Coupling of carbon from primary producers to bacteria can significantly influence the patterns of vertical flux of organic matter in the ocean. Because bacteria must hydrolyze particles before uptake, bacterial exohydrolases must assume a central role in carbon flux from particulate organic matter into the microbial loop. The expression of bacterial exohydrolases is regulated by substrate concentration and therefore may cease in waters depleted of particles and polymers. In high latitude waters there is no phytoplankton production during the protracted polar night. The hypothesis to be tested is that during the Antarctic winter, the production of bacterial exohydrolase ceases. Therefore, particles and polymers produced during the early spring bloom cannot be utilized by bacteria. Exohydrolases are expressed when organic matter accumulates to a critical level; consequently, the coupling between particulate organic matter and bacteria becomes strong. Field and laboratory manipulations will examine environmental cues which regulate exohydrolase activities. This knowledge should contribute to the understanding of biological production mechanisms and variability in the pathways of organic matter cycling in the Southern Ocean.
