Modeling and empirical measurements suggest that much of the ocean's margin is net heterotrophic, that is, utilizing more organic matter then is produced by photosynthesis. Seasonally, many continental shelves are dominated by autotrophic processes and may then export organic matter to the ocean's interior. This annual cycle of trophic status is largely the result of an interactive two-factor response by bacteria to low temperature and low substrate concentration. Bacterial isolates from the Arctic Ocean, the Labrador Current, and the subtropical southeastern continental shelf all indicate greatly reduced rates of growth when cultured at their annual minimum temperature and at low substrate concentrations, comparable to those normally present in seawater. Little is known, however, about net metabolism in arctic marine communities. Bacterial production is very low during the early spring period when most primary production is within the sea ice, and it is higher in late summer after the open-water phytoplankton bloom. This understanding is based on limited data, both seasonally and geographically. This project will result in an extensive concurrent data set on phytoplankton biomass, bacterial and microzooplankton abundance, nutrient uptake (nitrate and ammonium), inorganic nutrient concentration, hydrographic variables, primary production, microbial secondary production, and microbial respiration in the Arctic Ocean. Knowledge of the autotrophy-heterotrophy stauts of the arctic will be an important consideration for modeling the global carbon cycle and for predicting the effects of global climate change, as well as for understanding and modeling polar food webs.
