| During the summers of 2007 and 2008, we determined net, new and regenerated primary production and phytoplankton biomass in Arctic and Sub-Arctic marine waters around North America. Carbon and nitrogen uptake rates were measured using the 15N and 13C tracer technique in 24-hr on-deck incubations, and phytoplankton biomass was determined by in vitro fluorometry. Average net primary production was highest in the north Bering and south Chukchi Seas (998 mg C m-2 d -1) and defined as primarily new production (f-ratio of 0.57), potentially indicating high particulate export from surface waters. Phytoplankton biomass was also high (39 mg chl a m-2) in this region and comprised mostly (61%) of cells >5 microm, supporting the conclusion of a high export system. Average net primary production was lowest in the Canada Basin (50 mg C m-2 d-1) with an f-ratio of 0.17 and characterized by low phytoplankton biomass (8 mg chl a m-2), comprised of mostly (19%) cells <5 microm. In much of the study area, the presence of ice cover appeared influential in affecting Arctic primary production patterns. Water column stratification in the wake of retreating sea ice produced conditions favorable to initiating seasonal blooms, which most likely terminated due to nutrient exhaustion. Areas characterized by persistent sea ice cover were particularly unproductive, most likely due to light limitation, and nutrient exhaustion due to reduced wind-mixing. These results indicate that primary production in Arctic and Sub-Arctic waters is highly variable, and provide an important baseline for future studies of phytoplankton dynamics in this rapidly changing region. |
