BIOMASS AND PRODUCTION OF BACTERIA AND PHYTOPLANKTON DURING THE SPRING BLOOM IN THE WESTERN NORTH-ATLANTIC OCEAN

During the 1989 spring bloom in the western North Atlantic, we estimated the biomass and productivity of bacteria and phytoplankton at two sites (40 and 45-degrees-N) representing different water masses. At 40-degrees-N, almost all of the phytoplankton carbon could bc accounted for by photosynthetic nanoplankton and picoplankton; in contrast, at 45-degrees-N, only about half was thus accounted, implying a substantial contribution by photosynthetic microplankton. At both sites, bacterial abundance was quite high (up to 2 x 10(9) cells l-1), and the rates of bacterial production assessed by incorporation of [H-3]thymidine (up to 8 pmol l-1 h-1) and [H-3]leucine (up to 240 pmol l-1 h-1) were significant. Specific growth rates of bacteria based on [H-3]thymidine incorporation were 0.08-0.25 day-1. Taken together, our measurements and assumptions implied a demand for primary production in the order of 16-36% over the euphotic zone or 24-78% over the upper 100 m in the water column. We conclude that ultraphytoplankton and bacteria played significant roles in the flux of carbon during the 1989 North Atlantic spring bloom.