Abstract
Bacterial abundances were extensively measured using both the AO direct count method and the DAPI direct count method in the productive layer (upper 200m) of the North Pacific Ocean and the Bering Sea in order to determine the quantitative significance of bacterial biomass as a carbon pool in the euphotic zone. The bacterial abundances measured with the AO method, with a range of 1.5-33×105ml-1,revealed higher values in the upper 50 mand gradually decreased at depths below 50 min all regions. The bacterial abundances measured with the DAPI method, with a range of 1.0-23×105ml-1, were lower than those measured with the AO method, at all stations and depths. The difference between the DAPI method and the AO method in bacterial abundance varied in term of both region and depth. This difference meant that the abundance of non-bacterial organic particles varied with the region and with the depth, while real bacterial abundance also varied with the region and with the depth. The bacterial carbon biomass accounted for 2-18%(average;8±4%) of the total particulate organic carbon pool (which including bacterial carbon). This result suggested that the quantitative significance of bacterial carbon biomass might be comparable with that of the phytoplankton carbon biomass in the productive layer of the North Pacific Ocean.
