In order to convert the flow through fluorescence to Chl a concentration, discrete seawater samples were collected from Niskin bottles and about 0.5-2.0 L of seawater was filtered through Whatman GF/F filters and stored at -18°C. At the Alfred Wegener Institute for Polar and Marine Research, the filters were extracted in 90% acetone and analyzed with a spectrophotometer for higher values and with a Turner Design fluorometer for lower values.