Vertical distribution of chlorophyll a concentration in the water column at study site Helgoland. Shown are vertical chlorophyll a profiles during the second day of the spring campaign. (A) shows a surface grid calculated from fluorescence data by means of a Gaussian fit procedure using TC3D software (see M&M). (B) shows Chl a concentration profiles determined by means of the DMF-extraction method taken the same day. Vertical bars denote standard deviation.