Abstract

Bacterial biomass and productivity together with physico-chemical parameters in the northeast equatorial kPacific Ocean (7~10.5˚N) were investigated during a KODOS(Korea Deep Ocean Study) 96-1 cruise. Surface water dibvergence occurred at the boundary (8˚N) of the north equatorial current and the north equatorial counter current, and largely determined the horizontal and vertical distribution of physico-chemical and microbiological parameters. The diverging area (7~9˚N) was characterized by a shallower thermocline depth, higher nutrient and chlorophyll-a (Chl-a)concentrations, and a higher cyanobacterial cell number than those of the KODOS area (10~10.5˚N). Bacterial communities in the diverging area showed a high productivity but low biomass. Protozoa grazing seeded to be responsible for the low bacterial biomass. High bacterial turnover rate but low biomass suggested that bacteria in the diverging area may be a trophic link between a photosynthetic carbon source and protozoa, and thus accelerate the microbial loop. Relatively lower bacterial turnover but higher biomass in the KODOS area indicated that resources (organic carbon) limit the bacterial growth, and thus bacteria may play as a sink for photosynthetically ficed organic carbon. The results imply that major ecological role of hererotrophic bacteria in the microbial food web process in the two adjacent waters is different.

• Keywords: Eacterioplankton; Northeast equatorial Pacific; divergence; NEC; NECC