The NE subarctic Pacific in winter: II. Biological rate processes

Abstract

In winter phytoplankton growth rates may be controlled by available irradiance, whereas heterotrophic bacterial production is likely to be controlled by water temperature and substrate limitation. Microzooplankton grazing rates may be primarily limited by temperature, since observed prey concentrations are not reduced compared to summer. Despite the reduced microzooplankton grazing rates, limited winter observations suggest that their biomass remains comparable to that observed during summer. Mesozooplankton are present in low numbers in the upper water column. Thus, the maintenance of high microzooplankton stocks during winter, a requirement in order to prevent the development of the spring bloom, may result from low mesozooplankton grazing pressure rather than from low dispersal due to insufficient strong mixing. -from Authors