Bacterioplankton of the Kara Sea shelf

The principal zones of the Kara Sea shelf are distinguished on the basis of structural and functional characteristics of bacterioplankton. Estuarine regions are characterized by elevated bacterial abundance and production rates, while the adjacent shelf has high abundance but lower production values. The southwestern part of the Kara Sea has relatively low bacterial abundance; here, the activity of microorganisms depends on the availability of allochthonous organic matter. In the northern part of the Kara Sea shelf, high bacterial abundance and growth rates are observed in the upper brackish water layer. The upper water layer above the slope of the St. Anna Trough is characterized by low numbers of bacteria, and production rates decrease almost to zero values. It has been shown that the analysis of bacterial abundance in the upper mixed layer is enough for the characterization of quantitative changes in bacterial community of the shelf zone.