The research objectives of this study are to obtain an understanding of the annual cycles of bacterial biomass and production in the open sea. Such studies have previously been identified by the JGOFS program as necessary core measurements, which are considered essential for a better understanding of carbon and nitrogen fluxes through planktonic systems. The studies will be conducted at the Bermuda Biological Station for Research (BBSR) in the Bermuda Atlantic Time Series (BATS). In order to make high precision estimates of bacterial production initial studies will examine a number of radioactively labeled compounds such as thymidine, adenine, and leucine by conducting a series of calibration experiments for an empirical determination of conversion factors to be used for the different compounds. In the second year, regular sampling of the annual cycle of bacterial biomass and production at stations off Bermuda will begin in conjunction with the ongoing BBSR/JGOFS cruises. In addition, more detailed and intense studies will focus on two critical periods, the spring phytoplankton bloom and the conspicuous summer subsurface bacterial abundance maximum which has been identified in previous work conducted at Bermuda. Finally, work on modelling ecosystem structure at Bermuda will be continued and extended which will provide data for model validation, and developing new models of plankton dynamics.