The frequent formation of large blooms makes the cosmopolitan colony forming Haptophycea Phaeocystis an important primary producer in the world oceans. Despite frequent and massive occurrences of such blooms, the fate of the biomass built by Phaeocystis is largely unknown, partly because of its lack of mineral compounds, which hamperes microscopic recognition of detrital, Phaeocystis-derived material. In order to identify Phaeocystis-derived detrital matter, it is necessary to use algal-specific chemical tracers which remain longer intact than the structural integrity of Phaeocystis cells.As part of a joint project on the fate of phytoplankton in the Balsfjord in Northern Norway, the sedimentation of Phaeocystis pouchetii was investigated in spring 1996 during a massive bloom of this alga. Sediment traps were deployed at 40, 60, 100 and 170 m depth. Samples from the sediment traps and from the water column were taken in short intervals (1 day - 2 weeks). A multimarker approach (using pigments, fatty acids and sterols) was chosen to characterize suspended organic matter and sediment trap material. Biomarker patterns typical for Phaeocystis were detected at the Chlorophyll a maximum and in the sediment traps. The results give evidence for massive sedimentation of Phaeocystis derived organic matter below the euphotic zone in the Balsfjord.