of yellow substance absorption in the surface layer of the Baltic Sea , 1999 .

[2]  Giuseppe Zibordi,et al.  Measurements and modeling of the volume scattering function in the coastal northern Adriatic Sea. , 2007, Applied optics.

[3]  J. Wikner,et al.  Dynamics of Dissolved Organic Carbon in a Coastal Ecosystem. , 1995 .

[4]  G. Zibordi,et al.  An Evaluation of Depth Resolution Requirements for Optical Profiling in Coastal Waters , 2004 .

[5]  Andrew H. Barnard,et al.  A model for estimating bulk refractive index from the optical backscattering ratio and the implications for understanding particle composition in case I and case II waters , 2001 .

[6]  G. Zibordi,et al.  Ocean Colour Remote Sensing of the Optically Complex European Seas , 2008 .

[7]  T. Bianchi,et al.  Sources and composition of particulate organic carbon in the Baltic Sea: the use of plant pigments and lignin-phenols as biomarkers , 1997 .

[8]  B. Allard,et al.  River Discharge of Humic Substances and Humic-bound Metals to the Gulf of Bothnia , 1997 .

[9]  David Doxaran,et al.  Spectral variations of light scattering by marine particles in coastal waters, from the visible to the near infrared , 2009 .

[10]  Davide D'Alimonte,et al.  Validation of satellite ocean color primary products at optically complex coastal sites: Northern Adriatic Sea, Northern Baltic Proper and Gulf of Finland , 2009 .

[11]  Dariusz Stramski,et al.  Variations in the light absorption coefficients of phytoplankton, nonalgal particles, and dissolved organic matter in coastal waters around Europe , 2003 .

[12]  B. Woźniak,et al.  Light absorption in sea water , 2007 .

[13]  J. Seppälä,et al.  Spectral absorption and fluorescence characteristics of phytoplankton in different size fractions across a salinity gradient in the Baltic Sea , 2005 .

[14]  Menghua Wang,et al.  An assessment of the black ocean pixel assumption for MODIS SWIR bands , 2009 .