Correction to “Bio-optical relationships and ocean color algorithms for the north polar region of the Atlantic”

Abstract

Up to now, relatively few bio-optical measurements have been made in the high northern latitude waters, which allow sound relationship for ocean color remote sensing to be determined. We collected optical and chlorophyll a concentration, Chl, data in the north polar region of the Atlantic in summer season. The investigated region includes subarctic and arctic waters between 70°N and 80°N within the meridional zone between 1°E and 20°E. Our measurements show that the current NASA global algorithms, OC2, OC4, and chlor-MODIS, generally overpredict Chl in the investigated waters by a factor of about 2 at low pigment concentrations ( < 0.2 mg m -3 ) and underpredict Chl at higher concentrations (20-50% at 2-3 mg m -3 ). For our data set, the best two-band algorithm for Chl involves the ratio of remote-sensing reflectance, R rs (442)/R rs (555), at 442-nm and 555-nm light wavebands. We found that the general trend of variation in the blue-to-green reflectance ratio, R rs (442 /R rs (555) or R rs (490)/R rs (555), with Chl was driven primarily by Chl-dependent change in the green-to-blue ratio of absorption by pure seawater and particles. The effect of the blue-to-green backscattering ratio was of secondary importance. We observed a characteristic optical differentiation of waters within the investigated region. The majority of waters, which are here hypothesized to be dominated by diatoms, exhibited a relatively high blue-to-green reflectance ratio. The waters at several other stations, presumably dominated by dinoflagellates and/or prymnesiophytes, showed much lower reflectance ratio. Our data also show that the seemingly random variations in particulate absorption and backscattering coefficients at any given Chl are significant (more than a factor of 2) in the investigated waters.