Living diatom assemblages from North Pacific and Bering Sea surface waters during summer 1999

Diatom assemblages collected during July–August 1999 along an E–W transect comprising sixty-two North Pacific and Bering Sea surface water samples were identified and enumerated. Absolute abundance profiles of centric and raphid pennate diatoms show that the former group dominates in shallow coastal waters and through island passes, whilst the latter group, though less numerous, dominates the oceanic regions. This pattern is interpreted as nutrient-related, with centric diatoms (especially Chaetoceros (section Hyalochaete), Minidiscus and Thalassiosira spp.) preferring eutrophic and upwelling conditions, and raphid pennate diatoms (especially nitzschioid genera like Fragilariopsis, Neodenticula and Pseudo-nitzschia) preferring oligotrophic pelagic conditions. The absolute abundances of the two sections of Chaetoceros (Chaetoceros (ex Phaeoceros) and Hyalochaete) and some species belonging to the Thalassiosirales and Bacillariaceae show distribution patterns that can be interpreted as preferences for shallow or oceanic waters, subtropical or subarctic waters, or ice-related/arctic conditions.