North Pacific Phytoplankton Stocks in Gyre, Transition, and Subarctic Waters are Similar when Picoplankton are Included

Abstract

Large gradients have been reported in nutrients, biomass, and rates of production between subtropical and subarctic oceanic regions. We measured chlorophyll concentrations as a function of depth from 20°N to 48°N along 152°W during March, 1991. Surface chlorophyll concentrations (for GF/F filters, nominal pore size 0.7 μm) ranged from 0.021 to 0.404 μg/L, with the lowest values in subtropical waters and the highest values in subarctic waters. Deep subsurface chlorophyll maxima were located at approximately 100 meters in subtropical and transition waters, but were absent in subarctic water. Relative picoplankton abundance at the chlorophyll maximum was highest in subtropical water (85% of total) and lowest in subarctic water (35–50% of total).