Marine Research Division, Scripps Institution of Oceanography, 9500
La Jolla CA 92093-0218
Phytoplankton in high-latitude areas experience a strong seasonal cycle as a consequence of changes in day length. During the fall and winter of 2001, as part of two GLOBEC cruises, we measured phytoplankton daily primary production with simulated in situ experiments. Primary production from 0 to 30 m was very low and decreased from an average 14.76 ± 33.11 mg C m2/d in May to 2.54 ± 2.62 mg C m2/d in August. The decrease in phytoplankton biomass caused the lowering of primary production, despite a twofold increase in incident radiation between May and August. Chlorophyll a concentration was low in the fall and decreased further by two orders of magnitude later in the season. For example, integrated chlorophyll from 0 to 30 m decreased from 9.02 ± 11.0 mg/m2 to 0.60 ± 0.21 mg/m2, respectively. Spatially, there was a coherent pattern of primary production distribution between the seasons, with higher activity on the shelf off Adelaide Island. These results suggest that primary production in the water column is limited by phytoplankton biomass and that these conditions will remain until phytoplankton populations start to grow as ice recedes later in the season.