The biomass, taxonomy, size, and photosynthesis-irradiance responses of phytoplankton in the high Arctic (79 ¿N) were investigated in March--April 1987 in the Fram Strait marginal ice zone. Chlorophyll a concentrations in open water during this period were extremely low, with surface values averaging 0.022 μg L-1. Vertical mixed layers were deep, ranging from 40 to 200 m, and surface incident irradiance was low (average of 44 μmol photons m-2 s-1 at local noon). The biomass of the microplankton was dominated by three groups; autotrophic flagellates (less than 10 μm), heterotrophic flagellates (less than 10 μm) and heterotrophic dinoflagellates (from 10 to 35 μm). Detrital carbon contributed the largest fraction (on average 95%) to the particulate carbon pool. Photosynthesis-irradiance responses indicated that the resident phytoplankton populations were adapted to low irradiance levels, as would be expected after the long periods of darkness encountered during the Arctic winter. Estimates of primary productivity during the March--April period indicate that very little net carbon fixation was occurring (average 1.84 mg C m-2 d-1 with a maximum of 3.3 mg C m-2 d-1). Some small increases in surface chlorophyll concentrations (relative to those at the base of the mixed layer) were noted at a few stations, and hence the onset of spring growth may have just begun. However, in view of the biomas and productivity observed during this period, the accumulation of substantial phytoplankton standing stocks, which are often observed at the ice edge, cannot occur until much later in the growing season at this northerly location. ¿ American Geophysical Union 1991